Synthesis, structure, and coordination chemistry of a tridentate, six-electron-donor amidinate ligand

The coordination chemistry of ancillary amidinate ligands with a pendant pyridine functionality is described. Reaction of p-toluoyl- or p-Bu-t-benzoyl chloride with 2-aminoethylpyridine generates the amides 2-Py-(CH2)(2)NHCO(p-RPh) (R = Me 1a; Bu-t 1b); these amides are then converted to the amidines 2-Py-(CH2)(2)NHC(p-RPh)NR' (R = Me, R' = Ph (2a) ((LH)-H-Me); R = tBu, R' = 3,5-dimethylphenyl (2b) ((LH)-H-tBu)) by reaction with PCl5 followed by R'NH2. The amidines 2a,b were characterized by H-1 NMR and IR spectroscopy and elemental analyses, and 2b was characterized by X-ray crystallography. Reaction of 2a or 2b with homoleptic metal-alkyls or -amides yields the mono- or bis(amidinate) complexes (L-Me)(2)Mg (3a), (L-tBu)AlMe2 (4), (L-tBu)Zr(CH2Ph)(3) (5), and (L-Me)(2)La[N(SiMe3)(2)] (6). All metal complexes were characterized by 1H NMR and IR spectroscopy, elemental analyses, and X-ray crystallography. The X-ray crystal structures of compounds 3-6 show them to be monomeric, with the pendant pyridine coordinated intramolecularly in all cases. The tridentate amidinate coordinates meridionally to the metal center except in the case of the lanthanum derivative 6, where an approximate facial geometry is observed.