Synthesis of a Stable B₂H₅⁺ Analogue by Protonation of a Double Base‐Stabilized Diborane(4)

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.…”

Dehydrogenative Boron Homocoupling of an Amine‐Borane

“…By contrast, the homocoupling [5] of amine-boranes to form welldefined products with BÀB single bonds has not been reported, although dehydrogenation of H 3 4 ] has been reported to form insoluble polymeric materials with B À B bonds. Well-defined homocoupling of boranes, as mediated by transition metals, is essentially limited to B À B bond formation in polyhedral boranes, for example pentaborane(9) (A), [7,8] guanidine bases (B), [9] and most recently the homocoupling of HBCat and related derivatives to give the corresponding diboranes (C) [10][11][12] (Scheme 1). Well-defined homocoupling of boranes, as mediated by transition metals, is essentially limited to B À B bond formation in polyhedral boranes, for example pentaborane(9) (A), [7,8] guanidine bases (B), [9] and most recently the homocoupling of HBCat and related derivatives to give the corresponding diboranes (C) [10][11][12] (Scheme 1).…”

Diboranyl Phosphonium Cations: Synthesis and Chemical Properties

“…We assume that the B-H stretching band of the anion also appears in this region. The high wavenumber in comparison to the B-H stretching modes in 2 (2272 and 2249 cm -1 ) [21] can be explained by the positive charge of 5. Further experiments showed that PCy 3 in 5 could be substituted by strong Lewis bases.…”

“…[18] A starting reagent in our research in this area is the diborane [HB(hpp)] 2 (2; see Scheme 2, a; hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), which can be synthesized in high yield in a one-pot reaction from commercially available hppH and H 3 BǟNMe 3 (see Scheme 2,a). [20][21][22][23] We recently showed that hydride abstraction from [HB(hpp)] 2 (2) with B(C 6 F 5 ) 3 [24] results in the formation of the dication [H 2 B 4 (hpp) 4 ] 2+ (3) with a four-electron, fourcenter bond between the four boron atoms (see Scheme 2,b work, it was not possible to capture the postulated intermediate cation 4, which is isolobal to the ethyl cation. As opposed to the "nonclassical" structure with one bridging hydrogen atom of the ethyl cation, [25,26] quantum chemical calculations predict that 4 has a terminal B-H bond.…”