Mechanistic study on the fluorination of K[B(CN)4] with ClF enabling the high yield and large scale synthesis of K[B(CF3)4] and K[(CF3)3BCN].

The fluorination of K[B(CN)(4)] with ClF is studied by millimolar test reactions in aHF and CH(2)Cl(2) solution and by subsequent identification of intermediates such as B-CF═NCl, B-CF(2)-NCl(2), and B-CF(3) species as well as NCl(3) by (19)F, (11)B NMR, and Raman spectroscopy, respectively. At first one cyano group of K[B(CN)(4)] is converted fast into a CF(3) group, and with increasing fluorination the reaction becomes slower and several intermediates could be observed. On the basis of these results, a synthesis was developed for K[B(CF(3))(4)] on a 0.2 molar scale by treatment of K[B(CN)(4)] diluted in aHF with ClF. The course of the reactions was followed by (i) monitoring the vapor pressure inside the reactor, (ii) observing the heat dissipation during ClF uptake, and (iii) measuring the volume of the released nitrogen gas. Since the fluorination of the last cyano group proceeds very slowly, the selective synthesis of K[(CF(3))(3)BCN] on a 0.2 molar scale is possible, as well. The analysis of the mechanisms, thermodynamics, and kinetics of the fluorination reactions is supported by density functional theory (DFT) calculations.