Si-H bond activation by (Ph3P)2Pt(η2- C2H4) in dihydrosilicon tricycles that also contain O and N heteroatoms

Article abstract of DOI:10.1021/om060391b

Several tricyclic phenoxasilin and phenazasiline heterocycles were synthesized from the corresponding 2,2′-dilithio-diphenyl ether or diphenyl amine precursor and silicon tetrachloride (or trichlorosilane) followed by reduction with lithium aluminum hydride [H₂SiAr₂: Ar₂ = C₁₂H₈O (1); Ar₂ = C ₁₄H₁₂O (2); Ar₂ = C₁₃H₁₁N (3); Ar₂ = C₁₅H₁₅N (4); Ar₂ = C₁₃H₉Br₂N (5)]. The reactivity of hydrosilanes 1-5 with (Ph₃P)₂Pt(η²-C₂H ₄) (6) was investigated. At room temperature, mononuclear complexes, (Ph₃P)₂Pt(H)-(SiAr₂H) and (Ph ₃P)₂Pt(SiAr₂H)₂, were generally observed by NMR spectroscopy but were too reactive or unstable to isolate. Dinuclear and in some cases trinuclear Pt-Si-containing complexes were observed as the major products from the reactions. Symmetrical dinuclear complexes, [(Ph₃P)Pt(μ-η²-H-SiAr₂)]₂ (8 and 22, respectively), were produced from the reaction of 1 or 3 with 6. In contrast, reaction of silane 2 with 6 produced a trinuclear complex, [(Ph ₃P)Pt(μ-SiAr₂)]₃ (16), as the major product. However, reaction of 4 or 5 with complex 6 produced an unsymmetrical dinuclear complex, [(Ph₃P)₂Pt(H)(μ-SiAr₂)(μ- η²-H-SiAr₂)Pt(PPh₃)] (26 and 30, respectively), as the major component. The molecular structures of a symmetrical (22) and unsymmetrical dinuclear (30) complex as well as a trinuclear (16) complex were determined by X-ray crystallography.

Full text of DOI:10.1021/om060391b

3974
Organometallics 2006, 25, 3974-3988
Si-H Bond Activation by (Ph3P)2Pt(η2-C2H4) in Dihydrosilicon
Tricycles that Also Contain O and N Heteroatoms
Janet Braddock-Wilking,* Joyce Y. Corey, Lisa M. French, Eunwoo Choi,
Victoria J. Speedie, Michael F. Rutherford, Shu Yao, Huan Xu, and Nigam P. Rath
Department of Chemistry and Biochemistry, UniVersity of Missouri-St. Louis, St. Louis, Missouri 63121
ReceiVed May 8, 2006
Several tricyclic phenoxasilin and phenazasiline heterocycles were synthesized from the corresponding
2,2′-dilithio-diphenyl ether or diphenyl amine precursor and silicon tetrachloride (or trichlorosilane)
followed by reduction with lithium aluminum hydride [H2SiAr2: Ar2 ) C12H8O (1); Ar2 ) C14H12O (2);
Ar2 ) C13H11N (3); Ar2 ) C15H15N (4); Ar2 ) C13H9Br2N (5)]. The reactivity of hydrosilanes 1-5 with
(Ph3P)2Pt(η2-C2H4) (6) was investigated. At room temperature, mononuclear complexes, (Ph3P)2Pt(H)-
(SiAr2H) and (Ph3P)2Pt(SiAr2H)2, were generally observed by NMR spectroscopy but were too reactive
or unstable to isolate. Dinuclear and in some cases trinuclear Pt-Si-containing complexes were observed
as the major products from the reactions. Symmetrical dinuclear complexes, [(Ph3P)Pt(µ-η2-H-SiAr2)]2
(8 and 22, respectively), were produced from the reaction of 1 or 3 with 6. In contrast, reaction of silane
2 with 6 produced a trinuclear complex, [(Ph3P)Pt(µ-SiAr2)]3 (16), as the major product. However, reaction
of 4 or 5 with complex 6 produced an unsymmetrical dinuclear complex, [(Ph3P)2Pt(H)(µ-SiAr2)(µ-η2-
H-SiAr2)Pt(PPh3)] (26 and 30, respectively), as the major component. The molecular structures of a
symmetrical (22) and unsymmetrical dinuclear (30) complex as well as a trinuclear (16) complex were
determined by X-ray crystallography.
oxidative addition of an Si-H bond to give, for example,
(Ph3P)2Pt(H)(SiPh2H).3 Our recent studies of (Ph3P)2Pt(η2-C2H4)
with Ph2SiH2 and silafluorene (H2SiC12H8) showed that mono-
nuclear and dinuclear complexes are formed, but with silafluo-
rene an unexpected trinuclear complex was also produced.4 Our
studies have been extended to the study of the reaction of
phenoxasilin and phenazasiline rings containing two exocyclic
Si-H bonds, and herein we report the synthesis, characteriza-
tion, and reactivity of these ring systems with (Ph3P)2Pt(η2-
C2H4).
Introduction
Hydrosilanes are known to react with a variety of transition-
metal precursors in Si-H bond activation processes to generate
new complexes containing a TM-Si bond.1,2 Most early
transition-metal complexes are believed to interact with Si-H
bonds through a σ-bond metathesis pathway, whereas late metals
probably proceed through an oxidative-addition route.1 A variety
of Si-TM products can be generated depending upon the type
of hydrosilane and metal precursor used. The most studied
reactions involve a tertiary hydrosilane (HSiR3) with simple
organic groups where the expected product resulting from formal
insertion of the metal into the Si-H bond gives a complex with
the general formula LnM(H)(SiR3). However, with secondary
(R2SiH2) and primary (RSiH3) hydrosilanes, additional Si-H
bonds provide further potential sites of reactivity not available
with tertiary precursors. In general, these precursors can provide
mono-, di-, and multinuclear complexes containing M-Si bonds
with terminal and/or bridging silicon and hydride ligands.1,2
Results
Preparation and Characterization of Silicon Heterocycles.
The tricyclic silicon ring systems in the current study all contain
silicon and either an oxygen or a nitrogen atom in the central
six-membered ring (Scheme 1). There were two general
synthetic strategies that were used to prepare the heterocycles
1-5 (Scheme 1). The presence of the heteroatoms in the starting
diphenyl ethers or amines enabled the direct lithiation at the
site ortho to the heteroatom in the initial, generally commercially
available, hydrocarbon precursor. Alternatively, the appropriate
o,o′-dibromide precursor could be used to prepare the desired
dilithio reagent. The dibromide precursor has the disadvantage
that its preparation involves additional reaction steps and
purification can be complicated due to the difficulty of control-
ling the bromination reaction sequence, which results in several
In the early 1970s the Pt(0) complex (Ph3P)2Pt(η2-C2H4) was
found to react with diphenylsilane, Ph2SiH2, as well as a number
of triarylsilanes to provide mononuclear complexes through
* To whom correspondence should be addressed. E-mail:
wilkingj@umsl.edu. Fax: (314) 516-5342. Tel: (314) 516-6436.
(1) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
(2) (a) Aylett, B. J. AdV. Inorg. Chem. Radiochem. 1982, 25, 1. (b) Tilley,
T. D. Transition-Metal Silyl Derivatives. In The Chemistry of Organic
Silicon Compounds; Patai, S., Rappoport, Z.,Eds.; John Wiley and Sons:
New York, 1989; p 1416. (c) Schubert, U. AdV. Organomet. Chem. 1990,
30, 151. (d) Tilley, T. D. Transition-Metal Silyl Derivatives. In The Silicon
Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; John Wiley and Sons:
New York, 1991; p 245. (e) Schubert, U. Transition Met. Chem. 1991, 16,
126. (f) Tobita, H.; Ogino, H. AdV. Organomet. Chem. 1998, 42, 223. (g)
Eisen, M. S. Transition-Metal Silyl Complexes. In The Chemistry of Organic
Silicon Compounds; 1998; Vol. 2 (Part 3), p 2037. (h) Braunstein, P.; Boag,
N. M. Angew. Chem., Int. Ed. 2001, 40, 2427. (i). Nikonov, G. AdV.
Organomet. Chem. 2005, 53, 217.
(3) (a) Eaborn, C.; Ratcliff, B.; Pidcock, A. J. Organomet. Chem. 1974,
65, 181. (b) Eaborn, C.; Pidcock, A.; Ratcliff, B. J. Organomet. Chem.
1972, 43, C5.
(4) (a) Braddock-Wilking, J.; Corey, J. Y.; Trankler, K. A.; Xu, H.;
French, L. M.; Praingam, N.; White, C.; Rath, N. P. Organometallics 2006,
25, 2859. (b) Braddock-Wilking, J.; Corey, J. Y.; Trankler, K. A.; Dill, K.
M.; French, L. M.; Rath, N. P. Organometallics 2004, 23, 4576. (c)
Braddock-Wilking, J.; Corey, J. Y.; Dill, K. M.; Rath, N. P. Organometallics
2002, 21, 5467.
10.1021/om060391b CCC: $33.50 © 2006 American Chemical Society
Publication on Web 07/06/2006

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3975
Scheme 1
lation with butyllithium in the presence of TMEDA followed
by ring closure with silicon tetrachloride12 and reduction with
LiAlH4 (eq 2). The product 3 was obtained in 59% yield (GC),
but the several required purification steps provided only 4%
isolated yield as a tan solid.
The 2,5,8-trimethyl-10,10-dihydrophenazasiline, 4, and its
deuterium analogue 2,5,8-trimethyl-10,10-dideuterophenaza-
siline, 4-d2, were prepared from a sequence starting from the
reaction of bis(2-bromo-4-methylphenyl)-N-methylamine with
n-BuLi at low temperature. The corresponding dilithio reagent
was then reacted with trichlorosilane followed by addition of
LiAlH4 (or LiAlD4) (Scheme 1). The products 4 and 4-d2 were
isolated in 42 and 24% yield, respectively.
All of the silicon heterocycles 1-5 in this study exhibited
1
products containing varying numbers of bromine substituents.5
The two sequences converge at the dilithio stage; therefore a
one-pot synthesis can be performed from either direction
followed by quenching with either trichlorosilane or silicon
tetrachloride. The resulting dichloro-substituted silicon hetero-
cycle (or chloro(hydrido)silicon heterocycle from HSiCl3) need
not be isolated and can be reduced with lithium aluminum
hydride to give the secondary hydrosilanes (1-4). The bromo-
substituted phenazasiline 5 was prepared according to the
literature procedure utilizing the precursor 2,2′,4,4′-tetrabromo-
N-methyldiphenylamine.5 Despite the anticipated ease of prepar-
ing subsitituted ring systems, incorporation of groups on the
aromatic rings is generally difficult and can require multiple
steps.6 The phenoxasilin and phenazasiline rings 2, 3, and 4
are additional examples of these ring systems containing two
exocyclic hydride substituents at the silicon center.
Si-H resonances in the expected region near 5 ppm in the H
NMR spectrum. The 29Si{1H} signals for 1-5 were observed
between -54 and -64 ppm, in the region normally found for
secondary arylhydrosilanes.13 The presence of the Si-H unit
in 1-5 was also confirmed by IR spectroscopy, where strong
Si-H stretching bands were observed near 2100 cm-1 14
.
Reactivity Studies of Silicon Heterocycles 1-5 with
(Ph3P)2Pt(η2-C2H4) (6). The Pt(0) complex (Ph3P)2Pt(η2-C2H4)
(6) was found to react readily with all of the heterocyles (1-5)
at low temperature as well as room temperature and above. The
reactions were monitored by NMR spectroscopy, and the
experiments with each heterocycle are described in subsequent
paragraphs. Key NMR spectroscopic data for the major products
observed are listed in Table 1. Additional characterization data
for the complexes formed in the following reactions are provided
in the Experimental Section.
Compound 17 was prepared by a modified literature procedure
(Scheme 1).8,9 The dilithio reagent was prepared in THF at low
temperature by metalation of diphenyl ether with 3 equiv of
butyllithium followed by quenching with SiCl4 and then
reduction with lithium aluminum hydride to afford 1 as a
viscous, pungent-smelling liquid in approximately 20% yield.
The metalation of diphenyl ether in the presence of TMEDA
has also been reported;10 however, attempts to prepare 1 using
activation by TMEDA failed. When the dilithio reagent was
quenched with Si(OMe)4 instead of SiCl4 before reduction with
LiAlH4, formation of 1 was not observed. Compound 2 was
prepared in 11% isolated yield by a route similar to that shown
in Scheme 1 starting from p-tolyl ether.
Reaction of 10,10-Dihydrophenoxasilin (1) with (Ph3P)2Pt-
(η2-C2H4) (6). The unsubstituted phenoxasilin 1 reacted with
complex 6 immediately upon mixing at room temperature, as
evidenced by vigorous gas evolution of C2H4 and H2 and
1
observation of resonances for these compounds by H NMR
spectroscopy. The major product isolated from the reaction was
the symmetrical dinuclear complex [(Ph3P)Pt(µ-η2-H-SiC12H8O)]2
(8) (Scheme 2), which precipitated in the NMR tube within 30
min after mixing and was isolated as a sparingly soluble golden-
yellow solid in 71% yield. The 1H NMR spectrum for isolated
complex 8 in CD2Cl2 exhibited a resonance at 3.25 ppm for
the bridging (Pt‚‚‚H‚‚‚Si) hydride with both one- and two-bond
couplings to Pt. The 31P{1H} NMR spectrum showed a
resonance centered at 36 ppm for 8 with the expected pattern
of an AA′XX′ spin system similar to that which was observed
for the related symmetrical dinuclear Pt complexes previously
reported.15-17
The initial attempts to synthesize 10,10-dihydro-5-meth-
ylphenazasiline, 3, began with the multistep preparation of the
dibromo precursor o,o′-dibromophenyl-N-methylamine.11 Later,
a modified procedure was followed starting from commercial
N-methyldiphenylamine.12 The latter reaction involved meta-
When the reaction was performed at room temperature and
monitored by 1H NMR spectroscopy, the data collected within
(5) Corey, J. Y.; John, C. J.; Ohmstead, M. C.; Chang, L. S. J.
Organomet. Chem. 1986, 304, 93.
(11) (a) Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A.
R. Textbook of Practical Organic Chemistry, 5th ed.; Longman Scientific
& Technical: Essex, England, 1989; p 1261. (b) Jones, E. R.; Mann, F. G.
J. Chem. Soc. 1956, 786. (c) Gilman, H.; Zuech, E. A. J. Org. Chem. 1961,
26, 2013.
(12) Lee, M. E.; Cho, H. M.; Kim, C. H.; Ando, W. Organometallics
2001, 20, 1472.
(13) Williams, E. A. NMR spectroscopy of Organosilicon Compounds.
In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.
Eds.; John Wiley and Sons: New York, 1989; p 511.
(14) Crews, P.; Rodr´ıguez, J.; Jaspars, M. Organic Structure Analysis;
Oxford University Press: New York, 1998; p 317.
(15) Braddock-Wilking, J.; Corey, J. Y.; White, C.; Xu, H.; Rath, N. P.
Organometallics 2005, 24, 4113.
(6) See for example the preparation of 2,2′-dibromo-4,4′-dimethylbiphe-
nyl: (a) Gattermann, L. Ber. 1890, 23, 1219. (b) Niementowski. Ber. 1901,
34, 3327. (c) Schwechten, H.-W. Ber. 1932, 65, 1605. (d) We thank
Professor Peter P. Gaspar of Washington University for assistance in
translating the Experimental Sections in refs 6a-c.
(7) Reikhsfel’d, V. O.; Nesterova, S. V.; Skvortsov, N. K.; Kupce, E.;
Lukevics, E. Z. Obsh. Khim. 1986, 56, 1306.
(8) Kreisel, G.; Rudolph, G.; Schulze, D. K. W.; Poppitz. W. Monatsch.
Chem. 1992, 123, 1153.
(9) For additional reports on the preparation of related phenoxa ring
systems see: (a) Kostenko, N. L.; Nesterova, S. V.; Toldov, S. V.;
Skvortsov, N. K.; Reikhsfel’d, V. O. Zh. Obshch. Khim. 1987, 57, 716. (b)
Chang, V. H. T.; Corey, J. Y. J. Organomet. Chem. 1980, 190, 217. (c)
Reikhsfel’d, V. O.; Yakovlev, I. P.; Saratov, I. E. Zh. Obshch. Khim. 1979,
49, 776. (d) Meinema, H. A. J. Organomet. Chem. 1973, 63, 243. (e)
Gilman, H.; Trepka, W. J. J. Org. Chem. 1962, 27, 1418. (f) Oita, K.;
Gilman, H. J. Am. Chem. Soc. 1957, 79, 339.
(16) Tanabe, M.; Yamada, T.; Osakada, K. Organometallics 2003, 22,
2190.
(17) Auburn, M.; Ciriano, M.; Howard, J. A. K.; Murray, M.; Pugh, N.
J.; Spencer, J. L.; Stone, F. G. A.; Woodward, P. J. Chem. Soc., Dalton
Trans. 1980, 659.
(10) Fink, W. HelV. Chim. Acta 1973, 56, 355.

3976 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
Table 1. Comparison of Selected NMR Spectroscopic Data for Key Complexes in This Reporta
a In C7D8 solution unless otherwise noted. Chemical shifts are given in ppm and coupling constants in Hz. Si-H coupling not resolved. b Pt satellites not
c 2
resolved.
J
not resolved. d 29Si resonances located at 136 and 137 ppm by 2D 1H-29Si HMQC experiment. e 29Si resonance located at 128 ppm by 2D
PtP
1H-29Si HMQC experiment. f 195Pt{1H} resonance observed at -4376 ppm as a multiplet. g 29Si resonance observed at 239.6 ppm (s, 1JPtSi ) 976). h 195Pt{1H}
resonance observed at -4352 ppm as a multiplet. i 29Si resonance observed at 254.6 ppm (s, JPtSi ) 964).
1
10 min after mixing showed a broad terminal hydride signal
near -2 ppm that was assigned to the Pt-H in 7. In addition,
two resonances were observed in the Si-H region (between
5.4 and 5.8 ppm) that were assigned to 7 and to the bis(silyl)
platinum complex (Ph3P)2Pt(HSiC12H8O)2 (9) (Scheme 2). The
31P{1H} NMR spectrum also collected after 10 min exhibited
an intense broad signal centered at 11 ppm as well as a sharp
signal for 9 as the major resonances. No resolved signals for 7
or 8 were observed, but it is likely that the broad resonance at
11 ppm involved a fluxional process with one or both of these
complexes. The mononuclear complexes 7 and 9 appear to be
thermally unstable or highly reactive, and NMR signals for these
components are observed only in the early stages of the reaction.
A minor signal was also observed in the 31P NMR spectrum
that was assigned to the siloxy complex (Ph3P)2Pt[(SiC12H8O)2O]
(10). Complex 10 was probably formed by the reaction of 9
with adventitious oxygen or water in the reaction vessel. We
and other researchers have reported the preparation of related
platinum-disiloxy complexes previously.4a,18,19 After 6 days two
additional minor signals were observed by 31P{1H} NMR
spectroscopy and were assigned to the presence of trace amounts
of [(Ph3P)Pt(µ-SiC12H8O)]3 (11) and Pt(PPh3)4.20 In this and
other reactions described in this report, signals for OPPh3 and
PPh3 were observed in the 31P{1H} NMR spectra.
When the addition was carried out at low temperature (195
K) and monitored immediately by VT-NMR spectroscopy
(18) (a) Goikhman, R.; Karakuz, T.; Shimon, L. J. W.; Leitus, G.;
Milstein, D. Can. J. Chem. 2005, 83, 786. (b) Pham, E. K.; West, R. J.
Am. Chem. Soc. 1989, 11, 7667. (c) Pham, E. K.; West, R. Organometallics
1990, 9, 1517. (d) Bell, L. G.; Gustavson, W. A.; Thanedar, S.; Curtis, M.
D. Organometallics 1983, 2, 740. (e) Curtis, M. S.; Greene, J. J. Am. Chem.
Soc. 1978, 100, 6362.
(19) Osakada, K.; Tanabe, M.; Tanase, T. Angew. Chem., Int. Ed. 2000,
39, 4053.
(20) Sen, A.; Halpern, J. Inorg. Chem. 1980, 19, 1073.

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3977
Scheme 2
Scheme 3
starting at 223 K, well-resolved sharp signals for 7 were
1
observed in both the H and 31P{1H} NMR spectra along with
unreacted precursor 6. The proton signals for the hydrides in 7
were observed at 5.4 ppm for the Si-H unit (multiplet
overlapping with the signal for free C2H4) and at -1.5 ppm for
the terminal Pt-H as a doublet of doublets with platinum
satellites. The 31P{1H} NMR spectrum showed a broad singlet
at 34 ppm for the phosphorus trans to silicon in 7 and a broad
singlet at 33 ppm for the second phosphine trans to the hydride.
No signals were observed for complex 9 in the low-temperature
reaction. As the temperature was raised slowly to room
temperature, the signals for 7 began to broaden significantly.
When the temperature had reached 303 K (after 5 h), no resolved
signals were observed for 6 or 7 in the 1H NMR spectrum. The
31P{1H} NMR spectrum resembled that observed in the room-
temperature addition, showing a broad peak centered at 20 ppm
(range about 0-50 ppm) as the major signal. The latter signal
remained broad even when the temperature was lowered to 223
K, but at 183 K sharp signals for (Ph3P)4Pt and PPh3 were
observed.20
line flanked by a complex Pt satellite pattern due to the presence
of several isotopomers containing 195Pt.21
Upon cooling the reaction solution to 223 K, well-resolved
signals for the dinuclear complex 15 were observed in addition
to signals for 14, 16, and OPPh3. The 31P{1H} NMR spectrum
displayed a triplet at 30.3 for the Pt(PPh3) unit and a doublet at
20.3 ppm for the Pt(PPh3)2 group in 15, as well as a singlet at
-5 ppm for PPh3. After 6 days the intensity of the 31P{1H}-
NMR signal for 16 was dramatically increased, and it was the
major component in the reaction mixture. X-ray quality crystals
of 16 were obtained as the toluene solvate (see X-ray crystal-
lography section below). Complex 16 was found to be readily
soluble in C7D8, which allowed for characterization by 29Si-
{1H} and 195Pt{1H} NMR spectroscopy. The silicon resonance
appeared at 239 ppm as a single line flanked by Pt satellites, in
a region that is similar to the related triplatinum complexes
When the addition of 1 to 6 was performed at room
temperature followed by immediate heating of the solution in
the NMR magnet at 323 K, complex 8 was formed as the major
product, but also observed by 31P{1H} NMR spectroscopy was
the presence of the trinuclear complex 11, Pt(PPh3)4 and PPh3
(at low temperature), and complex 10 (Scheme 2).
[(Ph3P)Pt(µ-SiC12H8)]34b and [(Me3P)Pt(µ-Si(C6H5)2]3.19 The 195
-
Pt{1H} NMR spectrum exhibited a resonance centered at -4352
ppm as a complex pattern due to the presence of 195Pt
isotopomers (Figure 1).21
Reaction of 2,8-Dimethyl-10,10-dihydrophenoxasilin (2)
with (Ph3P)2Pt(η2-C2H4) (6). The reaction of the tricyclic ring
system 2 with the Pt(0) complex 6 at room temperature resulted
in the formation of the unsymmetrical dinuclear complex
(Ph3P)2(H)Pt(µ-SiC8H12O)(µ-η2-H-SiC8H12O)Pt(PPh3) (15) as
the major species (Scheme 3). The expected mononuclear
complex 12, analogous to 7, appears to be reactive and was
observed only in the low-temperature addition reaction. Complex
15 exhibits distinctive resonances in both the H and 31P{1H}
1
Figure 1. 195Pt{1H} NMR spectrum (107 MHz, C7D8, 300 K) for
complex 16.
low-temperature NMR spectra due to the unsymmetrical envi-
ronment at the Pt centers and dynamic behavior of the phosphine
ligands on the NMR time scale. In the reaction solution at room
temperature, a broad averaged resonance is observed at 0.4 ppm
with flanking broad platinum satellites for the two hydrides in
15. A broad peak was observed in the 31P{1H} NMR spectrum
centered at 19 ppm and probably involved an exchange process
between 15 and free PPh3 in the solution.4a Approximately 45
min after mixing, a signal for the triplatinum complex 16 was
observed in the 31P{1H} NMR spectrum at 68.7 ppm as a central
The low-temperature addition reaction of the phenoxasilin
precursor 2 to 6 showed results similar to the reaction between
1 and 6 at low temperature. The major resonances observed in
1
the H and 31P{1H} NMR spectra were for the mononuclear
complex 12 and unreacted 6. As the temperature was warmed
(21) Moor, A.; Pregosin, P. S.; Venanzi, L. M. Inorg. Chim. Acta 1981,
48, 153.

3978 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
Scheme 4
Scheme 5
In contrast, when the addition of 3 to 6 was performed at
room temperature then immediately placed in a preheated NMR
probe at 323 K, NMR signals for the trinuclear complex 21
were observed within 5 min by 31P{1H} NMR spectroscopy.
The low-temperature 31P{1H} NMR spectra collected 2-3 h
after heating to 323 K also indicated the formation of the
unsymmetrical dinuclear complex 20, as well as Pt(PPh3)420 and
PPh3 as the other major reaction components in addition to
complex 21.
slowly to room temperature in 20 K increments, the signals
associated with 6 and 12 began to broaden significantly. At 283
K, the 31P{1H} NMR spectrum showed a broad peak centered
at 25 ppm as the major resonance. When the temperature had
reached 303 K, a small-intensity signal was observed for the
trinuclear complex 16 in addition to the broad peak at 25 ppm.
Reaction of 5-Methyl-10,10-dihydrophenazasiline (3) with
(Ph3P)2Pt(η2-C2H4) (6). The room-temperature reaction of 3
with 6 resulted in gas evolution along with the formation of
Reaction of 2,5,8-Trimethyl-10,10-dihydrophenazasiline
(4) with (Ph3P)2Pt(η2-C2H4) (6). The room-temperature reaction
of 4 with 6 gave results similar to those shown in Scheme 3.
The mononuclear complex 23 was observed only when the
reaction was performed at low temperature (see below). A broad
resonance was observed in the 31P{1H} NMR spectrum,
indicating the formation of the fluxional unsymmetrical di-
nuclear complex 26 (major product) along with minor sharp
signals for the bis(silyl) complex 24, siloxyplatinum complex
25, and trinuclear complex 27 (Scheme 5). Upon cooling the
solution to 223 K after 1.5 h, well-resolved signals for 26 were
1
several Pt-Si-containing products, as determined by H and
31P{1H} NMR spectroscopy. NMR signals for the expected
mononuclear complex 17 were observed only in the early stages
of the reaction. Minor amounts of the bis(silyl) complex 18,
siloxane complex 19, and the trinuclear complex 21 were
detected by 31P NMR spectroscopy. The major component in
the reaction mixture was the unsymmetrical dinuclear complex
20 (Scheme 4). However, after 1-2 days, the symmetrical
dinuclear complex 22 was isolated as yellow crystals (55%
yield), which were suitable for X-ray crystallography (see X-ray
crystallography section below). Signals for 22 were not observed
in the reaction mixture by 1H and 31P{1H} NMR spectroscopy.
It is probable that elimination of a phosphine from 20 occurred
to produce complex 22, which precipitated due to its low
solubility in toluene-d8. Complex 22 was soluble in CD2Cl2 and
was characterized by 1H and 31P{1H} NMR spectroscopy, X-ray,
IR, and elemental analysis. The 31P{1H} NMR spectrum for 22
exhibited a singlet at 36.9 ppm with two sets of Pt satellites
with a pattern similar to that observed for complex 8.
1
observed in the H and 31P{1H} NMR spectra.
The low-temperature addition of 4 to 6 resulted in the clean
formation of complex 23 as the major Pt-Si-containing product
along with some unreacted precursor 6. When the solution was
warmed, the signals for 23 began to broaden (263 K), and at
room temperature only a broad, ill-defined spectrum was
observed (range 0-60 ppm). Upon cooling the solution to 223
K after 5 h, sharp signals for the unsymmetrical dinuclear
complex 26 (major species) and unreacted 6 were observed
along with minor signals for 25 and 27.
Reaction of 2,8-Dibromo-5-methyl-10,10-dihydrophena-
zasiline (5) with (Ph3P)2Pt(η2-C2H4) (6). The presence of
methyl substituents at the 2,8-positions on the aromatic rings
of the heterocyclic hydrosilane precursors as described above
does alter the product distribution. However, a much more
dramatic effect is observed when bromine substituents are
incorporated on the carbon centers para to the nitrogen of the
heterocycle. The room-temperature reaction of 5 with 6
produced the mononuclear complex 28 initially, but the signals
were broad (0-50 ppm in the 31P NMR spectrum). Upon
cooling to 223 K after 1 h, sharp resonances were observed for
The low-temperature addition of 3 to 6 resulted in the
formation of 17 as the major Pt-Si-containing product. As the
temperature was raised from 223 K to room temperature, the
NMR signals for 17 started to broaden. After 24 h, complex 22
again precipitated in the NMR tube as the major product. A
minor amount of complexes 19 and 21 was also observed in
the reaction solution.

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3979
Scheme 6
6 compared to that between 3 (phenazasiline) and 6 is the
absence of any signals for the unsymmetrical dinuclear complex
(Ph3P)2(H)Pt(µ-SiAr2)(µ-η2-HSiAr2)Pt(PPh3) in the former reac-
tion. In contrast, the major product initially formed in the
reaction between 3 and 6 was the unsymmetrical dinuclear
complex 20. Our previous results suggested that the fluxional
process observed for related unsymmetrical dinuclear complexes
probably involved dissociation/coordination of a phosphine at
the dinuclear framework proceeding through a symmetrical
dinuclear intermediate such as 8 and 22.4a
The formation of trinuclear complexes [(Ph3P)Pt(µ-SiAr2)]3,
11 and 21, from the reaction of 1 and 6 or between 3 and 6,
respectively, at room temperature did not occur at all or only
to a minor extent (3 + 6). However, the magnitude of trimer
formation could be increased when the addition was performed
followed by immediate heating of the reaction solution to 323
K. The mechanism of formation of the trinuclear complex is
not known but may involve a bimolecular reaction between two
dinuclear species or between a mononuclear and dinuclear
species.
We previously found that incorporation of substituents on
the aromatic ring had a significant effect on the reactivity of 6
with silafluorene compared to 3,7-di-tert-butylsilafluorene with
precursor 6.4 In the former reaction, mononuclear (not isolated),
unsymmetrical dinuclear and trinuclear complexes were ob-
served by NMR spectroscopy. However, the substituted si-
lafluorene provided the unsymmetrical dinuclear complex
(Ph3P)2(H)Pt(µ-SiC20H24)(µ-η2-HSiC20H24)Pt(PPh3) as the major
product in 86% yield.4b The presence of the bulky tert-butyl
groups at the ring positions meta to the silicon center inhibited
the formation of the trinuclear complex. We anticipated that
placement of other groups such as methyl would have a similar
effect. Surprisingly, reaction of 2,8-dimethylphenoxasilin 2 with
6 produced not only the expected mononuclear complex 12 from
Si-H bond activation and the unsymmetrical dinuclear complex
15 but also the trinuclear complex 16 was eventually isolated
in nearly quantitative yield. The reaction of silane precursor 4
with 6 provided similar results, but significant amounts of both
dinuclear 26 and trinuclear complex 27 were formed. The 2,8-
dibromophenazasiline precursor 5 produced very little trinuclear
complex 31 upon reaction with complex 6, and the unsym-
metrical complex 30 was the major product formed. The
presence of the electronegative Br substituents appears to inhibit
the formation of the trinuclear complex.
the unsymmetrical dinuclear complex 30. As with the other
reactions described herein, a minor amount of the siloxy
complex 29 was probably formed, but the 31P NMR signals
would overlap with those for 30. A trace amount of the trinuclear
complex 31 was also observed. After 24 h, orange crystalline
complex 30 was isolated in 51% yield (Scheme 6).
The low-temperature reaction between 5 and 6 showed results
similar to those described above for the other silicon hetero-
cycles. The mononuclear complex 28 was formed as the major
product at low temperature, and after reaching room temperature
the unsymmetrical complex 30 along with a minor amount of
29 and 31 were present. No signals were observed in either the
room-temperature or the low-temperature reaction for a bis-
(silyl) product, (Ph3P)2Pt(SiAr2H)2.
Discussion
The room-temperature reactions described in the results
section above (Schemes 2-6) for the hydrosilanes 1-5 with
the Pt(0) complex 6 showed that the expected, initially formed
mononuclear complexes (Ph3P)2Pt(H)(SiAr2H) (see Table 1)
were either highly reactive or thermally unstable. In some
reactions minor amounts of mononuclear bis(silyl) complexes
(Ph3P)2Pt(SiAr2H)2 were also detected in the early stages of the
reaction. The tentative assignments for complexes 9 and 18 are
based on spectroscopic data obtained for a related complex that
was isolated and characterized for the unsubstituted silafluorene.4a
The stable products isolated from these reactions are dinuclear
and/or trinuclear complexes.
Multinuclear NMR spectroscopy is a powerful tool to
determine the types of products formed in the reactions shown
in Schemes 2-6. Similar chemical shifts, multiplicity patterns,
and coupling constant values are observed for complexes of
the same general structural type as shown in Table 1. For
example, mononuclear complexes of the type (Ph3P)2Pt(H)-
(SiAr2H) (7, 12, 17, 23, 28) show two distinct hydride
1
resonances in the H NMR spectrum, near 5 ppm (multiplet,
It is interesting to note that the unsubstituted ring systems 1
and 3 favor the formation of the symmetrical dinuclear
complexes [(Ph3P)Pt(µ-η2-HSiAr2)]2, 8 and 22. The dinuclear
complex 8 is formed within 30 min after addition, but complex
22 precipitated from the reaction solution after 1 to 2 days.
Previous results from our laboratory have shown that complexes
of this type generally have low solubility in C6D6 or C7D8
solutions.22 Once the symmetrical dinuclear complex was
precipitated in the reaction mixture, further reaction ceased. One
notable difference between the reaction of 1 (phenoxasilin) and
SiH) and -1.5 ppm (doublet of doublets with prominent Pt
satellites, PtH). The two phosphines are inequivalent and
therefore couple to each other, giving rise to two doublets (near
30-35 ppm) each with one set of Pt satellites in the 31P NMR
spectrum. The strong trans influence exerted by silicon results
in a smaller 1JPtP coupling (∼1800 Hz) for the phosphorus center
positioned trans to silicon compared to ∼2400 Hz for the
phosphine cis to silicon.23 A number of stable mononuclear
complexes (R′3P)2Pt(H)(SiR2R′′) are known.24
The unsymmetrical dinuclear complexes [(Ph3P)2(H)Pt(µ-
SiR2)(µ-η2-HSiR2)Pt(PPh3)] (15, 20, 26, and 30) are unusual
since they have two distinct sites each for Pt, P, Si, and H. The
(22) Braddock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Organometallics
2000, 19, 5500.

3980 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
bridging hydride participates in a nonclassical, 3c-2e interaction
1
with Pt and Si (Pt‚‚‚H‚‚‚Si).1,2c,f,i The H NMR spectra for the
unsymmetrical dinuclear complexes (Table 1) show two unique
resonances for complexes 15 and 30; however, the bridging
hydrides were not located for 20 and 26 and were probably
obscured by other resonances. For complexes 15 and 30 a signal
appears near 3 ppm as a doublet as a consequence of coupling
to one phosphine for the (Pt‚‚‚H‚‚‚Si) unit; however, the JSiH
and JPtH coupling values could not be resolved. The other unique
resonance appears at a lower frequency between -5 and -6
ppm generally as a triplet with two sets of Pt satellites for the
terminal Pt-H.4
The 31P NMR spectra at room temperature for the unsym-
metrical dinuclear complexes exhibit a broadened signal centered
near 10-20 ppm, indicating fluxional behavior on the NMR
time scale. Related unsymmetrical dinuclear Pt complexes
containing bridging silafluorenyl groups4a and Pd complexes
with (µ-SiPh2)25 units were also reported to exhibit dynamic
temperature-dependent NMR spectra, by a proposed mechanism
involving dissociation of one of the two equivalent phosphines
followed by recoordination of the phosphine at the other metal
center. In the former case, the mechanism could also involve
concomitant transformation of bridging and terminal hydrides.4a
Exchange of free (p-Tol)3P with coordinated Ph3P was recently
confirmed for an unsymmetrical dinuclear Pt2 complex contain-
ing silafluorenyl bridging ligands.4a However, the low-temper-
ature (-50 °C) spectra for the unsymmetrical dinuclear com-
plexes show resolved resonances for the two different phosphorus
environments. The two equivalent phosphines, (Ph3P)2Pt, couple
to the other phosphine Pt(PPh3) and afford a doublet (near 20
ppm) and a triplet (near 30 ppm) pattern, respectively, each with
two sets of Pt satellites due to the presence of two Pt centers in
Figure 2. (a) Molecular structure of 16 (as 2.5 C7D8 solvate).
Selected bond lengths (Å) and angles (deg): Pt1-Pt2 2.7386(6),
Pt1-Pt3 2.7138(6), Pt2-Pt3 2.7199(7), Pt1-P1 2.252(3), Pt2-
P2 2.247(3), Pt3-P3 2.2469(3), Pt1-Si1 2.379(3), Pt1-Si3 2.373-
(3), Pt2-Si1 2.336(3), Pt2-Si2 2.360(3), Pt3-Si2 2.356(3), Pt3-
Si3 2.332(3); Pt2-Pt1-Pt3 59.843(16), Pt1-Pt2-Pt3 59.625(16),
Pt2-Pt3-Pt1 60.532(16), Pt1-Si1-Pt2 71.01(9), Pt2-Si2-Pt3
70.45(8), Pt3-Si(3)-Pt1 70.43(9). (b) Core structure of 16.
The trinuclear complexes [(Ph3P)Pt(µ-SiR2)]3 (11, 16, 21, 27,
and 31) contain only aromatic or methyl resonances and no
1
Pt-H or (Pt‚‚‚H‚‚‚Si) signals in the H NMR spectrum. The
31P{1H} NMR spectrum for the trinuclear complexes shows a
resonance near 70 ppm with a complex Pt satellite pattern due
to the presence of several isotopomers containing 195Pt.21 The
presence of 195Pt-containing isotopomers also results in a
complex 195Pt NMR spectrum (see Figure 1).21 The 29Si NMR
signals for the trinuclear complexes 16 and 21 were observed
at high frequency, near 240-250 ppm, in a region often
observed for bridging (µ-SiR2) groups.2f
1
the complex.4 Similar H and 31P NMR spectral features were
observed for a mixed Pt-Pd unsymmetrical dinuclear complex
reported by Osakada et al.26
In contrast, the symmetrical dinuclear complexes [(Ph3P)-
Pt(µ-η2-HSiR2)]2 (8 and 22) display one type of hydride
(Pt‚‚‚H‚‚‚Si) in the 1H NMR spectrum generally near 1-3 ppm,
in the region often observed for other related symmetrical
dinuclear Pt-Pt and Pd-Pd and mixed Pt-Pd complexes
containing (µ-η2-HSiR2) units.4a,16,17,22,25-27 Recently, the NMR
chemical shifts were predicted for the related hypothetical
complex [Pd2(SiH3)2(PH3)2]. The hydride shift in the 1H NMR
spectrum was calculated to be 2.11 ppm and can be described
as a hydride that lies between a silyl hydride and a metal hydride
environment.28 The symmetrical environment in these complexes
gives rise to one type of phosphorus environment, leading to a
sharp 31P resonance with two sets of Pt satellites as part of an
The structures of complexes 16, 22, and 30 were confirmed
by X-ray crystallography. The molecular structures of the deep
red trinuclear complex 16 along with selected bond distances
and angles are shown in Figure 2.
Complex 16 exhibits a nonplanar Pt3Si3 core. One of the
silicon centers (Si2) in one of the phenoxasilin ring systems
lies above the plane defined by the remaining Pt3Si2 atoms by
ca. 1.1 Å, and the phosphorus (P1) center lying opposite (Si2)
also lies above that plane by ca. 0.2 Å. This solid state
arrangement is likely due to packing forces. A similar solid state
1
AA′XX′ spin system with large JPtP coupling values.4a,16,17,26
The symmetrical dinuclear complexes described in the current
work did not show fluxional NMR behavior.
environment was also observed for the trinuclear complex
4b,c
[(Ph3P)Pt(µ-SiC12H8)]3
and the related complex (Me3P)Pt-
(µ-SiPh2)]3,19 both of which exhibited a nonplanar Pt3Si3 core.
The Pt-Pt, Pt-P, and Pt-Si bond distances found in 16 are
within the expected range.1
(23) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.
1973, 10, 335. (b) Coe, B. J.; Glenright, S. J. Coord. Chem. ReV. 2000,
203, 5.
(24) See for example: Chan, D.; Duckett, S. B.; Heath, S. L.; Khazal, I.
G.; Perutz, R. N.; Sabo-Etienne, S.; Timmins, P. L. Organometallics 2004,
24, 5744.
(25) (a) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.;
Yamamoto, T. Organometallics 1998, 17, 4929. (b) Kim, Y.-J.; Lee, S.-
C.; Park, J.-I.; Osakada, K.; Choi, J.-C.; Yamamoto, T. J. Chem. Soc., Dalton
Trans. 2000, 417.
(26) Yamada, T.; Tanabe, M.; Osakada, K.; Kim, Y.-J. Organometallics
2004, 23, 4771.
(27) Sanow, L. M.; Chai, M.; McConnville, D. B.; Galat, K. J.; Simons,
R. S.; Rinaldi, P. L.; Youngs, W. J.; Tessier, C. A. Organometallics 2000,
19, 192.
(28) Nakajima, S.; Sumimoto, M.; Nakao, Y.; Sato, H.; Sakaki, S.;
Osakada, K. Organometallics 2005, 24, 4029.
Complex 22 was isolated as an off-white crystalline solid,
and the molecular structure is shown in Figure 3 along with
selected bond distances and angles. Complex 22 exhibits a planar
central P2Pt2Si2 core due to a center of inversion. The hydrides
were located but not refined and were found to lie above and
below the central core, in contrast to related symmetrical
dinuclear complexes, where the bridging hydrides are found in
the same plane as the P2Pt2Si2 atoms.
The presence of the nonclassical (Pt‚‚‚H‚‚‚Si) interaction in
22 is supported by the solution NMR and IR spectroscopic data

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3981
Figure 3. Molecular structure of 22 (as C7D8 solvate). Selected
bond lengths (Å) and angles (deg): Pt1-Pt#1 2.7032(6), Pt1-P1
2.254(2), Pt1-Si1 2.411(2), Pt1-Si3 2.322(3), Pt1-H11a 1.54,
Si1-H11a 1.64; P1-Pt1-Pt#1 161.81(6), Pt1-Si1-Pt#1 69.63-
(7), Si1-Pt1-Si#1 110.37(7), P1-Pt1-Si#1 105.21(8), P1-Pt1-
Si1 144.34(9).
as well as the X-ray crystal structure. Two different and
alternating Pt-Si distances, 2.32 and 2.41 Å, are found in the
solid state structure for 22, where the longer distance is
associated with the Pt-Si bond bridged by the hydride. Another
notable feature found in the structure of 22 is the nonlinear P1-
Pt1-Pt#1 angle (162°). Related symmetrical dinuclear com-
plexes also exhibit the same phenomenon where the phosphine
bends away from the position of the bridging hydride.16,17,22,25,26
In complexes where the (Pt‚‚‚H‚‚‚Si) hydrides have been located
and refined by X-ray crystallography, elongated Pt-H and Si-H
distances are often observed, supporting the nonclassical 3c-2e
interaction.1,2c,i Although these distances involve unrefined
H-positions (for 22 and 30) where the distances are not as
accurate as those between heavier elements, a general bonding
environment can be deduced from the structure.
A recent theoretical study examined the bonding nature in
silyl-bridged dinuclear M2(SiH3)2(PH3)2 (M ) Pd, Pt) com-
plexes.28 The bonding environment in the complexes was
described as not a pure silyl group but having some silylene
(µ-SiR2) and hydride type character and can be represented by
the formula M2(µ-η2-H‚‚‚SiH2)2(PH3)2. The Pt-Pt bond was
considered to be stronger than a Pd-Pd bond in the complexes
M2(SiH3)2(PH3)2, and the nonclassical interaction between the
Si-H bond and Pt was stronger than in the Pd system. The
calculated bond distances for Pt2(SiH3)2(PH3)2 were in good
agreement with our experimental results (Pt-Pt 2.742 Å; Pt-P
2.281 Å; Pt-Si 2.372 Å, 2.480; Pt‚‚‚H 1.775 Å; Si‚‚‚H 1.715
Å).28 Other recent theoretical calculations for complexes with
the formula [LnM(µ-η2-HSiR2)]2 were found to exhibit shorter
Si‚‚‚H distances compared to mononuclear [LnM(η2-HSiR3)]
complexes due to the weaker back-donation from the metal to
the Si-H(σ*) orbital.29
The orange, unsymmetrical dinuclear complex 30 was also
structurally characterized by X-ray crystallography. The
molecular structure of 30 is shown in Figure 4 along with
selected bond distances and angles. The general structural
features of 30 are similar to those found for the related
unsymmetrical dinuclear complex [(Ph3P)2(H)Pt(µ-SiC20H24)-
(µ-η2-HSiC20H24)Pt(PPh3)],4b dipalladium complex (Me3P)Pd-
(µ-HSiPh2)2Pd(PMe3)2,25a and mixed Pt-Pd complex (Et3P)2-
Pt(µ-η2-HSiPh2)Pd(PEt3).26 Complex 30 exhibits an unsymmetrical
Figure 4. (a) Molecular structure of 30 (as 3 C7D8 solvate).
Selected bond lengths (Å) and angles (deg): Pt1-Pt2 2.7268(2),
Pt1-P1 2.2952(12), Pt1-P2 2.3902(12), Pt2-P3 2.24029(12),
Pt1-Si1 2.4984(13), Pt1-Si2 2.3409(13), Pt2-Si1 2.3151(13),
Pt2-Si2 2.3931(13), Pt1-H1 1.55, Si1-H1 1.73, Pt2-H2 1.79,
Si2-H2 1.89; P1-Pt1-P2 110.41(4), P3-Pt2-Pt1 163.56(3),
Si1-Pt1-Si2 106.46(4), Si1-Pt2-Si2 110.88(4), Pt1-Si1-Pt2
68.89(4), Pt1-Si2-Pt2 70.33(4), P2-Pt1-Pt2 108.93(3), P1-Pt1-
Pt2 137.34(3). (b) Molecular structure of 30 viewed along the Pt-
Pt bond. (c) Core structure of 30 showing selected bond distances.
environment in the solid state. Four distinct Pt-Si distances
were found (Figure 4). The longest distances (ca. 2.4-2.5 Å)
were observed between Pt1-Si1 and Pt2-Si2. The two hydrides
in 30 were located but not refined. The hydride bound to Pt1-
H1 showed a shorter distance (1.55 Å) to the metal center than
the distance to the silicon center (Si1-H1, 1.73 Å), in agreement
with the low-temperature solution state assignment of H1 as
terminal hydride. However, the Si-H distance is within the
range observed for nonclassical (Pt‚‚‚H‚‚‚Si) interactions, sug-
gesting that some interaction is possible in the solid state.1,2c,i
Much longer distances were found with the other hydride (Pt2-
H2, ca. 1.8 Å and Si2-H2, ca. 1.9 Å), in agreement with the
low-temperature NMR assignment for a bridging environment
(29) (a) Choi, S.-H.; Lin, Z. J. Organomet. Chem. 2000, 608, 42. (b)
Lin, Z. Chem. Soc. ReV. 2002, 31, 239.

3982 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
CCD area detector at 233 K. Melting points were obtained using a
Thomas-Hoover capillary melting point apparatus and are uncor-
rected. Elemental analysis determinations were performed by
Atlantic Microlabs, Inc., Norcross, GA.
for this hydride. The dihedral angle between the hydrides H1-
Pt1-Pt2-H2 was found to be 158°.
The reactivity of several silicon-containing tricyclic ring
systems 1-5 with the Pt(0) phosphine complex 6 was examined
and a variety of different products were obtained depending
upon the silicon precursor used. In all cases, mononuclear
complexes of the type P2Pt(H)(SiR2H) (or P2Pt(SiR2H)2) were
believed to be the initial products formed at room temperature
but were found to be highly reactive (or thermally unstable).
Dinuclear or trinuclear complexes were isolated as the major
products from these reactions. The unsubstituted ring systems
1 and 3 provided symmetrical dinuclear complexes [(Ph3P)Pt-
(µ-η2-HSiR2)]2 (8 and 22). In contrast, the methyl-substituted
ring system 2 provided the trinuclear complex [(Ph3P)Pt(µ-
SiR2)]3 (16) in almost quantitative yield, and precursor 4 also
provided significant amounts of the trinuclear complex 27 along
with the unsymmetrical dinuclear complex [(Ph3P)2(H)Pt(µ-
SiR2)(µ-η2-HSiR2)Pt(PPh3)] (26). The bromo-substituted silane
5 provided the unsymmetrical complex 30 in high yield. The
structures of complexes 16, 22, and 30 were confirmed by X-ray
crystallography. Current studies are underway to examine the
reactivity and potential catalytic activity of these di- and
trinuclear complexes.
Preparation of 10,10-Dihydrophenoxasilin (1). A modified
literature procedure was used.8,9 A solution of Ph2O (16.9 g, 99.4
mmol) in 125 mL of anhydrous THF was cooled to -30 °C, and
n-BuLi (120 mL, 2.5 M in hexanes, 300 mmol) was added dropwise.
The solution was warmed to room temperature overnight. The
resulting solution was added dropwise to distilled SiCl4 (26.8 g,
157.9 mmol) in 60 mL of anhydrous THF at -78 °C over 3 h. The
solution was warmed to room temperature and stirred overnight.
The volatile materials were then removed, and 100 mL of freshly
distilled Et2O was added. Caution: Failure to remove unreacted
SiCl4 before treatment with LiAlH4 can result in the formation
of pyrophoric silane, SiH4. Lithium aluminum hydride (2.6 g, 70
mmol) was added slowly at 0 °C over approximately 3 h. After
warming to room temperature overnight, the solution was hydro-
lyzed with saturated aqueous NH4Cl. The bright yellow organic
layer was extracted and washed with water, then dried over MgSO4.
The product was purified by Kugelrohr distillation at 65-67 °C/
0.2 mmHg (3.8 g, ca. 19% yield). Further purification was achieved
by preparative gas chromatography. 1H NMR (500 MHz, CDCl3):
δ 7.58 (dd, 2H, J ) 7, 2, aromatic ArH), 7.47 (dt, 2H, J ) 8, 2,
ArH), 7.22 (d, 2H, J ) 8, ArH), 7.16 (t, 2H, J ) 7, ArH), 4.96 (s,
1
2H, JSiH ) 211 Hz, SiH). 13C{1H} NMR (125 MHz, CDCl3): δ
Experimental Section
160.5, 135.9, 132.2, 122.9, 118.6, 110.7. 29Si{1H} NMR (99 MHz,
DEPT, CDCl3): δ -63.6. IR (neat) (ν, cm -1): 2139 (SiH). GC-
MS (EI, 70 eV): m/z (%) 198 (M+, 76), 197 (M+ - H, 100), 152
(39), 121 (13), 77 (21). HR-MS (EI, 70 eV): calcd for C12H10OSi,
198.05009; found, 198.0501.
General Procedures. All glassware was oven- or flame-dried
prior to use. Reactions were performed (or samples prepared) under
an argon or nitrogen atmosphere either on a double-manifold
Schlenk line or in an inert atmosphere drybox. Diethyl ether was
distilled over Na/benzophenone and THF was distilled over Na/9-
fluorenone before use. Silicon tetrachloride (Acros Organics) and
trichlorosilane (Aldrich) were distilled over anhydrous K2CO3
before use. Diphenyl ether (Fisher Scientific), di-p-tolyl ether (TCI
America or Aldrich), N-methyldiphenylamine (Acros Organics), di-
p-tolylamine (Aldrich or TCI America), lithium aluminum hydride
(or deuteride) powder (Aldrich), n-butyllithium (Aldrich), ethylene-
(bis)triphenylphosphine platinum(0) (Aldrich), and tetrakis(triph-
enylphosphine)platinum(0) (Strem) were used as received. TMEDA
(Aldrich or Acros Organics) was distilled over KOH before use.
2,8-Dibromo-5-methyl-10,10-dihydrophenazasiline (5) was prepared
according to a literature procedure.5 Toluene-d8, benzene-d6, and
methylene chloride-d2 were purchased from Cambridge Isotopes,
Inc., and for experiments involving an inert atmosphere the solvents
were degassed by freeze-pump-thaw vacuum cycles and stored
over activated molecular sieves inside an inert atmosphere drybox.
NMR spectroscopic data were recorded on a Bruker ARX-500
Preparation of 2,8-Dimethyl-10,10-dihydrophenoxasilin (2).
A reaction sequence similar to that described above was used for
the preparation of compound 2 by addition of n-BuLi (2.5 M, 30
mL, 75 mmol) to p-tolyl ether (4.9 g, 25 mmol) in 35 mL of THF
at -78 °C. The resulting solution was then transferred and added
to silicon tetrachloride (3.5 mL, 5.2 g, 31 mmol) in diethyl ether
(50 mL) at -78 °C. The reduction reaction was performed with
LiAlH4 (0.64 g, 17 mmol). After the usual workup, the organic
fraction was purified by Kugelrohr distillation, bp 112-140 °C/
0.2 mm, providing a white solid. Recrystallization from hot ethanol
gave product 2 (0.61 g, 11%), mp 94-95 °C. 1H NMR (300 MHz,
CDCl3): δ 7.36 (m, 2H, ArH), 7.25 (dd, 2H, J ) 8, 2, ArH), 7.09
1
(d, 2H, J ) 8, ArH), 4.91 (s, 2H, JSi-H ) 210 Hz), 2.36 (s, 6H,
ArMe). 13C{1H} NMR (125 MHz, CDCl3): δ 158.6, 135.7, 133.0,
131.9, 118.3, 110.2, 20.7 (Ar-Me). 29Si{1H} NMR (99 MHz, DEPT,
CDCl3): δ -63.5. IR (solid) (ν, cm -1): 2159 (SiH). GC-MS (EI,
70 eV): m/z (%) 226 (M+, 100), 211 (20), 166 (20), 165 (34), 91
(20), 89 (14), 65 (10). Anal. Calcd for C14H14OSi: C, 74.29; H,
6.23. Found: C, 74.22; H, 6.31.
1
spectrometer at 500 MHz for H, 99 MHz for 29Si, 125 MHz for
13C, and 202 MHz for 31P. Proton chemical shifts (δ) are reported
relative to residual protonated solvent: CDCl3 (7.27 ppm), C6D6
(7.15 ppm), CD2Cl2 (5.32 ppm), and C7D8 (2.09 ppm). Carbon
chemical shifts are reported relative to solvent: CDCl3 (77.23 ppm)
and C6D6 (128.39 ppm). Silicon chemical shifts (δ) are reported
relative to external TMS (0 ppm). Phosphorus chemical shifts (δ)
are reported relative to external H3PO4 (0 ppm). Chemical shifts
are given in ppm and coupling constants in Hz. NMR data were
collected at ambient temperature unless otherwise noted.
Preparation of 5-Methyl-10,10-dihydrophenazasiline (3). A
250 mL round-bottom flask was charged with N-methyldipheny-
lamine (12 mL, 68 mmol), TMEDA (21 mL, 136 mmol), and
hexanes (50 mL). A solution of n-BuLi (60 mL, 2.5 M in hexanes,
142 mmol diluted with an additional 34 mL of hexanes) was added
to the flask dropwise at room temperature. The resulting orange-
yellow reaction mixture was refluxed for 4 h, then cooled to room
temperature. The mixture was filtered to remove a soluble fraction,30
and the remaining white insoluble lithium reagent was then
dissolved in Et2O (170 mL). Silicon tetrachloride (10.5 mL, 15.6
g, 91.7 mmol) in Et2O (4 mL) was added over 15 min at -78 °C.
The reaction mixture was warmed to room temperature, and after
24 h, the volatile material was removed. Diethyl ether (120 mL)
was added to the reaction flask, and the contents were cooled to 0
°C followed by slow addition of solid LiAlH4 (1.4 g, 37 mmol).
After stirring overnight, the reaction mixture was quenched with
The majority of the NMR data listed for reaction mixtures formed
from Pt and Si precursors includes selected key resonances that
are characteristic for the particular product, and resonances for
aromatic protons, for example, are not included since there are many
overlapping resonances. Infrared spectra were recorded on a
Thermo-Nicolet Avatar 360 E.S.P. FT-IR spectrometer. GC-MS
(EI) data were recorded on a Hewlett-Packard GC/MS System
Model 5988A, and m/e values of g10% of the base peak are
indicated. The X-ray crystal structure determinations were per-
formed on a Bruker SMART 1K diffractometer equipped with a
(30) Bennett, B. K.; Richmond, T. G. J. Chem. Educ. 1998, 75, 1034.

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3983
saturated NH4Cl (25 mL). The organic layer was extracted with
Et2O and dried over MgSO4. GC analysis of the crude reaction
mixture indicated the desired product comprised 59% of the reaction
products. After removal of the volatile material, a Kugelrohr
distillation (110-115 °C/0.1 mmHg) was attempted but did not
provide adequate separation of 3 from the other impurities. A pure
sample of 3 was obtained by recrystallization of the distilled material
from hexanes/CH2Cl2 (70/30) and gave 5-methyl-10,10-dihydro-
phenazasiline (3) as a tan solid in 4% isolated yield (0.49 g): mp
platinum and hydrosilane precursors. A solution of the platinum
precursor (Ph3P)2Pt(η2-C2H4) (6) was made in approximately 0.5-
0.75 mL of C7D8 and transferred to a NMR tube capped with a
rubber septum. In a separate shortened NMR tube capped with a
septum was placed the hydrosilane precursor in 0.25-0.5 mL of
C7D8. The solutions were then cooled in a dry ice/acetone bath
(-78 °C unless otherwise noted), and the hydrosilane solution was
added by syringe to the NMR tube containing the platinum
precursor. After sitting for a few minutes at low temperature, the
tube was removed, shaken vigorously for a few seconds, then
returned to the cold bath. The sample was then placed in the
precooled NMR magnet at the desired temperature, and NMR data
were then collected at various reaction times and, in some cases,
different temperatures after addition.
1
95-96 °C. H NMR (500 MHz, CDCl3): δ 7.60 (d, 2H, J ) 7,
ArH), 7.44 (t, 2H, J ) 8, ArH), 7.11 (d, 2H, J ) 8, ArH), 7.06 (t,
1
2H, J ) 7, ArH), 4.90 (s, 2H, JSi-H ) 206, SiH), 3.57 (s, 3H,
NCH3). 13C{1H} NMR (125 MHz, CDCl3): δ 151.9, 135.5, 130.9,
120.9, 115.6, 115.5, 38.4 (NMe). 29Si{1H} NMR (99 MHz, DEPT,
CDCl3): δ -55.0. IR (solid) (ν, cm -1): 2097 (Si-H). GC-MS
(EI, 70 eV) m/z (%): 211 (100, M+), 210 (57), 196 (19), 182 (14),
181 (79, M - SiH2), 180 (36), 105 (12). Anal. Calcd for C13H13-
NSi: C, 73.88; H, 6.20. Found: C, 73.79; H, 6.11.
Reaction of (Ph3P)2Pt(η2-C2H4) (6) with 10,10-Dihydrophe-
noxasilin (1): Isolation of [(Ph3P)Pt(µ-η2-H-SiC12H8O)]2 (8). a.
Room-Temperature Reaction. 10,10-Dihydrophenoxasilin (1) (25
mg, 0.13 mmol) was reacted with (Ph3P)2Pt(η2-C2H4) (6) (77 mg,
0.10 mmol) in C6D6 (total volume ) 1 mL) in an inert atmosphere
drybox. Immediately upon addition, gas evolution was observed,
which continued for several minutes. After 10 min a golden-yellow
solid precipitated from the red-brown solution. After approximately
48 h, the golden-yellow solid was filtered and washed twice with
two small portions of C6D6. The solid was dried in vacuo to give
8 (46 mg, 71% yield based on unsolvated 8).
Synthesis of 2,5,8-Trimethyl-10,10-dihydrophenazasiline (4
and 4-d2). Butyllithium (7.1 mL, 15 mmol) was added dropwise
to a flask containing a solution of N-methyl-o,o′-dibromodi-p-
tolylamine (2.8 g, 7.6 mmol)31 in Et2O (50 mL) at -78 °C. After
ca. 30 min the temperature was raised slowly to 0 °C, then the
mixture was stirred for approximately 1 h. The resulting reaction
mixture was added dropwise to a solution of HSiCl3 (1.2 mL, 12
mmol) in Et2O (35 mL). After stirring for 19 h at room temperature,
the reaction mixture was treated slowly with lithium aluminum
hydride (0.7 g, 18.4 mmol). Caution: Failure to remove unre-
acted HSiCl3 before treatment with LiAlH4 can result in the
formation of pyrophoric silane, SiH4. After 48 h more Et2O was
added (100 mL) followed by the slow addition of saturated
ammonium chloride (15 mL). The organic layer was extracted and
the aqueous layer washed with Et2O (80 mL). The combined organic
layers were dried over anhydrous MgSO4. The organic residue was
filtered and the solvent removed under reduced pressure. The crude
product was recrystallized from hot EtOH, and the desired product
(4) was isolated in 42% yield (0.78 g, mp 103.0-104.5 °C). A
similar procedure that utilized silicon tetrachloride instead of
trichlorosilane was also attempted, but significantly lower yields
of 4 were obtained during efforts to remove impurities in the sample.
An analogous reaction was also performed to produce the
deuterium analogue 2,5,8-trimethyl-10,10-dideuterophenazasiline (4-
d2) starting from N-methyl-o,o′-dibromodi-p-tolylamine (2.0 g, 5.4
mmol), n-BuLi (5.4 mL, 13.5 mmol), SiCl4(1 mL, 8 mmol), and
LiAlD4 (0.43 g, 10.2 mmol). After workup, the product was isolated
in 24% yield (0.31 g), mp 102-104 °C.
1
Characterization Data for 8. H{31P} NMR (500 MHz, CD2-
1
2
Cl2): δ 7.7-6.9 (ArH), 3.25 (s, JPtH ) 691, JPtH ) 136, Pt‚‚‚
H‚‚‚Si). 31P{1H} NMR (121 MHz, CD2Cl2): δ 36.6 (s, 1JPtP ) 4369,
3
2JPtP ) 249, JPP ) 59). 1H-29Si HMQC (500 MHz, CD2-
1
Cl2): correlation observed between H resonance at 3.2 ppm and
Si resonance at 128 ppm. IR (solid) (ν, cm -1): 1686 (bridging
Pt‚‚‚H‚‚‚Si). Anal. Calcd for C60H50O2P2Pt2Si2: C, 54.95; H, 3.84.
Found: C, 56.54; H, 3.76 (may contain benzene-d6 of solvation,
C60H50O2P2Pt2Si2‚C6D6: C, 56.89; H, 3.47).
In a separate experiment, a solution of 1 (23 mg, 0.12 mmol, 1
mL of C7D8) was added to 6 (76 mg, 0.10 mmol). Gas evolution
was observed immediately. The red-brown reaction mixture was
transferred to a NMR tube and data collection begun within 10
min of initial mixing. After 30 min a golden-yellow solid (8, 46
mg) was present in the NMR tube.
Selected NMR Data Collected Starting 10 min after Mixing.
1H NMR (500 MHz, C7D8, 300 K): δ 5.85 (m, tentative assignment,
SiH for 9), 5.36 (br, overlapping with C2H4, SiH for 7), 5.25 (s,
C2H4), 5.06 (s, unreacted 1), 4.50 (s, H2), -1.86 (br s, 1JPtH ) 973,
PtH for 7). 31P{1H} NMR (202 MHz, C7D8, 300 K): δ 38.7 (s,
1JPtP ) 2134, tentative assignment, 9), 30.6 (s, 10, minor amount),
25.9 (s, OPPh3), 11.2 (br, covering range 0-20 ppm).
After 20 min the 1H NMR and 31P spectra were essentially
unchanged, but the signals at 5.36 and -1.86 in the proton spectrum
had decreased considerably in intensity. After 4 h, the 31P spectrum
showed only a minor signal for 9 and a larger resonance for 10. A
broad peak was present at 2.8 ppm (range -5 to 10 ppm). After
the golden-yellow solid was removed, the remaining amber solution
was analyzed by 31P{1H} NMR spectroscopy. 31P{1H} NMR data
1
Characterization Data for 4. H NMR (300 MHz, C6D6): δ
7.33 (d, 2H, J ) 2, ArH), 7.06 (dd, 2H, J ) 8, 2, ArH), 6.71 (d,
2H, J ) 8, ArH), 5.15 (s, 2H, 1JSiH ) 204, SiH), 2.97 (s, 3H, NCH3),
2.16 (s, 6H, ArCH3). 13C{1H} NMR (75 MHz, C6D6): δ 150.6,
136.5, 131.9, 129.8, 115.9, 115.7, 38.2 (NCH3), 20.8 (ArCH3). 29
-
Si{1H} NMR (99 MHz, DEPT, C6D6): δ -55.2. IR (solid) (ν, cm
-1): 2113 (SiH). GC-MS (EI, 70 eV): m/z (%) 239 (M+, 100),
238 (42), 224 (24), 209 (78), 194 (11), 119 (10).
Characterization Data for 4-d2. 1H NMR (300 MHz, CDCl3):
δ 7.40 (d, 2H, J ) 2, ArH); 7.23 (dd, 2H, J ) 8, 2, ArH), 6.99 (d,
for the amber solution after removal of 8 (202 MHz, C7D8, 300 K,
1
after 6 days): δ 67.9 (s, minor component, 11), 30.6 (s, JPtP
)
2
2H, J ) 8, ArH), 3.51 (s, 3H, NCH3), 2.34 (s, 6H, ArCH3). H
1701, 10), 26.5 (OPPh3), 9.4 (br, range 5-15 ppm). 31P{1H} NMR
data for the amber solution after removal of 8 (202 MHz, C7D8,
183 K, after 6 days): δ 30.5 (br, 10), 27.9 (b, OPPh3), 11.7 (s,
1JPtP ) 3819, Pt(PPh3)4), -6.4 (s, PPh3).
1
29
NMR (76 MHz, CHCl3/CDCl3): δ 4.92 (s, SiD, JSiD ) 32).
-
Si{1H} NMR (99 MHz, DEPT, C6D6): δ -55.6 (pent, 1JSiD ) 31).
IR (solid) (ν, cm -1): 1551 (SiD). Anal. Calcd for C15H15D2NSi:
C, 74.63; H, 7.93. Found: C, 74.42; H, 7.24.
b. Low-Temperature Reaction. A solution of 1 (16 mg, 0.081
mmol, 0.25 mL C7D8) was added to a solution of 6 (58 mg, 0.078
mmol, 0.75 mL of C7D8) at 77 K. After a few minutes the tube
was transferred to a cold bath at 195 K for approximately 1 min.
Then the contents were shaken vigorously for a few seconds. The
NMR tube was then transferred to a precooled NMR magnet at
223 K.
General Procedure for Low-Temperature Addition Reac-
tions. The reactions are typically run in a 1:1 ratio between the
(31) (a) Gilman, H.; Zuech, E. A. J. Org. Chem. 1959, 24, 1394. (b)
Gilman, H.; Zuech, E. A. J. Org. Chem. 1961, 26, 2013. (c) A modified
procedure decribed for the incorporation of a N-Et group was used: Gilman,
H.; Zuech, E. A. J. Org. Chem. 1961, 26, 3481.

3984 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
1
Selected NMR Data Collected Just after Mixing. H NMR
(500 MHz, C7D8, 223 K): δ 5.41 (m, overlapping with C2H4, SiH
for 7), 5.28 (s, C2H4), 4.54 (s, minor component, H2), 2.69 (s, 2JPtH
) 30, C2H4 for 6), -1.50 (dd, 1JPtP ) 973, 2JPH ) 156 (trans), 16
(cis), PtH for 7). 31P{1H} NMR (202 MHz, C7D8, 223 K): δ 34.2
10,10-dihydrophenoxasilin (2) (25 mg, 0.11 mmol) dissolved in
C7D8 (0.25 mL) was added to an NMR tube containing a solution
of (Ph3P)2Pt(η2-C2H4) 6 (83 mg, 0.11 mmol) in C7D8 (0.75 mL).
A small amount of gas evolution was observed, and the tube was
shaken for about 10 s to thoroughly mix the contents, providing a
reddish-amber solution. NMR experiments were begun within 10
min of initial mixing.
1
1
(br s, JPtP ) 1788, P trans to Si for 7), 34.0 (s, JPtP ) 3714, 6),
1
33.4 (br s, JPtP ) 2422, P trans to H for 7), 25.9 (s, OPPh3).
The H and 31P NMR spectra remained unchanged for 3 h at
Selected NMR Data Collected 10 min after Mixing. 1H NMR
(500 MHz, C7D8, 300 K): δ 5.83 (m, SiH, minor component,
tentative assignment, 13), 5.25 (s, C2H4), 5.13 (s, minor amount of
unreacted 2), 4.50 (s, H2), 0.36 (br, 1JPtH ≈ 640, PtH for 15), -1.8
(br s, minor component, 1JPtH ≈ 980 Hz, tentative assignment, 12).
31P{1H} NMR (202 MHz, C7D8, 300 K): δ 29.2 (s, minor
component, tentative assignment, 14), 24.3 (s, OPPh3), 19.2 (br,
covering range 12-25 ppm).
1
1
223 K. After 3 h the temperature was raised to 243 K and the H
and 31P NMR spectra obtained were similar to the data collected
at 223 K, but the signals for 6 and 7 had broadened. The NMR
tube contained a yellow solution (no solid was present at this time)
and was quickly removed and shaken, then immediately returned
to the precooled magnet. Further broadening of the signals occurred
when the temperature was raised to 263 K (4.5 h after mixing)
then 283 K (5 h after mixing).
Selected NMR Data Collected 45 min after Mixing. 31P{1H}
1
Selected NMR Data Collected 5 h after Mixing. 1H NMR (500
MHz, C7D8, 283 K): δ 5.43 (s, overlapping with C2H4, SiH for 7),
5.36 (br, C2H4), 4.51 (s, H2), -1.79 (br s, 1JPtH ) 972, PtH for 7).
31P{1H} NMR (202 MHz, C7D8, 283 K): δ 22 (br, range 5-40
ppm), 24.9 (s, OPPh3), minor resonances observed between 4 and
17 ppm (unassigned). A minor resonance was also observed at 29.3
(s, 10).
After 5 h, the NMR tube was again quickly removed and shaken,
then immediately returned to the NMR magnet. The tube now
contained a yellow solution and a yellow precipitate. The temper-
ature was raised to 303 K after 5.5 h, and the 31P{1H} NMR
spectrum was essentially identical to the data collected at 283 K
except for a minor resonance at 66 ppm tentatively assigned to 11.
The 1H NMR spectrum recorded at 303 K did not show any signals
attributable to complex 7.
After 6.25 h the temperature was lowered to 223 K, then to 183
K. 31P{1H} NMR data collected 6.25 h after mixing (202 MHz,
C7D8, 223 K): δ 65.5 (s, minor component, 11), 29.7 (s, minor
component, 10), 25.9 (s, OPPh3), 5 (br, range -15 to 40 ppm),
several unassigned minor resonance observed between 4 and 25
ppm. 31P{1H} NMR data collected 6.75 h after mixing (202 MHz,
C7D8, 183 K): δ 26.1 (s, OPPh3), 10.3 (s, 1JPtP ) 3833, Pt(PPh3)4),20
-7.8 (s, PPh3).
c. High-Temperature Reaction. A solution of 1 (27 mg, 0.14
mmol, 0.25 mL of C7D8) was added to a solution of 6 (97 mg,
0.13 mmol, 0.75 mL of C7D8) at room temperature. Then the NMR
tube containing the reaction mixture was immediately placed
in a preheated NMR magnet at 323 K. Selected NMR data collected
5 min after mixing: 1H NMR (500 MHz, C7D8, 323 K): δ 5.18
NMR (C7D8, 202 MHz, 300 K): δ 68.7 (s, 16), 29.2 (s, JPtP
)
1621, tentative assignment, 14), 24.3 (s, OPPh3), 18.9 (br, range
12-25 ppm). The proton and phosphorus NMR spectra remained
essentially unchanged until approximately 3.5 h after mixing, when
the temperature was lowered to approximately 223 K.
1
Selected NMR Data Collected 3.5 h after Mixing. H NMR
(500 MHz, C7D8, 225 K): δ 5.29 (s, C2H4), 4.55 (s, H2), 2.71 (br,
tentative assignment, Pt‚‚‚H‚‚‚Si for 15), -5.04 (br s, 1JPtH ) 544
Hz, Pt-H for 15). 31P{1H} NMR (C7D8, 202 MHz, 225 K): δ
68.9 (s, 16), 30.2 (br, Pt(PPh3) for 15), 28.9 (s, 14), 25.1 (s, OPPh3),
20.3 (br, Pt(PPh3)2 for 15), -5 (br, PPh3).
After 4 h the temperature was warmed to 300 K and the 1H and
31P NMR spectra looked essentially identical to the data collected
at room temperature approximately 1 h after mixing. After 6 days,
NMR measurements were again obtained on the reaction solution.
No solid was present in the NMR tube.
Selected NMR Data Collected 6 days after Mixing. 31P{1H}
1
1
NMR (202 MHz, C7D8, 300 K): δ 68.7 (s, JPtP ) 3475, JPtP
)
3
1
466, JPP ) 76, 16, major component), 29.2 (s, JPtP ) 1623 Hz,
14), 24.3 (s, OPPh3), 15.0 (br, 15). 1H NMR (500 MHz, C7D8, 223
K): δ 5.29 (s, C2H4), -5.04 (br s, JPtH ) 544, PtH for 15). 31P-
1
{1H} NMR (202 MHz, C7D8, 223 K): δ 68.7 (s, 16), 30.3 (t, 1JPtP
) 4081, 2JPtP ) 198, 3JPP ) 27, Pt(PPh3) for 15), 28.9 (s, 14), 25.2
1
3
(s, OPPh3), 20.3 (d, JPtP ) 3504, JPP ) 27, Pt(PPh3)2 for 15).
31P{1H} NMR (202 MHz, C7D8, 183 K): δ 68.9 (br, 1JPtP ) 3425,
16), 30.3 (br, 15), 28.6 (br, 14), 25.4 (s, OPPh3), 20.2 (br, 15),
1
10.2 (s, JPtP ) 3841, Pt(Ph3P)4), -7.9 (s, PPh3).
Two weeks after initial mixing, additional NMR experiments
were performed on the reaction solution. No solid was observed in
the solution. 29Si{1H}NMR (99 MHz, C7D8, 300 K): δ 244.6 (s,
1JPtSi ) 977, 16). 195Pt{1H}(108 MHz, C7D8, 300 K): δ -4353
(m).
1
2
(br s, C2H4), 4.49 (s, H2), 3.21 (s, JPtH ) 682, JPtH ) 128, Pt‚‚‚
H‚‚‚Si for 8). 31P{1H} NMR (202 MHz, C7D8, 323 K): δ 68.3 (s,
1JPtP ) 3454, JPtP ) 466, JPP ) 76, 11), 30.6 (s, JPtP ) 1625,
10), 30 (br, range 5-50 ppm), 25.6 (s, OPPh3). Some minor
unassigned resonances were observed between 10 and 40 ppm.
In a similar experiment, a solution of 1 (40 mg, 0.20 mmol, 0.10
mL of C7D8) was added to a solution of 6 (146 mg, 0.20 mmol,
1.0 mL of C7D8) at room temperature. Then the NMR tube
containing the reaction mixture was immediately placed in a
preheated NMR magnet at 323 K. After NMR data collection, a
light golden solid (8) was observed in the tube (92 mg crude yield,
72% based on Pt).
2
3
1
Approximately 3 months after initial mixing, evaporation of the
solvent provided glassy dark X-ray-quality red crystals (92 mg) of
16 (contains 2.5 molecules of toluene-d8 solvate). NMR spectro-
scopic data for 16: 31P{1H} (202 MHz, C7D8, 300 K): δ 68.7 (s,
2
3
1JPtP ) 3474, JPtP ) 466, JPP ) 76). 29Si{1H} (99 MHz, C7D8,
300 K): δ 239.6 (s, 1JSiPt ) 976). 195Pt{1H} NMR (107 MHz, C7D8,
300 K): δ - 4352 (m). The sample contains an OPPh3 impurity.
b. Low-Temperature Reaction. A solution of 2,8-dimethyl-
10,10-dihydrophenoxasilin (2) (25 mg, 0.11 mmol) dissolved in
C7D8 (0.25 mL) was added to an NMR tube containing a solution
of (Ph3P)2Pt(η2-C2H4) (6) (83 mg, 0.11 mmol) in C7D8 (0.75 mL)
at 77 K. After several minutes the NMR tube was placed in a 195
K bath for approximately 5 min. The tube was then shaken
vigorously, then placed in a precooled magnet at 223 K. NMR data
collection was begun within 5 min, and after ∼2.5 h, the temperature
was raised from 223 to 303 K, in 20 K increments over a 2 h period.
NMR data collection was performed at each temperature.
Selected 31P{1H} NMR (202 MHz, C7D8, 183 K, 7 h after
mixing): δ 26.1 (s, OPPh3), 10.3 (s, Pt(PPh3)4), -7.8 (s, PPh3).
195Pt{1H} NMR (107 MHz, C7D8, 300 K, 9 h after addition): δ
-4375 (m). The trinuclear complex 11 was not isolated from the
reaction mixture due to the difficulty in separation of the low yield
of material in the presence of a significant amount of PPh3 and
Pt(PPh3)4 as well as other minor impurities.
Reaction of (Ph3P)2Pt(η2-C2H4) (6) with 2,8-Dimethyl-10,10-
dihydrophenoxasilin (2): Isolation of [(Ph3P)Pt(µ-SiC14H12O)]3
(16). a. Room-Temperature Reaction. A solution of 2,8-dimethyl-
1
Selected NMR Data Collected 5-10 min after Mixing. H
NMR (500 MHz, C7D8, 223 K): δ 5.59 (m, Si-H for 12), 5.29 (s,

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
C2H4), 5.1 (br s, possibly unreacted 2), 4.55 (s, H2), 2.67 (s, JPtH
Organometallics, Vol. 25, No. 16, 2006 3985
2
1
(s, minor component, H2), 2.64 (s, 6), -1.38 (dd,, JPtH ) 987,
1
2
) 30, C2H4 for unreacted 6), -1.48 (dd, JPtH ) 977, JPH ) 154
(trans), 19 (cis), PtH for 12). 31P{1H} NMR (202 MHz, C7D8, 223
K): δ 33.9 (s, 1JPtP ) 3712, unreacted 6), 33.3 (resonance probably
2JPH ) 156 (trans), 19 (cis), PtH for 17). 31P{1H} NMR (202 MHz,
1
1
C7D8, 243 K): δ 36.4 (br s, JPtP ) 1808, 17), 35.4 (br s, JPtP
)
1
2456, 17), 34.2 (s, JPtP ) 3723, unreacted 6), 25.6 (s, OPPh3).
1
1
overlapping with unreacted 6, JPtP ) 1761, P trans to Si for 12),
Selected NMR Data Collected 2.75 h after Mixing. H NMR
(500 MHz, C7D8, 263 K): δ 5.27 (s, C2H4), 4.85 (br s, SiH for
17), 4.53 (s, minor component, H2), 2.59 (br, 6), -1.47 (br d, 1JPtH
) 985, 2JPH ) 152 (trans), PtH for 17). 31P{1H} NMR (202 MHz,
C7D8, 263 K): δ 35.5 (br, 17), 34.4 (s, 1JPtP ) 3733, unreacted 6),
25.6 (s, OPPh3).
1
2
33.2 (d, JPtP ) 2439, JPP ) 11, P trans to H for 12), 25.4 (s,
OPPh3).
1
Selected NMR Data Collected 2.75 h after Mixing. H NMR
(500 MHz, C7D8, 243 K): 5.61 (br m, SiH for 12), 5.47 (t,
unassigned), 5.28 (s, C2H4), 4.62 (m, unassigned minor component),
1
2
4.54 (s, H2), 2.64 (s, unreacted 6), -1.58 (br d, JPtH ) 975, JPH
) 143 (trans), PtH for 12), -1.69 (dd, probable PtH, unassigned
minor component, 2JPH ) 155, 24). 31P{1H} NMR (202 MHz, C7D8,
Selected NMR Data Collected 4 h after Mixing. 1H NMR (500
MHz, C7D8, 283 K): δ 5.26 (br s, C2H4), 4.85 (br m, SiH for 17),
1
4.51 (s, H2), 2.59 (br, 6), -1.56 (br s, JPtH ) 987, PtH for 17).
1
243 K): δ 34.2 (unreacted 6), 33.8 (br s, JPtP ) 1754, 12), 33.5
31P{1H} NMR (202 MHz, C7D8, 283 K): δ 32 (br, range 15-50
ppm), 24.7 (s, OPPh3). Several minor unassigned resonances were
observed between 5 and 40 ppm.
1
(br s, JPtP ) 2453, 12), 32.9 (br, unidentified minor component),
25.2 (s, OPPh3).
Selected NMR Data Collected 3.25 h after Mixing. H NMR
1
Selected NMR Data Collected 5.5 h after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 303 K): δ 66.2 (s, minor component, 21),
29.8 (s, 1JPtP ) 1628, 19), 28 (br, range 0-50 ppm), 24.5 (s, OPPh3).
Several minor unassigned resonances were observed between 0 and
2
(500 MHz, C7D8, 263 K): δ 5.68 (br s, JPtH ) 64, SiH for 12),
5.46 (t, J ) 49, unassigned), 5.27 (br s, C2H4), 4.59 (t, J ) 27,
1
unassigned), 4.52 (s, H2), 2.58 (br, 6), -1.68 (br d, JPtH ) 978,
2JPH ) 133, PtH for 12). 31P{1H} NMR (202 MHz, C7D8, 263 K):
1
30 ppm. No hydride resonances for 17 were observed in the H
1
1
δ 34.3 (br, 6), 33.7 (br, JPtP ) 2326, 12), 32.7 (s, JPtP ) 1777,
12), 24.9 (s, OPPh3).
Selected NMR Data Collected 3.75 h after Mixing. H NMR
NMR spectrum at 303 K.
After 24 h the NMR tube contained an orange solution and a
yellow solid (22). The soluble fraction was found to contain a
mixture of unreacted 6, OPPh3, and Pt(PPh3)4 along with a minor
amount of 21 and PPh3.
1
(500 MHz, C7D8, 283 K): δ 5.60 (minor component, 12), 5.46
(minor component, unassigned), 5.25 (br s, C2H4), 4.61 (t, minor
1
component, unassigned), 4.51 (s, H2), -1.77 (br s, JPtH ) 973,
Selected NMR Data Collected 24 h after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 223 K): δ 65.7 (s, minor component, 21),
34.0 (br s, 6), 29.7 (s, 19), 25.6 (s, OPPh3), 25 (br, range -10 to
50 ppm). Several minor unassigned resonances were observed
between 0 and 25 ppm. 31P{1H} NMR (202 MHz, C7D8, 183 K):
1
12), -7.71 (d, JPtH ) 729, JPH ) 16, PtH, unassigned minor
component). 31P{1H} NMR (202 MHz, C7D8, 283 K): δ 32.7 (s,
minor component, unassigned), 24.7 (s, OPPh3), 25.0 (br, range
0-50 ppm), 4.2 (s, minor component, unassigned).
1
The H NMR data collected at 303 K (5 h after mixing) were
1
δ 33.5 (s, 6), 25.7 (s, OPPh3), 10.2 (s, JPtP ) 3834, Pt (PPh3)4),
essentially the same as the 1H NMR data collected at 283 K listed
above, but the Si-H and Pt-H resonances had almost disappeared.
31P{1H} NMR (202 MHz, C7D8, 303 K, 5 h after mixing): δ 68.7
(s, minor component, 16), 29.2 (s, minor component, 14), 24.5 (s,
OPPh3), 22.2 (br, range 0-50 ppm).
-7.8 (s, minor component, PPh3).
b. Room-Temperature Reaction. A solution of 5-methyl-10,-
10-dihydrophenazasiline (3) (15 mg, 0.071 mmol) dissolved in C7D8
(0.25 mL) was added to a solution of (Ph3P)2Pt(η2-C2H4) (6) (53
mg, 0.071 mmol) in C7D8 (0.75 mL). Gas evolution was observed,
the mixture was transferred to a NMR tube, and NMR experiments
were begun within 10 min of initial mixing.
After the NMR experiments were completed, pentane (∼3 mL)
was added to the reaction solution and the NMR tube was placed
in a freezer at -40 °C for several weeks. An orange-red solid was
observed. 31P NMR spectroscopic data of the solid dissolved in
C7D8 at room temperature and -50 °C showed the presence of
several components. Resonances for 14 (minor component), 15
(major component), 16 (minor component), OPPh3, and PPh3 were
observed in the 31P NMR spectra (for δ and J values see above).
Complexes 14-16 were not isolated from the reaction mixture.
Reaction of (Ph3P)2Pt(η2-C2H4) (6) with 5-Methyl-10,10-dihy-
drophenazasiline (3): Isolation of [(Ph3P)Pt(µ-η2-H-SiC13H12N)]2
(22). a. Low-Temperature Reaction. A solution of 5-methyl-10,-
10-dihydrophenazasiline (3) (15 mg, 0.071 mmol) in C7D8 (ap-
proximately 0.25 mL) was added to a solution of (Ph3P)2Pt(η2-
C2H4) (6) (53 mg, 0.071 mmol) in C7D8 (∼0.75 mL) cooled in a
liquid N2 bath (77 K). The tube was then placed in a dry ice/acetone
bath (195 K). Once the solution had melted, the reaction tube was
shaken several times to mix the contents. The tube was then placed
in a precooled NMR magnet (223 K), and NMR experiments were
begun within 5 min.
Selected NMR Data Collected 10 min after Mixing. 1H NMR
(500 MHz, C7D8, 300 K): δ 5.25 (br s, C2H4), 4.86 (br s, tentative
1
assignment, SiH for 17), 4.50 (s, H2), -1.64 (br s, JPtH ) 990,
PtH for 17). 31P{1H} NMR (202 MHz, C7D8, 300 K): δ 66.2 (s,
minor component, 21), 37.9 (s, tentative assignment, minor
component, 18), 29.9 (s, 1JPtP ) 1630, minor component, 19), 24.8
(s, minor component, unassigned), 24.3 (s, OPPh3), 22 (br, range
1
10-40 ppm). The H NMR spectrum was essentially the same at
1.5 and 3 h after mixing, but the peaks at 4.86 and -1.64 eventually
disappeared and a new broad region was present near 0 ppm that
was tentatively assigned to an averaged Pt‚‚‚H‚‚‚Si signal for 20.
The 31P{1H} NMR spectrum was similar after 1.5 and 3 h, but the
signal at 37.9 ppm eventually disappeared.
1
Selected NMR Data Collected 4.5 h after Mixing. H NMR
(500 MHz, C7D8, 223 K): δ 5.29 (s, C2H4), 4.55 (s, H2), -5.98
(br s, JPtH ≈ 570, PtH for 20). 31P{1H} NMR (202 MHz, C7D8,
1
1
2
3
223 K): δ 65.7 (s, JPtP not resolved, JPtP ) 491, JPP ) 74, 21),
30.7 (br s, 1JPtP ) 4174, 2JPtP ) 278, PtPPh3 for 20), 29.7 (s, minor
component, 19), 25.1 (s, OPPh3), 18.6 (br s, 1JPtP ) 3666, Pt(PPh3)2
for 20). (Pt‚‚‚H‚‚‚Si for 20 not located/observed.)
1
Selected NMR Data Collected 5 min after Mixing. H NMR
(500 MHz, C7D8, 223 K): δ 5.29 (s, C2H4), 4.86 (m, SiH for 17),
2
1
2
2.70 (s, JPtH ) 60, C2H4 for 6), -1.28 (dd, JPtH ) 988, JPH
)
Selected NMR Data Collected 6 h after Mixing. 31P{1H} NMR
(202 MHz, C7D8, 183 K): δ 65.5 (s, minor component, 21), 31.9
156 (trans), 20 (cis), PtH for 17). 31P{1H} NMR (202 MHz, C7D8,
223 K): δ 36.6 (d, 1JPtP ) 1818, 2JPSi ) 153, 2JPP ) 10, P trans to
1
2
1
2
(br s, JPtP ) 4088, JPtP ) 298, PtPPh3 for 20), 25.5 (s, OPPh3),
Si for 17), 35.2 (d, JPtP ) 2447, JPP ) 10, P trans to H for 17),
18.6 (br s, JPtP ) 3652, Pt(PPh3)2 for 20), 10.2 (s,1JPtP ) 3831,
1
1
34.0 (s, JPtP ) 3714, unreacted 6), 25.8 (s, OPPh3). The spectra
Pt(PPh3)4), -7.8 (s, PPh3).
remained unchanged almost 2 h after mixing.
Selected NMR Data Collected 2 h after Mixing. 1H NMR (500
MHz, C7D8, 243 K): δ 5.28 (s, C2H4), 4.85 (m, SiH for 17), 4.54
After 24 h, a yellow crystalline solid was observed in the NMR
tube along with a red solution. X-ray crystallography revealed the

3986 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
structure of the yellow solid to be that of the symmetrical dimer
22. The structure also contained one molecule of C7D8.
the resonances for 23 were now broader and the doublet pattern
was no longer visible.
Selected NMR Data Collected 3 h after Mixing. 1H NMR (500
MHz, C7D8, 263 K): δ 5.27 (br s, C2H4), 4.96 (br, SiH for 23),
4.53 (s, H2), 2.59 (br s, C2H4 for 6), -1.47 (br d, 1JPtH ) 993, 2JPH
) 152 (trans), PtH for 23). 31P{1H} NMR (202 MHz, C7D8, 263
K): δ 50.4 (br, Pt(PPh3)3), 35.5 (br, 23), 34.4 (s, 6), 24.9 (s, OPPh3).
Selected NMR Data Collected 4 h after Mixing. 1H NMR (500
MHz, C7D8, 283 K): δ 5.26 (br, C2H4), 4.96 (m, minor component,
SiH for 23), 4.51 (s, H2), 2.6 (br, C2H4 for 6), -1.54 (br, PtH for
23). 31P{1H} NMR (202 MHz, C7D8, 283 K): δ 40 (br, range -5-
In a similar experiment, 10,10-dihydrophenazasiline (3) (11 mg,
0.052 mmol) dissolved in C7D8 (0.25 mL) was added to a solution
of (Ph3P)2Pt(η2-C2H4) (6) (40 mg, 0.054 mmol) in C7D8 (0.50 mL).
After 48 h, yellow microcrystalline 22 was observed (22 mg, 55%
based on 22‚C7D8). 1H NMR (500 MHz, CD2Cl2, 300 K): δ 7.38-
6.55 (ArH), 3.26 (s, NMe), 2.36 (s, Pt satellites not resolved,
tentative assignment, Pt‚‚‚H‚‚‚Si). 31P{1H} NMR (202 MHz, CD2-
Cl2 300 K): δ 36.9 (s, JPtP ) 4349, JPtP ) 265, JPP ) 60). IR
(solid, cm -1): 1687 (Pt‚‚‚H‚‚‚Si). Anal. Calcd for C61H54N2P2Si2-
Pt2‚C7D8: C, 57.73; H, 4.92. Found: C, 57.63; H, 4.33.
c. High-Temperature Reaction. A solution of 5-methyl-10,-
10-dihydrophenazasiline (3) (25 mg, 0.12 mmol) in C7D8 (∼0.25
mL) was added to a solution of (Ph3P)2Pt(η2-C2H4) (6) (90 mg,
0.12 mmol) in C7D8 (∼1 mL). Vigorous gas evolution was observed
immediately upon addition, and the solution turned a red-amber
color. The tube was shaken to mix the contents, then placed in a
preheated (50 °C) NMR magnet. NMR data collection was begun
within a few minutes.
1
2
3
1
70 ppm), 34.6 (br, JPtP ) 3723, 6), 29.7 (s, minor component,
25), 24.6 (s, OPPh3).
Selected NMR Data Collected 4.5 h after Mixing. The H
1
NMR data (303 K) did not exhibit hydride resonances for 23 or
other complexes. The 31P{1H} NMR data (303 K) were similar to
the data collected at 4 h (283 K), but the signal at 34 ppm was
broader. In addition, two minor resonances were present at 67.4
(s, 27) and 51.3 (unassigned).
Selected NMR Data Collected 5 h after Mixing. 1H NMR (500
MHz, C7D8, 223 K): δ 5.29 (br s, C2H4), 4.55 (s, H2), -6.06 (t,
1
Selected NMR Data Collected 5 min after Mixing. The H
2
1JPtH ) 565, JPH ) 13, PtH for 26). 31P{1H} NMR (202 MHz,
NMR data collected at 323 K were essentially the same as the data
for the room-temperature reaction collected just after mixing, but
there were no resolved hydride resonances observed. 31P{1H} NMR
C7D8, 223 K): δ 66.9 (s, minor component, 27), 34.0 (s, 6), 30.2
1
2
3
(t, JPtP ) 4058, JPtP ) 253, JPP ) 28, PtPPh3 for 26), 28.5 (s,
minor component, 25), 25.6 (s, OPPh3), 19.4 (d, 1JPtP ) 3682, 3JPP
) 29, Pt(PPh3)2 for 26).
1
2
(202 MHz, C7D8, 323 K): δ 66.4 (s, JPtP ) 3528, JPtP ) 490,
3JPP ) 76, 21), 29.9 (s, JPtP ) 1622, 19), 29.0 (br s, minor
1
Selected NMR Data Collected 5 h after Mixing. 1P{1H} NMR
(202 MHz, C7D8, 183 K): δ 33.5 (s, 6), 30.5 (br, 26), 24.4 (s,
OPPh3), 19.4 (br, 26), 10.2 (s, JPtP ) 3829, Pt(PPh3)4).
component, unassigned), 24.2 (s, OPPh3), 24 (br, range 10-40
ppm). Several small unassigned peaks were observed between 6
and 14 ppm. The spectra remained unchanged 1.5 h after mixing.
1
The major Pt-Si-containing product 26 from the reaction could
not be isolated in pure form from the complex reaction mixture.
(Some of unreacted 6 remained, but 4 was not present.)
1
Selected NMR Data Collected 2.5 h after Mixing. H NMR
(500 MHz, C7D8, 223 K): δ 5.29 (s, C2H4), 4.55 (s, H2), -6.01
(br s, 1JPtH ) 590, minor component, Pt-H for 20). 31P{1H} NMR
b. Room-Temperature Reaction. A solution of 2,5,8-trimethyl-
10,10-dihydrophenazasiline (4) (26 mg, 0.11 mmol) dissolved in
C7D8 (0.25 mL) was added to a solution of (Ph3P)2Pt(η2-C2H4) (6)
(73 mg, 0.098 mmol) in C7D8 (0.75 mL). Gas evolution was
observed immediately, the mixture was transferred to a NMR tube,
and NMR experiments were begun within 15 min of initial mixing.
Selected NMR Data Collected 15 min after Mixing. 1H NMR
(500 MHz, C7D8, 300 K): δ 5.24 (br s, C2H4), 4.50 (s, H2), -0.2
(br s, tentative assignment, averaged Pt‚‚‚H‚‚‚Si for 23). 31P{1H}
NMR (202 MHz, C7D8, 300 K): δ 67.4 (s, 1JPtP not resolved, minor
component, 27), 38.3 (s, 1JPtP not resolved, minor component, 24),
1
2
(202 MHz, C7D8, 223 K): δ 65.7 (s, JPtP ) 3467, JPtP ) 490,
3JPP ) 77, 21), 37.6 (d, minor component, 18), 29.7 (s, 19), 25.3
(s, OPPh3), 18.6 (br s, unassigned), 10 (br, range -15 to 45,
unsymmetrical). Several small unassigned peaks were observed
between 3 and 50 ppm (Pt‚‚‚H‚‚‚Si for 20 not located/observed).
Selected NMR Data Collected 3.5 h after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 183 K): δ 65.5 (s, minor component, 21),
1
25.5 (s, OPPh3), 10.2 (s, JPtP ) 3838, Pt(PPh3)4), -7.8 (s, PPh3).
Selected NMR Data Collected 6 h after Mixing. 29Si{1H} NMR
1
(99 MHz, C7D8,300 K): δ 254.6 (s, JPtSi ) 964, 21).
Reaction of (Ph3P)2Pt(η2-C2H4) (6) with 2,5,8-Trimethyl-10,-
10-dihydrophenazasiline (4). a. Low-Temperature Reaction. A
solution of 2,5,8-trimethyl-10,10-dihydrophenazasiline (4) (20 mg,
0.084 mmol) in C7D8 (approximately 0.25 mL) was added to a
cooled solution of (Ph3P)2Pt(η2-C2H4) (6) (63 mg, 0.084 mmol) in
C7D8 (∼0.75 mL) at 77 K. After the mixture had frozen, the tube
was placed in a -78 °C bath for ca. 2 min before it was removed,
shaken to mix contents, and placed into a precooled NMR magnet
at 223 K. Gas evolution was observed in the reaction solution. NMR
experiments were begun within about 5 min of mixing (precursor
4 was consumed, but some of 6 remained).
1
29.8 (s, JPtP ) 1626, 25), 26 (br, range 10-50 ppm), 24.4 (s,
OPPh3). Several minor unassigned resonances were observed
1
between 3 and 45 ppm. The H and 31P{1H} NMR spectra were
essentially the same 1 h after mixing, but several of the minor
resonances in the 31P spectrum were now absent.
Selected NMR Data Collected 1.5 h after Mixing. H NMR
1
(500 MHz, C7D8, 223 K): δ 5.29 (br s, C2H4), 4.55 (s, H2), -6.05
1
2
(br t, JPtH ) 568, JPH ≈ 13, PtH for 26). 31P{1H} NMR (202
MHz, C7D8, 223 K): δ 66.9 (s, minor component, 27), 30.2 (t,
1JPtP ) 4051, JPtP ) 282, JPP ) 28, PtPPh3 for 26), 29.6 (s, 25),
2
3
1
3
25.3 (s, OPPh3), 19.4 (d, JPtP ) 3676, JPP ) 29, Pt(PPh3)2 for
26). A broadened baseline region was observed between -10 and
45 ppm. Several minor unassigned resonances were also observed
between 5 and 40 ppm.
Selected NMR Data Collected 2.5 h after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 183 K): δ 30.4 (br, 26), 28.4 (br, 25),
1
Selected NMR Data Collected 5-10 min after Mixing. H
NMR (500 MHz, C7D8, 223 K): δ 5.29 (s, C2H4), 4.96 (m, SiH
for 23), 4.55 (s, minor component, H2), 2.69 (s, C2H4 for 6), -1.31
(dd, 1JPtH ) 996, 2JPH ) 155 (trans), 21 (cis), PtH for 23). 31P{1H}
1
2
NMR (202 MHz, C7D8, 223 K): δ 35.7 (d, JPtP ) 1798, JPP
)
10, P trans to Si for 23), 35.3 (d,1JPtP ) 2455, JPP ) 10, P trans
to H for 23), 34.0 (s, 1JPtP ) 3714, 6), 25.7 (s, OPPh3). The 1H and
31P{1H} NMR spectra remained unchanged after 1 h at 223 K.
2
1
25.6 (s, OPPh3), 19.3 (br, 26), 10.2 (s, JPtP ) 3838, Pt(PPh3)4),
-7.8 (s, PPh3).
The room-temperature 1H and 31P{1H} NMR spectra taken after
3.25 h were essentially unchanged from the room-temperature data
collected between 15 min and 1 h.
Selected NMR Data Collected 2 h after Mixing. The 1H NMR
data (243 K) were essentially identical to the data collected at earlier
time intervals at 223 K, but the hydride resonances for 23 were
slightly broadened. The 31P{1H} NMR data (243 K) were also
similar to the data collected earlier in the reaction at 223 K, but
Selected NMR Data Collected 2 days after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 300 K): δ 67.4 (s, JPtP ) 3495, JPtP
494, JPP ) 76, 27), 29.5 (s, 25), 28 (br, range 0-50 ppm), 24.4
1
2
)
3

Si-H Bond ActiVation by (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 25, No. 16, 2006 3987
(s, OPPh3). 31P{1H} NMR (202 MHz, C7D8, 183 K): δ 67.1 (m,
minor component, 27), 33.5 (s, JPtP ) 3696, minor compo-
a vial containing (Ph3P)2Pt(η2-C2H4) (6) (32 mg, 0.043 mmol). Gas
evolution was observed immediately upon addition. The red-brown
solution was then transferred to an NMR tube, and NMR experi-
ments were begun within 15 min of initial mixing. Similar results
were obtained when Pt(PPh3)4 was used as the precursor.
1
nent, tentative assignment, 6), 30.4 (br m, 26), 28.4 (br, 25), 25.6
(s, OPPh3), 19.3 (br, 26), 10.2 (s, Pt(PPh3)4), -7.8 (s, PPh3). (The
Pt‚‚‚H‚‚‚Si resonance for 26 was not observed/located.)
Reaction of (Ph3P)2Pt(η2-C2H4) (6) with 2,8-Dibromo-5-
methyl-10,10-dihydrophenazasiline (5). Isolation of [(Ph3P)2(H)-
Pt(µ-SiC13H9Br2N)(µ-η2-H-SiC13H9Br2N)Pt(PPh3)] (30). a. Low-
Temperature Reaction. A solution of 2,8-dibromo-5-methyl-10,10-
dihydrophenazasiline (5) (37 mg, 0.10 mmol) in C7D8 (∼0.25 mL)
was added a cooled solution of (Ph3P)2Pt(η2-C2H4) (6) (75 mg, 0.10
mmol) in C7D8 (∼0.50 mL) at 195 K. The tube was shaken to mix
the contents and then placed in a precooled NMR magnet at 223
K. Some gas evolution was observed in the dark reddish-brown
reaction solution. NMR experiments were begun within 5 min of
mixing.
Selected NMR Data Collected 15 min after Mixing. 1H NMR
(500 MHz, C7D8, 300 K): δ 5.25 (br s, C2H4), 4.86 (m, minor
component, unassigned), 4.64 (br m, Si-H for 28), 4.51 (s, H2),
1
-2.06 (br s, JPt-P ) 968 Hz, PtH for 28). 31P{1H} NMR (202
MHz, C7D8, 300 K): δ 36.3 (s, minor component), 34.1 (s, minor
component), 29.7 (s, minor component), 27 (br, range 0-50 ppm),
25.8 (s, OPPh3).
Selected NMR Data Collected 45 min after Mixing. 1H NMR
(500 MHz, C7D8, 223 K): δ 5.29 (s, C2H4), 4.64 (br, SiH for 28),
4.55 (s, H2), -1.82 (br, PtH for 28), -6.35 (t, PtH for 30), Pt‚‚‚
H‚‚‚Si resonance not resolved. 31P{1H} NMR (202 MHz, C7D8,
223 K): δ 74.5 (s, minor component, 31), 28.0 (t, PtPPh3 for 30),
26.7 (s, OPPh3), 20.0 (d, Pt(PPh3)2 for 30), -5.0 (br, PPh3), several
minor resonances were observed between 18 and 40 ppm.
In a similar experiment run at room temperature, a solution
containing 2,8-dibromo-5-methyl-10,10-dihydrophenazasiline (5)
(39 mg, 0.11 mmol) in C7D8 (1.0 mL) was reacted with (Ph3P)2-
Pt(η2-C2H4) (6) (76 mg, 0.10 mmol). Within 24 h an orange
crystalline solid, 30, was obtained (56 mg, 51% based on 30‚3C7D8).
NMR data for complex 30: 1H NMR (500 MHz, C7D8, 223 K): δ
1
Selected NMR Data Collected 5 min after Mixing. H NMR
(500 MHz, C7D8, 223 K): δ 5.74 (br s, unassigned), 5.29 (s, C2H4),
4.9 (m, unassigned), 4.80 (br s, unreacted 5), 4.65 (m, SiH for 28),
4.56 (s, H2), 2.71 (s, C2H4 for 6), -1.77 (dd, 1JPtH ) 973 Hz, 2JPH
) 156 (trans), 18 (cis), PtH for 28). 31P{1H} NMR (202 MHz,
C7D8, 223 K): δ 35.5 (d, minor component, unassigned), 35.0 (br
1
s, JPtP ) 1863, P trans to Si for 28), 33.9 (s, minor component,
6), 33.6 (br s, 1JPtP ) 2417, P trans to H for 28), 25.4 (s, OPPh3).
1
The H and 31P{1H} NMR spectra remained essentially the same
1
2
after 2 h at 223 K except the signals for 6 were no longer observed.
8.1-6.0 (ArH), 2.91 (d, JPtH not resolved, JPH ) 11, Pt‚‚‚H‚‚‚
1
2
Selected NMR Data Collected 3-4 h after Mixing. 31P{1H}
Si), 2.58 (s, NMe), 2.41 (s, NMe), -6.34 (t, JPtH ) 564, JPH
)
15, PtH). 31P{1H} NMR (202 MHz, C7D8, 223 K): δ 28.1 (t, 1JPtP
1
NMR (202 MHz, C7D8, 243 K): δ 34.8 (br s, JPtP ) 1860, 28),
2
3
1
33.8 (br s,1JPtP ) 2421, 28), 25.3 (s, OPPh3). 1H NMR (500 MHz,
C7D8, 243 K): δ 5.28 (s, C2H4), 4.9 (br, minor component,
unassigned), 4.63 (br m, SiH for 28), 4.54 (s, H2), -1.85 (br d,
) 4032, JPtP ) 280, JPP ) 28, PtPPh3), 18.5 (d, JPtP ) 3710,
2JPtP not resolved, Pt(PPh3)2). 31P-31P{1H} COSY NMR (202 MHz,
1
C7D8, 223 K): correlation between δ 28.1 (t) and 18.5 (d). H-
31P COSY NMR (500 MHz, C7D8, 223 K): correlation between δ
2.91 (d, Pt‚‚‚H‚‚‚Si) and 28.1 (t, PtPPh3); correlation between δ
-6.35 (t, PtH) and 18.5 (d, Pt(PPh3)2. 1H-29Si HMQC NMR (500
MHz, C7D8, 223 K): correlation between δ 2.91 (d) and 136;
correlation between δ -6.35 (t, PtH) and 137. IR (solid) (ν, cm
-1): 2276 (Pt-H), 1798 (Pt‚‚‚H‚‚‚Si). Anal. Calcd for C80H65-
Br4N2P3Pt2Si2‚3C7D8: C, 54.79; H, 5.14. Found: C, 54.03; H, 3.94.
X-ray Structure Determinations. X-ray-quality crystals of 16,
22, and 30 were obtained from a C7D8 solution. Crystals with
approximate dimensions 0.19 × 0.10 × 0.06 units (16), 0.17 ×
0.10 × 0.08 units (22), and 0.24 × 0.22 × 0.20 units (30) were
mounted on glass fibers in a random orientation. Preliminary
examination and data collection were performed using a Bruker
SMART 1K charge coupled device (CCD) detector system single-
crystal X-ray diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å) equipped with a sealed tube X-ray source
at 120 K. Preliminary unit cell constants were determined with a
set of 45 narrow frame (0.4° in $) scans. Typical data sets consisted
of 3636 frames with a frame width of 0.3° in $ and typical counting
time of 15-30 s/frame at a crystal-to-detector distance of 4.930
cm. The double-pass method of scanning was used to exclude any
noise. The collected frames were integrated using an orientation
matrix determined from the narrow frame scans. SMART and
SAINT software packages32 were used for data collection and data
integration. Analysis of the integrated data did not show any decay.
Final cell constants were determined by global refinement of xyz
centroids. Collected data were corrected for systematic errors using
SADABS33 based on the Laue symmetry using equivalent reflec-
tions. Crystal data and intensity data collection parameters are
provide in the Supporting Information.
2
1JPtH ) 969, JPH ) 146, PtH for 28).
Selected NMR Data Collected 5 h after Mixing. 1H NMR (500
MHz, C7D8, 263 K): δ 5.27 (s, C2H4), 4.63 (br m, SiH for 28),
1
2
4.48 (s, minor component, H2), -1.92 (br d, JPtH ) 968, JPH
)
149, PtH for 28). 31P{1H} NMR (202 MHz, C7D8, 263 K): δ 34.4
1
1
(br, JPtP ) 1858, 28), 33.9 (s, JPtP ) 2424, 28), 24.8 (s, OPPh3).
Selected NMR Data Collected 6 h after Mixing. 1H NMR (500
MHz, C7D8, 283 K): δ 5.26 (br s, C2H4), 4.63 (m, SiH for 28),
4.51 (s, H2), -1.98 (br s, 1JPtH ) 962, PtH for 28). 31P{1H} NMR
(202 MHz, C7D8, 283 K): δ 5-45 (br), 24.6 (s, OPPh3).
Selected NMR Data Collected 7 h after Mixing. The 1H NMR
spectrum did not exhibit any hydride signals for 28 or any other
complexes. 31P{1H} NMR (202 MHz, C7D8, 303 K): δ 22 (br,
range 5-45 ppm), 24.4 (s, OPPh3). Several minor unassigned
resonances appeared between 10 and 35 ppm.
Selected NMR Data Collected 22 h after Mixing. 31P{1H}
NMR (202 MHz, C7D8, 303 K): δ 66.2 (s, minor component, 31),
1
29.8 (s, minor component, unassigned), 28.4 (s, JPtP ) 1682 Hz,
1
29), 24.8 (s, minor component, unassigned), 24.5 (s, OPPh3). H
NMR (500 MHz, C7D8, 223 K): δ 4.6 (s, H2), 2.91 (d, 2JPH ) 11,
(Pt‚‚‚H‚‚‚Si) for 30), -6.35 (br t, Pt-H for 30). 31P{1H} NMR
(202 MHz, C7D8, 223 K): δ 65.1 (s, minor component, 31), 28.2
(s, 29), 26.8 (t, PtPPh3 for 30), 25.5 (s, OPPh3), 18.6 (d, Pt(PPh3)2
for 30), -6.6 (br s, PPh3).
After approximately one week, orange X-ray-quality crystals
were recovered from the reaction solution upon decanting the
orange, soluble fraction. The orange solid 30 cocrystallized with
three C7D8 solvent molecules.
Selected NMR Data for the Soluble Fraction after Removal
of Crystalline Solid (30) after ca. 3 weeks. 31P{1H} NMR (202
MHz, C7D8, 190 K): 28.1 (br s, minor component, 29), 25.4 (s,
OPPh3), 10.2 (s, 1JPtP ) 3831, major component, Pt(PPh3)4), -7.9
(s, major component, PPh3).
Structure solution and refinement were carried out using the
SHELXTL-PLUS software package.34 The structures were solved
(32) SMART and SAINT; Bruker Analytical X-Ray: Madison, WI, 2002.
(33) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(34) Sheldrick, G. M. SHELXTL-PLUS; Bruker Analytical X-Ray
Division: Madison, WI, 2002.
b. Room-Temperature Reaction. In an inert atmosphere drybox,
a solution containing 2,8-dibromo-5-methyl-10,10-dihydrophena-
zasiline (5) (16 mg, 0.043 mmol) in C7D8 (0.75 mL) was added to

3988 Organometallics, Vol. 25, No. 16, 2006
Braddock-Wilking et al.
by direct methods and refined successfully in the monoclinic space
group P21/c (30) and the triclinic space group P1h (16 and 22),
respectively. Full matrix least-squares refinement was carried out
by minimizing ∑w(Fo2 - Fc2)2. All three crystals were found to be
toluene-d8 solvates (two and one-half C7D8 for 16; one C7D8 for
22; three C7D8 for 30). The non-hydrogen atoms were refined
anisotropically to convergence. The hydrides bound to Pt for
structures 22 and 30 were located from the difference Fourier
synthesis but could not be refined. All other hydrogen atoms were
included in their calculated positions and treated using appropriate
riding models (AFIX m3). The projection view of the molecules
with non-hydrogen atoms are represented by 50% probability
ellipsoids and show the atom labeling for the asymmetric unit. The
final residual values and structure refinement parameters are listed
in the Supporting Information. Complete listings of positional and
isotropic displacement coefficients for hydrogen atoms and aniso-
tropic displacement coefficients for the non-hydrogen atoms are
listed in the Supporting Information and are deposited with the
Cambridge Crystallographic Data Center.
Acknowledgment. We are grateful for a grant from the
National Science Foundation (CHE-0316023) for support of this
work.
Supporting Information Available: Three CIF files con-
taining X-ray crystallographic data for complexes 16, 22, and 30.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM060391B