Quantum-chemical Investigation on the Potential Energy Surface of the Reaction of BH+2 with C2H2

The potential energy surface of the ion-molecular reaction of BH+2 with C2H2 in gas-phase has been investigated theoretically by using the B3LYP/6-311G(d, p) and the high-level electron-correlation CCSD (T)/6-311G (2df, p) single-point levels. Four isomers H2B+ [Closed Circle] C2H2 (a), HBCHCH+2 (b), H2BCCH+2 (c) and H2 [Closed Circle] BHCCH+ (d) are found, among which isomer (b) is the most stable both thermodynamically and kinetically while isomers (a), (c) and (d) are kinetically unstable. The mechanism for the reaction BH+2 + C2H2 -> HBCCH+ + H2 is discussed based on the potential energy surface. It is shown that BH+2 may carry out an electrophilic addition towards C2H2 followed by multi-step H-shifts and final H2-elimination to form product HBCCH+ + H2, the total reaction is barrier-free and largely exothermic. The calculated results presented in this paper may be helpful for understanding the chemical behavior of electron-deficient borohydride cations such as BH+2.