title: Isomerization of Internal Alkynes to Iridium(III) Allene Complexes via C-H Bond Activation: Expanded Substrate Scope, and Progress towards a Catalytic Methodology.
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.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA. neha.phadke@ttu.edu.
authors.forename: Neha
authors.initials: N
authors.lastname: Phadke
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA. Michael.Findlater@ttu.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Findlater
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D007495:Iridium / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; D000480:Alkynes; D007495:Iridium; C025947:propadiene; D002244:Carbon
keywords: allenes; crystal structure; iridium; isolation; isomerization; pincer; synthesis