2 research outputs found
Dinitrogen Splitting and Functionalization in the Coordination Sphere of Rhenium
[ReCl<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>(NCMe)] reacts with
pincer ligand HNÂ(CH<sub>2</sub>CH<sub>2</sub>P<i>t</i>Bu<sub>2</sub>)<sub>2</sub> (<i>H</i>PNP) to five coordinate rheniumÂ(III)
complex [ReCl<sub>2</sub>(PNP)]. This compound cleaves N<sub>2</sub> upon reduction to give rheniumÂ(V) nitride [ReÂ(N)ÂClÂ(PNP)], as the
first example in the coordination sphere of Re. Functionalization
of the nitride ligand derived from N<sub>2</sub> is demonstrated by
selective C–N bond formation with MeOTf
The Mechanism of Borane–Amine Dehydrocoupling with Bifunctional Ruthenium Catalysts
Borane–amine adducts have
received considerable attention,
both as vectors for chemical hydrogen storage and as precursors for
the synthesis of inorganic materials. Transition metal-catalyzed ammonia–borane
(H<sub>3</sub>N–BH<sub>3</sub>, AB) dehydrocoupling offers,
in principle, the possibility of large gravimetric hydrogen release
at high rates and the formation of B–N polymers with well-defined
microstructure. Several different homogeneous catalysts were reported
in the literature. The current mechanistic picture implies that the
release of aminoborane (e.g., Ni carbenes and Shvo’s catalyst)
results in formation of borazine and 2 equiv of H<sub>2</sub>, while
1 equiv of H<sub>2</sub> and polyaminoborane are obtained with catalysts
that also couple the dehydroproducts (e.g., Ir and Rh diphosphine
and pincer catalysts). However, in comparison with the rapidly growing
number of catalysts, the amount of experimental studies that deal
with mechanistic details is still limited. Here, we present a comprehensive
experimental and theoretical study about the mechanism of AB dehydrocoupling
to polyaminoborane with ruthenium amine/amido catalysts, which exhibit
particularly high activity. On the basis of kinetics, trapping experiments,
polymer characterization by <sup>11</sup>B MQMAS solid-state NMR,
spectroscopic experiments with model substrates, and density functional
theory (DFT) calculations, we propose for the amine catalyst [RuÂ(H)<sub>2</sub>PMe<sub>3</sub>{HNÂ(CH<sub>2</sub>CH<sub>2</sub>P<i>t</i>Bu<sub>2</sub>)<sub>2</sub>}] two mechanistically connected catalytic
cycles that account for both metal-mediated substrate dehydrogenation
to aminoborane and catalyzed polymer enchainment by formal aminoborane
insertion into a H–NH<sub>2</sub>BH<sub>3</sub> bond. Kinetic
results and polymer characterization also indicate that amido catalyst
[RuÂ(H)ÂPMe<sub>3</sub>{NÂ(CH<sub>2</sub>CH<sub>2</sub>P<i>t</i>Bu<sub>2</sub>)<sub>2</sub>}] does not undergo the same mechanism
as was previously proposed in a theoretical study