Organometallic bases

Under the action of strong organometallic bases, thiazole undergoes hydrogen-metal interconversion. Ethylmagnesium bromide reacts at 0°C with thiazole in ether to form an insoluble adduct that upon heating evolves ethane almost quantitatively and affords an etheral solution of thiazol-2-ylmagnesium bromide (155) (12). Proof of the structure of this... 

Similarly, highly enantioselective transformations were reported by using other chiral functionalised non-symmetric (138) or C2 symmetric NHC pro-ligands (139-140) (Fig. 2.24) in the presence of organometallic bases and copper salts [111, 112]. 

Equation 44).57 The amide hydrogen is acidic in these compounds and can be deprotonated with standard organometallic bases such as raBuLi to give the imido complex 28 (Equation 44). 

The balance between biocatalytic and other, organometallic-based, methodology is heavily biased in favour of the latter section when considering reduction reactions of importance in synthetic organic chemistry. Two areas will be described to illustrate the point, namely the reduction of carbonyl groups and the reduction of alkenes, not least since these points of focus complement experimental work featured later in the book. 

In (/) there is an abstraction of a proton by a strong organometallic base like BuLi because they are readily available. It is an extremely important reaction because it is used to generate other anions. 

Albrecht M, van Koten G. Platinum group organometallics based on pincer complexes sensors, switches, and catalysts. Angew Chem Int Ed 2001 40 3750-3781. 

An organometallic-based strategy for the cleavage of isoxazoles catalyzed by Co2(CO)s has been reported by de Wang and Alper335. 

For a discussion on the importance of tolerance to functional groups in organometallic-based synthesis, see Trnka, T. M. Grubbs, R. H. The Development of L2X2Ru=CHR Olefin Metathesis Catalysts an Organometallic Success Story. Acc. Chem. Res. 2001, 34, 18-29. 

The ylide is prepared by deprotonating a triphenylalkylphosphonium salt with a strong base, commonly an organometallic base such as butyllithium or phenyllithium. The hydrogens on the carbon that is bonded to the phosphorus of the salt are somewhat acidic because the carbanion of the conjugate base (the ylide) is stabilized by the inductive effect of the positive phosphorus atom. In addition, a resonance structure with five bonds to phosphorus makes a minor contribution to the structure and provides some additional stabilization. The triphenylalkylphosphonium salt can be prepared by an SN2 reaction of triphenylphosphine with the appropriate alkyl halide (see Section 10.9). 

Vogler A, Kunkely H. Excited state properties of organometallics based on interligand interactions between aromatic ligands. Coord Chem Rev 2005 249 1511-16. 

The incorporated -OH groups were transformed to alkoxides using an organometallic base (cumylpotassium) and a suitable cryptand to avoid the precipitation of the polyfunctional initiator. Addition of ethylene oxide produces the dumbbell polymers, as the following reactions indicate (Scheme 99). 

Thus, the first organic-based magnet was in fact an organometallic-based magnet formed by decamethylferro-cenium [Fe Cp 2] and the tetracyanoethylene anion, [TCNE] , reported in 1985. Such a discovery played a key... 

Carbon tetrachloride hydrodechlorination with organometallics based platinum and palladium catalysts on MgO EXAFS characterization and catalytic studies... 

It is interesting that systematic investigations on reactions of aliphatic diazo compounds with simple aldehydes and ketones were conducted relatively late, namely in the early 1970 s. Schollkopf and Frasnelli (1970) demonstrated that, using metallated diazocarbonyl compounds, aldehydes form aldols in excellent yields (>90 o), as shown in (9-8) for the example of benzaldehyde. Later, Schollkopf et al. (1974) showed that the metallation step is not necessary when organometallic bases, such as butyllithium are present in the aprotic, nonpolar system (e. g., in ether-THF-hexane). The method can be generalized for many aldehydes and ketones, even with KOH as base (Schollkopf and Scholz, 1976). 

Used for the isolation of amines, amino acids, complex cations and organometallic bases it forms sparingly soluble salts with all of the above these salts usually crystallize well. Also used as reagent in quantitative determination of Cu and Hg (procedure of C. Mahr) and of quaternary onium cations (procedure of F. Hein). 

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