Borirane

Abstract: B(npy)Ar2 (npy=2-(naphthalen-1-yl)pyridine) compounds bearing various nonbulky aryl groups undergo a clean and sequential two-step photoisomerization in which two aryl substituents on boron migrate to a carbon atom of the naphthyl moiety. The second isomerization step is the first example of a reversible photoisoermization between a borepin and a borirane. Both steric and electronic factors have been found to have a great impact on this photoreactivity. Furthermore, the borirane isomer reacts with oxygen, forming a rare oxaborepin dimer.

Abstract: Though the reaction chemistry of three-membered ring molecules such as cyclopropanes and their heteroatom-containing analogues has been extensively studied, the chemical properties of their boron analogues, boriranes, are little known thus far. This work describes the diverse reactivity patterns of carborane-fused borirane 2. This borirane engages in ring-opening reactions with different types of Lewis acids, such as BBr3, GeCl2, GaCl3, BH3(SMe2) and HBpin, affording a series of ring-opening products, in which M–X or B–H bonds add across the B–C(cage) bond of the three-membered ring in 2. On the other hand, borirane 2 can undergo ring-expansion reactions with unsaturated molecules such as PhCHO, CO2 and PhCN to give ring-expansion products, five-membered boracycles, via a concerted reaction mechanism as supported by DFT calculations. The results of this work not only enrich the reaction chemistry of boriranes, but also offer new routes to boron-containing compounds and heterocycles.

Abstract: As the first discovered organoboron compound with photochromic property, B(ppy)Mes2 (ppy=2-phenylpyridine, Mes=mesityl) displays rich photochemistry that constitutes a solid foundation for wide applications in optoelectronic fields. In this work, we investigated the B(ppy)Mes2 to borirane isomerization mechanisms in the three lowest electronic states (S0 , S1 , and T1 ) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the photoisomerization in the S1 state is dominant, which is initiated by the cleavage of the B-Cppy bond. After overcoming a barrier of 0.5 eV, the reaction pathway leads to a conical intersection between the S1 and S0 states (S1 /S0 )x , from which the decay path may go back to the reactant B(ppy)Mes2 via a closed-shell intermediate (Int1-S0 ) or to the product borirane via a biradical intermediate (Int2-S0 ). Although triplet states are probably involved in the photoinduced process, the possibility of the photoisomerization in T1 state is very small owing to the weakly allowed S1 →T1 intersystem crossing and the high energy barrier (0.77 eV). In addition, we found the photoisomerization is thermally reversible, which is consistent with the experimental observations.

Abstract: Borirane undergoes ring opening reaction with NOCl and HNF2 yielding the corresponding alkenes Ab initio and density functional investigations of this reaction with cis- and trans-2,3-dimethylboriranes reveal that these reactions take place in a single step through the formation of a prereactive complex and a transition state giving the alkene with the same stereochemistry Calculations clearly show that the concerted cleavage of CB bonds leads to retention of stereochemistry Further, it shows that HNF2 cleaves boriranes more efficiently than does NOCl Intrinsic reaction coordinate analyses and bond order analysis describe the nature of the transition state very well and fix the reaction mechanism Solvent effect calculations through PCM model, with acetonitrile and CCl4 as solvents, do not alter the gas phase results significantly © 2007 Wiley Periodicals, Inc Int J Quantum Chem, 2007