BINDING OF THE (MOFE3S4)(3+) CORE BY A TRIDENTATE THIOLATE AND CHEMICAL ANALOGS OF THE MOLYBDENUM COORDINATION ENVIRONMENT IN THE IRON-MOLYBDENUM COFACTOR OF NITROGENASE

The tridentate thiol 1,4,7-tris(4-sulfanylbenzoyl)-1,4,7-triazacyclononane (H(3)L) on deprotonation ligated to each of the molybdenum-iron-sulfur clusters [NEt(4)][MoFe3S4(SEt)(4)(dmpe)] 1 [dmpe = 1,2-bis(dimethylphosphino)ethane] and [NEt(4)](2)[MoFe3S4(SEt)(3)(tccat)(solv)] [H(2)tccat = 3,4,5,6-tetrachlorocatechol; solv = dimethyl sulfoxide (dmso) or MeCN], with elimination of ethanethiol, to give [NEt(4)][MoFe(3)S(4)L(SEt)(dmpe)] 2 and [NEt(4)](2)[MoFe(3)S(4)L(tccat)(solv)] (solv = dmso 4 or MeCN 5) respectively. Cluster 2 reacted with 1 equivalent of trimethylacetyl chloride to give [NEt(4)][MoFe(3)S(4)L(Cl)(dmpe)] 3. The clusters 2-5 have been characterised by H-1 NMR. IR and Mossbauer 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. NO2S3, is similar to that of molybdenum in the iron-molybdenum cofactor of nitrogenase. Similar reactions. were observed for the related cluster [NEt(4)](2)[MoFe3S4(SEt)(3)(tccat)(solv)]. Proton NMR, IR and Mossbauer parameters are reported.