Aryl-cobalt porphyrins

Structural types for organometallic rhodium and iridium porphyrins mostly comprise five- or six-coordinate complexes (Por)M(R) or (Por)M(R)(L), where R is a (T-bonded alkyl, aryl, or other organic fragment, and Lisa neutral donor. Most examples contain rhodium, and the chemistry of the corresponding iridium porphyrins is much more scarce. The classical methods of preparation of these complexes involves either reaction of Rh(III) halides Rh(Por)X with organolithium or Grignard reagents, or reaction of Rh(I) anions [Rh(Por)] with alkyl or aryl halides. In this sense the chemistry parallels that of iron and cobalt porphyrins. 

Cobalt Porphyrins. The primary synthetic method for generating cobalt porphyrins with a metal carbon a-bond is to react a chemically or electrochemically generated cobalt(I) anion, [(P)Co] , with an alkyl or an aryl halide(19-26). [(P)Co] is stable and... 

Electrocatalytic reductive coupling of aryl chlorides to afford biphenyls can be accomplished with dichloro(l,2-bis(di-propylphosphino)benzene)nickel(II) in yields as high as 96% with 2 mol % of the catalyst in polar, coordinating solvents (55). Similar couplings can also be achieved with nickel-2,2 -bipyridyl and Pd(PPh3)2Cl2 as catalysts (56, 57). Indirect electrochemical reduction of vicinal dibromides to alkenes occurs efficiently with iron and cobalt porphyrins as mediators (58). Vitamin B12 is a mediator for the indirect electrochemical reduction of a-halo acids (59). 

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... 

Stolzenberg and coworkers have used electrogenerated nickel(I) tetrapyrrole complexes for the catalytic reduction of dichloromethane and methyl iodide [364], alkyl halides [365-367], and aryl halides [367], and Lexa and coworkers [368] have discussed the catalytic reduction of frm75 -l,2-dibromocyclohexane to cyclohexene by electrogenerated nickel(I), cobalt(I), and iron(I) porphyrin complexes. 

Kadish KM, Ou Z, Shao J, Gros CP, Barbe JM, Jerome F, BolzeF, BurdetF, Guilard R (2002) Alkyl and aryl substituted corroles 3 reactions of cofacial cobalt biscorroles and porphyrin-corroles with pyridine and carbon monoxide. Inorg Chem 41 3990-4005... 

The above method has been used for the synthesis of metal alkyl (or aryl) o-bonded porphyrins of iron , cobalt rhodium titanium iridium gallium indium thallium, silicon germanium " " and tin ... 

An alternative route used in organometallic chemistry is the reaction of low valent organometallic derivatives with alkyl (aryl) halides. The two electron oxidative addition of alkyl (aryl) halides or cyclopropane derivatives to metalloporphyrins such as [M (Por)] leads to metal alkyl (aryl) o-bonded porphyrins of cobalt " rhodium and iridium ° (Scheme 2). Substitution of aryl and vinyl halides by electrochemically generated iron(I) porphyrins also leads to o-bonded Fe complexes ... 

Zhang and coworkers recently reported on the nse of a cobalt (II) tetraphenyl porphyrin complex, Co(TPP), as a catalyst for the intra-molecnlar amination of snUbnyl azides. Their work builds on early studies where Cenini and coworkers used Co(TPP) for the amination of benzylic C—H bonds with aryl azides. Reactions of primary, secondary, and tertiary sulfonyl azides with Co(TPP) in chlorobenzene in the presence of molecular sieves and under an inert atmosphere at SO C gave the desired sultams 296-301 in high yield. The authors noted that tertiary C—H bonds reacted to give higher product yields then than secondary and primary C—H bonds, respectively, in the formation of live-membered heterocyclic ring structures. 

---