Cyclometallated derivatives of rhodium(III). Activation of C(sp3)–H vs. C(sp2)–H bonds
Abstract
The reaction of RhCl3·3H2O with a series of 6-substituted-2,2′-bipyridines HL (N2C10H7R, R = CH2Ph, HLb; C(CH3)2Ph, HLdm; CH(CH3)2, HLip; C(CH3)3, HLtb; or CH2C(CH3)3, HLnp) in refluxing water–acetonitrile gave cyclometallated species, either neutral, [Rh(L)(CH3CN)Cl2], or cationic, [Rh(L)(CH3CN)2Cl]+, resulting from direct activation of C(sp2)–H or C(sp3)–H bonds. Surprisingly, in the case of R = C(CH3)2Ph metallation involved one of the methyls rather than the phenyl group. The crystal structure of [Rh(Lb)(CH3CN)Cl2] has been determined by X-ray diffraction. Adducts [Rh(HL)(CH3CN)Cl3], likely to be intermediates in the synthesis of the metallated species, have been isolated and characterized. Some aspects of the reactivity of the adducts and of the cyclometallated species are also reported.