Metal-tetrapyrrole complexes

Not only porphyrins, but tetrapyrrole ligands in general are interesting partners for the coordination of noble metals. This section will refer to the synthesis of some tetrapyrrole complexes other than porphyrins from time to time, derivatives of these ligands will be mentioned in the later sections on the reactions of noble metal porphyrins because most of these tetrapyrrole complexes behave similarly as regards their axial coordination chemistry. 

Phthalocyanines - Pthalocyanine complexes form a very large class among tetrapyrrole complexes. Their chemistry, physics, and applications for novel materials are being reviewed in a multi volume series [106]. Usually they are made by reductive tetramerization of phthalodinitrile with a metal salt (see below), but metallations of free phthalocyanine, H2(Pc), are also documented. Work in the last two decades has been concentrated on phthalocyanine complexes of Ru, Os, Rh, Pd, Pt, and Ag Berezin gives references on IrCl(Pc) and AuCl(Pc) [107]. 

The subject of this Section is photochemical processes in which polynuclear tetrapyrrole complexes with metal-metal or metal-bridge-metal bonds are formed from or decomposed to mononuclear tetrapyrrole ligand containing... 

The present Volume 84 of Structure and Bonding is entitled "Metal Complexes with Tetrapyrrole Ligands III" and completes a series of three volumes dedicated to this general topic which started with Volume 64 and continued with Volume 74. The first volume contained topics such as stereochemistry of metal lotetrapyrroles, infrared and Raman spectra, biomimetic porphyrins, or metal loporphyrins with metal-carbon single bonds and metal-metal bonds. In the second volume, subjects like extended X-ray absorption fine structure or metal tetrapyrroles with special electrical and optical properties were covered. 

D.K.R Ng, J. Jiang, K. Kasuga and K. Machida conclude this volume with an overview of rare-earth and actinide half-sandwich tetrapyrrole complexes. When tetrapyrrole molecules, such as porphyrins or phthalocyanines, are reacted with the rare earths and actinides, they are split in half, forming the half-sandwich complexes because the metal atoms are larger than the core size of the macrocyclic ligands. They also can form sandwich-type complexes in which the metal centers are sandwiched between the macrocycles. However, this chapter is devoted to the former class of compounds. Ng and co-workers discuss the synthesis, structure, and spectroscopic and electrochemical properties of half-sandwich complexes of porphyrins and phthalocyanines. The authors... 

A review14 discusses palladium and the other noble metals forming a variety of complexes M(P)LL with tetrapyrrole ligands. 

Octaethylbilindione (H3OEB) is a convenient model for the bile pigment biliverdin IXa. Key redox states of this ligand as observed in its complexes are shown in Figure 14. The redox behavior of the palladium complex of octaethylbilindione was examined in order to determine the generality of the redox behavior of this group of transition metal complexes.202 A preliminary report on the novel tetrameric Pd4(OEB)2, which contains palladium) ) ions 7r-bonded to C=C bonds of the tetrapyrrole ligand, and of Pdn(OEB ) has appeared.203... 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

Buchler, J. W., ElsSsser, K., Kihn-Botulinski, M., Scharbert, B. Angew. Chem. 1986, in press. Number 41 in the series Metal Complexes with Tetrapyrrole Ligands. 

As is known, the triplet and singlet tetrapyrrolic pigment states are caused by excitation of delocalized ir electrons of the heteroaromatic macrocycle (1 ). The most favourable structure of dimeric complexes for metal 1oporphyrin TTA seems to be a sandwich dimer as in the case when molecular orientation of plane to plane electronic shells reaches the maximum overlap. Quantum chemistry calculations of metalloporphyrin dimers indicates that for the dimeric emission process the 2 state is split into states of higher energy (SJ) and lower energy ( 2). In the case of a sandwich dimer of 04 symmetry, the following states are seen ... 

A ruthenium(VI) nitrido complex containing a tetrapyrrolic macrocycle ligand, [Ru (N)(L)] (82) (H4L = mcio-octamethylporphyrinogen), has been synthesized by the reaction of diphewldiazomethane with [Ru"(L)] , which is prepared from [Ru(cod)(Cl)2] and Na4(L) 4THF. X-ray crystal studies reveal that [Ru (N)(L)] has a Cjv symmetry, and it has the usual saddle conformation, with the metal atom displaced 0.482 A out of the N4 mean plane. The reactivities and redox chemistry of this complex are summarized in Scheme 12 (see also Section 5.6.5.2). 

Metal Complexes of Carbon-Based. Tetrapyrroles Other Than Metal Porphyrins... 

Corroles and corrinoids - For results on the noble metal complexes of this interesting class of tetrapyrroles, see the article by S. Licoccia in this volume [105]. 

The porphyrin complexes of ruthenium and osmium display a rich oxidation-reduction chemistry. Oxidation states +2, +3 +4, and + 6 are well documented. The scope of states that can be realised at the metal is restricted by the fact that the tetrapyrrole ligands (P)2 themselves can be oxidized or reduced to radicals (P )-1 or (P )-3, respectively, at potentials about + 0.7 or - 2.0 V. 

In this review we will focus on synthetic derivatives of the macrocycles where a tetrapyrrolic skeleton is maintained and on their metal complexes without taking into account their biologically active counterparts. 

Two major strategies have been considered in order to obtain metallocorrolates the first one consists of the reaction of the preformed macrocycle with metal ions, while the second involves the oxidative, base induced cycliz-ation of the open-chain tetrapyrrolic precursor dihydrobilin (1,19-dideoxybiladiene-a,c) in buffered alcoholic solution in the presence of metal salts. By proper tuning of the experimental conditions (reaction time, solvent, metal carrier) several metal complexes have been obtained and characterized. 

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