Metal-dependent stabilization of Si-S bonds to hydrolysis in iridium and rhodium silyls. Hydrolyzability as a probe for Si-H reductive elimination

Article abstract of DOI:10.1021/om950791r

The iridium (triethylthio) silyl complexes cis(PPh₃)₂(CO)IrH₂(Si(SEt)₃) (5), fac-(PMe₃)₃Ir(CH₃(H)-(Si(SEt)₃) (6), and mer-(PMe₃)₃Ir(C₆F₅)(H)(Si(SEt) ₃) (7) were synthesized by oxidative addition of HSi(SEt)₃ (1) to HIr(CO)(PPh₃)₃ (2), CH₃Ir(PMe₃)₄ (3), and C₆F₅-Ir(PMe₃)₃ (4), respectively. 4 was synthesized by the reaction between Ir(PMe₃)₄Cl and C₆F₅MgBr. The rhodium analog of 7, mer-(PMe₃)₃Rh(C₆F₅)(H)(Si(SEt) ₃) (9), was obtained similarly from C₆F₅Rh(PMe₃)₃, (8) and 1. Unlike the extremely easily hydrolyzable parent silane 1, compounds 5-7 are stable in H₂O/THF and even in NaOH/H₂O/THF solutions. This stabilization is attributed to the electron-donating capacity of the Ir centers, which efficiently reduces electrophilicity of the silicon. Reactivity of the rhodium complex 9 is strikingly different, cleanly producing in the presence of 5 equiv of H₂O the ethylthio-complex mer-(PMe₃)₃Rh(C₆F₅)(H)(SEt) (10). Compound 10 was identified spectroscopically and was synthesized independently from 8 and HSEt. A plausible scheme accounting for the generation of 10 under the hydrolysis conditions is presented. The observed difference in the reactivities of 5-7 and 9 is explained in terms of their different tendencies to reductively eliminate H-Si(SEt)₃.