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Nickel Complexes of 21‐Oxaporphyrin and 21, 23‐Dioxaporphyrin
Author(s) -
Chmielewski Piotr J.,
LatosGrażyński Lechoslaw,
Olmstead Marilyn M.,
Balch Alan L.
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030216
Subject(s) - nickel , furan , chemistry , electron paramagnetic resonance , crystallography , pyrrole , porphyrin , moiety , bond length , nmr spectra database , crystal structure , medicinal chemistry , stereochemistry , photochemistry , spectral line , nuclear magnetic resonance , organic chemistry , physics , astronomy
The nickel(I) and nickel(II) complexes of 5,20‐bis( p ‐tolyl)‐10, 15‐diphenyl‐21‐oxaporphyrin (ODTDPPH) and 5,10,15,20‐tetraphenyl‐21, 23‐dioxaporphyrin (O 2 TPP) have been investigated. These oxa analogues of 5,10,15,20‐tetraarylporphyrin, where one or two pyrrole rings are replaced by a furan moiety, have been synthesized by condensation of the respective precursors, namely 2,5‐bis(arylhydroxymethyl)furan, pyrrole, and arylaldehyde. Insertion of nickel(II) into ODTDPPH or O 2 TPP yielded high‐spin five‐ and six‐coordinate ([(ODTDPP)Ni II Cl] and [(O 2 TPP)NiIICl 2 ]) complexes, which can be reduced with moderate reducing reagents. The EPR spectra of [(ODTDPP)Ni I ] and [(O 2 TPP)Ni I Cl] revealed the Ni I oxa(dioxa)porphyrin rather than a Ni I anion radical electronic structure. In the structures of [(ODTDPP)Ni II Cl], [(O 2 TPP)Ni IICl 2 ], and [(ODTDPP)Ni I ], determined by X‐ray diffraction, the furan ring is planar and coordinates in the η 1 fashion through the trigonal oxygen atom; the nickel ion lies in the furan plane for the latter two complexes, but slightly outside it in [(ODTDPP)Ni II Cl]. The Ni–N and Ni–O bond lengths decrease upon reduction of high‐spin five‐coordinate [(ODTDPP)Ni II Cl] to four‐coordinate [(ODTDPP)Ni I ]. The pattern of downfield pyrrole resonances in 1 H NMR spectra of [(ODTDPP)Ni IICl ] and [(O 2 TPP)‐Ni II Cl 2 ] has been established. The downfield positions of furan resonances are unusual for Ni II heteroporphyrins; they have been accounted for by the nearly in‐plane coordination of the furan moiety as opposed to the side‐on coordination found for thiophene‐ or selenophene‐containing heteroporphyrins. An example of ion‐pair formation, [(O 2 TPPH) 2 ][Ni II Cl 4 ], was produced from [(O 2 TPP)Ni II Cl 2 ] by acidification with HCl.