Mono- and dizinc complexes of diporphyrins with flexible spacers of variable length

Abstract

The di- and mono-zinc(II) complexes of diporphyrins (D) were synthesized, in which two porphyrin halves were covalently linked through a variable length hydrocarbon spacer (–CH 2) n –, where n=2–4, D2–D4, respectively) attached via the ortho oxygen atom of the meso-phenyl ring. Three p-tolyl substituents were attached to other meso positions of both porphyrins. The zinc(II) complexes were studied by 1-D and 2-D COSY and NOESY 1H NMR spectroscopy. The stability constants of dizincdiporphyrins with azaaromatic ligands: pyridine (py), pyrazine (pyr), and 4,4 ′-bipyridyl (bipy) were determined by spectrophotometric titration. The discriminating factor for stability of dinuclear complexes with diazaaromatic ligands was the length of the diporphyrin spacer. The formation constant for ZnTTP with pyr and bipy were very close to that for py, whereas they were about 1.3 orders of magnitude larger for D2Zn 2 -pyr, D3Zn 2 -bipy, and D4Zn 2 -bipy complexes which was attributed to the formation of nitrogen base bridged species. The monozincdiporphyrin complexes were demonstrated to be a convenient starting material for synthesis of heterodimetallodiporphyrins. The Zn(II)/Cu(II)diporphyrin complex was synthesized and characterized by EPR spectroscopy.