Protonated cyanogen fluoride. Structure, stability, and reactivity of (FCN)H+ ions

Gaseous (FCN)H+ ions were obtained by protonation of cyanuric fluoride by s trong Bronsted acids such as H-3(+) (D-3(+)) and CnH5+ (n = 1, 2), and thei r structure and reactivity were examined by FT-ICR mass spectrometry and co mputational methods at the G2 level of theory. The results show that FCNHis considerably more stable than the HFCN+ protomer, the gap amounting to 3 60 kJ mol(-1) at the G2 level. The gas-phase basicity (GB) of FCN was estim ated by "bracketing" experiments by measuring the efficiency of H+ transfer from FCNH+ to reference bases. Utilizing a general correlation between the rate and the Delta G degrees change of the proton-transfer we obtain GB(FC N) = 668.4 +/- 10 kJ mol(-1), to be compared with the G2 computed GB of 651 .8 +/- 8 kJ mol(-1), both values beings referred to N protonation. The reac tions of FCNH+ with isolated (C2H4) and conjugated (C6H6) pi systems were a lso investigated. The ion behaves as a FC+ = NH electrophile promoting arom atic cyanation, e.g., yielding C6H5CNH+ from benzene. Consideration is give n to the reaction mechanism and its correlation with solution-chemistry cya nation.