“…Thel ongest classical oligoboranes isolated to date,l inear B 6 (NMe 2 ) 8 [19] and cyclic B 6 (NR 2 ) 6 (R = Me,E t), [17,23] are only formed as negligible by-products of otherwise unselective reductive coupling reactions.W hile the exact mechanism of these reactions is still unclear, the generation of highly reactive boryl radical and/or borylene intermediates tends to lead to unwanted side-reactions,such as radical hydrogen abstraction from solvent or borylene insertion into CÀHa nd CÀC bonds, [24] as observed, for example,byP ower and co-workers in their attempt to synthesize doubly bonded diborenes stabilized by bulky terphenyl groups (Scheme 2). [26] Ther eaction, yielding non-classical nido-metallaborane, 2,w ith aB ÀB bond length of 1.695 (7) ,was postulated to proceed via the dimerization of am ononuclear terminal borylene intermediate. [7,25] These new synthetic methods,a sw ell as early forays into the reactivity of BÀB multiple bonds,will be discussed in this Review.…”