Transition‐Metal‐Catalyzed Synthesis of Diboranes(4)

Abstract

The diboranes(4) bis(catecholato)diborane (B(2)Cat(2)) and bis(pinacolato)diborane (B(2)Pin(2)) are important precursors for organoboronic esters, which are versatile reagents for the formation of carbon-carbon bonds. A new catalytic synthesis for these compounds starts from catecholborane or pinacolborane and gives the dehydrocoupling products B(2)Cat(2) and B(2)Pin(2) with turnover numbers of up to 11,600 (see scheme).

Synthesis of Catechol‐, Pinacol‐, and Neopentylglycolborane through the Heterogeneous Catalytic BB Hydrogenolysis of Diboranes(4)

“…Because our best dehydrocoupling results were obtained by using heterogeneous Group 10 catalysts, such as platinum or palladium, on charcoal or aluminum oxide,7a,b we used these catalysts in our initial attempts at the hydrogenolysis of diboranes(4). These catalysts had the additional benefit of being easily removable and reusable after the reaction.…”

Formation and Reactivity of Electron‐Precise B−B Single and Multiple Bonds

“…[8] In the 1980s Sneddon and co-workers first reported the PtBr 2 -catalyzed dehydrogenative coupling of polyhedral carboranes and boranes,y ielding linked-cage compounds in ah ighly selective manner under mild reaction conditions. [35] Prior to this,M arder and co-workers had already observed the formation of small amounts of B 2 Pin 2 from HBPin as ab y-product during the rhodium-catalyzed synthesis of boronate esters. [34] Thereaction, however, remains limited to this one specific substrate.…”

The Catalytic Dehydrocoupling of Amine–Boranes and Phosphine–Boranes

“…In 2013, Weller and MacGregor reported the first well-characterised example of the B-B homocoupling of an amine-borane to yield the diborane (4) Me 3 N · BH 2 BH 2 · NMe 3 ligand sigma bound to rhodium [62]. B-B homocoupling of boranes has been otherwise limited to B-B bond formation in polyhedral boranes [73,74], guanidine bases [75] and catechol-and pinacolboranes [76][77][78] Sigma complexes of aminoboranes have also been isolated, where donation from the B-H bonds into a vacant metal orbital is reinforced by π back-donation from the metal into the π* B-N orbital of the aminoborane [80]. Various examples have been characterised with rhodium [13,66,80,81], iridium [17,19,80,82] and ruthenium [24,80,83,84], and a selection is presented in Fig.…”