Basicity organometallic complexes

Considerable progress has been made on C02 fixation in photochemical reduction. The use of Re complexes as photosensitizers gave the best results the reduction product was CO or HCOOH. The catalysts developed in this field are applicable to both the electrochemical and photoelectrochemical reduction of C02. Basic concepts developed in the gas phase reduction of C02 with H2 can also be used. Furthermore, electrochemical carboxyla-tion of organic molecules such as olefins, aromatic hydrocarbons, and alkyl halides in the presence of C02 is also an attractive research subject. Photoinduced and thermal insertion of C02 using organometallic complexes has also been extensively examined in recent years. 

In previous chapters, we have presented a great deal of information about structure and bonding in coordination compounds. This chapter will be devoted to describing some of the important chemistry in the broad areas of organometallic complexes and those in which there are metal-metal bonds. The body of literature on each of these topics is enormous, so the coverage here will include basic concepts and a general survey. 

The readers will be aware of the basic principles of bonding in organometallic complexes, especially the bonding of alkenes and carbon monoxide, and this will not be dealt with here. We will say a few words about ligands containing phosphorus as the donor element. 

Notes Useful for organometallic complexation. Selective base used for the Bavtiss-Hillman reaction. Has been used for the HaUer-Bauer cleavage reaction. Streitwieser1 has examined a new scale of amine basicity ( K,p ), where the lower the pKip values the stronger the base. In this analysis ... 

In comparing the overall size of the bulky Cp s to n-Cp (1) we would like to coin the additional term supracyclopentadienes for these systems to describe their large molecular size. These bulky or supra-Cp s and their applications as ligands in organometallic complexes are the subject of this article. Other basic bulky Cp s described in the literature, in addition to those sketched above, are di(isobutylXtert-butyl )-Cp (13), penta(isopen-tyl)-Cp [isopentyl = (HjC2)2CH—] (14), and tris(methoxycarbonyl)-Cp (15,16). However, these systems have had very limited application so far,... 

As discussed above in the mechanism of the alkene dimerization reaction, the polymerization of simple alkenes proceeds by the basic metathesis mechanism. Since polymers that are prepared from complex monomers require homogeneous catalysts, much of the early organometallic catalyst development has had polymer synthesis as the driving force. Recently, developments in the synthesis of organometallic complexes that serve as well-defined catalysts for metathesis have opened many opportunities in the area of polymer synthesis. ... 

A basic knowledge of the reaction types described in this section allows us to proceed to a discussion of the chemistry of selected organometallic complexes and (in Chapter 26) catalysis. Oxidative additions and alkyl migrations in particular are very important in the catalytic processes used in the manufacture of many organic chemicals selected important organometallic compounds used as catalysts are summarized in Box 23.3. 

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