Synthesis and molecular structures of the cobalt complexes (η⁴-C4Me4)Co(CO)2SnCl 3, (η⁴-C4Me4)Co(CO) 2(TeI2Ph), and (η⁴-C4Me 4)Co(CO)2 (TeBrIPh) with the shortened Co-Sn and Co-Te bonds

The complex (η4-C4Me4)Co(CO)2I (I) reacted with excess SnCl2 in boiling THF to give, through replacement of the iodide ligand by the fragment SnCl3, the mononuclear complex (η4-C4Me4)Co(CO)2SnCl3 (II) containing the Co-Sn bond (2.459(1) Å). In a reaction of complex I with phenyltellurenyl halides PhTeI and PhTeBr, an analogous insertion into the cobalt-iodine bond yielded (η−C4Me4)Co(CO)2(TeI2Ph) (III) and (η4-C4Me4)Co(CO)2(TeBrIPh) (IV), respectively. This type of coordination of the aryltellurenyl halide fragment to the transition metal atom was observed for the first time. X-ray diffraction analysis revealed a substantial shortening of the formally single Co-Sn and Co-Te bonds in complexes II–IV compared to the sum of the covalent radii of the corresponding atoms.