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

Gaseous (FCN)H+ ions were obtained by protonation of cyanuric fluoride by strong Bronsted acids such as H-3(+) (D-3(+)) and CnH5+ (n = 1, 2), and their structure and reactivity were examined by FT-ICR mass spectrometry and computational methods at the G2 level of theory. The results show that FCNH+ is considerably more stable than the HFCN+ protomer, the gap amounting to 360 kJ mol(-1) at the G2 level. The gas-phase basicity (GB) of FCN was estimated 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(FCN) = 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 reactions of FCNH+ with isolated (C2H4) and conjugated (C6H6) pi systems were also investigated. The ion behaves as a FC+ = NH electrophile promoting aromatic cyanation, e.g., yielding C6H5CNH+ from benzene. Consideration is given to the reaction mechanism and its correlation with solution-chemistry cyanation.