- Acceptorless alkane dehydrogenation catalyzed by iridium CCC-pincer complexes
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Iridium complexes of CCC-pincer bis-N-heterocyclic carbenes, including a newly synthesized trifluoromethyl-substituted complex, were examined as catalysts for the acceptorless dehydrogenation of cyclooctane and n-undecane. Up to 103 turnovers were observed for the dehydrogenation of cyclooctane, and up to 97 turnovers were observed for the dehydrogenation of n-undecane. The catalysts showed high initial turnover frequencies, followed by a gradual loss of activity over 24 h. Experiments indicate that this loss of activity is due to catalyst decomposition rather than product inhibition. Stoichiometric reactivity was investigated for the precatalysts, focusing on the synthesis of dihydride and trihydride complexes as well as the dissociation and addition of neutral ligands.
- Chianese, Anthony R.,Drance, Myles J.,Jensen, Kelsey H.,McCollom, Samuel P.,Yusufova, Nevin,Shaner, Sarah E.,Shopov, Dimitar Y.,Tendler, Jennifer A.
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- Lowering the barrier to C?H activation at IRIII through pincer ligand design
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Selective C?H activation of benzene and n-octane under mild conditions by a pincer IrIII carboxylate complex, (CCCMesityl)Ir(OAc)2(OH2) (1a), is described. A kinetic study of benzene activation was undertaken, and the resulting Eyring analysis informed the design of a tButylCCCMethyl-ligated IrIII carboxylate, which exhibited a ΔG? value for the reaction lower than that observed for 1a. Elimination of the aquo ligand was found to further lower the ΔG? value of benzene activation, enabling C?H activation by IrIII at temperatures as low as 30 °C.
- Chu, Wan-Yi,Goldberg, Karen I.,Rubashkin, Sophie B.
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supporting information
p. 1296 - 1302
(2021/05/29)
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- Electronic Ligand Modifications on Cobalt Complexes and Their Application toward the Semi-Hydrogenation of Alkynes and Para-Hydrogenation of Alkenes
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The effect of the electronic modification of a bis(carbene) pincer ligand, (MesCCCR), on cobalt catalysis has been investigated. The pincer ligand was modified in the para position of the aryl backbone with a tert-butyl and trifluoromethyl moiety to yield the electronic variants that were applied toward the synthesis and characterization of several cobalt complexes, (MesCCCR)Co. The application of the (MesCCCR)CoI(N2)PPh3 complexes toward the semihydrogenation of alkynes revealed that while the tert-butyl group does not impact reactivity, the loss of electron density at the metal center, by the installation of the CF3 group, does affect product ratios. Further inspection of the proposed mechanism suggested that the installation of the trifluoromethyl group slows down olefin hydrogenation. This finding was further supported in the application of the (MesCCCR)CoI-py (py = pyridine) complexes toward the parahydrogenation of ethyl acrylate, which demonstrated that the electron-withdrawing ligand variant produced less polarization.
- Muhammad, Safiyah R.,Nugent, Joseph W.,Tokmic, Kenan,Zhu, Lingyang,Mahmoud, Jumanah,Fout, Alison R.
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supporting information
p. 3132 - 3138
(2019/08/26)
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