Synthesis and characterization of ytterbium guanidinates stabilized by bridged bis(phenolate) ligand and their application for the hydrophosphonylation reaction of aldehydes

Abstract

A series of ytterbium guanidinato complexes stabilized by an amine-bridged bis(phenolate) ligand were prepared, and their catalytic property for the hydrophosphonylation reaction of aldehydes was explored. Metathesis reactions of amine-bridged bis(phenolate) ytterbium chlorides LYbCl(THF) [L = Me2NCH2CH2N{CH2-(2-OC6H2tBu2-3,5)}2] with corresponding lithium guanidinates in a 1:1 molar ratio in THF gave the expected ytterbium guanidinato complexes LYb[R2NC(NR1)2] [R1 = Cy, R2N = N(TMS)2 (1), N(CH2)5 (2); R1 = iPr, R2N = N(TMS)2 (3), NPh2 (4)]. These ytterbium complexes were well characterized by elemental analyses, IR spectroscopy and single-crystal X-ray structure determination. The metal ion is six-coordinated by two oxygen and two nitrogen atoms from the bis(phenolate) ligand, and two nitrogen atoms from one guanidinato group. The coordination geometry around ytterbium can be described as a distorted octahedron. It was found that these ytterbium guanidinato complexes are highly efficient catalysts for the hydrophosphonylation reaction of various aldehydes under mild conditions.