Synthesis of η~2-cyclooctene iridium and rhodium complexes supported by a novel P,N-chelate ligand and their reactivity toward hydrosilanes: Facile Cl migration from metal to silicon via silylene complex intermediates and formation of a base-stabilised silylene complex

摘要

η~2-Cyclooctene iridium and rhodium complexes bearing a P,N-chelate ligand C_6H_3Me-3-PCy_2-4-NMe _2 (abbreviated as P~(cy)N), (P~(cy)N-P,N) MCl(η~2-coe) (1: M = Ir, 2: M = Rh), were synthesised and reactions toward several sterically hindered hydrosilanes were investigated to clarify their reactivity. The reaction of 1 with H_2SiMes_2 (Mes = mesityl = 2,4,6-trimethylphenyl) proceeded at 40 °C to give a di-iridium complex bridged by a chlorosilylene ligand (P~(cy)N-P,N) _2Ir_2H_2(μ-Cl)(μ-H)(μ-SiClMes) (5). The reaction of 1 with HSiMe_2SiMes_2Me occurred at room temperature to afford HSiMesMe_2 and a silyl complex 6 formed by metallation of an ortho-methyl group of Mes, which slowly dimerised to give a dinuclear complex containing a chlorosilyl ligand (P~(cy)N-P,N) _2Ir_2H(μ-Cl)(μ-H)[μ-SiMeCl(C_6H _3-2,4-Me_2-6-CH)-Si,C,C] (7). The formation of complexes 5, 6 and 7 suggests that facile migration of Cl from Ir to Si occurs probably via silylene iridium intermediates. Treatment of 1 with HSiMe_2SiMe _2OMe at room temperature yielded a methoxy-bridged bis(silylene) complex (P~(cy)N-P,N)IrHCl[SiMe_2··O(Me) ··SiMe_2-Si,Si] (8) quantitatively, whose X-ray crystal structure was determined as the first iridium complex of this type. The reactions of 1 and 2 with a bulky trihydrosilane H_3SiC(SiMe _3)_3 underwent an intramolecular γ-Si-Me activation to afford (P~(cy)N-P,N)MH_n[SiMe_2C(SiMe _3)_2SiClMe-Si,Si] (9: M = Ir, n = 3; 10: M = Rh, n = 1). Complex 1 even reacted with an extremely sterically hindered terphenylhydrosilane H_3SiDmp (Dmp = 2,6-dimesitylphenyl) in the presence of PMe_3 to give a chlorosilyl complex (P~(cy)N-P,N) IrH_2(PMe_3)(SiHClDmp) (11) without intramolecular bond activation. Complex 1 also reacted with H_3SiTrip (Trip = 2,4,6-triisopropylphenyl) in the presence of excess 4-(dimethylamino)pyridine (DMAP) at room temperature to give a chlorido(dihydrosilyl) complex (P ~(cy)N-P,N)IrHCl(DMAP)(SiH_2Trip) (12) instantaneously. Treatment of complex 12 with LiB(C_6F_5)_4· 2.5Et_2O provided a cationic DMAP-stabilised silylene complex [(P ~(cy)N-P,N))IrH_2(DMAP)(SiHTrip ← DMAP)][B(C _6F_5)_4] (13).