Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen. CXXVI. Heterocyclen-carbene als phosphananaloge liganden in metallkomplexen

Carbenes L derived from imidazole and triazole, as generated from the corresponding azolium precursor salts, smoothly react with simple metal carbonyls such as M(CO)₆ (M Cr, Mo, W), Fe(CO)₅, and Ni(CO)₄ to give the substitution products M(CO)₅L, Fe(CO)₄L, Ni(CO)₃L, and Ni(CO)₂L₂, respectively, owing to the pronounced C-nucleophilicity of the free carbenes L. Dicarbenes L L form chelate complexes of type M(CO)₄(L L) upon treatment with M(CO)₆ (M Cr, Mo, W). The new bis(carbene)nickel (0) complex Ni(CO)₂L₂ and the first member of a metal complex M(CO)₄(L L) exhibiting a chelating dicarbene of the triazole series have been characterized by single-crystal X-ray diffraction. It is evident from the present study that heterocyclic mono- and (chelating) dicarbenes of the aza-type are congeners of phosphanes and diphosphanes, resp., with regard to their metal-coordination chemistry. Both in terms of ligand properties and metal complex synthesis, they closely resemble electron-rich phosphanes, e.g. trimethylphosphane.