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 silicon via silylene complex intermediates and formation of a base-stabilised silylene complex

eta(2)-Cyclooctene iridium and rhodium complexes bearing a P,N-chelate ligand C6H3Me-3-PCy2-4-NMe2 (abbreviated as (PN)-N-cy), ((PN)-N-cy-P,N) MCl(eta(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(2)SiMes(2) (Mes = mesityl = 2,4,6-trimethylphenyl) proceeded at 40 degrees C to give a di-iridium complex bridged by a chlorosilylene ligand ((PN)-N-cy-P, N)(2)Ir2H2(mu-Cl)(mu-H)(mu-SiClMes) (5). The reaction of 1 with HSiMe(2)SiMes(2)Me 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 ((PN)-N-cy-P,N)(2)Ir2H(mu-Cl)(mu-H)[mu-SiMeCl(C6H3-2,4-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 HSiMe2SiMe2OMe at room temperature yielded a methoxy-bridged bis(silylene) complex ((PN)-N-cy-P,N)IrHCl[SiMe2 center dot center dot O(Me)center dot center dot 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 gamma-Si-Me activation to afford ((PN)-N-cy-P,N)MHn[SiMe2C(SiMe3)(2)SiClMe-Si,Si] (9: M = Ir, n = 3; 10: M = Rh, n = 1). Complex 1 even reacted with an extremely sterically hindered terphenylhydrosilane H(3)SiDmp (Dmp = 2,6-dimesitylphenyl) in the presence of PMe3 to give a chlorosilyl complex ((PN)-N-cy-P,N)IrH2(PMe3)(SiHClDmp) (11) without intramolecular bond activation. Complex 1 also reacted with H(3)SiTrip (Trip = 2,4,6-triisopropylphenyl) in the presence of excess 4-(dimethylamino) pyridine (DMAP) at room temperature to give a chlorido(dihydrosilyl) complex (PcyN-P, N) IrHCl(DMAP)(SiH(2)Trip) (12) instantaneously. Treatment of complex 12 with LiB(C6F5)(4)center dot 2.5Et(2)O provided a cationic DMAP-stabilised silylene complex [((PN)-N-cy-P,N))IrH2(DMAP)(SiHTrip <- DMAP)][B(C6F5)(4)] (13).