Synthesis and reactivity of rare-earth-N,N'-(diphenyl)formamidinate and rare-earth-N,N'-bis(2,4-dimethylphenyl)formamidinate complexes

Redox transmetallation/protolysis reactions of rare earth metals, Hg(C6F5)2 and a formamidine (PhFormH = N, N'-(diphenyl)formamidine or DMFormH = N,N'-bis(2,4-dimethylphenyl)formamidine) in tetrahydrofuran (thf) or 1,2-dimethoxyethane (dme) were employed to synthesize a series of the rare earth N,N'-bis(aryl)for-mamidinate complexes. Accordingly, trivalent complexes with the composition [Ln(PhForm)3(thf)n].(solv.)m [n = 2, m = 0, Ln= La (1), Pr (2); n = 2, m = 0.5, solv = thf, Sm (3); n= 2, m = 1.5, solv. = PhMe, Ln= Nd (4); n= 2, m = 1.5, solv. = thf, Ln= Gd (5); n= 2, m = 3, solv. = thf, Ln= Tb (6), Dy (7), and Y (8); n= 1; m = 0, Ln= Ho (9), Er (10) and Lu (11)] or [Ln(DMForm)3(solv.)] [Ln = Sm (12), Gd (13), solv. = dme; Ln = Pr (14), Ho (15), solv. = DMFormH; Ln = Y (16), Lu (17), solv. = thf; Ln = Er (18), solv. = dmf; dmf = N,N-dime-thylformamide] were synthesized and characterized by X-ray crystallography. Complexes 1-8 have eight coordinate Ln metals with three chelating PhForm and two transoid thf ligands, whilst 9-11 are seven coordinate with a single thf ligand. Thus, there are three structural discontinuities, namely at Ho, Y, Er, the second of which occurs in defiance of a decrease in ion size. An investigation of catalytic reactivity of representative Ln complexes in the conversion of aldehydes into esters (Tishchenko reaction) revealed most have modest catalytic properties. [Y(PhForm)3(thf)2].3thf 7 and [Y(DMForm)3(thf)] 16 had the highest reactivity for their respective ligands, with 16 by far the most effective catalyst.

Automated summary

A series of rare earth N,N'-bis(aryl)formamidinate complexes were synthesized through redox transmetallation/protolysis reactions. The complexes exhibit different coordination modes and structural characteristics.