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Modulation of σ-Alkane interactions in [Rh(L2)(alkane)]+ solid-state organometallic (SMOM) systems by variation of the chelating phosphine and alkane: Access to η2,η2-σ-alkane Rh(I), η1-σ-alkane Rh(III) complexes, and alkane encapsulation

Modulation of σ-Alkane interactions in [Rh(L2)(alkane)]+ solid-state organometallic (SMOM) systems by variation of the chelating phosphine and alkane: Access to η2,η2-σ-alkane Rh(I), η1-σ-alkane Rh(III) complexes, and alkane encapsulation
Modulation of σ-Alkane interactions in [Rh(L2)(alkane)]+ solid-state organometallic (SMOM) systems by variation of the chelating phosphine and alkane: Access to η2,η2-σ-alkane Rh(I), η1-σ-alkane Rh(III) complexes, and alkane encapsulation
Solid/gas single-crystal to single-crystal (SC–SC) hydrogenation of appropriate diene precursors forms the corresponding σ-alkane complexes [Rh(Cy2P(CH2)nPCy2)(L)][BArF4] (n = 3, 4) and [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(L)][BArF4] (n = 5, L = norbornane, NBA; cyclooctane, COA). Their structures, as determined by single-crystal X-ray diffraction, have cations exhibiting Rh···H–C σ-interactions which are modulated by both the chelating ligand and the identity of the alkane, while all sit in an octahedral anion microenvironment. These range from chelating η2,η2 Rh···H–C (e.g., [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4], n = 3 and 4), through to more weakly bound η1 Rh···H–C in which C–H activation of the chelate backbone has also occurred (e.g., [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(η1-COA)][BArF4]) and ultimately to systems where the alkane is not ligated with the metal center, but sits encapsulated in the supporting anion microenvironment, [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4], in which the metal center instead forms two intramolecular agostic η1 Rh···H–C interactions with the phosphine cyclohexyl groups. CH2Cl2 adducts formed by displacement of the η1-alkanes in solution (n = 5; L = NBA, COA), [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(κ1-ClCH2Cl)][BArF4], are characterized crystallographically. Analyses via periodic DFT, QTAIM, NBO, and NCI calculations, alongside variable temperature solid-state NMR spectroscopy, provide snapshots marking the onset of Rh···alkane interactions along a C–H activation trajectory. These are negligible in [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4]; in [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(η1-COA)][BArF4], σC–H → Rh σ-donation is supported by Rh → σ*C–H “pregostic” donation, and in [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4] (n = 2–4), σ-donation dominates, supported by classical Rh(dπ) → σ*C–H π-back-donation. Dispersive interactions with the [BArF4]− anions and Cy substituents further stabilize the alkanes within the binding pocket.
0002-7863
14958-14970
Martínez-Martínez, Antonio J.
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Tegner, Bengt E.
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McKay, Alasdair I.
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Bukvic, Alexander J.
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Rees, Nicholas H.
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Tizzard, Graham J.
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Coles, Simon J.
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Warren, Mark R.
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Macgregor, Stuart A.
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Weller, Andrew S.
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Martínez-Martínez, Antonio J.
eeefda39-31de-470d-8d86-61e1d586e2dc
Tegner, Bengt E.
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McKay, Alasdair I.
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Bukvic, Alexander J.
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Rees, Nicholas H.
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Tizzard, Graham J.
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Coles, Simon J.
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Warren, Mark R.
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Macgregor, Stuart A.
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Weller, Andrew S.
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Martínez-Martínez, Antonio J., Tegner, Bengt E., McKay, Alasdair I., Bukvic, Alexander J., Rees, Nicholas H., Tizzard, Graham J., Coles, Simon J., Warren, Mark R., Macgregor, Stuart A. and Weller, Andrew S. (2018) Modulation of σ-Alkane interactions in [Rh(L2)(alkane)]+ solid-state organometallic (SMOM) systems by variation of the chelating phosphine and alkane: Access to η2,η2-σ-alkane Rh(I), η1-σ-alkane Rh(III) complexes, and alkane encapsulation. Journal of the American Chemical Society, 140 (44), 14958-14970. (doi:10.1021/jacs.8b09364).

Record type: Article

Abstract

Solid/gas single-crystal to single-crystal (SC–SC) hydrogenation of appropriate diene precursors forms the corresponding σ-alkane complexes [Rh(Cy2P(CH2)nPCy2)(L)][BArF4] (n = 3, 4) and [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(L)][BArF4] (n = 5, L = norbornane, NBA; cyclooctane, COA). Their structures, as determined by single-crystal X-ray diffraction, have cations exhibiting Rh···H–C σ-interactions which are modulated by both the chelating ligand and the identity of the alkane, while all sit in an octahedral anion microenvironment. These range from chelating η2,η2 Rh···H–C (e.g., [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4], n = 3 and 4), through to more weakly bound η1 Rh···H–C in which C–H activation of the chelate backbone has also occurred (e.g., [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(η1-COA)][BArF4]) and ultimately to systems where the alkane is not ligated with the metal center, but sits encapsulated in the supporting anion microenvironment, [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4], in which the metal center instead forms two intramolecular agostic η1 Rh···H–C interactions with the phosphine cyclohexyl groups. CH2Cl2 adducts formed by displacement of the η1-alkanes in solution (n = 5; L = NBA, COA), [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(κ1-ClCH2Cl)][BArF4], are characterized crystallographically. Analyses via periodic DFT, QTAIM, NBO, and NCI calculations, alongside variable temperature solid-state NMR spectroscopy, provide snapshots marking the onset of Rh···alkane interactions along a C–H activation trajectory. These are negligible in [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4]; in [tiebar above startRhH(Cy2P(CH2)2(tiebar above endCH)(CH2)2PCy2)(η1-COA)][BArF4], σC–H → Rh σ-donation is supported by Rh → σ*C–H “pregostic” donation, and in [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4] (n = 2–4), σ-donation dominates, supported by classical Rh(dπ) → σ*C–H π-back-donation. Dispersive interactions with the [BArF4]− anions and Cy substituents further stabilize the alkanes within the binding pocket.

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Accepted/In Press date: 10 October 2018
e-pub ahead of print date: 10 October 2018
Published date: 7 November 2018

Identifiers

Local EPrints ID: 425679
URI: http://eprints.soton.ac.uk/id/eprint/425679
ISSN: 0002-7863
PURE UUID: 18f3d69d-74f8-4d03-8514-029ef4ce95b9
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

Catalogue record

Date deposited: 31 Oct 2018 17:30
Last modified: 26 Nov 2021 05:31

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Contributors

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

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