MERCURATION OF SCHIFF-BASES OF SUBSTITUTED BENZYLIDENEANILINES

As part of an effort to investigate substituent effects on the intramolecular coordination between N and Hg, the mercuration of 36 substituted benzylideneanilines was studied. The structure characterization of the products by IR, H-1 NMR, C-13 NMR, and MS indicates that for all of the reactions examined, the mercury is directed to the ortho position of the N-phenyl ring or the para position of the N-phenyl ring when these sites are not occupied by a substituent. The position of the HgCl group in the mercurated product of N-(4-nitrobenzylidene)-beta-naphthylamine has been confirmed by single-crystal X-ray determination, which also provided circumstantial evidence for the existence of the N--> Hg intramolecular coordination with a four-membered ring. The possible mechanism of the reaction was proposed, in which the mercuration at the ortho position of the N-phenyl ring was facilitated by the imino moiety upon formation of a coordination complex with Hg(OAc)2 in the first step, followed by a subsequent electrophilic substitution at the ortho position of the N-phenyl ring. This reaction is different from the metalation of benzylideneanilines by transition metals, in which the metal atom is usually directed to the ortho position of the C-phenyl ring, and provides a new example of the so-called 'cyclometalation" reaction.