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

Abstract

G3 molecular orbital calculations predict that the insertions of boron into the CH, NH, and CN bonds of methylamine to form CH 2 (BH)NH 2 , CH 3 N(BH)H, and CH 3 BNH 2 are exothermic by 57.6, 93.9, and 111.8 kcal mol -1 , respectively. However, the addition of atomic boron to the N site of methylamine yeilds a weak additon complex CH 3 NH 2 ‚‚B, which is lower in energy than the reactants by only 17.2 kcal mol -1 . The dissociation of CH 3 N(BH)H to CH 3 and HNBH has a low activation energy of 28.7 kcal mol -1 and is the most energetically favored one amomg its three decomposition paths. One of the other two paths yielding the final product CH 3 NB has a rate-determining step with a high endothermicity of 111.4 kcal mol -1 , but the other leading to CNB has one with a high activation barrier of 105.7 kcal mol -1 instead. The conversions of CH 3 BNH 2 to the final products CH 2 BNH and CH 2 BNH 2 are respectively controlled by their endothermicities of 96.9 and 47.7 kcal mol -1 .

Structure and Stability of (HBNH)n Clusters

“…This makes the amido imido oligomers suitable intermediates in conversion of cyclotriborazane to polymeric imidoboranes. As can be seen ( Table 6), formation of (HBNH) 16 is the most favorable process in a broad temperature range.…”

“…14,15 It prefers a linear configuration with C ∞v symmetry, with the B-N bond distance of 0.1239 nm, in agreement with the previous value. 16 (HBNH) n (n＝2-5) clusters: As n was varied from 2 to 4, the alternate-bond ring was found to be the lowest energy isomer. As for (HBNH) 2 , 17 the butterfly structure in C 2 v symmetry is a real minimum.…”

“…Relative energies for the several considered isomers (n＝10, 12,13,14,16) are summarized in Table 1. Comparison shows that, with increasing oligomerization degree n, needle-shaped structures become more stable than cages.…”

“…In this article, we will report structures and thermodynamic properties for imido compounds (HBNH) n (n＝1- 16). We compare the stability of needle versus cage-like structures and consider their formation under chemical vapor deposition conditions.…”

Unusual substituent effects on the bonding of iminoboranes

“…Many theoretical calculations have also been carried out on HBNH, [13][14][15][16][17][18][19][20] with particular attention directed to the aminoboranylidine-iminoborane isomerization in both the singlet ground state 21 and the lowest triplet excited state. 22 Theoretical structural data for the monosubstituted 12,23 and disubstituted 12 methyl derivatives, as well as thermochemical data for the mono-and di-fluoro-substituted compounds 24 are available. However, no systematic analysis of the effect of substituents on the BRN bond of iminoborane has been reported previously.…”