Unmasking the Role of Schlenk Equilibria in Governing the Oxygenation of Heteroleptic Alkylzinc Complexes.

Schlenk equilibria govern the distribution of multiple chemical species in solutions of heteroleptic organometallic compounds. Yet, their role in modulating the reactivity of organozinc compounds toward O2 has not been systematically addressed. Herein, we demonstrate that the presence of free ZnR2 species in the initial reaction mixture of alkylzinc derivatives-arising from Schlenk equilibrium-mediated ligand scrambling-can markedly alter the course of their oxygenation. Specifically, we show that the oxygenation of a [Et2Zn3(dipf)4]/ZnEt2 mixture (dipf-H = N,N'-diphenylformamidine) proceeds predominantly via the more reactive ZnEt2 component. The resulting [EtZn(OEt)]4 species subsequently transfer ethoxide groups to dipf-containing coordination entities, ultimately affording a novel zinc alkoxido-amidinato octanuclear macrocycle [(EtO)Zn(dipf)]8. In contrast, the oxygenation of the pristine complex [Et2Zn3(dipf)4] leads primarily to the formation of the zinc-oxido cluster [(μ4-O)Zn4(dipf)6]. The progress of oxygenation in a series of model reaction systems was monitored using 1H NMR spectroscopy. The results provide deeper insight into the fundamental processes occurring during the oxygenation of alkylzinc compounds and reveal previously unrecognized consequences of Schlenk equilibria for the reactivity of organometallic systems.