Diphosphorus Release and Heterocumulene Oligomerisation by Nickel Complexes.

The generation of diphosphorus molecules P under mild conditions in solution is a useful strategy to generate diphosphines [4+2] cycloadditions. We recently described the release of P units from the nickel butterfly complex [{(IMes)Ni(CO)}(μ,η:η-P)] (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) upon addition of CO gas. Herein, we developed an alternative protocol for the same process using heterocumulenes. In addition to formation of P (the dimerisation product of P), the reactions afford nickel complexes of novel pincer-type ligands. Aryl isothiocyanates undergo a trimerisation within the coordination sphere of nickel and afford square planar nickel complexes with S-C-S pincer-ligand frameworks. Carbon disulfide coordinates to the [(IMes)Ni]-fragment in an η-fashion, affording a dinuclear complex. Similar products are formed when the N-heterocyclic carbene nickel(0) complex [(IMes)Ni(vtms)] is used as a precursor (vtms=vinyltrimethylsilane).