FORMATION OF ORGANOMETALLIC EXCIPLEXES OF THE TYPE [HG(ETA(2)-ARENE)]IN MERCURY PHOTOSENSITIZED REACTIONS OF AROMATIC-COMPOUNDS

The formation of an organometallic exciplex, (3)[Hg(eta(2)-C6H6)], bet ween tripler mercury (Hg) and the arene ring is proposed on the basis of experimental and MP2 PCI-80 theoretical studies to account for the unusual products in the Hg-photosensitized dehydrodimerization of a s eries of aromatic substrates. Apart from the usual C-H bond cleavage, C-C cleavage is also seen for PhCH(2)-CH3 and related systems. In this paper we demonstrate that these bond cleavage reactions occur, probe their mechanism, and explore ways to prevent or promote them. In parti cular, we propose that exciplex formation leads to tripler sensitizati on of the arene, which is followed by C-C bond cleavage via a pathway investigated by Otsuji and coworkers.