The Dichotomy of Mn-H Bond Cleavage and Kinetic Hydricity of Tricarbonyl Manganese Hydride Complexes.

Acid-base characteristics (acidity, pa, and hydricity, ΔG° or ) of metal hydride complexes could be a helpful value for forecasting their activity in various catalytic reactions. Polarity of the M-H bond may change radically at the stage of formation of a non-covalent adduct with an acidic/basic partner. This stage is responsible for subsequent hydrogen ion (hydride or proton) transfer. Here, the reaction of tricarbonyl manganese hydrides ,-[LMn(CO)H] (; L = P(OPh), ; L = PPh) and -[(L-L')Mn(CO)H] (, L-L' = PhPCHPPh (dppm); , L-L' = PhPCH-NHC) with organic bases and Lewis acid (B(CF)) was explored by spectroscopic (IR, NMR) methods to find the conditions for the Mn-H bond repolarization. Complex , bearing phosphite ligands, features acidic properties (pa 21.3) but can serve also as a hydride donor (ΔG = 19.8 kcal/mol). Complex with pronounced hydride character can be deprotonated with KHMDS at the CH-bridge position in THF and at the Mn-H position in MeCN. The kinetic hydricity of manganese complexes - increases in the order ,-[(P(OPh))Mn(CO)H] () < ,-[(PPh)Mn(CO)H] () ≈ -[(dppm)Mn(CO)H] () < -[(PhPCHNHC)Mn(CO)H] (), corresponding to the gain of the phosphorus ligand electron-donor properties.