Binding of the {MoFe3S4}3+ core by a tridentate thiolate and chemical analogues of the molybdenum co-ordination environment in the iron–molybdenum cofactor of nitrogenase

Abstract

The tridentate thiol 1,4,7-tris(4-sulfanylbenzoyi)-1,4,7-triazacyclononane (H₃L) on deprotonation ligated to each of the molybdenum–iron–sulfur clusters [NEt₄][MoFe₃S₄(SEt)₄(dmpe)]1[dmpe = 1,2-bis(dimethylphosphino)ethane] and [NEt₄]₂[MoFe₃S₄(SEt)₃(tccat)(solv)][H₂tccat = 3,4,5,6-tetrachlorocatechol; solv = dimethyl sulfoxide (dmso) or MeCN], with elimination of ethanethiol, to give [NEt₄][MoFe₃S₄L(SEt)(dmpe)]2 and [NEt₄]₂[MoFe₃S₄L(tccat)(solv)](solv = dmso 4 or MeCN 5) respectively. Cluster 2 reacted with 1 equivalent of trimethylacetyl chloride to give [NEt₄][MoFe₃S₄L(Cl)(dmpe)]3. The clusters 2–5 have been characterised by ¹H NMR, IR and Mössbauer spectroscopies and by elemental microanalyses. Reaction of 4 with imidazole, tetraethylammonium imidazolate, or the tetraethylammonium salt of histidine methyl ester generated clusters, isolated as black solids, in which the molybdenum co-ordination environment, NO₂S_3′ is similar to that of molybdenum in the iron–molybdenum cofactor of nitrogenase. Similar reactions were observed for the related cluster [NEt₄]₂[MoFe₃S₄(SEt)₃(tccat)(solv)]. Proton NMR, IR and Mössbauer parameters are reported.