Reversible Formation of Organyl(oxo)boranes (RBO) (R = C₆H₅or CH₃) from Boroxins ((RBO)₃):  A Matrix Isolation Study

Abstract

Flash vacuum pyrolysis of triphenyl- and trimethylboroxin and subsequent trapping of the gas phase products in a large excess of argon at T < 20 K allows matrix isolation and characterization by IR spectroscopy of phenyl(oxo)borane and methyl(oxo)borane. The nature of the matrix isolated species, monomeric CH3BO, 1:1 dimer complex of CH3BO, (CH3BO)2, and (CH3BO)3, depends strongly on the trapping temperature and matrix host gas (Ar vs Xe) with the boroxin dominating at 30 K (Ar) or 55 K (Xe). An ab initio investigation (second-order Møller−Plesset perturbation theory) of the potential energy surface for trimerization of CH3BO is in agreement with the experimental observations.

1,2‐Azaborine: The Boron‐Nitrogen Derivative of ortho‐Benzyne

“…All signals of 4 disappear simultaneously while new signals in the range 2305 – 2236 cm −1 of the isocyanate group of 8 and the signals 1965 and 2208 cm −1 of the BO unit [14] appear (Figure 2). The structure of 8 could be confirmed again through use of isotopically labelled carbon dioxide and is in excellent agreement with the corresponding computed isotopic shifts (B3LYP/6-311+G**, Supporting Information Table S4).…”

Gas-Phase Synthesis of Boronylallene (H2CCCH(BO)) under Single Collision Conditions: A Crossed Molecular Beams and Computational Study

“…14−16 However, oxoboranes are very reactive due to the highly polar boron−oxygen bond and readily form oligomers to compensate for their intrinsic electron deficiency. 17,18 As a result, the dehydration of boronic acids lead to the formation of oligomers of oxoborane instead of monomers. 17 Further, Bock et al reported the synthesis of methyloxoborane (CH 3 BO) via thermolysis of methyl-1,3,2-diborolane-4,5-dione, but the product promptly underwent cyclo-oligomerization to (CH 3 BO) 3 .…”

“…17,18 As a result, the dehydration of boronic acids lead to the formation of oligomers of oxoborane instead of monomers. 17 Further, Bock et al reported the synthesis of methyloxoborane (CH 3 BO) via thermolysis of methyl-1,3,2-diborolane-4,5-dione, but the product promptly underwent cyclo-oligomerization to (CH 3 BO) 3 . 19 The cyclo-oligomerization of RBO can be observed even at temperatures as low as 50 K; 17 isolated oxoboranes were reported either as reactive intermediates or in cryogenic matrices.…”

“…17 Further, Bock et al reported the synthesis of methyloxoborane (CH 3 BO) via thermolysis of methyl-1,3,2-diborolane-4,5-dione, but the product promptly underwent cyclo-oligomerization to (CH 3 BO) 3 . 19 The cyclo-oligomerization of RBO can be observed even at temperatures as low as 50 K; 17 isolated oxoboranes were reported either as reactive intermediates or in cryogenic matrices. 15,19,20 For example, Andrews et al detected methyloxoborane (CH 3 BO) and methyleneoxoborane (CH 2 BO) while studying reactions of laser-ablated boron atoms with methanol in a low-temperature argon matrices.…”

ChemInform Abstract: Cyclodimerization of an Oxoboryl Complex Induced by trans Ligand Abstraction.

“…Instead, these anhydrides of boronic acids were assigned cyclotrimeric structures. [7] However, considerable experimental efforts are necessary to obtain a glance at the elusive methyloxoborane or its cyclodimerization product (MeBO) 2 , as the trimer (MeBO) 3 is the predominant species even at very low trapping temperatures of 50 K. In contrast, sterically demanding substituents favor the formation of cyclodimeric structures. [2] The simplest derivative (HBO) 3 (1, Figure 1) was identified as the product of different high energetic redox processes, [3] and the monomeric counterpart HBO could be observed spectroscopically under similar reaction conditions, either in the gas phase [4] or in lowtemperature matrix isolation studies.…”