Synthesis and reactivity of homo- and hetero-dimetallic complexes bridged by diphenyl-2-pyridylphosphine and hydrides: regioselectivity of alkyne insertion into unsaturated M1(μ-PPh2Py)(μ-H)2M2 moieties

Abstract

New homo- and hetero-dimetallic complexes bridged by diphenyl-2-pyridylphosphine and hydrides [(Cp*Ir)(μ-PPh₂Py)(μ-H)₂(MCp*)][OTf]_n (3: M = Ir, n = 2; 4: M = Rh, n = 2; 5: M = Ru, n = 1) were synthesized. The reactions of 3 with terminal alkynes gave μ-vinyl complexes [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-C(R)=CH₂)(IrCp*)][OTf]₂ (6: R = H; 7: R = CO₂Me; 9: R = Ph) and [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-CHCHR)(IrCp*)][OTf]₂ (8: R = SiMe₃; 10: R = Ph). The reactions of 4 with alkynes gave [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-C(R)=CH₂)(RhCp*)][OTf]₂ (11a: R = H; 12a: R = CO₂Me; 13a: R = Ph), two of which are in equilibrium with [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-CH₂=C(CO₂Me))(RhCp*)][OTf]₂ (12b) and [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-CH₂=C(Ph))(RhCp*)][OTf]₂ (13b) at 50 °C, respectively. The reactions of 5 with alkynes gave [(Cp*Ir)(μ-PPh₂Py)(μ-H)(μ-CH₂=C(R))(RuCp*)][OTf] (14b: R = CO₂Me; 15b: R = Ph). Plausible pathways for the insertion of alkynes to the metal–hydride bonds and the interconversion of the μ-vinyl complexes are discussed. Structures of the cationic parts of 3, 8, 9, 13b, 14b and 15b have been confirmed by X-ray analysis.