Photoswitching a molecular catalyst to regulate CO2 hydrogenation

Nilusha Priyadarshani, Bojana Ginovska, J. Timothy Bays, John Linehan, Wendy J. Shaw

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Inspired by nature's ability to regulate catalysis using physiological stimuli, azobenzene was incorporated into Rh(bis)diphosphine CO2 hydrogenation catalysts to photoinitiate structural changes to modulate the resulting catalytic activity. The rhodium bound diphosphine ligands (P(Ph2)-CH2-N(R)-CH2-P(Ph2)) contain the terminal amine of a non-natural amino acid, with the R-group being either β-alanine (β-Ala) or γ-aminobutyric acid (GABA). For both β-Ala and GABA containing complexes, the carboxylic acids of the amino acids were coupled to the amines of diaminoazobenzene, creating a complex consisting of a rhodium bound to a photo-responsive tetradentate ligand. The photo-induced cis-trans isomerization of the azobenzene-containing complexes imposes structural changes on these complexes, as evidenced by NMR studies. We found that the CO2 hydrogenation activity for the β-Ala bound rhodium complex is 40% faster at 27°C with the light on, i.e. azobenzene in the cis-conformation (TOF = 16 s-1) than when the complex was in the dark and the azobenzene in the trans-conformation (TOF = 11 s-1). In contrast the γ-aminobutyric acid containing rhodium complex has the same rate (TOF ∼17 s-1) with the azobenzene in either the cis or the trans-conformation at 27°C. The corresponding (bis)diphosphine complexes without the attached azobenzene were also prepared, characterized, and catalytically tested for comparison, and have TOF's of 30 s-1. Computational studies were undertaken to evaluate if the difference in rate between the cis- and trans-azobenzene isomers for the β-Ala bound rhodium complex were due to structural differences. These computational investigations revealed major structural changes between all cis- and trans-azobenzene structures, but only minor structural changes that would be unique to the β-Ala bound rhodium complex. We postulate that the different rates between the cis- and trans-azobenzene β-Ala bound containing rhodium complexes are due to subtle changes in the bite angle arising from steric strain due to the azobenzene-containing tetradentate ligand. This strain alters the hydricity of the subsequent rhodium hydride and consequently the rate.

Original languageEnglish
Pages (from-to)14854-14864
Number of pages11
JournalDalton Transactions
Volume44
Issue number33
DOIs
Publication statusPublished - Jul 22 2015

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Rhodium
Hydrogenation
Catalysts
Aminobutyrates
Conformations
Ligands
gamma-Aminobutyric Acid
Amines
azobenzene
Amino Acids
Isomerization
Carboxylic Acids
Hydrides
Isomers
Alanine
Catalysis
Catalyst activity
Nuclear magnetic resonance

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Priyadarshani, N., Ginovska, B., Bays, J. T., Linehan, J., & Shaw, W. J. (2015). Photoswitching a molecular catalyst to regulate CO2 hydrogenation. Dalton Transactions, 44(33), 14854-14864. https://doi.org/10.1039/c5dt01649e

Photoswitching a molecular catalyst to regulate CO2 hydrogenation. / Priyadarshani, Nilusha; Ginovska, Bojana; Bays, J. Timothy; Linehan, John; Shaw, Wendy J.

In: Dalton Transactions, Vol. 44, No. 33, 22.07.2015, p. 14854-14864.

Research output: Contribution to journalArticle

Priyadarshani, N, Ginovska, B, Bays, JT, Linehan, J & Shaw, WJ 2015, 'Photoswitching a molecular catalyst to regulate CO2 hydrogenation', Dalton Transactions, vol. 44, no. 33, pp. 14854-14864. https://doi.org/10.1039/c5dt01649e
Priyadarshani, Nilusha ; Ginovska, Bojana ; Bays, J. Timothy ; Linehan, John ; Shaw, Wendy J. / Photoswitching a molecular catalyst to regulate CO2 hydrogenation. In: Dalton Transactions. 2015 ; Vol. 44, No. 33. pp. 14854-14864.
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