Snapshots of the Stopped Polymerization of a HinderedIsocyanide within the Coordination Sphere of Ni(II)

The use of cationic Ni­(II) complexes containing dialkyldithiophosphate ligands in conjunction with sterically hindered isocyanides suppresses polymerization, allowing the formation of well-defined monomeric cationic Ni­(II) complexes <b>3</b> that result from the coupling of three isocyanides. These complexes have been characterized, including X-ray structure determination, and represent a snapshot of the first steps of the polymerization of isocyanide. Studies via X-ray, IR, and NMR seem to indicate that the key active species in the Ni­(II)-catalyzed isocyanide polymerization and its so-called “merry-go-round” mechanism is not a carbene, as has been proposed, but actually a formamidinyl species. The use of the most sterically congested set of ligands enabled the isolation of the intermediate species <b>4c</b>, which contains only two coupled isocyanides and can be used in the stepwise and controlled synthesis of a rare mixed Ni­(II) complex <b>5</b> by using two different isocyanides.