Metal-alkyne complexes copper

The copper-alkoxo unit, which is usually synthesized in situ, plays a significant role in metal-promoted transformations of organic substrates by copper(I). To determine the reaction form of the Cu-OPh unit, Floriani and co-workers structurally characterized four complexes (772) (pseudotetrahedral Cu-Cu 3.223 AT (773) (pseudotetrahedral), (774) ( anion linear coordination) and (775) (planar trigonal).57 Using 3,3,6,6-tetramethyl-l-thia-4-cycloheptyne as terminal ligand the structural characterization of a copper(I)-alkyne complex (776) (Cu-Cu 2.940 A) was reported.573... 

A number of stable heterobimetallic copper alkyne complexes have been reported, based on the strategy of using another metal bis(alkynyl) complex as a chelating ligand for copper. The 1,4-diyne [(r -CsFGSiMe Ti-(C=GSiMe3)2]180 (or related complex) was found to stabilize the copper units GuX, with X = alkyl,180,181 vinyl,180... 

All the reagents listed can be used to cleave trimethylsilyl groups from acetylenes fluoride, potassium carbonate under basic conditions in methanol, or silver nitrate/potassium cyanide.9 With the third method advantage can be taken of the fact that the later transition metals (e.g., copper or silvei) complex readily with acety-lides. Workup with concentrated potassium cyanide solution causes compound 32 to be cleaved tu alkyne 33. In this way silylated a -kynes can be deprotected in the presence of 0-silyl groups. 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

One exception to this exclusion of late transition metals may be copper. CuH—MgXa complexes, prepared in situ from MgH2/CuX or from NaH/CuX/MgX2, react with terminal alkynes to give alke-nylcopper species. So far, these have only been used as sources for dialkenyl-coupling products, as in equation (54), but there is no obvious reason why other copper-based procedures should not be accessible, as was found for alkenylcopper obtained by transmetallation from Zr (Section 3.9.3.4.2). Al-kylcopper cannot be made by hydrometallation (nor by transmetallation), as CuH does not add to alkenes, except for special ones such as enones. ... 

CO-dependent mechanism seems appealing. The influence of the alkyne substituents on the CO release of dicobalt hexacarbonyl alkyne complexes is significant, leading either to compounds that are stable or to compounds with rapid CO release rates (fi/2=l.lmin) [125]. Indeed, decomposition of the Co2(CO)6 moiety of 31 has been observed after treatment with thiols [124]. On the other hand, UV/vis and HPLC analysis of 31 incubated in EMEM cell culture medium containing fetal calf serum did not clearly show any decomposition of 31 within 24 h [124]. Notably, other metal-based ASS derivatives without CO ligands, namely copper and silver derivatives, were also shown to have antiproliferative properties [126]. Based on these findings, CO release could potentially play a role in the activity of Co-ASS 31 although there is no clear evidence to date. 

Sonagashira coupling This coupling involves the use of terminal alkynes, Cu(l), and a base. Here, the base assists metallation of the Cu(l) with the terminal alkyne. The copper complex then transmetallates the alkyne to Pd as shown in Figure 12.16. Reductive elimination gives an alkyne. 

Although many transition metal complexes containing T) -bonded substituted acetylides are known, few are available in more than moderate yields via conventional reactions of metal halides with an anionic aUcynyl compound of an alkali metal, magnesium, or copper(I) or hy dehydrohalogenation in a reaction between the metal halide and a 1-alkyne. More recently, reactions between many 1-alkynes and RuCl(l Ph3)2(Tj -CsHs) have been shown to give cationic vinylidene complexes, which are readily deprotonated to give the corresponding substituted Tj -acetylides. The synthesis of the phenylethynyl derivative is typical the intermediate phenylvinylidene complex is not isolated. 

A unique method to generate the pyridine ring employed a transition metal-mediated 6-endo-dig cyclization of A-propargylamine derivative 120. The reaction proceeds in 5-12 h with yields of 22-74%. Gold (HI) salts are required to catalyze the reaction, but copper salts are sufficient with reactive ketones. A proposed reaction mechanism involves activation of the alkyne by transition metal complexation. This lowers the activation energy for the enamine addition to the alkyne that generates 121. The transition metal also behaves as a Lewis acid and facilitates formation of 120 from 118 and 119. Subsequent aromatization of 121 affords pyridine 122. 

The NHCs have been used as ligands of different metal catalysts (i.e. copper, nickel, gold, cobalt, palladium, rhodium) in a wide range of cycloaddition reactions such as [4-1-2] (see Section 5.6), [3h-2], [2h-2h-2] and others. These NHC-metal catalysts have allowed reactions to occur at lower temperature and pressure. Furthermore, some NHC-TM catalysts even promote previously unknown reactions. One of the most popular reactions to generate 1,2,3-triazoles is the 1,3-dipolar Huisgen cycloaddition (reaction between azides and alkynes) [8]. Lately, this [3h-2] cycloaddition reaction has been aided by different [Cu(NHC)JX complexes [9]. The reactions between electron-rich, electron-poor and/or hindered alkynes 16 and azides 17 in the presence of low NHC-copper 18-20 loadings (in some cases even ppm amounts were used) afforded the 1,2,3-triazoles 21 regioselectively (Scheme 5.5 Table 5.2). 

Metal acetylacetonates quench triplet species generated by flash photolysis of aromatic ketones and hydrocarbons.330-333 More recently, these reactions have been studied from a synthetic standpoint. Triplet state benzophenone sensitizes photoreduction of Cu(MeCOCHCOMe)2 by alcohols to give black, presumably polymeric, [Cu(MeCOCHCOMe)] . This reacts with Lewis bases to provide complexes of the type CuL2(MeCOCHCOMe) (L = bipyridyl/2, ethylenediamine/2, carbon monoxide, Ph3P). Disubstituted alkynes yield Cu(C2 R2 XMeCOCHCOMe) but terminal alkynes form CuQR acetylides.334 The bipyridyl complex of copper(I) acetylacetonate catalyzes the reduction of oxygen to water and the oxidation of primary and secondary alcohols to aldehydes and ketones.335... 

Terminal alkynes are readily deprotonated by Grignard reagents, and no further addition occurs to al-kynylmagnesium halides. In the presence of transition metal complexes of titanium,70 iron,70 rhodium,71 nickel,70 72 palladium70 or copper,73 the carbomagnesiation takes place in moderate yields. The regio- and stereo-selectivity of the additions are variable. In the presence of a copper(I) salt, however, only the syn... 

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