DOI: 10.1021/ct8002699

Structures, Bonding, and One-Bond B-N and B-H Spin-Spin Coupling Constants for a Series of Neutral and Anionic Five-Membered Rings Containing BN Bonds

The structures and bonding of a series of five-membered rings with BN bonds C_xN_yB_zH₅ (x + y + z = 5) and their most stable deprotonated anions C_xN_yB_zH₄⁻ as well as anionic rings C_xN_yB_zH₅⁻ have been investigated at the MP2/6−311++G(d,p) level of theory. The great majority of these rings present BN bond orders close to that found in borazine, suggesting that there is substantial electron delocalization in these rings. This observation is also supported by both NBO and ELF analyses. Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have also been performed to obtain the ¹⁵N−¹¹B and ¹H−¹¹B spin−spin coupling constants. For neutral systems, the former range from −10 to −35 Hz, thereby bracketing the value of ¹J(B−N) for borazine, which is −29 Hz. ¹J(B−N) spans an even greater range in the anions, from −3 to −36 Hz. The absolute value of ¹J(B−N) decreases upon deprotonation if coupling involves the deprotonated nitrogen or a boron atom bonded to the deprotonated N. ¹J(B−H) always decreases upon nitrogen deprotonation.