METALLACYCLIC ACYL CARBOXYLATES OF NICKEL - REACTIVITY OF THE ACYL GROUP AND POSSIBLE SYNTHESIS IN CROSS-COUPLING REACTIONS WITH ALKYLHALIDES

2-Cyclohexene-1,2-dicarboxylic acid-anhydride reacts with electron-rich nickel(0) centres to form nickel(0) complexes, whereas the isomeric 4-cyclohexene-1,2-dicarboxylic acid-anhydride reacts with ring opening of the anhydride to yield thermally stable acyl-carboxylato-nickel(II) compounds. The structure of a typical compound with (TMED)Ni0 as a complex fragment was determined by single crystal X-ray structural analysis, the crystal also containing the product of CO-elimination, the nickelalactone. The cross-coupling reaction of metallacyclic acyl-carboxylato complexes of Ni with R-X can be used for the formation of side chains of steroids containing gamma-ketocarboxylic acids. These compounds are interesting precursors for the preparation of analogues of vitamin D3 metabolites.