Bisborohydride yttrium complexes containing amidinate ligands [o-Me2NC6H4CH2C(NR)2]Y(BH4)2L n (R = Pri, L = DME, n = 1; R = Cy, L = THF, n = 2). Synthesis, structure, and catalytic activity in polymerization of rac-lactide and isoprene

Abstract

A reaction of o-N,N-dimethyltoluidine lithium derivative (o-Me2NC6H4CH2Li) with carbodiimides (RN=C=NR, where R = Pri, Cy) in THF at room temperature leads to lithium complex of the general formula [{o-Me2NC6H4CH2C(NR)2}Li(THF)2]2 (R = Pri (1), Cy (2)) containing a new tridentate amidinate ligand. X-ray diffraction studies showed that complexes 1 and 2 are dimeric due to the coordination of the nitrogen atoms of the amidinate group with different lithium atoms. The nitrogen atoms of the aminobenzyl fragment are not involved in the complexation. The exchange reactions of Y(BH4)3(THF)3 with lithium amidinates 1 and 2 carried out with the equimolar ratio of reagents in solution in THF proceeded with the formation of neutral amidinatebisborohydride complexes of the general formula [o-Me2NC6H4CH2C(NR)2]Y(BH4)2Ln (3: R = Pri, L = DME (with added DME), n = 1; 4: R = Cy, L = THF, n = 2). According to the X-ray diffraction data, compounds 3 and 4 are monomeric, borohydride ligands are coordinated to the rare-earth metal atom by the η3- and η2-type. The donor NMe2 groups of the amidinate ligands are not involved in the metal—ligand interaction. Yttrium complexes 3 and 4 exhibit catalytic activity in polymerization of rac-lactide and isoprene.