Copper salt CuCl

It is now well established that Cu(l)-catalyzed [2 + 2]-photocycloaddition of alkenes requires formation of a complex in which one copper is coordinatively linked with two alkene units. Among the various copper salts (CuCl, CuBr, CuOTf) used, the triflate anion in CuOTf has exceptional weak coordinating ability compared to halide ions, which compete with alkene for coordination with copper. Thus, CuOTf exhibits a strong tendency to form 1 2 Cu-alkene complexes compared to CuCl or CuBr. This is reflected in improved yields of adducts obtained with CuOTf rather than CuCl or CuBr (vide infra). In addition, CuOTf is soluble in most organic solvents and is stable under the photochemical reaction conditions. Hence, CuOTf is the catalyst of choice for [2 + 2]-photocycloaddition between two nonconjugated alkenes. 

Transmetalations of alkenylstannanes with copper salts are reversible if they are performed with CuCl in polar solvents [101]. This has found application in cyclization reactions (Scheme 2.49) [102]. 

Several specific oxidative transformations of nitrogen compounds can be carried out in the presence of copper salts. Oxidation of o-phenylenediamine with molecular oxygen in the presence of a twofold excess of CuCl in pyridine results in the formation of cis,cw-mucononitrile in high yield (equation 286).618 619 The bis- i-oxo tetranuclear complex Cu4Cl402(py)4 was found to be the active species in this transformation.618 A similar procedure can be used for the selective oxidative coupling of diphenylamine to tetraphenylhydrazine by CuCl/py/02 or Cu4Cl402py4 (equation 287).619... 

Dimethyl carbonate is an interesting material which can be used instead of toxic dimethyl sulfate as a multipurpose alkylating reagent.438-578 Its synthesis can be performed in one step from cheap methanol, CO and oxygen materials in the presence of copper salts (e.g. copper(ll) methoxychloride or CuCl/py) at ca. 100 °C and 15-70 atm (equation 290).578,62S This reaction is thought to proceed in two steps 578 (a) formation of copper(II) methoxychloride from the reaction of copper(I) chloride, 02 and methanol (equation 291) and (b) reduction of copper(II) methoxychloride with CO to form dimethyl carbonate and regenerate copper(I) chloride (equation 292).626... 

The most common and useful additives are copper(I) salts (such as CuCl), which produce high yields of 1 1 adducts in many cases.174 Several examples from the extensive work of the Ciba-Geigy group in Basel are compiled in Scheme 54, with an emphasis on subsequent conversions of the highly functionalized products into important heterocycles.175 These procedures are very simple and have been conducted on a multigram scale. Typically, the halogen component and the acceptor are heated without solvent at 110 °C in the presence of 1-10% CuCl. After several hours, the copper salts are removed by filtration and the product is isolated by distillation. It is clear that the copper additive behaves as more than just an initiator, the additions of electrophilic radicals to electron deficient alkenes like those shown in Scheme 54 would not be likely to succeed otherwise. 

Two processes are commonly used for the production of copper phthalocyanine the phthalic anhydride-urea process patented by ICI [33,34] and the I.G. Farben dinitrile process [48], Both can be carried out continuously or batchwise in a solvent or by melting the starting materials together (bake process). The type and amount of catalyst used are crucial for the yield. Especially effective as catalysts are molybdenum(iv) oxide and ammonium molybdate. Copper salts or copper powder is used as the copper source [35-37] use of copper(i) chloride results in a very smooth synthesis. Use of copper(i) chloride as starting material leads to the formation of small amounts of chloro CuPc. In the absence of base, especially in the bake process, up to 0.5 mol of chlorine can be introduced per mole of CuPc with CuCl, and up to 1 mol with CuCl2. 

The oxidation of alcohols using azodicarboxylates has been previously reported (Yoneda, F. Suzuki, K. Nitta, Y. J. Org. Chem 1967,32,727—729). Control experiments were therefore performed to establish the need for copper salts in our oxidation procedure. Thus under our reaction conditions no aldehyde or ketone could be detected in the absence of the CuCl Phen catalyst even if phenanthroline was added as an activating base. Moreover, certain reactive alcohols were oxidized partially by CuCl Phen in the absence of the azo-derivative 19, though only in moderate yields. These control experiments thus clearly establish the key-role of the copper ion in these oxidations. 

Aryl iodides. Aryl iodides can be prepared in fair to good yields from aromatic hydrocarbons by the action of iodine and a copper salt. The observed reactivity order of various copper salts is CuClj > CuFj > CuCl > CufOOCCHjlj. The reaction is considered to involve a two-step sequence ... 

As can be seen in the following examples, both Cu and Cu" salts such as CuCl. CuBr, Cul, CuCN, Cu(acac)2, and Li2CuCl4 (known as Kochi s catalyst [22]), introduced at 0.2 10% to a Grignard or a substrate are most typical for these reactions. The choice of copper salts is dependent on their intrinsic reactivities, as well as on physical properties, such as solubility and ease of handling. For example, Li2CuCl4 is soluble in tetrahydrofuran (THF) and is frequently quite useful to obtain clean cross-coupled products. An added Cu species is considered to be reduced to Cu in situ by the Grignard reagent to participate in the catalytic cycle [see Eq. (36)]. 

Copper salts vary from simple inorganic and organic salts, such as CuCl, CuBr, Cul, and CuBr Mc2S, to more sophisticated ones, which will be discussed in the following text. As described in the previous section, a Cu" species is most likely to be reduced in the reaction medium to a Cu species, which catalyzes the 1,4-addition. This Cu"-Cu issue was revisited recently and, in accord with the foregoing statement, Cu was reconfirmed to be an active catalyst, even though the added copper salt was divalent [160,161],... 

MeTpMs has been synthesized by Dias and Wang as T1 salt.202 The copper complex [CuCl(MeTpMs)] has been employed to polymerize cleanly the aniline dimer, A-(4-aminophenyl)aniline under mild conditions to obtain polyaniline.203 [Ag(CO)(MeTpMs)], [Ag(C2H4)(MeTpMs)] and [Tl(MeTprBu)] have been also described and characterized.204... 

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