Schlenk-Type Equilibria of Grignard-Analogous Arylberyllium Complexes: Steric Effects.

The presence of complex Schlenk equilibria is a central property of synthetically invaluable Grignard reagents substantially affecting their reactivity and selectivity in chemical transformations. In this work, the steric effects of aryl substituents on the Schlenk-type equilibria of their lighter congeners, arylberyllium bromides, are systematically studied. Combination of diarylberyllium complexes Ar Be(OEt ) (1Ar, Ar=Tip, Tcpp; Tip=2,4,6-iPr C H , Tcpp=2,4,6-Cyp C H , Cyp=c-C H ), containing sterically demanding aryl groups, and BeBr (OEt ) (2) affords the Grignard-analogous arylberyllium bromides ArBeBr(OEt ) (3Ar, Ar=Tip, Tcpp). In contrast, Mes Be(OEt ) (1Mes, Mes=2,4,6-Me C H ) and 2 exist in a temperature-dependent equilibrium with MesBeBr(OEt ) (3Mes) and free OEt . Ph Be(OEt ) (1Ph) reacts with 2 to afford dimeric [PhBeBr(OEt )] ([3Ph] ). Moreover, the influence of replacing the OEt donor by an N-heterocyclic carbene, IPr Me (IPr Me =C(iPrNCMe) ), on the redistribution reactions was investigated. The solution- and solid-state structures of the diarylberyllium and arylberyllium bromide complexes were comprehensively characterized using multinuclear ( H, Be, C) NMR spectroscopic methods and single-crystal X-ray diffraction, while DFT calculations were employed to support the experimental findings.