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 1H 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 Cu3 face of the tetrahedron is bridged
by a η1(N),μ2(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 °C.