The reaction of C6D6 + B((2)p) is investigated by crossed molecular beam experiments at a collision energy of 5.5 kcal mol(-1) and by electronic structure computations. The latter were performed employing hybrid Hartree-Fock/density functional theory (B3LYP), coupled cluster theory with single, double, and a perturbative estimate of triple excitations [CCSD(T)], complete active space self consistent field (CASSCF), and multiconfiguration quasi-degenerate perturbation theory to second order (MC-QDPT2) in conjunction with 6-31G*, 6-311+G**, and cc-pVTZ basis sets. Final energies were obtained at the CCSD(T)/cc-pVTZ//B3LYP/ 6-311+G** + ZPVE level of theory. Two possible addition channels to the benzene a system were characterized. One involves a weakly bound benzene-boron pi complex and proceeds over a barrier, which lies below the energy of separated reactants, to an eta(1) C6H6-B sigma complex (4). The second channel is the symmetric attack (eta(2)) to a pi bond of benzene. This addition mode following the (2)A" potential energy surface involves a valley ridge inflection (VRI) point and therefore results in 4. This VRI point also makes the formation of the 7-boranorbornadiene-7-yl radical (6, (2)A') via nonadiabatic transition from (2)A" to (2)A' unlikely. The primary addition products 4 (and 6) can rearrange over barriers below the energy of separated reactants to finally reach the phenylboryl radical (10, (2)A'). This is the most stable C6H6B species identified. Cleavage of an o-CH bond goes along with closure of a C-B bond and yields benzoborirene (1, (1)A(1)) and hydrogen atom (- 19.2 kcal mol(-1); -16.7 kcal mol(-1) for the [D6]-benzene system). Abstraction of hydrogen by boron,to produce phenyl radical ((2)A(1)) and borylene ((1)Sigma(+)) is endoergic by +30.4 kcal mol(-1) (C6D5 + BD, +31.6 kcal mol(-1)) and is therefore not viable under our experimental conditions. The features of this C6D6B potential energy surface identified computationally-no entrance barrier with respect to separated reactants, exoergicity of -16.7 kcal mol(-1), transition state energy and structure in the exit channel (6.5 kcal mol(-1) with respect to 1 + D)-are in agreement with crossed-beam data (exoergicity - 14.8 +/- 1.2 kcal mol(-1); exit channel barrier 2.4-4.8 kcal mol(-1)). Phenylborylene 2 and didehydroborepine 3 are alternative C6H5B species, but these are higher in energy than 1 by 32 and 43 kcal mol(-1) and are therefore not formed in the crossed-beam experiment.