Protonated Cyanogen Fluoride. Structure, Stability, and Reactivity of (FCN)H+ Ions

Abstract

Gaseous (FCN)H+ ions were obtained by protonation of cyanuric fluoride by strong Bronsted acids such as H3+ (D3+) 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 ΔG° 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 being referred to N protonation. The reactions of FCNH+ with isolated (C2H4) and conjugated (C6H6) π systems were also investigated. The ion behaves as a FC+ = NH electrophile promoting aromatic cyanation, e.g., yielding C6H5CNH+ from benzene. Consideration is give...