Synthesizing Organometallics

Among the several strategies developed for carbazole syntheses, organometallic approaches to carbazoles have received special attention, since they have led, in many cases, to highly convergent total syntheses of carbazole alkaloids (8,10, 570-572). The iron-mediated retrosynthesis of 1-oxygenated carbazoles 7-11 leads to cyclohexadiene (597) and the corresponding arylamines 598-600 as synthetic precursors (Scheme 5.32). 

Many polymerizations used to synthesize organometallic polymers involve cleavage of a bond to the metal atom of one reactant followed by attachment at that metal of a fragment derived from a second reactant [Carraher et al., 1978 Kaliyappan and Kannan, 2000 Manners, 1996 Nguyen et al., 1999 Pittman et al., 1987 Sheets et al., 1985]. 

A wide range of reactions have been used, but only a few are illustrated here. Carboxylate and sulfide groups have been used to obtain organometallic polymers (Eqs. 2-235 and 2-236). These types of reactions have been used to synthesize organometallic polymers of a wide variety of other metals (e.g., Zr, Hf, Si, Ge, Pb, As, Sb, Bi, Mn, B, Se). The polymer obtained... 

An alternate synthetic approach to organometallic polymers is to perform reactions where the metal atom is not the reaction site. An example is a polyesterification between an organometallic monomer containing two carboxyl groups and a diol (Eq. 2-238). Reaction of the diacid with a diamine would yield an organometallic polymer via polyamidation. A wide range of other reactions covered in this chapter can be used to synthesize organometallic polymers. 

Without doubt, the most noteworthy aspect of the redox behavior of the synthesized organometallic dendritic macromolecules 1-6, having a predetermined number of noninteracting ferrocenyl redox centers, is their ability to modify electrode surfaces. In this way, for the first time, electrode surfaces have been successfully modified with films of dendrimers containing reversible four- and eight-electron redox systems, resulting in detectable electroactive materials persistently attached to the electrode surfaces. ... 

This chapter does not intend to provide a complete collection of newly synthesized organometallic or coordination complexes for alkene polymerization, but rather aims to review a cross-section of transition metal catalysts from the viewpoint of polymers and polymerization reactions. We focus particularly on polymers that are difficult or virtually impossible to prepare using conventional catalysts. In this light, we narrow our attention to well-defined molecular catalysts, including a study of progress in the understanding of active species, reactive intermediates, and reaction mechanisms that are indispensable for the synthesis of such polymers. 

The organometallic chemist often wishes to start his investigations with some quite sophisticated compound, which ideally should be available in high yield by a simple synthesis from readily available precursors. Detailed procedures for syntheses of this type are available in the series Inorganic Syntheses, Organometallic Syntheses, and to a lesser extent. Organic Syntheses (Fl-3). These books contain tested syntheses of commonly used materials, and the first and last of these titles appear at frequent intervals. 

A group of water-soluble tertiary phosphines that can be used as ligands to synthesize organometallic complexes soluble in aqueous solution are shown in Fig. 2. These individual phosphines can be synthesized by the sulfonation of triphenylphosphine, 1 (Eq. 16) (40) the reaction between... 

Thus far we have synthesized organometallic monomers and modified organic polymers fabricated such modified organic pol3miers into fibers followed by their thermal processing into ceramics. These features are summarized in Scheme I. 

In order to directly synthesize organometallic hyperbranched polymers, all the above described established methods could be utilized to knit metal-containing monomers together, provided they are stable under the applied polymerization conditions and do not interfere with the reaction mechanism. As an alternative, suitable pure organic hyperbranched polymers can be functionalized with organometallic complexes. Both approaches have been utilized by other research groups and will be briefly reviewed at the beginning of Chapters 3 and 4. 

Recently Ferber et al synthesized organometallic complexes bearing a formyl-cyclopentadienyl connected to Ci7 via an ethynyl linkage. The compounds possess a metallocene planar chirality that is not in any way natural [136,137]. The aim was to see whether the estradiol a- and p-receptors were capable of distinguishing between the two chiral species, as either 1,2- or 1,3-disubstituted isomers. Compounds such as the following were studied [138]. 

On standing, the solutions of Eu and Yb decompose with the formation of a precipitate. The europium precipitate consists of the amide Eu(NH2)2, but the ytterbium precipitate is only 20-75% in Yb(NH2)2 (Hadenfeldt et al, 1970X Solution of ytterbium in liquid ammonia has been used to synthesize organometallic compounds. Addition of cyclooctatetraene to ytterbium dissolved in anhydrous ammonia yields cyclooctatetraenyl ytterbium, which is insoluble in ammonia, hydrocarbons and ethers but dissolves in more basic solvents such as pyridine or DMF (Hayes, 1969) ... 

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