Zwitterionic and cationic bis(phosphine) platinum(II) complexes: Structural, electronic, and mechanistic comparisons relevant to ligand exchange and benzene C-H activation processes

Article abstract of DOI:10.1021/ja0296071

Structurally similar but charge-differentiated platinum complexes have been prepared using the bidentate phosphine ligands [Ph₂B(CH₂PPh₂)₂], ([Ph₂BP₂], [1]), Ph₂Si(CH₂PPh₂)₂, (Ph₂SiP₂, 2), and H₂C(CH₂PPh₂)₂, (dppp, 3). The relative electronic impact of each ligand with respect to a coordinated metal center's electron-richness has been examined using comparative molybdenum and platinum model carbonyl and alkyl complexes. Complexes supported by anionic [1] are shown to be more electron-rich than those supported by 2 and 3. A study of the temperature and THF dependence of the rate of THF self-exchange between neutral, formally zwitterionic [Ph₂BP₂]Pt(Me)(THF) (13) and its cationic relative [(Ph₂SiP₂)Pt(Me)(THF)][B(C₆ F₅)₄] (14) demonstrates that different exchange mechanisms are operative for the two systems. Whereas cationic 14 displays THF-dependent, associative THF exchange in benzene, the mechanism of THF exchange for neutral 13 appears to be a THF independent, ligand-assisted process involving an anchimeric, η³-binding mode of the [Ph₂BP₂] ligand. The methyl solvento species 13, 14, and [(dppp)Pt(Me)(THF)][B(C₆F₅)₄] (15), each undergo a C-H bond activation reaction with benzene that generates their corresponding phenyl solvento complexes [Ph₂BP₂]Pt(Ph)(THF) (16), [(Ph₂SiP₂)Pt(Ph)(THF)][B(C₆ F₅)₄] (17), and [(dppp)Pt(Ph)(THF)][B(C₆F₅)₄] (18). Examination of the kinetics of each C-H bond activation process shows that neutral 13 reacts faster than both of the cations 14 and 15. The magnitude of the primary kinetic isotope effect measured for the neutral versus the cationic systems also differs markedly (k(C₆H₆)/k(C₆D₆): 13 = 1.26; 14 = 6.52; 15 ～ 6). THF inhibits the rate of the thermolysis reaction in all three cases. Extended thermolysis of 17 and 18 results in an aryl coupling process that produces the dicationic, biphenyl-bridged platinum dimers [{(Ph₂SiP₂)Pt}₂(μ-η³: η³-biphenyl)][B(C₆F₅)₄] ₂ (19) and [{(dppp)Pt}₂(μ-η³:η³-biphenyl)] [B(C₆F₅)₄]₂ (20). Extended thermolysis of neutral [Ph₂BP₂]Pt(Ph)(THF) (16) results primarily in a disproportionation into the complex molecular salt {[Ph₂BP₂]PtPh₂}^- {[Ph₂BP₂]Pt(THF)₂}⁺. The bulky phosphine adducts [Ph₂BP₂]Pt(Me){P(C₆F₅) ₃} (25) and [(Ph₂SiP₂)Pt(Me){P(C₆F₅) ₃}][B(C₆F₅)₄] (29) also undergo thermolysis in benzene to produce their respective phenyl complexes, but at a much slower rate than for 13-15. Inspection of the methane byproducts from thermolysis of 13, 14, 15, 25, and 29 in benzene-d6 shows only CH₄ and CH₃D. Whereas CH₃D is the dominant byproduct for 14, 15, 25, and 29, CH₄ is the dominant byproduct for 13. Solution NMR data obtained for 13, its C-labeled ¹³C-labeled derivative [Ph₂BP₂]Pt(¹³CH₃)(THF) (13-^13CH₃), and its deuterium-labeled derivative [Ph₂B(CH₂P(C₆D₅)₂) ₂]Pt(Me)(THF) (13-d₂₀), establish that reversible [Ph₂BP₂]-metalation processes are operative in benzene solution. Comparison of the rate of first-order decay of 13 versus the decay of d₂₀-labeled 13-d₂₀ in benzene-d₆ affords k₁₃/k_13-d20 ～ 3. The NMR data obtained for 13, 13-¹³CH₃, and 13-d₂₀ suggest that ligand metalation processes involve both the diphenylborate and the arylphosphine positions of the [Ph₂BP₂] auxiliary. The former type leads to a moderately stable and spectroscopically detectable platinum(IV) intermediate. All of these data provide a mechanistic outline of the benzene solution chemistries for the zwitterionic and the cationic systems that highlights their key similarities and differences.

Full text of DOI:10.1021/ja0296071

Published on Web 06/17/2003
Zwitterionic and Cationic Bis(phosphine) Platinum(II)
Complexes: Structural, Electronic, and Mechanistic
Comparisons Relevant to Ligand Exchange and Benzene C-H
Activation Processes
J. Christopher Thomas and Jonas C. Peters*
Contribution from the DiVision of Chemistry and Chemical Engineering,
Arnold and Mabel Beckman Laboratories of Chemical Synthesis,
California Institute of Technology, Pasadena, California 91125
Received December 5, 2002; E-mail: jpeters@caltech.edu
Abstract: Structurally similar but charge-differentiated platinum complexes have been prepared using the
bidentate phosphine ligands [Ph2B(CH2PPh2)2], ([Ph2BP2], [1]), Ph2Si(CH2PPh2)2, (Ph2SiP2, 2), and
H2C(CH2PPh2)2, (dppp, 3). The relative electronic impact of each ligand with respect to a coordinated metal
center’s electron-richness has been examined using comparative molybdenum and platinum model carbonyl
and alkyl complexes. Complexes supported by anionic [1] are shown to be more electron-rich than those
supported by 2 and 3. A study of the temperature and THF dependence of the rate of THF self-exchange
between neutral, formally zwitterionic [Ph2BP2]Pt(Me)(THF) (13) and its cationic relative [(Ph2SiP2)Pt(Me)-
(THF)][B(C6F5)4] (14) demonstrates that different exchange mechanisms are operative for the two systems.
Whereas cationic 14 displays THF-dependent, associative THF exchange in benzene, the mechanism of
THF exchange for neutral 13 appears to be a THF independent, ligand-assisted process involving an
anchimeric, η3-binding mode of the [Ph2BP2] ligand. The methyl solvento species 13, 14, and [(dppp)Pt-
(Me)(THF)][B(C6F5)4] (15), each undergo a C-H bond activation reaction with benzene that generates
their corresponding phenyl solvento complexes [Ph2BP2]Pt(Ph)(THF) (16), [(Ph2SiP2)Pt(Ph)(THF)][B(C6F5)4]
(17), and [(dppp)Pt(Ph)(THF)][B(C6F5)4] (18). Examination of the kinetics of each C-H bond activation
process shows that neutral 13 reacts faster than both of the cations 14 and 15. The magnitude of the
primary kinetic isotope effect measured for the neutral versus the cationic systems also differs markedly
(k(C6H6)/k(C6D6): 13 ) 1.26; 14 ) 6.52; 15 ∼ 6). THF inhibits the rate of the thermolysis reaction in all
three cases. Extended thermolysis of 17 and 18 results in an aryl coupling process that produces the
dicationic, biphenyl-bridged platinum dimers [{(Ph2SiP2)Pt}2(µ-η3:η3-biphenyl)][B(C6F5)4]2 (19) and [{(dppp)-
Pt}2(µ-η3:η3-biphenyl)][B(C6F5)4]2 (20). Extended thermolysis of neutral [Ph2BP2]Pt(Ph)(THF) (16) results
primarily in a disproportionation into the complex molecular salt {[Ph2BP2]PtPh2}-{[Ph2BP2]Pt(THF)2}+.
The bulky phosphine adducts [Ph2BP2]Pt(Me){P(C6F5)3} (25) and [(Ph2SiP2)Pt(Me){P(C6F5)3}][B(C6F5)4]
(29) also undergo thermolysis in benzene to produce their respective phenyl complexes, but at a much
slower rate than for 13-15. Inspection of the methane byproducts from thermolysis of 13, 14, 15, 25, and
29 in benzene-d6 shows only CH4 and CH3D. Whereas CH3D is the dominant byproduct for 14, 15, 25, and
29, CH4 is the dominant byproduct for 13. Solution NMR data obtained for 13, its 13C-labeled derivative
[Ph2BP2]Pt(13CH3)(THF) (13-13CH3), and its deuterium-labeled derivative [Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF)
(13-d20), establish that reversible [Ph2BP2]-metalation processes are operative in benzene solution.
Comparison of the rate of first-order decay of 13 versus the decay of d20-labeled 13-d20 in benzene-d6
affords k13/k13-d20 ∼ 3. The NMR data obtained for 13, 13-13CH3, and 13-d20 suggest that ligand metalation
processes involve both the diphenylborate and the arylphosphine positions of the [Ph2BP2] auxiliary. The
former type leads to a moderately stable and spectroscopically detectable platinum(IV) intermediate. All of
these data provide a mechanistic outline of the benzene solution chemistries for the zwitterionic and the
cationic systems that highlights their key similarities and differences.
phosphine and amine donors.3 The neutral complexes of interest
to us are characterized by (phosphino)- and (amino)borate
ligands in which a borate unit is contained within the ligand
backbone, partially insulated from the coordinated metal center,
so as to preserve reactivity associated with their cationic
relatives. Zwitterionic systems of this type may ultimately
complement their cationic cousins by virtue of (i) their solubility
I. Introduction
Organometallic cations are ubiquitous in homogeneous
catalysis, with applications spanning catalytic C-E bond
forming reactions (E ) H, C, Si), polymerizations, and alkane
activation processes.1,2 Our group is exploring the chemistry of
neutral, formally zwitterionic complexes that are related to
reactive organometallic cations supported by conventional
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10.1021/ja0296071 CCC: $25.00 © 2003 American Chemical Society

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
and high activity in less polar, noncoordinating solvents, (ii)
their potential to show increased tolerance to polar or coordinat-
ing functional groups that one might expect to attenuate the
reactivity of cationic systems, and (iii) the attenuation of
counterion effects which may be present in discrete salt systems.
To begin evaluating this approach to catalysis, it needs to be
established whether these neutral systems will give rise to
reaction profiles traditionally associated with their cationic
analogues. Many factors are likely to impact this issue, but it
seems plausible that a borate counteranion rigidly fastened in
close proximity to a coordinated metal center will, to some
extent, alter the complex’s overall reactivity and the operational
mechanism by which it mediates a reaction transformation.
Therefore, it was of interest to study how the mechanisms of
electronically distinct but structurally related neutral and cationic
systems compare for a shared organometallic reaction process.
Surprisingly little attention has been devoted to such issues
previously.4
In the present study, we examine the kinetic and mechanistic
profiles of structurally related neutral and cationic platinum(II)
systems that each mediate an elementary C-H bond activation
process in benzene solution. In light of the intense interest in
electrophilic C-H activation reactions mediated by late transi-
tion metal centers,5-13 a C-H activation study that compares a
neutral with a cationic system is timely. Three platinum(II)
systems supported by the structurally related, bidentate phos-
phine ligands, [Ph2BP2] [1], Ph2SiP2 (2), and dppp (3) (Figure
1) are featured. The major structural difference between
complexes supported by [1], 2, and 3 is in the ligand backbone,
relatively remote from the phosphine-coordinated metal center.
Ligand [1] contains an anionic borate unit that, when bound to
a PtII(X)(L) species, affords a neutral and formally zwitterionic
[Ph2BP2]Pt(X)(L) complex. In this neutral system, the anion is
structurally contained within the ligand framework at a distance
of ∼4 Å from the coordinated platinum center in the solid-
state. Ligand 2 replaces the diphenylborate unit of [1] with a
structurally similar diphenylsilane unit, and ligand 3 contains
the more common methylene backbone. Systems supported by
2 and 3 provide access to more conventional cationic species
of the type [P2PtII(X)(L)][X′], where the primary difference is
that, in solution, the counteranion is at an ill-defined distance
from the coordinated platinum center with the potential to ion-
pair with the metal center. Because a methyl solvento complex
of each system proved capable of mediating an elementary
benzene C-H bond activation process (Figure 1), the three
systems provided an excellent opportunity for a comparative
mechanistic study.
Herein, we provide structural, electronic, and kinetic infor-
mation for the phosphine-supported neutral and cationic plati-
num(II) systems. We consider these data with respect to the
mechanistic profile of each system in benzene solution, and we
highlight several important and unexpected mechanistic distinc-
tions between the systems.
II. Results
II.1. Synthesis and Characterization of Precursor Com-
plexes. The syntheses for the anionic borate [Ph2BP2] (1) and
the key neutral complex [Ph2BP2]Pt(Me)(THF) (13) have been
reported previously.3a Structurally related complexes were
prepared using the neutral ligands Ph2Si(CH2PPh2)2 (Ph2SiP2,
2) and 1,3-bis(diphenylphosphino)propane (dppp, 3). The
synthesis of ligand 2 has not been reported but was synthesized
readily by addition of two equivalents of Ph2PCH2Li(TMEDA)
to Ph2SiCl2 (5.28 g, 82.3% yield). The chemical shifts (31P
NMR) for ligands [1], 2, and 3 are shown in Table 1.
Dimethyl platinum(II) complexes of ligands 1-3 were
obtained by reaction with (COD)PtMe2 in THF. The substitution
reactions proceeded cleanly to displace cyclooctadiene and
generate [[Ph2BP2]PtMe2][ASN] (7),3a (Ph2SiP2)PtMe2 (8), and
(dppp)PtMe2 (9)14 in high isolated yield (>90%). Selected NMR
data for these three complexes are also presented in Table 1.
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Lett. 2001, 3, 1701-1704. (d) Oi, S.; Terada, E.; Ohuci, K.; Kato, T.;
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A. K.; Matsuda, H. Org. Lett. 1999, 1, 2157-2159. (f) Madine, J. W.;
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1169-1203.
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activation and functionalization include: (a) Arndtsen, B. A.; Bergman,
R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154-
162. (b) Lohrenz, J. C. W.; Jacobsen, H. Angew. Chem., Int. Ed. Engl.
1996, 35, 1305-1307. (c) Sen, A. Acc. Chem. Res. 1998, 31, 550-557.
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1998, 37, 2181-2192. (e) Balzarek, C.; Weakley, T. J. R.; Tyler, D. R. J.
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G. B. ActiVation and Catalytic Reactions of Saturated Hydrocarbons in
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(b) Lu, C. C.; Peters, J. C. J. Am. Chem. Soc. 2002, 124, 5272-5273. (c)
Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2002, 124,
11 238-11 239. (d) Jenkins, D. M.; Di Bilio, A. J.; Allen, M. J.; Betley,
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S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 322-323.
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8176-8177. (b) Seymore, S. B.; Brown, S. N. Inorg. Chem. 2000, 39,
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C-H bond activation include: (a) Brainard, R. L.; Nutt, W. R.; Lee, T.
R.; Whitesides, G. M. Organometallics 1988, 7, 2379-2386. (b) Peters,
R. G.; White, S.; Roddick, D. M. Organometallics 1998, 17, 4493-4499.
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1998, 120, 2843-2853. See also ref 12.
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A R T I C L E S
Thomas and Peters
Figure 1. Labeling scheme for the phosphine ligands featured in this paper and the model benzene C-H activation reaction used for the comparative study.
Table 1. Selected NMR Shifts (δ) and Coupling Constants (Hz)
for Ligands [1], 2, and 3, and Platinum Dimethyl Complexes 7, 8,
and 9 (acetone-d6)
cleanly by protonation of the corresponding diphenyl compounds
(Ph2SiP2)PtPh2 (22) and (dppp)PtPh2 (23) with [H(Et2O)2]-
[B(C6F5)4] in dichloromethane in the presence of ca. 40-100
equiv of THF. The phenyl derivatives 16, 17, and 18 proved
less thermally stable than their corresponding methyl analogues
(vide infra).
16
31P{1H}
NMR
1H NMR
Pt-Me
3JP-H
Pt-Me
2JPt-H
Pt-Me
compound
1JPt-P
[Ph2BP2][ASN] [1]
(Ph2SiP2) (2)
dppp (3)
-8.78
-22.65
-16.29
II.2. Structural and NMR Comparisons of 7, 8, 9, and
13. X-ray diffraction studies were carried out on crystals of the
dimethyl complexes 7-9 and the neutral methyl solvento
complex [Ph2BP2]Pt(Me)(THF) (13) to confirm their structural
analogy. Relevant structural representations are shown in Figure
2, and noteworthy bond lengths and angles are presented in
Table 2. As anticipated, the solid-state structures of 7-9 are
very similar. The Pt-P and Pt-C bond lengths are nearly
identical for the three derivatives. The modest deviation
observed in the C-Pt-C and P-Pt-P bond angles present in
7, 8, and 9 may reflect the presence of a countercation in the
unit cell of anionic [[Ph2BP2]PtMe2][ASN] (7) that is not present
in neutral (Ph2SiP2)PtMe2 (8) or (dppp)PtMe2 (9). The extended
lattice structure of 7 (see the Supporting Information) shows
that the ammonium cation packs very tightly within the wedge
of a diphenylborate unit, and is also in close proximity to the
methyl ligands of an adjacent platinum anion. This solid-state
arrangement of the cation of 7 may slightly alter the ligand
conformation of [Ph2BP2] in 7 relative to 8 and 9. For
comparison, the solid-state structure of zwitterionic 13 reveals
a P-Pt-P angle (91.96(3)°) that is closer to the bite angles
observed for both 8 and 9.
[[Ph2BP2]PtMe2][ASN] (7)
(Ph2SiP2)PtMe2 (8)
(dppp)PtMe2 (9)
20.60 1892 0.08 (t)
12.00 1848 0.17 (dd) 6.6, 8.1 69
5.47 1812 0.25 (dd) 5.4, 6.9 69
12
68
Protonation of the neutral dimethyl species 8 and 9 in
dichloromethane in the presence of ca. 40-100 equiv of THF
with [H(Et2O)2][B(C6F5)4]15 resulted in the clean formation of
the salts [(Ph2SiP2)Pt(Me)(THF)][B(C6F5)4] (14) and [(dppp)-
Pt(Me)(THF)][B(C6F5)4] (15). In comparison to dimethyl com-
plexes 8 and 9, anionic [[Ph2BP2]PtMe2][ASN] (7) was readily
protonated by weaker ammonium acids of the type [HNR3+],
consistent with a more electron-rich, anionic metal center. The
cationic methyl solvento complexes 14 and 15 were markedly
more stable to both vacuum and halogenated solvents than
zwitterionic [Ph2BP2]Pt(Me)(THF) (13). Complex 13 exhibited
decomposition within minutes in dichloromethane at ambient
temperature, whereas both 14 and 15 were stable for hours under
similar conditions. Also, prolonged exposure of [Ph2BP2]Pt-
(Me)(THF) (13) to vacuum resulted in its degradation. Thus,
to remove residual THF in the preparation of 13, it was critical
to dry the sample carefully with a gentle stream of argon.
In addition to the precursor methyl solvento complexes 13-
15, we also independently prepared and characterized their
corresponding phenyl derivatives [Ph2BP2]Pt(Ph)(THF)3a (16),
[(Ph2SiP2)Pt(Ph)(THF)][B(C6F5)4] (17), and [(dppp)Pt(Ph)-
(THF)][B(C6F5)4] (18). Compounds 17 and 18 were generated
Another structural parameter of interest concerns the Pt-B
distance in (phosphino)borate complexes [[Ph2BP2]PtMe2][ASN]
(7) and [Ph2BP2]Pt(Me)(THF) (13). The borate anion in 7 is
well-separated from the Pt-center at 4.117(1) Å. This compares
(16) (a) Romeo, R.; Scolaro, L. M.; Pluntio, M. R.; Del Zotto, A. Transition
Met. Chem. 1998, 23, 789-793. (b) Alibrandi, G.; Bruno, G.; Lanza, S.;
Minniti, D.; Romeo, R.; Tobe, M. L. Inorg. Chem. 1987, 26, 185-190.
(15) Jutzi, P.; Mu¨ller, C.; Stammler, A.; Stammler, H.-G. Organometallics 2000,
19, 1442-1444.
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Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
Figure 2. 50% displacement ellipsoid representations of platinum dimethyl complexes [[Ph2BP2]PtMe2][ASN] (7), (Ph2SiP2)PtMe2‚toluene (8‚toluene),
(dppp)PtMe2 (9), and platinum methyl solvento complex [Ph2BP2]Pt(Me)(THF)‚2THF (13‚2THF). Hydrogen atoms, counterions (ASN, 7), and solvent
molecules (toluene, 8; 2 THF, 13) are omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 7, 8, 9, and 13
complex
Pt−C
Pt−P
C−Pt−C
P−Pt−P
[[Ph2BP2]PtMe2][ASN] (7)
(Ph2SiP2)PtMe2 (8)
(dppp)PtMe2 (9)
2.134(3), 2.132(3)
2.142(3), 2.122(3)
2.102(3), 2.113(3)
2.087(6)
2.2829(7), 2.2776(7)
2.2828(7), 2.2804(7)
2.2724(8), 2.2714(8)
2.313(2)a
86.6(1)
83.8(1)
85.9(1)
91.2(1)b
90.64(2)
94.63(3)
94.30(3)
91.94(6)
[Ph2BP2]Pt(Me)(THF) (13)
a P trans to methyl. b C-Pt-O angle.
well with the Pt-Si distance in neutral (Ph2SiP2)PtMe2 (8)
(4.192(1) Å) and is slightly longer than the relevant Pt-C1
distance (3.838(1) Å) in (dppp)PtMe2 (9) due to a slightly
puckered chelate ring in the latter. The Pt-B distance contracts
only slightly in moving from anionic 7 to zwitterionic 13 (Pt-B
) 4.007(6) Å in 13).
(CH3)2 chemical shift moves downfield for less donating
phosphines. Both of these trends are observed in the data
presented here, consistent with suggesting that the bis(phos-
phino)borate ligand [1] provides a platinum center that is to
some extent more electron-rich than the isostructural derivatives
supported by ligands 2 and 3.
II.3. Gauging Electronic Effects using Metal Carbonyl
Complexes. In this paper, we often refer to complexes of the
type [Ph2BP2]Pt(X)(L) (e.g., complex 13) as formally “zwitter-
ionic”. We choose this descriptor to highlight that the di-
phenylborate unit in these systems is not resonance-delocalized
to the phosphine donor atoms, at least not by conventional
resonance contributors. Regardless of this distinction, charge
in both the neutral and cationic complexes, like all covalent
systems, is highly distributed and assigning a formal charge to
any atom or unit is invariably misleading. We do think, however,
that the zwitterionic description for complexes of the type
[Ph2BP2]Pt(X)(L) is beneficial, especially when considering
them in a comparative context with respect to their formally
cationic cousins [P2Pt(X)(L)]+.
To address the relative electrophilicity between the platinum
centers of [Ph2BP2]Pt(X)(L) and [P2Pt(X)(L)]+ type systems,
the platinum(II) methyl carbonyl complexes were generated. A
key assumption we make in this paper is that the relative energy
of the CO vibration is a reasonable way to gauge whether the
[Ph2BP2] ligand is more electron-releasing than its neutral
relatives Ph2SiP2 and dppp.19 In a separate paper, the limitations
of this assumption are discussed in greater detail.20 In brief, we
underscore the likelihood that electrostatic factors contribute
significantly to the overall magnitude of the difference in a CO
stretching frequency between a cationic and a neutral complex.
However, we also emphasize the ambiguity that arises if one
tries to separate electrophilicity from electrostatic factors.
Reaction of the solvento complexes 13-15 with excess
carbon monoxide in THF ([Ph2BP2]Pt(Me)(THF), 13) or di-
Structural and NMR parameters potentially sensitive to
electronic differences between the neutral and cationic systems
include the relative Pt-Me and Pt-P bond lengths obtained
from the X-ray structures of 7-9, and chemical shifts and
coupling constants observed from their NMR spectra. Data of
this type can be used to gauge the relative trans influence of a
ligand coordinated to a square planar platinum(II) center. Our
data establish that the structural parameters are relatively
insensitive to the placement of an anionic diphenylborate unit
in [[Ph2BP2]PtMe2][ASN] (7) versus incorporation of a neutral
diphenylsilane in (Ph2SiP2)PtMe2 (8) (or a neutral methylene
in (dppp)PtMe2 (9)). The average Pt-C bond lengths between
isostructural 7 and 8 are virtually indistinguishable (ca. 2.13
Å), as are their Pt-P bond distances (ca. 2.28 Å) (Table 2),
consistent with structural data obtained for various (Ar3P)2PtMe2
complexes that have been reported elsewhere.17 In considering
2
the comparative NMR data, the magnitudes of the JPt-H
coupling constants for 7-9 are all very similar (68, 69, and 69
Hz respectively, Table 1), as expected.18 NMR parameters that
do show variation among the three systems are the 31P{1H}
NMR chemical shift, the 1JPt-P coupling constant, the Pt-(CH3)2
chemical shift in the 1H NMR spectrum, and the 3JP-H coupling
constant (Table 1). The relationship between the electronic
nature of a phosphine-coordinated PtMe2 center and the coupling
constant 1JPt-P and the Pt-(CH3)2 chemical shift in the 1H NMR
spectrum has also been examined previously.18 The trends
observed for para-substituted aryl phosphine adducts of di-
1
methyl platinum(II) suggest that JPt-P decreases and the Pt-
(17) Smith, D. C., Jr.; Haar, C. M.; Stevens, E. D.; Nolan, S. P.; Marshall, W.
J.; Moloy, K. G. Organometallics 2000, 19, 1427-1433.
(18) Haar, C. M.; Nolan, S. P.; Marshall, W. J.; Moloy, K. G.; Prock, A.; Giering,
W. G. Organometallics 1999, 18, 474-479.
(19) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2953-2956 and references
therein.
(20) Thomas, J. C.; Peters, J. C. Inorg. Chem. 2003, in press.
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8873

A R T I C L E S
Thomas and Peters
Table 3. Comparative Infrared Carbonyl Frequencies (cm-1) for
Model Platinum (10-12) and Molybdenum (4-6) Complexes (KBr
cell in CH2Cl2 solution)
complex
ν(CO)
[Ph2BP2]Pt(Me)(CO) (10)
2094
2118
2118
2005
2018
2018
[(Ph2SiP2)Pt(Me)(CO)][B(C6F5)4] (11)
[(dppp)Pt(Me)(CO)][B(C6F5)4] (12)
[[Ph2BP2]Mo(CO)4][ASN] (4)
(Ph2SiP2)Mo(CO)4 (5)
(dppp)Mo(CO)4 (6)
Figure 3. (a) Plot of kex versus THF equivalents for [Ph2BP2]Pt(Me)(THF)
(13, ×), [Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20, [), and [(Ph2SiP2)-
Pt(Me)(THF)]+ (14, O). (b) Eyring plot of ln(kex/T) versus 1000/T for neutral
methyl solvento complex 13 (×) and cationic methyl solvento complex 14
(O).
Scheme 1
II.4. Determination of Relative THF Ligand Exchange
Rates for 13 and 14. The relative rates and mechanisms of
ligand exchange in benzene solution are important to mecha-
nistic considerations discussed in the next section. Measurement
of the rate of THF self-exchange for [Ph2BP2]Pt(Me)(THF) (13)
and [(Ph2SiP2)Pt(Me)(THF)]+ (14) was therefore examined in
benzene-d6 in the presence of excess THF through the NMR
technique of magnetization transfer using a DANTE pulse
sequence23 (Scheme 2). Saturation of the free downfield THF
resonance (ca. 3.6 ppm) transferred intensity to the downfield
platinum-bound THF resonance (ca. 2.9 ppm) in each case, and
the rate constant for THF exchange (kex) was extracted from
the NMR data using the computer program CIFIT.24
Scheme 2
The dependence of the observed rate constant kex on the
concentration of THF was strikingly different between the
neutral and cationic platinum systems. For neutral [Ph2BP2]Pt-
(Me)(THF) (13), kex showed no [THF] dependence over a range
of THF concentration (0.146-0.468 M). In sharp contrast,
cationic [(Ph2SiP2)Pt(Me)(THF)]+ (14) showed a first-order
dependence on [THF] (0.0766-0.237 M) for the observed rate
constant (Figure 3a). The extrapolated intercept for the plot of
kex versus THF equivalents for 14 intersects at the origin and
thereby suggests negligible mechanistic dependence on the
solvent (benzene) and/or the [B(C6F5)4] anion.25
chloromethane ([(Ph2SiP2)Pt(Me)(THF)]+, 14; [(dppp)Pt(Me)-
(THF)]+, 15) solution resulted in the rapid formation of the
neutral and cationic methyl carbonyl complexes [Ph2BP2]Pt-
(Me)(CO) (10), [(Ph2SiP2)Pt(Me)(CO)][B(C6F5)4] (11), and
[(dppp)Pt(Me)(CO)][B(C6F5)4] (12), respectively. Solution IR
spectra for these derivatives were recorded in dichloromethane
in a KBr cell (Table 3). The carbonyl stretching frequencies
observed for the two cations are identical (11: 2118 cm-1, 12:
2118 cm-1). The neutral complex 10, however, shows a ν(CO)
vibration that is 24 cm-1 lower in energy (10: 2094 cm-1).
These data suggest that the neutral complex 10 is more electron-
rich, and suggest that the [Ph2BP2] ligand is likely more electron-
releasing than its neutral analogues.
The absolute difference in the rate constant of THF self-
exchange (kex) at a given temperature between complex
[Ph2BP2]Pt(Me)(THF) (13) and [(Ph2SiP2)Pt(Me)(THF)]+ (14)
is only modest. For example, at 25 °C, the rate constant for
We also examined the phosphine ligands 1-3 within the
conventional L2Mo(CO)4 infrared model system. Crabtree has
previously suggested that the highest frequency CO vibration,
presumed to be an a1 vibration, in tetracarbonyl molybdenum
complexes is a reasonable gauge of the relative electron-
releasing/accepting character for a bidentate chelate.21 Reaction
of the appropriate bisphosphine ligand 1-3 with Mo(CO)6 in
refluxing THF for 24-36 h provided the required species
[[Ph2BP2]Mo(CO)4][ASN] (4), (Ph2SiP2)Mo(CO)4 (5), and
1
neutral 13 (kex(298K)(13) ) 12.0 s-1) is ∼ /3 as large as that
for cationic 14 (kex(298K)(14) ) 38.5 M-1 s-1). More interesting
is that the temperature dependence of kex varies dramatically
between 13 and 14. The rate constant kex of [Ph2BP2]Pt-
(Me)(THF) (13) was examined over the temperature range
11.2-48.9 °C and provided an entropy and enthalpy of
activation as follows: ∆Sq ) 0.1 ( 5.4 e.u.; ∆Hq ) 16.0 ( 1.6
kcal/mol (Figure 3b). Analogous data collected for cationic
[(Ph2SiP2)Pt(Me)(THF)]+ (14) over the temperature range
22
(dppp)Mo(CO)4 (6), respectively (Scheme 1). Measurement
16.0-44.6 °C provided distinctly different values: ∆Sq
)
of their respective IR spectra in dichloromethane solution
established a trend similar to that of the platinum system: The
highest frequency CO vibration for anionic 4 is 2005 cm-1
whereas the same vibration for both 5 and 6 is 2018 cm-1. These
data are in accord with those obtained for the platinum system,
supporting the notion that [1] is more electron-releasing.
-30.2 ( 5.2 e.u. and ∆Hq ) 1.9 ( 0.5 kcal/mol (Figure 3b).
The activation parameters obtained for [(Ph2SiP2)Pt(Me)-
(THF)]+ (14) (∆Sq ) - 30.2 ( 5.2 e.u.; ∆Hq ) 1.9 ( 0.5
kcal/mol) are consistent with a classic associative mechanism
(23) Morris, G. A.; Freeman, R. J. Magn. Res. 1978, 29, 433-462.
(24) Bain, A. D.; Cramer, J. A. J. Magn. Res. 1996, 118, 21-27.
(25) Langford, C. H.; Gray, H. B. Ligand Substitution Processes; Benjamin:
New York, 1966; pp 18-54.
(21) Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 621-627.
(22) Dietsche, W. H. Tetrahedron Lett. 1966, 49, 6187-6191.
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8874 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
of ligand exchange, in accord with the linear dependence of
the exchange rate constant on THF concentration.25 Associative
ligand exchange is commonplace for ligand substitution in
square planar platinum(II) systems25 and is the mechanism we
had anticipated for 14. Particularly noteworthy is that ∆Hq for
14 suggests that THF exchange is a nearly thermoneutral
processsthe degree of Pt-O bond making and bond breaking
being symmetric in the transition state.
(Me)(THF)]+ (14) and [(dppp)Pt(Me)(THF)]+ (15) reacted
similarly, liberating methane to produce the corresponding
phenyl derivatives [(Ph2SiP2)Pt(Ph)(THF)]+ (17) and [(dppp)-
Pt(Ph)(THF)]+ (18) (Figure 1). The phenyl complexes 16-18
were not stable to extended thermolysis, as evidenced by the
growth of new signals in their respective 31P{1H} NMR spectra.
Cationic phenyl complexes 17 and 18 each gave rise to
quantitative formation of a single new product. Spectroscopic
and structural evidence27 established the products formed to be
the orange dinuclear species [{(Ph2SiP2)Pt}2(µ-η3:η3-biphenyl)]-
[B(C6F5)4]2 (19) and [{(dppp)Pt}2(µ-η3:η3-biphenyl)][B(C6F5)4]2
(20), the apparent products of a bimolecular aryl coupling
process. It is noted that the addition of excess THF significantly
inhibited the degradation of pure samples of 16-18 in benzene
solution. Curiously, whereas complex 19 proved relatively stable
to hydrolysis, complex 20 is quite moisture sensitive. During
the course of this study, Konze, Scott, and Kubas reported a
related coupling reaction for similar cationic bisphosphine
platinum(II) complexes; however, the aryl intermediates that
presumably result from C-H bond activation processes were
not obserVed.12 We presume that a common mechanism for aryl
coupling is prevalent in both sets of systems, but that subtle
differences in the bisphosphine ligands give rise to different
reaction rates for the step converting the mononuclear phenyl
species to their bridged biphenyl products.
Prolonged thermolysis of an independently prepared sample
of [Ph2BP2]Pt(Ph)(THF) (16) resulted in two apparent reac-
tion pathways. The dominant pathway was that of dis-
proportionation to generate the colorless molecular salt
{[Ph2BP2]Pt(Ph)2}-{[Ph2BP2]Pt(THF)2}+. Formation of this
cation/anion pair was suggested by the appearance of two
singlets (31P{1H} NMR) in a 1:1 ratio, and by a positive
identification of each ion by electrospray mass spectroscopy.
Additionally, the species [[Ph2BP2]Pt(Ph)2][ASN] was inde-
pendently prepared and characterized. A small amount of a
presumed bridged-biphenyl species was also evident by 31P{1H}
NMR and by the orange solution color that developed upon
prolonged thermolysis. An independent X-ray diffraction study
on crystals of this minor species obtained by fractional crystal-
lization provided connectivity consistent with the dinuclear
complex {[Ph2BP2]Pt}2(µ-η3:η3-biphenyl).
Interpreting the activation parameters and lack of [THF]
dependence on kex of [Ph2BP2]Pt(Me)(THF) (13) is less
straightforward. The remarkable difference in ∆Hq between 13
and [(Ph2SiP2)Pt(Me)(THF)]+ (14) reflects a change in mech-
anism, which could include an energy barrier for significant
THF dissociation, or association of a more hindered ligand to
displace THF. Perhaps the simplest scenario to put forward for
ligand exchange is therefore that of a purely dissociative
mechanism that proceeds via a neutral 3-coordinate intermediate,
“[Ph2BP2]Pt(Me)”. If the platinum center in [Ph2BP2]Pt(Me)-
(THF) (13) is indeed more electron-rich relative to [(Ph2SiP2)-
Pt(Me)(THF)]+ (14), then dissociation of a σ-donor ligand might
be expected to be more favorable. However, simple dissociative
exchange mechanisms are rarely observed in platinum(II)
substitution chemistry.26a Even in cases where they have been
reported, such as the systems elegantly put forth by Romeo,26
certain assumptions are required to suggest the presence of a
truly 3-coordinate intermediate species. Therefore, two ad-
ditional mechanisms for THF exchange in [Ph2BP2]Pt(Me)(THF)
(13) need also to be considered: solvolytic displacement of the
bound THF from 13 by benzene itself and an anchimeric
mechanism whereby a bond pair from the ancillary [Ph2BP2]
ligand coordinates the platinum center prior to appreciable Pt-O
bond breaking. These latter two possibilities constitute associa-
tive interchange mechanisms involving discrete 5-coordinate,
rather than 3-coordinate, intermediates. Although we cannot
distinguish between dissociative, solvent-assisted, or ligand-
assisted exchange pathways from the data exchange data alone,
the solution NMR data that are discussed below suggest that
an anchimeric pathway for ligand exchange is most likely
operative for neutral [Ph2BP2]Pt(Me)(THF) (13).
To probe for the possibility of an isotope-dependent change
in the rate of THF self-exchange for neutral [Ph2BP2]Pt(Me)-
(THF) (13), we also investigated the d20-labeled complex
[Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20) (see section II.9c).
The [THF] dependence of kex for THF self-exchange for 13-
II.6. Benzene C-H Bond Activation Kinetics for 13, 14,
and 15. To evaluate the benzene C-H bond reactivity of the
methyl solvento systems [Ph2BP2]Pt(Me)(THF) (13), [(Ph2SiP2)-
Pt(Me)(THF)]+ (14), and [(dppp)Pt(Me)(THF)]+ (15), reaction
rates were measured under comparative conditions by monitor-
ing the decay of the starting precursors 13-15 by either 31P{1H}
d20 was determined at several THF concentrations (0.116-0.497
M) and was found to be independent of [THF] (Figure 3a). The
observed rate constant, kex(13-d20) ) 11.6 ( 0.9 s-1 was similar
in magnitude to that measured for [Ph2BP2]Pt(Me)(THF) (13)
under similar conditions (kex(13) ) 10.3 ( 2.1 s-1).
II.5. Reaction Pathways of 13, 14, and 15 when Thermo-
lyzed in Benzene between 45 and 55 °C. As previously
reported, [Ph2BP2]Pt(Me)(THF) (13) reacts in benzene solution
at 50 °C over a period of several hours to form [Ph2BP2]Pt-
(Ph)(THF) (16) as the major product (∼80%) with concomitant
liberation of methane.3a The cationic derivatives [(Ph2SiP2)Pt-
1
NMR or H NMR spectroscopy. The observed rate constants
and half-lives are summarized in Table 4, and relevant first-
order plots are presented in Figures 4 and 5.
Both [Ph2BP2]Pt(Me)(THF) (13) and [(Ph2SiP2)Pt(Me)-
(THF)]+ (14) displayed clean first-order decay at 45 °C and 55
°C, respectively. The decay of [(dppp)Pt(Me)(THF)]+ (15) was
more complex. In all cases, the addition of five equivalents of
THF slowed the thermal degradation of the starting methyl
derivatives, though the attenuation in decay rate was more
pronounced for the cations (by ca. a factor of 2). The absence
of first-order kinetics for cationic 15 can be attributed to the
(26) (a) Romeo, R. Comments Inorg. Chem. 1990, 11, 21-57. (b) Romeo, R.;
Scolaro, L. M.; Nastasi, N.; Arena, G. Inorg. Chem. 1996, 35, 5087-5096.
(c) Romeo, R.; Alibrandi, G. Inorg. Chem. 1997, 36, 4822-4830. (d)
Romeo, R.; Plutino, M. R.; Elding, L. I. Inorg. Chem. 1997, 36, 5909-
5916. (e) Plutino, M. R.; Scolaro, L. M.; Romeo, R.; Grassi, A. Inorg.
Chem. 2000, 39, 2712-2720.
(27) The results of an X-ray diffraction study of 19 are contained in the
Supporting Information.
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8875

A R T I C L E S
Thomas and Peters
Table 4. Kinetic Rate Data Fit to a First Order Decay of 13, 14, and 15 under Various Conditions
complex
solvent
T (°C)
additive
rate (s-1
)
t1/2 (min)
[Ph2BP2]Pt(Me)(THF) (13)
C6H6
C6D6
C6H6
C6H6
C6D6
C6H6
C6H6
C6D6
C6H6
C6H6
C6H6
C6D6
C6H6
45
45
45
45
55
55
55
55
55
55
55
55
55
1.42(5) × 10-4
1.13(3) × 10-4
9.0(3) × 10-6
1.37(3) × 10-4
3.7(2) × 10-4
3.18(11) × 10-4
1.80(6) × 10-4
2.76(7) × 10-5
6.0(6) × 10-6
1.34(3) × 10-4
g1.8 × 10-4
81
102
1280
84
31
360
64
430
1900
86
e65
e400
2700
5 equiv THF
1 equiv [nBu4N][B(C6F5)4]
5 equiv THF
[(Ph2SiP2)Pt(Me)(THF)]+ (14)
[(dppp)Pt(Me)(THF)]+ (15)
5 equiv THF
1 equiv [nBu4N][B(C6F5)4]
g3.0 × 10-5
5 equiv THF
4.2(4) × 10-6
For each system the benzene thermolysis of 13-15 was carried
out in both benzene and benzene-d6. The measured k(C6H6)/
k(C6D6) ratio for [Ph2BP2]Pt(Me)(THF) (13) at 45 °C was 1.26.
We were unable to make a comparable measurement at 55 °C
due to the absence of a viable spectroscopic method. This value
is strikingly different from that measured for [(Ph2SiP2)Pt(Me)-
(THF)]+ (14) and that estimated for [(dppp)Pt(Me)(THF)]+ (15)
at 55 °C. The measured k(C6H6)/k(C6D6) ratio for 14 was 6.52
and that for 15 was similar, estimated to be ca. 6 by fitting the
decay of 15 to a simple first-order model.
II.7. Preparation and Benzene Activation Chemistry
of Neutral [Ph2BP2]Pt(Me){P(C6F5)3} (25) and Cationic
[(Ph2SiP2)Pt(Me){P(C6F5)3}][B(C6F5)4], (29). In addition to
THF as the coordinatively labile donor L in this study, we also
sought a more sterically hindered derivative. We chose the
phosphine P(C6F5)3 as an appropriate L ligand candidate because
of its relatively poor sigma donor ability and its unusually large
Tolman cone angle (184°).28 It also lacks potentially reactive
aryl C-H bonds. We found that P(C6F5)3 displaced THF from
[Ph2BP2]Pt(Me)(THF) (13) to provide the phosphine adduct
complex [Ph2BP2]Pt(Me){P(C6F5)3} (25) cleanly and in favor-
able crystalline yield (83%). A structural representation of
complex 25, along with a space filling representation, is shown
in Figure 6. It is presumed from the solid-state structure of 25
that the P(C6F5)3 coligand, in conjunction with the [Ph2BP2]
auxiliary, effectively blocks the platinum center with respect
to associative approach of a fifth ligand.
Although the platinum center is buried beneath the protective
organic aromatic rings, complex [Ph2BP2]Pt(Me){P(C6F5)3} (25)
nonetheless reacts in benzene to quantitatively form the phenyl
complex [Ph2BP2]Pt(Ph){P(C6F5)3} (26) with concomitant
liberation of methane (Scheme 3). As might be expected, the
benzene C-H activation process is much slower for 25 than
for the corresponding THF adduct complex [Ph2BP2]Pt(Me)-
(THF) (13). The half-life for 25 was approximately 230 min at
90 °C. The product phenyl complex 26 was also appreciably
more stable at this elevated temperature than that of its neutral
THF counterpart [Ph2BP2]Pt(Ph)(THF) (16). The addition of 5
equiv of P(C6F5)3 to a benzene solution of 25 significantly
attenuated its rate of decay.
Figure 4. Representative plots of (a) [Ph2BP2]Pt(Me)(THF) (13) in C6H6
([) and C6D6 (×) acquired at 45 °C, and (b) [(Ph2SiP2)Pt(Me)(THF)]+
(14) in C6H6 ([) and C6D6 (×) acquired at 55 °C.
Figure 5. Representative plots of (a) [Ph2BP2]Pt(Me)(THF) (13) ([) and
[(Ph2SiP2)Pt(Me)(THF)]+ (14) (×) in C6D6 acquired at 55 °C, and (b) 13
([), 14 (×), and [(dppp)Pt(Me)(THF)]+ (15) (O) in C6H6 with 5 equiv of
THF acquired at 55 °C.
kinetically competitive degradation of [(dppp)Pt(Ph)(THF)]+
(18) to the biphenyl complex 20. An inhibitory build-up of THF
occurs at such a rate that it complicates the kinetics of 15 by
comparison to 13 and 14.
The effect on the rate of changing the ionic concentration of
the solution was examined by the addition of one equivalent of
[nBu4N][B(C6F5)4]. The addition of [nBu4N][B(C6F5)4] to
[Ph2BP2]Pt(Me)(THF) (13) had no measurable effect on its rate
of decay. However, the rate of decay of [(Ph2SiP2)Pt(Me)-
(THF)]+ (14) was slowed somewhat upon inclusion of a
stoichiometric equivalent of [nBu4N][B(C6F5)4]. Worth mention-
ing is that a second platinum compound was observed by
31P{1H} NMR spectroscopy upon addition of 1 equiv of [nBu4N]-
[B(C6F5)4] to 14 that represented ∼24% of the total integrated
phosphorus signal. The spectrum of this secondary species
differs only slightly from the starting complex 14, and it is
tempting to assign this secondary species as the anion-
coordinated ion-pair [(Ph2SiP2)Pt(Me)]+[(B(C6F5)4)]-; however,
we have not been able to rigorously isolate or thoroughly
characterize this species.
The analogous P(C6F5)3-ligated cationic complex, [(Ph2SiP2)-
Pt(Me){P(C6F5)3}][B(C6F5)4] (29) was prepared by similar
means and its thermolysis in benzene-d6 was briefly examined
(Scheme 3). Complex 29 underwent conversion to the cationic
(28) Fernandez, A. L.; Wilson, M. R.; Prock, A.; Giering, W. P. Organometallics
2001, 20, 3429-3435.
9
8876 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
Table 5. Methane Isotopomer Ratios Resulting from Thermolysis
of Methyl Complexes in Benzene-d6
compound
T (°C)
CH :CH D
4 3
[Ph2BP2]Pt(Me)(THF) (13)
55
55
55
55
90
90
3.0:1.0
1.0:7.3
1.0:7.6
1.0:5.8
1.0:5.9
1.0:5.5
[Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20)
[(Ph2SiP2)Pt(Me)(THF)]+ (14)
[(dppp)Pt(Me)(THF)]+ (15)
[Ph2BP2]Pt(Me){P(C6F5)3} (25)
[(Ph2SiP2)Pt(Me){P(C6F5)3}]+ (29)
Figure 7. Representative 1H NMR spectra of the aryl region of [Ph2BP2]-
Pt(Me)(THF) (13) in benzene-d6 (a) before thermolysis, and (b) after
thermolytic conversion to predominantly complex [Ph2BP2]Pt(Ph)(THF)
(16). The complexity of spectrum (b) reflects deuterium incorporation from
benzene-d6 into the [Ph2BP2] ligand.
as an average of three separate experiments. Only two methane
byproducts, CH4 and CH3D, were observed for each of these
five systems, and in no case was either isotopomer produced
exclusively. The relative ratio of the two byproducts favored
CH4 for neutral [Ph2BP2]Pt(Me)(THF) (13): this result was
markedly different from cationic [(Ph2SiP2)Pt(Me)(THF)]+ (14)
and [(dppp)Pt(Me)(THF)]+ (15) and the bulky phosphine-ligated
complexes [Ph2BP2]Pt(Me){P(C6F5)3} (25) and [(Ph2SiP2)Pt-
(Me){P(C6F5)3}]+ (29), all of which favored CH3D. We also
noted that the aryl region of the 1H NMR spectrum of [Ph2BP2]-
Pt(Me)(THF) (13) grew increasingly complex during the time
course of its thermolysis (Figure 7), suggesting possible
deuterium incorporation into the aryl positions of the [Ph2BP2]
ligand.
Figure 6. (a) 50% displacement ellipsoid representation of [Ph2BP2]Pt-
(Me){P(C6F5)3}‚C6H6 (25‚C6H6). Hydrogen atoms and benzene solvent
molecule are omitted for clarity. Selected interatomic distances (Å) and
angles (°): Pt-C39, 2.120(3); Pt-P1, 2.3412(12); Pt-P2, 2.3361(10); Pt-
P3, 2.2662(12); Pt-B, 3.845(4); C39-Pt-P1, 87.94(9); C39-Pt-P3,
81.40(9); P1-Pt-P2, 86.04(4); P2-Pt-P3, 104.89(4). (b) Space filling
representation of 25, looking down the platinum-methyl bond.
Scheme 3
II.9a. Spectral Analysis of Zwitterionic 13 in C6D6
-
Evidence for Intermediate Pt(IV) Species Arising from
Reversible Ligand Metalation Processes. The high degree of
CH4 liberated when [Ph2BP2]Pt(Me)(THF) (13) was incubated
in benzene-d6 suggested to us the possibility of reversible
[Ph2BP2] ligand metalation processes and prompted a closer
examination of its 31P{1H} and 1H NMR spectra at lower
temperature. When a sample of 13 slightly wetted with excess
phenyl complex [(Ph2SiP2)Pt(Ph){P(C6F5)3}][B(C6F5)4] (30) at
90 °C at a rate similar to the conversion of [Ph2BP2]Pt(Me)-
{P(C6F5)3} (25) to [Ph2BP2]Pt(Ph){P(C6F5)3} (26). Complex 30
was, however, less stable under the thermolysis conditions and
gradually afforded the dinuclear, biphenyl-bridged complex 19.
The collection of accurate rate data was precluded for 29 due
to its poor solubility in benzene.
II.8. Isotopic Incorporation into Methane Byproduct. The
degree of deuterium incorporated into the methane byproduct
was determined after thermolysis of complexes 13-15, 25, and
29 in benzene-d6. The data are presented in Table 5. The nature
of the methane byproduct released in the benzene-d6 C-D bond
activation reaction was examined by first executing each reaction
in a sealed J. Young tube, and then inspecting the methane
region of the 1H NMR spectrum after completion of the reaction.
The integrated ratio of the methane byproducts reported is taken
1
THF was dissolved in benzene-d6, its H and 31P{1H} NMR
spectra revealed complex 13 to be the only detectable solution
species. However, when analytically pure 13, obtained by careful
drying under an argon purge to remove residual THF, was
dissolved in benzene-d6 and examined at 25 °C by 31P{1H}
NMR spectroscopy, additional signals were observed that
indicated the presence of species distinct from 13. In contrast
to neutral [Ph2BP2]Pt(Me)(THF) (13), cationic complexes
[(Ph2SiP2)Pt(Me)(THF)]+ (14) and [(dppp)Pt(Me)(THF)]+ (15)
provided unremarkable NMR spectra at 25 °C in benzene and
in benzene-d6, indicative of the presence of a single solution
species (see the Supporting Information). Selected regions of
1
the 31P{1H} and H{31P} NMR spectra of 13 in benzene-d6 at
25 °C are shown in Figure 8 to aid their interpretation.
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8877

A R T I C L E S
Thomas and Peters
Figure 9. Possible structures for the ortho-metalated platinum(IV) methyl
hydride intermediate B. 5- and 6-coordinate geometries for B can be
envisioned.
platinum(IV) product derived from metalation at the di-
phenylborate unit of the [Ph2BP2] ligand, rather than an
arylphosphine position. Moreover, the chemical shift and
coupling data for the hydride and methyl ligands of B are
consistent with them being trans to a phosphine donor of the
[Ph2BP2] ligand.29 These NMR data are consistent with two
possible structures (Figure 9) for the intermediate referred to
as B that we cannot distinguish. Both 5- and 6-coordinate
platinum(IV) species have literature precedent, though 6-coor-
dinate structures are certainly more common.30
At least one and possibly two other methyl resonances distinct
from those for [Ph2BP2]Pt(Me)(THF) (13) and B could also be
distinguished in the 1H{31P} NMR spectrum. More data is
provided below to verify the presence of four spectroscopically
detectable methyl-containing species when pure 13 is dissolved
in benzene-d6 at 25 °C. The only well-resolved hydride signal
that could be assigned with confidence at 25 °C, however, was
that arising from B.
Figure 8. Representative NMR spectra of complex [Ph2BP2]Pt(Me)(THF)
(13) at 25 °C in benzene-d6 showing (a) the 31P{1H} NMR containing the
expected resonances for 13 and additional resonances corresponding to
species B, C and D, and (b) the 1H{31P} NMR signals for methyl and
hydride resonances assigned to species B.
II.9b. Preparation of the 13C-Labeled Complex [Ph2BP2]-
Pt(13CH3)(THF) (13-13CH3) and its Characterization by
NMR Spectroscopy in Benzene-d6 at 25 °C. As a means to
more definitively determine the number of methyl-containing
species in solution, we chose to incorporate a 13C-labeled methyl
group into complex [Ph2BP2]Pt(Me)(THF) (13). Preparation of
[Ph2BP2]Pt(13CH3)(THF) (13-13CH3) proceeded from the same
Examination of the 31P{1H} NMR spectrum of [Ph2BP2]Pt-
(Me)(THF) (13) dissolved in C6D6 at 25 °C displayed three sets,
and possibly a fourth set, of resonances, signifying multiple
species in solution. The major set of resonances (labeled 13;
∼80%) appears as two doublets at 34.1 and 16.1 ppm (2JP-P
)
22 Hz), respectively, and corresponds to complex 13. Another
set of signals arising as two doublets centered at 23.0 and 19.3
ppm (2JP-P ) 20 Hz), respectively, labeled B, represents ∼10%
of the total integrated intensity. There is a third, and perhaps
fourth, set of resonances in the 31P{1H} NMR spectrum (labeled
C and D) centered at 21.7 and 20.4 ppm that can be crudely
assigned as doublets with P-P coupling evident (2JP-P ≈ 20
Hz). These signals represent only ∼5-7% of the total integrated
intensity and correspond to possibly two other species.
method as for 13, using (COD)Pt(13CH3)2 as the starting
31
platinum material.
Dissolving [Ph2BP2]Pt(13CH3)(THF) (13-13CH3) in C6D6 and
examining its NMR spectra at 25 °C provided additional
information about the species in solution. Definitely three and
more likely four distinct sets of platinum-bound methyl reso-
1
nances could be discerned in the H{31P} NMR spectrum of
13-13CH3. The methyl resonances of 13-13CH3 that correlate
to those assigned for unlabeled [Ph2BP2]Pt(Me)(THF) (13)
To further examine the additional species in solution, the
1
showed the expected JC-H coupling arising from the labeled
1H{31P} NMR spectrum of [Ph2BP2]Pt(Me)(THF) (13) in C6D6
carbon in 13-13CH3, and the signature 195Pt satellites were
discernible. The hydride signal at -4.4 ppm remained un-
changed by comparison to the unlabeled derivative 13. We
conclude that cis two-bond coupling between the methyl and
hydride ligands of species B is therefore not resolvable.
The presence of four discrete methyl resonances in the
benzene-d6 13C{1H} NMR spectrum of [Ph2BP2]Pt(13CH3)(THF)
1
was also examined at 25 °C. The H{31P} NMR spectrum of
the same sample reveals a well-defined hydride signal at -4.4
ppm, (1JPt-H ) 667 Hz), and a distinct methyl resonance at -1.2
ppm with 195Pt satellites (2JPt-H ) 24 Hz) that is well separated
from the more intense methyl resonance of 13. These methyl
and hydride resonances appear to correlate to the 31P{1H} NMR
signals assigned to B, in that they all appear to decay at similar
rates as [Ph2BP2]Pt(Me)(THF) (13) is slowly converted to
[Ph2BP2]Pt(Ph)(THF) (16) at 25 °C. Also, the methyl resonance
assigned to B integrates as three times the intensity of the hy-
dride resonance. Therefore, we assign a hydride, a methyl, and
a [Ph2BP2] ligand to a single platinum center in B, which we
think is most consistent with a [Ph2BP2]-metalated platinum(IV)
complex. Because the hydride signal we assign to B is present
even when the deuterated system [Ph2B(CH2P(C6D5)2)2]Pt(Me)-
(THF) (13-d20) is examined (vide infra), we suggest that B is a
(29) Puddephatt, R. J. Coord. Chem. ReV. 2001, 219-221, 157-185.
(30) For examples of 5-coordinate platinum(IV): (a) Ulrich, F.; Kaminsky, W.;
Goldberg, K. I. J. Am. Chem. Soc. 2001, 123, 6423-6424. (b) Ulrich, F.;
Goldberg, K. I. J. Am. Chem. Soc. 2002, 124, 6804-6805. (c) Reinartz,
S.; White, P. S.; Brookhart, M.; Templeton, J. L. J. Am. Chem. Soc. 2001,
124, 6425-6426. For lead references on 6-coordinate platinum(IV): (d)
Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; John Wiley & Sons: New York, 1999; pp
1080-1082. (e) Roundhill, D. M. In ComprehensiVe Coordination Chem-
istry, Vol. 5; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, 1987; pp 353-531.
(31) Nozaki, K.; Sato, N.; Tonomura, Y.; Yasutomi, M.; Takaya, H.; Hiyama,
T.; Matsubara, T.; Koga, N. J. Am. Chem. Soc. 1997, 119, 12 779-12 795.
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8878 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
not formed in the case of [Ph2BP2]Pt(Me)(THF) (13) is that
the signal due to 13CH4 in Figure 10 is very weak. This signal
most likely results from very modest benzene or ligand
activation at 25 °C during the time course of the data collection
(hours). We conclude that the species B, C, and D that were
observed in the 31P{1H} NMR of 13 each contain a methyl group
and are therefore formed prior to reductiVe elimination of
methane.
II.9c. Preparation, Spectroscopic Characterization, and
Benzene Reaction Chemistry of the d20-Labeled Complex
[Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20). We also prepared
the d20-[Ph2BP2] ligand [Ph2B(CH2P(C6D5)2)2] according to
Scheme 4. Although d10-methyldiphenylphosphine was obtained
in very pure form with virtually no detectable aryl protons (1H
NMR), subsequent lithiation followed by addition of diphenyl-
chloroborane to form the required borate ligand gave rise to a
small degree (<10%) of proton incorporation in the phenyl rings.
The complex [Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20)
1
2
was subsequently prepared and studied by H and H NMR
spectroscopies. Most important was the use of these spectra to
aid the assignment of B. The hydride signal at -4.4 ppm that
appears when [Ph2BP2]Pt(Me)(THF) (13) is dissolved in
1
benzene-d6 is still present in the H NMR spectrum of 13-d20:
its intensity is not appreciably diminished, as would be expected
if the hydride were derived from the d-labeled phenylphos-
phines. The H NMR spectrum of 13-d20 was also scrutinized
thoroughly: no platinum deuteride could be detected. As
mentioned above, we interpret these data by formulating B as
a platinum(IV) methyl hydride metalated at the diphenylborate
position.
Figure 10. 13C{1H} NMR spectrum of [Ph2BP2]Pt(13CH3)(THF) (13-13CH3)
when dissolved in benzene-d6 at 25 °C. The spectrum shows four distinct
sets of platinum methyl resonances, the major set corresponding to complex
13-13CH3 itself.
2
(13-13CH3), presented in Figure 10, corroborates our assignment
of four distinct species in the 31P{1H} NMR spectrum of
[Ph2BP2]Pt(Me)(THF) (13), although we cannot definitively
Two other important results were revealed from examination
of the rate of benzene C-H bond activation exhibited by
[Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20). The rate of decay
of 13-d20 was observed in benzene and benzene-d6 at 55 °C,
and the half-lives were approximately 54 and 95 min, respec-
tively. This provided an isotope effect of k(C6H6)/k(C6D6) ∼1.8.
Also, the rate of decay of 13-d20 was about three times slower
than that of unlabeled [Ph2BP2]Pt(Me)(THF) (13) in benzene-
d6 at 55 °C, providing a k13/k13-d20 of ∼3 between the two
systems. Additionally, the methane byproduct released during
the benzene-d6 thermolysis of 13-d20 showed predominantly
CH3D (1.0 CH4 :7.3 CH3D) rather than CH4, as was the case
for 13 (Table 5). The implication of these labeling results to
the overall solution chemistry of 13 will be more thoroughly
discussed in the next section. We simply note for now the
likelihood that reversible metalation at a phenylphosphine arm
of 13 is likely operative, and a contributing factor to the rate of
its intermolecular benzene C-H activation chemistry.
Considering the NMR data for [Ph2BP2]Pt(Me)(THF) (13),
[Ph2BP2]Pt(13CH3)(THF)(13-13CH3),and[Ph2B(CH2P(C6D5)2)2]-
Pt(Me)(THF) (13-d20) as a whole, it is possible to assign with
confidence the presence of 13 and also intermediate B. Species
C and D may represent isomers of a ligand-metalated species,
in which we simply do not detect the hydride signals, but we
think that they more likely represent stable Pt(II) species where
THF is no longer coordinated in the fourth position. Other
alternative ligands that would occupy that site include a benzene
adduct, an isomer in which the [Ph2BP2] ligand is bound η3, or
perhaps a three-coordinate platinum center, the latter possibility
seeming least likely. Given the recent characterization of an
2
correlate the observed signals. The JC-P coupling can be
discerned in each resonance and, in three cases, the 195Pt
satellites are observed. One doublet of doublets at 12.0 ppm
1
2
(labeled 13-13CH3, JPt-C ) 543 Hz, JP-C ) 4.4, 85 Hz) is
consistent with the previously observed methyl for unlabeled
[Ph2BP2]Pt(Me)(THF) (13). Three additional doublets of dou-
blets are also present, and are labeled as x, o, and * in Figure
2
10. The signal for species x (13.5 ppm, JP-C ) 5, 90 Hz) is
partially obscured by the platinum satellites of the methyl group
of 13-13CH3, and its low intensity prevents the detection of
platinum coupling. The signals assigned as o and * are separated
from 13-13CH3 and x, and each displays coupling to one
platinum and two phosphorus atoms, arising at 5.5 ppm (1JPt-C
2
) 367 Hz, JP-C ) 5, 88 Hz) and 4.1 ppm (1JPt-C ) 525 Hz,
2JP-C ) 6, 86 Hz), respectively. Each of these signals displays
coupling to 31P that is consistent with one cis and one trans
relationship.
The region between 150 and 400 ppm of the 13C{1H} NMR
spectrum was also carefully inspected for the presence of any
“methylene-hydride” type species, such as [Ph2BP2]PtdCH2(H),
that might arise from R-hydride migration processes exhibited
by [Ph2BP2]Pt(13CH3)(THF) (13-13CH3). No evidence for any
such species was obtained. Formation of a carbene-hydride
species from a THF activation process with concomitant
expulsion of methane would also have been plausible given that
such a process was observed for the cationic system [(TMEDA)-
Pt(Me)(L)]+ (L ) OEt2, THF) reported by Holtcamp, Labinger,
and Bercaw.6 Further confirmation that carbene hydrides are
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8879

A R T I C L E S
Thomas and Peters
Scheme 4
η2-benzene adduct of platinum(II)10b and that benzene is the
solvent, we propose that one of species C or D is most likely
[Ph2BP2]Pt(Me)(η2-benzene).
rate reflect different operative mechanisms and therefore do not
clearly provide information concerning how the relative elec-
trophilicities of each system correlate to the rate of the
elementary C-H bond-breaking step they each exhibit.
III. Discussion
Each case showed a slowing of the rate of C-H activation
in the presence of additional equivalents of THF. It seems
reasonable to assume for cationic [(Ph2SiP2)Pt(Me)(THF)]+ (14)
that THF is competing with benzene to bind to the metal center,
in accord with the THF self-exchange data acquired in benzene-
d6. Given that kex for neutral [Ph2BP2]Pt(Me)(THF) (13) shows
no [THF] dependence for THF self-exchange, we interpret the
[THF] dependence of the decay rate of 13 in benzene to imply
that the addition of THF affects an equilibrium process preceding
C-H activation which is not ligand exchange.
III.1. Comparative Aspects of Benzene C-H Activation
Chemistry Exhibited by 13 and 14. Complexes [Ph2BP2]Pt-
(Me)(THF) (13), [(Ph2SiP2)Pt(Me)(THF)]+ (14), and [(dppp)-
Pt(Me)(THF)]+ (15) each react in benzene to generate the phenyl
derivatives [Ph2BP2]Pt(Ph)(THF) (16), [(Ph2SiP2)Pt(Ph)(THF)]+
(17), and [(dppp)Pt(Ph)(THF)]+ (18), respectively.11 Our pri-
mary aim in this section is to assemble the many pieces of data
presented in the results section into a reasonable model that
describes the intimate benzene solution chemistry of neutral 13
in comparison to its cationic analogues 14 and 15. Within this
context, we will try to describe the mechanisms by which
benzene enters the coordination sphere of the respective
platinum centers, the factors that dictate the rate at which it
undergoes C-H activation, and the role of the auxiliary
phosphine ligand in each case. Because the solution chemistries
of cationic 14 and 15 appear to be very similar, we confine our
comparative discussion to systems [Ph2BP2]Pt(Me)(THF) (13)
and [(Ph2SiP2)Pt(Me)(THF)]+ (14) and note by analogy that our
conclusions between these two systems map to similar conclu-
sions between 13 and [(dppp)Pt(Me)(THF)]+ (15).
The measured rates of first-order decay exhibited by
[Ph2BP2]Pt(Me)(THF) (13) and [(Ph2SiP2)Pt(Me)(THF)]+ (14)
in both benzene and benzene-d6 provided two important pieces
of data. First, complex 13 is more reactive toward intermolecular
benzene C-H activation than 14. This was at first surprising.
At the outset of our study, much attention was being drawn to
increasingly electrophilic platinum systems,5-12 the rationale
being that more electrophilic systems would undergo C-H
activation more rapidly. This study, in addition to recent studies
by Bercaw7 and Bergman,13 establishes that a variety of factors
dominate the overall rate of intermolecular C-H activation and
that electronic factors can play an indirect, often nonintuitive,
role.
III.2. Evidence for Reversible Ligand Metalation Processes
Operative in the Chemistry of Neutral 13. The solution NMR
data obtained for unlabeled [Ph2BP2]Pt(Me)(THF) (13) and its
13C-CH3 and d20-[Ph2BP2]-labeled derivatives [Ph2BP2]Pt(13CH3)-
(THF) (13-13CH3) and [Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-
d20) allow us to suggest that reversible [Ph2BP2] ligand
metalation processes dominate the chemistry of neutral 13. In
comparison, the solution data obtained for [(Ph2SiP2)Pt(Me)-
(THF)]+ (14) and [(dppp)Pt(Me)(THF)]+ (15) provide no direct
evidence for related processes: inspection of the 31P{1H} NMR
spectrum of analytically pure 14 and 15 at 25 °C showed only
a single species. Although the observation of small amounts of
CH4 upon thermolysis of [(Ph2SiP2)Pt(Me)(THF)]+ (14) and
[(dppp)Pt(Me)(THF)]+ (15) in benzene-d6 suggests the likeli-
hood that ligand activation processes may be operative to some
modest extent, they are certainly much less prevalent. For neutral
[Ph2BP2]Pt(Me)(THF) (13), [Ph2BP2] metalation processes
involve both the arylphosphine positions and the diphenylborate
unit. Most striking is that the NMR data provides strong
evidence for a spectroscopically observable platinum(IV) methyl
hydride (intermediate B), a species that would result from
metalation of the diphenylborate unit. Species such as B are
typically not observable due to facile reductive elimination to
regenerate platinum(II). The chelate structure postulated for B
(Figure 9) is expected to be stable given the excellent chelate
Due in part to the pronounced kinetic deuterium isotope effect
measured for [(Ph2SiP2)Pt(Me)(THF)]+ (14), k(C6H6)/k(C6D6)
) 6.52 at 55 °C, compared to the modest if not negligible effect
measured for [Ph2BP2]Pt(Me)(THF) (13), k(C6H6)/k(C6D6) )
1.26 at 45 °C, the rate of C-D activation in benzene-d6 is
approximately fourteen times faster for 13 than it is for 14 (t1/2
at 55 °C ) 31 and 430 min, respectively). If we assume that
the isotope effect remains relatively constant over temperature,
we can extrapolate that the difference in rates in C6H6 at 55 °C
to be small, however, with [Ph2BP2]Pt(Me)(THF) (13) being
about a factor of 2 faster. The measured differences in absolute
properties of the tris(phosphino)borate ligand [PhBP3],32
a
tripodal ligand whose chelate ring sizes compare well with those
shown in B.
If our assignment of B is correct, neutral [Ph2BP2]Pt(Me)-
(THF) (13) represents the first system in which a reVersibly
formed platinum(IV) intermediate is observable within a plati-
num(II) system that also mediates a well-defined, intermolecular
(32) We note that the 6-coordinate platinum(IV) complex [PhBP3]PtMe3 has
been prepared and is thermally very robust. J. C. Thomas, J. C. Peters,
unpublished results.
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8880 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
Table 6. Summary of Key Mechanistic Observables for the Degradation of 13 and 14 in Benzene
• rate of C-H activation at 55 °C: k ) 1.80(6) × 10-4 s-1
• rate of C-D activation at 55 °C: k ) 2.76(7) × 10-5 s-1
• k(C6H6)/k(C6D6) for 14 ) 6.52 at 55 °C
• rate of C-H activation at 45 °C: k ) 1.42(5) × 10-4 s-1
• rate of C-D activation at 45 °C: k ) 1.13(3) × 10-4 s-1
• k(C6H6)/k(C6D6) at 45 °C for 13 ) 1.26
• k(C6H6)/k(C6D6) at 45 °C for 13-d20 ) 1.8
• k13/k13-d20 in C6D6 at 55 °C is ∼3.1
• k13/k14 in C6D6 at 55 °C is ∼14
• k13/k14 in C6H6 at 55 °C is ∼2.5
• k13/k13-d20 in C6H6 at 55 °C is ∼2
• mechanism of THF self-exchange is associative
activation parameters:
• mechanism of THF self-exchange is ligand-assisted (or dissociative)
activation parameters:
∆Sq ) -30.2 ( 5.2 e.u. and
∆Sq ) -0.1 ( 5.4 e.u. and
∆Hq ) 1.9 ( 0.5 kcal/mol
∆Hq ) 16.0 ( 1.6 kcal/mol
• CH4:CH3D ratio for methane byproduct
after thermolysis of 14 in C6D6: 1.0:7.6
• CH4:CH3D ratio for methane byproduct after
thermolysis of 13 in C6D6: 3.0:1.0
• CH4:CH3D ratio for methane byproduct after
thermolysis of 13-d20 in C6D6: 1.0:7.3
• negligible deuterium incorporation into the
(Ph2SiP2) ligand after thermolysis in benzene-d6
• significant deuterium incorporation into the
[Ph2BP2] ligand after thermolysis in benzene-d6
• (Ph2SiP2) metalation in benzene solution is kinetically
noncompetitive with benzene C-H activation processes
• [Ph2BP2] metalation in benzene solution is kinetically
very competitive with benzene C-H activation processes
• no spectroscopically observable intermediates
• several spectroscopically observable intermediates
C-H bond activation process. Given the similarity between a
[Ph2BP2] phenyl ring substrate and benzene itself, it is quite
reasonable to suggest that the intermolecular benzene activation
process also proceeds via a platinum(II/IV) couple, as has been
asserted for a host of related platinum(II) systems that display
intermolecular C-H activation chemistry.5-12
consider in a mechanistic light are summarized in Table 6 and
underscore the observation that [Ph2BP2]Pt(Me)(THF) (13)
appears to undergo ligand metalation chemistry.
For the cationic system [(Ph2SiP2)Pt(Me)(THF)]+ (14) (and
by analogy [(dppp)Pt(Me)(THF)]+, 15), the neutral bis(phos-
phine) chelate appears to be relatively innocent with respect to
the C-H activation and THF exchange chemistry studied. From
the THF self-exchange data for [(Ph2SiP2)Pt(Me)(THF)]+ (14),
we infer that ligand substitution proceeds in a bimolecular,
associative fashion. We assume that this is true for THF
displacement by benzene in benzene solution, a process we
could not measure directly but can reasonably deduce by
comparison to the THF self-exchange data. The C-H activation
processes that occur in benzene solution for 14 appear also to
be predominantly intermolecular in nature. Although we cannot
rule-out the possibility of reversible ligand metalation processes
operative in the benzene solution chemistry of 14sindeed, a
small amount of CH4 is invariably observed as a byproduct upon
thermolysis of 14 in benzene-d6swe suggest that any intra-
molecular activation processes are sufficiently dominated by
intermolecular processes that it is a justifiable simplification to
mechanistically focus on the latter type. In Figure 11, we outline
the simplest plausible mechanism (Path A) by which cationic
14 undergoes intermolecular benzene activation. The outlined
mechanism is consistent with our data and is generally similar
to that proposed for other L2Pt(Me)+ systems that have been
thoroughly described elsewhere.5-12 Key points to note in
Path A are that benzene coordination to the cationic platinum
center is likely an associative process, and the benzene activation
step is likely to be rate-determining, intimated by the large
primary kinetic isotope effect that was observed for 14 (k(C6H6)/
k(C6D6) ) 6.52). Although we might favor a benzene C-H
activation step for the cationic system that occurs by oxidative
addition from platinum(II) to give a platinum(IV) phenyl
hydride, our data is unbiased and neither supports nor refutes
this hypothesis.
It appears to be possible to inhibit ligand metalation processes
prevalent in [Ph2BP2]Pt(Me)(THF) (13) by turning to an L-type
ligand that is more sterically encumbered. Such a comparison
is provided by the solution chemistry of [Ph2BP2]Pt(Me)-
{P(C6F5)3} (25). Although 25 exhibits a similar benzene C-H
activation reaction, thermolysis of 25 in benzene-d6 gives rise
to a very different ratio in the released methane isotopomers
by comparison to 13. The observed ratio for [Ph2BP2]Pt(Me)-
{P(C6F5)3} (25) was very similar to that observed for its cationic
counterpart [(Ph2BP2)Pt(Me){P(C6F5)3}]+ (29). To explain these
data, we suggest that the steric bulk of 25 prohibits anchimeric
η3-binding of its [Ph2BP2] ligand, thereby attenuating [Ph2BP2]
ligand metalation processes that favor the release of CH4 over
1
CH3D. Worth noting is that the 31P{1H} and H NMR spectra
of 25 indicate a single solution species prior to and during
thermolysis, similar to the case for [(Ph2SiP2)Pt(Me)(THF)]+
(14) and [(dppp)Pt(Me)(THF)]+ (15).
III.3. Overall Mechanistic Summary. The benzene solution
chemistry we have observed for the neutral [Ph2BP2]Pt(Me)-
(THF) (13) is generally comparable to that observed for its
isostructural but cationic relatives [(Ph2SiP2)Pt(Me)(THF)]+ (14)
and [(dppp)Pt(Me)(THF)]+ (15). Each system mediates an
intermolecular benzene C-H bond activation process under a
similar set of reaction conditions. The zwitterionic descriptor
ascribed to [Ph2BP2]Pt(Me)(THF) (13) seems to comparatively
predict its overall reactivity. However, important mechanistic
differences exist that can be attributed to the role that the bis-
(phosphine)-ligand auxiliary plays in each respective system.
These mechanistic distinctions most likely reflect electronic
rather than steric differences. The most relevant points to
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A R T I C L E S
Thomas and Peters
Figure 11. Postulated mechanisms for the predominant pathways leading to intermolecular benzene C-H activation chemistry for cationic [(Ph2SiP2)Pt-
(Me)(THF)]+ (14) (upper mechanism, Path A) and zwitterionic [Ph2BP2]Pt(Me)(THF) (13) (lower mechanism, Paths B, C, and D).
The neutral system [Ph2BP2]Pt(Me)(THF) (13) differs from
[(Ph2SiP2)Pt(Me)(THF)]+ (14) in that the bis(phosphine) aux-
iliary is intimately involved in both ligand exchange and C-H
activation processes operative in benzene solution. The zero-
order dependence in THF for THF self-exchange reflects the
ability of the [Ph2BP2] ligand to assist in ligand exchange by
an η3-binding mode, an intramolecular process akin to a solvent-
assisted ligand substitution process. Although THF loss might
also be dissociative based upon our exchange data, the prevailing
ligand metalation chemistry of [Ph2BP2]Pt(Me)(THF) (13)
persuades us to discount this latter possibility. This propensity
for the [Ph2BP2] ligand to achieve an η3-binding mode dramati-
cally impacts the nature of the C-H activation processes that
are observed in benzene solution.
In Figure 11, we outline three mechanistic pathways to
account for the solution chemistry of [Ph2BP2]Pt(Me)(THF) (13).
These are labeled Path B, Path C, and Path D, respectively.
Association of an aryl ring from the diphenylborate unit of 13
leads down Path B to a metalation process that generates a
platinum(IV) methyl hydride complex (product B), an interme-
diate that can be spectroscopically detected. We do not think
product B precedes an intermolecular benzene C-H activation
step. Rather, we think that metalation at the diphenylborate unit
is reversible and that product B is ultimately funneled along
Paths C and D. Common to Paths C and D is an η3-binding
mode for the [Ph2BP2] auxiliary that involves the arylphosphine
donor rather than the diphenylborate unit. Path C proceeds along
a simpler scenario that invokes a [Ph2BP2]-assisted benzene-d6
substitution for THF, followed by oxidative addition of benzene-
d6 and reductive elimination of CH3D, the methane byproduct
expected. The key distinction between Path C and Path A is
the mechanism by which benzene enters the platinum coordina-
tion sphere. Our intuition is to suggest that the rate-determining
step along Path C is the C-H activation step, and that the
negligible primary kinetic isotope effect that was measured for
[Ph2BP2]Pt(Me)(THF) (13) (k(C6H6)/k(C6D6) ) 1.26) is due to
the kinetic dominance of the fourth path, Path D. In this last
pathway, arylphosphine ligand metalation processes occur that
produce platinum(IV) methyl hydride-species distinct from
product B (shown in Path B). After ligand metalation, benzene-
d6 enters the platinum coordination sphere at one of several
indistinguishable stages, each of which involves the reductive
elimination of CH4 (for simplicity only one scenario is presented
in Figure 11 explicitly). C-D activation of benzene-d6, followed
by a reverse metalation process that transfers dueteride into the
[Ph2BP2] ligand, ultimately leads to the phenyl platinum
complex. Path D thus accounts for the high degree of CH4
released by 13 in benzene-d6 and the incorporation of deuteride
into the [Ph2BP2] ligand. We are comfortable explicitly invoking
platinum(IV) intermediates along both Paths C and D that arise
from oxidative addition of benzene-d6 because of our spectro-
scopic evidence for a platinum(IV) species resulting from
[Ph2BP2] metalation (product B, Path B). Also, we emphasize
that our inability to detect the platinum(IV) hydride species
produced by [Ph2BP2] metalation along Path D is because the
ligand metalation process is itself rate-determining. Recall a key
piece of evidence that supports this assertionsin both benzene
and benzene-d6, the rate of decay of the d20-labeled derivative
[Ph2B(CH2P(C6D5)2)2]Pt(Me)(THF) (13-d20) is significantly
slower than that of [Ph2BP2]Pt(Me)(THF) (13) itself (k13/k13-d20
≈ 3 in benzene-d6). Under conditions in which Path D
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Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
dominates and ligand metalation is rate-determining, this is just
what we expect.
standard purple solution of sodium benzophenone ketyl in
tetrahydrofuran in order to confirm effective oxygen and
moisture removal. Deuterated chloroform, benzene, dichloro-
methane, acetonitrile, and acetone were purchased from Cam-
bridge Isotope Laboratories, Inc. and were degassed by repeated
freeze-pump-thaw cycles and dried over activated 3-Å mo-
lecular sieves prior to use. (COD)PtCl2,33 (COD)PtMeCl,33
(COD)PtMe2,34 (COD)Pt(13CH3)2,31 (COD)PtMePh,35 (COD)-
PtPh2,36 Ph2PMe,37 Ph2PCH2Li(TMEDA),38 ASNBr,39 [Li-
(Et2O)2][B(C6F5)4],40 [H(Et2O)2][B(C6F5)4],15 [nBu4N][B(C6F5)4],41
(dppp)Mo(CO)4,22 (dppp)PtMe2,14b and P(C6F5)342 were prepared
The observation that the rate of decay of [Ph2B(CH2P-
(C6D5)2)2]Pt(Me)(THF) (13-d20) is modestly slower in benzene-
d6 than in protio benzene (for 13-d20, k(C6H6)/k(C6D6) ≈ 1.8)
is perhaps more curious, but is conveniently explained as
follows: deuteration of the aryl positions of the [Ph2BP2] ligand
slows the rate of ligand metalation, and thereby attenuates the
overall rate by which 13-d20 traverses down Path D. This in
turn funnels more of the system down Path C, a path insensitive
to arylphosphine deuteration. In this manner, a preequilibrium
shift in benzene-d6 serves to amplify the primary kinetic isotope
effect of Path C and thereby expose C-H activation as rate-
determining along this path as well. We can therefore suggest
that a C-H activation process of some sort is rate-determining
for each of the four distinct pathways that are outlined in Figure
11.
16
by previously described methods. (dppp)PtPh2 was prepared
by reaction of (COD)PtPh2 with dppp in THF solution. B(C6F5)3
was purchased from Aldrich and recrystallized from pentane at
-35 °C prior to use. [HNEt3][BPh4] was prepared by stirring
an aqueous solution of HNEt3Cl and NaBPh4. [HNEtiPr2]-
[BPh4]43 was prepared by acidifying an aqueous solution of
NEtiPr2 with HCl (aq) and adding NaBPh4. The resulting white
precipitate was collected by filtration and dried under heat and
vacuum for 24 h prior to use. All other chemicals were
purchased from commercial vendors and used without further
purification. NMR spectra were recorded at ambient temperature
on Varian Mercury 300 MHz and Inova 500 MHz, and Joel
The final task we are left with is to account for the large role
that the [Ph2BP2] ligand plays in the solution chemistry of
neutral [Ph2BP2]Pt(Me)(THF) (13), whereas the Ph2SiP2 ligand
appears to be far more innocent with respect to the solution
chemistry of cationic [(Ph2SiP2)Pt(Me)(THF)]+ (14). The key
distinction between the two ligands is the propensity for the
[Ph2BP2] ligand to achieve an η3-binding mode, a binding mode
that is less prevalent for the neutral ligand Ph2SiP2. Because
each ligand is sterically very similar, we commit ourselves to
an electronic explanation that underscores the more electron-
rich nature of 13 relative to 14. It seems reasonable to suggest
that some of the anionic borate charge is disseminated to the
aryl groups of the [Ph2BP2] ligand. This results in aryl groups
in the [Ph2BP2] ligand that are better electron-pair donors than
the aryl groups of the neutral Ph2SiP2 ligand. Therefore, although
benzene outcompetes the aryl donors of the Ph2SiP2 ligand with
respect to coordinating platinum, thereby leading to the inter-
molecular solution chemistry observed, benzene does not out-
compete the aryl groups of the [Ph2BP2] ligand, and intramo-
lecular processes become prevalent. This subtle electronic
distinction might thereby have the effect of skewing the overall
mechanistic bias between the neutral and cationic systems.
1
400 MHz spectrometers, unless otherwise noted. H and 13C
NMR chemical shifts were referenced to residual solvent. 31P
NMR, 11B NMR, and 19F NMR chemical shifts are reported
relative to an external standard (0 ppm) of 85% H3PO4, neat
BF3‚Et2O, and neat CFCl3 respectively. IR spectra were recorded
on a Bio-Rad Excalibur FTS 3000 spectrometer at 2 cm-1
resolution controlled by Win-IR Pro software using a KBr
solution cell. Elemental Analyses were performed by Desert
Analytics, Tucson, AZ. X-ray diffraction experiments were
carried out by the Beckmann Institute Crystallographic Facility
on a Siemens CCD diffractometer.
[Ph2B(CH2PPh2)2][ASN] ([Ph2BP2], 1). Solid pale yellow
Ph2PCH2Li(TMEDA) (4.82 g, 15.0 mmol) was dissolved in
diethyl ether (180 mL) in a Schlenk flask with a stir bar and
sealed with a septum. The reaction vessel was cooled to -78
°C in a dry ice/acetone bath. Ph2BCl (1.514 g, 7.553 mmol),
dissolved in toluene (10 mL), was introduced dropwise via
syringe to the cooled reaction flask. The reaction was stirred
and warmed gradually to r.t. over 14 h, providing a pale yellow
precipitate. Volatiles were removed under reduced pressure, and
the resulting solids were isolated in a drybox on a sintered glass
frit and washed with diethyl ether [5 × 10 mL]. Drying under
reduced pressure provided pale yellow solid [Ph2B(CH2PPh2)2]-
[Li(TMEDA)2] (5.67 g).
The propensity for a structurally related neutral and cationic
platinum(II) system to mediate intermolecular benzene C-H
activation is generally comparable. However, the operational
mechanism by which each system mediates this chemistry is
distinct. The mechanism by which substrate coordination occurs,
and the propensity for intramolecular ligand C-H activation
processes, is clearly different between the neutral and cationic
systems. This study, along with several others,3 now allows us
to conclude that zwitterions of the type described herein are
generally capable of undergoing organometallic reactions akin
to their cation cousins. However, understanding the intimate
mechanism by which these zwitterions mediate elementary
reaction transformations will help to define a unique and
complementary role for zwitterions in catalysis.
Solid [Ph2B(CH2PPh2)2][Li(TMEDA)2] was dissolved in
ethanol (40 mL). ASNBr (1.8 g, 8.7 mmol) was dissolved in
ethanol (8 mL) and added to stirring 1. A white precipitate
(33) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-428.
(34) Costa, E.; Pringle, P. G.; Ravetz, M. Inorg. Synth. 1995, 31, 284-286.
(35) Hackett, M.; Whitesides, G. M. Organometallics 1987, 6, 403-410.
(36) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738-747.
(37) Seyferth, D.; Burlitch, J. M. J. Org. Chem. 1963, 28, 2463.
(38) Schore, N. E.; Benner, L. S.; Labelle, B. E. Inorg. Chem. 1981, 20, 3200-
3208.
Experimental. Unless otherwise noted, all syntheses were
carried out in the absence of water and dioxygen, using standard
Schlenk and glovebox techniques. Tetrahydrofuran, diethyl
ether, toluene, benzene, dichloromethane, and petroleum ether
were deoxygenated and dried by thorough sparging with N2 gas
followed by passage through an activated alumina column.
Hydrocarbon and ethereal solvents were typically tested with a
(39) Blicke, F. F.; Hotelling, E. B. J. Am. Chem. Soc. 1954, 76, 5099-5103.
(40) Stehling, U. M.; Stein, K. M.; Kesti, M. R.; Waymouth, R. M. Macro-
molecules 1998, 31, 2019-2027.
(41) LeSuer, R. J.; Geiger, W. E. Angew. Chem., Int. Ed. 2000, 39, 248-250.
(42) Kemmitt, R. D. W.; Nichols, D. I.; Peacock, R. D. J. Chem. Soc. A 1968,
2149-2152.
(43) Bakshi, P. K.; Linden, A.; Vincent, B. R.; Roe, S. P.; Adhikesavalu, D.;
Cameron, T. S.; Knop, O. Can. J. Chem. 1994, 72, 1273-1293.
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8883

A R T I C L E S
Thomas and Peters
formed immediately. The mixture was stirred for 10 min, and
white solids were subsequently collected by filtration. The solids
were washed with ethanol [2 × 10 mL] and diethyl ether [3 ×
10 mL] and dried under reduced pressure for 24 h, providing 1
as a pure, white solid (4.30 g, 6.23 mmol, 83.1%).
(128.3 MHz, CD3CN): δ -14.1. IR: (CH2Cl2) νCO ) 2005,
1896, 1849 cm-1. Anal. Calcd. for C50H50BMoNO4P2: C, 66.90;
H, 5.61; N, 1.56. Found: C, 67.04; H, 5.82; N, 1.52.
(Ph2SiP2)Mo(CO)4 (5). Solid Mo(CO)6 (50.3 mg, 191 µmol)
and solid Ph2Si(CH2PPh2)2 (108.2 mg, 186.3 µmol) were
combined and dissolved in THF (3 mL). The sealed vessel was
placed under partial vacuum and heated to 65 °C for 36 h. The
resulting colorless solution was cooled to r.t., and volatiles were
removed under reduced pressure. The off-white solids were
washed with petroleum ether [3 × 2 mL] and dried under
reduced pressure, providing analytically pure (Ph2SiP2)Mo(CO)4
(139.5 mg, 95.0%).
1H NMR (300 MHz, CDCl3): δ 7.46 (m, 8H), 7.26 (m, 12H),
7.21 (m, 2H), 7.05 (t, 4H, JH-H ) 7.8 Hz), 6.95 (dd, 4H, JH-H
) 1.5, 7.8 Hz), 2.29 (d, 4H, JP-H ) 7.8 Hz). 13C{1H} NMR
(75.4 MHz, CDCl3): δ 215.4 (dd, JP-C ) 7.6, 7.6 Hz), 210.8
(t, JP-C ) 8.5 Hz), 139.3 (m), 134.6 (m), 134.3, 131.9 (m),
129.6, 129.5, 128.4 (m), 127.9, 13.6 (m). 31P{1H} NMR (121.4
MHz, CDCl3): δ 23.50. IR: (CH2Cl2) νCO ) 2018, 1922, 1896
cm-1. Anal. Calcd. for C42H34MoO4P2Si: C, 63.96; H, 4.35.
Found: C, 64.15; H, 4.09.
[[Ph2BP2]Pt(Me)2][ASN] (7). Solid [Ph2BP2][ASN] (391.8
mg, 0.5680 mmol) was suspended in THF (6 mL). A solution
of (COD)Pt(Me)2 (189.3 mg, 0.5679 mmol) in THF (2 mL)
was added to the suspension, and the reaction homogenized as
it stirred. A white precipitate formed after 1 h. The resulting
mixture was concentrated under reduced pressure and triturated
with pentane [2 × 2 mL]. The off white solids were dried under
reduced pressure, providing 7 as an off-white solid (511.2 mg,
98.4%). Crystals suitable for X-ray diffraction were grown from
slow evaporation of an acetonitrile solution of 7.
1H NMR (300 MHz, acetone-d6): δ 7.29 (br, 4H, ortho
B(C6H5)2), 7.17 (m, 8H, ortho P(C6H5)2), 7.00 (m, 12H, meta
B(C6H5)2 and P(C6H5)2), 6.74 (m, 4H, para P(C6H5)2), 6.62 (m,
2H, para B(C6H5)2), 3.65 (m, 8H, ((CH2CH2)2)2N), 2.23 (m,
8H, ((CH2CH2)2)2N), 1.64 (br, 4H, Ph2B(CH2PPh2)2). 13C{1H}
NMR (125.7 MHz, acetone-d6): δ 165 (br, ipso B(C6H5)2),
1
147.4 (d, ipso P(C6H5)2, JP-C ) 22 Hz), 134.7 (s, ortho
2
B(C6H5)2), 133.6 (d, ortho P(C6H5)2, JP-C ) 19 Hz), 127.1
3
(s, meta P(C6H5)2, JP-C ) 6 Hz), 126.0 (s, para P(C6H5)2),
125.3 (s, meta B(C6H5)2), 121.5 (s, para B(C6H5)2), 63.1
(((CH2CH2)2)2N), 25.7 (br, [Ph2B(CH2PPh2)2]), 22.1 (((CH2-
CH2)2)2N). 31P{1H} NMR (121.4 MHz, acetone-d6): δ -8.78
(2JP-B ) 10.0 Hz). 11B{1H} NMR (128.3 MHz, acetone-d6): δ
-12.6. Anal. Calcd. for C46H50BNP2: C, 80.11; H, 7.31; N,
2.03. Found: C, 79.89; H, 7.45; N, 2.15.
(C6H5)2Si(CH2PPh2)2 (Ph2SiP2, 2). Solid pale yellow
Ph2PCH2Li(TMEDA) (7.1300 g, 22.119 mmol) was suspended
in diethyl ether (100 mL) in a 250 mL Schlenk flask with a
stirbar and a septum. The flask was cooled to -78 °C in a dry
ice/acetone bath. Separately, diphenyldichlorosilane (2.7981 g,
11.051 mmol) was dissolved in diethyl ether (10 mL) and was
transferred by syringe to the cold reaction flask. The mixture
was allowed to stir and warm gradually over 7 h. Volatiles were
removed under reduced pressure, and the resulting solids were
collected on a sintered glass frit and washed with diethyl ether
[3 × 10 mL], removing yellow impurities and leaving white
solids. The solids were dissolved in dichloromethane (50 mL),
and the hazy solution was filtered over Celite on a sintered glass
frit. Volatiles were removed under reduced pressure from the
resulting clear, colorless solution, providing white solid
Ph2Si(CH2PPh2)2 (5.2838 g, 82.3%).
1H NMR (300 MHz, C6D6): δ 7.46 (dd, 4H), 7.31 (m, 8H),
7.05 (m, 6H), 6.97 (m, 12H), 1.89 (s, 4H, Ph2Si(CH2PPh2)2).
13C{1H} NMR (125.7 MHz, C6D6): δ 141.6, 136.0, 133.3,
129.8, 128.8, 128.2, 116.7, 12.4 (dd, Ph2Si(CH2PPh2)2, J ) 33
Hz, J ) 4.8 Hz). 31P{1H} NMR (121.4 MHz, C6D6): δ -23.29.
31P{1H} NMR (121.4 MHz, acetone-d6): δ -22.65. 29Si{1H}
NMR (99.3 MHz, THF): δ -10.42 (t, 2JSi-P ) 17.0 Hz). Anal.
Calcd. for C38H34P2Si: C, 78.59; H, 5.90. Found: C, 78.89; H,
5.78.
1H NMR (300 MHz, acetone-d6): δ 7.40 (m, 8H), 7.07 (m,
12H), 6.88 (m, 4H), 6.64 (m, 4H), 6.58 (m, 2H), 3.71 (m, 8H),
2.26 (m, 8H), 1.98 (br, 4H), 0.08 (t, 6H, 3JP-H ) 12 Hz, 2JPt-H
) 68 Hz). 13C{1H} NMR (125.7 MHz, acetone-d6): δ 167 (br),
140.1 (d), 134.4 (m), 133.5, 128.2, 127.3 (m), 126.3 (m), 122.0,
1
2
63.7, 22.9 (br), 22.8, 5.5 (dd, JPt-C ) 600 Hz, JP-C ) 103
Hz, 2JP-C ) 9.1 Hz). 31P{1H} NMR (121.4 MHz, acetone-d6):
δ 20.60 (1JPt-P ) 1892 Hz). 11B{1H} NMR (128.3 MHz,
acetone-d6): δ -13.7. Anal. Calcd. for C48H56BNP2Pt: C,
63.02; H, 6.17; N, 1.53. Found: C, 62.97; H, 5.90; N, 1.81.
(Ph2SiP2)PtMe2 (8). Solid 2 (199.7 mg, 0.3439 mmol) and
CODPtMe2 (114.4 mg, 0.3432 mmol) were dissolved in THF
(4 mL). After 30 min, volatiles were removed under reduced
pressure. The resulting solids were triturated with petroleum
ether (4 mL), and the solution was decanted. The resulting off-
white solids were dried under reduced pressure, providing 8
(253.9 mg, 91.6%). Crystals suitable for X-ray diffraction were
grown from petroleum ether vapor diffusion into a toluene
solution of 8.
[[Ph2BP2]Mo(CO)4][ASN] (4). Solid Mo(CO)6 (53.4 mg, 202
µmol) and solid [Ph2BP2][ASN] (133.0 mg, 192.8 µmol) were
combined and dissolved in THF (3 mL). The sealed vessel was
placed under partial vacuum and heated to 65 °C for 36 h. The
resulting pale yellow solution was cooled to r.t., and volatiles
were removed under reduced pressure. The pale yellow solids
were washed with petroleum ether [3 × 2 mL] and dried under
reduced pressure, providing analytically pure [[Ph2BP2]Mo-
(CO)4][ASN] (168.5 mg, 97.3%).
1H NMR (300 MHz, CD3CN): δ 7.36 (m, 8H), 7.11 (m,
12H), 6.94 (br d, 4H), 6.69 (m, 4H), 6.61 (m, 2H), 3.37 (m,
8H), 2.11 (m, 8H), 1.98 (br, 4H). 13C{1H} NMR (75.4 MHz,
CD3CN): δ 220.0 (m), 213.6 (m), 166 (br), 143.6 (m), 133.6,
133.0 (m), 128.6, 128.1, 126.6, 122.6, 63.8, 23.9 (br), 22.7.
31P{1H} NMR (121.4 MHz, CD3CN): δ 29.37. 11B{1H} NMR
1H NMR (300 MHz, CDCl3): δ 7.52 (m, 8H), 7.2-7.3 (m,
14H), 7.06 (t, 4H), 6.95 (dd, 4H), 2.29 (d, 4H, 2JP-H ) 9.9 Hz,
3
2
3JPt-H ) 25 Hz), 0.31 (dd, 6H, JP-H ) 6.3, 8.7 Hz, JPt-H
)
68 Hz). 1H NMR (300 MHz, acetone-d6): δ 7.56 (m, 8H), 7.2-
7.3 (m, 14H), 7.08 (m, 8H), 2.41 (d, 4H, 2JP-H ) 9.9 Hz, 3JPt-H
) 25 Hz), 0.17 (dd, 6H, 3JP-H ) 6.6, 8.1 Hz, 2JPt-H ) 69 Hz).
13C{1H} NMR (125.7 MHz, CDCl3): δ 135.4 (m), 134.9 (m),
134.1 (s), 133.5 (m), 129.8 (s), 129.4 (s), 127.9 (m), 127.9 (s),
10.5 (m), 5.7 (dd, 6H, 2JP-C ) 7.9, 101 Hz, 1JPt-C ) 596 Hz).
31P{1H} NMR (121.4 MHz, CDCl3): δ 14.35 (1JPt-P ) 1822
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A R T I C L E S
Hz). 31P{1H} NMR (121.4 MHz, acetone-d6): δ 12.00 (1JPt-P
) 1848 Hz). 29Si{1H} NMR (99.3 MHz, THF): δ -13.57. Anal.
Calcd. for C40H40P2PtSi: C, 59.62; H, 5.00. Found: C, 59.36;
H, 5.07.
reduced pressure. The resulting film was triturated with
petroleum ether (2 mL) and dried under reduced pressure,
providing [(dppp)Pt(Me)(CO)][B(C6F5)4] as a white solid (50.2
mg, 96.0%).
[Ph2BP2]Pt(Me)(CO) (10). A THF solution (2 mL) of
[Et3NH][BPh4] (47.5 mg, 0.113 mmol) was added to a stirring
THF solution (15 mL) of 7 (103.3 mg, 0.1129 mmol). Formation
of a white precipitate occurred gradually over 15 min. The
reaction was filtered, removing the white solids, and the solution
was transferred to a 50 mL Schlenk flask and sealed with a
septum and a needle valve. A stream of CO was passed through
the flask for 5 min. The septum was exchanged for a stopper
under an N2 flow, and the volatiles were removed under reduced
pressure. The resulting solids were dissolved in THF (10 mL),
filtered, concentrated, triturated with pentane [2 × 2 mL],
washed with Et2O [3 × 2 mL], and dried under reduced pressure,
providing 10 (78.1 mg, 86.3%).
1H NMR (300 MHz, CDCl3): δ 7.30-7.65 (20H, aryl
3
protons), 2.69 (m, 4H), 2.17 (m, 2Η), 0.76 (“t”, JP-H ) 6.00
2
Hz, JPt-H ) 57.3 Hz). 13C{1H} NMR (75.4 MHz, CDCl3): δ
176.9 (dd, Pt-CO, JP-C ) 134.0 Hz, JP-C ) 8.6 Hz, JPt-C
)
1320 Hz), 150.0, 146.8, 140.0, 138.1, 136.7, 134.8, 133.2, 132.7,
132.3, 129.9, 124.8, 124.0, 24.6, 24.1, 18.8, -0.9 (dd, Pt-CH3,
JP-C ) 59.8 Hz, JP-C ) 4.6 Hz, JPt-C ) 396 Hz). 19F{1H}
NMR (282 MHz, CDCl3): δ -132.9 (d), -163.2 (t), -166.9
(t). 31P{1H} NMR (121.4 MHz, CDCl3): δ 2.32 (d, JP-P ) 34.8
Hz, JPt-P ) 3126 Hz), -4.88 (d, JP-P ) 34.8 Hz, JPt-P ) 1547
Hz). 11B{1H} NMR (128.3 MHz, CDCl3): δ -17.1. IR:
(CH2Cl2) νCO ) 2118 cm-1. Anal. Calcd. for C53H29BF20OP2-
Pt: C, 47.88; H, 2.20. Found: C, 47.89; H, 1.99.
1H NMR (300 MHz, CDCl3): δ 7.12-7.34, 6.85-6.92,
6.72-6.83 (aryl protons), 2.14 (br, 2H, JPt-H ) 61 Hz), 2.09
[Ph2BP2]Pt(Me)(THF) (13). Solid 7 (49.3 mg, 53.9 µmol)
was dissolved in THF (2 mL). A THF solution (1 mL) of
[iPr2EtNH][BPh4] (24.3 mg, 54.1 µmol) was added to the stirring
solution of 7. The clear, colorless reaction rapidly produced a
white precipitate. The mixture was stirred for 15 min, and the
white solids (ASNBPh4) were filtered away. The solution was
concentrated under reduced pressure, and pentane (2 mL) was
added, precipitating solid 13 as a spectroscopically pure solid.
The solid was collected by filtration and washed with petroleum
ether [2 × 4 mL]. The collected solid was dried under a stream
of dry gas (dinitrogen or argon). Crystals suitable for X-ray
diffraction were grown from THF at -35 °C.
1H NMR (300 MHz, C6D6): δ 7.64 (m, 4H), 7.48 (m, 4H),
7.24 (m, 4H), 7.00 (m, 18H), 2.90 (br, 4H), 2.51 (d, 2H, 2JP-H
) 18 Hz), 2.37 (d, 2H, 2JP-H ) 14 Hz), 0.71 (br, 4H), 0.35 (br
d, 3H, Pt-CH3, 3JP-H ) 6 Hz, 2JPt-H ) 40 Hz). 13C{1H} NMR
(125.7 MHz, THF, -5 °C): δ 160.3 (br), 134.1 (d), 130.9 (d),
130.8 (d), 130.1 (d), 129.7, 127.3, 126.9, 125.5 (d), 125.1 (d),
123.5, 119.2, 64.9, 22.6, 21.2 (br), 15.3 (br), 8.2 (dd, Pt-CH3,
2JP-C(trans) ) 85.5 Hz, 2JP-C(cis) ) 4.8 Hz). 31P{1H} NMR (121.4
3
(br, 2H, 3JPt-H ) 54 Hz), 0.45 (t, 3H, 2JPt-H ) 58 Hz, 3JPt-P
)
6.0 Hz). 13C{1H} NMR (125.7 MHz, CDCl3): δ 180.5 (dd, Pt-
1
2
2
CO, JPt-C ) 1291 Hz, JP(trans)-C ) 131 Hz, JP(cis)-C ) 6.9
Hz), 162 (br), 136.2 (d), 133.5 (d), 132.5 (d), 132.3, 131.2 (d),
130.5 (d), 130.1 (d), 128.4 (d), 128.2 (d), 126.6, 122.8, 18.2
(br), 16.4 (br), -2.6 (d, 2JP-C ) 60 Hz). 31P{1H} NMR (121.4
MHz, CDCl3): δ 20.15 (d, 1JPt-P ) 3053 Hz, 2JP-P ) 31 Hz),
1
2
15.53 (d, JPt-P ) 1637 Hz, JP-P ) 31 Hz). 11B{1H} NMR
(160.4 MHz, CDCl3): δ -14.2. IR: (Nujol mull) νCO ) 2087
cm-1. IR: (CH2Cl2) νCO ) 2094 cm-1. Anal. Calcd. for C40H37-
BOP2Pt: C, 59.94; H, 4.65. Found: C, 60.37; H, 5.27.
[(Ph2SiP2)Pt(Me)(CO)][B(C6F5)4] (11). Solid off-white
[(Ph2SiP2)Pt(Me)(THF)][B(C6F5)4] (48.2 mg, 31.3 µmol) was
dissolved in dichloromethane (5 mL) in a round-bottom flask
containing a stirbar and sealed with a septum. The flask was
purged with carbon monoxide gas for 5 min, and allowed to
stir for 1 h under carbon monoxide. The flask was dried under
a stream of dinitrogen. The resulting film was triturated and
washed with petroleum ether [2 × 2 mL] and dried under
reduced pressure, providing [(Ph2SiP2)Pt(Me)(CO)][B(C6F5)4]
as a white solid (43.4 mg, 92.6%).
1
2
MHz, THF): δ 33.44 (d, JPt-P ) 1820 Hz, JP-P ) 22 Hz),
15.96 (d, JPt-P ) 4478 Hz, JP-P ) 22 Hz). 31P{1H} NMR
(121.4 MHz, C6D6): δ 34.14 (d, 1JPt-P ) 1813 Hz, 2JP-P ) 21
Hz), 16.09 (d, 1JPt-P ) 4453 Hz, 2JP-P ) 21 Hz). 11B{1H} NMR
(128.3 MHz, THF): δ -14.5. Anal. Calcd. for C43H45BOP2Pt:
C, 61.07; H, 5.36. Found: C, 61.14; H, 5.32.
1
2
1H NMR (300 MHz, CD2Cl2): δ 7.28-7.52 (m, 22H, aryl
H), 7.11 (t, 4H, J ) 7.5 Hz), 6.91 (d, 4H, J ) 6.9 Hz), 2.51 (d,
2H, JP-H ) 14.1 Hz, JPt-H ) 28.2 Hz), 2.43 (dd, 2H, J ) 3.3
Hz, JP-H ) 15.3 Hz, JPt-H ) 46.2 Hz), 0.62 (dd, 3H, JP-H
)
[(Ph2SiP2)Pt(Me)(THF)][B(C6F5)4] (14). Solid white (Ph2SiP2)-
PtMe2 (320.0 mg, 397.1 µmol) was dissolved in dichloro-
methane (2 mL) with THF (0.5 mL). Separately, [H(Et2O)2]-
[B(C6F5)4] (324.9 mg, 397.0 µmol) was dissolved in dichloro-
methane (3 mL) and added slowly to the stirring solution of
(Ph2SiP2)PtMe2, evolving gas. After addition was complete, the
reaction was stirred for 10 min. Volatiles were removed under
reduced pressure, and the mixture was triturated and washed
with petroleum ether [2 × 2 mL]. The resulting white solids
were dried under reduced pressure, providing off-white 14
(574.2 mg, 93.8%).
1H NMR (300 MHz, C6D6): δ 7.31 (m, 4H), 7.20 (m, 4H),
7.04 (m, 6H), 6.96 (m, 8H), 6.87 (t, 4H, J ) 7.6 Hz), 6.63 (d,
4H, J ) 6.7 Hz), 2.91 (m, 4H), 2.07 (d, 2H, J ) 2.4 Hz), 1.19
(d, 4H, J ) 12.2 Hz), 0.81 (m, 4H), 0.32 (dd, 3H, JP-H ) 1.8,
7.3 Hz, JPt-H ) 41.5 Hz). 13C{1H} NMR (125.7 MHz, C6D6):
δ 150.2, 148.3, 140.0, 138.1, 136.2, 133.7, 132.9 (m), 132.1,
6.0 Hz, JPt-H ) 56.4 Hz). 13C{1H} NMR (75.4 MHz, CD2Cl2):
δ 177.5 (dd, JP-C ) 137.9 Hz, JP-C ) 8.2 Hz), 148.7 (d), 138.8
(d), 136.9 (d), 134.0, 133.8 (d), 133.2 (d), 132.6 (m), 132.5
(m), 131.0, 130.0 (d), 129.8 (d), 128.9, 127.5 (m), 126.7 (m),
9.2 (m), 7.2 (m), -1.2 (dd, JP-C ) 61.6 Hz, JP-C ) 5.2 Hz,
JPt-C ) 400 Hz). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ 10.31
(d, JP-P ) 29.3 Hz, JP-Pt ) 3238 Hz), 7.16 (d, JP-P ) 29.3 Hz,
JP-Pt ) 1665 Hz). 11B{1H} NMR (128.3 MHz, CD2Cl2): δ
-16.9. 19F{1H} NMR (282.1 MHz, CD2Cl2): δ -133.5, -163.9
(t), -167.7. IR: (CH2Cl2) νCO ) 2118 cm-1. Anal. Calcd. for
C64H37BF20OP2PtSi: C, 51.32; H, 2.49. Found: C, 51.44; H, 2.26.
[(dppp)Pt(Me)(CO)][B(C6F5)4] (12). Solid off-white [(dppp)-
Pt(Me)(THF)][B(C6F5)4] (54.0 mg, 39.3 µmol) was dissolved
in dichloromethane (2 mL) in a round-bottom flask containing
a stirbar and sealed with a septum. The flask was purged with
carbon monoxide gas for 15 min, and subsequently dried under
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8885

A R T I C L E S
Thomas and Peters
132.0, 131.7, 131.6, 130.1, 129.0 (d), 128.7 (d), 127.5, 125.2
(br), 72.3, 24.4, 12.1 (dd, JPt-C ) 903 Hz, JP-C ) 59 Hz, JP-C
) 11 Hz), 11.6 (m), 7.3 (m). 31P{1H} NMR (121.4 MHz,
C6D6): δ 26.48 (d, JPt-P ) 1808 Hz, JP-P ) 15.9 Hz), 5.09
(d, 1JPt-P ) 4694 Hz, 2JP-P ) 15.9 Hz). 19F{1H} NMR (282.1
MHz, C6D6): δ -132.2, -162.9 (t, J ) 21.4 Hz), -166.5 (t, J
) 17.1 Hz). Anal. Calcd. for C67H45BF20OP2PtSi: C, 52.19;
H, 2.94. Found: C, 53.52; H, 2.91.
(2 mL) with THF (0.5 mL). Separately, [H(Et2O)2][B(C6F5)4]
(25.8 mg, 31.5 µmol) was dissolved in dichloromethane (2 mL)
and added slowly to the stirring solution of (Ph2SiP2)PtPh2. After
addition was complete, the reaction was stirred for 10 min.
Volatiles were removed under reduced pressure, and the mixture
was triturated and washed with petroleum ether [2 × 2 mL].
The resulting white solids were dried under reduced pressure,
providing off-white 17 (49.2 mg, 97.4%).
1
2
[(dppp)Pt(Me)(THF)][B(C6F5)4] (15). Solid (dppp)PtMe2
(155.1 mg, 243.3 µmol) was dissolved in dichloromethane (1
mL) with THF (0.5 mL). Separately, [H(Et2O)2][B(C6F5)4]
(199.0 mg, 243.2 µmol) was dissolved in dichloromethane (3
mL) and added slowly to the stirring solution of (dppp)PtMe2,
evolving gas. After addition was complete, the reaction was
stirred for 10 min. Volatiles were removed under reduced
pressure, and the mixture was triturated and washed with
petroleum ether [2 × 2 mL]. The resulting white solids were
dried under reduced pressure, providing analytically pure 15
(323.1 mg, 96.7%).
1H NMR (500 MHz, CD2Cl2): δ 6.4-7.8 (aryl protons), 3.24
(4H, m), 2.58 (2H, dd, JP-H ) 3.0, 15.5 Hz, JPt-H ) 80 Hz),
2.43 (2H, dd, JP-H ) 12.5 Hz, JPt-H ) 94 Hz), 1.15 (4H, m).
13C{1H} NMR (125.7 MHz, CD2Cl2): δ 159 (d), 149.7, 147.8,
139.8, 137.9, 135.8, 128-134, 125.0, 124.3, 68.9, 24.5, 12.1
(m), 8.3 (m). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ 21.0 (d,
JP-P ) 17.1 Hz, JPt-P ) 1746 Hz), 0.2 (d, JP-P ) 17.1 Hz,
JPt-P ) 4645 Hz). 19F{1H} NMR (282 MHz, CD2Cl2): δ
-133.5, -163.9, -167.7. 11B{1H} NMR (128 MHz, CD2Cl2):
δ -18.4. Anal. Calcd. for C72H47BF20OP2PtSi: C, 53.91; H,
2.95. Found: C, 53.55; H, 3.26.
1H NMR (500 MHz, CD2Cl2): δ 7.30-7.65 (20H, aryl
protons), 2.65 (4H, m), 1.92 (2H, m), 1.28 (2H, m), 0.86 (2H,
[(dppp)Pt(Ph)(THF)][B(C6F5)4] (18). Solid white (dppp)-
PtPh2 (32.1 mg, 42.1 µmol) was dissolved in dichloromethane
(2 mL) with THF (0.5 mL). Separately, [H(Et2O)2][B(C6F5)4]
(34.5 mg, 42.2 µmol) was dissolved in dichloromethane (2 mL)
and added slowly to the stirring solution of (dppp)PtPh2. After
addition was complete, the reaction was stirred for 10 min.
Volatiles were removed under reduced pressure, and the mixture
was triturated and washed with petroleum ether [2 × 2 mL].
The resulting white solids were dried under reduced pressure,
providing off-white 18 (54.0 mg, 89.3%).
1H NMR (300 MHz, CD2Cl2): δ 7.7 (4H, m), 7.6 (6H, m),
7.4 (6H, m), 7.3 (4H, m), 7.0 (2H, m), 6.7 (3H, m), 3.33 (4H,
m), 2.75 (4H, m), 1.7 (2H, m), 1.18 (4H, m). 13C{1H} NMR
(125.7 MHz, CD2Cl2): δ 158.9 (dd), 149.7, 147.8, 139.8, 137.9,
136.0, 133.6 (d), 133.4 (d), 132.4, 130.0 (d), 129.3 (d), 128.5
(d), 125.1, 73.0, 27.2 (d), 27.1 (d), 24.6, 18.6. 31P{1H} NMR
(121.4 MHz, CD2Cl2): δ 12.0 (d, JP-P ) 22.5 Hz, JPt-P ) 1620
Hz), -3.0 (d, JP-P ) 22.5 Hz, JPt-P ) 4524 Hz). 19F{1H} NMR
(282 MHz, CD2Cl2): δ -133.5, -163.9, -167.7. 11B{1H} NMR
(128 MHz, CD2Cl2): δ -19.1. Anal. Calcd. for C61H39BF20-
OP2Pt: C, 51.03; H, 2.74. Found: C, 51.21; H, 2.74.
3
2
m), 0.42 (3H, dd, Pt-CH3, JP-H ) 1.50, 7.00 Hz, JPt-H
)
38.0 Hz). 13C{1H} NMR (125.7 MHz, CD2Cl2): δ 149.7, 147.8,
139.8, 137.8, 135.9, 133.4 (br m), 132.6 (br m), 129.7 (br m),
127.9, 127.4, 125.0 (br m), 73.3 (JPt-C ) 96 Hz), 26.9, 25.3,
19.0, 13.4 (dd). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ 17.25
(d, 1JPt-P ) 1680 Hz, 2JP-P ) 23.2 Hz), 2.28 (d, 1JPt-P ) 4550
2
Hz, JP-P ) 23.2 Hz). 19F{1H} NMR (282 MHz, CD2Cl2): δ
-133.6, -164.0 (t), -167.8. 11B{1H} NMR (128.3 MHz,
CD2Cl2): δ -17.2. Anal. Calcd. for C56H37BF20OP2Pt: C,
48.96; H, 2.71. Found: C, 49.36; H, 2.77.
[Ph2BP2]Pt(Ph)(THF) (16) (a) Solid [[Ph2BP2]Pt(Me)(Ph)]-
[ASN] (23.6 mg, 24.2 µmol) was dissolved in THF (2 mL).
While stirring, solid B(C6F5)3 (12.5 mg, 24.4 µmol) was added.
After 10 min, 31P NMR analysis showed the formation of one
major product, consistent with the formulation of 16 (see b).
(b) Solid [[Ph2BP2]Pt(Me)(Ph)][ASN] (51.4 mg, 52.6 µmol)
was dissolved in THF (2 mL). A THF solution (2 mL) of
[iPr2EtNH][BPh4] (23.5 mg, 52.3 µmol) was added to the stirring
solution. The clear, colorless reaction slowly produced a white
precipitate. The mixture was stirred for 1 h, and the white solids
were filtered away. The solution was concentrated under reduced
pressure, and pentane (2 mL) was added, precipitating white
solids. The solids were collected by filtration. NMR analysis
of the solids was consistent with the formulation of 16 as the
major product (∼80%). Due to the lability of the coordinated
THF molecule, obtaining satisfactory combustion analysis was
problematic.
[{(Ph2SiP2)Pt}2(µ-η3:η3-biphenyl)][B(C6F5)4]2 (19). Ther-
molysis of 14 (24.5 mg, 15.9 µmol) in benzene at 55 °C for 24
h resulted in the formation a single product as evidenced by
31P NMR. Isolation of orange solids by removal of volatiles
under reduced pressure followed by washing with petroleum
ether [2 × 2 mL] provided 19 (21.7 mg, 89.1%). Crystals of
19 were obtained by slow cooling of a saturated solution of 19
in o-xylene.
1H NMR (300 MHz, C6D6): δ 7.56 (m, 4H), 7.46 (m, 4H),
7.21 (m, 4H), 6.95 (m, 18H), 6.88 (m, 2H), 6.78 (m, 2H), 6.73
1H NMR (300 MHz, acetone-d6): δ 7.77 (1H, m), 7.49 (16H,
m), 7.27 (28H, m), 7.15 (2H, m), 7.10 (8H, m), 6.92 (8H, m),
6.54 (2H, d), 5.64 (m, 1H), 4.24 (2H, bd), 4.03 (2H, bt), 2.73
(8H, d, JP-H ) 13.2 Hz, JPt-H ) 62.4 Hz). 13C{1H} NMR (125.7
MHz, acetone-d6): δ 150.6, 148.7, 140.6, 138.7, 135.1, 134.1,
133.6, 132.9, 130.5, 129.3, 126.5, 107.4, 95.7, 81.2, 76.1, 9.3.
31P{1H} NMR (121.4 MHz, acetone-d6): δ 8.42 (JPt-P ) 3940
Hz). 19F{1H} NMR (282 MHz, acetone-d6): δ -132.5, -163.6 (t),
-167.6. ES MS: m/z 852.8 ([M2+]). Anal. Calcd. for C136H78B2-
F40P4Pt2Si2: C, 53.31; H, 2.57. Found: C, 51.82; H, 2.35.
[{(dppp)Pt}2(µ-η3:η3-biphenyl)][B(C6F5)4]2 (20). Thermoly-
sis of 18 (32.7 mg, 22.8 µmol) in benzene at 55 °C for 4 h
2
(m, 1H), 2.87 (br, 4H), 2.64 (d, 2H, JP-H ) 17 Hz), 2.42 (d,
2H, 2JP-H ) 14 Hz), 0.46 (br, 4H). 13C{1H} NMR (125.7 MHz,
THF): δ 161 (br), 136.3, 135.4 (d), 133.0 (d), 132.9 (d), 132.1
(d), 131.5, 129.2, 129.1, 127.6 (d), 126.9 (d), 126.4 (d), 125.5,
122.6, 121.2, 67, 26, 21 (br), 17 (br). 31P{1H} NMR (121.4
1
2
MHz, THF): δ 28.60 (d, JPt-P ) 1740 Hz, JP-P ) 23 Hz),
11.20 (d, JPt-P ) 4393 Hz, JP-P ) 23 Hz). 11B{1H} NMR
1
2
(128.3 MHz, THF): δ -14.9.
[(Ph2SiP2)Pt(Ph)(THF)][B(C6F5)4] (17). Solid white (Ph2SiP2)-
PtPh2 (29.3 mg, 31.5 µmol) was dissolved in dichloromethane
9
8886 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003

Bis(phosphine) Platinum(II) Complexes
A R T I C L E S
resulted in the formation of two products as evidenced by 31P
NMR. Removal of volatiles under reduced pressure provided a
mixture of 20 and a second species which is presumed to be
the hydroxy-bridged dimer, [(dppp)Pt(µ-OH)]2[B(C6F5)4]2. Spec-
tral analysis was consistent with the formulation of the major
product as 20 by comparison to 19 and previously reported
systems.12
1H NMR (300 MHz, CD2Cl2): δ 6.6-7.8 (aryl protons), 5.15
(m, 1H), 4.21 (br, 2H), 3.67 (br, 2H), 2.63 (br, 8H), 1.64 (m,
4H). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ 0.20 (JPt-P ) 3737
Hz). 19F{1H} NMR (282 MHz, CD2Cl2): δ -133.4, -163.7
(t), -167.5.
[[Ph2BP2]Pt(Ph)2][ASN] (21). A THF solution (2 mL) of
(COD)Pt(C6H5)2 (45.5 mg, 99.5 µmol) was added to a stirring
suspension of [Ph2BP2][ASN] (68.6 mg, 99.5 µmol) in THF (3
mL). The reaction was stirred for 1 h, during which the mixture
became a homogeneous solution. The solution was concentrated
and triturated with pentane [3 × 2 mL]. The resulting off-white
solids were dried under reduced pressure, providing 21 (101.0
mg, 97.7%).
1H NMR (300 MHz, CD3CN): δ 7.21 (m, 8H), 7.01 (m, 4H),
6.90 (m, 12H), 6.80 (m, 4H), 6.60 (m, 4H), 6.53 (m, 2H), 6.30
(m, 4H), 6.18 (m, 2H), 3.28 (m, 8H), 2.08 (m, 8H), 2.02 (br,
4H). 13C{1H} NMR (125.7 MHz, CD3CN): δ 168.3 (dd, ipso
Pt(C6H5)2, 2JP-C(trans) ) 111 Hz, 2JP-C(cis) ) 12 Hz), 165, 138.5,
137.4 (s, ortho Pt(C6H5)2, 2JPt-C ) 29 Hz), 133.8, 132.4, 127.9,
126.9 (s, meta Pt(C6H5)2, 3JPt-C ) 8.9 Hz), 126.2, 126.0, 121.6,
119.4, 63.3, 22.3, 20.3 (br). 31P{1H} NMR (121.4 MHz,
CD3CN): δ 13.99 (1JPt-P ) 1772 Hz). 11B{1H} NMR (128.3
MHz, CD3CN): δ -14.4. ES MS: m/z 912.3 ([M-]). Anal.
Calcd. for C58H60BNP2Pt: C, 67.05; H, 5.82; N, 1.35. Found:
C, 66.23; H, 5.96; N, 1.48.
(Ph2SiP2)Pt(Ph)2 (22). Solid Ph2SiP2 (70.3 mg, 0.121 mmol)
and CODPtPh2 (55.4 mg, 0.121 mmol) were dissolved in THF
(2 mL). After 20 min, volatiles were removed under reduced
pressure. The resulting solids were triturated with petroleum
ether (3 mL), and the solution was decanted. The resulting off-
white solids were dried under reduced pressure, providing 22
(103.2 mg, 91.7%).
1H NMR (300 MHz, CDCl3): δ 7.36 (m, 8H), 7.18 (m, 6H),
7.05 (m, 12H), 6.93 (m, 4H), 6.87 (m, 4H), 6.44 (m, 4H), 6.31
(m, 2H), 2.41 (d, 4H, JP-H ) 9.6 Hz, JPt-H ) 33 Hz). 13C{1H}
NMR (125.7 MHz, CDCl3): δ 162.7 (dd, JP-C ) 12, 113 Hz),
136.1 (JPt-C ) 31 Hz), 135.2, 133.7, 133.3 (m), 129.7, 127.9,
127.8 (m), 126.8 (JPt-C ) 66 Hz), 120.3, 9.7 (m). 31P{1H}
NMR (121.4 MHz, CDCl3): δ 6.02 (JPt-P ) 1720 Hz). Anal.
Calcd. for C50H44P2PtSi: C, 64.57; H, 4.77. Found: C, 64.73;
H, 5.12.
[Ph2BP2]Pt(Me){P(C6F5)3} (25). A THF solution (2 mL) of
13 (104.5 mg, 123.6 µmol) was added to solid P(C6F5)3 (66.1
mg, 124.2 µmol). The resulting solution was concentrated under
reduced pressure. Toluene (4 mL) was added, and the solution
was concentrated under reduced pressure. Petroleum ether (2
mL) was added, forming a white precipitate, which was collected
by filtration and washed with additional petroleum ether (2 mL).
The solids were dissolved in benzene (2 mL), and the solution
was filtered. Volatiles were removed under reduced pressure,
providing white solid 25 (133.2 mg, 82.5%). Crystals suitable
for X-ray diffraction were grown from petroleum ether diffusion
into a benzene solution of 25.
1H NMR (300 MHz, C6D6): δ 7.44 (br, 4H), 7.26-7.30 (br,
8H), 7.06 (m, 6H), 6.93 (br, 6H), 6.81 (br, 6H), 2.63 (br d, 2H,
JP-H ) 15 Hz, JPt-H ) 53 Hz), 2.24 (dd, 2H, JP-H ) 10, 14
Hz, JPt-H ) 59 Hz), 0.04 (ddd, 3H, JP-H ) 5.4, 5.4, 11 Hz,
JPt-H ) 54 Hz). 13C{1H} NMR (125.7 MHz, C6D6): δ 163 (br),
148.3, 146.2, 145.1, 143.0, 138.9, 136.9, 133.9, 132.8, 130.2,
1
129.9, 128, 127.1, 123.1, 103.6, 23.4, 19.8, 0.75 (br d, JPt-C
2
) 500 Hz, JP-C(trans) ) 69 Hz). 31P{1H} NMR (121.4 MHz,
C6D6): δ 22.83 (dd, 1JPt-P ) 3139 Hz, 2JP-P ) 29.9, 433 Hz),
1
2
18.84 (dd, JPt-P ) 1945 Hz, JP-P ) 17.1, 29.2 Hz), -17.97
(br d, 1JPt-P ) 2499 Hz, 2JP-P ) 430 Hz). 11B{1H} NMR (128.3
MHz, C6D6): δ -19.1. 19F{1H} NMR (282.1 MHz, C6D6): δ
-124.5 (br sh), -127.0 (br), -135.2 (br), -145.4 (br), -155.4
(br sh), -157.6 (br), -159.6 (br). Anal. Calcd. for C57H37-
BF15P3Pt: C, 52.43; H, 2.86. Found: C, 52.51; H, 2.63.
[Ph2BP2]Pt(Ph){P(C6F5)3} (26). Thermolysis of 25 (43.2 mg)
in benzene (0.7 mL) at 80 °C over 24 h led to the quantitative
formation of 26.
1H NMR (300 MHz, C6D6): δ 6.2-7.8 (35H, aryl protons),
2.0-2.8 (br, 4H). 31P{1H} NMR (121.4 MHz, C6D6): δ 17.92
(dd, JP-P ) 28, 419 Hz, JPt-P ) 3132 Hz), 10.85 (br m, JPt-P
) 1770 Hz), -24.01 (br d, JP-P ) 422 Hz, JPt-P ) 2462 Hz).
11B{1H} NMR (128.3 MHz, C6D6): δ -15.5. 19F{1H} NMR
(282.1 MHz, C6D6): δ -126.4 (br), -129.5 (br), -133.1 (br),
-145 (br), -158.3 (br), -160.1 (br). Anal. Calcd. for C62H39-
BF15P3Pt: C, 54.44; H, 2.87. Found: C, 54.58; H, 2.62.
[[Ph2BP2]Pt(Me)(Ph)][ASN] (27). A THF solution (1 mL)
of (COD)Pt(Me)(Ph) (70.6 mg, 0.179 mmol) was added to a
stirring suspension of [Ph2BP2][ASN] (123.1 mg, 0.1785 mmol)
in THF (2 mL). The reaction was stirred for 30 min and became
homogeneous. The solution was concentrated under reduced
pressure, and off-white solids were precipitated with diethyl
ether (2 mL). The supernatant was removed, and the solids were
washed with ethanol [2 × 2 mL] and diethyl ether [2 × 2 mL]
and dried under reduced pressure, producing off-white 27 (122.4
mg, 70.2%).
1H NMR (300 MHz, acetone-d6): δ 7.47 (m, 4H), 7.24 (m,
4H), 7.12 (m, 2H), 7.09 (m, 4H), 6.98 (m, 4H), 6.87 (m, 8H),
6.62 (m, 4H), 6.57 (m, 2H), 6.43 (m, 2H), 6.29 (m, 1H), 3.69
(m, 8H,), 2.26 (m, 8H), 2.10 (br, 2H), 2.02 (br, 2H), 0.08 (dd,
3H, 3JP-H(cis) ) 6.9 Hz, 3JP-H(trans) ) 7.8 Hz, 2JPt-H ) 69 Hz).
13C{1H} NMR (125.7 MHz, acetone-d6): δ 166 (br), 144, 140.5
(d), 139.8 (d), 138.7, 135.0 (m), 134.7 (m), 133.8, 128.9, 128.4,
127.9 (d), 127.5 (d), 127.0, 126.8, 122.4, 120.0, 64.3, 23.3, 23
(br), 22 (br), 5.5 (dd, 2JP-C(trans) ) 93 Hz). 31P{1H} NMR (121.4
1
2
MHz, acetone-d6): δ 18.3 (d, JPt-P ) 1775 Hz, JP-P ) 19
Hz), 17.29 (d, 1JPt-P ) 1868 Hz, 2JP-P ) 19 Hz). 11B{1H} NMR
(128.3 MHz, acetone-d6): δ -13.8. Anal. Calcd. for C53H57-
BNP2Pt: C, 65.16; H, 5.98; N, 1.43. Found: C, 64.90; H, 6.05;
N, 1.54.
(Ph2SiP2)Pt(Me)(Ph) (28). Solid 2 (39.7 mg, 68.4 µmol) and
CODPt(Me)(Ph) (27.0 mg, 68.3 µmol) were dissolved in THF
(2 mL) and stirred for 10 min. Volatiles were removed under
reduced pressure, and the mixture was triturated with petroleum
ether [3 × 3 mL]. The resulting off-white solids were dried
under reduced pressure to provide 28 (52.6 mg, 88.7%).
1H NMR (300 MHz, C6D6): δ 7.64 (m, 4H), 7.53 (m, 2H),
2
7.39 (m, 4H), 7.04-6.80 (m, 25H), 2.27 (d, 2H, JP-H ) 10.8
2
Hz), 2.19 (d, 2H, JP-H ) 11.4 Hz), 1.09 (dd, 3H, Pt(CH3),
3
2
3JP-H ) 7.2 Hz, JP-H ) 9.6 Hz, JPt-H ) 70 Hz). 31P{1H}
9
J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003 8887

A R T I C L E S
Thomas and Peters
NMR (121.4 MHz, C6D6): δ 8.96 (1JPt-P ) 1792 Hz, 2JP-P
)
perature-dependent peak separation of methanol or ethylene
glyocol. The J. Young tube was inserted into the probe and
allowed to thermally equilibrate. The 90° pulse width of the
peak to be inverted (downfield peak of free THF, ∼3.6 ppm)
was determined before each experiment at the appropriate
temperature. Magnetization transfer experiments were performed
using the DANTE pulse sequence23 and selectively inverting
the downfield free THF peak. The peak areas for free and bound
THF were measured after different pulse-mixing times (30 µs
to 50 s) using a nonselective 90° pulse. Between 25 and 40
data points were acquired as four repetitions with a 50 s
relaxation delay. The rate of exchange was determined using
the CIFIT computer program.24
Kinetics Experiments. In a typical experiment, 20-30 mg
of the appropriate methyl solvento complex (13-15) or methyl
phosphine complex (25) (and when appropriate, [nBu4N]-
[B(C6F5)4] or THF) was dissolved in C6H6 or C6D6 (0.64 mL)
and filtered into a J. Young tube holding a capillary containing
an internal integration standard (PMe3 (31P NMR) or Cp2Fe (1H
NMR) in C6D6). The sealed tube was then heated in a
temperature equilibrated heating block or in the NMR probe.
Heating block temperature was calibrated using a thermocouple
device, and NMR probe temperature was calibrated using an
ethylene glycol standard. The reaction was monitored either by
31P NMR and integrating the most downfield peak (correspond-
ing to the ligated phosphorus atom trans to the methyl ligand
in each case) versus the internal standard (PMe3), or by 1H NMR
and integrating the peak corresponding to the methyl ligand
versus the internal standard (Cp2Fe). The resulting data was fit
to a pseudo-first-order decay of the methyl solvento species.
Each experiment was repeated in triplicate. The value of the
rate constant is an average of three experimental results, and
the error reported is the standard deviation of the three observed
rate constants.
14 Hz), 8.08 (1JPt-P ) 1715 Hz, 2JP-P ) 14 Hz). Anal. Calcd.
for C45H42P2PtSi: C, 62.27; H, 4.88. Found: C, 61.47; H, 4.87.
[(Ph2SiP2)Pt(Me){P(C6F5)3}][B(C6F5)4] (29). Solid 14 (29.0
mg, 18.8 µmol) was dissolved in dichloromethane (2 mL) with
P(C6F5)3(10.0 mg, 18.8 µmol) and the solution was stirred for
10 min. Volatiles were removed under reduced pressure. The
resulting solids were triturated with toluene (2 mL), washed
with petroleum ether [2 × 2 mL], and dried under reduced
pressure, providing 29 (29.7 mg, 79.0%).
1H NMR (300 MHz, CD2Cl2): δ 7.40 (br), 7.32 (m), 7.28
2
(m), 7.13 (t, 4H), 6.93 (d, 4H), 2.58 (d, 2H, JP-H ) 12.9 Hz,
2
2
3JPt-H ) 34 Hz), 2.15 (dd, 2H, JP-H ) 5.7 Hz, JP-H ) 15.0
3
3
Hz, JPt-H ) 48 Hz), 0.03 (ddd, 3H, JP-H ) 6.6, 10.8, 12.0
Hz, 2JPt-H ) 51 Hz). 13C{1H} NMR (125.7 MHz, CD2Cl2): δ
149.7, 148.4, 147.8, 146.4, 143.9, 139.5, 137.9, 135.9, 134.0,
133.8, 132.9, 132.4, 130.9, 129.4, 128.9, 124.3, 102.2, 11.8,
9.8, 5.8 (m). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ 13.09
2
1
2
(dd, JP-P ) 449, 27.5 Hz, JPt-P ) 3246 Hz), 9.37 (dd, JP-P
1
2
) 21.4, 27.5 Hz, JPt-P ) 1984 Hz), -19.03 (br d, JP-P
)
443 Hz, JPt-P ) 2796 Hz). 19F{1H} NMR (282 MHz,
CD2Cl2): δ -126.9 (br), -133.7, -143.7 (br), -157.7 (br),
-163.9, -167.8. Anal. Calcd. for C81H37BF35P3PtSi: C, 48.59;
H, 1.86. Found: C, 46.88; H, 2.09.
1
[(Ph2SiP2)Pt(Ph){P(C6F5)3}][B(C6F5)4] (30). Solid 21 (26.5
mg, 28.5 µmol) was dissolved in dichloromethane (1 mL) with
P(C6F5)3 (15.2 mg, 28.6 µmol). While stirring, a dichloro-
methane solution (1 mL) of [H(Et2O)2][B(C6F5)4] (23.3 mg, 28.5
µmol) was added slowly. After 10 min, volatiles were removed
under reduced pressure. The solids were washed with petroleum
ether [2 × 2 mL] and dried under reduced pressure (51.4 mg).
The resulting solids were composed of 90-95% 30 and 5-10%
19; therefore, elemental analysis was not obtained.
1H NMR (300 MHz, CD2Cl2): δ 7.0-7.6, 6.77 (m), 6.46
(m), 6.23 (br), 2.64 (br, 2H), 2.33 (br, 2H). 31P{1H} NMR (121.4
MHz, CD2Cl2): δ 6.79 (dd, JP-P ) 25, 445 Hz, JPt-P ) 3319
Hz), 3.04 (dd, JP-P ) 19, 25 Hz, JPt-P ) 1870 Hz), 26.61 (dd,
JP-P ) 19, 440 Hz, JPt-P ) 2785 Hz). 19F{1H} NMR (282 MHz,
CD2Cl2): δ -124.3 (br), -133.5, -144.1 (br), -158.2 (br),
-163.9, -167.8.
MeP(C6D5)2 (31). C6D5Br (10.0533 g, 62.034 mmol) was
reacted with Mg0 (3.033 g, 124.8 mmol) in Et2O at reflux over
2h to form the aryl Grignard reagent. The solution was
transferred by cannula to a Schlenk flask containing MePCl2
(3.6193 g, 30.953 mmol) in Et2O (100 mL) at -78 °C. The
reaction was stirred and warmed gradually over 4h. Volatiles
were removed under reduced pressure, and the resulting sludge
was extracted with petroleum ether (100 mL) and filtered. The
solution was concentrated under reduced pressure, providing
31 (2.702 g, 41%).
Acknowledgment. The authors acknowledge financial support
from the NSF (CHE-0132216), BP, and the ACS PRF. J.C.T.
is grateful for an NSF graduate fellowship and a Moore
fellowship. Dr. Michael Day, Lawrence Henling, and Theodore
Betley are acknowledged for assistance with crystallographic
studies. Prof. John Bercaw, Dr. Alan Heyduk, Dr. Gregory
Kubas, and Dr. Jennifer Love are acknowledged for insightful
discussions.
Note Added after ASAP: The version published on the Web
06/17/2003 was not the corrected version. The version published
on the Web 06/25/2003 and the print version are correct.
Supporting Information Available: Crystallographic experi-
mental details for complexes 7, 8, 9, 13, 19, and 25,44 additional
graphs of kinetic results, and 31P{1H} NMR figures of 14 and
15. This material is available free of charge via the Internet at
http://pubs.acs.org.
1H NMR (300 MHz, CDCl3): δ 1.65 (d, JP-H ) 3.3 Hz).
31P{1H} NMR (121.4 MHz, CDCl3): δ -26.9. GC MS: m/z
210 ([M+]).
THF Exchange Experiments. A known amount (ca. 20 mg)
of methyl solvento complex 13 or 14 was dissolved in C6D6
with a known concentration (3-15 equiv) of THF in a J. Young
tube. The temperature of the probe on a Varian Inova 500
spectrometer was equilibrated and determined using the tem-
JA0296071
(44) Crystallographic data have been deposited at the CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, and copies can be obtained on request, free of
charge, by quoting the publication citation and the deposition number
151640 (7), 198492 (8‚toluene), 198491 (9), 156632 (13‚2THF), 186231
(19‚4(o-xylene)), 198490 (25‚benzene).
9
8888 J. AM. CHEM. SOC. VOL. 125, NO. 29, 2003