Amines sulfur ligands

Cobalt in its trivalent state forms many stable complexes in solution. In these complexes, the coordination number of Co + is six. The Co2+ ion also forms complexes where the coordination number is four. Several complexes of both the trivalent and divalent ions with ammonia, amines, ethylene diamine, cyanide, halogens and sulfur ligands are known (see also Cobalt Complexes). 

The Fe-Fe bonds in [CpFe(CO)(PR3)(/i-CO)] 2 are as basic as weak amines (p-Kj, 6) and concomitant shift of p-CO to terminal positions occurs on protonation [Eq. (10.12)]44 Protonation of the Fe-Fe bond in [Fe(CO)2(PR3)(/i-SR )]2 occurs in preference to protonation of the sulfur ligands [Eq. (10.13)].45 These axe, however, Fe1 centers, and analogous protonation of Feu-Fen is not well known. The basicities of M-M bonds such as in [CpRu(CO)2]2 are substantially higher than that of the metal sites in related 18e mononuclear complexes and are highly sensitive to the nature of the ancillary ligands.43 As discussed above, theoretical studies of [NiFe] H-ase mechanisms indicate that p-H intermediates are energetically favorable. As shown in the reverse sequence of Scheme 2. the hydride could then shift to a terminal position and be protonated to a readily dissociable H2 ligand, and the cycle would continue. 

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