A new structural type of dinuclear rhodium(II) compounds: synthesis by serendipity and design; catalytic behaviour in carbene transfer reactions†

Abstract

The compound [Rh₂(µ-O₂CCH₃)₃(O₂CCH₃)[η²-(o-CH₃OC₆H₄)P(C₆H₅)₂] 1, having one phosphine acting as a chelating, equatorial (P)–axial(O), ligand has been structurally characterized. A new family of structurally related dirhodium(II) compounds of general formula [Rh₂(µ-O₂CR)₂(X)₂{η²-(o-YC₆H₄)P(C₆H₅)₂}₂] (R = CH₃, X = CH₃CO₂, Y = CH₃O 2; R = CF₃, X = CF₃CO₂, Y = CH₃O 3; R = CH₃, X = Cl 4 or R = CH₃, X = Cl, Y = CH₃O 5) has been synthesized. All these compounds are structurally related; they have two orthofunctionalized phosphines acting as equatorial (P) and axial (Cl, O) donor ligands and two bridging carboxylates. The two remaining equatorial sites around the rhodium atoms are occupied by two monodentate carboxylates (2, 3) or two chlorine atoms (4, 5). Compounds 4 and 5 have been structurally characterized by X-ray methods. Compound 4, initially obtained in low yield by serendipity, was also prepared in moderate yield from rhodium acetate and P(o-ClC₆H₄)(C₆H₅)₂ in the presence of a stoichiometric amount of Me₃SiCl. Compounds 2 and 3 were prepared by treating the corresponding rhodium tetracarboxylate with two moles of P(o-CH₃OC₆H₄)(C₆H₅)₂ and 5, obtained by serendipity, was best synthesized from the reaction of 2 and two moles of Me₃SiCl.