Cadmium(II), Nickel(II), and Zinc(II) Complexes of Vacataporphyrin: A Variable Annulene Conformation inside a Standard Porphyrin Frame
5,10,15,20-Tetraaryl-21-vacataporphyrin, 1 (butadieneporphyrin, annulene−porphyrin hybrid), which contains a vacant space instead of heteroatomic bridge, gives diamagnetic zinc(II) 1-ZnCl and cadmium(II) 1-CdCl and paramagnetic nickel(II) 1-NiCl complexes. A metal ion is bound in the macrocyclic cav...
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Published in | Inorganic chemistry Vol. 44; no. 24; pp. 8794 - 8803 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
28.11.2005
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Online Access | Get full text |
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Summary: | 5,10,15,20-Tetraaryl-21-vacataporphyrin, 1 (butadieneporphyrin, annulene−porphyrin hybrid), which contains a vacant space instead of heteroatomic bridge, gives diamagnetic zinc(II) 1-ZnCl and cadmium(II) 1-CdCl and paramagnetic nickel(II) 1-NiCl complexes. A metal ion is bound in the macrocyclic cavity by three pyrrolic nitrogens. Coordination imposes a steric constraint on the geometry of the ligand and leads to two stereoisomers with a butadiene fragment oriented toward 1-MCl-i or outward 1-MCl-o of the macrocyclic center. 1-CdCl-o, 1-ZnCl-o, and the free base share a common 1H NMR spectral pattern as the basic structural features of 1 are preserved after metal ion insertion. The 1H NMR spectra of 1-CdCl-i and 1-ZnCl-i reflect a decrease of aromaticity accounted for by the inverted butadiene geometry. The proximity of the butadiene fragment to the metal ion induces direct couplings between the spin-active nucleus of the metal (111/113Cd) and the adjacent 1H nuclei of butadiene. The pattern of chemical shifts detected for isomeric 1-NiCl-i and 1-NiCl-o is typical for high-spin nickel(II) complexes of porphyrin analogues. Resonances 2,3-H of 1-NiCl-o or 1-NiCl-i present the chemical shift typical for the β-H pyrrolic position despite the vacancy in the location of nitrogen-21. Coordination of imidazole, methanol-d 4, acetonitrile-d 3, or chloride converts 1-NiCl-i and 1-NiCl-o into distinct species which contain two axial ligands: 1-Ni(Im)2 +; 1-Ni(CD3OD)2 +; 1-Ni(CD3CN)2 +; 1-Ni(Cl)2 -. The density functional theory (DFT) has been applied to model the molecular and electronic structure of feasible 1-CdCl stereoisomers. The total energies calculated using the B3LYP/LANL2DZ approach demonstrate a very small energy difference (2.3 kcal/mol) between 1-CdCl-o and 1-CdCl-i stereoisomers consistent with their concurrent formation. |
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Bibliography: | ark:/67375/TPS-52ZVPG4M-0 istex:3A5D3B5C64AE7813D5404740C2536E12270959C4 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0020-1669 1520-510X |
DOI: | 10.1021/ic0511470 |