Syntheses and structural characterization of tris- and tetrakis(aminopyridinate) complexes of lanthanum

Abstract

Treatment of three equivalents of potassium salts of N-arylated 2-pyridyl amines, [HN(C6H3Pri2-2,6)(2-C5H3N)] (1) and [HN(C6H3Pri2-2,6)(2-C5H3N-6-Me)] (2) with anhydrous LaBr3 in tetrahydrofuran (THF), afforded after workup in hexane the corresponding rare examples of tris(amiopyridinate) La(III) complexes, [La{N(C6H3Pri2-2,6)(2-C5H3N)}3(thf)] (3) and [La{N(C6H3Pri2-2,6)(2-C5H3N-6-Me)}3] (4) in 77% and 71% yields, respectively. X-ray analysis of 4 further confirms the monomeric nature in the solid state. Owing to the low steric bulk of the aminopyridine ligand in 3, one thf ligand is coordinated to La atom. Attempted reduction of 3 with KC8 in the presence of 12-crown-4-ether to synthesize the corresponding La(II) complex, instead resulted in the formation of [La{N(C6H3Pri2-2,6)(2-C5H3N)}4{K(12-crown-4-ether)] (5). In contrast, the analogous reaction with 4 led to [K{N(C6H3Pri2-2,6)(2-C5H3N-6-Me)}{(12-crown-4-ether)2}] along with unidentified products. Complex 5 is the first example of mononuclear tetrakis(aminopyridinate) lanthanoidate complexes.