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Molecules 2015, 20(11), 20195-20205; doi:10.3390/molecules201119686

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

Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA
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Author to whom correspondence should be addressed.
Academic Editor: Derek J. McPhee
Received: 1 June 2015 / Revised: 29 October 2015 / Accepted: 2 November 2015 / Published: 10 November 2015
(This article belongs to the Special Issue C-H Bond Activation and Functionalization)
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Abstract

The synthesis of a series of allene complexes (POCOP)Ir(η2-RC=.=CR’) 1b4b (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 1b4b 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. View Full-Text
Keywords: iridium; allenes; pincer; isomerization; synthesis; isolation; crystal structure iridium; allenes; pincer; isomerization; synthesis; isolation; crystal structure
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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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, 20195-20205.

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