Electrophilic platinum complexes: Methyl transfer reactions and catalytic reductive elimination of ethane from a tetramethylplatinum(IV) complex

Article abstract of DOI:10.1021/om9809419

Methyl ligand transfer reactions occur easily between tetramethylplatinum(IV) complexes [PtMe₄(LL)] [LL = 4,4′-di-tert-butyl-2,2′-bipyridine (bu₂bpy) (1), N,N,N′,N′-tetramethylethylenediamine (tmeda) (2), bis(2,6-diisopropylphenyl)-1

Full text of DOI:10.1021/om9809419

1408
Organometallics 1999, 18, 1408-1418
Electr op h ilic P la tin u m Com p lexes: Meth yl Tr a n sfer
Rea ction s a n d Ca ta lytic Red u ctive Elim in a tion of
Eth a n e fr om a Tetr a m eth ylp la tin u m (IV) Com p lex
Geoffrey S. Hill,† Glenn P. A. Yap,‡ and Richard J . Puddephatt*,†
Department of Chemistry, The University of Western Ontario,
London, Ontario N6A 5B7, Canada, and Department of Chemistry and Biochemistry,
The University of Windsor, Windsor, Ontario N9B 3P4, Canada
Received November 20, 1998
Methyl ligand transfer reactions occur easily between tetramethylplatinum(IV) complexes
[PtMe4(LL)] [LL ) 4,4′-di-tert-butyl-2,2′-bipyridine (bu2bpy) (1), N,N,N′,N′-tetramethyleth-
ylenediamine (tmeda) (2), bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Ar2NN) (3), 1,2-
bis(diphenylphosphino)ethane (dppe) (4)] and electrophilic platinum complexes fac-[PtMe3(SO3-
CF3)(LL)] [LL ) bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )] or [PtMe(SO3CF3)(dppe)] (10a ). It is
proposed that the complexes 6a , 7a , 8a , or 10a undergo initial dissociation of the triflate
ligand to give an electrophilic platinum cation which attacks one of the mutually trans
methylplatinum ligands of [PtMe4(LL)]. The reaction of [PtMe4(LL)] [LL ) bu2bpy (1), tmeda
(2), Ar2NN (3)] with fac-[PtMe3(SO3CF3)(L′L′)] [L′L′ ) bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )]
gives an equilibrium mixture between the reactants and fac-[PtMe3(SO3CF3)(LL)] and [PtMe4-
(L′L′)], in which [PtMe4(LL)] is favored in the same order as the π-accepting properties of
the LL ligand (Ar2NN . bu2bpy > tmeda). The reaction of [PtMe4(dppe)] (4) with 6a , 7a ,
8a , or 10a results in rapid room-temperature catalytic, C-C bond reductive elimination to
give C2H6 and [PtMe2(dppe)] (5). It is proposed that the actual reductive elimination step
occurs from the five-coordinate species [PtMe3(dppe)]+, formed by methyl ligand transfer
from 4 to the electrophilic platinum complex (6a , 7a , 8a or 10a ). The triflato complexes
6a -10a are in rapid equilibrium with the cationic aqua complexes fac-[PtMe3(OH2)(LL)]SO3-
CF3 [LL ) bu2bpy (6b), tmeda (7b), Ar2NN (8b), dppe (9b)] and [PtMe(OH2)(dppe)]SO3CF3
(10b), respectively, thus confirming lability of the triflate ligands.
In tr od u ction
(Rδ+) to a nucleophilic complex (Mδ-),3 or by a free-
radical mechanism4 is highly dependent on the elec-
tronic properties of the transition-metal complexes
involved. For example, the reaction of cis-[PtMe2(PMe2-
Ph)2] with cis,cis,trans-[PtMe2(NO3)2(PMe2Ph)2] to give
trans-[PtMe(NO3)(PMe2Ph)2] and fac-[PtMe3(NO3)(PMe2-
Ph)2] occurs by the transfer of a nucleophilic methyl-
platinum(II) ligand to the electrophilic platinum(IV)
complex.2c,f In contrast, the methyl ligand exchange
reaction between fac-[M(X)Me3(NN)] and [PtMe2(NN)]
[M ) Pt, Pd; X ) halide; NN ) 2,2′-bipyridine (bpy),
1,10-phenanthroline (phen)] to yield [MMe2(NN)] and
fac-[PtXMe3(NN)] proceeds by the SN2 mechanism and
involves a redox reaction initiated by nucleophilic attack
of the electron-rich [PtMe2(NN)] on an electrophilic
M-CH3 ligand in fac-[M(X)Me3(NN)] (Scheme 1).3
The research reported below was prompted by the
following observations. An attempt to prepare the alkyl-
Alkyl ligand transfer reactions from main-group to
transition-metal atoms are ubiquitous in the field of
organometallic chemistry and provide a classic route to
the synthesis of alkyl transition-metal complexes, and
it is now well established that the transfer of alkyl lig-
ands between two transition-metals can occur readily.1-4
Whether the reaction occurs by the transfer of a nu-
cleophilic alkyl group (Rδ-) to an electrophilic complex
(Mδ+),2 by the transfer of an electrophilic alkyl group
† The University of Western Ontario.
‡ The University of Windsor.
(1) (a) Rashidi, M.; Fakhroeian, Z.; Puddephatt, R. J . J . Organomet.
Chem. 1990, 406, 261. (b) Hadj-Bagheri, N.; Puddephatt, R. J .
Polyhedron 1988, 7, 2695. (c) Collman, J . P.; Brauman, J . I.; Madonik,
A. M. Organometallics 1986, 5, 215. (d) Bryndza, H. E.; Evitt, E. R.;
Bergman, R. G. J . Am. Chem. Soc. 1980, 102, 4948. (e) J awad, J . K.;
Puddephatt, R. J . Inorg. Chim. Acta 1978, 31, L391. (f) J ohnson, A.;
Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1976, 1360. (g) Rice,
G. W.; Tobias, R. S. J . Organomet. Chem. 1975, 86, C37. (h) Tamaki,
A.; Kochi, J . K. J . Organomet. Chem. 1974, 64, 411.
(2) (a) Ozawa, F.; Fujimori, M.; Yamamoto, T.; Yamamoto, A.
Organometallics 1986, 5, 2144. (b) Scott, J . D.; Puddephatt, R. J .
Organometallics 1983, 2, 1643. (c) Puddephatt, R. J .; Thompson, P. J .
J . Organomet. Chem. 1979, 166, 251. (d) Puddephatt, R. J .; Thompson,
P. J . J . Chem. Soc., Dalton Trans. 1977, 1219. (e) Puddephatt, R. J .;
Thompson, P. J . J . Organomet. Chem. 1976, 120, C51. (f) Puddephatt,
R. J .; Thompson, P. J . J . Chem. Soc., Dalton Trans. 1976, 2091. (g)
Puddephatt, R. J .; Thompson, P. J . J . Chem. Soc., Dalton Trans. 1975,
1810. (h) Thompson, P. J .; Puddephatt, R. J . J . Chem. Soc., Chem.
Commun. 1975, 841.
(3) (a) Canty, A. J .; J in, H.; Roberts, A. S.; Skelton, B. W.; White,
A. H. Organometallics 1996, 15, 5713. (b) Canty, A, J .; Honeyman, R.
T.; Roberts, A. S.; Treill, P. R. J . Organomet. Chem. 1994, 471, C8. (c)
Markies, B. A.; Canty, A. J .; Boersma, J .; van Koten, G. Organome-
tallics 1994, 13, 2053. (d) Aye, K.-T.; Canty, A. J .; Crespo, M.;
Puddephatt, R. J .; Scott, J . D.; Watson, A. A. Organometallics 1989,
8, 1518.
(4) (a) Ram, M. S.; Riordan, C. G.; Yap, G. P. A.; Liable-Sands, L.;
Rheingold, A. L.; Marchaj, A.; Norton, J . R. J . Am. Chem. Soc. 1997,
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10.1021/om9809419 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 03/16/1999

Electrophilic Platinum Complexes
Organometallics, Vol. 18, No. 8, 1999 1409
equiv of [PtMe4(NN)] and 1 equiv of [PtHMe2(NN)]+,
which would be deprotonated by H- to give [PtMe2(NN)]
(Scheme 2).
Sch em e 1
It is probably the large trans influence of the hydride
ligand that is responsible for the enhanced nucleophilic
character of the trans methylplatinum ligand of fac-
[PtHMe3(NN)] and thus the reactivity shown in Scheme
2.5 This then suggested that the mutually trans meth-
ylplatinum ligands of the analogous tetramethylplati-
num(IV) complexes [PtMe4(LL)] (LL ) diimine, diphos-
phine)swhich have been shown to be highly nucleophilic
and very susceptible to electrophilic attack by a variety
of reagents6sshould exhibit chemistry similar to fac-
[PtHMe3(NN)] shown in Scheme 2. In this paper we
report a study of the methyl ligand transfer reactions
from electron-rich tetramethylplatinum(IV) complexes
of the type [PtMe4(LL)] [LL ) bu2bpy (1), tmeda (2), Ar2-
NN (3), 1,2-bis(diphenylphosphino)ethane (dppe) (4)] to
electrophilic platinum complexes either of the type fac-
[PtMe3(SO3CF3)(NN)] [NN ) bu2bpy (6a ), tmeda (7a ),
Ar2NN (8a )], fac-[PtMe3(SO3CF3)(dppe)] (9a ), or [PtMe-
(SO3CF3)(dppe)] (10a ). It is also shown by low-temper-
ature NMR [1H, 19F, 31P{1H}] spectroscopic studies that
the electrophilic triflato complexes 6a -10a are in rapid
equilibrium with the corresponding cationic complexes
fac-[PtMe3(OH2)(LL)]SO3CF3 [LL ) bu2bpy (6b), tmeda
(7b), Ar2NN (8b), dppe (9b)] and [PtMe(OH2)(dppe)]SO3-
CF3 (10b), in moist solvent, respectively. In the case
where LL ) Ar2NN, both of the isomers fac-[PtMe3(SO3-
CF3)(Ar2NN)] and fac-[PtMe3(OH2)(Ar2NN)]SO3CF3 have
been characterized based on X-ray crystallographic data,
confirming the presence of the coordinated water ligand.
The methyl transfer reactions reported here provide the
first examples of the transfer of a nucleophilic methyl-
platinum(IV) ligand to an electrophilic transition-metal
complex. All previous reports of the transition-metal to
transition-metal methyl ligand transfers from Pt(IV)
were shown to follow the nucleophilic, redox mechanism
shown in Scheme 1.3 Furthermore, it is shown that
electrophilic methyl ligand abstraction from [PtMe4-
(dppe)] (4) results in rapid room-temperature catalytic
C-C bond reductive elimination to give exclusively
[PtMe2(dppe)] (5) and C2H6. This result is remarkable
since the reductive elimination of ethane from com-
plexes of the type fac-[PtXMe3(P2)] (X ) halide, CH3; P
Sch em e 2
(hydrido)platinum(IV) complex fac-[PtHMe3(bu2bpy)]
(bu2bpy ) 4,4′-di-tert-butyl-2,2′-bipyridine) by treatment
of fac-[PtMe3(SO3CF3)(bu2bpy)] with NaBH4 gave in-
stead the (µ-hydrido)diplatinum(IV) complex [Pt2(µ-
H)Me6(bu2bpy)2]SO3CF3.5 It was proposed that [Pt2(µ-
H)Me6(bu2bpy)2]SO3CF3 is formed by electrophilic attack
of fac-[PtMe3(SO3CF3)(bu2bpy)] on the nucleophilic hy-
drido ligand of the anticipated product, fac-[PtHMe3(bu2-
bpy)] (Scheme 2). This mechanism suggested that the
formation of fac-[PtHMe3(NN)] should be favored in
these reactions if the NN ligand used is bulky enough
to prevent the reaction between fac-[PtHMe3(NN)] and
fac-[PtMe3(SO3CF3)(NN)] to give [Pt2(µ-H)Me6(NN)2]SO3-
CF3. The reaction of fac-[PtMe3(SO3CF3)(NN)] [NN )
N,N,N′,N′-tetramethylethylenediamine (tmeda), bis(2,6-
diisopropylphenyl)-1,4-diaza-1,3-butadiene (Ar2NN)] with
NaBH4 gave neither fac-[PtHMe3(NN)] nor [Pt2(µ-H)-
Me6(NN)2]SO3CF3, but gave a 1:1 mixture of [PtMe2-
(NN)] and [PtMe4(NN)] (Scheme 2). A possible mecha-
nism might involve an electrophilic attack of fac-
[PtMe3(SO3CF3)(NN)] not on the hydrido ligand but on
the methyl ligand trans to hydride of fac-[PtHMe3(NN)].
Complete methyl ligand transfer would then give 1
1
) phosphine, /2 diphosphine) generally occurs only at
high temperatures.6,7 A likely mechanism for this
unprecedented catalysis is presented, and its relevance
to the fundamentally important area of C-C bond
formation/cleavage reactions is discussed. A preliminary
account of parts of this work has been published.5c
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Com p lexes.
The complexes [PtMe4(LL)] [LL ) bu2bpy (1), tmeda (2),
(6) (a) Kondo, Y.; Ishikawa, M.; Ishihara, K. Inorg. Chim. Acta 1996,
241, 81. (b) Roy, S.; Puddephatt, R. J .; Scott, J . D. J . Chem. Soc., Dalton
Trans. 1989, 2121. (c) Hux, J . E.; Puddephatt, R. J . J . Organomet.
Chem. 1988, 346, C31. (d) Hux, J . E.; Puddephatt, R. J . Inorg. Chim.
Acta 1985, 100, 1. (e) Lashanizadehgan, M.; Rashidi, M.; Hux, J . E.;
Puddephatt, R. J .; Ling, S. S. M. J . Organomet. Chem. 1984, 269, 317.
(7) (a) Goldberg, K. I.; Yan, J .; Breitung, E. M. J . Am. Chem. Soc.
1995, 117, 6889. (b) Goldberg, K. I.; Yan, J .; Winter, E. L. J . Am. Chem.
Soc. 1994, 116, 1573. (c) Brown, M. P.; Puddephatt, R. J .; Upton, C.
E. E. J . Chem. Soc., Dalton Trans. 1974, 2457. (d) Brown, M. P.;
Puddephatt, R. J .; Upton, C. E. E. J . Organomet. Chem. 1973, 49, C61.
(5) (a) Hill, G. S.; Puddephatt, R. J . J . Am. Chem. Soc. 1996, 118,
8745. (b) Hill, G. S.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1997, 16, 1209. (c) Hill, G. S.; Puddephatt, R. J . Organometallics 1997,
16, 4522.

1410 Organometallics, Vol. 18, No. 8, 1999
Hill et al.
Sch em e 3
effects and more electron-withdrawing properties of the
chelating diphosphine compared to diimine ligand.7,8
Selected NMR [1H, 19F, 31P{1H}] spectroscopic data
for complexes 6-9 in CD2Cl2 and acetone-d6 recorded
at 22 and -70 °C are presented in Table 1. NMR spectra
for fac-[PtMe3(SO3CF3)(dppe)] (9a ) were recorded only
at -70 °C because of its thermal instability. Variable
1
temperature H NMR experiments performed between
30 and 0 °C with the complexes fac-[PtMe3(SO3-
CF3)(NN)] [NN ) bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )]
suggest a rapid scrambling of the methylplatinum
ligands about the platinum center as shown in Scheme
4. At low temperature (ca. 0 °C for 7a , 8a and ca. 20 °C
Ar2NN (3), dppe (4)] were prepared by the reaction of
[Pt2Me8(µ-SMe2)2] with 2 equiv of the ligand LL. The
1H NMR spectra of [PtMe4(LL)] showed the expected
two sets of methylplatinum resonances for the Pt-Me
ligands trans to LL [2J (PtH) ) 62-73 Hz] and trans to
methyl [2J (PtH) ) 41-44 Hz] and require no further
discussion.5b,6e
1
for 6a ) the H NMR spectra of these complexes exhibit
a pattern typical for a complex with a fac-[PtMe3X(NN)]
arrangement with two sets of methylplatinum reso-
nances in a 2:1 ratio for the Pt-Me ligands trans to NN
[2J (PtH) ) ca. 66 Hz] and trans to SO3CF3 [2J (PtH) )
ca. 80 Hz], respectively.5b These two sets of signals
coalesce into one resonance with statistically averaged
The complexes fac-[PtMe3(SO3CF3)(NN)] [NN
)
bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )] were prepared by
treatment of the corresponding dimethylplatinum(II)
complex [PtMe2(NN)] with CH3OSO2CF3. In contrast,
treatment of [PtMe2(dppe)] (5) with CH3OSO2CF3 gives
exclusively C2H6 and [PtMe(SO3CF3)(dppe)] (10a). Moni-
2
values of δ and J (PtH) upon warming the solution (to
ca. 20 °C for 7a , 8a and ca. 30 °C for 6a ) (Table 1).
Intramolecular methyl ligand scrambling within [MMe3-
(X)L2] complexes is common when either the ligand X
or L is readily dissociated.7c,8,10 Dissociation of the SO3-
CF3 ligand in complexes 6a -8a is particularly facile,9
and thus the scrambling of the methylplatinum ligands
observed here is very fast.
1
toring this reaction in acetone-d6 at -70 °C by H and
31P{1H} NMR spectroscopy revealed that the reaction
initially gave the oxidative addition product, fac-
[PtMe3(SO3CF3)(dppe)] (9a ), which upon warming to
room temperature reductively eliminated ethane to give
10a . Ethane was detected by 1H NMR (δ ) 0.82 in
acetone-d6) and by GC-MS. Because of this instability
toward reductive elimination, 9a could not be isolated,
but it was fully characterized by low-temperature
(-70 °C) 1H and 31P{1H} NMR spectroscopy (see later).
Since the analogous iodo complex, fac-[PtIMe3(dppe)],
is stable to room-temperature reductive elimination
(decomposing only at 150-200 °C in the solid state),7
the instability of 9a observed here must be due to the
presence of the weakly coordinating SO3CF3 ligand. It
is known7 that reductive elimination from complexes of
the type fac-[PtXMe3(PP)] (X ) halide; PP ) diphos-
phine) to give [PtXMe(PP)] and C2H6 proceeds by
dissociation of the ligand X to give the five-coordinate
cationic intermediate [PtMe3(PP)]+, which then under-
goes easy reductive elimination (Scheme 3).7,8 Dissocia-
tion of the weakly coordinating SO3CF3 ligand in com-
plex 9a is a facile process,9 and thus the exceptionally
high reactivity of 9a toward C2H6 reductive elimination
relative to that of fac-[PtIMe3(dppe)] (in which iodide
is a good ligand for platinum and thus does not readily
dissociate) is fully consistent with the mechanism shown
in Scheme 3.
Upon further cooling of the NMR solutions of fac-
[PtMe3(SO3CF3)(NN)] [NN ) bu2bpy (6a ), tmeda (7a ),
Ar2NN (8a )], the 1H NMR resonances broaden and
eventually (at ca. -70 °C) separate into two distinct sets,
both displaying the typical fac-[PtMe3X(NN)] pattern.
Furthermore, the single room-temperature 19F reso-
nance observed for 6a -8a separates into two distinct
resonances at -70 °C. This phenomenon is reversible,
as raising the temperature of the solution again results
in coalescence of the two sets of resonances. We propose
that, in solution in moist solvent, the electrophilic tri-
flato complexes 6a -8a are in rapid equilibrium with
the corresponding cationic complexes fac-[PtMe3(OH2)-
(NN)]SO3CF3 [NN ) bu2bpy (6b), tmeda (7b), Ar2NN
(8b)] (Scheme 5). The reactions are strongly affected by
traces of adventitous water which coordinates in strong
preference to the solvent, which is present in large
excess. The ratios of the triflato complexes (a ) to the
(9) (a) Hill, G. S.; Manojlovic-Muir, Lj.; Muir, K. W.; Puddephatt,
R. J . Organometallics 1997, 16, 525. (b) Hill, G. S.; Rendina, L. M.;
Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1996, 1809. (c) Stang,
P. J .; Cao, D. H.; Poulter, G. T.; Arif, A. M. Organometallics 1995, 14,
1110. (d) Bennett, B. L.; Birnbaum, J .; Roddick, D. M. Polyhedron 1995,
14, 187. (e) Fallis, S.; Anderson, G. K. J . Organomet. Chem. 1994, 474,
223. (f) Oliver, D. L.; Anderson, G. K. Polyhedron 1992, 11, 2415. (g)
Stang, P. J .; Huang, Y. H. J . Organomet. Chem. 1992, 431, 247. (h)
Kao, L. C.; Sen, A. New J . Chem. 1991, 15, 575. (i) Drent, E.; van
Broekhoven, J . A. M.; Doyle, M. J . J . Organomet. Chem. 1991, 417,
235. (j) Fallis, S.; Anderson, G. K.; Rath, N. P. Organometallics 1991,
10, 3180. (k) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405. (l)
Brainard, R. L.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M. Organo-
metallics 1988, 7, 2379. (m) Diver, C.; Lawrance, G. A. J . Chem. Soc.,
Dalton Trans. 1988, 931. (n) Lawrance, G. A. Chem. Rev. 1986, 86,
17. (o) Davies, J . A.; Hartley, F. R. Chem. Rev. 1981, 81, 79.
(10) (a) Byers, P. K.; Canty, A. J .; Skelton, B. W.; Traill, P. R.;
Watson, A. A.; White, A. H. Organometallics 1992, 11, 3085. (b) Byers,
P. K.; Canty, A. J .; Skelton, B. W.; White, A. H. Organometallics 1990,
9, 826. (c) de Graaf, W.; Boersma, J .; Smmets, W. J . J .; Spek, A. L.;
van Koten, G. Organometallics 1989, 8, 2907. (d) Byers, P. K.; Canty,
A. J .; Crespo, M.; Puddephatt, R. J .; Scott, J . D. Organometallics 1988,
7, 1363 (e) Meakin, P.; Muetterties, E. L.; J esson, J . P. J . Am. Chem.
Soc. 1972, 94, 5271.
The marked difference in stability toward ethane
reductive elimination between fac-[PtMe3(SO3CF3)(NN)]
[NN ) bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )] (which are
stable to reductive elimination) and fac-[PtMe3(SO3CF3)-
(dppe)] (9a ) is presumably due to the greater steric
(8) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (b) Low, J . J .;
Goddard, W. A. J . Am. Chem. Soc. 1986, 108, 6115. (c) Low, J . J .;
Goddard, W. A. Organometallics 1986, 5, 609. (d) Norton, J . R. Acc.
Chem. Res. 1979, 12, 139. (e) Peters, R. G.; White, S.; Roddick, D. M.
Organometallics 1998, 17, 4493. (f) Holtcamp, M. W.; Labinger, J . A.;
Bercaw, J . E. J . Am. Chem. Soc. 1997, 119, 848. (g) Wick, D. D.;
Goldberg, K. I. J . Am. Chem. Soc. 1997, 119, 10235.

Electrophilic Platinum Complexes
Organometallics, Vol. 18, No. 8, 1999 1411

1412 Organometallics, Vol. 18, No. 8, 1999
Hill et al.
Sch em e 4
Sch em e 5
cationic complexes (b) are difficult to reproduce since
they are highly dependent on the purity of the solvent.
For example, using capped rather than flame-sealed
NMR tubes, the ratio of b to a increases during the
course of the low-temperature NMR experiment in CD2-
Cl2 and especially in the relatively hygroscopic acetone-
d6, as the concentration of adventitous water in solution
increases. Furthermore, NMR spectra recorded in the
presence of 1 equiv of H2O showed only the presence of
the proposed aqua species (b) at -70 °C (Scheme 5).
Neither of the two species a or b appears to be the cat-
ionic solvated species, fac-[PtMe3(S)(NN)]+ (S ) CD2-
Cl2), since rigorously dried 1H NMR solutions of fac-
[PtIMe3(NN)] and AgPF6 (presumably, generating fac-
[PtMe3(S)(NN)]+ in situ) showed no resonances com-
parable to those due to either a or b and since the low-
temperature spectra of 6-8 in rigorously dry CD2Cl2
solvent in flame-sealed NMR tubes did not give reso-
nances due to cationic complexes b. In dry acetone-d6,
the NMR spectra of 6-8 in sealed NMR tubes at low
temperature still did give minor peaks assigned to the
cationic complexes, and in this case, it is possible that
these are due to the acetone-solvated cations, whose
NMR spectra are indistinguishable from the aqua com-
plexes. However, the data clearly show a remarkable
preference for aqua over acetone coordination.
is unstable at elevated temperatures, see earlier) re-
vealed the presence of two species, and by analogy with
the complexes fac-[PtMe3(X)(NN)] [NN ) bu2bpy (6),
tmeda (7), Ar2NN (8); X ) SO3CF3 (a ), H2O (b)], these
are assigned to fac-[PtMe3(SO3CF3)(dppe)] (9a ) and fac-
[PtMe3(OH2)(dppe)]SO3CF3 (9b) (Table 1, Scheme 5).
The NMR data for 9a and 9b are fully consistent with
the proposed formulations and require no further dis-
cussion (Table 1), except to reiterate that the cationic
complex may be present as a mixture of acetone and
aqua complexes.
The methylplatinum 1H NMR resonances for all of
the proposed aquated complexes (b) are shifted to lower
frequency relative to those of the corresponding triflato
complexes (a ). This trend has been observed before in
complexes of the type fac-[PtMe3(X)(NN)] (NN ) di-
imine: X ) halide, solvent) and fully supports our
proposed formulations for complexes a and b.10,11 The
NMR spectra for all a and b show a strong temperature
dependence of proton or fluorine chemical shifts, with
1H NMR resonances generally shifting to lower fre-
quency and 19F NMR resonances shifting to higher
frequency at lower temperatures (Table 1). This obser-
vation as well as the inherent complexity of a system
undergoing reversible intramolecular scrambling (Scheme
4) as well as reversible intermolecular H2O (and possibly
acetone) for SO3CF3 exchange (Scheme 5) rendered the
extraction of any kinetic or thermodynamic data virtu-
ally impossible.12
1
The room-temperature H and 31P{1H} NMR spectra
of [PtMe(SO3CF3)(dppe)] (10a ) confirm the expected
1
structure. The H NMR spectrum displays a resonance
3
for the methylplatinum ligand at δ ) 0.38 [dd, J (PaH)
) 1.5 Hz, 3J (PbH) ) 7.5 Hz] with the magnitude of
2J (PtH) typical for a Pt-Me ligand trans to P (48
Hz).5b,9a,13 Furthermore, the two phosphorus atoms of
dppe resonate in the 31P{1H} NMR at δ ) 56.0 and 36.0
with a magnitude of 1J (PtP) typical for P trans to methyl
(1853 Hz) and SO3CF3 (4646 Hz), respectively.5b,9a,13 As
for the platinum(IV) complexes 6-9, H2O (and, possibly,
acetone) for SO3CF3 exchange was observed in the low-
1
temperature (-70 °C) H and 31P{1H} NMR spectra of
acetone-d6 solutions of [PtMe(SO3CF3)(dppe)] (10a )
(Scheme 5). The data are presented in Table 1, and no
further discussion is necessary.
Similarly, low-temperature (-70 °C) NMR (1H, 19F,
The most convincing evidence for the proposed for-
mulations of complexes a and b comes from an X-ray
crystallographic study of fac-[PtMe3(X)(Ar2NN)] [X )
31P{1H}) spectra of fac-[PtMe3(SO3CF3)(dppe)] (9a) (which
(11) (a) Crespo, M.; Puddephatt, R. J . Organometallics 1987, 6, 2548.
(b) Puddephatt, R. J .; Scott, J . D. Organometallics 1985, 4, 1221.
(12) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
New York, 1982.
(13) Monaghan, P. K.; Puddephatt, R. J . Organometallics 1984, 3,
444.

Electrophilic Platinum Complexes
Organometallics, Vol. 18, No. 8, 1999 1413
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for fa c-[P tMe3(OH2)(Ar 2NN)]SO3CF 3‚a ceton e
(8b)
(a) Bond Distances
Pt-C(1)
Pt-C(2)
Pt-C(3)
2.052(10)
2.060(9)
2.049(10)
Pt-N(1)
Pt-N(2)
Pt-O(1)
2.205(6)
2.200(7)
2.207(7)
(b) Bond Angles
C(1)-Pt-C(2)
C(1)-Pt-C(3)
C(1)-Pt-N(1)
C(1)-Pt-N(2)
C(1)-Pt-O(1)
C(2)-Pt-C(3)
C(2)-Pt-N(1)
C(2)-Pt-N(2)
86.1(4)
87.9(6)
93.4(4)
97.1(4)
177.1(3)
87.7(4)
99.9(3)
174.1(3)
C(2)-Pt-O(1)
C(3)-Pt-N(1)
C(3)-Pt-N(2)
C(3)-Pt-O(1)
N(1)-Pt-N(2)
N(1)-Pt-O(1)
N(2)-Pt-O(1)
91.8(3)
172.4(3)
97.4(4)
90.0(4)
75.0(2)
89.0(2)
85.2(2)
exception being the N(1)-Pt-N(2) bond angles [both
75.0°(2)] which depart significantly from the ideal 90°
octahedral angle, due to the restricted bite of the NN
chelating ligand.5b,14 The lengths of the Pt-C(3) and Pt-
C(4) bonds of both structures do not differ significantly
[ranging from 2.030(4) to 2.060(9) Å] and are of typical
magnitude for a methylplatinum(IV) ligand trans to an
imine N.5b,14 The Pt-C(1) bond lengths for the methyl-
platinum ligands trans to O of both complexes are very
similar [2.021(5) (8a ), 2.052(10) (8b‚acetone)], and very
similar to those for the methylplatinum ligands trans
to N (see earlier). This similarity is somewhat surprising
since, based on the magnitude of 2J (PtH) obtained from
1
the H NMR spectra of 8a and 8b [ca. 67 Hz (trans to
N), ca. 82 Hz (trans to O), Table 1], a shorter Pt-C bond
length would be expected for the Pt-Me ligands trans
to O. The Pt-O bond length for 8a [2.276(3) Å ] is
slightly longer than that for 8b ‚acetone [2.207(7) Å],
with both being of typical magnitude for a Pt(IV)-O
bond trans to a methyl ligand.9a For complex 8b‚acetone,
the presence of a coordinated H2O ligand (giving a
cationic complex), and not a OH ligand (giving a neutral
complex), is supported by two results, namely, the
successful location of both of the hydrogen atoms of the
H2O ligand and the presence of the SO3CF3 anion in
the unit cell.
Meth yl Liga n d Exch a n ge Rea ction s. The methyl
ligand exchange reactions between the electron-rich
complexes [PtMe4(NN)] [NN ) bu2bpy (1), tmeda (2),
Ar2NN (3)] and the electrophilic complexes fac-[PtMe3-
(SO3CF3)(NN)] [NN ) bu2bpy (6a ), tmeda (7a ), Ar2NN
(8a )] are shown in Scheme 6.
F igu r e 1. ORTEP diagrams of (a) fac-[PtMe3(SO3CF3)(Ar2-
NN)] (8a ) and (b) fac-[PtMe3(OH2)(Ar2NN)]+ (8b). Thermal
ellipsoids are shown at the 50% probability level. The
hydrogen atoms have been omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for fa c-[P tMe3(SO3CF 3)(Ar 2NN)] (8a )
(a) Bond Distances
Pt-C(1)
Pt-C(2)
Pt-C(3)
2.021(5)
2.044(4)
2.030(4)
Pt-N(1)
Pt-N(2)
Pt-O(1)
2.213(3)
2.191(3)
2.276(3)
(b) Bond Angles
C(1)-Pt-C(2)
C(1)-Pt-C(3)
C(1)-Pt-N(1)
C(1)-Pt-N(2)
C(1)-Pt-O(1)
C(2)-Pt-C(3)
C(2)-Pt-N(1)
C(2)-Pt-N(2)
85.9(2)
87.2(2)
93.9(2)
96.2(2)
178.1(2)
89.4(2)
99.0(2)
173.8(2)
C(2)-Pt-O(1)
C(3)-Pt-N(1)
C(3)-Pt-N(2)
C(3)-Pt-O(1)
N(1)-Pt-N(2)
N(1)-Pt-O(1)
N(2)-Pt-O(1)
92.3(2)
171.6(2)
96.5(2)
93.0(2)
75.0(2)
86.2(1)
85.6(1)
The reaction of [PtMe4(bu2bpy)] (1) and fac-[PtMe3(SO3-
CF3)(tmeda)] (7a ) in acetone-d6 solution results in the
immediate formation of an equilibrium mixture between
the reactants and [PtMe4(tmeda)] (2) and fac-[PtMe3(SO3-
CF3)(bu2bpy)] (6a ). The same equilibrium mixture is
obtained by reacting complexes 2 and 6a (Scheme 6).
The equilibrium highly favors complexes 1 and 7a with
Keq ) [2][6a ]/[1][7a ] ) 3 × 10-2 (Scheme 6). The reaction
of fac-[PtMe3(SO3CF3)(Ar2NN)] (8a ) and [PtMe4(NN)]
[NN ) bu2bpy (1), tmeda (2)] immediately proceeded to
SO3CF3 (8a ), H2O (8b)]. Slow solvent evaporation of a
THF solution of fac-[PtMe3(X)(Ar2NN)] gave large or-
ange crystals of 8a , and an ORTEP diagram is shown
in Figure 1a. Slow diffusion of n-pentane into an acetone
solution of fac-[PtMe3(X)(Ar2NN)] gave yellow platelike
crystals of 8b‚acetone, and an ORTEP diagram is shown
in Figure 1b. Tables2 and 3 contain selected bond
distances and angles of 8a and 8b‚acetone, respectively.
The X-ray molecular structures of 8a and 8b‚acetone
are very similar (Figure 1). In both complexes, the Ar2-
NN ligand shows no exceptional features with the Ar
rings twisted nearly orthogonal to the PtMe2N2 coordi-
nation plane. The geometries at both the platinum
centers are close to octahedral with the only notable
1
completion (by H NMR) to give 1 equiv of [PtMe4(Ar2-
NN)] (3) and 1 equiv of fac-[PtMe3(SO3CF3)(NN)] [NN
) bu2bpy (6a ), tmeda (7a )] (Scheme 6). In agreement,
mixtures of complex 3 and either complex 6a or 7a gave
1
no reaction (by H NMR).
(14) Levy, C. J .; Vittal, J . J .; Puddephatt, R. J . Organometallics
1996, 15, 2108.

1414 Organometallics, Vol. 18, No. 8, 1999
Hill et al.
Sch em e 6
were detected at room temperature. No CH4 or C2H4
was detected (by 1H NMR). The reaction of eq 1 involves
electrophilic methyl ligand abstraction from PtMe4-
(dppe)] (4) by fac-[PtMe3(SO3CF3)(NN)] [NN ) bu2bpy
(6a ), tmeda (7a ), Ar2NN (8a )] to yield [PtMe4(NN)] [NN
) bu2bpy (1), tmeda (2), Ar2NN (3)] and fac-[PtMe3(SO3-
CF3)(dppe)] (9a ). The complexes [PtMe4(NN)] and fac-
[PtMe3(SO3CF3)(dppe)] (which could not be detected at
room temperature) were detected and fully character-
ized upon monitoring the stoichiometric reaction by low-
1
temperature (-70 °C) H and 31P{1H} NMR spectros-
copy (Table 1, see earlier). Stoichiometric reactions
performed at room temperature could not be monitored
by NMR since they are too rapid and catalytic reactions
employ a concentration of catalyst (and hence a con-
centration of intermediates) too low to detect by NMR.
Complex 4 then undergoes rapid C-C bond reductive
elimination to give [PtMe(SO3CF3)(dppe)] (10a ) and
C2H6 (eq 2). Equations 3 and 4 involve methyl ligand
transfer from either [PtMe4(NN)] (1, 2, or 3) or [PtMe4-
(dppe)] (4) to the electrophile [PtMe(SO3CF3)(dppe)]
(10a ), giving the product [PtMe2(dppe)] (5) and regen-
erating fac-[PtMe3(SO3CF3)(NN)] (6a , 7a , or 8a ) or fac-
[PtMe3(SO3CF3)(dppe)] (9a ), respectively. The possibility
was considered that these methyl transfer reactions
might proceed by a nucleophilic, redox mechanism as
shown in Scheme 1, but the highly electrophilic proper-
ties of the platinum(II) species9 and the electron-rich
nature of the tetramethylplatinum(IV) species6 disfavor
this mechanism. Independent experiments show that
the reactions of both eqs 3 and 4 occur easily, since
mixtures of complex 10a and complex 1, 2, 3, or 4 in
acetone-d6 rapidly react to give 5 and 6a , 7a , 8a , or 9a ,
respectively. The net reaction is thus the reductive
elimination of C2H6 from [PtMe4(dppe)] (4) to give
[PtMe2(dppe)] (5) (eq 5). The occurrence of redox reac-
tions analogous to those in Scheme 1 such as fac-
[PtMe3(SO3CF3)(LL)] + [PtMe2(dppe)] a [PtMe2(LL)] +
[PtMe3(SO3CF3)(dppe)] can be ruled out, as mixtures of
[PtMe2(dppe)] (5) and fac-[PtMe3(SO3CF3)(NN)] show no
reaction even after several days in solution (LL ) NN,
dppe; NN ) bu2bpy, tmeda, Ar2NN). This observed
absence of reaction is not simply a highly unfavorable
equilibrium, as a mixture of 5 and fac-[Pt(CD3)3(SO3-
CF3)(bu2bpy)] (6a *) showed no intermolecular Pt-CH3
for Pt-CD3 scrambling (by 1H NMR) even after several
days in solution. The instability of fac-[PtMe3(SO3CF3)-
(dppe)] (9a ) toward reductive elimination (see earlier)
did not allow an analogous reaction between 5 and [Pt-
(CD3)3(SO3CF3)(dppe)] (9a *) to be performed.
It is proposed that the reactions proceed by initial
dissociation of the SO3CF3 ligand of fac-[PtMe3(SO3CF3)-
(NN)] to give the electrophilic five-coordinate intermedi-
ate [PtMe3(NN)]+, which then attacks one of the highly
nucleophilic mutually trans methylplatinum ligands of
[PtMe4(N′N′)] to give fac-[PtMe3(SO3CF3)(N′N′)] and
[PtMe4(NN)]. This methyl ligand transfer step is analo-
gous to the SE2 mechanism established for the cleavage
of a methylplatinum bond of [PtMe4(NN)] (NN ) 2,2′-
bipyridine, 1,10-phenanthroline) by electrophilic re-
agents such as H+ and SO2.6a,d The presence of the
weakly coordinating triflate ligand in complexes 6a , 7a ,
and 8a is essential. For example, the analogous trifluo-
roacetato complexes, fac-[PtMe3(O2CCF3)(NN)] (where
O2CCF3 is a better ligand for platinum than SO3CF3),
do not react easily with [PtMe4(NN)]. The presence of
the highly nucleophilic, mutually trans methylplatinum
ligands of complexes 1-3 is also critical. For example,
the methylplatinum ligands that are trans to µ-H in the
complex [Pt2(µ-H)Me6(bu2bpy)2]SO3CF3 [which show
reactivity intermediate between those in [PtMe4(LL)]
and those in the less reactive fac-[PtMe3X(LL)] (X )
halide)] give no reaction with 6a , 7a , or 8a .5
The reactions shown in Scheme 6 favor [PtMe4(NN)]
(and hence disfavor fac-[PtMe3(SO3CF3)(NN)]) in the
same order as the π-accepting properties of the NN
ligand, i.e., Ar2NN . bu2bpy > tmeda.15 The complexes
with better π-accepting NN ligands are better able to
stabilize the tetramethylplatinum unit having the stron-
gest σ-donor methyl ligands.
In an attempt to study the effect of changing the
chelating ligand from a N donor to a P donor on the
reactions in Scheme 6, [PtMe4(dppe)] (4) was reacted
with a stoichiometric amount of fac-[PtMe3(SO3CF3)(NN)]
[NN ) bu2bpy (6a ), tmeda (7a ), Ar2NN (8a )] in acetone-
d6 solution to give 1 equiv each of [PtMe2(dppe)] (5),
ethane, and fac-[PtMe3(SO3CF3)(NN)]. The reaction is
truly catalytic in fac-[PtMe3(SO3CF3)(NN)] and is very
fast. For example, the reaction reaches completion (by
1H and 31P{1H} NMR) within ca. 60 min with ca. 5 mol
% catalyst and within seconds when reacted stoichio-
metrically.
Tetramethylplatinum(IV) complexes are generally
very stable to reductive elimination, evolving ethane
only at elevated temperatures, and thus the unprec-
edented room-temperature reductive elimination pre-
sented here is remarkable.6b For example, thermogravi-
metric analysis (TGA) reveals that PtMe4(dppe)] (4)
decomposes only at ca. 110 °C in the solid state. Pre-
sumably it is the easy reductive elimination of C2H6
from complex 9a that enables the catalytic decomposi-
tion of 4 to take place. Since the complexes fac-[PtMe3-
(SO3CF3)(NN)] [NN ) bu2bpy (6a ), tmeda (7a ), Ar2NN
(8a )] are stable to reductive elimination (see earlier),
no catalysis is observed in the reactions shown in
Scheme 6.
The proposed mechanism for this reaction is shown
in Scheme 7. Monitoring the reaction at room temper-
ature by 1H and 31P{1H} NMR spectroscopy shows only
the presence of the catalyst (complex 6a , 7a , or 8a ), 4,
5, and ethane (δ ) 0.82 in acetone-d6); no intermediates
(15) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151.

Electrophilic Platinum Complexes
Organometallics, Vol. 18, No. 8, 1999 1415
Sch em e 7
Sch em e 8
If the mechanism in Scheme 7 is correct, complex 10a
alone should be a suitable catalyst for the decomposition
of 4 via eq 4 and eq 2 only, greatly simplifying the
proposed mechanism (Scheme 8). This prediction was
upheld, as treatment of 4 with either 10a or HOSO2-
CF3 {which generates 10a in situ via the protonation
product of 4, fac-[PtMe3(SO3CF3)(dppe)] (eq 2)} in
acetone-d6 solution gave rapid catalytic production of
[PtMe2(dppe)] and C2H6. Only ca. 10 mol % of HOSO2-
CF3 was needed for the reaction to be complete within
ca. 60 min. The kinetics of the reaction of [PtMe4(dppe)]
(4) with [PtMe(SO3CF3)(dppe)] (10a ) (Scheme 8) in
acetone-d6 were studied by 31P{1H} NMR spectroscopy
at 22 °C. A typical set of spectra was shown in the
preliminary communication; under kinetic conditions,
only resonances due to [PtMe4(dppe)] and [PtMe2(dppe)]
were observed since the concentration of 10a was too
low to allow its resonances to be observed.5c
Figure 2a shows a graph of the concentration of
[PtMe4(dppe)] (4) versus time as it reacts according to

1416 Organometallics, Vol. 18, No. 8, 1999
Hill et al.
Monitoring the reaction of 4 with a stoichiometric
1
amount of 10a in acetone-d6 at -70 °C by H and 31P-
{1H} NMR spectroscopy revealed that 9a (and 9b) was
present at detectable and varying concentration ranging
from ca. 10-20% of total platinum concentration at
intermediate stages of reaction. Furthermore, this low-
temperature NMR experiment revealed that the ratio
[9a ][5]/[4][10a ] did not remain constant throughout the
course of the reaction. Hence, it is not possible to make
the steady-state approximation for [9a ] nor to assume
a rapid equilibrium between 9a + 5 and 10a + 4 at least
under these conditions. Stoichiometric reactions per-
formed at room temperature could not be monitored by
NMR since they are too rapid and catalytic reactions
(Figure 2) employ a concentration of catalyst (and hence
a concentration of intermediates) too low to detect by
NMR. To establish whether eq 4 is reversible, a H/D
scrambling experiment was performed. If eq 4 is rapidly
reversible, it would be expected that the reaction of [Pt-
(CD3)4(dppe)] (4*) with [Pt(CH3)SO3CF3(dppe)] (10a )
would give statistical CH3 for CD3 scrambling among
the methylplatinum ligands of all the complexes in
Scheme 8. However, monitoring the stoichiometric reac-
1
tion of 4* with 10a by low-temperature H and 31P{1H}
NMR spectroscopy (-70 °C, see Experimental Section)
showed no evolution of either C2H6 or CD3CH3 and no
incorporation of Pt-CH3 ligands into either 4* or 9a *,
suggesting that the reverse reaction of eq 4 is insignifi-
cant. Nevertheless, attempts to fit the data in Figure
2a to the rate expression obtained if k2 ) 0, or indeed
by making no assumptions about relative rates, were
also unsuccessful. Another problem with Scheme 8 is
that it is somewhat oversimplified and does not consider
the aquation reactions of complexes 9a and 10a (giving
9b and 10b , respectively). Presumably [PtMe(OH2)-
(dppe)]SO3CF3 (10b) and fac-[PtMe3(OH2)(dppe)]SO3CF3
(9b) undergo similar methyl transfer and reductive
elimination reactions, respectively, to the corresponding
triflato complexes and should thus be included in the
proposed mechanism shown in Schemes 7 and 8. The
curves shown in Figure 2 are most readily interpreted
in terms of the mechanism of Scheme 8, with the
complications outlined above but also with the compli-
cation of slow catalyst decomposition during the reac-
tion, this having its greatest effect at lowest catalyst
concentrations when the reactions are slow. Under these
conditions, it can be seen that the reactions begin as
expected but then slow and may fail to reach completion.
In other words, the catalysts have a limited active
lifetime.
F igu r e 2. Graphs of the concentration of [PtMe4(dppe)]
(4) versus time for eq 5 (acetone-d6, 22 °C) using various
initial concentrations of catalyst as measured by 31P{1H}
NMR spectroscopy. (a) Catalyst ) [PtMe(SO3CF3)(dppe)]
(10a ). (b) Catalyst ) fac-[PtMe3(SO3CF3)(Ar2NN)] (8a ). In
all cases t ) 0 is the time of initial mixing.
eq 5, as a function of the initial concentration of [PtMe-
(SO3CF3)(dppe)] (10a ) and shows that the rates of
reaction increase with increasing initial catalyst con-
centration. The same qualitative dependence on initial
catalyst concentration was observed in a similar experi-
ment using fac-[PtMe3(SO3CF3)(Ar2NN)] (8a ) as the
catalyst (Figure 2b, Scheme 7). The data presented in
Figure 2 are reproducible.
Although Figure 2 clearly establishes the catalytic
effect, attempts to simulate the kinetic curves, for
example using equations based on either the steady-
state approximation for the intermediate fac-[PtMe3(SO3-
CF3)(dppe)] (9a ) shown in Scheme 8 or on the assump-
tion that the reaction of eq 4 constitutes a rapid
equilibrium, were unsuccessful.16 The following obser-
vations are relevant to understanding this problem.
Con clu sion s
In conclusion, electrophilic platinum(II) and platinu-
m(IV) complexes react with electron-rich tetramethyl-
platinum(IV) complexes to provide the first examples
of the transfer of a nucleophilic methylplatinum(IV)
ligand to an electrophilic transition-metal complex.
These reactions occur very rapidly at room temperature
and are highly dependent on the electronic properties
of both the complexes involved. Electrophilic methyl
ligand abstraction from [PtMe4(dppe)] to give the five-
coordinate species [PtMe3(dppe)]+ is followed by rapid
reductive elimination to give C2H6 and [PtMe2(dppe)].
This observation has led to the successful catalysis of
(16) Segel, I. H. Enzyme Kinetics; Wiley-Interscience Books: New
York, 1975; p 55.

Electrophilic Platinum Complexes
Organometallics, Vol. 18, No. 8, 1999 1417
observed with resonances occurring at progressively lower
frequency with increased deuteration. Only single resonances
for both 4 and 9 (assigned to the perdeuterated complexes 4*
and 9*, respectively) were observed, fully consistent with the
proposed absence of Pt-CH3 for Pt-CD3 exchange in eq 4.
P r ep a r a tion of Com p lexes. [P tMe4(tm ed a )] (2). A mix-
ture of [Pt2Me8(µ-SMe2)2] (0.10 g, 0.157 mmol) and tmeda (100
µL, 0.46 mmol) in diethyl ether (25.0 mL) was stirred for 2 h
under a N2 atmosphere. The solvent was removed from the
solution in vacuo to give a white powder. Yield: 0.105 g (90%).
Anal. Calcd for C10H28N2Pt: C, 32.3; H, 7.6; N, 7.5. Found: C,
the reductive elimination of ethane from [PtMe4(dppe)].
The mechanism proposed is supported by the detection
of intermediates by low-temperature 1H and 31P{1H}
NMR spectroscopy and by isotopic labeling experiments.
This work gives strong support to the theory that C-H
and C-C bond reductive elimination reactions from
organoplatinum(IV) complexes occur after initial ligand
dissociation and provides further insight into the fun-
damentally important area of alkane activation/forma-
tion reactions.
1
32.5; H, 7.7; N, 7.1. H NMR in acetone-d6: δ ) 2.72 [s, 4H,
3
3J (PtH) ) 6.8 Hz, tmeda-CH2], 2.46 [s, 12H, J (PtH) ) 12.5
Exp er im en ta l Section
Hz, tmeda-Me], 0.53 [s, 6H, 2J (PtH) ) 73.1 Hz, Pt-Me (trans
2
to tmeda)], -0.31 [s, 6H, J (PtH) ) 41.0 Hz, Pt-Me (trans to
Gen er a l P r oced u r es. All reagents were synthesized under
a N2 atmosphere using standard Schlenk techniques, unless
otherwise stated. All solvents were freshly distilled, dried and
degassed prior to use. NMR spectra were recorded using a
Varian Gemini spectrometer (1H at 300.10 MHz, 19F at 282.32
MHz, 31P{1H} at 121.44 MHz). Chemical shifts are reported
in ppm with respect to TMS (1H), CFCl3 (19F), or H3PO4/D2O
Me)].
[P tMe4(Ar 2NN)] (3). This complex can be generated in situ
either by the reaction of [Pt2Me8(µ-SMe2)2] with 2 equiv of
Ar2NN or by the reaction of [PtMe4(NN)] [NN ) bu2bpy (1),
tmeda (2)] with fac-[PtMe3(SO3CF3)(Ar2NN)] (see text). Com-
plex 3 could not be isolated since decomposition ensues after
ca. 30 min in solution. 1H NMR in acetone-d6: δ ) 9.14 [s, 2H,
3J (PtH) ) 31.0 Hz, imine], 7.32 [m, 6H, phenyl], 3.22 [septet,
1
(31P). The H, 19F, and 31P{1H} NMR spectra are referenced to
the residual protons of the deuterated solvents or to CFCl3 or
H3PO4/D2O contained in a coaxial insert, respectively. The
temperature of the NMR spectrometer probe was calibrated
using the supplied MeOH calibration routine (Varian), and all
temperatures reported have been corrected. Dry CD2Cl2 and
acetone-d6 were distilled on a vacuum line from P2O5 or
molecular sieves respectively onto the complex in flame-dried
NMR tubes, which were then flame-sealed when rigorously
dry conditions are specified. Otherwise, freshly opened vials
of the NMR solvent were used without further purification,
and samples were prepared in a drybox. Elemental analyses
were determined by Guelph Chemical Laboratories, Canada.
Thermogravimetric (TGA) studies were performed using a
Perkin-Elmer TGA 7 Thermogravimetric Analyzer equipped
with a Perkin-Elmer TAC 7/DX Thermal Analysis Controller.
Samples for TGA analysis were heated in platinum pans under
a N2 atmosphere in the range 20-1000 °C at a rate of 20 °C/
min.
The reagents Ar2NN,15,17 [PtMe4(bu2bpy)] (1),5b [PtMe4-
(dppe)] (4),6e [PtMe2(bu2bpy)],18 [PtMe2(tmeda)],13,19 [PtMe2(Ar2-
NN)],13,20 [PtMe2(dppe)] (5),13 fac-[PtMe3(SO3CF3)(bu2bpy)]
(6a ),5b [Pt2Me8(µ-SMe2)2],6e fac-[PtMe3(O2CCF3)(bu2bpy)],5b and
[Pt2(µ-H)Me6(bu2bpy)2]SO3CF35b were synthesized according to
literature procedures.
Kin etics Exp er im en ts. All stock solutions were prepared
in a Vacuum Atmospheres drybox. The reactions were per-
formed at 22 °C in acetone-d6 and were monitored mainly by
31P{1H} NMR spectroscopy using a known amount of OP-
(OMe)3 as an internal integration standard. The [PtMe4(dppe)]
(4) stock solution was filtered through Celite filter-aid prior
to use, eliminating any undissolved [PtMe4(dppe)]. Integrations
from the 31P{1H} NMR spectra agreed well with those obtained
from 1H NMR spectra acquired periodically throughout the
experiment.
3
i
3
4H, J (HH) ) 7.0 Hz, Pr-H], 1.29 [d, 12H, J (HH) ) 7.0 Hz,
iPr-Me], 1.08 [d, 12H, 3J (HH) ) 7.0 Hz, iPr-Me], 0.59 [s, 6H,
2J (PtH) ) 73.4 Hz, Pt-Me trans to Ar2NN], -0.08 [s, 6H,
2J (PtH) ) 43.9 Hz, mutually trans Pt-Me].
fa c-[P tMe3(SO3CF 3)(tm ed a )] (7a ). To a suspension of
[PtMe2(tmeda)] (0.75 g, 2.19 mmol) in diethyl ether (25.0 mL)
was added MeOSO2CF3 (0.400 mL, 3.53 mmol). After stirring
the solution under a N2 atmosphere for 18 h, the solvent was
removed in vacuo to give a very hygroscopic, off-white powder.
Yield: 1.10 g (99%). Anal. Calcd for C10H25F3N2O3PtS: C, 23.8;
H, 5.0; N, 5.5. Found: C, 23.5; H, 4.6; N, 5.5. 1H NMR in
acetone-d6 (22 °C): δ ) 2.98 [br m, 4H, tmeda-CH2], 2.66 [br
m, 6H, tmeda-Me], 2.55 [br m, 6H, tmeda-Me], 0.96 [br s,
9H, 2J (PtH) ) 72.0 Hz, Pt-Me]. 19F NMR in acetone-d6 (22
1
°C): δ ) -79 (s). H NMR in CD2Cl2 (22 °C): 2.80 [br m, 4H,
tmeda-CH2], 2.62 [br m, 6H, tmeda-Me], 2.40 [br m, 6H,
tmeda-Me], 0.90 [br s, 9H, 2J (PtH) ) 66.0 Hz, Pt-Me]. 19F
NMR in CD2Cl2 (22 °C): δ ) -79 (s).
fa c-[P tMe3(SO3CF 3)(Ar 2NN)] (8a ). To a solution of [PtMe2-
(Ar2NN)] (0.20 g, 0.33 mmol) in diethyl ether (25.0 mL) was
added MeOSO2CF3 (0.100 mL, 0.88 mmol). After stirring the
solution under a N2 atmosphere for 3 h, the solvent was
removed in vacuo to give a hygroscopic, orange powder. Yield:
0.24 g (94%). Anal. Calcd for C30H45F3N2O3PtS: C, 47.0; H,
1
5.9; N, 3.7. Found C, 46.7; H, 5.8; N, 3.5. H NMR in acetone-
d6 (22 °C): δ ) 9.48 [s, 2H, 3J (PtH) ) 25.2 Hz, imine], 7.42
i
[m, 6H, phenyl], 2.92 [septet, 4H, 3J (HH) ) 6.8 Hz, Pr-H],
i
3
1.32 [d, 12H, 3J (HH) ) 6.8 Hz, Pr-Me], 1.15 [d, 12H, J (HH)
) 6.9 Hz, Pr-Me], 1.05 [br s, 9H, 2J (PtH) ) 74.2 Hz, Pt-
i
Me]. 19F NMR in acetone-d6 (22 °C): δ ) -79 (s). H NMR in
1
CD2Cl2 (22 °C): δ ) 8.82 [s, 2H, 3J (PtH) ) 21.0 Hz, imine],
3
i
7.4 [m, 6H, phenyl], 2.96 [septet, 4H, J (HH) ) 7 Hz, Pr-H],
i
3
1.36 [d, 12H, 3J (HH) ) 7.0 Hz, Pr-Me], 1.18 [d, 12H, J (HH)
) 7.0 Hz, Pr-Me], 1.05 [br s, 9H, 2J (PtH) ) 70.0 Hz, Pt-
i
H/D Exch a n ge Exp er im en ts betw een 4* a n d 10a .
Complexes 4* and 10a were combined in a 5 mm NMR tube
charged with acetone-d6 at -78 °C, shaken, and immediately
inserted into the precooled (-70 °C) spectrometer probe.
Me]. 19F NMR in CD2Cl2 (22 °C): δ ) -79 (s).
fa c-[P tMe3(SO3CF 3)(d p p e)] (9a ). This complex can be
generated in situ at -70 °C either by treatment of an NMR
solution (acetone-d6) of [PtMe2(dppe)] with 1 equiv of MeOSO2-
CF3 or by treatment of an NMR solution (acetone-d6) of [PtMe4-
(dppe)] (4) with either fac-[PtMe3(SO3CF3)(NN)] (6a -8a ) or
[PtMe(SO3CF3)(dppe)] (10a ) (see text). Rapid reductive elimi-
nation of C2H6 from fac-[PtMe3(SO3CF3)(dppe)] (9a ) to afford
[PtMe(SO3CF3)(dppe)] (10a ) precludes the synthesis and isola-
tion of 9a (see text). 1H NMR of fac-[PtMe3(SO3CF3)(dppe)] (9a )
in acetone-d6 (-70 °C): δ ) 1.22 [br t, 6H, 2J (PtH) ) ca. 55
1
Monitoring the reaction by H NMR spectroscopy revealed no
resonances at the typical chemical shifts of C2H6 or the
methylplatinum ligands of either 4 or 9. An isotope effect on
the 31P{1H} NMR chemical shifts for both 5 and 10a was
(17) (a) Kliegman, J . M.; Barnes, R. K. Tetrahedron 1970, 26, 2555.
(b) Kliegman, J . M.; Barnes, R. K. J . Org. Chem. 1970, 35, 3140.
(18) Achar, S.; Scott, J . D.; Vittal, J . J .; Puddephatt, R. J . Organo-
metallics 1993, 12, 4592.
(19) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
(20) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117 6414.
3
3
Hz, J (PH) + J (P′H) ) ca. 5 Hz, Pt-Me trans to dppe], 0.25
[br t, 3H, 2J (PtH) ) ca. 75 Hz, 3J (PH) ) ca. 5 Hz, Pt-Me trans
to SO3CF3]. 31P{1H} NMR of fac-[PtMe3(SO3CF3)(dppe)] (9a )

1418 Organometallics, Vol. 18, No. 8, 1999
Hill et al.
Ta ble 4. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 8a a n d 8b
[P tMe(SO3CF 3)(d p p e)] (10a ). To a solution of [PtMe2-
(dppe)] (5) (0.50 g, 0.80 mmol) in diethyl ether (25.0 mL) was
added MeOSO2CF3 (0.150 mL, 1.32 mmol). After stirring the
solution under a N2 atmosphere for 18 h, the solvent was
removed in vacuo to give a white powder. Yield: 0.58 g (96%).
Due to the hygroscopic nature of 10a (and thus the subsequent
formation of 10b, see text), reproducible microanalyses could
8a
8b
empirical formula
fw
C30H45F3N2O3PtS C33H53F3N2O5PtS
765.83
841.92
temp
wavelength
cryst syst
space group
unit cell dimens
298(2) K
0.710 73 Å
monoclinic
P2(1)/n
a ) 12.3957(2) Å a ) 10.1436(3) Å
b ) 14.3533(1) Å b ) 10.4667(3) Å
298(2) K
0.710 73 Å
triclinic
P1h
1
not be obtained. H NMR in acetone-d6: δ ) 7.6-7.9 [m, 20H
dppe-phenyl], 2.85 [m, 2H, dppe-CH2], 2.60 [m, 2H, dppe-
2
3
CH2], 0.38 [br dd, 3H, J (PtH) ) ca. 48 Hz, J (PaH) ) 1.5 Hz,
3J (PbH) ) 7.5 Hz, Pt-Me]. 31P{1H} NMR in acetone-d6: δ )
36.0 [br s, 1P, 1J (PtP) ) 4646 Hz, P trans to SO3CF3]; 56.0 [br
c ) 19.1125(1) Å
R ) 90°
c ) 21.4047(6) Å
R ) 100.704(1)°
1
â ) 91.9760(10)° â ) 101.342(1)°
s, 1P, J (PtP) ) 1853 Hz, P trans to Me].
γ ) 90°
γ ) 96.004(1)°
2165.8(1) Å3, 2
1.291 Mg/m3
3.334 mm-1
852
Cr ysta l Str u ctu r e An a lyses of fa c-[P tMe3(SO3CF 3)-
(Ar 2NN)], 8a , a n d fa c-[P tMe3(OH2)(Ar 2NN)]SO3CF 3‚a ce-
ton e, 8b. Crystals of 8a and 8b of size 0.2 × 0.2 × 0.2 mm in
each case were mounted on glass fibers. Data were collected
by using a Siemens P4 diffractometer fitted with a CCD
detector. Structures were solved by direct methods and refined
by full-matrix least-squares on F2. The crystal and refinement
data are given in Table 4.
volume, Z
density (calcd)
abs coeff
3398.46(6) Å3, 4
1.497 Mg/m3
4.237 mm-1
1536
F(000)
no. of data/restraints/params 5935/0/362
5478/0/409
1.001
goodness-of-fit on F2
1.051
final R indices [I > 2σ(I)]
R1 ) 0.0278
wR2 ) 0.0683
R1 ) 0.0353
wR2 ) 0.0718
R1 ) 0.0475
wR2 ) 0.1271
R1 ) 0.0575
wR2 ) 0.1559
R indices (all data)
Ack n ow led gm en t. We thank the NSERC (Canada)
for financial support to R.J .P. and for a postgraduate
scholarship to G.S.H.
in acetone-d6: δ ) 25.5 [s, 1J (PtP) ) 1120 Hz, dppe]. 19F NMR
in of fac-[PtMe3(SO3CF3)(dppe)] (9a ) acetone-d6 (-70 °C): δ
) -76 (s). At -70 °C, in acetone-d6 complex 9a is in equilib-
rium with its aquation isomer, fac-[PtMe3(OH2)(dppe)]SO3CF3
(9b) (see text). 1H NMR of fac-[PtMe3(OH2)(dppe)]SO3CF3 (9b)
in acetone-d6 (-70 °C): δ ) 1.23 [br t, 6H, 2J (PtH) ) ca. 55
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and thermal parameters of the non-hydrogen atoms, bond
distances and angles, and hydrogen atom coordinates for 8a
and 8b. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
3
Hz, J (PH) + J (P′H) ) ca. 5 Hz, Pt-Me trans to dppe], 0.02
[br t, 3H, 2J (PtH) ) ca. 75 Hz, 3J (PH) ) ca. 5 Hz, Pt-Me trans
to SO3CF3]. 31P{1H} NMR of fac-[PtMe3(OH2)(dppe)]SO3CF3
1
(9b) in acetone-d6: δ ) 20.5 [s, J (PtP) ) 1115 Hz]. 19F NMR
of fac-[PtMe3(OH2)(dppe)]SO3CF3 (9b) in acetone-d6 (-70 °C):
δ ) -75 (s).
OM9809419