SYNTHESIS AND PROPERTIES OF TRIMERIC ORTHO-CHELATED (ARENETHIOLATO)COPPER(I) COMPLEXES

Neutral (arenethiolato)copper(I) complexes [CuSC6H3(CH(R')NMe2)-2-R"-3]3 (R' = H, R" = H, Cl; R' = Me, R" = H) with an intramolecularly coordinating ligand have been prepared and characterized. Crystals of [CuSC6H4(R-CH(Me)NMe2)-2]3.THF are hexagonal, space group P6(3), with a = 13.743 (1) angstrom, b = 11.248 (1) angstrom, V = 1839.8 (3) angstrom 3, Z = 2, and final R = 0.054 for 1448 reflections with I greater-than-or-equal-to 2.5-sigma(I) and 140 variables. The crystals are triboluminescent. The structure contains a Cu3S3 six-membered ring in a chairlike conformation with alternating copper and sulfur atoms, and on each sulfur atom the C6H3(R-CH (Me)NMe2)-2 group is bonded equatorially with respect to this ring. Coordination of the nitrogen atoms of the o-CH(Me)NMe2 substituents to the copper atoms (Cu-N = 2.077 (7) angstrom) provides three six-membered CuSCCCN chelate rings. The bridge bonding of the arenethiolate has striking structural features, an acute Cu-S-Cu angle of 79.63 (7)-degrees, Cu-S bond lengths of 2.231 (2) angstrom and 2.186 (2) angstrom, and a short Cu...Cu distance of 2.828 (1) angstrom. These features reflect an electron-deficient two-electron three-center Cu2S bond in which there is interaction of a sulfur sp2 hybrid orbital with a bonding combination of empty orbitals on the two copper atoms. In solution the [CUSC6H3(CH(R')NMe2)-2-R"-3]3 complexes remain trimeric but exist as two conformers that are in equilibrium through inversion at the bridging sulfur atoms. H-1 and "C NMR studies reveal that the ratio of these two conformers can be influenced by changing R' and R" in the arenethiolate ligand. The low free activation energy barrier (DELTA-G not-equal = +/- 50 kJ/mol) for sulfur inversion is explained by a new mechanism which is based on a rotation (wagging) process around the axis through the sp2 hybrid orbital in the electron-deficient Cu2S unit. Evidence for the occurrence of separate intermolecular exchange processes is presented.