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.