Selective C-C bond activation of 2-aryl-1-methylenecyclopropanes promoted by Ir(I) and Rh(I) hydrido complexes. Mechanism of ring-opening isomerization of the strained molecules

[IrH(CO)(PPh₃)₃] promotes ring opening of 2-phenyl-1-methylenecyclopropane at room temperature to produce the Ir complex with a chelating 2-phenyl-3-butenyl ligand, [Ir{η₂-CH ₂CH(Ph)CH=CH₂-κC¹}(CO)(PPh ₃)₂] (1). The reaction of excess 2-phenyl-1- methylenecyclopropane with [IrH(CO)(PPh₃)₃] at 50 °C yields [Ir{η²-(o-C₆H₄)CH(Me)CH= CH ₂-κC¹}(CO)(PPh₃)₂] (2), accompanied by the formation of 1-phenyl-1,3-butadiene and 2-phenyl-1,3- butadiene. 2,2-Diphenyl-1-methylenecyclopropane reacts with [IrH(CO)(PPh ₃)₃] to afford [Ir{η²-CH ₂CPh₂CH=CH₂-κC¹}(CO)-(PPh ₃)₂] (3) at 50 °C and [Ir{η²-(o-C ₆H₄)CMe(Ph)CH=CH₂-κC¹}(CO) (PPh₃)₂] (4) at 100 °C. Heating a solution of 3 at 100 °C also forms 4 quantitatively. X-ray crystallography of 3 reveals a penta-coordinated structure around the Ir center bonded to a chelating 2,2-diphenyl-3-butenyl ligand. The reactions of 2,2-diphenyl-1- methylenecyclopropane and of 2,2-di(4-fluorophenyl)-1-methylenecyclopropane with [RhH(CO)(PPh₃)₃] at room temperature yield [Rh{η²-CH₂CAr₂CH=CH₂- κC¹}(CO)(PPh₃)₂] (5a: Ar = Ph, 5b: Ar = C₆H₄-F-4). The reactions at 50 °C cause ring opening of the substrate and orthometalation of the phenyl group to afford [Rh{η²-(o-C₆H₄)CMe(Ph)CH=CH ₂-κC¹}-(CO)(PPh₃)₂] (6a) and [Rh{η²-(o-C₆H₃-F-4)CMe(C₆H ₄-F-4)CH=CH₂-κC¹}(CO)(PPh ₃)₂] (6b), respectively. Formation of 1,1-diaryl-1,3- butadiene is observed during the reaction. Heating a solution of Sa at 50 °C produces 1,1-diphenyl-1,3-butadiene and an allylrhodium complex, 8, rather than 6a, although the reaction of excess 2,2-diphenyl-1-methylene-cyclopropane with 5a at 50 °C affords 6a in 60%. The mechanisms of the above reactions are discussed based on the products and reaction rates. Coordination of P(OMe) ₃ to the Rh center of 5a causes insertion of the CO ligand into the Rh-C bond to afford [Rh{η²-CO-CH₂CPh ₂CH=CH₂-κC¹}(P(OMe)₃) ₃] (7).