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Though numerous catalysts for the dehydrogenation of ammonia borane (AB) are known, those that release >2 equiv of H2 are uncommon. Herein, we report the synthesis of Mo complexes supported by a para-terphenyl diphosphine ligand, 1, displaying metal–arene interactions. Both a Mo0 N2 complex, 5, and a MoII bis(acetonitrile) complex, 4, exhibit high levels of AB dehydrogenation, releasing over 2.0 equiv of H2. The reaction rate, extent of dehydrogenation, and reaction mechanism vary as a function of the precatalyst oxidation state. Several Mo hydrides (MoII(H)2, [MoII(H)]+, and [MoIV(H)3]+) relevant to AB chemistry were characterized.

Site-selective transformation of benzylic C−H bonds into diverse functional groups is achieved via Cu-catalyzed C−H fluorination with N-fluorobenzenesulfonimide (NFSI), followed by substitution of the resulting fluoride with various nucleophiles. The benzyl fluorides generated in these reactions are reactive electrophiles in the presence of hydrogen-bond donors or Lewis acids, allowing them to be used without isolation in C−O,

Deoxygenative coupling of CO to value-added C≥2 products is challenging and mechanistically poorly understood. Herein, we report a mechanistic investigation into the reductive coupling of CO, which provides new fundamental insights into a multielectron bond-breaking and bond-making transformation. In our studies, the formation of a bis­(siloxycarbyne) complex precedes C–O bond cleavage. At −78 °C, over days, C–C coupling occurs without C–O cleavage. However, upon warming to 0 °C, C–O cleavage is observed from this bis­(siloxycarbyne) complex. A siloxycarbyne/CO species undergoes C–O bond cleavage at lower temperatures, indicating that monosilylation, and a more electron-rich Mo center, favors deoxygenative pathways. From the bis­(siloxycarbyne), isotopic labeling experiments and kinetics are consistent with a mechanism involving unimolecular silyl loss or C–O cleavage as rate-determining steps toward carbide formation. Reduction of Mo­(IV) CO adducts of carbide and silylcarbyne species allowed for the spectroscopic detection of reduced silylcarbyne/CO and mixed silylcarbyne/siloxycarbyne complexes, respectively. Upon warming, both of these silylcarbynes undergo C–C bond formation, releasing silylated C2O1 fragments and demonstrating that the multiple bonded terminal MoC moiety is an intermediate on the path to deoxygenated, C–C coupled products. The electronic structures of Mo carbide and carbyne species were investigated quantum mechanically. Overall, the present studies establish the elementary reactions steps by which CO is cleaved and coupled at a single metal site.