Transition-metal-coordinated carbonyls reactions with

The Diels-Alder reaction is a key reaction in organic synthesis. Its high versatility in the synthesis of six-membered ring compounds and its potential for the control of up to four stereogenic centers have attracted much attention. Lewis acid catalysis has further enhanced the scope of this reaction. Lewis acids activate the dienophile by coordination to a Lewis basic substituent (usually a carbonyl group) and direct the stereochemistry. Boron Lewis acids are often the catalysts of choice for the Diels-Alder reaction. Early (Ti(IV)) and late (Cu(II)) transition metal complexes in combination with chiral ligands have also been used with much success and the reader is referred to the relevant chapters in this book. 

This is a special volume of Inorganic Syntheses that focuses on complexes that are likely to be useful as starting materials for the preparations of new transition metal coordination and organometallic compounds. There are chapters on complexes with weakly coordinated and therefore easily displaced ligands, low-valent complexes that undergo oxidative-addition reactions, substituted metal carbonyl complexes, nucleophilic metal carbonyl anions, transition metal clusters, a variety of cyclopentadienyl complexes, lanthanide and actinide complexes, and a range of other useful ligands and complexes. 

Two commonly used synthetic methodologies for the synthesis of transition metal complexes with substituted cyclopentadienyl ligands are important. One is based on the functionalization at the ring periphery of Cp or Cp metal complexes and the other consists of the classical reaction of a suitable substituted cyclopentadienyl anion equivalent and a transition metal halide or carbonyl complex. However, a third strategy of creating a specifically substituted cyclopentadienyl ligand from smaller carbon units such as alkylidynes and alkynes within the coordination sphere is emerging and will probably find wider application [22]. 

In homogeneous solutions NO disproportionation maybe promoted by transition metal complexes, and a variety of mechanisms seem to be available owing to the many possible modes of coordination. One example is the reaction of NO with nickel carbonyl shown in Eq. (35) (76),... 

Coordination chemistry of ER The monomeric fragments E-R are isolobal to carbon monoxide, and many complexes analogous to transition metal carbonyls have been synthesized (41 to 43, see Figure 2.3-7) [68], In most cases these reactions started with those clusters which have a high tendency to dissociate and to form monomers, such as pentamethylcyclopentadienylaluminum(I) or the alkylgal-lium(I) or alkylindium(I) derivatives. Often the products are isostructural to the respective metal carbonyls, but exceptions are the gallium compounds 44 and 45. 

Zerovalent transition metal carbonyl moieties may act as electron acceptors, and thus activate coordinated polyene ligands toward nucleophilic attack. Reaction of (C.411<5 )-Fe(CO)3 with KBHEt3 (—80 °C) proceeds via attack at a coordinated carbon monoxide to generate the anionic iron-formyl species 185 (Scheme 47)184. Upon warming to... 

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