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Selection and amplification of mixed-metal porphyrin cages from dynamic combinatorial libraries

Selection and amplification of mixed-metal porphyrin cages from dynamic combinatorial libraries
Selection and amplification of mixed-metal porphyrin cages from dynamic combinatorial libraries
Mixed metallo-porphyrin cages were selected and amplified from dynamic combinatorial libraries (DCLs) by using appropriate templates. The cages are composed of two bisphosphine substituted zinc(ii) porphyrins as ligand donors and two rhodium(m) or thenium(II) porphyrins as ligand acceptors, and are connected through metal-phosphorus coordination. Ru and Rh porphyrins that display a large structural diversity were employed. The templating was achieved by using 4,4'-bpy, 3,3'-dimethyl-4,4'-bipyridine and benzo[lmn]-3,8-phenanthroline, and acts through zinc-nitrogen coordination. The absolute amount of amplification from the DCLs is strongly dependent on the combination of the Ru/Rh porphyrin and the template; cages with sterically demanding porphyrins can only form with smaller templates. In the case of tert-butyl-substituted TPP TPP=tetra-phenylporphyrin), cages are not formed at all. The formation of the cages is usually complete within 24 h at an ambient temperature; in the case of the cage containing (RhOEP)-O-III (OEP = octaethylporphyrin) and bpy, the pseudo-first-order rate constant of cage formation was determined to be 2.1 +/- 0.1 x 10(-4) s(-1) (CDCl3, 25degreesC). Alternatively, heating the mixtures to 5degreesC and cooling to room temperature yields the cages within minutes. The H-1 NMR chemical shifts of several characteristic protons show large differences upon changing the identity of the Ru/ Rh porphyrin and the central metal; this is most likely to arise from variations in the geometry of the cages. The X-ray crystal structure of a cage, which contains Rh... OEP as a porphyrin acceptor and bpy as template, demonstrates that the cages can adopt severely distorted conformations to accommodate the relatively short templates. An extension to mixed DCLs showed that only limited selectivity is displayed by the various templates. Formation of mixed cages that contain two different rhodium porphyrins prevents effective selection, although the kinetic lability of the systems allows for some amplification. This lability, however, also prevents isolation of the individual cages. Removal of the template leads to re-equilibration, thus the templates act as scaffolds to keep the structures intact.
phosphonite complexes, building-blocks, chemistry, coordination, phosphine, ruthenium(ii), receptors, cluster, ligands
0947-6539
6039-6048
Stulz, E.
9a6c04cf-32ca-442b-9281-bbf3d23c622d
Scott, S.M.
5404592a-5c50-41be-9216-5158e770904c
Bond, A.D.
13963962-651c-4172-b606-0ddcc20daa45
Teat, S.J.
6a3b9a8f-3681-49fc-9a8b-0cf1a4c88c18
Sanders, J.K.M.
bcb99bef-e0c2-4399-89ab-5c1cb445446b
Stulz, E.
9a6c04cf-32ca-442b-9281-bbf3d23c622d
Scott, S.M.
5404592a-5c50-41be-9216-5158e770904c
Bond, A.D.
13963962-651c-4172-b606-0ddcc20daa45
Teat, S.J.
6a3b9a8f-3681-49fc-9a8b-0cf1a4c88c18
Sanders, J.K.M.
bcb99bef-e0c2-4399-89ab-5c1cb445446b

Stulz, E., Scott, S.M., Bond, A.D., Teat, S.J. and Sanders, J.K.M. (2003) Selection and amplification of mixed-metal porphyrin cages from dynamic combinatorial libraries. Chemistry - A European Journal, 9 (24), 6039-6048. (doi:10.1002/chem.200305265).

Record type: Article

Abstract

Mixed metallo-porphyrin cages were selected and amplified from dynamic combinatorial libraries (DCLs) by using appropriate templates. The cages are composed of two bisphosphine substituted zinc(ii) porphyrins as ligand donors and two rhodium(m) or thenium(II) porphyrins as ligand acceptors, and are connected through metal-phosphorus coordination. Ru and Rh porphyrins that display a large structural diversity were employed. The templating was achieved by using 4,4'-bpy, 3,3'-dimethyl-4,4'-bipyridine and benzo[lmn]-3,8-phenanthroline, and acts through zinc-nitrogen coordination. The absolute amount of amplification from the DCLs is strongly dependent on the combination of the Ru/Rh porphyrin and the template; cages with sterically demanding porphyrins can only form with smaller templates. In the case of tert-butyl-substituted TPP TPP=tetra-phenylporphyrin), cages are not formed at all. The formation of the cages is usually complete within 24 h at an ambient temperature; in the case of the cage containing (RhOEP)-O-III (OEP = octaethylporphyrin) and bpy, the pseudo-first-order rate constant of cage formation was determined to be 2.1 +/- 0.1 x 10(-4) s(-1) (CDCl3, 25degreesC). Alternatively, heating the mixtures to 5degreesC and cooling to room temperature yields the cages within minutes. The H-1 NMR chemical shifts of several characteristic protons show large differences upon changing the identity of the Ru/ Rh porphyrin and the central metal; this is most likely to arise from variations in the geometry of the cages. The X-ray crystal structure of a cage, which contains Rh... OEP as a porphyrin acceptor and bpy as template, demonstrates that the cages can adopt severely distorted conformations to accommodate the relatively short templates. An extension to mixed DCLs showed that only limited selectivity is displayed by the various templates. Formation of mixed cages that contain two different rhodium porphyrins prevents effective selection, although the kinetic lability of the systems allows for some amplification. This lability, however, also prevents isolation of the individual cages. Removal of the template leads to re-equilibration, thus the templates act as scaffolds to keep the structures intact.

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Published date: 2003
Keywords: phosphonite complexes, building-blocks, chemistry, coordination, phosphine, ruthenium(ii), receptors, cluster, ligands

Identifiers

Local EPrints ID: 41071
URI: http://eprints.soton.ac.uk/id/eprint/41071
ISSN: 0947-6539
PURE UUID: f486d59d-ddc5-4d35-9a20-ed6ff7584e7d
ORCID for E. Stulz: ORCID iD orcid.org/0000-0002-5302-2276

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Date deposited: 14 Jul 2006
Last modified: 16 Mar 2024 03:51

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Contributors

Author: E. Stulz ORCID iD
Author: S.M. Scott
Author: A.D. Bond
Author: S.J. Teat
Author: J.K.M. Sanders

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