Experimental and Theoretical Investigation of an SN2-type Pathway for Borate-Fluorine Bond Cleavage by Electron-Rich Late-Transition Metal Complexes.

B-F σ-bond activation of a fluoroborate has been experimentally achieved through reactions with electron-rich iridium(I) and palladium(0) complexes. The selectivity of B-F σ-bond cleavage by iridium complexes was improved through the high nucleophilicity of the iridium center, implying that a different pathway from that of well-accepted F- abstraction was in effect. The palladium(0) complex was found to promote exclusive B-F σ-bond cleavage even at ambient temperature. Density functional theory (DFT) calculations suggested that B-F σ-bond activation occurred through an SN2-type pathway, which is, to our knowledge, the first proposal of SN2-type borate-fluorine σ-bond cleavage mediated by a transition metal complex. The high feasibility of the SN2-type pathway appears to be attributed to the relatively low deformation energy of the transition state. It was also found that countercation Cs+ effectively stabilized the transition state and product by serving as a F- acceptor.