Reactions of beryllium alkyls with carbonyl and azomethine groups: addition, reduction, complex formation, and ortho-metallation
Abstract
Reaction of beryllium alkyls with ketones and aldehydes yields compounds of the type RBeOCHR′2 and RBeOCH2R′ respectively, where R is Et, Bui, But, and R′ is But and Ph. These alkoxides are all dimeric except BuiBeOCH2But which is trimeric. t-Butylberyllium chloride gives (ClBeOCHBut2)2 and (ClBeOCH2But,OEt2)1–2 respectively. The latter readily loses ether in vacuo giving benzene-insoluble ClBeOCH2But, and reacts with NNN′N′-tetramethylethylenediamine (tmed) giving (ClBeOCH2But)2(tmed). These reductions proceed via a yellow or orange colour at –78°, except for benzophenone (purple), likely due to formation of a π-complex between the carbonyl group and the beryllium alkyl during or prior to hydride transfer. Dimethylberyllium adds to But2CO, and (Me3SiCH2)2Be adds to Ph2CO giving (MeBeOCMeBut2)2 and (Me3SiCH2BeOCPh2CH2SiMe3)2 respectively, the latter by way of a red colour at –78°. Diphenylberyllium and (Me3SiCH2)2Be give colourless co-ordination complexes with Ph2CO, Ph2CO → BeR2. In contrast to the rapid reduction of aldehydes and ketones only a few azomethines and no alkyl cyanides are reduced, addition and complex formation being observed. Di-t-butylberyllium reduces PhCHNMe and PhCHCHCHNPh giving dimeric [ButBeN(Me)CH2Ph]2 and [ButBeN(Ph)CH2CHCHPh]2 respectively though it forms a red complex with benzylideneaniline, But2Be,N(Ph)CHPh. Diphenylberyllium gives a tan complex with PhCHN(p-tolyl) though a colourless one with PhCHNMe. The colourless complexes Me2Be,N(Me)CHPh. But2Be,N(Me)CHPri, ButBeCl,NCBut were also prepared. Diethylberyllium adds across the CN in PhCHNMe and PhCHNPh yielding [EtBeN(Me)CHEtPh2] and [EtBeN(Ph)CHEtPh]2. Dimethylberyllium gives the benzene-insoluble alkylation product, MeBeN(Ph)CHMePh, with the latter azomethine though the p-toluidine derivative is a dimer. Reaction of PhCHNBut with Et2Be gives the yellow dimeric ortho-metallation product ethyl-2-(N-t-butylformimidoylphenyl) beryllium. The t-butyl analogue has a degree of association between 1 and 2.