Synthesis of η2-cyclooctene iridium and rhodium complexes supported by a novel P,N-chelate ligand and their reactivity toward hydrosilanes: facile Cl migration from metal to siliconviasilylene complex intermediates and formation of a base-stabilised silylene complex

Abstract

η²-Cyclooctene iridium and rhodium complexes bearing a P,N-chelate ligand C₆H₃Me-3-PCy₂-4-NMe₂ (abbreviated as P^cyN), (P^cyN-P,N)MCl(η²-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 H₂SiMes₂ (Mes = mesityl = 2,4,6-trimethylphenyl) proceeded at 40 °C to give a di-iridium complex bridged by a chlorosilylene ligand (P^cyN-P,N)₂Ir₂H₂(μ-Cl)(μ-H)(μ-SiClMes) (5). The reaction of 1 with HSiMe₂SiMes₂Me occurred at room temperature to afford HSiMesMe₂ 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^cyN-P,N)₂Ir₂H(μ-Cl)(μ-H)[μ-SiMeCl(C₆H₃-2,4-Me₂-6-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 HSiMe₂SiMe₂OMe at room temperature yielded a methoxy-bridged bis(silylene) complex (P^cyN-P,N)IrHCl[SiMe₂··O(Me)··SiMe₂-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 H₃SiC(SiMe₃)₃ underwent an intramolecular γ-Si–Me activation to afford (P^cyN-P,N)MH_n[SiMe₂C(SiMe₃)₂SiClMe-Si,Si] (9: M = Ir, n = 3; 10: M = Rh, n = 1). Complex 1 even reacted with an extremely sterically hindered terphenylhydrosilane H₃SiDmp (Dmp = 2,6-dimesitylphenyl) in the presence of PMe₃ to give a chlorosilyl complex (P^cyN-P,N)IrH₂(PMe₃)(SiHClDmp) (11) without intramolecular bond activation. Complex 1 also reacted with H₃SiTrip (Trip = 2,4,6-triisopropylphenyl) in the presence of excess 4-(dimethylamino)pyridine (DMAP) at room temperature to give a chlorido(dihydrosilyl) complex (P^cyN-P,N)IrHCl(DMAP)(SiH₂Trip) (12) instantaneously. Treatment of complex 12 with LiB(C₆F₅)₄·2.5Et₂O provided a cationic DMAP-stabilised silylene complex [(P^cyN-P,N))IrH₂(DMAP)(SiHTrip ← DMAP)][B(C₆F₅)₄] (13).