Metathesis methods

Before discussing the preparation of late transition metal complexes resulting from the activation of O-H bonds by late transition metal complexes, we wbl describe metathesis methods for the preparation of hydrido(hydroxo), hydrido(alkoxo), and hydrido(carboxylato) complexes. Though many methods of preparation of transition metal hydroxides, alkoxides, etc. by a metathesis reaction have been reported [1], only a limited number of examples of the preparation of hydrido(hydroxo), hydri-do(alkoxo) complexes etc. by metathesis are available. 

Wipf et al. <2005OL4483> elaborated a new metathesis method including ring opening in order to generate dynamic combinatorial libraries. The transformation is shown in Scheme 12. The essence of this method is the recognition that an equilibrium takes place with 93 and an aldehyde in aqueous conditions at pH 4 in a phosphate buffer. With the help of this transformation, a series of new R2-substituted products 94 - not available via direct ring closure - have been synthesized. 

Yves Chauvin France development of the metathesis method in organic synthesis... 

The Pd-catalyzed C-C coupling (Sonogashira coupling) was applied to polymer synthesis about 20 years ago [23-25], and has especially been developed for the synthesis of n-conjugated poly(aryleneethynylene)s (PAEs) (for reviews, see refs. [16,26-33]). Recently other synthetic routes for PAEs were also developed, e.g., the alkyne metathesis method [28, 34] and the coupling reaction of =C-MR3 with R X (M=Si [35, 36] or Sn [37, 38]). In this review, we are concerned with the synthesis and chemical properties of PAEs with heteroaromatic rings. 

The preparation of doubly unsaturated macrocyclic ketones is provided (3). The synthesis of functionalized macrocycles by ring closing metathesis methods are described (4). 

The amidinato-imido titanium complexes shown in Scheme 246 have been obtained by salt metathesis methods.90,656 Complexes containing a Gp and the N-alkylated benzamidinato ligands have been synthesized by treatment... 

Chauvin, Yves. (1930- ). Bom in France, Chauvin won the Nobel Prize for chemistry in 2005 for his pioneering work concerning the development of the metathesis method in organic synthesis. Chauvin received his degree from the Lyons School of Chemistry, Physics and Electronics in 1954. He is honorary research director at the Institut Francis du Petrole and a member of the French Academy of Science. 

Tetraphenylbismuthonium nitrate, perchlorate, tetraphenylborate, cyanate, thiocyanate, perchlorate, tetrafluoroborate, hexafluorophosphate and trichloro-acetate have been prepared by this metathesis method [52LA(578)136, 73JCS(D)1394]. Unsymmetrical tetraarylbismuth(V) compounds can be prepared similarly [68LA(720)198]. 

In Section 24.12, we introduced alkene (olefin) metathesis, i.e. metal-catalysed reactions in which C=C bonds are redistributed. The importance of alkene and alkyne metathesis was recognized by the award of the 2005 Nobel Prize in Chemistry to Yves Chauvin, Robert H. Grubbs and Richard R. Schrock for the development of the metathesis method in organic synthesis . Examples of alkene metathesis are shown in Figure 27.3. The Chauvin mechanism for metal-catalysed alkene metathesis involves a metal alkyli-dene species and a series of [2 + 2]-cycloadditions and cycloreversions (Figure 27.4). Scheme 27.6 shows the mechanism for alkyne metathesis which involves a high oxidation state metal alkylidyne complex, L M=CR. 

M. C. lovu, E. E. Sheinsi, R. R. Gil, R. D. McCullough, Experimental Evidence for the Quasi- living Nature of the Grigucud Metathesis Method for the Synthesis of Regioregular Poly(3-Alkylthiophenes). Macromolecules 2005, 38, 8649-8656. 

SCHEME 9.3 The Grignard metathesis method for the synthesis of regjoregular HT-PATs. 

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