Unexpected cluster formation upon hydroboration of a neutral diborene with 9-BBN

Abstract

The reaction of the neutral, base-stabilised diborenes 1a,b with the well-known hydroboration reagent 9-borabicyclo[3.3.1]nonane (9-BBN) is presented. This leads to the formation of a nonclassical structural motif with a B3 core concomitant with the cleavage of a B-C bond. This compound has been characterised in solution and by X-ray crystallography. According to Wade's rules these rare B3 clusters follow the arachno classification (2n + 6 electrons) and represent doubly base-stabilised B3H5 analogues.

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

“…[101] 5.5. [103] This divergent reactivity was tentatively assigned to the lack of electronic stabilization at the trigonal 9-BBN fragment after the initial hydroboration step,prompting the formation of multicenter bonds. Hydroboration Thea ddition of E À Hb onds across unsaturated carboncarbon multiple bonds,n otable examples of which include hydroboration, hydroamination, and hydrogenation, is hugely important for the functionalization of organic molecules.…”

Spontaneous trans‐Selective Transfer Hydrogenation of Apolar Boron–Boron Double Bonds

“…[13] We have thus demonstrated that Nheterocyclic carbene (NHC)-stabilized diheteroaryldiborenes undergo spontaneous syn-hydroboration with catecholborane [14] and 9-borabicyclo[3.3.1]nonane (9-BBN). [15] We have also shown that as aturated NHC-stabilized diboryne featuring aformal BBtriple bond and adiboracumulene stabilized by p-acidic cyclic (alkyl)(amino)carbene (CAAC) ligands undergo facile uncatalyzed hydrogenation to the corresponding trans-dihydrodiborenes. [16] In contrast, the direct hydrogenation of diborenes has eluded our efforts,w ith the exception of our recently reported diiododiborene, (PCy 3 ) 2 B 2 I 2 ,w hich undergoes stepwise hydrogenation, first to the rather unstable 1,2-dihydrodiborane,( Cy 3 P) 2 B 2 H 2 I 2 , and then to the (dihydro)iodoborane (Cy 3 P)BH 2 Iw ith concomitant B À Bb ond cleavage.…”

Spontane trans‐selektive Transferhydrierung von unpolaren B=B‐Doppelbindungen

“…Daraufhin kommt es zur Bildung eines sechsgliedri-gen Übergangzustands,w oraufhin sowohl der protische als auch der hydridische Wasserstoff in einem konzertierten Mechanismus an die ungesättigte Bindung abgegeben werden (Abbildung 1a). [13] Wirh aben dabei gezeigt, dass mit N-heterocyclischen Carbenen (NHCs) stabilisierte Diheteroaryldiborene eine spontane syn-Hydroborierung mit Catecholboran [14] und 9-Borabicyclo[3.3.1]nonan (9-BBN) [15] eingehen. Anschließend findet ein Protonentransfer zum borylierten Kohlenstoffatom statt, woraufhin das Aminoboran als Nebenprodukt freigesetzt wird (Abbildung 1b).…”