Activation of unsaturated substrates by cobalt complexes. Crystal structure and reactivity of a complex of octacarbonyl dicobalt with N-methylbis(α,α-dimethylpropargyl)amine

Abstract

A new complex of octacarbonyl dicobalt with N-methyl(α,α-dimethylpropargyl)amine was prepared and characterized by spectroscopic and X-ray diffraction methods. Each triple bond is coordinated to a hexacarbonyldicobalt fragment and each metal shows a pseudo-octahedral geometry. The structure of the free ligand having NH in place of N-methyl has also been determined for comparison. Thermal decomposition of the complex in toluene or in benzonitrile afforded a series of products, mainly resulting from the rearrangement of the original complex to a metallacyclic structure, able to incorporate either the acetylenic triple bond or carbon monoxide in the case of toluene and either the acetylenic or the nitrile triple bond in the case of benzonitrile. CN bond cleavage of the starting amine was observed as a side reaction. Catalytic reactions leading to benzonitrile incorporation were also observed. A cross experiment with a 1 1 mixture of diynes, either with or without geminal methyl groups α to triple bonds showed that for conformation reasons the metallacycle moiety mainly comes from the substrate containing geminal groups, whilst for steric reasons the other substrate is preferentially incorporated into the metallacycle.