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A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane

A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane
A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane
Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H–C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H–C interactions with the geminal C–H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]− anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.
0002-7863
5106-5120
Bukvic, Alexander J.
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Burnage, Arron L.
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Tizzard, Graham J.
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Martínez-Martínez, Antonio J.
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McKay, Alasdair I.
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Rees, Nicholas H.
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Tegner, Bengt E.
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Krämer, Tobias
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Fish, Heather
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Warren, Mark R.
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Coles, Simon J.
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Macgregor, Stuart A.
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Weller, Andrew S.
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Bukvic, Alexander J.
96c0de35-304c-479f-8291-0b0872f7095b
Burnage, Arron L.
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Tizzard, Graham J.
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Martínez-Martínez, Antonio J.
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McKay, Alasdair I.
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Rees, Nicholas H.
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Tegner, Bengt E.
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Krämer, Tobias
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Fish, Heather
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Warren, Mark R.
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Coles, Simon J.
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Macgregor, Stuart A.
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Weller, Andrew S.
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Bukvic, Alexander J., Burnage, Arron L., Tizzard, Graham J., Martínez-Martínez, Antonio J., McKay, Alasdair I., Rees, Nicholas H., Tegner, Bengt E., Krämer, Tobias, Fish, Heather, Warren, Mark R., Coles, Simon J., Macgregor, Stuart A. and Weller, Andrew S. (2021) A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane. Journal of the American Chemical Society, 143 (13), 5106-5120. (doi:10.1021/jacs.1c00738).

Record type: Article

Abstract

Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H–C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H–C interactions with the geminal C–H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]− anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.

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Accepted/In Press date: 26 March 2021
e-pub ahead of print date: 26 March 2021
Published date: 7 April 2021

Identifiers

Local EPrints ID: 453775
URI: http://eprints.soton.ac.uk/id/eprint/453775
ISSN: 0002-7863
PURE UUID: efef21bf-1e7b-40a3-bcb4-8fe2e778398a
ORCID for Graham J. Tizzard: ORCID iD orcid.org/0000-0002-1577-5779
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272

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Date deposited: 24 Jan 2022 17:46
Last modified: 17 Mar 2024 02:53

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Contributors

Author: Alexander J. Bukvic
Author: Arron L. Burnage
Author: Antonio J. Martínez-Martínez
Author: Alasdair I. McKay
Author: Nicholas H. Rees
Author: Bengt E. Tegner
Author: Tobias Krämer
Author: Heather Fish
Author: Mark R. Warren
Author: Simon J. Coles ORCID iD
Author: Stuart A. Macgregor
Author: Andrew S. Weller

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