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

The compound [Rh-2(mu-O2CCH3)(3)(O2CCH3)[eta(2)-(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 [Rh-2(mu-O2CR)(2)(X)(2){eta(2)-( o-YC6H4)P(C6H5)(2)}(2)] (R = CH3, X = CH3CO2, Y = CH3O 2; R = CF3, X = CF3C O2, 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 or thofunctionalized phosphines acting as equatorial (P) and axial (Cl, O) don or ligands and two bridging carboxylates. The two remaining equatorial site s 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 a nd P(o-ClC6H4)(C6H5)(2) in the presence of a stoichiometric amount of Me3Si Cl. Compounds 2 and 3 were prepared by treating the corresponding rhodium t etracarboxylate 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.