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A systematic route to homometallic cube-type compounds bearing M4S4 cores is reported as a starting point to a new family of early transition metal sulfur clusters.
Treatment of the imido complexes [MCl3(NR)py2] (R = tBu, 2,6-Me2C6H3; M = Nb 1, 3; Ta 2, 4) (Xyl = 2,6-Me2C6H3) with (Me3Si)2S in a 1:1 ratio afforded the new cube-type sulfide clusters [MCl(NR)py(μ3-S)]4 (R = tBu, 2,6-Me2C6H3; M = Nb 5, 7; Ta 6, 8) with loss of Me3SiCl. Reactions of 5 and 6 with cyclopentadienyllithium in 1:4 ratio resulted in the rupture of the coordinative M–S bonds and the replacement of a pyridine molecule and a chlorine atom by an η5-cyclopentadienyl group in each metal center, affording the compounds [M(η5-C5H5)(NtBu)(μ-S)]4 (M = Nb 9, Ta 10). These processes may develop through formation of the complexes [M4(η5-C5H5)2(μ-Cl)(NtBu)4py2(μ3-S)2(μ-S)2](C5H5) (M = Nb 11, Ta 12), also obtained by reaction of 5 and 6 with cyclopentadienyllithium in 1:3 ratio. As further evidence, 11 and 12 led to complexes 9 and 10 by treatment with one more equivalent of the lithium reagent. The structural study of these metal sulfide clusters has been also performed by X-ray crystallography.
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