Hexameric and tetrameric copper(I) thioamidates

The two copper(I) thioamidates {Cu[RCS(NR')]}(x) (R = n-Bu, R' = t-Bu; R, R' = Me) are obtained via reaction of copper(I) chloride with lithium thioamidates. Both occur as a mixture of hexamer and tetramer, detectable in solution by H-1 NMR spectroscopy The hexamer is favored for methyl substituents, whereas the tetramer is the major product when bulkier butyl groups are used. These clusters are the first examples of copper(I) thioamidates and are the first metal thioamidates prepared via metathesis. The X-ray structures of {Cu[MeCS-(NMe)]}(6) and {Cu[(n-Bu)CS(N-t-Bu)]}(4) are presented, and a mechanism for their formation based on aggregation of dimeric units is suggested. The core of the tetramer comprises a CU4 tetrahedron with short Cu...Cu distances. Each Cu-3 face of the tetrahedron is bridged by a eta (1)(N),mu (2)(S) thioamidate unit. A:similar bridging arrangement is seen in the hexamer, but in this case the ligands are organized in a paddle-wheel fashion about a Cu6S6 pseudohexagonal prismatic core. In the case of {Cu[(n-Bu)CS(N-t-Bu)]}(x) (x = 4, 6) the two oligomers are easily separated and the tetramer can be converted to the hexamer on heating above 100 degreesC.