Copper I alkoxides

Tab. 10.8 summarizes the application of rhodium-catalyzed allylic etherification to a variety of racemic secondary allylic carbonates, using the copper(I) alkoxide derived from 2,4-dimethyl-3-pentanol vide intro). Although the allyhc etherification is tolerant of linear alkyl substituents (entries 1-4), branched derivatives proved more challenging in terms of selectivity and turnover, the y-position being the first point at which branching does not appear to interfere with the substitution (entry 5). The allylic etherification also proved feasible for hydroxymethyl, alkene, and aryl substituents, albeit with lower selectivity (entries 6-9). This transformation is remarkably tolerant, given that the classical alkylation of a hindered metal alkoxide with a secondary alkyl halide would undoubtedly lead to elimination. Hence, regioselective rhodium-catalyzed allylic etherification with a secondary copper(l) alkoxide provides an important method for the synthesis of allylic ethers. 

Copper(I) alkoxides (CuOR) and aryloxides (CuOAr) are yellow substances that can be made, for example, by the reactions... 

The best available method for converting nonactivated aryl halides into aryl alkyl ethers employs copper(I). Aryl bromides and iodides react with copper(I) alkoxides in pyridine to give the ethers in high yield, Eq. (30). Although substitution... 

Neils, T. L. L., and Burlitch, J. M., A soluble alkoxyzinc hydride, [HZnOCMesJa. Synthesis and reactions with copper(I) alkoxides, Inorg. Chem., 28, 1607 (1989). 

Copper(I) alkoxides were mandatory to achieve rhodium-catalyzed allylie etherifications with aliphatic alkoxide derivatives (eq 29). A one-pot procedure that involves the treatment of the corresponding alcohol with LHMDS to generate the lithium enolate, followed by the addition of a copper salt, allowed the preparation of the requisite copper alkoxide. 

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

Reactions with alkoxides of alkali metals produce yellow copper(I) alkox-ides. For example, reaction with sodium ethoxide yield copper(I) ethoxide, a yellow compound that can be sublimed from the product mixture ... 

The intensive development of the chemistry of homo- and heterometallic alkoxides of copper started more than 10 years ago in connection with the prospects of their application in the preparation of materials and initially in high temperature superconductors. In the search for the appropriate precursors in sol-gel and MOCVD techniques, attention was focused on the alkoxides of copper (I) and the fluorinated alkoxides of copper (II) — oligomeric derivatives soluble in non-polar solvents and existing not only in condensed but also in the gas phase. The derivatives of copper (II) and aliphatic alcohols, even rather branched or functional ones (such as alkoxyalkoxides) turned out to be polymeric substances uninteresting for further application. 

Copper(I) Carboxylates, Triflate, Alkoxides, and Dialky lamides. Thecarbox-ylates have varied structures. The acetate that is obtained as white air-sensitive crystals by reduction of Cu11 acetate by Cu in pyridine or MeCN has a planar chain structure (17-H-I). By contrast the trifluoroacetate [Cu02CCF3]4-2C,H6, and benzoate [Cu02CPh]4 complexes are tetramers with bridging carboxylates as in (17-H-II). This is only one type of Cut polynuclear structure (see later). There are also bridged pyrazole and pyrazolylborate compounds. 

Several methods have been recommended for the preparation of pure methylcopper, each having advantages over previously reported methods. Costa et al. consider the [Pb(CH3)4 + Cu(N03)2] method superior to the Grignard route, as reproducible analyses are obtained 82). However, Thiele and Kohler recommend the reaction of zinc dialkyls with cop-per(II) chloride in ether at — 78°C for the preparation of pure yellow methylcopper, red-brown ethylcopper, and orange propylcopper, uncontaminated by copper alkoxides (277). The mechanism was considered to be a reduction of copper(II) to copper(I) chloride, followed by the reaction of the latter with the zinc dialkyl. The results from the recent... 

An interesting heterobimetallic alkoxide derivative containing copper(I) and zirconium, Cu2Zr2(O-/-Pr),0, was assigned the Structure XV crystallographi-cally (248), and consists of a Zr2(0-/-Pr)9 face-sharing bioctahedron with two... 

Ito, Kawakami and Sawamura recently described the borylation of al-lylic carbonates by B2pin2, catalyzed by bis(phosphine)copper(I) alkox-ides. It was proposed that bis(phosphine)copper(I) boryl species formed by alkoxide/boryl a-bond metathesis are key intermediates in the catalytic cycle [231]. Making use of related N-heterocyclic carbene stabilized precursors, Sadighi and co-workers have very recently isolated the thermally labile copper boryl complex (IPr)CuBpin (11.1) together with the products of oxygen atom, styrene and aldehyde insertion into the Cu-B bond (11.2-11.5 Scheme 24) [232,233,237]. The structure of 11.1 in the solid state reveals an approximately linear Cu(I) coordination geometry [ZB-Cu-C 168.1(2)°] and a Cu-B distance [2.002(3) A] which is somewhat shorter than the sum of the expected covalent radii [2.05 A] [106]. Yet further evidence for the... 

The hydrolysis of coordinated nitriles has recently attracted some attention. A very facile hydrolysis of nitriles to the corresponding amides at platinum(IV) centers has been described.The complex [Cu(H2NCOCH2CONHNH2)Cl] is formed from the reaction NCCH2CONHNH2 the copper(II) both promotes the hydrolysis and is reduced to copper(I). The hydrolysis of 2-cyanopyridine to 2-pyridinecarboxamide is accelerated several hundred times by the copper(II) complexes of the ligands (21) and (22). In the case of the (22) some picolinic acid was formed, resulting from the intramolecular attack of alkoxide to yield an intermediate iminoester. ... 

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