Tris(mercaptoimidazolyl)hydroborato complexes of cobalt and iron, [TmPh]2M (M = Fe, Co):: structural comparisons with their tris(pyrazolyl)hydroborato counterparts

The ti is(mercaptophenylimidazolyl)borate iron and cobalt complexes [Tm-Ph](2)M (M = Fe, Co) have been synthesized by reaction of [Tm-Ph]T1 With MI2. Structural characterization by X-ray diffraction demonstrates that the potentially tridentate [Tm-Ph] ligand binds through only two sulfur donors in these 'sandwich' complexes and that the 'tetrahedral' metal centers supplement the bonding by interactions with the two B-H groups. Comparison of the structures of [Tm-Ph](2)M (M = Fe, Co) with the related tris(pyrazolyl)borate [Tp(Ph)](2)M counterparts indicates that the tris (mercaptoimidazolyl) ligand favors lower primary coordination numbers in divalent metal complexes. The trivalent complexes, {[Tp(Ph)](2)Fe}[ClO4] and {[pzBm(Me)](2)Co}I, however, exhibit octahedral coordination, with the ligands binding using their full complement of donor atoms. (C) 2001 Elsevier Science Ltd. All rights reserved.