The reaction of (C5Me5)(2)Si Or (C5Me5)SiMe3 with B2Cl4 leads to the adduct
s (C5Me5)B-->BCl2SiCl3 (5a) or (C5Me5)B-->BCl3 (5b), in which the Lewis aci
ds stabilize the boranediyl fragments. Spectroscopic data and X-ray structu
re analyses confirm the adducts.