Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond

Abstract

Homoatomic triple bonds between main-group elements have been restricted to alkynes, dinitrogen, and a handful of reactive compounds featuring trans-bent heavier elements of groups 13 and 14. Previous attempts to prepare a compound with a boron-boron triple bond that is stable at ambient temperature have been unsuccessful, despite numerous computational studies predicting their viability. We found that reduction of a bis(N-heterocyclic carbene)-stabilized tetrabromodiborane with either two or four equivalents of sodium naphthalenide, a one-electron reducing agent, yields isolable diborene and diboryne compounds. Crystallographic and spectroscopic characterization confirm that the latter is a halide-free linear system containing a boron-boron triple bond.

Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens

“…[23] The boron-boron bond lengths in 5 and 6 were found to be 1.490(6) Å and 1.494(10) Å, respectively. These are moderately longer than the B≡B length in 4 (1.449(3) Å), [19] yet substantially shorter than those typically found in diborenes (~1.58 -1.61 COMMUNICATION Å). [10,13] Similar structural features are found in the organic tellurirenium, which has a central C-C bond measuring 1.288(14) Å [21a] -longer than the central bond in di-tert-butyl acetylene (1.202(2) Å) [24] but significantly shorter than the ~1.34 Å typical of the double bond in alkenes.…”

Increasing the Reactivity of Diborenes: Derivatization of NHC‐Supported Dithienyldiborenes with Electron‐Donor Groups

“…[4] The first base-stabilized 1,2-dihydrodiborenes,i solated a decadea go by Robinsona nd co-workers,w ere by-products of the reduction of N-heterocyclic carbene (NHC) supported tribromoboranes, (I Ar )BBr 3 (I Ar =(1,3-Ar 2 )imidazol-2-ylidene, Ar=2,6-iPr 2 C 6 H 3 (Dip), 2,4,6-Me 3 C 6 H 2 (Mes), Figure 1A), resulting from unwanted radical hydrogen abstraction reactions. [3] Af ew years later our group isolated ad eep-green 1,2-dibromodiborene from the selectivet wo-electron reductiono ft he tetrabromodiborane (6) [5] The targeted synthesis of dihydrodiborenes was only recently achieved with excellents electivity and yield by the direct 1,2-hydrogenation of aN HC-stabilized diboryne, [(SI Dep Me 4 )pyrrolidin-2-ylidene). [6] Thermal decomposition of the bis-(tert-butyl)isocyanide adduct of the latter also provided the first 1,2-dicyanodiborene, [(cAAC)B(CN)] 2 ,w hichp resents two distinct 11 BN MR shifts duet oa nu nsymmetrical arrangement of the cAAC ligands, one being coplanar with, and the other orthogonal to, the dicyanodiborene core.…”

Uncatalyzed Hydrogenation of First‐Row Main Group Multiple Bonds

“…[21] There has, however, been no report of a rational selective synthetic route toward 1,2-dihydrodiborenes. In light of the facile hydrogenation of digermynes [10] attempts were made to hydrogenate diboryne 3a, (IDip)2B2, [22] in order to access the corresponding 1,2-dihydrodiborene, 1 (Scheme 2a). While no reaction was observed at room temperature under an atmosphere of H2, higher temperatures invariably led to irreproducible mixtures of BHcontaining products and B-B bond cleavage, as observed by 11 B NMR spectroscopy.…”