An Experimental and Computational Comparison of the Reactions of N2O and CO2 in Several Inorganic Systems

A series of four inorganic systems were examined to gain insight into the complex bonding patterns of nitriles, CO₂ and N₂O and their potential to be used as a chemical feedstock. In the first system, a thorough computational comparison of nitriles (RCN) binding to V(N[tBu]Ar)₃ (VL₃) and Mo(N[tBu]Ar)₃ (MoL₃) (Ar=3,5-Me₂C₆H₃) revealed the importance of the ligand environment and electronic state. In the first complex, kinetic measurements of various nitriles (RCN) binding to VL₃ revealed two distinct binding mechanisms dependent on R.

The reactivity of (R3Sn)₂O (R= Ph, Cy) toward N₂O and CO₂ was examined in a detailed experimental and computational study. N₂O binding to (R₃Sn)₂O to form trans- (R₃Sn)₂N₂O₂ is predicted to be unfavorable at all temperatures for both Ph and Cy derivatives. The rate and activation parameters of the reverse reaction of N₂O extrusion from trans-(R₃Sn)₂N₂O₂ was studied through thermal decomposition of the hyponitrite complexes by FTIR. CO₂ binds to (R3Sn)₂O for both Ph and Cy at room temperature to form their respective (R3Sn)₂CO₃. A mechanism for both reactions is proposed.

Kinetic studies on the carboxylative cyclization of a propargylamine by Au(IPr)X were performed to gain insights into the mechanism of CO₂ incorporation by a gold catalyst. A variety of experiments were run to determine optimal reaction conditions, mechanistic details and activation parameters. An important vinyl gold intermediate was synthesized and characterized crystallographically. The relative reaction rates of different gold compounds [Au(IPr)X] X= (Cl, vinyl) and [Au₂(L)X₂] were compared, with the digold achieving the highest reaction rates.

The mechanochemical milling of Na₂O and N₂O in the presence of other additives is reported. Mechanochemical milling of these samples produces cis-Na₂N₂O₂ in moderate yields at room temperature in few hours. Further milling leads to production of NaNO₃ at yields approaching 50% after 50 hours. This work represents the first total oxidation of nitrous oxide to nitrate and may significant industrial relevance.