Exploring the Reactivity of Metal-Ligand Cooperative Complexes with Dioxazolones, Terminal Alkynes, and 2-Ethynylbenzyl Alcohol
Abstract
N-Acyl ketenimines were attempted to be synthesized catalytically by [Ru(Cp)(PPh2NPh2)(NCMe)]PF6 with phenylacetylene and 3-phenethynyl-1,2,4-dioxazol-5-one. Trapping agents were employed to identify the major product of the reaction, as many products were formed. [Ru(Cp)(PPh2NPh2)(NCMe)]PF6 reacts with 3-phenethynyl-1,2,4-dioxazol-5-one generating an isocyanate via the Curtius rearrangement, confirmed by a forced Curtius rearrangement with 3-phenethynyl-1,2,4-dioxazol-5-one and 1,2,4-triazole. Rates of vinylidene formation using [Ru(Cp)(PPh2NPh2)(NCMe)]PF6 and various terminal alkynes of different sterics and electronics were evaluated using a Hammett analysis for and simple rate comparisons. Negligible trends were observed at 70 ºC. The rate of vinylidene formation with [Ru(Cp)(PCy2NPh2)(NCMe)]PF6 and phenylacetylene was faster than that of [Ru(Cp)(PPh2NPh2)(NCMe)]PF6 due to the difference in steric and electronic properties of the metal. Hydrofunctionalization reactions of 2-EBA using an [Ru(Cp)(PCy2NPh2)(NCMe)]PF6 were spiked with different alkali salts which had a positive effect on 2-EBA consumption. Different weakly coordinating anions were coordinated in-situ to Ru(Cp)(PCy2NPh2)Cl for the hydrofunctionalization of 2-EBA. It was found that the PF6-anion gave the highest consumption of 2-EBA.