Reactivity of TpMe2Ir(C2H4)(DMAD) with carboxylic acids. A DFT study on geometrical isomers and structural characterization

The thermally unstable adduct TpMe2Ir(C2H4)(DMAD), which was generated “in situ” by the reaction of DMAD with TpMe2Ir(C2H4)2 (1) at low temperature, reacted with different carboxylic acids to produce the following compounds: TpMe2Ir(E-C(CO2Me)CH(CO2Me))(H2O)(OC(O)C6H4R), (R = H, 2a; o-OH, 2b; o-Cl, 2c; m-Cl, 2d; o-NO2, 2e; m-NO2, 2f;o-Me, 2g;p-Me, 2h) and TpMe2Ir(E-C(CO2Me)CH(CO2Me))(H2O)(OC(O)Me) 3. In the reaction of derivative 2a with Lewis bases, TpMe2Ir(E-C(CO2Me)CH(CO2Me))(L)(OC(O)C6H5), (L = Py, 4a; m-Br–Py, 4b; m-Cl–Py, 4c; NCMe, 5) were obtained, of which 4b and 4c were isolated as a mixture of two isomers in which the substituted pyridine ring was present at different rotational orientations. All new compounds prepared were characterized by 1H and 13C{1H} NMR spectroscopy, the structure of compounds 2d, 2h and 4a being determined by X-ray diffraction analysis. DFT was used to analyze the relative stability and the structural orientation of the isomers.

The reaction of TpMe2Ir(C2H4)(DMAD) with several carboxylic acids produces iridium E-alkenyl complexes, derived from the formal insertion of the alkenyl into the hydride ligand by protonation with the acid. The reactivity of these derivatives with Lewis bases was studied, founding a mixture of two isomers, DFT calculations were performed to disclose their relative stability and the structures of some of these compounds have been analyzed by X-ray diffraction studies.Figure optionsDownload as PowerPoint slideResearch highlights
► The TpMe2Ir(C2H4)2(DMAD) reacts with carboxylic acids to yield alkenyl derivatives.
► The E-alkenyl derivatives react with Lewis bases by substitution of the coordinated water.
► The derivatives of m-substituted pyridines were observed as two isomers.
► DFT studies were performed to analyze the nature of both isomers.