Coordination Chemistry and Reactivity of New Zwitterionic Rhodium and Iridium Complexes Featuring the Tripodal Phosphine Ligand [PhB(CH_2P~iPr_2)_3]~-·Activation of H-H,Si-H,and Ligand B-C Bonds

摘要

The synthesis,characterization,and reactivity of zwitterionic rhodium and iridium complexes containing the tris(phosphino)borate ligand [PhB(CH_2P~iPr_2)_3]~- ([PhBP_3']~-) are reported.The allyl complexes [PhBP_3']IrH(eta~3-C_8H_(13)) (3) and [PhBP_3']IrH(eta~3-C_3H_5) (4) were prepared by reaction of [PhBP_3']Li(THF) (2) with the corresponding [(alkene)_2IrCl]_2 complex.Complex 3 reacted with secondary silanes (H_2SiR_2,with R=Et,Ph) to give silyl-capped trihydride complexes of the type [PhBP_3']IrH_3(SiHR_2) (R=Et,5;Ph,6) with concomitant beta-hydride elimination of 1,3-cyclooctadiene.Complex 5 underwent H/D exchange with D2 to incorporate deuterium into both the Ir-H and Si-H positions.The reaction of 5 with 1 equiv of PMe_3 resulted in elimination of Et_2SiH_2 to form the corresponding dihydride complex,[PhBP_3']Ir(H)_2(PMe_3) (7).Complexes of the type [PhBP_3']Ir(H)_2(L) (L=PMe_3,7;PH_2Cy,8;CO,9) could also be prepared directly by the reaction of 3 with L.The observed reactivity of [PhBP_3']Ir complexes is compared with that of the related [PhB(CH_2PPh_2)_3]~- ([PhBP_3]~-) species.The Rh(I) complexes [kappa~2-PhBP_3']Rh(PMe_3)_2 (10) and [PhBP_3']Rh(CO)_2 (11) are also reported.Variable-temperature ~1H and ~(31)P NMR experiments did not reveal evidence for kappa~2-kappa~3 interconversion for 10 and 11.However at elevated temperatures 10 was found to engage in a dynamic equilibrium process involving dissociation of the PMe_3 ligands and reversible migration of a -CH_2 group in the ligand backbone from B to Rh.The product of this migration,[PhB(CH_2P~iPr_2)_2]RhCH_2P~iPr_2 (12),was prepared independently by the reaction of 2 with [RhCl(C_2H_4)_2]_2 and was structurally characterized by X-ray crystallography.Complex 10 reacted with H_2 to give the oxidative addition product [PhBP_3']Rh(H)_2(PMe_3) (13).The reaction of 10 with 1 equiv of Ph_2SiH_2 resulted in loss of a ligand arm to give the bis(phosphino)borane complex [PhB(CH_2P~iPr_2)_2]Rh(H)_2(SiHPh_2)(PMe_3) (14).Complex 11 reacted with H_2 in the presence of 1 equiv of Me_3NO to give the oxidative addition product [PhBP_3']Rh(H)_2(CO) (15),with concomitant liberation of Me_3N.