Nucleophilic and Electrophilic Molybdenum Terminal Oxo Complexes by Coordination-Induced Bond Weakening of Hydroxo O-H Bonds.

The extent of coordination-induced bond weakening in aquo and hydroxo ligands bonded to a molybdenum(III) center complexed by a dianionic, pentadentate ligand system was probed by reacting the known complex (BPzPy)Mo(III)-NTf, , with degassed water or dry lithium hydroxide. The aquo adduct was not observed, but two LiNTf-stabilized hydroxo complexes were fully characterized. Computational and experimental work showed that the O-H bond in these complexes was significantly weakened (to ≈57 kcal mol), such that these compounds could be used to form the diamagnetic, neutral terminal molybdenum oxo complex (BPzPy)Mo(IV)O, , by hydrogen atom abstraction using the aryl oxyl reagent ArO• (Ar = 2,4,6-tri--butylphenyl). Oxidation of the neutral hydroxo derivative further facilitated the production of by significantly enhancing the acidity of the hydroxyl proton. Speciation in these processes was probed by electrochemical and chemical experiments. The terminal oxo complex was smoothly oxidized by one electron to the cationic [(BPzPy)Mo(V)O][A] derivatives (A = NTf or Al[OC(CF)] depending on the oxidizing agent used). Both Mo(IV) and Mo(V) oxo complexes were fully characterized with their nucleophilic and electrophilic reaction behavior probed by conducting reactions with the Lewis acid B(CF) and the Lewis base PPh. Neutral oxo complex reacts only with the Lewis acid, while the cationic reacts only with PPh, the former by adduct formation and the latter via phosphine oxidation.