Novel π HgCl2 complexes of tropothione

HgCl2 complexes of tropothione derivatives and tropone are studied both experimentally and theoretically. IR spectroscopic data of these complexes are compared with theoretical ones derived from vibrational analyses. Tropone is linked with HgCl2 in the form of a sigma complex. But, tropothione and its derivatives give pi complexes. Model BF3, BCl3, AlCl3 and HgCl2 complexes of acetone, thioacetone and tropone are all confirmed to be sigma complexes. Large Lewis acids are bonded with tropothiones in pi complexes. The sigma-pi selectivity of the Lewis-acid coordination is ascribed to the difference of HOMO shapes of tropone and tropothione. (C) 1997 Elsevier Science B.V.