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 L₃Ir(CH₃)(H)(SiR₃) (L = PMe₃; R = EtO (2), Ph (3), Et (4)) result from oxidative addition of the corresponding silanes to MeIrL₄. The three compounds are fully characterized spectroscopically and the mutual cis arrangement of H, CH₃, and SiR₃ groups is confirmed by X-ray crystallographic studies of 3 and 4. Crystal data for 3: monoclinic, P2₁/n, a = 10.050(2) Å, b = 31.459(6) Å, c = 10.325(2) Å, β = 114.61(3)°, Z = 4. Crystal data for 4: triclinic, P1, a = 8.653(2) Å, b = 10.090(2) Å, c = 14.988(3) Å, α = 92.43(3)°, β = 94.53(3)°, γ = 113.69(3)°, Z = 2. Based on the X-ray structural data, the following order of increasing trans influence is deduced: CH₃ <H <SiPh₃ <SiEt₃. On heating to 100 °C, 2 and 3 reductively eliminate methane exclusively. The resulting Ir(I) silyls quantitatively cyclometalate to produce novel iridasilacycles L₃Ir(H)(CH₂CH₂OSi(OEt)₂) (5) and L₃Ir(H)(o-C₆H₄SiPh₂) (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 ≈ 4. The resulting highly reactive intermediate complexes [HIrL₃], [MeIrL₃], and [Et₃SiIrL₃] 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 HSiEt₃, H₂, and C₆H₆ to HIrL₄ and PhIrL₃. A plausible scheme accounting for the formation of the observed complexes is proposed.