Metalloporphyrins metal-carbon bond containing

One family of porphyrin complexes that will be treated in the review, even though they do not contain metal-carbon bonds, are metalloporphyrin hydride and dihydrogen complexes. As in classical organometallic chemistry, hydride complexes play key roles in some reactions involving porphyrins, and the discovery of dihydrogen complexes and their relationship to metal hydrides has been an important advance in the last decade. 

ELECTROCHEMISTRY OF METALLOPORPHYRINS CONTAINING A METAL-METAL OR METAL-CARBON BOND... 

Electrochemistry of Metalloporphyrins Containing a Metal-Metal or Metal-Carbon Bond K.M. Kadish... 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

Electrosynthesis and Electrochemistry of Metalloporphyrins Containing a Metal—Carbon cr-Bond... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

Metalloporphyrins containing a metal-carbon a-bond are currently limited to complexes with eight different transition metals (Ti, Ni, Fe, Ru, Co, Rh, Ir and In) and seven different non-transition metals (Al, Ga, In, Tl, Si, Ge, and Sn). These compounds have been the subject of several recent reviews(1-33 which have discussed their synthesis and physicochemical properties. 

The synthesis of metalloporphyrins which contain a metal-carbon a-bond can be accomplished by a number of different methods(l,2). One common synthetic method involves reaction of a Grignardreagent or alkyl(aryl) lithium with (P)MX or (PMX)2 where P is the dianion of a porphyrin macrocycle and X is a halide or pseudohalide. Another common synthetic technique involves reaction of a chemically or electrochemically generated low valent metalloporphyrin with an alkyl or aryl halide. This latter technique is similar to methods described in this paper for electrosynthesis of cobalt and rhodium a-bonded complexes. However, the prevailing mechanisms and the chemical reactions... 

KADISHETAL. Metalloporphyrins Containing Metal-Carbon o-Bonds 453... 

KADISHETAL. Metalloporphyrins Containing Metal—Carbon a-Bonds 457... 

Figure 6.2.3 The bond lengths in porphyrins are more or less alternating, feigning polyene character, if the pyrrolic carbon-carbon bonds are included. The inner ring containing the pyrrole and pyrrolenine nitrogen is, however, fully aromatic. The bond lengths are all close to 1.37 A. It is this macrocycle in connection with the electron-donating or -withdrawing power of the central metal ions that determines both the redox and photochemistry of metalloporphyrins. The bond lengths in the center correspond to NH bonds.

Metalloporphyrins containing different <7-bonded alkyl or aryl groups [3, 45, 56-64] or the diatomic molecules NO [27, 65-77] or CO (see following sections) have been electrochemicaUy investigated and several reviews of the general electrochemical behavior of these compounds have been published [7, 12, 78]. Metalloporphyrins with 29 different central ions are now known to form carbon cr-bonded complexes (see Fig. 5) [12] and the electrochemical behavior of these compounds has been shown to depend on the central metal ion. 

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