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, HL^b; C(CH₃)₂Ph, HL^dm; CH(CH₃)₂, HL^ip; C(CH₃)₃, HL^tb; or CH₂C(CH₃)₃, HL^np) 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(L^b)(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.

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