Experimental And Theoretical Investigation Of An S(N)2-Type Pathway For Borate-Fluorine Bond Cleavage By Electron-Rich Late-Transition Metal Complexes

B-F sigma-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 sigma-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 sigma-bond cleavage even at ambient temperature. Density functional theory (DFT) calculations suggested that B-F sigma-bond activation occurred through an S(N)2-type pathway, which is, to our knowledge, the first proposal of S(N)2-type borate-fluorine a-bond cleavage mediated by a transition metal complex. The high feasibility of the S(N)2-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.