Snapshots of the Stopped Polymerization of a Hindered Isocyanide 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 3 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 4c, which contains only two coupled isocyanides and can be used in the stepwise and controlled synthesis of a rare mixed Ni(II) complex 5 by using two different isocyanides.