Diphospha- and diarsa-diboretanes. Four-membered rings containing boron and phosphorus or arsenic

Diphospha- and diarsa-diboretanes, (REBR′)2, (E = P, As; R = mesityl, R′= 2,2,6,6-tetramethylpiperidino) have been prepared and the structure of the diphosphadiboretane and RP(H)B(Cl)R′ have been established by X-ray crystallography.