Pentacoordinate Silicon Complexes with N-(2-pyridylmethyl)-salicylamide as a Dianionic (ONN′) Tridentate Chelator

The title compound, N-(2-pyridylmethyl)salicylamide (1), was synthesized by ester aminolysis of methyl salicylate and 2-picolylamine. In the presence of triethylamine as a supporting base, the salicylamide moiety reacts with the organodichlorosilanes RR'SiCl2 to form the desired six-membered heterocycles of the type RR'SiO(o-C6H4)C(=O)N(pic), with pic being the 2-pyridylmethyl (i.e., 2-picolyl) moiety and RR' = Me, Me (2a); Me, Ph (2b); Ph, Ph (2c); Bn, Bn (2d); All, Ph (2e) and Ph, H (2f). Despite the absence of notable ring strain release Lewis acidity (i.e., only a six-membered chelate is formed by the dianion, and smaller rings are not present in the compound), the poor electron withdrawal from silicon by its C or H substituents and the flexible methylene bridge between the salicylamide and the pyridine moiety, the pyridine N donor atom furnishes pentacoordinate silicon coordination spheres in all of these compounds 2a2f. The coordination number of the silicon atom was confirmed by single-crystal X-ray diffraction analysis for the solid state and by 29Si NMR spectroscopy for the solution state.