From Saturated BN Compounds to Isoelectronic BN/CC Counterparts: An Insight from Computational Perspective

In the present study, the inorganic analogues of alkanes as well as their isoelectronic BN/CC counterparts that bridge the gap between organic and inorganic chemistry are comparatively studied on the grounds of static DFT and Car–Parrinello molecular dynamics simulations. The BN/CC butanes CH₃CH₂BH₂NH₃, BH₃CH₂NH₂CH₃, and NH₃CH₂BH₂CH₃ were considered and compared with their isoelectronic counterparts NH₃BH₂NH₂BH₃ and CH₃CH₂CH₂CH₃. In addition, systematical replacement of the NH₂BH₂ fragment by the isoelectronic CH₂CH₂ moiety is studied in the molecules H₃N(NH₂BH₂)_3–m(CH₂CH₂)_mBH₃ (for m=0, 1, 2, or 3) and H₃N(NH₂BH₂)_2–m(CH₂CH₂)_mBH₃ (for m=0, 1, or 2). The DFT and Car–Parrinello simulations show that the isosteres of the BN/CC butanes CH₃CH₂BH₂NH₃, BH₃CH₂NH₂CH₃, and NH₃CH₂BH₂CH₃ and of larger oligomers of the type (BN)_k(CC)_l where k≥l are stable compounds. The BN/CC butane H₃NCH₂CH₂BH₃ spontaneously produces molecular hydrogen at room temperature. The reaction, prompted by very strong dihydrogen bonding NH???HB, undergoes through the neutral, hypervalent, pentacoordinated boron dihydrogen complex R?BH₂(H₂) [R=(CH₂CH₂)_nNH₂]. The calculations suggest that such intermediate and the other BN/CC butanes CH₃CH₂BH₂NH₃, BH₃CH₂NH₂CH₃, and NH₃CH₂BH₂CH₃ as well as larger BN/CC oligomers are viable experimentally. A simple recipe for the synthesis of CH₃CH₂BH₂NH₃ is proposed. The strength of the dihydrogen bonding appeared to be crucial for the overall stability of the saturated BN/CC derivatives.