Rotaxane synthesis exploiting the M(i)/M(III) redox couple
Rotaxane synthesis exploiting the M(i)/M(III) redox couple
In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1p;:p;1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t < 5 min @ RT) in CH2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.
11645-11655
Emerson-King, Jack
6ee84728-72a7-496a-a05c-48720dea9d48
Knighton, Richard C.
5a63128e-0ebd-466a-b327-3aee6e85a76d
Gyton, Matthew R.
2ea653e0-f115-4f1c-b5c6-87d3049a821f
Chaplin, Adrian B.
6af87db8-8153-44ea-88ef-e25eb2cd5f9d
Emerson-King, Jack
6ee84728-72a7-496a-a05c-48720dea9d48
Knighton, Richard C.
5a63128e-0ebd-466a-b327-3aee6e85a76d
Gyton, Matthew R.
2ea653e0-f115-4f1c-b5c6-87d3049a821f
Chaplin, Adrian B.
6af87db8-8153-44ea-88ef-e25eb2cd5f9d
Emerson-King, Jack, Knighton, Richard C., Gyton, Matthew R. and Chaplin, Adrian B.
(2017)
Rotaxane synthesis exploiting the M(i)/M(III) redox couple.
Dalton Transactions, 46 (35), .
(doi:10.1039/c7dt02648j).
Abstract
In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1p;:p;1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t < 5 min @ RT) in CH2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.
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c7dt02648j
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Accepted/In Press date: 15 August 2017
e-pub ahead of print date: 24 August 2017
Identifiers
Local EPrints ID: 482025
URI: http://eprints.soton.ac.uk/id/eprint/482025
ISSN: 0300-9246
PURE UUID: 08c6fe5c-8ab0-451c-ba06-7ba14d02b50a
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Date deposited: 15 Sep 2023 16:46
Last modified: 18 Mar 2024 04:15
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Author:
Jack Emerson-King
Author:
Richard C. Knighton
Author:
Matthew R. Gyton
Author:
Adrian B. Chaplin
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