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ChemRxiv210_Aug22.pdf (2.83 MB)
Redox–state Dependent Activation of Silanes and Ammonia with Reverse Polarity (PCcarbeneP)Ni Complexes: Electrophilic vs. Nucleophilic Carbenes
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submitted on 22.08.2018 and posted on 24.08.2018by Warren Piers, Etienne A. LaPierre, Chris Gendy
rigidified PCalkylP ligand allowed for the synthesis and
charactarization of cationic and radical PCCarbeneP nickel complexes
in which the carbene anchor of the pincer framework is electrophilic rather
than nucleophilic. Alpha-hydride abstraction from (PCalkylP)nickel
halide complex readily leads to the cationic carbene complex, which furnishes the
radical carbene complex by one electron reduction. The reactivity of these
reverse polarity carbene complexes towards small molecules (H2, CO,
CO2, R3SiH, NH3) reveals different modes of
activation when compared to previously reported nucleophilic nickel carbene
complexes, and a clear dependence on the redox state of the complex. For H2,
CO and CO2, no reaction is observed, but silanes react via hydride
transfer and formation of solvated silylium ions. Ammonia is activated in a
novel way, wherein it coordinates the carbene carbon and is deprotonated to
form a robust C-N bond. This is not only a rare example of ammonia activation
by a first row transition metal but also evidence of the intermediacy of group
10 carbenes in direct C-N bond forming reactions.