The new ligand (Me3Si)2 NC(Ph)NP(Ph)2 N(SiMe3) (1) reacts with MOOCl 4 to yield the green metallacycle 4. 4 was characterized by X-ray diffraction. Crystals of 4 are monoclinic, space group P21/n with a = 1061.2(10). b = 1590.5(10), c = 1737.4(20) pm, β = 104.84(7)° and Z = 4. Mo is coordinated octahedrally by two nitrogens of the bifunctional ligand. by one oxygen and three chlorine atoms. The ligand undergoes cyclization, a bond being formed between N and one phenylic o-position.