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Transformation of a norbornadiene unit to ethylenylcyclopentene requiring cooperation between boron and rhodium centers

Transformation of a norbornadiene unit to ethylenylcyclopentene requiring cooperation between boron and rhodium centers
Transformation of a norbornadiene unit to ethylenylcyclopentene requiring cooperation between boron and rhodium centers
The synthesis of the lithium salt of a bis-substituted borohydride anion containing a phenyl substituent and a 2-mercaptopyridyl unit (mp) is reported herein. This salt has been used as a pro-ligand for the synthesis of rhodium(I) complex, [Rh{κ3-H,H,S-H2B(Ph)(mp)}(NBD)] (1) (where NBD = 2,5-norbornadiene). The new boron-based ligand coordinates to the rhodium center via the thione donor and the two B–H bonds of the BPhH2 unit, with a dihydroborate motif. Reaction of complex 1 with two equivalents of triphenylphosphine leads to an unprecedented rearrangement and transfer of the former norbornadiene ligand to the boron center. The transformation occurs via an initial hydride migration from boron to rhodium center followed by a hydroboration of one of the double bonds. Finally, a ring-opening process occurs involving both boron and rhodium centers leading to an unusual boron-bound ethylenylcyclopentene unit. The product of this reaction was confirmed as [R⌈{η1-S,η2-B,C-B(Ph)(⌉CHCH2(C5H7)(mp)}(PPh3)2] (2). The net result of these transformations is the incorporation of the two hydrogen atoms from the secondary borohydride ligand [BPhH2(mp)]− into the former norbornadiene unit. The end point positions of these hydrogen atoms were confirmed by deuterium labeling experiments. Complex 2 was further reacted with carbon monoxide to generate [⌈Rh{η1-S,η2-B,C-B(Ph)(⌉CHCH2(C5H7)(mp)}(CO)(PPh3)] (3) via ligand substitution. The new ligand and the three complexes, 1, 2, and 3, have been characterized by spectroscopic techniques as well as by X-ray crystallography. Detailed characterization of 2 and 3 revealed an unusual η2-B,C coordination mode within these complexes. Further studies have demonstrated that complexes 2 and 3 react with hydrogen gas (or dimethylamine borane as a source of H2) to generate the hydrogen addition products involving the unprecedented activation of the Rh−η2-B,C motif. Complexes 2 and 3 were further found to be active catalysts for the hydrogenation of olefins and the dehydrogenation of dimethylamine borane.
0276-7333
Iannetelli, Angelo
3f6fd91d-6ac8-433e-9e46-1c0831be4ed7
Da Costa, Rosenildo Correa
ce76806a-0dba-4086-99c2-626e9b932c80
Guwy, Alan J.
a78123af-3953-4791-84d3-ade657813e94
Tizzard, Graham J.
8474c0fa-40df-43a6-a662-7f3c4722dbf2
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Owen, Gareth R.
fd633ee9-dcaa-438c-9b3b-82e9d091a1c6
Iannetelli, Angelo
3f6fd91d-6ac8-433e-9e46-1c0831be4ed7
Da Costa, Rosenildo Correa
ce76806a-0dba-4086-99c2-626e9b932c80
Guwy, Alan J.
a78123af-3953-4791-84d3-ade657813e94
Tizzard, Graham J.
8474c0fa-40df-43a6-a662-7f3c4722dbf2
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Owen, Gareth R.
fd633ee9-dcaa-438c-9b3b-82e9d091a1c6

Iannetelli, Angelo, Da Costa, Rosenildo Correa, Guwy, Alan J., Tizzard, Graham J., Coles, Simon J. and Owen, Gareth R. (2020) Transformation of a norbornadiene unit to ethylenylcyclopentene requiring cooperation between boron and rhodium centers. Organometallics. (doi:10.1021/acs.organomet.0c00155).

Record type: Article

Abstract

The synthesis of the lithium salt of a bis-substituted borohydride anion containing a phenyl substituent and a 2-mercaptopyridyl unit (mp) is reported herein. This salt has been used as a pro-ligand for the synthesis of rhodium(I) complex, [Rh{κ3-H,H,S-H2B(Ph)(mp)}(NBD)] (1) (where NBD = 2,5-norbornadiene). The new boron-based ligand coordinates to the rhodium center via the thione donor and the two B–H bonds of the BPhH2 unit, with a dihydroborate motif. Reaction of complex 1 with two equivalents of triphenylphosphine leads to an unprecedented rearrangement and transfer of the former norbornadiene ligand to the boron center. The transformation occurs via an initial hydride migration from boron to rhodium center followed by a hydroboration of one of the double bonds. Finally, a ring-opening process occurs involving both boron and rhodium centers leading to an unusual boron-bound ethylenylcyclopentene unit. The product of this reaction was confirmed as [R⌈{η1-S,η2-B,C-B(Ph)(⌉CHCH2(C5H7)(mp)}(PPh3)2] (2). The net result of these transformations is the incorporation of the two hydrogen atoms from the secondary borohydride ligand [BPhH2(mp)]− into the former norbornadiene unit. The end point positions of these hydrogen atoms were confirmed by deuterium labeling experiments. Complex 2 was further reacted with carbon monoxide to generate [⌈Rh{η1-S,η2-B,C-B(Ph)(⌉CHCH2(C5H7)(mp)}(CO)(PPh3)] (3) via ligand substitution. The new ligand and the three complexes, 1, 2, and 3, have been characterized by spectroscopic techniques as well as by X-ray crystallography. Detailed characterization of 2 and 3 revealed an unusual η2-B,C coordination mode within these complexes. Further studies have demonstrated that complexes 2 and 3 react with hydrogen gas (or dimethylamine borane as a source of H2) to generate the hydrogen addition products involving the unprecedented activation of the Rh−η2-B,C motif. Complexes 2 and 3 were further found to be active catalysts for the hydrogenation of olefins and the dehydrogenation of dimethylamine borane.

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Manuscript NBD Activation CH2Cype_FINAL_Author Submitted Version - Accepted Manuscript
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Accepted/In Press date: 24 April 2020
Published date: 24 April 2020

Identifiers

Local EPrints ID: 440687
URI: http://eprints.soton.ac.uk/id/eprint/440687
ISSN: 0276-7333
PURE UUID: 2ad0dac9-c175-457c-a509-5aef9be6ff61
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: 13 May 2020 16:35
Last modified: 29 Jul 2020 01:34

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