Hydrogen-transfer catalysis with Cp*IrIII complexes

The influence of the ancillary ligands

U Hintermair, Jesus Campos, Timothy P. Brewster, Lucas M Pratt, Nathan D Schley, Robert H Crabtree

Research output: Contribution to journalArticle

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Abstract

Fourteen Cp*IrIII complexes, bearing various combinations of N- and C-spectator ligands, are assayed in hydrogen-transfer catalysis from isopropyl alcohol to acetophenone under various conditions to investigate ligand effects in this widely used reaction. The new cationic complexes bearing monodentate pyridine and N-heterocyclic carbene (NHC) ligands were characterized crystallographically and by variable-temperature nuclear magnetic resonance (VT-NMR). Control experiments and mercury poisoning tests showed that iridium(0) nanoparticles, although active in the reaction, are not responsible for the high activity observed for the most active precatalyst [Cp*Ir(IMe)2Cl]BF4 (6). For efficient catalysis, it was found necessary to have both NHCs in monodentate form; tying them together in a bis-NHC chelate ligand gave greatly reduced activity. The kinetics of the base-assisted reaction showed induction periods as well as deactivation processes, and H/D scrambling experiments cast some doubt on the classical monohydride mechanism.
Original languageEnglish
Pages (from-to)99-108
Number of pages10
JournalACS Catalysis
Volume4
Issue number1
Early online date9 Dec 2013
DOIs
Publication statusPublished - 3 Jan 2014

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Catalysis
Hydrogen
Bearings (structural)
Ligands
Iridium
2-Propanol
Pyridine
Alcohols
Experiments
Nuclear magnetic resonance
Nanoparticles
Kinetics
Temperature
carbene

Cite this

Hintermair, U., Campos, J., Brewster, T. P., Pratt, L. M., Schley, N. D., & Crabtree, R. H. (2014). Hydrogen-transfer catalysis with Cp*IrIII complexes: The influence of the ancillary ligands. ACS Catalysis, 4(1), 99-108. https://doi.org/10.1021/cs400834q

Hydrogen-transfer catalysis with Cp*IrIII complexes : The influence of the ancillary ligands. / Hintermair, U; Campos, Jesus; Brewster, Timothy P.; Pratt, Lucas M; Schley, Nathan D; Crabtree, Robert H.

In: ACS Catalysis, Vol. 4, No. 1, 03.01.2014, p. 99-108.

Research output: Contribution to journalArticle

Hintermair, U, Campos, J, Brewster, TP, Pratt, LM, Schley, ND & Crabtree, RH 2014, 'Hydrogen-transfer catalysis with Cp*IrIII complexes: The influence of the ancillary ligands', ACS Catalysis, vol. 4, no. 1, pp. 99-108. https://doi.org/10.1021/cs400834q
Hintermair, U ; Campos, Jesus ; Brewster, Timothy P. ; Pratt, Lucas M ; Schley, Nathan D ; Crabtree, Robert H. / Hydrogen-transfer catalysis with Cp*IrIII complexes : The influence of the ancillary ligands. In: ACS Catalysis. 2014 ; Vol. 4, No. 1. pp. 99-108.
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AB - Fourteen Cp*IrIII complexes, bearing various combinations of N- and C-spectator ligands, are assayed in hydrogen-transfer catalysis from isopropyl alcohol to acetophenone under various conditions to investigate ligand effects in this widely used reaction. The new cationic complexes bearing monodentate pyridine and N-heterocyclic carbene (NHC) ligands were characterized crystallographically and by variable-temperature nuclear magnetic resonance (VT-NMR). Control experiments and mercury poisoning tests showed that iridium(0) nanoparticles, although active in the reaction, are not responsible for the high activity observed for the most active precatalyst [Cp*Ir(IMe)2Cl]BF4 (6). For efficient catalysis, it was found necessary to have both NHCs in monodentate form; tying them together in a bis-NHC chelate ligand gave greatly reduced activity. The kinetics of the base-assisted reaction showed induction periods as well as deactivation processes, and H/D scrambling experiments cast some doubt on the classical monohydride mechanism.

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