Organometallic heterocycles Subject

Volume 78 of Advances in Heterocyclic Chemistry contains four contributions. A. P. Sadimenko of Fort Hare University of South Africa has covered organometal-lic compounds of furan, thiophene, and their benzannulated derivatives. This constitutes the first installment of a projected series on the organometallic chemistry of heteroaromatic ligands, a subject of great fundamental and technical importance that has exploded in the 1990s. 

Volume 72 of Advances in Heterocyclic Chemistry consists of six chapters. The first considers the role of five- and six-membered heteroaromatic compounds as ct and ir ligands. Authored by Professors A. D. Garnovskii (Rostov-on-Don, Russia) and A. P. Sadimenko (Fort Hare, South Africa), it gives an overview of the multitude of structural types that can arise when heterocycles are used as ligands in organometallic derivatives. Many such compounds are of great industrial importance in catalytic and other processes. No previous comprehensive overview of this subject has been available. 

Conformational properties of these heterocyclic systems usually result from the increased CN numbers of arsenic, antimony, and bismuth. Tricoordinate systems show interesting solid state conformational behavior as displayed in l,l -biheteroles (Sections 2.16.10.2 and 2.16.11.2) and organometallic complexes (Section 2.16.10.3). More detailed treatment of this subject is found in the references in these sections. 

Particularly interesting new work includes the development of remote and abnormal NHCs (see Chapter 5 for further details). Also, NHCs have not only been used as ligands in transition metal chemistry but also as nucleophilic organocatalysts. In an extension of this concept, Lavallo and Grubbs presented recently the first organometallic transformation catalyzed by NHCs. This illustrate nicely that almost 20 years after Arduengo s first report on an N-heterocyclic carbene, new NHCs as well as new applications for these interesting and versatile molecules are still and will be for some time the subject of intensive research. 

The final chapter in this volume by Alexander Sadimenko (University of Fort Hare, South Africa) continues a series by this author on the oiganometallic chemistry of heterocycles, of which 0,S monoheterocycles and NJ, Si,B monohete-rocycles were published in volumes 78 and 79, res tively. The organometallic chemistry of pyrazole is so broad that the present overview does not include the polyfunctional, chelating frameworks ccmtaining Rnazolyl units, which are typified by the pyrazolylborate derivatives. These will be the subject of a future chapter. 

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