A Matrix Isolation Spectroscopic Investigation of the Reaction Products of Transition Metal Centres With Ethene and Water

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Thompson, Matthew G. K.
The reaction products of thermally generated atomic V with ethene and ethene isotopomers have been investigated by matrix isolation ultraviolet visible and Fourier transform infrared (FTIR) spectroscopy. When V is deposited into matrices of pure Ar, evidence for V and V2 are present in the UV-visible absorption spectra. Addition of trace amounts of ethene results in the elimination of absorptions due to V2 on deposition, likely due to the formation of V…(C2H4) van der Waals complexes on matrix condensation. Irradiation of matrices containing V and trace C2H4 in Ar, with light corresponding to atomic V electronic excitations, eliminates all UV-visible absorptions due to atomic V in the Infrared analysis of matrices containing V and C2H4 give evidence for a new product on deposition, consistent with a kinetically formed H-V-C2H3 isomer. Following further irradiation of the matrix, several new products of C-H bond insertion by the metal atom, including additional H-V-C2H3 conformational isomers, and H2V(η2-C2H2) products are observed in the infrared spectrum. Additionally, the formation of ethane is evident as a major product immediately following deposition of V + C2H4 + H2O in Ar. The formation of this product is consistent with alkene insertion into the V-H bond of an H-V-OH intermediate, followed by a photo-induced elimination to give C2H6. Under higher C2H4 concentrations, competitive ethane formation in which a sacrificial hydrogenation mechanism involving two ethene molecules is observed, analogous to the mechanism proposed to account for V + H2O + C2H4. Isotopic investigations aimed at confirming key aspects of the proposed mechanisms are also presented. Similar reactivity is observed for several metals, suggesting that this reaction is a generalized reaction, whenever transition metal hydrides are formed. The additional observation of ethene hydrogenation where the initiating hydride source is either water, or ethene, suggests that this reaction could also easily generalize to other initiating hydride sources. The mechanism could also extend to the insertion of other π-bond containing species, as well.
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