Isomerization of Internal Alkynes to Iridium(III) Allene Complexes via C–H Bond Activation: Expanded Substrate Scope, and Progress towards a Catalytic Methodology

Date
2015
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Abstract

The synthesis of a series of allene complexes (POCOP)Ir(η2-RC==CR’) 1b–4b (POCOP = 2,6-bis(di-tert-butylphosphonito)benzene) via isomerization of internal alkynes is reported. We have demonstrated that the application of this methodology is viable for the isomerization of a wide variety of alkyne substrates. Deuterium labeling experiments support our proposed mechanism. The structures of the allene complexes 1b–4b were determined using spectroscopic data analysis. Additionally, the solid-state molecular structure of complex 2b was determined using single crystal X-ray diffraction studies and it confirmed the assignment of an iridium-bound allene isomerization product. The rates of isomerization were measured using NMR techniques over a range of temperatures to allow determination of thermodynamic parameters. Finally, we report a preliminary step towards developing a catalytic methodology; the allene may be liberated from the metal center by exposure of the complex to an atmosphere of carbon monoxide.

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© 2015 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license ( http://creativecommons.org/licenses/by/4.0/).
Keywords
Iridium, Allenes, Pincer, Isomerization, Synthesis, Isolation, Crystal Structure
Citation
Phadke N, Findlater M. Isomerization of Internal Alkynes to Iridium(III) Allene Complexes via C–H Bond Activation: Expanded Substrate Scope, and Progress towards a Catalytic Methodology. Molecules. 2015; 20(11):20195-20205. https://doi.org/10.3390/molecules201119686
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