Isocyanides reactions with Fischer carbene complexes

The metal-free eyclobutane-1,2-dioxime can be generated by oxidative displacement. It is interesting to note that, unlike ketene dimerization, head-to-head dimerization takes place here. The chromium ketenimine complex 20 is prepared by reaction of the Fischer-type chromium carbene complex with alkyl isocyanides.60 A cyclobutane-1,2,3,4-tetraimine 24 has been reported from the reaction of the ketenimine phosphonium ylide 22.61 Bisimine 23 has been proposed as the intermediate in this transformation. 

While the advent of NHC ligands brought much new activity to the field of nickel carbene chemistry, important progress was also made with more traditional Fischer-type carbene complexes. The typical route to methoxy(amino) or bis(amino) Fischer-type carbene complexes is the nucleophilic attack of alcohols or amines on coordinated isocyanides. " A new and efficient route to heteroatom-stabilized carbene nickel(ii) complexes was recently reported to occur by a protonation reaction of the nickel(O) complex Ni(GNXyl)(triphos)." Addition of 2 equiv. of HBF4 to solution of Ni(CNXyl)(triphos) in THF affords the stable dicationic nickel carbene complex [Ni C(H)N(H)Xyl (triphos)]2+(BF4-)2 (Equation (16)). 

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