Binding of molybdenum–iron–sulfur clusters by amino acid esters
Abstract
Reaction of both the double-cubane and monocubane clusters [NEt4]3[Mo2Fe7S8(µ-SEt)6(SEt)6]1 and [NEt4]3[MoFe3S4(SEt)3{Fe(cat)3}]2(H2cat = catechol) with L-cysteine ethyl ester hydrochloride (HCys-OEt·HCl) gives the common double-cubane product [NEt4]4[Mo2Fe7S8(µ-SEt)6(Cys-OEt·HCl)6]3. The cysteinate-bound cluster has been characterised by 1H NMR, UV/VIS, IR and Mössbauer spectroscopies. The conversion of the ethanethiolate-bound cluster 1 into the cysteinate cluster 3 proceeds through the chloro-intermediate [Mo2Fe7S8(µ-SEt)6Cl6]3–4. Reaction of cluster 1 or 2 with L-tyrosine methyl ester hydrochloride forms only the chloro-substituted cluster 3 or [NEt4]3[MoFe3S4Cl3{Fe(cat)3}]5, respectively. The monocubane chloro-substituted cluster 5 has been isolated by this and other routes, and fully characterised. On reaction of chloro-substituted dicubane 4 with 6 equivalents of tetraethylammonium L-tyrosinate methyl ester [NEt4][Tyr-OMe] the tyrosinate-bound cluster [Mo2Fe7S8(µ-SEt)6(Tyr-OMe)6]3–6 is formed. Proton NMR, UV/VIS, IR and Mössbauer parameters are reported.