Synthesis of V/Fe/S Clusters Using Vanadium(III) Thiolate Complexes Bearing a Phenoxide-Based Tridentate Ligand

Vanadium­(III) thiolate complexes
carrying a phenoxide-based tridentate ligand were prepared from the
reactions of V­(NMe2)4 with the protonated forms
of tridentate ligands (H2­(O,P,O) = bis­(3,5-di-tert-butyl-2-hydroxy­phenyl)­phenylphosphine or
H2(O,O,O) = bis­(3,5-di-tert-butyl-2-hydroxy­phenyl)­phenyl­phosphine­oxide)
and thiols (HSR; R = mesityl (Mes), 2,4,6-iPr3C6H2 (Tip)). The vanadium–thiolate
complexes were subjected to the V/Fe/S cluster synthesis via treatment
with an Fe­(II) thiolate complex [(TipS)­Fe]2­(μ-SDmp)2 (4, Dmp = 2,6-(mesityl)2­C6H3) and elemental sulfur in toluene, leading to
the formation of two new V/Fe/S clusters. One is an edge-bridged double-cubane-type
[VFe3S4]-[VFe3S4] cluster
[(O,P,O)­VFe3S4­(SDmp)­(HNMe2)]2 (5) having face-capping tridentate
(O,P,O) ligands on vanadium atoms. The other is a [VFe3S4-Fe] cluster [(μ-O,O,O)­VFe3S4­(SDmp)­(STip)­Fe­(μ-SDmp)] (6), the core of which consists of a cubane-type [VFe3S4] unit and an external iron atom. The external iron
is bound to an SDmp ligand and two oxygen atoms of the tridentate
(O,O,O) ligand. Cluster 6 is structurally relevant to
the active site of nickel-dependent CO dehydrogenase, and their common
structural features include a cubane-type unit with a heterometal,
one more iron atom besides the cubane unit, and a bridging ligand
between the external iron and the heterometal of the cubane unit.