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

The tridentate thiol ,7-tris(4-sulfanylbenzoyl)-1,4,7-triazacyclononan e (H(3)L) on deprotonation ligated to each of the molybdenum-iron-sulf ur clusters [NEt(4)][MoFe3S4(SEt)(4)(dmpe)] 1 [dmpe = 1,2-bis(dimethyl phosphino)ethane] and [NEt(4)](2)[MoFe3S4(SEt)(3)(tccat)(solv)] [H(2)t ccat = 3,4,5,6-tetrachlorocatechol; solv = dimethyl sulfoxide (dmso) o r 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 = dms o 4 or MeCN 5) respectively. Cluster 2 reacted with 1 equivalent of tr imethylacetyl 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 spe ctroscopies and by elemental microanalyses. Reaction of 4 with imidazo le, tetraethylammonium imidazolate, or the tetraethylammonium salt of histidine methyl ester generated clusters. isolated as black solids, i n which the molybdenum co-ordination environment. NO2S3, is similar to that of molybdenum in the iron-molybdenum cofactor of nitrogenase. Si milar reactions. were observed for the related cluster [NEt(4)](2)[MoF e3S4(SEt)(3)(tccat)(solv)]. Proton NMR, IR and Mossbauer parameters ar e reported.