Synthesis and reactivity of the iridium(I) mesityl complex Ir(CO)(mes)(dppe). Oxidative addition and ligand activation reactions

Article abstract of DOI:10.1021/ja00117a020

The complex Ir(CO)(mes)dppe (1) (mes = 1,3,5-trimethylphenyl, dppe = 1,2-bis(diphenylphosphino)-ethane) has been synthesized from the reaction of IrBr(CO)(dppe) and mesitylmagnesium bromide. Complex 1 crystallizes in the monoclinic space group, P2₁/n (No. 14), with Z = 4, a = 8.953(3) ?, b = 22.752(6) ?, c = 16.212(6) ?, and β = 99.00(3)°, and displays a slight tetrahedral distortion from square planarity. A benzene solution of 1 undergoes an unusual transformation when heated to 90 °C under ethylene to form the five-coordinate dimethylbenzyl complex Ir(η²-C₂H₄)(CH₂C ₆H₃(CH₃)₂)(CO)(dppe) (2) via o-methyl C-H activation. An X-ray determination of 2 shows that it crystallizes in the orthorhombic space group, Pbca (No. 61), with Z = 8, a = 19.113(8) ?, b = 16.243(9) ?, c = 23.174(7) ?. Complex 1 under CO undergoes aryl migration to form the dicarbonyl adduct Ir(CO)₂(C(O)C₆H₂(CH₃) ₃)(dppe) (6). After a benzene solution of complex 6 is heated, an equilibrium of trans-IrH(CO)(CH₂C₆H₂(CH₃) ₂C(O))(dppe) (7), cis-IrH(CO)(CH₂C₆H₂(CH₃) ₂C(O))(dppe) (8), and 6 is formed. Complexes 7 and 8 are formed by o-methyl C-H activation. A crystal structure determination of 8 shows that it crystallizes in the monoclinic space group P2₁/n (No. 14), with Z = 4, a = 10.701(3) ?, b = 14.554(3) ?, c = 20.760(6) ?, and β = 90.19(3)°. Solutions of complex 1 undergo stereospecific oxidative additions of HY (Y = SiHPh₂, H) to form IrH(Y)(CO)(mes)(dppe) (9) (Y = SiHPh₂) and 10 (Y = H), respectively. The complex IrI₂-(C(O)C₆H₂(CH₃) ₃)(dppe), 11, is formed when a benzene solution of 1 is treated with a benzene solution of I₂. Under HCl gas, a CD₂Cl₂ solution of 1 is readily converted to IrHCl₂(CO)(dppe) (12) and free mesitylene.