(Phosphinoalkyl)silyl complexes .11. Structural influence of the chelate dimethyl((diphenylphosphino)ethyl)silyl group. Irregular 5-coordinate geometry at a d(6) center. X-ray crystal and molecular structures of three silyliridium(III) complexes [Ir(chel)(2)Cl, IrH(chel)(PPh(3))(CO)Cl, IrH(chel)(cod)Cl; Chel=PPh(2)CH(2)CH(2)SiMe(2)-, cod=cycloocta-1,5-diene]

The bis((phosphinoalkyl)silyl)iridium(III) complex Ir(chel)(2)Cl (6; chel = PPh(2)CH(2)CH(2)-SiMe(2-)), which has been characterized by using single-crystal X-ray crystallography, displays a distorted trigonal bipyramidal (dist-TBP) geometry in which the equatorial Si-Ir-Si angle is very narrow, at 86.3(3)degrees, with the Si-Ir-Cl angles correspondingly wide, 134.8(2) and 138.9(2)degrees. All bonds to Ir in the equatorial plane are short compared with corresponding distances in two directly related structures, those of the six-coordinate ((phosphinoalkyl)-silyl)iridium(III) compounds IrH(chel)(PPh(3))(CO)Cl (7) and IrH(chel)(cod)Cl (8; cod = cycloocta-1,5-diene): thus Ir-Si = 2.302(7), 2.315(8) Angstrom in 6 vs 2.41(1), 2.364(5) Angstrom in 7 and 8, respectively, while Ir-Cl = 2.381(6) Angstrom in 6 vs 2.503(8), 2.495(5) Angstrom in 7 and 8, respectively. The distortions in the dist-TBP geometry of 6 are discussed in relation to structures of a small family of related 16e complexes and in terms of ligand trans influences.