Facial complexes L(3)Ir(CH3)(H)(SiR(3)) (L = PMe(3); R = EtO (2), Ph (3), Et (4)) result from oxidative addition of the corresponding silanes to MeIrL(4). The three compounds are fully characterized spectroscopically and the mutual cis arrangement of H, CH3, and SiR(3) groups is confirmed by X-ray crystallographic studies of 3 and 4. Crystal data for 3 : monoclinic, P2(1)/n, a = 10.050(2) Angstrom, b = 31.459(6) Angstrom, c = 10.325(2) Angstrom, beta = 114.61(3)degrees, Z = 4. Crystal data for 4 : triclinic, P (1) over bar, a = 8.653(2) Angstrom, b = 10.090(2) Angstrom, c = 14.988(3) Angstrom, alpha = 92.43(3)degrees, beta = 94.53(3)degrees, gamma = 113.69(3)degrees, Z = 2. Based on the X-ray structural data, the following order of increasing trans influence is deduced : CH3 < H < SiPh(3) < SiEt(3). On heating to 100 degrees C, 2 and 3 reductively eliminate methane exclusively. The resulting Ir(I) silyls quantitatively cyclometalate to produce novel iridasilacycles L(3)Ir(H)(CH2CH2OSi(OEt)(2)) (5) and L(3)Ir(H)(o-C(6)H(4)SiPh(2)) (6). 5 and 6 are fully characterized spectroscopically and complex 6 also crystallographically. Compound 4 on heating eliminates C-H, C-Si, and H-Si bonds competitively (the latter one reversibly). The upper Limit of the relative rates of C-H and C-Si bond formation is estimated as k(C-H)/k(C-Si) approximate to 4. The resulting highly reactive intermediate complexes [HIrL(3)], [MeIrL(3)], and [Et(3)SiIrL(3)] react further with the solvent benzene and triethylsilane to yield a mixture of C-H and Si-H addition products. These were identified by carrying out independent oxidative addition reactions of HSiEt(3), H-2, and C6H6 to HIrL(4) and PhIrL(3). A plausible scheme accounting for the formation of the observed complexes is proposed.