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

The coordination chemistry of ancillary amidinate ligands with a pendant py ridine 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 amidine s 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 mon o- or bis(amidinate) complexes (L-Me)(2)Mg (3a), (L-tBu)AlMe2 (4), (L-tBu)Z r(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 t o be monomeric, with the pendant pyridine coordinated intramolecularly in a ll cases. The tridentate amidinate coordinates meridionally to the metal ce nter except in the case of the lanthanum derivative 6, where an approximate facial geometry is observed.