A Systematic Exploration of B-F Bond Dissociation Enthalpies of Fluoroborane-Type Molecules at the CCSD(T)/CBS Level

Fluoroborane-type molecules ((RRB)-R-1-B-2-F) are of interest in synthetic chemistry, but to date, apart from a handful of small species (such as H2BF, HBF2, and BF3), little is known concerning the effect of substituents in governing the strength of the B-F bonds of such species toward homolytic dissociation in the gas phase. In this study, we have calculated the bond dissociation enthalpies (BDEs) of thirty unique B-F bonds at the CCSD(T)/CBS level using the high-level W1w thermochemical protocol. The B-F bonds in all species considered are very strong, ranging from 545.9 kJ mol(-1) in (H2B)(2)B-F to 729.2 kJ mol(-1) HBF2. Nevertheless, these BDEs still vary over a wide range of 183.3 kJ mol(-1). The structural properties that affect the BDEs are examined in detail, and the homolytic BDEs are rationalized based on molecule stabilization enthalpies and radical stabilization enthalpies. Since polar B-F bonds may represent a challenging test case for density functional theory (DFT) methods, we proceed to examine the performance of a wide range of DFT methods across the rungs of Jacob & PRIME;s Ladder for their ability to compute B-F BDEs. We find that only a handful of DFT methods can reproduce the CCSD(T)/CBS BDEs with mean absolute deviations (MADs) below the threshold of chemical accuracy (i.e., with average deviations below 4.2 kJ mol(-1)). The only functionals capable of achieving this feat were (MADs given in parentheses): & omega;B97M-V (4.0), BMK (3.5), DSD-BLYP (3.8), and DSD-PBEB95 (1.8 kJ mol(-1)).

Automated summary

This study investigates the bond dissociation enthalpies of fluoroborane-type molecules (RRB-R-1-B-2-F) and finds that the B-F bonds have high bond dissociation enthalpies that vary widely based on structural properties. The study also evaluates the performance of different density functional theory methods in calculating the B-F BDEs and identifies a few methods that can accurately reproduce the experimental results.