Cyclometalation reactions are among the oldest C-H activation processes, and those involving aromatic phosphines are well known in electron-rich complexes of the late transition metals. We have recently been able to effect cyclometalation reactions for the first time at basic cobalt centers by using imine group. It is also of general interest to study the reactivity of trimethylphosphine stabilized cobalt compounds toward aromatic imines. Imine ligands are reacts smoothly under mild conditions with cobalt (I) adducts to form five-membered metallacycles.The reaction of N-(1-naphthylmethylene) aniline, N-(1-naphthylmethylene)-2,6-dimethylaniline and N-Benzylbenzylidene imine with CoCH₃ (PMe₃)₄ to give ortho-metalated Co (I) & (III) complexes 1, 2, 3 and 4. All complexes are given from 1- 4 were characterized through IR, NMR and X-ray diffraction.