Cyclometallation of unsaturated carboxylic acids by pentamethylcyclopentadienyl-rhodium and -iridium complexes. Crystal structures of [(C5Me5)Ir(CPhCHCO–O)(Me2SO)] and [(C5Me5)Ir(CPhCHCO–OMe)I]+

Abstract

Reaction of [(C₅Me₅)MMe₂(Me₂SO)](C₅Me₅=η-pentamethylcyclopentadienyl) with cinnamic acid gave [(C₅Me₅)[graphic omitted])(Me₂SO)](2; M = Rh) and (3a; M = Ir), while the complexes [(C₅Me₅)[graphic omitted](Me₂SO)](3b; R¹= Me, R²= H), (3c; R¹= R²= Me), and (3d; R¹= H, R²= Me) were made from the appropriate unsaturated acids. Complex (3b) was also made by reaction of [(C₅Me₅)IrCl₂(Me₂SO)] with silver crotonate. Reaction of (2), (3a), (3b), and (3d) with methyl iodide gave the complexes [(C₅Me₅)[graphic omitted]–OMe)I](6; M = Rh, R¹= Ph, R²= H), (7a; M = Ir, R¹= Ph, R²= H), (7b; M = Ir, R¹= Me, R²= H), and (7d- M = Ir R¹= H, R²= Me). The complexes were characterised by their n.m.r. spectra and by single crystl X-ray determinations for (3a) and (7a). In each case these showed the presence of a cyclometallated five-membered ring. The MC bonds in (6) and (7), but not in (2) or (3), are associated with quite substantial carbenoid character, MC[graphic omitted] Reaction of (3a) or (3b) with CO merely caused displacement of the dimethyl sulphoxide to give [(C₅Me₅) [graphic omitted](CO)](5); however, (7b) ring-opened with CO to give the σ-alkenyl complex [(C₅Me₅)Ir(CMeCHCO₂Me)(CO)I](8).