Silanes [R3SiH;
R3 = Cl3, MeCl2, (EtO)3,
Ph3] undergo irreversible oxidative addition to planar iridium(I)
complexes IrClL3 (L = PPh3, PMePh2 or AsPh3)
to give silyliridium(III) hydrides IrHCl(SiR3)Ln
(n = 2 or 3). The yellow, five-coordinate, probably tetragonal pyramidal
complexes(n = 2) are formed mainly when L = PPh3 or AsPh3,
and also in the case of L = PmePh2, R = Ph, whereas the colourless,
six-coordinate, presumably octahedral adducts are formed predominantly when L =
PMePh2. Both five- and six-coordinate adducts can be isolated from
the addition of dichloro(methyl)silane to IrCl(AsPh3)3.
Most of the adducts react with carbon monoxide under ambient conditions to give
silyliridium(III) hydrido carbonyls, IrHCl(SiR3)(CO)L2,
which may undergo partial or complete reductive elimination to IrCl(CO)L2 and R3SiH; the ease with
which this occurs depends on L (PPh3 > PMePh2 >
AsPh3) and on R3 [Ph3 > (EtO)3 > Cl3 ≈ MeCl2].
The reactions of silanes with IrClL3, RhClL3 and IrCl(CO)(PPh3)2 are compared, and the
trends observed in the case of IrClL3 are discussed in terms of
electronic and steric effects in the silyl and Group
5 donors. Structural assignments for the new complexes are based on i.r., far-i.r. and 1H
N.M.R. data.
