Experimental and Computational Determination of a M-Cl Homolytic Bond Dissociation Free Energy: Mn(III)Cl-Mediated C-H Cleavage and Chlorination.

This study confirms the hypothesis that [MnCl 3 (OPPh 3 ) 2 ] ( 1 ) and acetonitrile-solvated MnCl 3 (i.e., [MnCl 3 (MeCN) x ]) can be used as synthons to prepare Mn(III) chloride complexes with facially coordinating ligands. This was achieved through the preparation and characterization of six new {Mn III Cl} complexes using anionic ligands Tp H (tris(pyrazolyl)borate) and Tp Me (tris(3,5-dimethylpyrazolyl)borate). The Mn III -chloride dissociation and association equilibria ( K eq ) and Mn III/II reduction potentials were quantified in DCM. These two thermochemical parameters ( K eq and E 1/2 ), in addition to the known Cl-atom reduction potential in DCM, enabled the quantification of the Mn-Cl bond dissociation (homolysis) free energy of 21 and 23 ± 7 kcal/mol at room temperature for R = H and Me, respectively. These are in reasonable agreement with the bond dissociation free energy (BDFE M-Cl ) of 34 ± 6 kcal/mol calculated using density functional theory. The BDFE M-Cl of 1 was also calculated (25 ± 6 kcal/mol). These energies were used in predictive C-H bond reactivity.