Alkylberyllium alkoxides and some of their reactions with bases

Abstract

A series of alkylberyllium alkoxides has been prepared by alcoholysis of beryllium dialkyls. Most of the alkoxides are tetrameric in benzene, but lower degrees of association result when the organic groups are large, e.g., (EtBeOCEt₃)₃, (MeBeOCPh₃)₂, and (Bu^tBeOBu^t)₂. The alkoxides (MeBeOPrⁱ)₄, (MeBeOBu^t)₄, and (EtBeOCEt₃)₃ were also obtained by addition of the beryllium dialkyl to MeCHO, Me₂CO, and Et₂CO, respectively, without detectable alkane elimination. The t-butoxide, (MeBeOBu^t)₄, which gives [Be(OBu^t)₂]₃ on reaction with acetone, was also formed from dimethylberyllium and either beryllium t-butoxide or di-t-butyl peroxide. Methylberyllium n-propoxide, (MeBeOPrⁿ)₄, is formed from Me₂Be and propan-1-ol or ethylene oxide. Beryllium triethylmethoxide is dimeric in benzene.

Though methylberyllium t-butoxide crystallises, ether-free, from diethyl ether and is tetrameric (isopiestically, 0·022M) in that solvent as well as in benzene (cryoscopically), both it and four other methylberyllium alkoxides are dimeric in very dilute solution (0·002–0·007M, as dimer) in diethyl ether (ebullioscopically). Some other alkoxides form ether and other complexes which are monomeric in benzene, e.g., MeBeOCPh₃(OEt₂) and PhBeOMe(OEt₂), or give mixtures containing free base when dissolved in hydrocarbons, e.g., MeBeOPh(OEt₂) and MeBeOBu^t(py). Methylberyllium methoxide yields a monomeric bispyridine adduct Me(MeO)Be py₂.

The proton magnetic resonance spectra of several of the above compounds are reported, there being pronounced solvent effects in several instances.