Organometallics 1997, 16, 3973-3980
3973
Str u ctu r e a n d Ch em ica l P r op er ties of
Ch lor oh yd r id o(d ia r ylsilyl)r h od iu m (III) Com p lexes,
m er -Rh Cl(H)(SiHAr 2)(P Me3)3. Th er m a lly In d u ced Ch lor o
Tr a n sfer fr om Rh od iu m to Silicon in th e Com p lexes a n d
Sila n e Exch a n ge
Kohtaro Osakada,* Susumu Sarai, Take-aki Koizumi, and Takakazu Yamamoto*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226, J apan
Received May 12, 1997X
Reactions of the diarylsilanes H2SiPh2, H2Si(C6H4Me-p)2, H2Si(C6H4OMe-p)2, H2Si(C6H4F-
p)2, and H2Si(C6H4CF3-p)2 with [Rh(PMe3)4]Cl involve oxidative addition of an Si-H bond
of the substrates to give mer-RhCl(H)[SiH(C6H4X-p)2](PMe3)3 (1, X ) H; 2, X ) Me; 3, X )
OMe; 4, X ) F; 5, X ) CF3). X-ray crystallography of 1, 3, 4, and 5 shows a distorted-
octahedral coordination around the Rh center with three meridional PMe3 ligands and with
the chloro and diarylsilyl ligands at mutually trans positions. The Rh-Si bond distances of
the complexes are in the range 2.311-2.319 Å. Addition of H2Si(C6H4Me-p)2 to a toluene
solution of 1 results in partial conversion of the complex into 2 accompanied by liberation of
H2SiPh2. The exchange of the diphenylsilyl ligand of 1 on addition of the other diarylsilanes
proceeds reversibly at 10-50 °C with the thermodynamic parameters of the reactions 1 +
H2Si(C6H4X-p)2 ) mer-RhCl(H)[SiH(C6H4X-p)2](PMe3)3 + H2SiPh2 as ∆H° ) 4.16 kJ mol-1
and ∆S° ) 8.2 J mol-1 K-1 for X ) Me, ∆H° ) 6.51 kJ mol-1 and ∆S° ) 11.7 J mol-1 K-1 for
X ) OMe, and ∆H° ) -2.33 kJ mol-1 and ∆S° ) -5.3 J mol-1 K-1 for X ) F, respectively.
Enthalpy of the reactions of 1 with H2Si(C6H4X-p)2 (X ) Me, OMe, and F) decreases with
increase in the σp value of X. Heating a toluene solution of 1 at 50 °C and at 110 °C gives
mixtures of fac-Rh(H)2(SiClPh2)(PMe3)3 (6) and RhCl(H)(SiClPh2)(PMe3)3 (7). The structure
of 6 has been determined by X-ray crystallography, while 7 was characterized by comparison
of the NMR (1H, 31P{1H}, 13C{1H}, and 29Si{1H}) peaks with those of the complex prepared
independently from the reaction of HSiClPh2 with [Rh(PMe3)4]Cl.
In tr od u ction
process for the formation of active species from added
transition-metal complexes has not been revealed well
in most cases.
The structure and chemical properties of complexes
containing Rh-Si bonds are of current interest1 in
relation to the mechanisms of Rh complex catalyzed
reactions such as hydrosilylation,2 silylformylation,3 and
dehydrogenative condensation of SiH and EH groups
(E ) O, N, S)4 because these reactions are believed to
involve silylrhodium complexes as the intermediates.
There seems to be, however, several unclarified issues
on the above catalytic reactions. For example, a detailed
H2PtCl6 is believed to react with organosilanes to
generate Pt(0) species which act as the active species
in the catalytic hydrosilylation. Dichloroplatinum(II)
complexes as well as IrCl(CO)(PPh3)2 react with tri-
organosilanes to give active hydrido complexes of these
elements and chlorotriorganosilanes.5 RhClLn is also
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X Abstract published in Advance ACS Abstracts, August 15, 1997.
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