σ-Bonded organotransition-metal ions. Part XIV. Characterisation of monomeric and bridged anionic complexes of organocobaloximes

Abstract

A number of alkyl-, alkenyl-, and alkynyl-bis(dioximato)cyanocobaltate(III) ions have been prepared and characterised as tetraphenylarsonium and tetra-alkylammonium salts. Corresponding dimeric bridged anionic complexes, in which two organocobalt groups are bonded to the same cyanide ligand, have been isolated and/or characterised in solution. The cyanide stretching frequency of the dimeric complexes is ca. 30–40 cm–1 greater than that of the monomeric complexes, and both increase with the electronegativity of the α-carbon of the organic group(s). Bridged cyanide complexes in which the two organocobalt components differ have been shown to rearrange and disproportionate by an intermolecular mechanism. A trimeric compound containing two cyanide bridges has also been isolated. Similar monomeric and dimeric azido- and thiocyanato-complexes have been isolated. Both Sand N-bonded thiocyanate complexes are believed to coexist and to exchange in solution, the latter being slightly favoured. Only monomeric cyanate complexes have been prepared, and may involve a rapidly established equilibrium between the O- and the N-bonded species in solution.