Transition metal silyl complexes. Part 63. Influence of the phosphane ligands and the metal complex geometry on the silyl group exchange between L2Pt(SiMe2Ph)2 (L2 = R2PCH2CH2PR2 or 2PR3) and HSiR'3

Article abstract of DOI:10.1016/S0020-1693(00)00175-4

The exchange of the silyl ligands upon reaction of [(κ²-P,P)-R₂PCH₂CH:PR₂]Pt(SiMe₂Ph)₂ (R = Ph, Me, cyclohexyl) with HSi(OMe)₃ or 1,2-bis(dimethylsilyl)benzene was investigated by NMR spectroscopy. The exchange rate is considerably lower than in the complexes cis-(R₃P)₂Pt(SiMe₂Ph)₂, and decreases in the order R = Ph > Me > cyclohexyl. No exchange was observed in the analogous reactions of trans-(R₃P)₂Pt(SiMe₂Ph)₂. The isomerization of cis-(PhMe₂P)₂Pt(SiMe₂Ph)₂ into trans-(PhMe₂P)₂Pt-(SiMe₂Ph)₂ is catalyzed by di- and oligosilanes. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00175-4

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Inorganica Chimica Acta 306 (2000) 211–214
Transition metal silyl complexes.ꢀ
Part 63. Influence of the phosphane ligands and the metal complex
geometry on the silyl group exchange between L2Pt(SiMe2Ph)2
(L2=R2PCH2CH2PR2 or 2PR3) and HSiR%
3
Dominique Kalt, Ulrich Schubert *
Institut fu¨r Anorganische Chemie, Technische Uni6ersita¨t Wien, Getreidemarkt 9, A-1060 Vienna, Austria
Received 18 February 2000; accepted 17 April 2000
Abstract
The exchange of the silyl ligands upon reaction of [(k2-P,P)-R2PCH2CH2PR2]Pt(SiMe2Ph)2 (R=Ph, Me, cyclohexyl) with
HSi(OMe)3 or 1,2-bis(dimethylsilyl)benzene was investigated by NMR spectroscopy. The exchange rate is considerably lower than
in the complexes cis-(R3P)2Pt(SiMe2Ph)2, and decreases in the order R=Ph\Me\cyclohexyl. No exchange was observed in the
analogous reactions of trans-(R3P)2Pt(SiMe2Ph)2. The isomerization of cis-(PhMe2P)2Pt(SiMe2Ph)2 into trans-(PhMe2P)2Pt-
(SiMe2Ph)2 is catalyzed by di- and oligosilanes. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Platinum complexes; Silyl complexes; Isomerization
1. Introduction
Ph3, i.e. rapid exchange is observed if the substituents
in the entering silyl group are more electronegative than
those of the leaving silane.
Silyl group exchange reactions, upon treatment of
transition metal silyl complexes with HSiR3, are an
interesting option for the synthesis of metal silyl com-
plexes which are otherwise difficult to prepare [2]. Al-
though several exchange reactions are known, little is
known about the exchange mechanism and the steric
and electronic features that control the exchange
reactions.
(1)
In this article, we discuss the influence of the phos-
phane ligands and the geometry of the metal complex
on the exchange reaction of the complexes
(R3P)2Pt(SiMe2Ph)2.
We have reported recently that reaction of cis-
(R3P)2Pt(SiPhMe2)2 with an excess of HSiR% (HSiR% =
3
3
HSi(OMe)3, HSiPh3, HSi3Ph7, HPh2SiSiMe3 or
H2SiPh2) results in the stepwise exchange of both silyl
ligands (Eq. (1)) [3]. The exchange rate depends on the
nature of the R% groups and decreases in the order
HSi(OMe)3ꢀH2SiPh2\HPh2SiSiMe3ꢀHSi3Ph7\HSi-
2. Results
In the reaction of cis-(R3P)2Pt(SiMe2Ph)2 with an
excess of HSi(OMe)3, we had observed previously some
influence of the phosphane ligands on the exchange rate
[3]. The exchange rate decreased in the order
PPh2Me\PEt3\PPhMe2 (complete exchange after 30,
45, or 60 min, respectively), which correlates with the
cone angle of PR3 (PPh2Me 136°\PEt3 132°\
PPhMe2 122° [4]). To further test the influence of the
ꢀ For Part 62, see Ref. [1].
* Corresponding author. Tel.: +43-1-58801 15320; fax: +43-1-
58801 15320.
E-mail address: uschuber@mail.zserv.tuwien.ac.at (U. Schubert).
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00175-4

212
D. Kalt, U. Schubert / Inorganica Chimica Acta 306 (2000) 211–214
phosphane ligands on the exchange rates and the ex-
change mechanism, we have employed chelating bis(-
phosphane) ligands.
The complexes [(k2-P,P)-R2PCH2CH2PR2]Pt(SiMe2-
Ph)2 (R=Ph [dppe], Me [dmpe], Cy [dcpe, Cy=cyclo-
hexyl]) were reacted with HSi(OMe)3 and 1,2-bis-
(dimethylsilyl)benzene (Eq. (2)). The 31P NMR spectra
allowed a clear distinction between the starting com-
plexes and the exchange products. Partially exchanged
complexes were not observed, and there were no side or
decomposition reactions, i.e. after complete exchange of
the silyl ligands, the 31P NMR spectra of the reaction
mixtures only showed one new singlet with 195Pt satel-
lites. The time needed for the complete exchange of the
silyl ligands was considerably longer than for the com-
plexes with monodentate PR3 ligands. While both silyl
ligands of (R3P)2Pt(SiPhMe2)2 were exchanged with
HSi(OMe)3 in 30–60 min (depending on the PR3 lig-
and), 1 day was needed for the dppe complex to
completely react with HSi(OMe)3, likewise with 1,2-
bis(dimethylsilyl)benzene under the same conditions.
Four days were needed for the dmpe complex and 20
days for the dcpe complex. Thus, the order of reactivity
was 2PR3\ \ \dppe\dmpe\ \dcpe.
(3)
Surprisingly, there was no indication of a silyl group
exchange within 9 days when trans-(PhMe2P)2Pt-
(SiMe2Ph)2 was treated with an excess of HSi(OMe)3 or
HSiMe2SiPh3 under the same conditions as employed
for cis-(PhMe2P)2Pt(SiMe2Ph)2.
Although trans-(PhMe2P)2Pt(SiMe2Ph)2 does not ex-
change the silyl groups, phosphane exchange reactions
are possible. When cis- or trans-(PhMe2P)2Ptz
(SiMe2Ph)2 was reacted with a 20-fold excess of the
slightly less basic PMePh2 phosphane, slow exchange
was observed in both cases and cis- or trans-
(Ph2MeP)2Pt(SiMe2Ph)2 was formed. Reaction of the
cis complex was complete in 18 days, and that of the
trans complex in 6 days under the same conditions.
3. Discussion
Phosphane dissociation or displacement is often the
first step in reactions of d8 complexes. Even the reduc-
tive elimination of MeꢀEPh3 (E=Si, Ge) from cis-
[(PhMe2P)2Pt(EPh3)Me]
in
the
presence
of
diphenylacetylene is initiated by such a process [5]. All
experimental evidence shows that this is also the rate-
determining step in the silyl group exchange reactions
of L2Pt(SiMe2Ph)2 complexes (L2=R2PCH2CH2PR2 or
2PR3). Decoordination of one phosphorus centers of a
chelating bisphosphane ligand is less favored than elim-
ination of one monodentate PR3. Therefore, the silyl
exchange reactions of [(k2-P,P)-R2PCH2CH2PR2]Ptz
(SiMe2Ph)2 are strongly retarded relative to the corre-
sponding (R3P)2Pt(SiMe2Ph)2 complexes. The notion
that the reversible decoordination of one phosphorus
donor is the initial step of the reaction is also supported
by our recent finding that platinum complexes contain-
ing hemilabile P,N-chelating ligands are considerably
more reactive towards silanes than their bis(phosphane)
counterparts due to the reversible de-coordination of
the nitrogen center [1,6].
In the series of (R3P)2Pt(SiMe2Ph)2 complexes with
monodentate PR3 ligands, the reactivity order was de-
termined by the size of the PR3 ligands, with bulkier
ligands resulting in faster reactions. This is in line with
the proposed mechanism as bulkier ligands are more
easily eliminated. The reactivity order within the series
of complexes with chelating bisphosphane ligands ap-
pears to be more dependent on the basicity of the
phosphorus centers rather than by their steric proper-
ties; more basic phosphorus atoms retard the exchange
reaction. The strongly retarding chelate effect appears
to override the steric influence of the phosphane
substituents.
(2)
We also tested whether the silyl ligands of cis-
(PhMe2P)2Pt(SiMe2Ph)2 were exchanged when the com-
plex is reacted with di- and oligosilanes instead of
hydrosilanes. When benzene solutions of cis-
(PhMe2P)2Pt(SiMe2Ph)2 were treated with a 20-fold ex-
cess of Si5Ph10, (PhMe2Si)2 or (Ph2MeSi)2, various new
signals, which could not be assigned, developed in the
31P NMR spectra. However, in every case, all signals
eventually merged into the signal of trans-
(PhMe2P)2Pt(SiMe2Ph)2 (Eq. (3)). For example, inter-
mediate signals at 0.25 ppm (1JPtP=2870 Hz) and
−2.01 ppm (1JPtP=940 Hz) were observed in the pres-
ence of (Ph2MeSi)2, and signals at 0.25 ppm (1JPtP
=
2870 Hz) and −18.87 ppm (1JPtP=3597 Hz) in the
presence of Si5Ph10. The disilanes thus promote isomer-
ization, and the isomerization rate depends on the
nature of the silane. Complete isomerization occurred
within 9 days in the presence of Si5Ph10, within 13 days
with (Ph2MeSi)2 and within 18 days with (PhMe2Si)2.
The bis(silyl) complex also isomerizes in the absence of
a disilane but at a distinctly lower rate.

D. Kalt, U. Schubert / Inorganica Chimica Acta 306 (2000) 211–214
213
Once the three-coordinate complex (R3P)Pt(SiMe2-
Ph)2 is formed, the exchange reaction probably pro-
ceeds by adding the entering silane to the metal center,
i.e. formation of an intermediate five-coordinate Pt(IV)
complex (R3P)PtH(SiR3)3. If one assumes a square-
pyramidal geometry with the hydrogen in the axial
position (this requires the least movement of atoms
around the metal) then elimination of the silyl group
transoid to another silyl ligand is more favorable than
elimination of the silyl group transoid to the PR3 lig-
and, due to the strong trans effect of silyl ligands (see
Ref. [1] for an example on the magnitude of the trans
effect of silyl ligands). Thus, the complex retains the cis
geometry once the leaving silane is eliminated and PR3
ligand re-coordinates (the assumption of any other
geometry for the intermediate species would lead to the
same result, particularly because they would intercon-
vert by Berry pseudorotation).
The failure of a silyl group exchange for the com-
plexes trans-(PhMe2P)2Pt(SiMe2Ph)2 parallels the ob-
servation that cis-L2Pt(SiPh3)Me (L=PMe2Ph,
PMePh2) readily reacts with phenylacetylene to give the
insertion products cis-L2Pt[CPhꢁCH(SiPh3)]Me, while
trans-L2Pt(SiPh3)Me is totally unreactive towards inser-
tion under the same conditions [7]. Kinetic data indi-
cated that the displacement of a PR3 ligand by
phenylacetylene was the rate-determining step. It was
assumed that cis-L2Pt(SiPh3)Me is more reactive to-
ward PR3 displacement than the trans isomer due to the
greater trans effect of the SiR3 ligand. The inhibited
elimination of a PR3 ligand is also the only reasonable
explanation for the failure of the silyl group exchange
reaction of trans-(PhMe2P)2Pt(SiMe2Ph)2.
weeks. This very slow isomerization could be the reason
why cis/trans isomerization was not observed more
often.
It is known that the cis/trans isomerization of Pt(II)
complexes L2PtX2 is catalyzed by nucleophiles [12].
They allow the intermediate formation of five-coordi-
nate compounds and Berry-type rearrangements. The
results presented in this paper suggest that di- and
oligosilanes can act as rearrangement-promoting nucle-
ophiles. Although no stable oxidative addition product
is observed, the SiꢀSi bonds may weakly coordinate
(via
a
three-center bond) and thus facilitate
isomerization.
4. Conclusions
The rate of the exchange of the silyl ligands in the
complexes (R3P)2Pt(SiR3)2 upon treatment with hy-
drosilanes HSiR% not only depends on the relative
3
strengths of the involved PtꢀSi bonds, but also on the
ability of the metal complex to form three-coordinate
intermediates (R3P)Pt(SiR3)2. While these intermediates
easily form from the starting complex cis-
(R3P)2Pt(SiR3)2 by dissociation of one PR3 ligand, the
use of chelating phosphane ligands in [(k2-P,P)-
R2PCH2CH2PR2]Pt(SiR3)2 renders dissociation of one
phosphorus center more difficult due to the chelate
effect and thus retards the silyl group exchange reac-
tion. In the cis-(R3P)2Pt(SiR3)2 complexes both PR3
ligands are trans to the strongly activating silyl ligands.
Contrary to that, dissociation of a PR3 ligand in trans-
(R3P)2Pt(SiR3)2 is inhibited by the much weaker trans-
effect of the PR3 ligand.
The fact that both cis- and trans-(PhMe2P)2Pt-
(SiMe2Ph)2 slowly exchange the PR3 ligands is no con-
tradiction to the observed trends in the silane exchange
reactions, because the former reactions probably pro-
ceed via a five-coordinate intermediate (i.e. an associa-
Promotion of the cis/trans-isomerization of
(R3P)2Pt(SiR3)2 in the presence of di- and oligosilanes
indicates that weak coordination of the SiꢀSi group to
the metal center takes place which facilitates isomeriza-
tion via a five-coordinate intermediate.
tive mechanism) rather than
intermediate [8].
a
three-coordinate
The cis/trans isomerization of (R3P)2PtMe2 is an
equilibrium reaction which varies with the basicity of
the PR3 ligands. With less basic ligands the equilibrium
is on the side of the cis form, and with more basic
ligands on the trans side [9]. Cis/trans equilibration was
also observed for the complexes (R3P)2Pt(SiHaryl2)2
(R=Me, Et) [10]. The equilibria were slightly depen-
dent on the solvent and the PR3 ligands. Less polar
solvents and the use of PMe3 as the auxiliary ligand
increased the portion of the trans isomer. Most other
known Pd(II) and Pt(II) bis(silyl) complexes were ob-
tained as the cis isomers, although steric effects appear
to play an important role [11]. The results reported in
this paper show that the preferred occurrence of the cis
isomer may also be a kinetic phenomenon. The cis
isomer of (PhMe2P)2Pt(SiMe2Ph)2 converts in solution
to the trans isomers on a time-scale of many days to
5. Experimental
All operations were performed in an atmosphere of
dry and oxygen-free argon with standard Schlenk-tube
techniques, using dried and argon-saturated solvents.
All reported chemical shift data refer to 31P NMR
spectra recorded on Bruker AC250 spectrometer
(101.25 MHz) in benzene-d6 solutions. The solvent was
dried over molecular sieve (4 A) and was stored under
argon.
(dppe)Pt(SiMe2Ph)2 (l=56.54 ppm, JPtP=1308 Hz)
,
1
was prepared as reported [13]. (dcpe)Pt(SiMe2Ph)2 (l=
1
69.83 ppm, JPtP=1398 Hz) and (dmpe)Pt(SiMe2Ph)2
(l=34.23 ppm, 1JPtP=1237 Hz) were prepared
analogously.

214
D. Kalt, U. Schubert / Inorganica Chimica Acta 306 (2000) 211–214
5.1. Reactions of
monitor the progress of the reaction. After 18 (cis
complex) or 6 days (trans complex) at room tempera-
ture, cis-(Ph2MeP)2Pt(SiMe2Ph)2 (l=7.59 ppm,
1JPtP=1629 Hz) or trans-(Ph2MeP)2Pt(SiMe2Ph)2 (l=
−0.38 ppm, 1JPtP=2613 Hz) was obtained
quantitatively.
[(s2-P,P)-R2PCH2CH2PR2]Pt(SiMe2Ph)2 with
hydrosilanes
A 20-fold excess of HSi(OMe)3 or 1,2-bis(dimethylsil-
yl)benzene was added to a benzene-d6 solution of [(k2-
P,P)-R2PCH2CH2PR2]Pt(SiMe2Ph)2 in an NMR tube.
The NMR tube was sealed under argon, and 31P NMR
spectra were recorded at regular intervals to monitor
the progress of the reaction.
Acknowledgements
We thank the Fonds zur Fo¨rderung der wis-
senschaftlichen Forschung (FWF), Vienna, for support-
ing this work and Dr Ju¨rgen Pfeiffer for valuable
discussions.
5.1.1. (dppe)Pt(SiMe2Ph)2
After 24 h at room temperature, only (dppe)Pt[Si-
(OMe)3]2 (l=60.14 ppm, JPtP=1354 Hz) or (dppe)Pt-
1
(SiMe2C6H4SiMe2) was observed (l=58.95 ppm,
1JPtP=1394 Hz).
References
5.1.2. (dcpe)Pt(SiMe2Ph)2
After 20 days at room temperature, only
(dcpe)Pt[Si(OMe)3]2 (l=75.11 ppm, 1JPtP=1405 Hz)
or (dcpe)Pt(SiMe2C6H4SiMe2) was observed (l=73.42
[1] J. Pfeiffer, G. Kickelbick, U. Schubert, Organometallics 19
(2000) 62.
[2] (a) U. Schubert, S. Grubert, Organometallics 15 (1996) 4707. (b)
U. Schubert, C. Mu¨ller, J. Organomet. Chem. 418 (1991) C6. (c)
R. Karch, U. Schubert, Inorg. Chim. Acta 259 (1997) 151. (d) S.
Gilbert, M. Knorr, S. Mock, U. Schubert, J. Organomet. Chem.
480 (1994) 241. (e) H. Tobita, H. Izumi, S. Ohnuki, M.C.
Ellerby, M. Kikuchi, S. Inomata, H. Ogino, J. Am. Chem. Soc.
117 (1995) 7013. (f) H. Yamashita, M. Tanaka, M. Goto,
Organometallics 16 (1997) 4696. (g) A.F. Clemmit, F. Glockling,
J. Chem. Soc., Chem. Commun. (1970) 705. (h) H. Tobita, K.
Ueno, H. Ogino, Bull. Chem. Soc. Jpn. 61 (1988) 2797. (i) F.R.
Anderson, M.S. Wrighton, J. Am. Chem. Soc. 106 (1984) 995. (j)
R.N. Hazeldine, L.S. Malkin, R.V. Parish, J. Organomet. Chem.
182 (1979) 323. (k) J. Ruiz, P.M. Maitlis, J. Chem. Soc., Chem.
Commun. (1986) 862. (l) H.G. Woo, R.H. Heyn, T.D. Tilley, J.
Am. Chem. Soc. 114 (1992) 5698. (m) H.G. Woo, F.F. Walzer,
T.D. Tilley, J. Am. Chem. Soc. 114 (1992) 7047. (n) K.A.
Kreutzer, R.A. Fisher, W.M. Davis, E. Spaltenstein, S.L. Buch-
wald, Organometallics 10 (1991) 4032. (o) A. Antinol, F. Carillo-
Hermosilla, A. Castel, Organometallics 17 (1998) 1523.
[3] U. Schubert, D. Kalt, H. Gilges, Monatsh. Chem. 130 (1999)
207.
[4] (a) C.A. Tolman, Chem. Rev. 77 (1977) 313. (b) T. Kobayashi,
T. Hayashi, H. Yamashita, M. Tanaka, Chem. Lett. (1988) 1411.
[5] F. Ozawa, T. Hikida, K. Hasebe, T. Mori, Organometallics 17
(1998) 1018.
[6] J. Pfeiffer, U. Schubert, Organometallics 18 (1999) 3245.
[7] F. Ozawa, T. Hikida, Organometallics 15 (1996) 4501.
[8] R.L. Rominger, J.M. McFarland, J.R. Jeitler, J.S. Thompson,
J.D. Atwood, J. Coord. Chem. 31 (1994) 7.
[9] F. Ozawa, A. Yamamoto, J. Organomet. Chem. 279 (1985) 1985.
[10] Y.J. Kim, J.I. Park, S.C. Lee, K. Osakada, M. Tanabe, J.C.
Choi, T. Koizumi, T. Yamamoto, Organometallics 18 (1999)
1349.
[11] H. Gilges, U. Schubert, Eur. J. Inorg. Chem. (1998) 897.
[12] W.J. Louw, Inorg. Chem. 16 (1977) 2147.
1
ppm, JPtP=1429 Hz).
5.1.3. (dmpe)Pt(SiMe2Ph)2
After
5
days at room temperature, only
1
(dmpe)Pt[Si(OMe)3]2 (l=41.67 ppm, JPtP=1310 Hz)
or (dmpe)Pt(SiMe2C6H4SiMe2) was observed (l=37.89
1
ppm, JPtP=1323 Hz).
5.2. Isomerization of cis-[(Me2PhP)2Pt(SiMe2Ph)2] in
the presence of di- and oligosilanes
A 20-fold excess of Si2Me4Ph2, Si2Me2Ph4 or Si5Ph10
was added to
a
benzene-d6 solution of cis-
[(Me2PhP)2Pt(SiMe2Ph)2] in a NMR tube. The NMR
tube was sealed under argon, and 31P NMR spectra
were recorded at regular intervals to monitor the pro-
gress of the reaction. The signals of several intermediate
compounds were observed which eventually disappear
after 18, 13 and 9 days, respectively. After this period,
only trans-[(PhMe2P)2Pt(SiMe2Ph)2] (l= −5.24 ppm,
1JPtP=2860 Hz) was observed.
5.3. Phosphane exchange reactions of
cis-(PhMe2P)2Pt(SiMe2Ph)2
A 20-fold excess of PMePh2 was added to a benzene-
d6 solution of cis- or trans-[(PhMe2P)2Pt(SiMe2Ph)2] in
an NMR tube. The NMR tube was sealed under argon.
31P NMR spectra were recorded at regular intervals to
[13] J. Chatt, C. Eaborn, J. Chem. Soc. A (1970) 1343.
.