Theoretical Study of the Reaction of Boron with Methanol and the Decomposition Paths of the Reaction Products

Abstract

Gaussian-2 molecular orbital calculations predict that the insertions of boron into the CH, OH and CO bonds of methanol to form CH2(BH)OH, CH3OBH, and CH3BOH are exothermic by 56.3, 92.8, and 115.9 kcal mol-1, respectively. The dissociation of CH3OBH into CH3 and HBO has a low activation energy of 17.6 kcal mol-1. Although the loss of a methyl hydrogen from CH3BOH has a moderate barrier (53.5 kcal mol-1), the elimination of its hydroxyl hydrogen to yield CH3BO has only a very low endothermicity (4.8 kcal mol-1). CH3BO may eventually yield the final product CH2BO observed either by dehydrogenation with a high endothermicity of 100.2 kcal mol-1 or by 1,3-H shift to CH2BOH with a high barrier of 91.7 kcal mol-1 and subsequent dehydrogenation. Hence, these two paths via which CH2BO is formed are, energywise, almost equally probable.

Gaussian-3 Molecular Orbital Study of the Reaction of Boron with Methylamine and the Decomposition Paths of the Reaction Products

“…The present theoretical prediction that the CH bond insertion reaction is the thermodynamically least favored reaction among the three is in line with the fact that no products formed from the decompostion of CH 2 (BH)NH 2 have been identified in the FTIR experiment . Hence, in view of the FTIR results, the much smaller exothermicity of the reaction, and the larger bond energy (average bond energies: 19 CH = 98.8, NH = 93.4, and CN = 69.7 kcal mol -1 ), the CH bond insertion reaction may be considered relatively much less important in comparison with the other two insertion reactions and is thus neglected in the boron−methylamine reaction, as in the case of the boron−methanol reaction …”

“…1 Hence, in view of the FTIR results, the much smaller exothermicity of the reaction, and the larger bond energy (average bond energies: 19 CH ) 98.8, NH ) 93.4, and CN ) 69.7 kcal mol -1 ), the CH bond insertion reaction may be considered relatively much less important in comparison with the other two insertion reactions and is thus neglected in the boron-methylamine reaction, as in the case of the boron-methanol reaction. 7 In addition to the insertion reactions considered above, atomic boron (with empty 2p orbitals) may add onto the N site (with a lone pair) of methylamine. The attack is found to be roughly in the direction of the nitrogen lone pair (Figure 1).…”

“…In the MP2/D95* calculations of Lanzisera et al, transition state structures and rate-determining steps associated with the reactions have not been investigated, and the energetic data reported are only the energy changes for the formation of the insertion products CH 3 N(BH)H, CH 3 BNH 2 , and CH 2 (BH)NH 2 from CH 3 NH 2 and B. Hence, it is thought desirable to carry out, as a continuation of our theoretical work on the reaction of boron with methanol, a high level ab initio calculation involving detailed characterization of transition states and rate-determining steps of the above proposed reactions 1−6. In addition, the adduct CH 3 NH 2 ··B has also been examined (reaction 7).…”

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

“…The methyl derivative 1b has been the subject of a number of computational investigations aimed at understanding its electronic structure as well as at deriving experimentally inaccessible data. − The similarity of the photoelectron spectrum of 1b with that of the isoelectronic CH 3 CN molecule led Bock et al to conclude that the BO bond in this oxoborane is a triple bond . This interpretation of the bonding in 1b is in agreement with a computational analysis of HBO, which was concluded to have “essentially a dative triple character” …”

The Lewis Acidity of the BO Triple Bond in Methyl(oxo)­borane

“…Lanzisera and Andrews detected and characterized 1 by IR spectroscopy as one of the reaction products that form during the co‐deposition of boron atoms and methanol in cryogenic matrix isolation experiments 12. The reaction of B + CH 3 OH and the IR spectrum of 1 were also studied theoretically 9,10. Although organly(oxo)boranes are thermodynamically rather stable,11,13 they have a strong tendency to form either cyclic dimers or trimers depending on the size of the organic group.…”