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.