Structural and Chemical Properties of Zwitterionic Iridium Complexes Featuring the Tripodal Phosphine Ligand [PhB(CH_2PPh_2)_3]^-

Abstract

Several new iridium compounds bearing the PhB(CH_2PPh_2)_3^- (herein abbreviated as [PhBP_3]) ligand have been prepared and characterized, and a comparison of steric, electronic, and chemical properties is made with those of related pentamethylcyclopentadienyl (Cp^*) and hydridotris(3,5-dimethylpyrazolyl)borate (Tp^(Me)_2) complexes. The complexes [PhBP_3]Ir(H)(η_3-C_8H_(13)) (2) and [PhBP_3]Ir(H)(η^3-C_3H_5) (3) were synthesized from the reaction of [Li(TMED)][PhBP_3] (1) with the corresponding [(alkene)_2IrCl]_2 complex. These allyl complexes serve as precursors to the dihalides [PhBP_3]IrX_2 (10, X = I; 12, X = Cl). In addition to these dihalides, the five-coordinate species [PhBP_3]IrMe_2 (16) and [ClB(CH_2PPh_2)_3]IrCl_2 (13) have been isolated. Addition of CO to 2 or 3 gave [PhBP_3]Ir(CO)_2 (7), while reaction of H_2 with 2 yielded {[PhBP_3]IrH_2}_2 (8) in benzene and [PhBP_3]Ir(COE)H_2 (9) in THF (where COE = cyclooctene). Complex 2 reacted with PMePh_2 to give [PhBP_3]Ir(PMePh_2)H_2 (5) and 1,3-cyclooctadiene. The protonation of 5 with [H(OEt_2)]{B[3,5-C_6H_3(CF_3)_2]_4} gave the classical hydride complex {[PhBP_3]Ir(PMePh_2)H_3}{B[3,5-C_6H_3(CF_3)_2]_4} (6). In addition to the formation of allyl complexes 2 and 3, several C−H activation reactions have been observed; addition of P^(Me)_3 to 2 provided the cyclometalated product {PhB[(CH_2PPh_2)_2(CH_2PPhC_6H_4)]}Ir(H)(PMe_3)(4) and COE. Photolysis of 5 gave PhB[(CH_2PPh_2)_2(CH_2PPhC_6H_4)]}Ir(H)(PMePh_2) (A) and [PhBP_3]Ir(H)(PMePhC_6H_4) (B). Complex 9 catalyzes H/D exchange between COE and benzene-d_6. Metathesis reactions of diiodide 10 with LiBHEt_3 gave [Li(THF)_n]{[PhBP_3]Ir(H)_2I} (14a) and [Li(THF)_n]{[PhBP_3]Ir(H)_3} (15). Comparison of the spectroscopic properties of related [PhBP_3]Ir, Cp^*Ir, and Tp^(Me)_2Ir complexes suggests that relative donating abilities follow the trend [PhBP_3] ≥ Cp^* > Tp^(Me)_2, and structural comparisons indicate that [PhBP_3] is the most sterically demanding ligand.

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