Comparative studies with zwitterionic platinum(II) bis(pyrazolyl)borate and 2,2′-bipyridylborate complexes

Article abstract of DOI:10.1021/om050538j

A comparison between the mononuclear platinum complexes of three structurally different monoanionic borato ligands is presented: [Ph ₂(pyrazolyl)₂]^- ([Ph₂B(pz) ₂], 1), [4-Ph₃B(2,2′-bipyridine)]^- ([(4-BPh₃)bpy], 2), and [Ph₂B(CH₂PPh ₂)₂]- ([Ph₂BP₂], 3). The new bipyridylborate ligand 2 is introduced in this study. The relative trans influence of these ligands has been assessed by comparison of the structural and spectroscopic (NMR) data of the platinum dimethyl complexes [[Ph ₂B(pz)₂]Pt(Me)₂][NBu₄] (4), [[(4-BPh₃)bpy]Pt(Me)₂] [NBu₄] (5), and [[Ph₂BP₂]Pt(Me)₂][ASN] (6). The neutral complexes [Ph₂B(pz)₂]Pt(Me)(NCCH₃) (7), [Ph₂B(pz)₂]Pt(Me)(CO) (8), [Ph₂B(pz) ₂]Pt(Me)(P(C₆F₅)₃) (9), [(4-BPh ₃)bpy]Pt(Me)(NCCH₃) (10), [(4-BPh₃)bpy]Pt(Me) (CO) (11), and [(bpy)Pt(Me)(CO)] [BPh₄] (12) were prepared, and the carbonyl complexes 8, 11, and 12 provide information pertaining to the relative electronreleasing character of each ligand type. The CO stretching frequencies suggest that the charged borate moiety renders the borato ligands more electron-donating than their neutral analogues. Of the neutral platinum methyl solvento complexes supported by ligands 1, 2, and 3, only those of 1 display very different C - H activation propensities. Upon protonation or methide abstraction in benzene at room temperature, complex 4 rapidly activates two molecules of benzene to generate [[Ph₂B(pz)₂]Pt(Ph) ₂][NBu₄] (13). Isotopic scrambling of deuterium into methane in C₆D₆ solvent suggests the intermediacy of a methane oadduct in this reaction. The double C-H activation reaction can be halted by addition of acetonitrile to trap the intermediate [Ph ₂B(pz)₂]Pt(Ph)(NCCH₃) (14). Complex 3 also displays reactivity toward the benzylic C-H bonds of mesitylene at room temperature to form [Ph₂(pz)₂]-Pt(pzH)(CH ₂C₆H₃(CH₃)₂) (15) in modest yield.

Full text of DOI:10.1021/om050538j

5858
Organometallics 2005, 24, 5858-5867
Comparative Studies with Zwitterionic Platinum(II)
Bis(pyrazolyl)borate and 2,2′-Bipyridylborate Complexes
Christine M. Thomas and Jonas C. Peters*
Division of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of
Chemical Synthesis, California Institute of Technology, Pasadena, California 91125
Received June 28, 2005
A comparison between the mononuclear platinum complexes of three structurally different
monoanionic borato ligands is presented: [Ph2B(pyrazolyl)2]- ([Ph2B(pz)2], 1), [4-Ph3B(2,2′-
bipyridine)]- ([(4-BPh3)bpy], 2), and [Ph2B(CH2PPh2)2]- ([Ph2BP2], 3). The new bipyridylborate
ligand 2 is introduced in this study. The relative trans influence of these ligands has been
assessed by comparison of the structural and spectroscopic (NMR) data of the platinum
dimethyl complexes [[Ph2B(pz)2]Pt(Me)2][NBu4] (4), [[(4-BPh3)bpy]Pt(Me)2][NBu4] (5), and
[[Ph2BP2]Pt(Me)2][ASN] (6). The neutral complexes [Ph2B(pz)2]Pt(Me)(NCCH3) (7), [Ph2B-
(pz)2]Pt(Me)(CO) (8), [Ph2B(pz)2]Pt(Me)(P(C6F5)3) (9), [(4-BPh3)bpy]Pt(Me)(NCCH3) (10),
[(4-BPh3)bpy]Pt(Me)(CO) (11), and [(bpy)Pt(Me)(CO)][BPh4] (12) were prepared, and the
carbonyl complexes 8, 11, and 12 provide information pertaining to the relative electron-
releasing character of each ligand type. The CO stretching frequencies suggest that the
charged borate moiety renders the borato ligands more electron-donating than their neutral
analogues. Of the neutral platinum methyl solvento complexes supported by ligands 1, 2,
and 3, only those of 1 display very different C-H activation propensities. Upon protonation
or methide abstraction in benzene at room temperature, complex 4 rapidly activates two
molecules of benzene to generate [[Ph2B(pz)2]Pt(Ph)2][NBu4] (13). Isotopic scrambling of
deuterium into methane in C6D6 solvent suggests the intermediacy of a methane σ-adduct
in this reaction. The double C-H activation reaction can be halted by addition of acetonitrile
to trap the intermediate [Ph2B(pz)2]Pt(Ph)(NCCH3) (14). Complex 3 also displays reactivity
toward the benzylic C-H bonds of mesitylene at room temperature to form [Ph2B(pz)2]-
Pt(pzH)(CH2C6H3(CH3)2) (15) in modest yield.
Introduction
ies in our group have focused on monoanionic bidentate
ligands such as bis(phosphino)borates and bis(amino)-
borates, in which a borate moiety is linked to tertiary
phosphine or amine donors via a methylene linker.3 We
have found that zwitterionic complexes often display
reactivity quite similar to their cationic congeners, but
important reactivity and mechanistic differences can be
prevalent. For example, bis(phosphino)borate rhodium
catalysts show tolerance to relatively polar donor sol-
vents such as acetonitrile, in contrast to their cationic
bis(phosphine) relatives.3e Also, comparative structural,
electronic, and mechanistic studies of zwitterionic and
cationic bis(phosphine) platinum(II) complexes suggest
that more electron-rich, platinum(II) zwitterions are
equally, if not more, competent than their isostructural
cations with respect to their propensities for benzene
C-H activation. Subtle mechanistic differences distin-
guish the benzene solution chemistry of the two sys-
tems, leading to different overall reaction rates.3c
Motivated by the versatility of organometallic cations
for processes such as polymerization, C-H bond activa-
tion, and C-E bond forming reactions (E ) H, C, Si),
our group has studied various neutral, formally zwit-
terionic complexes to examine the effect of electrophi-
licity on the reactivity of late transition metal centers.1,2
These zwitterions utilize ligands in which a borate
moiety is incorporated within the ligand framework but
is partially insulated from the coordinated metal center.
Our goal has been to study the effect of the anionic
borate unit on the reactivity of these complexes by
comparison to cationic complexes supported by structur-
ally similar neutral ligands. Accordingly, previous stud-
* To whom correspondence should be addressed. E-mail: jpeters@
caltech.edu.
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169-1203. (b) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev.
2000, 100, 3009-3066. (c) Crabtree, R. H. Acc. Chem. Res. 1979, 12,
331-337. (d) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1971,
93, 3089-3091.
(2) For recent discussions of C-H bond activation and functional-
ization mediated by cationic metal centers, see: (a) Lersch, M.; Tilset,
M. Chem. Rev. 2005, 105, 2471-2526. (b) Arndtsen, B. A.; Bergman,
R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154-
162. (c) Sen, A. Acc. Chem. Res. 1998, 31, 550-557. (d) Stahl, S. S.;
Labinger, J. A.; Bercaw, J. E. Angew. Chem., Int. Ed. 1998, 37, 2181-
2192. (e) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 2437-
2450. (f) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic
Reactions of Saturated Hydrocarbons in the Presence of Metal Com-
plexes; Kluwer: Boston, 2000.
Square planar platinum(II) centers supported by
nitrogen donor ligands have been more thoroughly
(3) (a) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001, 123,
5100-5101. (b) Betley, T. A.; Peters, J. C.; Inorg. Chem. 2002, 41,
6541-6543. (c) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2003,
125, 8870-8888. (d) Thomas, J. C.; Peters, J. C. Inorg. Chem. 2003,
42, 5055-5073. (e) Betley, T. A.; Peters, J. C. Angew. Chem., Int. Ed.
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2002, 124, 5272-5273.
10.1021/om050538j CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/22/2005

Zwitterionic Pt(II) Bis(pyrazolyl)borate Complexes
Organometallics, Vol. 24, No. 24, 2005 5859
examined with respect to alkane activation reactions
than phosphine-supported systems.4,5 One case perti-
nent to the present paper concerns various studies of
the C-H activation reactivity of platinum tris(pyra-
zolyl)borate (Tp) complexes.6 In this regard it is note-
worthy that little attention has yet focused on bis-
(pyrazolyl)borate group 10 metal complexes, despite the
fact that various platinum studies exploiting Tp ligands
feature κ2 Tp precursors and/or intermediates. The
limited reports of platinum bis(pyrazolyl)borate systems
have not described their utility for C-H activation
chemistry.7
In addition to Tp platinum complexes, a range of Pt
diimine species exhibit C-H activation activity. Among
the more noteworthy diimine-type systems are the (2,2′-
bipyrimidyl)platinum(II) complexes examined by Peri-
ana et al.8 and a host of platinum diimine complexes
that have proven particularly advantageous for careful
mechanistic studies.9 Platinum complexes of the 2,2′-
bipyridine (bpy) ligand and its derivatives have also
been investigated extensively, for example with respect
to oxidative addition processes.10,11 There are several
reports that describe instances of C-H activation reac-
tions mediated by platinum(II) bipyridyl complexes,
although these reactions tend to involve intramolecular
ligand C-H activation processes.12
Figure 1. [Ph2B(pz)2] (1), [(4-BPh3)bpy] (2), and [Ph2BP2]
(3) ligands, each possessing a borate anion incorporated
within the ligand framework.
the ligand 2,2′-bipyridylborate [(4-BPh3)bpy]. This ligand
and the bidentate borate [Ph2B(pz)2] comprise the
specific ligands of interest herein (Figure 1). We present
a comparison of the structural and electronic properties
of their platinum derivatives as determined by X-ray
crystallography, IR spectroscopy, and 1H NMR spec-
troscopy. Also discussed is the proclivity of several
platinum derivatives to undergo C-H bond activation
processes. Most interesting in this context is the dis-
covery of a double C-H bond activation reaction: it is
observed that exposure of a coordination site of the
precursor {[Ph2B(pz)2]Pt(Me)2}- in benzene solution
leads to the rapid production of {[Ph2B(pz)2]Pt(Ph)2}-
at ambient temperature. This reaction is reminiscent
of Goldberg’s earlier discovery of a {κ2-[Tp*]PtMe2}-
precursor that reacts with alkanes upon exposure of a
coordination site to yield stable octahedral Pt(IV) prod-
ucts in which the Tp ligand is κ3.6e,6g,13
In the present study, we report on platinum com-
plexes supported by bidentate pyrazolyl and bipyridyl
borate ligands. To extend borate incorporation into the
ubiquitous bipyridyl ligand class, we have synthesized
(4) See for example: (a) Rostovtsev, V. V.; Henling, L. M.; Labinger,
J. A.; Bercaw, J. E. Inorg. Chem. 2002, 41, 3608-3619. (b) Rostovtsev,
V. V.; Labinger, J. A.; Bercaw, J. E. Organometallics 1998, 17, 4530-
4531. (c) Rendina, L. M.; Puddephatt, R. J. Chem. Rev. 1997, 97, 1735-
1754.
(5) See for example: (a) Fekl, U.; Goldberg, K. I. J. Am. Chem. Soc.
2002, 124, 6804-6805. (b) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E.
J. Am. Chem. Soc. 1996, 118, 5961-5976.
(6) (a) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L. J.
Am. Chem. Soc. 2001, 123, 12724-12725. (b) Lo, H. C.; Haskel, A.;
Kapon, M.; Keinan, E. J. Am. Chem. Soc. 2002, 124, 3226-3228. (c)
Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L. J. Am. Chem.
Soc. 2001, 123, 6425-6426. (d) Reinartz, S.; White, P. S.; Brookhart,
M.; Templeton, J. L. Organometallics 2000, 19, 3854-3866. (e) Wick,
D. D.; Goldberg, K. I. J. Am. Chem. Soc. 1997, 119, 10235-10236. (f)
Haskel, A.; Keinan, E. Organometallics 1999, 41, 2808-2810. (g)
Jensen, M. P.; Wick, D. D.; Reinartz, S.; White, P. S.; Templeton, J.
L.; Goldberg, K. I. J. Am. Chem. Soc. 2003, 125, 8614.
Results and Discussion
Synthesis of Precursor Complexes. The [Ph2B-
(pz)2][NBu4] (1) ligand was synthesized using a modi-
fication of the procedure reported in the literature.14
Excess pyrazole and sodium tetraphenylborate were
heated to a melt (80-100 °C) for several hours. This
was followed by salt metathesis with NBu4Br in CH2-
Cl2 to generate 1 in 76% yield.
The [(4-BPh3)bpy][NBu4] (2) ligand was synthesized
from 4-iodo-2,2′-bipyridine15 via formation of a bipyridyl
Grignard reagent (4-MgX)bpy using iPrMgCl at -78 °C
in diethyl ether (Scheme 1). The Grignard was then
quenched with BPh3 and the magnesium salt [(4-
BPh3)bpy]2Mg was isolated as a red solid. It is note-
worthy that traditional lithio reagents (i.e., nBuLi,
tBuLi, etc.) and Mg0 proved ineffective for the synthesis
of this ligand. Strong chelation to magnesium made
metalation of the magnesium derivative [(4-BPh3)bpy]2-
(7) (a) Onishi, M.; Hiraki, K. Inorg. Chim. Acta 1994, 224, 131-
135. (b) Clark, H. C.; von Werner, K. J. Organomet. Chem. 1975, 101,
347-358. (c) Reger, D. L.; Baxter, J. C.; Lebioda, L. Inorg. Chim. Acta
1989, 165, 201-205.
(8) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560-564.
(9) (a) Johansson, L.; Tilset, M.; Labinger, J. A.; Bercaw, J. E. J.
Am. Chem. Soc. 2000, 122, 10846-10855. (b) Johansson, L.; Ryan, O.
B.; Romming, C.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 6579-6590.
(c) Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739-740.
(d) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am Chem. Soc. 2002,
124, 1378-1399.
(10) See for example: (a) Klein, A.; van Slageren, J.; Zalis, S. Eur.
J. Inorg. Chem. 2003, 1927-1938. (b) Doppiu, A.; Cinellu, M. A.;
Minghetti, G.; Stoccoro, S.; Zucca, A.; Manassero, M.; Sansoni, M. Eur.
J. Inorg. Chem. 2000, 2555-2563. (c) Bayler, A.; Canty, A. J.; Skelton,
B. W.; White, A. H. J. Organomet. Chem. 2000, 595, 296-299. (d) Hill,
G. S.; Rendina, L. M.; Puddephatt, R. J. Organometallics 1995, 14,
4966-4968. (e) Chaudhury, N.; Puddephatt, R. J. J. Organomet. Chem.
1975, 84, 105-115. (f) Achar, S.; Catalano, V. J. Polyhedron 1997, 16,
1555-1561. (g) Hill, G. S.; Manojlovic-Muir, L.; Muir, K.; Puddephatt,
R. J. Organometallics 1997, 16, 525-530.
(12) (a) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B. Zucca,
A. Organometallics 2003, 22, 4770-4777. (b) Zucca, A.; Stoccoro, S.;
Cinellu, M. A.; Minghetti, G.; Manassero, M.; Sansoni, M. Eur. J. Inorg.
Chem. 2002, 3336-3346. (c) Zucca, A.; Doppiu, A.; Cinellu, M. A.;
Stoccoro, S.; Minghetti, G.; Manassero, M. Organometallics 2002, 21,
783-785. (d) Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca, A.;
Manassero, M. J. Chem. Soc., Dalton Trans. 1995, 5, 777-781.
(13) Aspects of this work have been briefly described in an ACS
Symposium Series contribution: Peters, J. C.; Thomas, J. C.; Thomas,
C. M.; Betley, T. A. Activation and Functionalization of C-H Bonds;
Goldberg, K., Goldman, A., Eds.; ACS Symposium Series No. 885;
American Chemical Society: Washington, DC, 2004; Chapter 20, pp
334-354.
(11) (a) Hill, R. H.; Puddephatt, R. J. J. Am. Chem. Soc. 1985, 107,
1218-1225. (b) Crespo, M.; Puddephatt, R. J. Organometallics 1987,
6, 2548-2550. (c) Kuyper, J. Inorg. Chem. 1978, 17, 1458-1463. (d)
Kuyper, J. Inorg. Chem. 1977, 16, 2171-2176. (e) Kuyper, J. Inorg.
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Soc. 1997, 119, 10127-10136.
(14) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288-6293.
(15) (a) Wenkert, D.; Woodward, R. B. J. Org. Chem. 1983, 48, 283-
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1994, 26, 696-701.

5860 Organometallics, Vol. 24, No. 24, 2005
Thomas and Peters
Figure 2. Displacement ellipsoid representations (50%) of two different views of (a) [[Ph2B(pz)2]Pt(Me)2][NBu4] (4), (b)
[[(4- BPh3)bpy]Pt(Me)2][NBu4] (5), and (c) [[Ph2BP2]Pt(Me)2][ASN] (6)3a,c displaying their geometries and Pt-B interatomic
distances. The NBu4 and ASN cations and hydrogen atoms have been omitted for clarity.
Table 1. Relevant NMR and Structural Data for Complexes 4, 5, and 6
complex
2JPt-H (Hz)
Pt-B (Å)
Pt-C (Å)
2.040c
C-Pt-C (deg)
P-Pt-P or N-Pt-N (deg)
[[Ph2B(pz)2]Pt(Me)2][NBu4] (4)
[[(4-BPh3)bpy]Pt(Me)2][NBu4] (5)
[[Ph2BP2]Pt(Me)2][ASN] (6)b
83a
3.460
6.570
4.117
89.30 (1)
89.52(13)
86.6(1)
89.73(9)
77.96(10)
90.64(2)
85, 86a
68a
2.044(3), 2.036(3)
2.133c
a NMR measurements were collected in acetone-d6 on a 300 MHz instrument. b Previously reported. c Average of both bond distances.
Scheme 1
square planar geometry but exhibit notable differences
due to geometric constraints imposed by their respective
donor ligands. Both N-donor complexes 4 and 5 have
C-Pt-C angles near 90°, while 6 has a slightly con-
tracted C-Pt-C angle (86.6°). A more significant dif-
ference is observed in the ligand bite angles. While both
complexes 4 and 6 have ligand bite angles near 90°
(90.64° and 89.73°, respectively), the rigid bipyridine
ligand leads to a much smaller N-Pt-N angle (77.96°)
in complex 5.
Another significant difference in ligand geometry is
apparent upon looking into an edge of the square plane
of each respective complex. While the [(4-BPh3)bpy]
ligand is rigidly planar, the [Ph2B(pz)2] ligand is canted
out of the square plane and the pyrazole rings eclipse
one another. The [Ph2BP2] ligand, on the other hand,
has more flexible methylene connectors that allow it to
maintain a staggered conformation that minimizes
steric interactions. These differences in ligand geometry
lead to variations in the distance between the Pt center
and the negatively charged borate moiety. Complex 4
exhibits a Pt-B distance appreciably shorter than in 6
(3.460 Å compared to 4.117 Å), while complex 5 has a
much longer Pt-B interatomic distance (6.570 Å).
A comparison of the average Pt-C bond lengths
observed in these complexes is indicative of the relative
trans influence of the borato ligands. Due to the strongly
trans influencing nature of its phosphine donors, com-
plex 6 exhibits an average Pt-C bond length signifi-
cantly longer than either complex 4 or 5 (2.133 Å,
compared to 2.040 (4) and 2.044/2.036 Å (5)). The NMR
Mg difficult; however, salt metathesis with NBu4Br in
a 1:1 mixture of CH2Cl2 and H2O generated a more
useful reagent, 2, in moderate overall yield (35%). The
dimethyl platinum precursors [[Ph2B(pz)2]Pt(Me)2]-
[NBu4] (4) and [[(4-BPh3)bpy]Pt(Me)2][NBu4] (5) were
prepared in good yield (76% and >95%, respectively) by
displacement of dimethyl sulfide from [(Me)2Pt(µ-
SMe2)]2 in THF solution. Substitution reactions with
(COD)PtMe2 (COD ) cyclooctadiene) were ineffective.
Structural and Spectroscopic Characterization
Data. Single crystals of 4 and 5 suitable for X-ray
diffraction were grown by vapor diffusion of petroleum
ether into a concentrated THF solution.16 The resulting
structures (Figure 2) are to be compared with the
structure previously reported for the bis(phosphino)-
borate dimethyl complex [[Ph2BP2]Pt(Me)2][ASN] (6)
(ASN ) 5-azonia-spiro[4.4]nonane.3a,c Relevant NMR
data, interatomic distances, and bond angles are pre-
sented in Table 1. All three complexes adopt a typical
(16) See Table 3 and the Supporting Information for crystallographic
details.

Zwitterionic Pt(II) Bis(pyrazolyl)borate Complexes
Organometallics, Vol. 24, No. 24, 2005 5861
Table 2. Infrared Carbonyl Frequencies for
Platinum Methyl Carbonyl Complexes
a
complex
νCO (cm-1
)
[Ph2B(pz)2]Pt(Me)(CO) (8)
[(4-BPh3)bpy]Pt(Me)(CO) (11)
[(bpy)Pt(Me)(CO)][BPh4] (12)
[Ph2BP2]Pt(Me)(CO)b
2078
2098
2107
2094
2118
[[Ph2SiP2]Pt(Me)(CO)][B(C6F5)4]b
a KBr cell in CH2Cl2. b Previously reported.3c,d,10b
Scheme 2
Figure 3. Optical absorption spectra of (A) 5 (solid line)
and (B) (bpy)Pt(Me)2 (dashed line) in acetonitrile solution
at 298 K.
coupling constants are consistent with this description.
2
For example, JPt-H for 6 is much lower than that for
Similarly, protonation of 5 with [HNEt3][BPh4] in THF
followed by addition of excess carbon monoxide led to
the formation of both isomers of [(4-BPh3)bpy]Pt(Me)-
(CO) (11) in an identical 2.8:1 ratio.
either 4 or 5 (65 Hz, compared to 83 and 85/86 Hz).
Evident from the NMR data and the observed Pt-C
bond lengths is that the [(4-BPh3)bpy] ligand in 5 and
the [Ph2B(pz)2] ligand in 4 exert comparable trans
influences. In addition, neutral (bpy)Pt(Me)2 has an
Considering Electronic Factors Using Methyl
Carbonyl Derivatives. To probe the electronic differ-
ences between ligands 1, 2, and 3, we have synthesized
several neutral platinum methyl carbonyl complexes.
The relative energies of the CO vibrations in these
neutral complexes are effective indicators of the elec-
tronic environment around the platinum center. The
relevant carbonyl stretching frequency data are reported
in Table 2. Bis(pyrazolyl)borate complex 8 possesses a
CO stretching frequency 16 cm-1 lower than that of the
[Ph2BP2]Pt(Me)(CO) complex,3c,d indicating that, for the
present square planar platinum system, the bidentate
pyrazolyl ligand acts as a better electron donor than the
bidentate phosphine. This result is surprising and
contrasts other data from our group clearly suggesting
that, in general, (phosphino)borate ligands are stronger
field donors than (pyrazolyl)borates.3c,17 The [(4-BPh3)-
bpy] complex 11 possesses the highest CO stretching
frequency (2098 cm-1), suggesting that the bipyridyl
ligand is the poorest donor of the three monoanionic
ligands. This trend can be correlated to the Pt-B
interatomic distances established for complexes 4-6 via
X-ray diffraction (Table 1). The complex in which the
borate is farthest removed from the platinum center (5,
6.570 Å) also corresponds to the methyl carbonyl
complex with the highest CO stretching frequency (11).
Complex 4 has the shortest Pt-B distance (3.460 Å),
and its methyl carbonyl complex (8) exhibits the lowest
CO stretching frequency.
2
average Pt-C bond length and JPt-H nearly identical
to 5, indicating that the borate has a negligible effect
on the overall trans influence of the bipyridylborate
ligand.
Although the [Ph2BP2] and [Ph2B(pz)2] complexes 4
and 6 are colorless, the [(4-BPh3)bpy] complex 5 is
intensely colored. This characteristic red-orange color
can be attributed to a metal to ligand charge transfer
2
(MLCT) {Pt dz to ligand π*} transition, as observed for
similar bipyridine complexes.10 Interestingly, the ab-
sorption maximum (λmax) for 5 is blue shifted to 385 nm
from the λmax observed for the neutral (bpy)Pt(Me)2 at
456 nm (Figure 3). This large blue shift is likely a
qualitative measure of the degree of destabilization of
the bipyridyl-centered LUMO upon incorporation of the
anionic borate unit.
Protonolysis of Monoanionic Platinum Dimeth-
yl Complexes. As has been reported previously, pro-
tonation of 6 with an ammonium salt (e.g., [HNR3]-
[BPh4]) in the presence of an L donor (L ) THF, CO,
P(C6F5)3, etc.) leads to clean formation of neutral [Ph2-
BP2]Pt(Me)(L) complexes.3a,c Likewise, it is found that
protonation of 4 with [HNiPr2Et][BPh4] in THF in the
presence of excess L cleanly generates several [Ph2B-
(pz)2]Pt(Me)(L) complexes (see Experimental Section;
L ) NCCH3, 7; CO, 8; P(C6F5)3, 9).
In the case of complex 5, protonolysis by [HNEt3]-
[BPh4] in acetonitrile solution led to formation of the
two possible isomers of [(4-BPh3)bpy]Pt(Me)(NCCH3)
(10) in a 2.8:1 ratio (Scheme 2). The major isomer
formed in this reaction was determined to be that in
which acetonitrile occupies the site cis to the borate-
substituted pyridyl ring. This was established by NMR
spectroscopy using a two-dimensional NOESY experi-
ment. An identical ratio of products is observed when
the reaction is performed at both high and low temper-
atures (-78 to 60 °C). The formation of appreciable
amounts of both isomers in this reaction suggests that
the trans effect of the pyridyl donor featuring a p-borate
unit is quite similar to the unsubstituted donor ring.
In addition to comparing the carbonyl data among the
neutral methyl carbonyl complexes, comparisons can be
made between the neutral complexes and structurally
analogous cationic complexes lacking a borate moiety.
It is important to note, however, that the absolute
difference in CO stretching frequency, at least when
comparing formally neutral complexes with formally
cationic complexes, is strongly influenced by electro-
static factors.18 The difference in CO stretching fre-
quency (∆νCO) between the neutral complex [Ph2BP2]-
(17) Jenkins, D. M.; DiBilio, A. J.; Allen, M. J.; Betley, T. A.; Peters,
J. C. J. Am. Chem. Soc. 2002, 124, 15336-15350.

5862 Organometallics, Vol. 24, No. 24, 2005
Thomas and Peters
Scheme 3
Pt(Me)(CO) and the cationic complex [[Ph2SiP2]Pt-
(Me)(CO)][B(C6F5)4] is reported to be 24 cm-1, confirm-
ing that the [Ph2BP2] ligand is more electron-releasing
than its neutral silane analogue.3c Although no data
have been reported for a cationic analogue of 8, the
infrared data for 11 can be compared with the carbonyl
stretch of 2107 cm-1 observed for the cationic complex
[(bpy)Pt(Me)(CO)][BPh4] (12). On the basis of the ∆νCO
of 9 cm-1, it can be concluded that the borate unit does
affect the electronic environment of the platinum center,
but to a much lesser extent than the borate of [Ph2BP2].
The aryl ring of the bipyridyl ligand serves as a much
better insulator than the methylene linker of [Ph2BP2].
Reactivity of Platinum Derivatives with Aro-
matic Substrates. Platinum complexes supported by
ligands 1, 2, and 3 display varied solution chemistry in
benzene. For example, we have previously reported that
[Ph2BP2]Pt(Me)(L) species are readily converted to their
corresponding [Ph2BP2]Pt(C6D5)(L) derivatives when
gently heated in benzene-d6 solution (where L ) THF,
P(C6F5)3).3c For comparison we attempted to isolate the
complex [Ph2B(pz)2]Pt(Me)(THF) but found it too reac-
tive (vide infra). The complex [Ph2B(pz)2]Pt(Me)(P(C6F5)3)
(9) is conveniently accessible. Choice of the P(C6F5)3
ligand is based on the presupposition that it provides a
potentially labile donor ligand due to its high steric bulk
and that it should feature relatively inert aryl rings.
When 9 was subjected to the same reaction conditions
as [Ph2BP2]Pt(Me)(P(C6F5)3) (80 °C, 24 h, C6D6), no
reaction was observed, whereas we have previously ob-
served that [Ph2BP2]Pt(Me)(P(C6F5)3) proceeds cleanly
to the phenyl product [Ph2BP2]Pt(C6D5)(P(C6F5)3).3c The
increased reactivity of [Ph2BP2]Pt(Me)(P(C6F5)3) might
be attributable to the lability of the P(C6F5)3 ligand
because of a greater trans effect of the [Ph2BP2] ligand,
though equally likely is that steric interactions between
the [Ph2BP2] ligand and the sterically bulky P(C6F5)3
donor serve to more greatly labilize the latter than in
the case of the bis(pyrazolyl)borate system.
When a stronger and more soluble acid is used, such
as [H(OEt2)2][BAr4] (Ar ) C6H3(CF3)2), the reaction
proceeds similarly but is more facile. The C-H activa-
1
tion process can be observed by H NMR in toluene-d8
at temperatures as low as -20 °C using the mild acid
[HNiPr2Et][BPh4]. The reaction was monitored by the
production of methane and the disappearance of starting
material; however, due to the formation of multiple
toluene activation products, the kinetics of this reaction
could not be followed closely. Addition of substoichio-
metric amounts of [HNiPr2Et][BPh4] or [H(OEt2)2][BAr4]
(0.1 equiv) leads to much slower consumption of the
starting precursor 4 (48 h), but nonetheless generates
13 quantitatively. This observation implies that acid
catalyzes the double C-H activation process.
The above observations are consistent with several
possible reaction mechanisms. Perhaps the simplest and
most reasonable scenario, at least based upon literature
precedent, concerns an associative oxidative addition/
reductive elimination cycle (Scheme 4).6,9a The first
likely step of such a mechanism (a) is protonation at
the metal center to form a six-coordinate platinum(IV)
species (with the other axial site presumably occupied
by a solvent molecule).20 This is followed by reductive
elimination of methane and coordination of benzene to
form an η2-benzene adduct (b). The benzene molecule
is then oxidatively added to form another platinum(IV)
hydride (c), from which another molecule of methane is
reductively eliminated (d). Oxidative addition of another
benzene molecule (e) would then lead to a platinum-
(IV) hydride species from which the [HNR3][BPh4] salt
could be regenerated (f), allowing the reaction to proceed
via addition of catalytic acid. A related cycle to consider
involves initial protonation and dissociation of one of
the ligand pyrazole rings to open a metal coordination
site, allowing benzene to coordinate. Scenarios related
to this have been previously suggested for Tp platinum-
(IV) complexes during acid-assisted reductive elimina-
tion processes.6
Another interesting difference in reactivity between
complexes 4-6 is observed upon attempts to protolyti-
cally cleave or abstract a methyl ligand by B(C6F5)3 in
benzene solution. Thus, protonation of 4 with 1 equiv
of [HNiPr2Et][BPh4] in benzene solution leads to the
rapid C-H activation of 2 equiv of benzene, leading to
the formation of a single product, [[Ph2B(pz)2]Pt(Ph)2]-
[NBu4] (13), with concomitant loss of 2 equiv of methane
(Scheme 3).19
An interesting aspect of this benzene activation
process is that the reaction proceeds rapidly in the
presence of a labile two-electron donor such as tetrahy-
drofuran, but is quenched upon addition of a modestly
stronger donor such as acetonitrile. Thus, protonation
of 4 in benzene, followed by immediate addition of
acetonitrile, leads to the formation of [Ph2B(pz)2]Pt(Ph)-
(NCCH3) (14) in high yield. Binding of acetonitrile to
the platinum center apparently prohibits formation of
the much more weakly coordinating η2-benzene ligand
(Scheme 4d).9a Completion of the double C-H activation
process in the presence of THF implies that benzene can
(18) (a) Goldman, A. S.; Krogh-Jespersen, K. J. Am. Chem. Soc.
1996, 118, 12159-12166. (b) Caulton, K. G.; Fenske, R. F. Inorg. Chem.
1968, 7, 1273-1284. (c) Hush, N. S.; Williams, M. I. J. Mol. Spectrosc.
1974, 50, 349-368.
(19) See Table 3 and the Supporting Information for crystallographic
details.
(20) Wik, B. J.; Lersch, M.; Tilset, M. J. Am. Chem. Soc. 2002, 124,
12116-12117.

Zwitterionic Pt(II) Bis(pyrazolyl)borate Complexes
Organometallics, Vol. 24, No. 24, 2005 5863
Scheme 4
compete with THF, to some extent, for the platinum
binding site. This is also true of neutral [Ph2BP2]PtMe-
(THF) complexes.3a,c
isotopomers of methane (including CH4) are observed
in C6D6. It is difficult to exclude that the proton source
for generating CH4 in this reaction is adventitious
water, similar to the result suggested by Goldberg.6 As
for the reaction with [HNR3][BPh4], the ratio of deu-
terium-containing isotopomers of methane to CH4 is
greater at -64 °C than at room temperature. One can
envision mechanisms similar to those suggested for the
protonation route with this Lewis acid, with the excep-
tion that the first step in this case is methide abstraction
rather than protonation (Scheme 5).
An estimate of the overall kinetic isotope effect for
this reaction was obtained by performing the reaction
with 1 equiv of [HNR3][BPh4] in a 1:1 C6H6/C6D6
mixture. The resulting product was analyzed by 1H
NMR, and it was determined that 51% of the platinum
phenyl groups in 13 were deuterated. This indicates that
there is a negligible overall kinetic isotope effect
(kH/kD ≈ 1.0). Since there are likely multiple equilibria
involved, the only conclusion that can be drawn from
these data is that benzene C-H bond breaking is not
significantly rate contributing.24 We suspect that the
rate-determining step is initial protonation based upon
the acid concentration dependence of the overall reac-
tion profile (i.e., the reaction slows when substoichio-
metric amounts of acid are added).
In contrast to complex 4, bis(phosphino)borate com-
plex 6 shows very different reactivity under both pro-
tonation and methide abstraction conditions in benzene.
When 6 is exposed to either B(C6F5)3 or [HNiPr2Et]-
[BPh4] in benzene-d6 at room temperature, the reaction
is slower than that of 4 (∼24 h) and a complex mixture
of products is formed. In addition, only CH4 and CH3D
are observed under these conditions, indicating there
is a smaller barrier to methane loss relative to the bis-
(pyrazolyl)borate complex. This difference can be at-
tributed to the strong trans influence of the phosphine
donors in 6.
When the protonation reaction is monitored in ben-
zene-d6, CH4, CH3D, CH2D2, and CHD3 are all observed
by 1H NMR. Even when a deuterated acid such as
[DNiPr2Et][BPh4] is used, all of the mixed H/D isoto-
pomers of methane, including CH4, are observed. Since
there is only 1 equiv of H+ in the reaction mixture, 1
equiv each of CH4 (where the acid is the proton source)
and CH3D (where benzene-d6 is the proton source)
might be expected. Observation of isotopic enrichment
of the methane is indicative of the formation of an
intermediate methane adduct that can be reversibly
activated prior to dissociation.5b,21 It is interesting to
note that at -20 °C the ratio of deuterium-containing
isotopomers of methane relative to CH4 is greater,
hinting that the relative rate of methane loss from the
platinum methane adduct might be slowed considerably
compared to the rate of H/D exchange at low tempera-
ture.
The observation that substoichiometric amounts of
acid catalyze C-H activation is consistent with previous
reports in which a catalytic amount of B(C6F5)3 pro-
motes C-H activation of solvent.22 This extremely
electrophilic Lewis acid has proven useful in abstracting
a methide anion in a variety of other cases.23 When
either one or less than one equivalent of B(C6F5)3 is
added to 4, the major product obtained is, indeed, the
double benzene activation product 13. The reaction rate
is much faster than that of the Brønsted acid-assisted
reaction. Such a rapid reaction at room temperature
makes this reaction pathway very promising; even more
encouraging is that the reaction proceeds with B(C6F5)3
at temperatures as low as -64 °C in toluene-d8. Much
like the acid-assisted case, all deuterium-containing
(21) Johannson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739-
740.
(22) Reinhartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L.
Organometallics 2001, 20, 1709-1712.
Complex 5 also shows limited reactivity with respect
to C-H activation upon in situ protonation or methide
(23) (a) Hill, G. S.; Manojlovic-Muir, L.; Muir, K. W.; Puddephatt,
R. J. Organometallics 1997, 16, 525-540. (b) Hill, G. S.; Rendina, L.
M.; Puddephatt. R. J. J. Chem. Soc., Dalton Trans. 1996, 1809.
(24) Jones, W. D.; Acc. Chem. Res. 2003, 36, 140-146.

5864 Organometallics, Vol. 24, No. 24, 2005
Thomas and Peters
Scheme 5
Scheme 6
abstraction in benzene-d6. Under both sets of reaction
conditions, the reaction proceeds much more slowly than
the [Ph2B(pz)2] case. An ill-defined mixture of products
forms, but no evidence for C-H activation is observed.
CH4 is the only methane byproduct that can be detected
under these conditions.
prepared and compared to previously reported bis-
(phosphino)borate complexes in an effort to better
understand the extent of charge delocalization in struc-
turally different borato ligands. NMR and structural
data for the anionic dimethyl complexes 4, 5, and 6
indicate that the phosphine donors of the [Ph2BP2]
ligand exert a stronger trans influence than the N-donor
ligands; however, the [Ph2B(pz)2] ligand has been shown
through IR carbonyl stretching frequency data to be the
most electron-releasing of the three ligands. This may
be a result of the closer proximity of the borate unit to
the metal center in complex 4 in comparison to com-
plexes 5 and 6.
The structural and electronic differences between
these ligands appear to have a substantial effect on the
reactivity of their platinum complexes with respect to
C-H activation. While [Ph2BP2]Pt(Me)(L) complexes are
effective toward activation of aryl C-H bonds at el-
evated temperatures, analogous [Ph2B(pz)2] complexes
are completely unreactive under these conditions. [[Ph2B-
(pz)2]Pt(Me)2][NR4] complexes, however, are highly ac-
tive with respect to C-H activation of aryl C-H bonds
upon protonation or methide abstraction in situ, in the
absence of a donor ligand poison. These reactions are
facile at temperatures well below 0 °C. Moreover,
whereas coordination of a third pyrazolyl arm in the
previously reported {κ2-[Tp*]PtMe2}- system occurs
upon methide abstraction, thereby leading to {κ3-[Tp*]-
Pt(Me)(H)(R)} Pt(IV) products in the presence of alkane
substrate, for the present bis(pyrazolyl)borate system
only Pt(II) species are observed. Destabilization of the
Pt(IV) intermediate due to the lack of a third donor
chelate arm enables the double C-H activation process
to proceed efficiently. We have also observed that
structurally related [Ph2BP2] and [(4-BPh3)bpy] com-
plexes are protonated much more slowly under analo-
gous conditions, and these systems appear to lead to
very different (and ill-defined) product distributions.
Upon further investigation, we determined that [Ph2B-
(pz)2] platinum complexes also show reactivity in the
presence of acid and other aromatic substrates. Expo-
sure of complex 4 to [HNiPr2Et][BPh4] in toluene and
p-xylene gives rise to a mixture of products that includes
η1-bound benzylic species.9b,25 In contrast, when 4 is
stirred with [HNiPr2Et][BPh4] in mesitylene at room
temperature for 18 h, the major product isolated is
[Ph2B(pz)2]Pt(CH2C6H3(CH3)2)(pzH) (15) (Scheme 6).26
This product provides an interesting example of C-H
activation of an sp3-hybridized C-H bond position, but
the relatively low yield (∼50%) and the presence of a
coordinated pyrazole ring establish that the formation
of 15 is accompanied by undesired borate ligand deg-
radation. The benzylic C-H activation process also
occurs when the reaction is carried out in the presence
of a donor ligand such as acetonitrile, THF, or pyridine,
and an analogous product distribution is observed under
such conditions. C-H activation was not observed with
pentane, methylcyclohexane, or other nonaromatic hy-
drocarbons even at elevated temperatures, indicating
that sp3-hybridized C-H bond activation is operative
only for more reactive benzylic C-H bonds in this
system.
Concluding Remarks. Platinum bis(pyrazolyl)bo-
rate and 2,2′-bipyridylborate complexes have been
(25) (a) Heyduk, A. F.; Driver, T. G.; Labinger, J. A.; Bercaw, J. E.
J. Am. Chem. Soc. 2004, 126 (46), 15034-15035. (b) Heyduk, A. F.;
Zhong, A. H.; Labinger, J. A.; Bercaw, J. E. Activation and Function-
alization of C-H Bonds; Goldberg, K., Goldman, A., Eds.; ACS
Symposium Series No. 885; American Chemical Society: Washington,
DC, 2004; pp 250-263.
(26) See Table 3 and the Supporting Information for crystallographic
details.

Zwitterionic Pt(II) Bis(pyrazolyl)borate Complexes
Organometallics, Vol. 24, No. 24, 2005 5865
Table 3. X-ray Diffraction Experimental Details for [(Ph2B(pz)2)Pt(Me)2][NBu4] (4),
[((4-BPh3)bpy)Pt(Me)2][NBu4] (5), [(Ph2B(pz)2)Pt(C6D5)2][NBu4] (13), and
(Ph2B(pz)2)Pt(pzH)(CH2C6H3(CH3)2) (15)
4
5
13
15
chemical formula
fw
C
36H58BN5Pt
C46H64BN3Pt
864.90
C46H62BN5Pt
890.91
C33H39BN4Pt
697.58
766.77
-177
T (°C)
-173
-177
-175
λ (Å)
0.71073
9.7813(6)
23.218(1)
15.7888(9)
90
0.71073
9.057(1)
11.888(3)
20.348(6)
87.71(1)
84.19(2)
70.316
0.71073
14.839(1)
17.029(1)
17.118(1)
90
103.087(1)
90
0.71073
8.2302(7)
14.205(1)
14.603(1)
67.300(1)
74.056(1)
82.565(1)
1513.9(2)
P1h
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
92.114(1)
90
3583.2(4)
P21/c
2052.2(8)
P1h
4213.0(6)
P21/c
space group
Z
4
2
4
2
Dcalcd (g/cm3)
1.421
1.400
1.824
1.530
µ (cm-1
)
3.947
3.453
3.368
4.662
R1, wR2a
0.0299, 0.0721
0.0427, 0.0724
0.0306, 0.0509
0.0306, 0.0713
(I > 2σ(I))
2
2
a R1 ) ∑||Fo| - |Fo||/∑|Fo|, wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2
.
per individual complex. The crystals were mounted on a glass
fiber with Paratone N oil. Structures were determined using
direct methods with standard Fourier techniques using the
Bruker AXS software package. Table 3 includes the X-ray
diffraction experimental details, while the full crystallographic
tables are included in the Supporting Information.
[Ph2B(pz)2][Na(pzH)2]. A mixture of solid NaBPh4 (8.908
g, 26.03 mmol) and solid pyrazole (22.731 g, 333.9 mmol) was
heated to a melt and stirred in a 50 mL flask fitted with a
Dean-Stark trap and condenser to collect benzene as it
distilled from the reaction mixture. The reaction was heated
at 80-100 °C until a nearly stoichiometric amount of benzene
(4.22 mL, 1.81 equiv) was collected (3 h). The reaction was
extracted with boiling hexanes (4 × 200 mL). The solids were
then dried under reduced pressure to yield a white powder
(8.0090 g, 67.1%). Note: This is a variation of the literature
method,14 which is reported to provide [Ph2B(pz)2][Na]. The
literature method replaces the extraction with a distillation to
remove the excess pyrazole.
Experimental Section
General Considerations. All syntheses reported were
carried out using standard glovebox and Schlenk techniques
in the absence of water and dioxygen, unless otherwise noted.
Acetonitrile, benzene, dichloromethane, diethyl ether, petro-
leum ether, tetrahydrofuran, and toluene were degassed and
dried by sparging with N2 gas followed by passage through
an activated alumina column. Pentane, mesitylene, and p-
xylene were deoxygenated via sparging with N2, dried over
CaH, and distilled prior to use. Ethanol was deoxygenated via
sparging with N2, dried over NaOEt, and distilled prior to use.
All solvents were stored over 3 Å molecular sieves. Deuterated
benzene, chloroform, acetonitrile, acetone, and toluene were
purchased from Cambridge Isotope Laboratories, Inc., de-
gassed via repeated freeze-pump-thaw cycles, and dried over
3 Å molecular sieves. Nonhalogenated solvents were frequently
tested using a standard solution of sodium benzophenone ketyl
in tetrahydrofuran to confirm the absence of oxygen and
moisture. [Me2Pt(µ-SMe2)]2,27 [HNiPr2Et][BPh4],3 [HNEt3]-
[BPh4],28 P(C6F5)3,29 [H(OEt2)2][B(C6H3(CF3)2)4],30 3,3a 6,3a,c,d
(bpy)Pt(Me)2,31 and 4-iodo-2,2′-bipyridine15 were prepared us-
ing literature methods. [DNiPr2Et][BPh4] was prepared by
acidifying an aqueous solution of NiPr2Et and NaBPh4 with
aqueous DCl. B(C6F5)3 was recrystallized from pentane at
-35 °C prior to use. All other chemicals were purchased from
Aldrich, Strem, Alfa Aesar, or Lancaster and used without
further purification. NMR spectra were recorded at ambient
temperature, unless otherwise stated, on Varian Mercury 300
MHz, Varian Inova 500 MHz, and JEOL 400 MHz spectrom-
eters. 1H and 13C NMR chemical shifts were referenced to
residual solvent. 31P NMR chemical shifts were referenced to
85% H3PO4. IR spectra were recorded on a Bio-Rad Excalibur
FTS 3000 spectrometer controlled by Win-IR Pro software.
Elemental analyses were performed by Desert Analytics,
Tuscon, AZ. X-ray diffraction experiments were carried out by
the Beckman Institute Crystallographic Facility on a Bruker
Smart 1000 CCD diffractometer.
[Ph2B(pz)2][NBu4] (1). Solid [Ph2B(pz)2][Na(pzH)2] (3.7573
g, 8.1982 mmol) was dissolved in dichloromethane (80 mL)
along with NBu4Br (2.6733 g, 8.2924 mmol). The hazy solution
was stirred for 10 min and filtered over Celite on a sintered
glass frit. The filtrate was concentrated by rotary evaporation.
Hexanes (80 mL) was added and stirred vigorously, forming
white solids. The solids were collected by filtration and washed
with toluene (3 × 20 mL) and hexanes (2 × 20 mL). The
resulting solids were suspended in toluene (20 mL) and stirred
for 5 min, then collected by filtration and washed with hexanes
(2 × 20 mL). The resulting white solids were dried under
reduced pressure (4.2889 g, 96.6%). 1H NMR (300 MHz
3
acetone-d6): δ 7.40 (d, 2H, JH-H ) 1.8 Hz, pz-3H), 7.21 (m,
4H, o-Ph), 7.15 (d, 2H, 3JH-H ) 2.4 Hz, pz-5H), 6.97-7.05 (m,
3
6H, m,p-Ph), 5.95 (dd, 2H, JH-H ) 1.8, 2.1 Hz, pz-4H), 3.70
(m, 8H, NBu4), 1.77 (m, 8H, NBu4), 1.40 (m, 8H, NBu4), 0.97
3
(t, 12H, JH-H ) 7.8 Hz, NBu4).
[(4-BPh3)bpy][NBu4] (2). Solid 4-iodo-2,2′-bipyridine (1.3330
g, 4.72 mmol) was dissolved in Et2O (50 mL) and cooled to
-78 °C with stirring (upon cooling, the mixture becomes
X-ray Crystallography Procedures. X-ray quality crys-
tals were grown as indicated in the experimental procedures
i
heterogeneous). To this suspension was added PrMgCl (2.36
(27) Scott, J. D.; Puddephatt, R. J. Organometallics 1983, 2, 1643-
1648.
(28) Rodima, T.; Kaljurand, I.; Pihl, A.; Maeemets, V.; Leito, I.;
Koppel, I. A. J. Org. Chem. 2002, 67 (6), 1873-1881.
(29) Kemmitt, R. D. W.; Nichols, D. I.; Peacock, R. D. J. Am. Chem.
Soc. A 1968, 2149-2152.
(30) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920.
(31) Monaghan, P. K.; Puddephatt, R. J. Organometallics 1984, 3,
444-449.
mL, 2.0 M in Et2O, 4.72 mmol) dropwise over 10 min. The
suspension became deep red upon addition. After stirring for
1 h, BPh3 (1.1413 g, 4.72 mmol) in THF (10 mL) was added
and the resulting solution was allowed to warm to room
temperature over 3 h. The resulting red solids were collected
on a sintered glass frit and washed with Et2O (3 × 10 mL).
The solids were taken up in CH2Cl2 (20 mL), and solid NBu4-
Br (1.5216 g, 4.72 mmol) was added. 40 mL of H2O was added

5866 Organometallics, Vol. 24, No. 24, 2005
Thomas and Peters
and the mixture was stirred vigorously for 30 min. The CH2-
Cl2 layer was then collected and washed with additional H2O
(2 × 20 mL). The combined CH2Cl2 layers were collected, dried
with Na2SO4, and evaporated in vacuo. The remaining solids
were recrystallized via vapor diffusion of petroleum ether into
THF to yield white needles (0.8187 g, 1.28 mmol, 27%). 1H
NMR (300 MHz, acetone-d6): δ 8.65 (br m, 1H, 3-bpy), 8.41-
1.09 (s, 3H, 2JPt-H ) 77.2 Hz, Pt-Me), 0.24 (s, 3H, 4JPt-H ) 6.9
Hz, NCCH3). 13C NMR (75.409 MHz, benzene-d6): δ 140.8,
139.4, 138.5, 137.2, 135.1, 127.9, 127.1, 126.0, 104.9, 104.6,
30.7 (NCCH3), 1.56 (NCCH3), -18.8 (Pt-Me). ES-MS (m/z,
negative): 549 (M - H+). Anal. Calcd for C21H22BN5Pt: C,
45.83; H, 4.03; N, 12.73. Found: C, 46.64; H, 3.99; N, 12.02.
(Ph2B(pz)2)Pt(Me)(CO) (8). Solid 4 (0.0480 g, 0.0625
mmol) was dissolved in tetrahydrofuran (2 mL) under N2 in a
25 mL Schlenk flask equipped with a rubber septum. CO was
bubbled through the solution using a long needle for 2 min.
To this was added a solution of [HNiPr2Et][BPh4] (0.278 g,
0.0619 mmol) in tetrahydrofuran (3 mL) via syringe. The
solution immediately turned yellow upon addition of the
ammonium salt, but slowly faded to a cloudy white slurry over
a period of 5 min. Solvent was removed in vacuo. The resulting
solids were extracted with benzene (3 × 2 mL) and filtered
through Celite. Solvent was removed from the filtrate to yield
white solids (85%). 1H NMR (300 MHz benzene-d6): δ 7.44
(m, 2H, pz-3H), 7.33 (m, 2H, pz-5H), 7.24 (m, 4H, o-Ph), 7.23
3
8.45 (m, 2H, 6,3′-bpy), 8.19 (d, 1H, JH-H ) 5.1 Hz, 6′-bpy),
3
7.73 (ddd, 1H, JH-H ) 8.4, 7.2, 2.1 Hz, 4′-bpy), 7.35 (m, 7H,
3
o-Ph + 5-bpy), 7.18 (m, 1H, 4′-bpy), 6.96 (t, 6H, JH-H ) 7.5
3
Hz, m-Ph), 6.81 (m, 3H, JH-H ) 6.9 Hz, p-Ph), 3.44 (m, 8H,
NBu4), 1.82 (m, 8H, NBu4), 1.42 (m, 8H, NBu4), 0.98 (t, 12H,
3JH-H ) 7.2 Hz, NBu4). 13C NMR (75.409 MHz, acetone-d6): δ
160.5, 149.9, 137.5, 137.4, 133.8, 131.9, 130.3, 126.8, 123.4,
123.2, 121.9, 59.8 (NBu4), 24.9 (NBu4), 20.8 (NBu4), 14.4
(NBu4). Anal. Calcd for C44H58BN3: C, 82.60; H, 9.14; N, 6.57.
Found: C, 82.04; H, 9.24; N, 6.81.
[(Ph2B(pz)2)Pt(Me)2][NBu4] (4). Solid [Me2Pt(µ-SMe2)]2
(0.3775 g, 1.215 mmol) and solid 1 (0.6573 g, 1.213 mmol) were
suspended in tetrahydrofuran (10 mL). The resulting cloudy
white mixture was stirred for 3 h, then dried in vacuo. The
resulting solids were collected on a sintered glass frit and
washed with petroleum ether (3 × 5 mL) and benzene (3 × 5
mL). The off-white solids were dried further in vacuo to yield
analytically pure 4 (0.7091 g, 76.1%). Crystals for X-ray
diffraction were grown via vapor diffusion of petroleum ether
3
(m, 4H, m-Ph), 7.07 (m, 2H, p-Ph), 5.87 (m, 1H, JH-H ) 2.1
3
Hz, pz-4H), 5.77 (t, 1H, JH-H ) 1.5 Hz, pz-4H), 0.79 (s, 3H,
2JPt-H ) 70.2 Hz, Pt-Me). IR (cm-1): 2087. Anal. Calcd for
C20H19BN4OPt: C, 44.71; H, 3.56; N, 10.43. Found: C, 46.59;
H, 3.58; N, 11.02. Samples of this species repeatedly analyzed
high in carbon content.
(Ph2B(pz)2)Pt(Me)(P(C6F5)3) (9). Solid 4 (0.0347 g, 0.0452
mmol), solid [HNiPr2Et][BPh4] (0.0271 g, 0.0603 mmol), and
solid P(C6F5)3 (0.0449 g, 0.0844 mmol) were suspended in
tetrahydrofuran (2 mL) and stirred for 30 min. The solvent
was removed from the resulting mixture in vacuo. The
remaining solids were extracted with benzene/petroleum ether
(10:1) and filtered through Celite. These extracts were dried
in vacuo, and the resulting off-white solids were extracted into
petroleum ether and recrystallized at -35 °C. The resulting
white solids were washed with cold petroleum ether (1 mL) to
1
into tetrahydrofuran. H NMR (300 MHz acetone-d6): δ 7.76
(m, 2H, 3JPt-H ) 5.4 Hz, pz-3H), 7.12 (dd, 2H, 3JH-H ) 2.3, 0.9
3
Hz, p-Ph), 7.08 (d, 2H, JH-H ) 1.2 Hz, pz-5H), 7.06 (m, 4H,
3
o-Ph), 6.83 (dd, 4H, JH-H ) 6.9, 3.0 Hz, m-Ph), 6.05 (t, 2H,
3JH-H ) 1.8 Hz, pz-4H), 3.45 (m, 8H, NBu4), 1.80 (m, 8H,
NBu4), 1.40 (m, 8H, NBu4), 0.97 (t, 12H, 3JH-H ) 7.8 Hz, NBu4),
2
0.36 (s, 6H, JPt-H ) 83 Hz, Me). 13C NMR (75.409 MHz,
acetone-d6): δ 138.0, 135.6, 134.7, 126.9, 125.7, 103.0, 59.2 (s,
NBu4), 24.5 (s, NBu4), 20.3 (s, NBu4), 14.0 (s, NBu4), -18.9 (s,
Pt-Me). Anal. Calcd for C36H58BN5Pt: C, 56.39; H, 7.62; N,
9.13. Found: C, 56.68; H, 7.78; N, 9.28.
[((4-BPh3)bpy)Pt(Me)2][NBu4] (5). Solid [Me2Pt(µ-SMe2)]2
(0.0267 g, 0.0466 mmol) was dissolved in THF (3 mL). To this
stirring solution was added 2 (0.0596 g, 0.0933 mmol) in THF
(5 mL), and the mixture was allowed to stir for 1 h. The
resulting red solution was dried in vacuo and the remaining
solids were washed with Et2O (3 × 5 mL) to afford analytically
pure product as a red-orange powder (0.0804 g, 0.0930 mmol,
1
yield analytically pure product (42.4%). H NMR (300 MHz,
3
benzene-d6): δ 7.47 (d, 1H, JH-H ) 2.1 Hz, pz-3H), 7.42 (d,
2H, 3JH-H ) 2.1 Hz, pz-3H, pz-5H), 7.32 (m, 4H, o-Ph), 7.21-
7.27 (m, 6H, m,p-Ph), 6.50 (d, 1H, 3JH-H ) 1.8 Hz, pz-5H), 5.78
3
(m, 1H, pz-4H), 5.53 (t, 1H, JH-H ) 2.4 Hz, pz-4H), 0.36 (d,
3H, 2JPt-H ) 72 Hz, 3JP-H ) 6.0 Hz, Pt-Me). 31P NMR (121.368
1
MHz, benzene-d6): δ -36.21 (s, JPt-P ) 5800 Hz). 13C NMR
(75.409 MHz, benzene-d6): δ 150.0 (m, P(C6F5)3), 146.6 (m,
P(C6F5)3), 142.8 (m, P(C6F5)3), 140.1, 139.8, 139.3, 138.9, 137.5,
133.4, 127.1, 105.4, 104.8, -14.9 (Pt-Me). Anal. Calcd for
C37H19BF15N4PPt: C, 42.67; H, 1.84; N. 5.38. Found: C, 42.50;
H, 2.07; N, 5.06.
99%). 1H NMR (300 MHz, acetone-d6): δ 9.11 (d, 1H, 3JH-H
)
3
3
7.5 Hz, JPt-H ) 24 Hz, 6-bpy), 8.71 (d, 1H, JH-H ) 5.4 Hz,
3JPt-H ) 21 Hz, 6′-bpy), 8.24 (br s, 1H, 3-bpy), 8.13 (ddd, 1H,
3
3JH-H ) 9.6, 8.1, 0.3 Hz, 5′-bpy), 7.79 (d, 1H, JH-H ) 7.8 Hz,
((4-BPh3)bpy)Pt(Me)(NCCH3) (10). Solid 5 (0.0481 g,
0.0557 mmol) was stirred in THF with [HNEt3][BPh4] (0.0234
g, 0.0557 mmol). To this mixture was added 3 drops of
acetonitrile. After 1 h, the solvent was evaporated in vacuo.
The resulting solids were extracted into benzene (2 × 10 mL).
These extracts were dried in vacuo to yield both isomers in a
2.8:1 ratio (0.0286 g, 0.0440 mmol, 79%). 1H NMR (300 MHz,
acetone-d6): δ 8.91 (d, 1H, 3JH-H ) 8.7 Hz, 6-bpy), 8.41 (d, 1H,
3JH-H ) 5.4 Hz, 6′-bpy), 8.31 (br s, 1H, 3-bpy), 8.21 (ddd, 1H,
3′-bpy), 7.58 (br s, 1H, 5-bpy), 7.48 (m, 1H, 4′-bpy), 7.31 (br s,
3
6H, o-Ph), 7.01 (t, 6H, JH-H ) 5.4 Hz, m-Ph), 6.87 (t, 3H,
3JH-H ) 7.5 Hz, p-Ph), 3.41 (m, 8H, NBu4), 1.79 (m, 8H, NBu4),
1.39 (m, 8H, NBu4), 0.96 (t, 12H, 3JH-H ) 7.5 Hz, NBu4), 0.92
(3H, 2JPt-H ) 86 Hz, Pt-Me), 0.82 (3H, 2JPt-H ) 85 Hz, Pt-Me).
13C NMR (75.409 MHz, acetone-d6): δ 160.3, 159.7, 153.3,
147.3, 143.7, 137.6, 137.0, 136.0, 131.4, 127.1, 123.7, 123.2,
59.5 (NBu4), 24.8 (NBu4), 20.7 (NBu4), 14.4 (NBu4), -15.0 (Me),
-15.3 (Me). Anal. Calcd for C46H64BN3Pt: C, 63.88; H, 7.46;
N, 4.86. Found: C, 63.91; H, 7.80; N, 4.65.
3
3JH-H ) 8.4, 3.0, 1.2 Hz, 4′-bpy), 7.92 (d, 1H, JH-H ) 9.0 Hz,
3′-bpy), 7.66 (m, 2H, 5-bpy, 5′-bpy), 7.32 (m, 6H, o-Ph), 7.03
3
3
(t, 6H, JH-H ) 7.2 Hz, m-Ph), 6.90 (m, 3H, JH-H ) 7.2 Hz,
(Ph2B(pz)2)Pt(Me)(NCCH3) (7). Solid 4 (0.0595 g, 0.0775
mmol) and solid [HNiPr2Et][BPh4] (0.0343 g, 0.0764 mmol)
were combined in a mixture of tetrahydrofuran (2 mL) and
acetonitrile (3 drops). The resulting clear solution was stirred
for 2 h at room temperature and then dried in vacuo. The
remaining solids were extracted with benzene and filtered
through Celite to remove [NBu4][BPh4]. The filtrate was dried
in vacuo to yield analytically pure product as an off-white solid
4
p-Ph), 2.79 (major)/2.84 (minor) (s, 3H, NCCH3, JPt-H ) 25
2
Hz), 0.94 (major)/0.86 (minor) (s, 3H, Pt-Me, JPt-H ) 73 Hz).
13C NMR for major isomer (75.409 MHz, acetone-d6): δ 161.7,
160.5 (br), 156.4, 148.8, 145.8, 141.3, 136.9, 135.9, 132.1, 128.1,
127.5, 124.1, 123.5, 41.4, 4.5, -14.0 (Me). Anal. Calcd for
C31H28BN3Pt: C, 57.42; H, 4.35; N. 6.48. Found: C, 57.17; H,
4.13; N, 5.99.
(60%). 1H NMR (300 MHz benzene-d6): δ 7.77 (d, 1H, 3JH-H
)
((4-BPh3)bpy)Pt(Me)(CO) (11). Solid 5 (0.0356 g, 0.0412
mmol) was stirred in THF with [HNEt3][BPh4] (0.0173 g,
0.0412 mmol). This mixture was placed under a blanket of CO
and stirred for 1 h. The solvent was evaporated in vacuo, and
the resulting solids were extracted into benzene (2 × 10 mL).
3
3
2.1 Hz, JPt-H ) 25 Hz, pz-3′H), 7.59 (d, 1H, JH-H ) 2.4 Hz,
3
pz-3H), 7.49 (d, 1H, JH-H ) 2.1 Hz, pz-5′H), 7.38 (d, 1H,
3JH-H ) 2.7 Hz, pz-5H), 7.27 (m, 10H, Ph), 6.14 (t, 1H,
3JH-H ) 2.1 Hz, pz-4H), 5.88 (m, 1H, 3JH-H ) 2.1 Hz, pz-4′H),

Zwitterionic Pt(II) Bis(pyrazolyl)borate Complexes
Organometallics, Vol. 24, No. 24, 2005 5867
These extracts were dried in vacuo to yield both isomers in a
2.8:1 ratio (0.0227 g, 0.0357 mmol, 87%). 1H NMR (300 MHz,
CD2Cl2): δ 8.65 (d, 1H, 3JH-H ) 5.7 Hz, 3JPt-H ) 21 Hz, 6-bpy),
8.52 (br s, 1H, 3-bpy), 8.32 (d, 1H, 3JH-H ) 5.7 Hz, 3JPt-H ) 33
(Ph2B(pz)2)Pt(C6D5)(NCCH3) (14). Solid 4 (0.0366 g,
0.0477 mmol) and solid [HNiPr2Et][BPh4] (0.0223 g, 0.0496
mmol) were dissolved in benzene-d6 (2 mL). Three drops of
acetonitrile were added, and the mixture was stirred for 1 h.
The resulting solution was filtered through Celite, and the
filtrate was dried in vacuo. The resulting solids were extracted
into petroleum ether and dried in vacuo to yield spectroscopi-
cally pure product as an off-white solid (∼80%). 1H NMR (300
MHz, benzene-d6): δ 7.58 (d, 1H, 3JH-H ) 2.4 Hz, pz-3H), 7.45
(m, 2H, pz-3H, pz-5H), 7.28-7.36 (m, 5H, o-Ph, pz-5H), 7.18
3
Hz, 6′-bpy), 8.12 (ddd, 1H, JH-H ) 8.3, 8.3, 1.5 Hz 4′-bpy),
8.01 (d, 1H, 3JH-H ) 8.4 Hz, 3′-bpy), 7.56 (m, 1H, 5-bpy), 7.32
(m, 7H, o-Ph, 5′-bpy), 7.13 (t, 6H, 3JH-H ) 7.2 Hz, m-Ph), 7.00
3
(m, 3H, JH-H ) 7.2 Hz, p-Ph), (major)/(minor) 1.27/1.19 (s,
3H, Pt-Me, 2JPt-H ) 69 Hz). 13C NMR for major isomer (75.409
MHz, CD2Cl2): δ 192.0, 160.0 (br), 151.1, 143.1, 142.8, 141.5,
135.8, 135.4, 134.7, 131.6, 128.1, 127.1, 123.9, 123.7, -12.3
(Me). IR (CH2Cl2): 2098 cm-1. Anal. Calcd for C30H25BN2OPt:
C, 56.71; H, 3.97; N. 4.41. Found: C, 59.70; H, 4.02; N, 4.98.
Samples of this species repeatedly analyzed high in carbon
content.
3
3
(t, 4H, JH-H ) 7.2 Hz, m-Ph), 7.06 (t, 2H, JH-H ) 9.3 Hz,
3
p-Ph), 6.09 (t, 1H, JH-H ) 2.1 Hz, pz-4H), 5.63 (t, 1H,
4
3JH-H ) 2.2 Hz, pz-4H), -0.02 (s, 3H, JPt-H ) 7.2 Hz,
Pt-NCCH3). 13C NMR (75.409 MHz, benzene-d6): δ 144.2,
139.9, 138.5, 138.2, 137.7, 137.2, 135.0, 127.7, 127.3, 124.2,
104.8 (pz-4), 30.8 (NCCH3), 1.3 (NCCH3). Anal. Calcd for
C26H19D5BN5Pt: C, 50.58; H, 4.73; N, 11.34. Found: C, 50.72;
H, 4.16; N, 11.17.
[(bpy)Pt(Me)(CO)][BPh4] (12). Solid (bpy)Pt(Me)2 (0.0260
g, 0.0682 mmol) was stirred in THF, and CO was bubbled
through the solution for 20 min. To this was added a solution
of [HNEt3][BPh4] (0.0287 g, 0.0682 mmol) in THF. This
mixture was allowed to stir under a blanket of CO for 1 h.
The solvent was evaporated in vacuo, and the resulting solids
were washed with benzene (2 × 10 mL) and dried in vacuo to
yield the yellow product (∼80%). Spectroscopic data were
similar to those reported previously for [(bpy)Pt(Me)(CO)]+
cations.10b 1H NMR (300 MHz, acetone-d6): δ 9.07 (d, 1H,
Reaction of Complex 4 with [HNEt3][BPh4] in Toluene
and p-Xylene. Solid 4 (0.0657 g, 0.0885 mmol) was stirred in
toluene (or p-xylene) (10 mL) for 3 h with [HNiPrEt2][BPh4]
(0.0398 g, 0.0886 mmol). The resulting solution was filtered
through Celite, and the filtrate was then dried in vacuo.
Solution NMR data revealed the following diagnostic signals:
2
toluene: 1H NMR (300 MHz, benzene-d6): δ 3.24 (s, JPt-H
)
3
3JH-H ) 9.0 Hz, 6-bpy), 8.98 (d, 1H, JH-H ) 7.5 Hz, 6′-bpy),
99 Hz, benzylic activation), 2.36, 2.31, 2.24 (aryl activation
3
products, o, p, m, respectively); p-xylene: 1H NMR (300 MHz,
8.66 (d, 1H, JH-H ) 5.7 Hz, 3-bpy), 8.48 (m, 2H, 4′-bpy, 3′-
2
bpy), 8.40 (m, 1H, 4′-bpy), 7.91 (m, 1H, 5-bpy), 7.40 (m, 1H,
acetone-d6): δ 2.90 (s, JPt-H ) 104 Hz, benzylic activation).
5′-bpy), 7.33 (m, 8H, BPh4), 6.92 (t, 8H, 3JH-H ) 7.8 Hz, BPh4),
(Ph2B(pz)2)Pt(pzH)(CH2C6H3(CH3)2) (15). Solid 4 (0.0115
g, 0.0149 mmol) was stirred in mesitylene (2 mL) for 18 h with
[HNEt3][BPh4] (0.0066 g, 0.0153 mmol). Volatiles were re-
moved from the resulting solution in vacuo. The remaining
solids were extracted with benzene (3 × 1 mL) and filtered
through Celite. The filtrate was dried in vacuo to yield 15 as
a white solid (∼50%). Crystals of 15 suitable for X-ray
diffraction were obtained by vapor diffusion of petroleum ether
into a concentrated benzene solution. 1H NMR (300 MHz,
3
6.77 (t, 4H, JH-H ) 6.9 Hz, BPh4), 1.28 (s, 3H, Pt-Me,
2JPt-H ) 68 Hz). ES-MS (m/z): 394 [M]+. IR (CH2Cl2): 2107
cm-1
.
Generation of [(Ph2B(pz)2)Pt(C6D5)2][NBu4] (13). Solid
4 (0.0345 g, 0.0449 mmol) and solid [HNiPr2Et][BPh4] (0.0200
g, 0.0045 mmol) were stirred in benzene-d6 (2 mL) for 30 min.
The resulting reaction mixture was filtered through Celite.
Upon standing for 1 h, solids precipitated. These off-white
solids were collected and washed with petroleum ether (3 × 2
mL) and benzene (2 × 2 mL). The remaining solids were dried
further in vacuo to yield clean product (87% yield was detected
by NMR using a ferrocene standard; however, only 40% was
isolated). Crystals were grown for X-ray diffraction by dissolv-
ing product in benzene and layering with petroleum ether at
room temperature. 1H NMR (300 MHz, benzene-d6): δ 7.58 (d,
3
benzene-d6): δ 12.5 (br, 1H), 7.79 (d, 1H, JH-H ) 1.8 Hz, pz-
3H), 7.58 (d, 1H, 3JH-H ) 2.4 Hz, pz-3H), 7.49 (d, 3JH-H ) 2.1
Hz, 1H, pz-3H), 7.07-7.26 (m, 10H, BPh), 6.88 (m, 1H, Mes),
6.65 (m, 1H, pz-5H), 6.58 (m, 1H, pz-5H), 6.43 (m, 2H, Mes),
6.03 (m, 1H, pz-5H), 5.96 (t, 1H, 3JH-H ) 2.1 Hz, pz-4H), 5.87
3
(t, JH-H ) 2.1 Hz, 1H, pz-4H), 5.36 (m, 1H, pz-4H), 3.07 (s,
2H, CH2, 2JPt-H ) 104.9 Hz), 2.13 (s, 6H, CH3). XRD analysis
confirmed the identity of this degradation product. Further
characterization of this material was not pursued.
3
3
2H, JH-H ) 2.7 Hz, pz-3H), 7.19 (m, 4H, JH-H ) 6.6 Hz,
3
o-BPh), 7.40 (t, 4H, JH-H ) 7.2 Hz, m-BPh), 7.31 (m, 2H,
p-BPh), 7.28 (d, 2H, JH-H ) 1.2 Hz, pz-5H), 5.92 (t, 2H,
3
3JH-H ) 2.1 Hz, pz-4H), 1.73 (br m, 8H, NBu4), 0.89 (m, 8H,
NBu4), 0.77 (t, 12H, 3JH-H ) 7.8 Hz, NBu4), 0.66 (m, 8H, NBu4).
13C NMR (75.409 MHz, acetone-d6): δ 150 (br), 142 (br), 141.3,
140 (br), 136.4 (br), 135.6, 134.9, 127.1, 126.1, 103.0, 59.2
(NBu4), 24.4 (NBu4), 20.4 (NBu4), 13.9 (NBu4). ES-MS(-) (m/
z): 648 [M]. Anal. Calcd for C46H52D10BN5Pt: C, 61.32; H, 8.05;
N, 7.77. Found: C, 61.66; H, 6.84; N, 8.13. Alternatively, 5
can be prepared by (a) using 0.1 equiv [HNiPr2Et][BPh4], but
reaction time must be lengthened from 30 min to 48 h; (b)
using [H(OEt2)2][B(C6H3(CF3)2)4] in place of [HNiPr2Et][BPh4];
(c) using B(C6F5)3 in place of [HNiPr2Et][BPh4]. Using 0.05
equiv of B(C6F5)3 and using 1.0 equiv results in nearly identical
reaction time and yield.
Acknowledgment. The authors acknowledge J.
Christopher Thomas for insightful discussions. BP
(Methane Conversion Cooperative) and the NSF (CHE-
01232216) are acknowledged for funding. Larry Henling
and Theodore A. Betley are acknowledged for crystal-
lographic assistance.
Supporting Information Available: Crystallographic
data for 4, 5, 13, and 15 in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM050538J