The addition of alkylberyllium hydrides to some unsaturated compounds

Abstract

Organoberyllium hydrides (RBeH; R = Me, Et, Ph) can be prepared, as diethyl ether complexes, from R₂Be, BeBr₂, and LiH. The liquid diethyl ether complex of methylberyllium hydride is a dimer, (MeBeH,Et₂O)₂, in benzene like the pyridine complex (MeBeH,py)₂. About five-sixths of the ether can be removed from the ether complexes by gentle heating under reduced pressure, whereupon broad infared absorptions develop similar to that of beryllium hydride. Methylberyllium hydride in the presence of ether slowly reduces methyl iodide to methane, and it rapidly adds to benzylideneaniline and to benzaldehyde giving [PhCH₂(Ph)NBeMe]₂ and (PhCH₂OBeMe)₄, respectively. Benzophenone in contrast gives the monomeric complexes Ph₂CHOBeMe,Et₂O and Ph₂CHOBeMe, tetrahydrofuran. Sodium diethylberyllium hydride reacts readily with ethylene in the presence of diethyl ether, but very slowly in its absence. Ethylberyllium hydride reacts rapidly with terminal olefins in the presence of ether at ca. 80°, very slowly with pent-2-ene, and no reaction with 2-methylbut-2-ene could be observed. Beryllium hydride adds to pent-1-ene in the presence of a little ethylberyllium hydride, but not detectably in its absence.