Synthesis and characterization of compounds with boron-boron double bonds

✍ Scribed by Philip P. Power

• Book ID: 104138783
• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 565 KB
• Volume: 198-200
• Category: Article
• ISSN: 0020-1693
• DOI: 10.1016/s0020-1693(00)92388-0

✦ Synopsis

The diborane(4) derivatives Mes,BB(Mes)Ph and Me,N(Ph)BB(Ph)NMe, readily react with lithium powder in ether to give the doubly reduced salts [{(Et,O)Li},Mes,,BB(Mes)Ph] and [{(EtzO)Li}~Me,N(Ph)BB(Ph)NMe~]. Both species, which were isolated as red crystals, have been characterized by X-ray crystallography, "B NMR and electronic spectroscopy. The structural data reveal planar or almost planar B,C, or B&N* cores with B-B distances near 1.63 A (cf. B-B=1.71 A in the neutral non-planar precursors) consistent with the formation of a r-bond between the boron centers. Their rlB NMR spectra display peaks that are shifted upfield relative to the starting compounds. In the case of the amido derivative, two RN r-bonds were cleaved in the reduction process. The electronic absorption spectrum of this compound in Et,0 displays an intense absorption at 320 nm which may be attributed to the rr-rr* transition of the B-B T-bond. This suggests that the strength of this bond is of the order of 40 kcal mol-'. The compounds, which may be considered as boron analogues of the corresponding alkenes, represent the first structurally characterized acyclic species that possess formal B-B double bonds.