The influence of the second and outer coordination spheres on Rh(diphosphine)2 CO2 hydrogenation catalysts

J. Timothy Bays; Nilusha Priyadarshani; Matthew S. Jeletic; Elliot B. Hulley; Deanna L. Miller; John C. Linehan; Wendy J. Shaw

doi:10.1021/cs5009199

The influence of the second and outer coordination spheres on Rh(diphosphine)₂ CO₂ hydrogenation catalysts

J. Timothy Bays, Nilusha Priyadarshani, Matthew S. Jeletic, Elliot B. Hulley, Deanna L. Miller, John C. Linehan, Wendy J. Shaw

Pacific Northwest National Laboratory

Research output: Contribution to journal › Article › peer-review

25 Citations (Scopus)

Abstract

A series of [Rh(PCH₂X^RCH₂P)₂]⁺ complexes was prepared to investigate second and outer coordination sphere effects on CO₂ hydrogenation catalysis, where X is CH₂ (dppp) or X-R is N-CH₃, N-CH₂COOH (glycine), N-CH₂COOCH₃ (Gly-OMe), or N-CH₂C(O)N-CH(CH₃)COOCH₃ (GlyAla-OMe). All of these complexes were active for CO₂ reduction to formate, with the N-CH₃ derivative offering an 8-fold enhancement over the dppp derivative, which is consistent with increased electron density around the metal. Despite the increase in rate with the addition of the pendant nitrogen, the addition of electron withdrawing amino acids and dipeptides to the amine resulted in complexes with reductions in rate of 1 to 2 orders of magnitude, most consistent with a change in pK_a of the pendant amine, resulting in lower activity. Collectively, the data suggest multiple contributions of the pendant amine in this catalytic system.

Original language	English
Pages (from-to)	3663-3670
Number of pages	8
Journal	ACS Catalysis
Volume	4
Issue number	10
DOIs	https://doi.org/10.1021/cs5009199
Publication status	Published - Oct 3 2014

Keywords

CO hydrogenation
amino acid catalysts
homogeneous catalysis
in situ NMR
outer coordination sphere

ASJC Scopus subject areas

Catalysis
Chemistry(all)

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10.1021/cs5009199

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The influence of the second and outer coordination spheres on Rh(diphosphine)₂ CO₂ hydrogenation catalysts. / Bays, J. Timothy; Priyadarshani, Nilusha; Jeletic, Matthew S.; Hulley, Elliot B.; Miller, Deanna L.; Linehan, John C.; Shaw, Wendy J.

In: ACS Catalysis, Vol. 4, No. 10, 03.10.2014, p. 3663-3670.

Research output: Contribution to journal › Article › peer-review

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abstract = "A series of [Rh(PCH2XRCH2P)2]+ complexes was prepared to investigate second and outer coordination sphere effects on CO2 hydrogenation catalysis, where X is CH2 (dppp) or X-R is N-CH3, N-CH2COOH (glycine), N-CH2COOCH3 (Gly-OMe), or N-CH2C(O)N-CH(CH3)COOCH3 (GlyAla-OMe). All of these complexes were active for CO2 reduction to formate, with the N-CH3 derivative offering an 8-fold enhancement over the dppp derivative, which is consistent with increased electron density around the metal. Despite the increase in rate with the addition of the pendant nitrogen, the addition of electron withdrawing amino acids and dipeptides to the amine resulted in complexes with reductions in rate of 1 to 2 orders of magnitude, most consistent with a change in pKa of the pendant amine, resulting in lower activity. Collectively, the data suggest multiple contributions of the pendant amine in this catalytic system.",

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AU - Shaw, Wendy J.

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N2 - A series of [Rh(PCH2XRCH2P)2]+ complexes was prepared to investigate second and outer coordination sphere effects on CO2 hydrogenation catalysis, where X is CH2 (dppp) or X-R is N-CH3, N-CH2COOH (glycine), N-CH2COOCH3 (Gly-OMe), or N-CH2C(O)N-CH(CH3)COOCH3 (GlyAla-OMe). All of these complexes were active for CO2 reduction to formate, with the N-CH3 derivative offering an 8-fold enhancement over the dppp derivative, which is consistent with increased electron density around the metal. Despite the increase in rate with the addition of the pendant nitrogen, the addition of electron withdrawing amino acids and dipeptides to the amine resulted in complexes with reductions in rate of 1 to 2 orders of magnitude, most consistent with a change in pKa of the pendant amine, resulting in lower activity. Collectively, the data suggest multiple contributions of the pendant amine in this catalytic system.

AB - A series of [Rh(PCH2XRCH2P)2]+ complexes was prepared to investigate second and outer coordination sphere effects on CO2 hydrogenation catalysis, where X is CH2 (dppp) or X-R is N-CH3, N-CH2COOH (glycine), N-CH2COOCH3 (Gly-OMe), or N-CH2C(O)N-CH(CH3)COOCH3 (GlyAla-OMe). All of these complexes were active for CO2 reduction to formate, with the N-CH3 derivative offering an 8-fold enhancement over the dppp derivative, which is consistent with increased electron density around the metal. Despite the increase in rate with the addition of the pendant nitrogen, the addition of electron withdrawing amino acids and dipeptides to the amine resulted in complexes with reductions in rate of 1 to 2 orders of magnitude, most consistent with a change in pKa of the pendant amine, resulting in lower activity. Collectively, the data suggest multiple contributions of the pendant amine in this catalytic system.

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KW - outer coordination sphere

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