Chemistry of iron complexation

Precious metals have faced a significant price increase and the fear of depletion. By contrast, iron is a highly abundant metal in the crust of the earth (4.7 wt%) of low toxicity and price. Thus, it can be defined as an environmentally friendly material. Therefore, iron complexes have been studied intensively as an alternative for precious-metal catalysts within recent years (for reviews of iron-catalyzed organic reactions, see [12-20]). The chemistry of iron complexes continues to expand rapidly because these catalysts play indispensable roles in today s academic study as well as chemical industry. 

Due this recent revival, there is the need for an authoritative review of this important chemistry. It is the purpose of this book not only to introduce the chemistry community to the most recent achievements in the field of catalysis, but also to create a deeper understanding of the underlying fundamentals in the organometallic chemistry of iron complexes. 

Until the last decade, the chemistry of iron complexes in organic synthesis has been mostly connected with their stoichiometric application. They may be used to activate otherwise unreactive functions. Moreover, iron complex moieties can be employed as stereocontrolling or protecting groups. Their chemistry has been reviewed several times. The previous edition of this book also contains an overview of the most important examples of organoiron chemistry up to the end of the 1990s. The present chapter will briefly repeat fundamental reactions and support them with more recent examples. Additionally, new developments fi om the last decade are outlined. 

The activation of silylene complexes is induced both photochemically or by addition of a base, e.g. pyridine. A similar base-induced cleavage is known from the chemistry of carbene complexes however, in this case the carbenes so formed dimerize to give alkenes. Finally, a silylene cleavage can also be achieved thermally. Melting of the compounds 4-7 in high vacuum yields the dimeric complexes 48-51 with loss of HMPA. The dimers, on the other hand, can be transformed into polysilanes and iron carbonyl clusters above 120 °C. In all cases, the resulting polymers have been identified by spectroscopic methods. 

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

The chemistry of iron has been reviewed in COMC (1982) and COMC (1995)312-314 as well as in Comprehensive Coordination Chemistry 7/.315 More recent reviews cover iron-catalyzed transformations with samarium(ll) iodide,18d the chemistry of tricarbonyliron-diene complexes,316 and iron-catalyzed reactions in organic synthesis in general.317... 

Professor Mahy received his Ph.D. in 1990 from the University of Paris 6 on a bioinorganic subject dealing with the importance of the complexes with an Fe—N bond in the chemistry of iron-porphyrin and hemoproteins. 

There have been two books devoted to the chemistry of iron, " and many reviews devoted to various aspects of its coordination chemistry, including structures and photochemistry (iron(III)). Iron complexes appear in a multi-author volume on the history of coordination chemistry, but there is disappointingly little about iron—just a brief mention of hexacyanoferrates in connection with pigments—in an otherwise excellent overview of the history of chemistry. ... 

The chemistry of iron in aqueous solution is dominated by the 4 2 and 4 3 states, which are well characterized. The 4 3 state in acid solution is a good oxidizing agent the 4 2 state is the most stable. The [Fe(H20)6]3 + complex ion is a violet colour in the solid chlorate(VII) salt, but in solution it undergoes hydrolysis to give the familiar orange-red colour. The first stage of the hydrolysis may be written as ... 

Tt is well known that iron is a common constituent of works of art and of artifacts of archaeological interest. This is undoubtedly because of its occurrence in most rocks of the earths crust and in a variety of colored compounds. The chemistry of iron compounds is fairly complex, and the form in which it is eventually found in an object can provide information on the source and the technique of manufacture of that object. Mossbauer effect spectroscopy (MES) is particularly suitable for studying iron and its compounds. Already there are two published reports 1,2) of MES applied to the study of ancient pottery. However, those studies, like most MES work, required sample taking and preparation. We have explored the possibility of nondestructive MES and now report on practicality of this method. Since there are many good descrip-... 

The central role of the complexes [Fe(NO)2(SR)2]- in the reaction chemistry of iron-sulfur-nitrosyl complexes and their very ready formation both in in vitro and in vivo (108,123-125,128,129) suggest that the antimicrobial activity of nitrite depends not only upon the disruption of respiration [by destruction of the natural iron-sulfur clusters of redox proteins (70S)] but also specifically upon the formation... 

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