Mechanistic studies on the hydrolysis of a dimeric alkylzinc bis(2-pyridylmethyl) amide

Bis(2-pyridylmethyl) amine 7 reacts with selected dialkylzinc compounds to give dimeric alkylzinc bis(2-pyridylmethyl) amides 8. Regardless of the steric bulk of the alkyl substituent, dimers with central Zn2N2 rings are formed. Compounds 8 undergo spontaneous hydrolysis reactions upon exposure to air/moisture which can be partially controlled if the alkyl substituent R is bulky enough [R=CH(SiMe3)(2)]. A dimeric compound 9 containing both zinc-alkyl substituents and a l-OH functionality results. In the course of this reaction, an amide instead of the expected RH is eliminated. Extensive DFT calculations show that the facile formation of a three-centered Zn[mu(HO center dot center dot center dot H center dot center dot center dot NHR)] Zn functionality is a crucial step. Further evidence for the importance of Zn[mu-(X center dot center dot center dot H center dot center dot center dot Y)]Zn intermediates (X, Y = O and now N) in the general mechanism of hydrolysis catalyzed by binuclear zinc compounds is thus provided. (C) 2007 Elsevier B. V. All rights reserved.