N-(o-Aminophenyl)-2-oxy-4-methoxybenzophenoneimine – Si-chelation by a tridentate ONN ligand system versus benzimidazoline formation

Reaction of 2-hydroxy-4-methoxybenzophenone (o-HO-p-MeO–C6H3–C(Ph) = O) with o-phenylenediamine (o-H2N–C6H4–NH2) yielded the tridentate chelating ligand 1a (N-(o-aminophenyl)-2-oxy-4-methoxybenzophenoneimine, o-HO-p-MeO–C6H3–C(Ph) = N-(o-C6H4)–NH2). Ligand 1a reacts with diphenyldichlorosilane in the presence of triethylamine to yield the pentacoordinate silicon compound 2a (Ph2Si[o-O-p-MeO–C6H3–C(Ph) = N-(o-C6H4)–NH]). N-acetylation of 1a yields 1b, the reaction of which with Ph2SiCl2 surprisingly yields a silylated benzimidazoline 3.