Synthesis and characterization of 14-electron cyclopentadienyl chromium(II) complexes containing a heterocyclic carbene ligand

Chromocene reacts with 1,3-dimesitylimidazolium chloride in THF to yield cy clopentadiene and CpCrCl(1,3-dimesitylimidazolin-2-ylidene) (1), which cont ains an N,N-heterocyclic carbene ligand. This new complex is a relatively r are example of a CpCr(II) complex containing four unpaired electrons. The r eaction of 1 with phenylmagnesium bromide yields CpCrPh(1,3-dimesitylimidaz olin-2-ylidene) (2). An X-ray crystallographic investigation of 2 reveals a two-legged piano stool structure with a planar central Cr atom.