Activation of aromatic C-H bonds by (dmpe)Pt(Me)X (X = Me, O2CCF3, OTf) systems

Article abstract of DOI:10.1021/om980334l

A series of complexes (dmpe)Pt(X)₂ (X = Me, Cl, O₂CCF₃, OTf) have been prepared and their thermal stabilities examined. In contrast to (dmpe)Pt(Me)(Cl), which is stable up to 150 °C in benzene solution, thermolysis of (dmpe)Pt(Me)(O₂CCF₃) in benzene at 125 °C results in methane loss and the formation of (dmpe)Pt(Ph)(O₂CCF₃) as the major product, along with small amounts of the disproportionation products (dmpe)Pt(O₂CCF₃)₂ and (dmpe)Pt(Ph)₂ (8-10%). Kinetic studies in C₆H₆ and C₆D₆ indicate that the disappearance of (dmpe)Pt(Me)(O₂CCF₃) is first-order, with an overall kinetic isotope effect of 3.3(2). Methyl/ aryl metathesis rates are not inhibited by added TBA⁺O₂CCF₃^-. Thermolysis of (dmpe)Pt(Me)₂ in benzene at 180 °C for 18 h gave a mixture of unreacted (dmpe)Pt(Me)₂ (15%), (dmpe)Pt(Me)(Ph) (51%), and (dmpe)Pt(Ph)₂ (34%). Thermolysis of (dmpe)Pt(Me)(O₂CCF₃) in either 1,2- or 1,4-difluorobenzene at 125 °C afforded 2:1:1 statistical mixtures of (dmpe)Pt(Ar)(O₂CCF₃), (dmpe)Pt(Ar)₂, and (dmpe)Pt(O₂CCF₃)₂ (Ar = 2,3-C₆H₃F₂ or 2,5-C₆H₃F₂, respectively). Thermolysis of (dmpe)Pt(Me)(O₂CCF₃) in toluene affords a mixture of ortho, meta, and para tolyl products, (dmpe)Pt(C₆H₄Me)(O₂CCF₃). The metathesis rate for polar 1,2-difluorobenzene is not significantly different than that observed for the nonpolar aromatic substrates. Surprisingly, the aryl/aryl exchange rates for (dmpe)Pt(Ph)(O₂CCF₃) in C₆D₆ and C₇D₈ are 10-20 times faster than observed methyl/aryl exchange rates. These data may be accommodated by a mechanism involving a rate-limiting addition of aryl C-H bonds directly to a 4-coordinate (dmpe)Pt(II) or a 3-coordinate (η¹-dmpe)Pt(II) center.

Full text of DOI:10.1021/om980334l

Organometallics 1998, 17, 4493-4499
4493
Activa tion of Ar om a tic C-H Bon d s by (d m p e)P t(Me)X
(X ) Me, O2CCF 3, OTf) System s
R. Gregory Peters, Shannon White, and Dean M. Roddick*
Department of Chemistry, Box 3838, University of Wyoming, Laramie, Wyoming 82071
Received April 30, 1998
A series of complexes (dmpe)Pt(X)2 (X ) Me, Cl, O2CCF3, OTf) have been prepared and
their thermal stabilities examined. In contrast to (dmpe)Pt(Me)(Cl), which is stable up to
150 °C in benzene solution, thermolysis of (dmpe)Pt(Me)(O2CCF3) in benzene at 125 °C results
in methane loss and the formation of (dmpe)Pt(Ph)(O2CCF3) as the major product, along
with small amounts of the disproportionation products (dmpe)Pt(O2CCF3)2 and (dmpe)Pt-
(Ph)2 (8-10%). Kinetic studies in C6H6 and C6D6 indicate that the disappearance of
(dmpe)Pt(Me)(O2CCF3) is first-order, with an overall kinetic isotope effect of 3.3(2). Methyl/
aryl metathesis rates are not inhibited by added TBA+O2CCF3-. Thermolysis of (dmpe)Pt-
(Me)2 in benzene at 180 °C for 18 h gave a mixture of unreacted (dmpe)Pt(Me)2 (15%),
(dmpe)Pt(Me)(Ph) (51%), and (dmpe)Pt(Ph)2 (34%). Thermolysis of (dmpe)Pt(Me)(O2CCF3)
in either 1,2- or 1,4-difluorobenzene at 125 °C afforded 2:1:1 statistical mixtures of (dmpe)-
Pt(Ar)(O2CCF3), (dmpe)Pt(Ar)2, and (dmpe)Pt(O2CCF3)2 (Ar ) 2,3-C6H3F2 or 2,5-C6H3F2,
respectively). Thermolysis of (dmpe)Pt(Me)(O2CCF3) in toluene affords a mixture of ortho,
meta, and para tolyl products, (dmpe)Pt(C6H4Me)(O2CCF3). The metathesis rate for polar
1,2-difluorobenzene is not significantly different than that observed for the nonpolar aromatic
substrates. Surprisingly, the aryl/aryl exchange rates for (dmpe)Pt(Ph)(O2CCF3) in C6D6
and C7D8 are 10-20 times faster than observed methyl/aryl exchange rates. These data
may be accommodated by a mechanism involving a rate-limiting addition of aryl C-H bonds
directly to a 4-coordinate (dmpe)Pt(II) or a 3-coordinate (η1-dmpe)Pt(II) center.
In tr od u ction
The activation of both aliphatic and aromatic C-H
bonds by a wide range of transition metal systems is
well established.1 Although the direct detection and/
or isolation of initially-formed metal alkyl hydride
complexes has been observed in an increasing number
of cases,2 the addition of C-H bonds to metal centers
has been more commonly inferred from the isolation of
alkyl- or aryl-metathesis products. Four primary reac-
tion mechanisms have been proposed for these types of
transformations: (1) oxidative addition of R′-H followed
by reductive elimination of R-H, (2) reductive elimina-
tion of R-X (X ) H, halide, etc.) followed by oxidative
addition of substrate R′-X bonds, and (3) concerted (σ-
bond metathesis)3 or stepwise (heterolytic) interchange
In the case of platinum C-H activation chemistry,
nearly all of these reaction types have been either
demonstrated or suggested. The intermediacy of reac-
tive Pt(0) intermediates in the activation of hydrocarbon
substrates has been established by Whitesides and
Hoffmann in [(Cy)2PCH2CH2P(Cy)2]Pt(R)H and [(Cy)2-
PCH2P(Cy)2]Pt(R)H systems, respectively.4,5 Alterna-
tively, both the addition of C-H bonds to Pt(II) alkyl
complexes to form Pt(IV) alkyl hydride intermediates
of R and R′.
(1) (a) Davies, J . A.; Watson, P.L.; Liebman, J . F.; Greenberg, A.
Selective Hydrocarbon Activation; VCH Publishers, Inc.: New York,
1990. (b) Hill, C. L.; Activation and Functionalization of Alkanes; J ohn
Wiley & Sons: New York, 1989. (c) Crabtree, R. H. Chem Rev. 1985,
85, 245. (d) J anowicz, A. H.; Periana, R. A.; Buchanan, J . M.; Kovac,
C. A.; Stryker, J . M.; Wax, M. J .; Bergman, R. G.; Pure Appl. Chem.
1984, 56, 13.
(2) (a) J ones, W. D.; Feher, F. J . Acc. Chem. Res. 1989, 22, 91. (b)
J anowicz, J . M.; Bergman, R. G. J . Am. Chem. Soc. 1982, 104, 352. (c)
Buchanan, J . M; Stryker, J . M.; Bergman, R. G.; J . Am. Chem. Soc.
1986, 108, 1537. (d) Hoyano, J . K.; Graham, W. A. G. J . Am. Chem.
Soc. 1982, 104, 3723. (e) Ghosh, C. K.; Graham, W. A. G. J . Am. Chem.
Soc. 1987, 109, 4726. (f) Thompson, M. E.; Baxter, S. W. P.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 203. (g) Tolman, C. A.; Ittel, S. D.;
English, A. D.; J esson J . P. J . Am. Chem. Soc. 1979, 101, 1742. (h)
Field, L. D.; Baker, M. V. J . Am. Chem. Soc. 1986, 108, 7436. (i) Harper,
T. G. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. J . Am. Chem.
Soc. 1988, 110, 7915.
(3) Thompson, M.E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am. Chem.
Soc. 1987, 109, 203.
(4) (a) Hackett, M.; Ibers, J . A.; Whitesides, G. M. J . Am. Chem.
Soc. 1988, 110, 1436. (b) Hackett, M.; Whitesides, G. M. J . Am. Chem.
Soc. 1988, 110, 1448.
(5) Hoffman, P.; Heiss, H.; Neiteler, P.; Mu¨ller, G.; Lachmann, J .
Angew. Chem. Int. Ed. Engl. 1990, 29, 880.
S0276-7333(98)00334-3 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/12/1998

4494 Organometallics, Vol. 17, No. 20, 1998
Peters et al.
Sch em e 1
and alkane heterolysis (nonoxidative) mechanisms have
been proposed for “Shilov type” hydrocarbon activation
chemistry.6
of (dmpe)Pt(Me)X compounds. It was anticipated that
the dmpe ancillary ligand would more effectively mimic
the innocent nature of the dfepe ligand by avoiding
phosphine metalation reactions commonly observed
with higher phosphine congeners possessing â or γ C-H
groups.12 In this paper, we report the thermal reactions
of a series of (dmpe)Pt(R)(X) (X ) O2CCF3, OTf; R )
Me, aryl) complexes with aromatic C-H bonds, and
some observations concerning the mechanism of Ar-H
bond activation in this electron-rich ancillary phosphine
system.
The situation is particularly complicated in Pt(II)
systems which contain potentially labile anionic (X-)
ligands, since direct oxidative addition of R′-H to either
LnPt(R)X or LnPt(R)+ Pt(II) intermediates as well as
alkane heterolysis by LnPt(R)+ are possible. A number
of years ago, Whitesides reported the reaction of trans-
(Ph3P)2Pt(CH2tBu)(OTf) with benzene-d6 to form trans-
(Ph3P)2Pt(C6D5)(OTf) and neopentane-d1.7 On the basis
of anion dependence studies, a mechanism involving an
initial dissociation of triflate and oxidative addition of
C6D6 to the cationic 14-electron intermediate (Ph3P)2-
Pt(CH2tBu)+ was proposed. Unfortunately, this study
was limited by extensive thermal decomposition of the
metal-containing products. More recently, Bercaw has
demonstrated C-H bond metathesis between methane
Resu lts
Syn th esis of (d m p e)P tX2 Com p lexes (X ) Me, Cl,
O2CCF 3, OTf). (dmpe)Pt(Cl)2 serves as a convenient
precursor to both (dmpe)Pt(X)2 and (dmpe)Pt(Me)(X)
systems. Treatment of (dmpe)PtCl2 with 2 equiv of
methylmagnesium bromide in ether afforded (dmpe)-
PtMe2 (1) as a crystalline solid in 77% yield (Scheme
1). Addition of excess triflic or trifluoroacetic acid to
solutions of (dmpe)PtMe2 in dichloromethane gave the
corresponding (dmpe)PtX2 complexes (X ) O2CCF3 3,
O3SCF3 4), which were isolated as analytically pure
solids after solvent removal and repeated washings of
the residue with diethyl ether to remove all traces of
any excess acid.
Addition of 1 equiv of trifluoroacetic acid to (dmpe)-
PtMe2 in acetone at -78 °C selectively afforded the
monomethyl complex (dmpe)Pt(Me)(O2CCF3) (2). The
triflate derivative (dmpe)Pt(Me)(OTf) (6) was prepared
using either the procedure reported by Milstein13a or
from the reaction of (dmpe)Pt(Me)(Cl) (5) with 1 equiv
of AgOTf. 5 was prepared by the addition of 1 equiv of
HCl to (dmpe)Pt(Me)2 in CH2Cl2.
-
and higher alkanes with (tmeda)Pt(Me)(NC5F5)+BArf
in pentafluoropyridine,8 and Goldberg has trapped and
directly characterized a Pt(IV) R-H addition intermedi-
ate, (η3-Tp′)Pt(Me)(H)(R).9 Aryl C-H bond addition to
a Pt(II) diaryl complex has also been recently reported.10
During the course of our studies of highly electron-
poor (fluoroalkyl)phosphine platinum systems (dfepe)-
Pt(Me)(X) (dfepe ) (C2F5)2PCH2CH2P(C2F5)2; X ) O2-
CCF3, OTf),11 we observed that, in contrast to reactive
(L)2Pt(R)(X) (L ) donor ligand) systems, (dfepe)Pt(Me)X
complexes are thermally stable in benzene up to at least
180 °C. This lack of reactivity with aromatic C-H
bonds may be due to either the lower lability of X- in
electrophilic (dfepe)Pt(II) systems or the inaccessibility
of (dfepe)Pt(IV) intermediates. In an effort to more
closely compare (dfepe)Pt chemistry to more electron-
rich Pt(II) analogues, we elected to study the chemistry
The coordination environment of (dmpe)Pt(Me)X com-
pounds is well defined by 1H and 31P NMR spectroscopy.
For example, the 1H methyl proton resonance of (6)
exhibits coupling to both the cis (3J PH ) 2 Hz) and trans
(3J PH ) 7 Hz) phosphorus atoms, with characteristic
platinum satellites (2J PtH ) 48 Hz). The sensitivity of
(6) (a) Stahl, S. S.; Labinger, J . A. Bercaw, J . E. J .Am. Chem. Soc.
1996, 118, 5961. (b) Sen, A. Platinum Metals Rev. 1991, 35, 126. (c)
Shilov, A. E. Activation of Saturated Hydrocarbons by Transition Metal
Complexes; D. Riedel: Dordrecht, The Netherlands, 1984.
(7) Brainard, R. L.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M.
Organometallics 1988, 7, 2379.
(8) Holtcamp, M.W.; Labinger, J .A.; Bercaw, J .E. J . Am. Chem. Soc.
1997, 119, 848.
(9) Wick, D.D.; Goldberg, K. I. J . Am. Chem. Soc. 1997, 119, 10235.
(10) Edelbach, B. L.; Lachicotte, R. J .; J ones, W. D. J . Am. Chem.
Soc. 1998, 120, 2843.
(11) Bennett, B. L.; J . Birnbaum, J .; Roddick, D. M. Polyhedron
1995, 14, 187.
(12) Ryabov, A. D. Chem. Rev. 1990, 90, 403.
(13) Syntheses of (dmpe)Pt(Me)2 and (dmpe)Pt(Me)(OTf)a have
a,b
been previously communicated: (a) Goikhman, R.; Aizenberg, M.;
Shimon, L. J . W.; Milstein, D. J . Am. Chem. Soc. 1996, 118, 10894. (b)
Alcock, N. W.; Brown, J . M.; MacLean, T. D. J . Chem. Soc., Chem.
Commun. 1984, 1689.

Activation of Aromatic C-H Bonds
Organometallics, Vol. 17, No. 20, 1998 4495
1J PtP coupling constants to trans ligand donor abilities
is well established and is reflected in the progressively
higher trans-P coupling values observed for X ) Cl (3930
Hz), O2CCF3 (4111 Hz), and OTf (4572 Hz), consistent
CCF3)2 at a rate qualitatively consistent with its ap-
pearance in eq 2. However, the amount of the expected
accompanying disproportionation product (dmpe)Pt(Ph)2
formed in thermolysis experiments typically ranged
between 25 and 66% of that expected from dispropor-
tionation. We are unable to account for this consistently
low yield of (dmpe)Pt(Ph)2. No (dmpe)Pt(Me)2 was
observed in the thermolysis of (dmpe)Pt(Me)(O2CCF3),
indicating that (dmpe)Pt(O2CCF3)2 is not formed from
the disproportionation of 2 prior to alkyl metathesis.
When the thermolysis of (dmpe)Pt(Me)(O2CCF3) was
carried out in C6D6, CH3D as well as significant amounts
of CH4 (CH3D/CH4 ) 7) were observed by 1H NMR
spectroscopy. The CH3D:CH4 ratio remained essentially
constant throughout the reaction in both 99.8 and 100
atom% benzene-d6. Essentially the same CH3D:CH4
ratio was found using rigorously flame-dried and silated
glassware. Exhaustive thermolysis of (dmpe)Pt(Ph)(O2-
CCF3) in C6D6 at 125 °C does not scramble deuterium
into the dmpe methyl groups (see below); however, it is
possible that the traces of CH4 observed derive from a
minor reaction pathway involving a slightly more favor-
able dmpe metalation in the methyl derivative. No
metal products in the thermolysis of (dmpe)Pt(Me)(OTf)
were identified; however, the major methane isotopomer
observed using C6D6 as a solvent was CH4 (CH3D:CH4
) 1 to 1.3), which suggests that significant metalation
and/or H/D exchange with the dmpe ancillary ligand
may indeed be occurring in this particular system.
The thermal stabilities of the dialkyl and diaryl
complexes 1 and 8 in benzene-d6 were examined for
comparison with (dmpe)Pt(R)(X) systems. (dmpe)Pt-
(Me)2 was completely unreactive at 150 °C. After 5 h
at 180 °C, however, 31P NMR spectra showed the major
species remaining in solution to be unreacted dimethyl
(67%), together with resonances attributable to (dmpe)-
Pt(Me)(Ph) (9) (30%) and a small amount of (dmpe)Pt-
(Ph)2. After 18 h, the major species observed were 9
(51%), diphenyl (34%), and residual dimethyl (15%) (eq
3). 1H NMR spectra revealed an approximate 1:1 ratio
of CH3D:CH4 at this point, indicating that phosphine
ligand metalation may be occurring at these higher
temperatures. (dmpe)Pt(Ph)2 was stable in C6D6 at 125
°C, and there was no evidence for C6D5 incorporation.
with the relative anion donor abilities Cl- > O2CCF3
-
> OTf- in this system. The significant difference
1
between the J PtP value found for 6 in CD2Cl2 (4572 Hz)
and that previously reported in acetone (4305 Hz)13a is
similar in magnitude to differences observed for (dfepe)-
Pt(Me)X systems, and indicates that solvation to form
-
[(dmpe)Pt(Me)(acetone)]+OTf in this solvent is prob-
ably occurring.11
(d m p e)P t(X)2 Th er m olysis Stu d ies. Intramolecu-
lar C-H bond activation (cyclometalation) involving
ligand pendant alkyl groups is quite common in orga-
nometallic chemistry. H/D exchange into alkylphos-
phine substituents by protic solvents via metallacycle
intermediates in particular has been previously estab-
lished for Pt(II) systems.14 To test for the possibility of
reversible cyclometalation in (dmpe)Pt(II) compounds,
the stability of compounds 3 and 4 in their respective
1
acids was evaluated by H and 31P NMR spectroscopy.
(dmpe)Pt(O2CCF3)2 did not undergo any significant H/D
incorporation into the dmpe methyl groups after 72
hours in trifluoroacetic acid-d1 at 180 °C. However, in
neat DOTf significant H/D scrambling (∼25%) into the
1
methyl groups of (dmpe)Pt(OTf)2 was apparent by H
NMR spectra after 24 h at 150 °C (eq 1).
Ar om a tic C-H Bon d Activa tion Stu d ies. The
reactions of (dmpe)Pt(Me)X systems with aromatic
substrates are dependent on the nature of X. The
chloride derivative 5 is stable in benzene up to 150 °C,
while the triflate analogue 6 thermally decomposes in
benzene at 80 °C to give an uncharacterized oily residue.
In contrast, thermolysis of (dmpe)Pt(Me)(O2CCF3) in
benzene at 125 °C results in methane loss and the
formation of (dmpe)Pt(Ph)(O2CCF3) (7) as the primary
product, together with smaller but significant amounts
of both (dmpe)Pt(O2CCF3)2 (3) and (dmpe)Pt(Ph)2 (8)
(8-10%) (eq 2). Products 7 and 8 were confirmed by
their independent synthesis (see Experimental Section).
Kin etic Stu d ies. The reaction progress for (dmpe)-
Pt(Me)(O2CCF3) in C6H6 and C6D6 at 125 °C was
followed by 31P NMR spectroscopy. The disproportion-
ation of initially-formed (dmpe)Pt(Ph)(O2CCF3) was
taken into account by integration of 2 resonances versus
the total (dmpe)Pt species observed in solution. The
disappearance of 2 in C6H6 followed first-order behavior
for over three half-lives, with an apparent rate constant
of 1.40(8) × 10-4 s-1. The thermolysis rate in C6D6 at
125 °C was found to be 4.29(10) × 10-5 s-1, correspond-
The origin of the side products 3 and 8 is of interest.
Thermolysis of the primary product (dmpe)Pt(Ph)(O2-
CCF3) in benzene at 125 °C does not afford (dmpe)Pt(O2-
(14) Kiffen, A. A.; Masters, C.; Raynand, L. J . Chem. Soc., Dalton
Trans. 1975, 853.

4496 Organometallics, Vol. 17, No. 20, 1998
Peters et al.
ture was not separated; however, we formulated these
products as (dmpe)Pt(C6H3F2)(O2CCF3) 10 and (dmpe)-
Pt(C6H3F2)2 11 on the basis of characteristic 1J PtP data.
Separate phosphorus resonances for 10 appear at δ 31.9
(dd, J PF ) 13, 17 Hz; 1J PtP ) 2008 Hz) and δ 11.8 (1J PtP
) 4494 Hz), and a single fluorine-coupled resonance for
11 appears at δ 24.4 (dd, J PF ) 12, 18 Hz; 1J PtP ) 1950
Hz). At intermediate stages of the thermolysis a set of
additional resonances were observed at δ 30.7 (d, J PF
1
∼ 5 Hz; J PtP ) 1795 Hz) and δ 10.2 (1J PtP ) 4218 Hz)
which we tentatively assign as a regioisomer (10a ) that
is thermodynamically unstable with respect to the
ultimate product 10. The regiochemistries of either of
these fluoroarylated products could not be unambigu-
1
ously determined from H and 31P NMR data. However,
a thermodynamic preference for C-H bond addition
ortho to fluorine has been noted previously16 and leads
us to tentatively assign 10 and 11 as 2,3-C6H3F2 aryl
products and 10a as (dmpe)Pt(3,4-C6H3F2)(O2CCF3).
F igu r e 1. Monitoring of the thermolysis of (dmpe)Pt(Me)-
(O2CCF3) (3) in C6H6 (b) and C6D6 (9) at 125 °C by 31P
NMR spectroscopy.
ing to an overall kinetic isotope effect of 3.3(2) (Figure
1). Thermolysis of the aryl platinum complex (dmpe)-
Pt(C6H5)(O2CCF3) in C6D6 at 125 °C resulted in com-
plete conversion to (dmpe)Pt(C6D5)(O2CCF3) after 1 h
(t1/2 ∼ 15 min), indicating that degenerate aryl C-H
activation also occurs, but at a rate approximately
twenty times that of aryl C-H bond addition to (dmpe)-
Pt(Me)(O2CCF3) (eq 4). No significant scrambling of
deuterium into the ancillary dmpe ligand in the ther-
molyses of either 2 or 7 was apparent by 1H NMR
spectroscopy under these conditions.
A similar result was obtained in the reaction of 2 and
1,4-difluorobenzene: after 12 hrs at 125 °C, clean con-
version to a 2:1:1 statistical mixture of (dmpe)Pt(2,5-
difluorophenyl)(O2CCF3) (12), (dmpe)Pt(2,5-difluorophe-
nyl)2 (13), and 3 occurred. Despite the considerable
difference in solvent polarities and also potential ring
substituent effects, there was no significant difference
in the rate of Pt-aryl product formation for either of
these fluorinated substrates relative to the parent
benzene system. A more direct comparison of relative
aryl C-H bond activation rates was obtained by the
thermolysis of 2 in a 1:1 v/v mixture of C6H6 and 1,2-
difluorobenzene. After 35 min at 125 °C, partial con-
version (∼8%) to (dmpe)Pt(C6H5)(O2CCF3) was appar-
ent. After 1 h, however, an approximately equimolar
amount of (10, 10a , 11) compared to 7 had appeared,
and after a total of 4 h at 125 products and 3 were
present. Thus, activation of C6H6 aryl bonds has a
modest kinetic preference, while 10 and 11 are ther-
modynamically favored.
The role of anion dissociation in the reactions of
(dmpe)Pt(R)(X) complexes with aromatic substrates was
probed by examining the effect added salts on the rate
of Pt-aryl complex formation. Thermolysis of (dmpe)-
Pt(Me)(O2CCF3) in C6D6 at 125 °C in the presence
-
of equimolar amounts of either Bu4N+O2CCF3 or
Bu4N+BF4 (ca. 0.05 M) was monitored by 31P NMR
-
spectroscopy. In contrast to Whiteside’s report of tri-
flate anion inhibition for trans-(Ph3P)2Pt(CH2tBu)-
(OTf), the thermal conversion of 2 to 7 with added
Bu4N+O2CCF3 was approximately three times faster
-
(k ∼ 1.0 × 10-4 s-1) than in the absence of added
trifluoroacetate, whereas the observed conversion rate
-
in the presence of Bu4N+BF4 was essentially un-
changed. Investigation of higher added salt ratios was
not possible due to limited tetraalkylammonium salt
solubilities in benzene.
Su bstr a te Effects. The generation of any cationic
platinum intermediates prior to the formation of 7
should be sensitive to solvent polarity effects. To test
this, the thermal stability of (dmpe)Pt(Me)(O2CCF3) in
the polar aromatic solvent 1,2-difluorobenzene (µ )
2.59)15 was examined. Thermolysis of 2 in 1,2-difluo-
robenzene at 125 °C cleanly afforded a 2:1:1 statistical
mixture of new complexes 10, 11, as well as the bis-
acetate, (dmpe)Pt(O2CCF3)2 (eq 5). This product mix-
The possibility of electrophilic aryl C-H bond activa-
tion was evaluated by examining the regiospecificity of
toluene addition. Thermolysis of (dmpe)Pt(Me)(O2-
CCF3) in toluene at 125 °C for 105 min resulted in a
∼45% conversion (31P NMR) to a 1:1.4:2.8 mixture of
three (dmpe)Pt(C6H4Me)(O2CCF3) products 14a , 14b,
and 14c, respectively, as well as the bis-trifluoroacetate
3 (10%). The observed rate of reaction (kobs ∼ 1.3 × 10-4
s-1) was essentially identical to that found in C6H6.
(15) O’Toole, T. R.; Younathan, J . N.; Sullivan, B. P.; Meyer, T. J .
Inorg. Chem. 1989, 28, 3923, and refs therein.
(16) Selmeczy, A. D.; J ones, W. D.; Partridge, M. G.; Perutz, R. N.
Organometallics 1994, 13, 522.

Activation of Aromatic C-H Bonds
Organometallics, Vol. 17, No. 20, 1998 4497
Although the specific regioisomers corresponding to 14a ,
14b, and 14c were not assigned, the observation of all
three possible isomers indicates that there is no pro-
nounced preference for meta, para, or ortho C-H bond
addition in this system. Thermolysis of (dmpe)Pt(Ph)-
(O2CCF3) in toluene-d8 at 125 °C afforded the same
relative ratios of (dmpe)Pt(C 6D5(CD3))(O2CCF3). Again,
the qualitative rate of aryl/aryl exchange (t1/2 ∼ 30 min)
in toluene was significantly faster (∼10 times) than Me/
aryl exchange with 2.
result in increased anion lability. We are unable to
account for the modest rate acceleration observed by us
in the presence of TBA+O2CCF3-; in any event, inter-
pretations of added anion effects in strongly ion-paired
solvent systems such as benzene should be viewed with
some caution.
The possibility of phosphine dissociation to form a
reactive (η1-dmpe)Pt(Me)(O2CCF3) intermediate is more
difficult to address. Under the conditions of alkyl/aryl
metathesis (125 °C), 31P NMR spectra of 2 show no loss
1
in J PtP coupling. However, because of the large mag-
1
nitudes of J PtP exchange decoupling would only be
Discu ssion
manifested for phosphine dissociation rates of greater
than 103 s-1, which is many orders of magnitude faster
than the observed metathesis rates.18 Young has con-
sidered a continuum of possibilities for intramolecular
(L)2Pt(R)2 cyclometalation reactions involving chelating
ligands, which range from rate-determining phosphine
The (dmpe)Pt(Me)(O2CCF3) alkyl/aryl metathesis re-
sults described in this paper are complicated to some
extent by (dmpe)Pt(Ar)(X) product disproportionation
and also methane label scrambling. The observation of
CH4 product formation in C6D6 reactions could be due
to a competing phosphine metalation process, but for
reactions involving (dmpe)Pt(Me)(O2CCF3) the observed
CH4 accounts for only 15-20% of the total methane
product and does not significantly perturb the kinetic
results. In the case of (dmpe)Pt(Ph)(O2CCF3), ∼10%
disproportionation is observed during the course of the
metathesis, whereas complete ligand redistribution
occurs in the thermolysis of (dmpe)Pt(Me)(O2CCF3) in
1,2- and 1,4-difluorobenzene. Since these aryl dispro-
portionation reactions appear to be subsequent to rate-
determining methyl/aryl exchange, we can address
several issues pertaining to aryl C-H bond activation
in these systems.
There is a substantial body of evidence which sup-
ports the intermediacy of 14-electron unsaturated in-
termediates in the intra- and intermolecular activation
of C-H bonds for group 9 as well as group 10 d8 metal
systems.8,9,17 A mechanism involving homolysis of Pt-R
bonds is deemed unlikely, since the lower stability of
aryl radicals is not in accord with the enhanced observed
rate of degenerate aryl/aryl exchange and the absence
of any radical coupling products. For (dmpe)Pt(R)(X)
systems, this would require either the dissociation of
X- or a pre-equilibrium phosphine labilization to form
a pendant η1-dmpe ligand. In our system, (1) the
absence of any significant solvent polarity or anion
inhibition effects and (2) the observation that (dmpe)-
Pt(Me)2 also undergoes methyl/aryl ligand metathesis
in the absence of potentially labile anionic ligands
(albeit at higher temperatures) together suggest that
anion dissociation is not a prerequisite for C-H bond
activation. We note, however, that the qualitative
thermal stability ordering for (dmpe)Pt(Me)(X) of X )
Cl > O2CCF3 > OTf does in fact follow expected lability
trends. Thus, while anion dissociation does not appear
likely, the nature of the X group nevertheless is impor-
tant in determining the ease of Pt-C bond metathesis.
The contrasting kinetic behavior of added X- salts for
cis complexes (dmpe)Pt(R)(X) and Whiteside’s trans-
(Ph3P)2Pt(CH2tBu)(OTf) systems may at least be par-
tially ascribed to a stronger trans influence of alkyl
ligands relative to phosphorus ligands, which would
D
dissociation (kobsH/kobs ∼ 1) to direct C-H addition to
four-coordinate Pt(II) (kobsH/kobs g 3).19 On the basis
D
of our observed kobsH/kobsD ) 3.3(2), C-H addition to the
platinum center is certainly kinetically important, but
a preequilibrium involving phosphine dissociation can-
not be excluded.
Aryl metathesis rates found for benzene, toluene,
o-difluorobenzene, and p-difluorobenzene C-H bonds
are all comparable and are inconsistent with electro-
philic attack at the aromatic ring. These observations
are in accord with earlier studies by Parshall, who
reported a modest kinetic preference for fluorinated
aromatic C-H bond activation for Cp2Nb(H)3 but es-
sentially no discrimination by Cp2Ta(H)3.20 The fact
that ortho toluene C-H bond addition, inferred by the
presence of a third tolyl regioisomer, is not observed for
trans-(Ph3P)2Pt(CH2tBu)(OTf) or Cp*Ir(Me3P)(Me)(OTf)21
suggests that steric constraints may not be as severe
for (dmpe)Pt(R)(X).22 The lack of a substrate depen-
dence could be considered support for a rate-determin-
ing phosphine dissociation mechanism. However, this
is not consistent with the high observed kinetic isotope
effect or the qualitative dependence of reactivity for
(dmpe)Pt(Me)(X) systems on the nature of X, since dmpe
labilization is expected to occur trans to the methyl
group rather than the weakly trans-influencing X group,
and therefore should be relatively insensitive to the
nature of X.
The significantly enhanced rate of aryl/aryl exchange
relative to methyl/aryl exchange is a surprising result
that we are unable to account for. If the direct oxidative
addition of aromatic C-H bonds to (dmpe)Pt(R)(Y)
systems is rate-determining, it is not obvious how R )
aryl would significantly enhance this process over R )
alkyl. Nevertheless, it is clear from the qualitative
thermal stability ordering (dmpe)Pt(Me)(OTf) > (dmpe)-
1
(18) This assumes a coalescence condition of kex ∼ 2.22 J PtP for
exchange decoupling. See Sanders, J . K. M., Hunter, B. K. Modern
NMR Spectroscopy, 2nd ed.; Oxford University Press: New York, 1993;
Chapter 7.
(19) (a) Ankianiec, B. C.; Hardy, D. T.; Thomson, S. K.; Watkins,
W. N.; Young, G. B. Organometallics 1992, 11, 2591. (b) Griffiths, D.
C.; Young, G. B. Organometallics 1989, 8, 875.
(20) Klabunde, U.; Parshall, G. W. J . Am. Chem. Soc. 1972, 94, 9081.
(21) Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
10462.
(22) Small (∼8%) amounts of a ortho tolyl C-H addition product
have been observed for Cp*Rh(Me3P)(H)2: J ones, W. D.; Feher, F. J .
J . Am. Chem. Soc. 1984, 106, 1650.
(17) (a) Flood, T. C. In Electron Deficient Boron and Carbon Clusters;
Olah, G. A., Ed.; Wiley: New York, 1991, Chapter 13 and refs therein.
(b) DiCosimo, R.; Moore, S. S.; Sowinski, A. F.; Whitesides, G. M. J .
Am. Chem. Soc. 1982, 104, 124. (c) Brainard, R. L.; Miller, T. M.;
Whitesides, G. M. Organometallics 1986, 5, 1481.

4498 Organometallics, Vol. 17, No. 20, 1998
Peters et al.
15 mL of diethyl ether and filtered. The filtrate volume was
reduced to 5 mL, and the white product was precipitated at
-78 °C and isolated by cold filtration. The isolated yield of 2
was 0.106 g (85%). Anal. Calcd for C9H19F3O2P2Pt: C, 22.84,
H, 4.05. Found: C, 23.16, H, 3.81. IR (cm-1): 1702(vs), 1295-
(w), 1202(vs), 1179(s), 1121(vs), 1080(sh), 941(s), 842(w), 726
(m). 1H NMR (acetone-d6, 399.65 MHz, 20 °C): δ 2.08-1.92
(m, 4H: PCH2), 1.68 (m, 6H; PCH3), 1.37 (m, 6H; PCH3), 0.28
(d, 2J PtH ) 48 Hz, 3J PH ) 2 Hz, 3H; PtCH3). 31P NMR (benzene-
Pt(Ph)(O2CCF3) > (dmpe)Pt(Me)(O2CCF3) > (dmpe)Pt-
(Me)2, (dmpe)Pt(Me)(Cl) that activities are strongly
dependent on the nature of both R and X. In light of
previous reports concerning the kinetic selectivity of H2
addition to related d8 (L)2Ir(X)(CO) systems, it would
be worthwhile to probe for similar ancillary ligand
effects in group 10 systems.
In summary, given sufficiently labile anionic or
neutral ancillary ligands, prior studies have shown that
dissociative pathways are generally preferred in square
planar d8 metal systems. Nevertheless, when suf-
ficiently labile ancillary ligands are not present, the
more energetically-demanding direct addition of aryl
C-H bonds to four-coordinate (dmpe)Pt(II) is a reason-
able alternative. Although dmpe chelate dissociation
cannot be ruled out, the high observed kinetic isotope
effect for aryl C-H addition suggests a direct oxidative
addition for the this particular Pt(II) system.
1
d6, 161.70 MHz, 20 °C): δ 35.5 (s, J PtP ) 1764 Hz; trans to
1
Pt-CH3), 12.7 (s, J PtP ) 4146 Hz; trans to Pt-O2CCF3). 19F
NMR (benzene-d6, 376.05 MHz, 20 °C): δ -75.1 (s). 13C NMR
(acetone-d6, 100.40 MHz, 20 °C): 5.03 (td, 1J CH ) 126 Hz, 2J PC
) 95 Hz; PtCH3), 10.10-15.65 (m; PCH3).
(d m p e)P t(O2CCF 3)2 (3). To a flask containing (dmpe)Pt-
(Me)2 (0.230 g 0.607 mmol) and 12 mL of CH2Cl2 was added 4
mL of CF3CO2H at -78 °C. The immediate evolution of
methane was observed upon addition. After warming to
ambient temperature, the volatiles were removed, and the
residue was extracted with dichloromethane. Removal of CH2-
Cl2 and addition of diethyl ether afforded after filtration and
drying 0.275 g (79%) of 3 as a white solid. Anal. Calcd for
C
10H16F6O4P2Pt: C, 21.03; H, 2.82. Found: C, 21.31; H, 2.64.
IR(cm-1): 1691(vs), 1577(w), 1411(m), 1294(m), 1196(s), 1139-
(s), 950(m), 913(w), 841(m), 725(s). 1H NMR (CD2Cl2, 399.65
MHz, 20 °C): δ 1.86 (m, 4H; PCH2), 1.81 (m, 12H; PCH3). 19F
NMR (CD2Cl2, 376.05 MHz, 20 °C): δ -74.4 (s). 31P NMR
1
(benzene-d6, 161.70 MHz, 20 °C): δ 23.0 (s, J PtP ) 3735 Hz).
Exp er im en ta l Section
(d m p e)P t(OSO2CF 3)2 (4). To a 25 mL flask charged with
0.210 g (dmpe)Pt(Me)2 (0.561 mmol) and 15 mL of CH2Cl2 at
-78 °C was added (0.150 mL of HOSO2CF3 (1.70 mmol) via
syringe. The solution was allowed to warm to ambient
temperature, the solvent was removed, and 4 was precipitated
as a white solid by the addition of diethyl ether. Filtration
and repeated washings with ether afforded 0.295 g (82%) of
analytically pure 4. Anal. Calcd for C8H16F6O6P2PtS2: C,
14.94; H, 2.51. Found: C, 14.98; H, 2.63. IR (cm-1): 1335(s),
1318(m), 1302(m), 1237(s), 1194(s), 1174(s), 1029(m), 1012-
(m), 950(s), 914(s), 731(m). 1H NMR (CF3SO3D, 399.65 MHz,
20 °C): δ 1.47 (m, 4H; PCH2), 1.32 (m, 12H; PCH3). 31P NMR
Gen er a l P r oced u r es. All manipulations were conducted
under an atmosphere of purified nitrogen using high-vacuum,
Schlenk, and/or glovebox techniques. Water- and oxygen-free
solvents were prepared according to established procedures.
Aprotic deuterated solvents used in NMR experiments were
dried over activated 3 Å molecular sieves. Triflic acid (CF3-
SO3H, Aldrich) was vacuum distilled prior to use and stored
at -30 °C under a nitrogen atmosphere. CF3SO3D acid was
prepared by treatment of triflic anhydride (Aldrich) with D2O
followed by removal of excess anhydride under vacuum.
Trifluoroacetic acid (CF3CO2H, Aldrich) was dried over acti-
vated 3 Å sieves and stored under vacuum. CF3CO2D was
obtained from Cambridge Isotope Laboratories and was used
as received. Elemental analyses were performed by Desert
1
(CF3SO3D, 161.70 MHz, 20 °C): δ 33.4 (s, J PtP ) 4114 Hz).
(d m p e)P t(Me)(Cl) (5). To 0.304 g (0.810 mmol) of (dmpe)-
Pt(Me)2 and 30 mL of CH2Cl2 was added 38.2 mL (390 torr,
0.801 mmol) of hydrochloric acid gas in two 19.1 mL portions
at -78 °C. The solution was stirred for 90 min, and the
evolved methane was removed before the addition of the
second portion. After a further 90 min of stirring, the volatiles
were removed and the residue was extracted with dichlo-
romethane. Removal of filtrate solvent and the addition of
diethyl ether at -78 °C afforded 0.210 g (66%) of 5 as a white
powder. Anal. Calcd for C7H19ClP2Pt: C, 21.25; H, 4.84.
Found: C, 21.22; H, 4.68. IR (cm-1): 1418(s), 1297(w), 1287-
(s), 1128(w), 1092(w), 939(vs), 919(m), 902(s), 847(s), 796(w),
753(m), 720(s). 1H NMR (acetone-d6, 399.65 MHz, 20 °C): δ
2.07-1.91 (m, 4H; PCH2), 1.63 (m, 6H; PCH3), 1.49 (m, 6H;
Analytics. Infrared spectrum were obtained on either
a
Perkin-Elmer 1600 or Bomem MB100 FTIR instrument as
Nujol mulls. NMR spectra were recorded with a J EOL GSX-
400 or a Bruker Avance DRX-400 instrument. 31P NMR
spectra were referenced to an 85% H3PO4 external standard
and 19F NMR spectra were referenced to CF3CO2Et or CFCl3
as external standards. (dmpe)PtCl2 was prepared according
to established literature procedures.23
(d m p e)P t(Me)2 (1). To a solution of (dmpe)PtCl2 (2.000 g,
4.88 mmol) in 125 mL of ether was added 3.3 mL of methyl
magnesium bromide (3.0 M in diethyl ether, 9.90 mmol). After
3 h the solvent was removed, and the residue was extracted
with hexanes. Cooling the concentrated filtrate to -78 °C
followed by filtration gave 1.397 g (77%) of 1 as a pure,
microcrystalline, white solid. Anal. Calcd for C8H22P2Pt: C,
25.60; H, 5.91. Found: C, 25.22; H, 5.91. IR (cm-1): 1412
(s), 1282 (s), 1130 (m), 1078 (m), 933 (s), 838 (m), 710 (s). 1H
NMR (CD2Cl2, 399.65 MHz, 20 °C): δ 1.59 (m, 4H; PCH2), 1.43
2
3
PCH3), 0.31 (dd, J PtH ) 54 Hz, J PH ) 7.9, 3.6, 3H; PtCH3).
31P NMR (acetone-d6, 161.70 MHz, 20 °C): δ 37.2 (s, J PtP
)
1
1725 Hz, trans to Pt-CH3), 21.84 (s, 1J PtP ) 3930 Hz, trans to
Pt-Cl).
(d m p e)P t(Me)(OSO2CF 3) (6). A slurry of AgOTf (0.500
g, 1.958 mmol) and 0.740 g (1.870 mmol) of 5 in 50 mL of
dichloromethane was stirred under nitrogen in the absence of
light. After 24 h the reaction mixture was filtered, and the
filtrate volume was reduced to 5 mL. Addition of ether and
precipitation at -78 °C gave 6 as an off-white powder in 71%
crude yield. Recrystallization from a fluorobenzene/ether
2
3
(m, 12H; PCH3), 0.33 (t, J PtH ) 68 Hz, J PH ) 8 Hz, 6H;
PtCH3). 31P NMR (CD2Cl2, 161.70 MHz, 20 °C): δ 26.6 (s, 1J PtP
) 1743 Hz).
(d m p e)P t(Me)(O2CCF 3) (2). 20 µL (0.27 mmol) of HO2-
CCF3 was added dropwise via syringe to a flask containing
0.100 g (0.266 mmol) (dmpe)Pt(Me)2 in 15 mL of acetone under
nitrogen at -78 °C. After warming to room temperature, the
volatiles were removed and the residue was taken up in ca.
mixture yielded analytically pure 6. Anal. Calcd for C9H19
-
F3O3P2PtS: C, 18.87; H, 3.76. Found: C, 19.01 H, 3.76. IR
(cm-1): 1413(s), 1312(s), 1244(vs), 1168(s), 1094(w), 1030(vs),
945(s), 921(m), 906(m), 845(w), 801(w), 755(m). 1H NMR (CD2-
Cl2, 399.65 MHz, 20 °C): δ 1.99-1.81 (m, 2H; PCH2), 1.70-
(23) Anderson, G. K.; Lumetta, G.L. Inorg. Chem. 1987, 26, 1523.

Activation of Aromatic C-H Bonds
Organometallics, Vol. 17, No. 20, 1998 4499
2
1.65 (m, 2H; PCH2), 1.70 (m, 6H; PCH3), 1.65 (m, 6H; PCH3),
(C6H5)), 6.72 (t, J HH ) 15 Hz, 1H; p-Pt(C6H5)), 1.69 (m, 4H;
0.47 (dd, J PtH ) 40 Hz, J PH ) 7 Hz, 1.5 Hz, 3H; PtCH3). 31P
PCH2), 1.28 (m, 12H; PCH3). 31P NMR (benzene-d6, 161.99
MHz, 20 °C): δ 21.8 (s, J PtP ) 1638 Hz).
2
3
1
1
NMR (CD2Cl2, 161.7 MHz, 20 °C): δ 41.1 (s, J PtP ) 1789 Hz
1
P trans to Pt-CH3), 14.9 (s, J PtP ) 4572 Hz P trans to Pt-
Th er m olysis P r od u cts of (d m p e)P t(Me)(O2CCF 3) in
1,2- a n d 1,4-C6H4F 2. Approximately 10 mg samples of 2 in
0.5 mL of 1,2- and 1,4-difluorobenzene were sealed off in flame-
dried 5 mm NMR tubes. After 4 h at 125 °C, 31P NMR spectra
showed 2:1:1 statistical mixtures of (dmpe)Pt(aryl)(O2CCF3),
(dmpe)Pt(aryl)2, and 3 as products, which were not separated.
31P NMR data (benzene-d6, 161.99 MHz, 20 °C) for 10: δ 31.9
(dd, J PF ) 13, 17 Hz; 1J PtP ) 2008 Hz), 11.8 (1J PtP ) 4494 Hz).
OTf). 19F NMR (CD2Cl2, 376.05 MHz, 20 °C): δ -77.3 (s, 3F;
SO3CF3).
(d m p e)P t(P h )(O2CCF 3) (7). A 23 µL (0.30 mmol) amount
of HO2CCF3 was added dropwise via syringe to a flask
containing 0.158 g (0.300 mmol) of (dmpe)Pt(Ph)2 in 23 mL of
dichloromethane at room temperature. The reaction mixture
was extracted with dichloromethane, and the filtrate volatiles
were removed. The residual was slurried in an ether/
petroleum ether mixture (2 mL/3 mL) and filtered at -78 °C,
yielding 0.138 g of 7 (86%). Anal. Calcd for C14H21F3O2P2Pt:
C, 31.41; H, 3.95. Found: C, 31.30; H, 3.88. IR(cm-1): 3049
(m), 1696 (vs), 1567 (m), 1412 (m), 1285 (w), 1196 (vs), 1138
(vs), 939 (s) 907 (m), 834 (m), 794 (w), 742 (m), 723 (s). 1H
NMR (CDCl3, 400.13 MHz, 20 °C): δ 7.40 (t, J HH ) 13 Hz,
3J PtH ) 38 Hz, 2H; o-Pt(C6H5)), 7.09 (t, 3J HH ) 15 Hz, 2H; m-Pt-
31P NMR data for 10a : δ 30.7 (d, J PF ∼ 5 Hz; J PtP ) 1795
1
Hz), 10.2 (1J PtP ) 4218 Hz). 31P NMR data for 11: δ 24.4 ((dd,
J PF ) 12, 18 Hz; J PtP ) 1950 Hz). 31P NMR data for 12: δ
1
26.2 (d, J PF ) 13 Hz; 1J PtP ) 1960 Hz), 14.3 (1J PtP ) 4570 Hz).
31P NMR data for 13: δ 34.4 (d, J PF ) 14 Hz; J PtP ) 2020
1
Hz).
Th er m olysis P r od u ct s of (d m p e)P t (Me)(O2CCF 3) in
Tolu en e. Thermolyses were carried out as described above
for 10-13. After 2 h at 125 °C, a 1:1.4:2.8 mixture of tolyl
products 14a , 14b, and 14c were observed, along with ∼10%
of 3. This mixture was not separated and was characterized
by 31P NMR. 31P NMR data for 14a : δ 33.3 (1J PtP ) 1705 Hz),
3
(C6H5)), 6.96 (t, J HH ) 15 Hz, 1H; p-Pt(C6H5)), 1.90-1.50 (m,
4H; PCH2), 1.65 (m, 6H; PCH3), 1.45 (m, 6H; PCH3). 19F NMR
(benzene-d6, 376.49 MHz, 20 °C): δ -77.1 (s). 31P NMR
1
(benzene-d6, 161.99 MHz, 20 °C): δ 32.8 (s, J PtP ) 1696 Hz;
1
trans to Pt-Ph group), 12.0 (s, J PtP ) 4100 Hz; trans to Pt-
12.5 (1J PtP ) 4090 Hz). 31P NMR data for 14b: δ 32.7 (1J PtP
)
O2CCF3).
1690 Hz), 12.0 (1J PtP ) 4110 Hz). 31P NMR data for 14c: δ
32.5 (1J PtP ) 1680 Hz), 11.9 (1J PtP ) 4110 Hz).
(d m p e)P t(P h )2 (8). To a solution of (cod)Pt(Ph)2 (0.158 g,
0.345 mmol) and 10 mL of petroleum ether was added 60 µL
of dmpe at room temperature under a nitrogen atmosphere.
Immediate precipitation occurred and collection by filtration
afforded 0.158 g (92 %) of 8 as a flaky white powder. Anal.
Calcd for C18H26P2Pt: C, 43.29; H, 5.25. Found: 42.83; H, 5.05.
IR (cm-1): 3045(s), 1572(s), 1416(m), 1280(s), 1136(m), 1021-
(w), 993(w), 935(vs), 900(s), 835(m) 741(vs), 706(s), 652(m). 1H
NMR (CD2Cl2, 400.13 MHz, 20 °C): δ 7.33 (t, J HH ) 15 Hz,
2J PtH ) 56 Hz, 2H; o-Pt(C6H5)), 6.95 (t, 2J HH ) 15 Hz, 2H; m-Pt-
Ack n ow led gm en t. This work has been supported
by the National Science Foundation (Grant No. CHE-
9615985), and the donors of the Petroleum Research
Fund, administered by the American Chemical Society.
Thanks is given to Prof. W. D. J ones for helpful
discussions.
OM980334L