Synthesis, Structures, and Reactivities of Guanidinatozinc Complexes and Their Catalytic Behavior in the Tishchenko Reaction

Treatment of a secondary amine (pipH, Bz2NH, Et2NH) with sequentially diethylzinc and N,N′-dicyclohexylcarbodiimide in hexane has afforded in good yield the new crystalline guanidinatozinc complexes. Each has been X-ray and solution NMR spectrally characterized. Three are dimeric (mono)­guandinatozinc alkyls, two are dinuclear (tris)­guanidinatozinc amides, and one is a homoleptic zinc bis­(guanidinate). The reactions of dinuclear (tris)­guanidinatozinc amides with diethylzinc and N,N′-dicyclohexylcarbodiimide in the molar ratios of 1:2:1 led to the dimeric (mono)­guandinatozinc alkyls; homoleptic zinc bis­(guanidinate) with an equimolar portion of diethylzinc also yielded dimeric (mono)­guandinatozinc alkyls. Each of the complexes exhibited good to excellent catalytic activity for the solvent-free Tishchenko reaction under mild conditions.