Cyclometallated derivatives of rhodium(III). Activation of C(sp(3))-H vs. C(sp(2))-H bonds

The reaction of RhCl3. 3H(2)O with a series of 6-substituted-2,2'-bipyridin es HL (N2C10H7R, R = CH2Ph, HLb; C(CH3)(2)Ph, HLdm; CH(CH3)(2), HLip; C(CH3 )(3), HLtb; or CH2C(CH3)(3), HLnp) in refluxing water-acetonitrile gave cyc lometallated species, either neutral, [Rh(L)(CH3CN)Cl-2], or cationic, [Rh( L)(CH3CN)(2)Cl](+), resulting from direct activation of C(sp(2))-H or C(sp( 3))-H bonds. Surprisingly, in the case of R = C(CH3)(2)Ph metallation invol ved one of the methyls rather than the phenyl group. The crystal structure of [Rh(L-b)(CH3CN)Cl-2] has been determined by X-ray diffraction. Adducts [ Rh(HL)(CH3CN)Cl-3], likely to be intermediates in the synthesis of the meta llated species, have been isolated and characterized. Some aspects of the r eactivity of the adducts and of the cyclometallated species are also report ed.