The complex [MnCl 3 (OPPh 3 ) 2 ] (1) is a bench-stable and easily prepared source of MnCl 3 . It is prepared by treating acetonitrile solvated MnCl 3 (2) with Ph 3 PO and collecting the resulting blue precipitate. 1 is useful in coordination reactions by virtue of the labile Ph 3 PO ligands, and this is demonstrated through the synthesis of {Tpm*}MnCl 3 (3). In addition, methodologies in synthesis that rely on difficult or cumbersome to prepare solutions of reactive MnCl 3 can be accomplished using 1 instead. This is demonstrated through alkene dichlorinations in a wide range of solvents, open to air, and with good substrate scope. Lightaccelerated halogenation and radical sensitive experiments support a radical mechanism involving stepwise Cl-atom transfer(s) from 1.

This study confirms the hypothesis that [MnCl3(OPPh3)2] (1) and acetonitrile-solvated MnCl3 (i.e., [MnCl3(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 {MnIIICl} complexes using anionic ligands TpH (tris­(pyrazolyl)­borate) and TpMe (tris­(3,5-dimethylpyrazolyl)­borate). The MnIII–chloride dissociation and association equilibria (K eq) and MnIII/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 (BDFEM–Cl) of 34 ± 6 kcal/mol calculated using density functional theory. The BDFEM–Cl of 1 was also calculated (25 ± 6 kcal/mol). These energies were used in predictive C–H bond reactivity.