Synthesis and X-ray Structures of the Conformational Isomers of the Mixed Bimetal Complex (t-BuNC)4Mo(μ-t-BuS)2CuBr

Article abstract of DOI:10.1021/ja00340a018

The molecular fragment cis-Mo(t-BuS)2 has been found to act as a bidentate ligand, exhibiting affinity toward d¹⁰ metals.Reaction of Mo(t-BuS)4 or cis-(Mo(t-BuS)2(t-BuNC)4 with CuBr(t-BuNC)3 in acetone under dinitrogen gives crystals of formula (t-BuNC)4Mo(μ-t-BuS)2CuBr.Two isomers have been isolated in the solid state, differing only in the relative arrangements of tert-butyl substituents on the thiolato bridges.The anti-upright isomer 1 crystallizes from an acetone-toluene mixture with a molecule of diphenylacetylene in a monoclinic cell of dimensions a = 11.702 (2), b = 20.134 (4), and c = 10.455 (4) Angstroem, β = 98.85 (2) deg, Z = 2, and space group P2₁.Refinement by block-diagonal least-squares methods on F using 3690 unique, diffractometer data converted at R = 0.09.Compound 1 contains a MoS2Cu core, with Mo-Cu = 2.628 (2) Angstroem.The Mo atom has a distorted octahedral coordination geometry, with a large S-Mo-S angle of 105 (1) deg.The Cu atom has almost ideal trigonal-planar geometry.A second isomer, 2, may be crystallized from acetone in the orthorhombic space group Pnma, cell dimensions a = 21.994 (2), b = 16.411 (3), and c = 10.605 (1) Angstroem, with Z = 4.Full-matrix least-squares refinment on F using 2882 averaged data converted at R = 0.08. m symmetry is imposed upon the molecule, which differs from 1 only in the t-Bu substituents on the thiolato bridges adopt a syn-upright conformation.The interconversion of 1 and 2 has been demonstrated by variable-temperature 1H NMR, and values of ΔG^* = 7.1 (7) kcal mol^-1, ΔH^* = 4.9 (2) kcal mol ^-1, and ΔS^* = -6 (2) cal mol^-1 deg^-1 estimated for the conformational change.