FACIAL (METHYL)(HYDRIDO)(SILYL) COMPLEXES OF IRIDIUM - SYNTHESIS, X-RAY STRUCTURES, AND REDUCTIVE ELIMINATION-REACTIONS - FACILE FORMATION OF SILAMETALLACYCLES BY METALATION OF SILYL LIGANDS

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 silane s to MeIrL(4). The three compounds are fully characterized spectroscop ically 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 f or 3: monoclinic, P2(1)/n, a = 10.050(2) Angstrom, b = 31.459(6) Angst rom, c = 10.325(2) Angstrom, beta = 114.61(3)degrees, Z = 4. Crystal d ata for 4: triclinic, P (1) over bar, a = 8.653(2) Angstrom, b = 10.09 0(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 a nd 3 reductively eliminate methane exclusively. The resulting Ir(I) si lyls 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 cry stallographically. Compound 4 on heating eliminates C-H, C-Si, and H-S i 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 intermediat e complexes [HIrL(3)], [MeIrL(3)], and [Et(3)SiIrL(3)] react further w ith the solvent benzene and triethylsilane to yield a mixture of C-H a nd Si-H addition products. These were identified by carrying out indep endent oxidative addition reactions of HSiEt(3), H-2, and C6H6 to HIrL (4) and PhIrL(3). A plausible scheme accounting for the formation of t he observed complexes is proposed.