Nickel complexes sulfur ligands

Ligand (119) yields nickel complexes of type [Ni2L](BF4)4 (low spin) and [Ni2L(NCS)4].2H20 (high spin). For each of these complexes, physical studies indicate that the macrocycle circumscribes the two nickel ions such that each ion is surrounded by four sulfur donors in a planar array. 

In Table 108 significant examples of nickel(II) complexes with mixed-donor macrocycles of various denticity are reported. Apart from the nitrogen atoms, the heteroatoms in the macrocyclic rings are usually either O or S, or in a few cases P. Few examples of nickel complexes with macrocycles containing all-sulfur or all-phosphorus donor atoms have been reported to date they are also included in Table 108. In nickel(II) complexes formed by mixed-donor penta- and hexa-dentate ligands the oxygen atoms of the macrocycle are often only weakly coordinated or are not coordinated at all. 

Hydrides of Ni(I) and Ni(II) are known (37). A Ni(II) hydride appears to be an intermediate in the catalysis of olefin isomerization by phosphine complexes of nickel (61). Dilworth (62) has pointed out that stable hydride species are not obtained in model complexes with sulfur ligands. However, they may be possible within the confines of a protein chelate. 

These reactions demonstrated the selective alkylation of sulfur donors in dithiolene ligands. However, they appeared to be confined to nickel triad dithiolene complexes, and the resulting multidentate sulfur ligand could not be decoordinated. 

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