Copper support-bound

Other reagents that have been used to reduce support-bound aromatic nitro compounds include phenylhydrazine at high temperatures (Entry 5, Table 10.12), sodium borohydride in the presence of copper(II) acetylacetonate [100], chromium(II) chloride [196], Mn(0)/TMSCl/CrCl2 [197], lithium aluminum hydride (Entry 3, Table... 

Vinylations and arylations of polystyrene-bound 2-bromofurans have been accomplished by treatment with stannanes [98] or boronic acids [99] in the presence of palladium complexes. Alternatively, 2-furylstannanes can be coupled with support-bound aryl iodides or bromides in the presence of palladium or copper complexes (Entries 5-7, Table 15.8). 

The EPR spectrum due to Cu in the native Zn site in the Ag CuSOD derivative indicates that Cu is in a very different environment than when it is in the native copper site (Figure 5.20C). The spectrum is strongly rhombic, with a low value of Ay (97 G), supporting the conclusion based on the visible spectrum that copper is bound in a tetrahedral or five-coordinate environment. This type of site is unusual either for copper coordination complexes or for copper proteins in general, but does resemble the Cu EPR signal seen when either laccase or cytochrome c oxidase is partially reduced (see Figure 5.21). Partial... 

The absolute configuration of products obtained in the highly stereoselective cycloaddition reactions with inverse electron-demand catalyzed by the t-Bu-BOX-Cu(II) complex can also be accounted for by a square-planar geometry at the cop-per(II) center. A square-planar intermediate is supported by the X-ray structure of the hydrolyzed enone bound to the chiral BOX-copper(II) catalyst, shown as 29b in Scheme 4.24. 

Metal ion complexes. These classic CSPs were developed independently by Davankov and Bernauer in the late 1960s. In a typical implementation, copper (II) is complexed with L-proline moieties bound to the surface of a porous polymer support such as a Merrifield resin [28-30]. They only separate well a limited number of racemates such as amino acids, amino alcohols, and hydroxy acids. 

Divalent Co substitution in copper amine oxidase revealed 19% of the native specific activity (for MeNH2) and 75% of the native reactivity toward phenylhydrazine. The major cause of this was a 68-fold increase in Km for 02. These investigations support the idea that electrons flow directly to bound 02 without the need for a prior metal reduction and that the Cu does not redox cycle but simply provides electrostatic stabilization during reduction of 02 to 02-. 1211... 

Transition metal catalysis on solid supports can also be applied to indole formation, as shown by Dai and coworkers [41]. These authors reported a palladium- or copper-catalyzed procedure for the generation of a small indole library (Scheme 7.23), representing the first example of a solid-phase synthesis of 5-arylsulfamoyl-substituted indole derivatives. The most crucial step was the cydization of the key polymer-bound sulfonamide intermediates. Whereas the best results for the copper-mediated cydization were achieved using l-methyl-2-pyrrolidinone (NMP) as solvent, the palladium-catalyzed variant required the use of tetrahydrofuran in order to achieve comparable results. Both procedures afforded the desired indoles in good yields and excellent purities [41]. 

Immobilizing DENs within a sol-gel matrix is another potential method for preparing new supported catalysts. PAMAM and PPI dendrimers can be added to sol-gel preparations of silicas " and zinc arsenates to template mesopores. In one early report, the dendrimer bound Cu + ions were added to sol-gel silica and calcined to yield supported copper oxide nanoparticles. Sol-gel chemistry can also be used to prepare titania supported Pd, Au, and Pd-Au nanoparticle catalysts. Aqueous solutions of Pd and Au DENs were added to titanium isopropoxide to coprecipitate the DENs with Ti02. Activation at 500°C resulted in particles approximately 4 nm in diameter. In this preparation, the PAMAM dendrimers served two roles, templating both nanoparticles and the pores of the titania support. 

The observation of nonlinear effects, both vith chalcone and with cyclohexe-none, further supports this catalyst stoichiometry. The nonlinear effects can be explained by the involvement of diastereomeric complexes L2CUR, with two chiral ligands bound to copper (Fig. 7.2) [45]. 

Asymmetric Diels-Alder reactions have also been achieved in the presence of poly(ethylene glycol)-supported chiral imidazohdin-4-one [113] and copper-loaded silica-grafted bis(oxazolines) [114]. Polymer-bound, camphor-based polysiloxane-fixed metal 1,3-diketonates (chirasil-metals) (37) have proven to catalyze the hetero Diels-Alder reaction of benzaldehyde and Danishefsky s diene. Best catalysts were obtained when oxovanadium(lV) and europium(III) where employed as coordinating metals. Despite excellent chemical yields the resulting pyran-4-ones were reported to be formed with only moderate stereoselectivity (Scheme 4.22). The polymeric catalysts are soluble in hexane and could be precipitated by addition of methanol. Interestingly, the polymeric oxovanadium(III)-catalysts invoke opposite enantioselectivities compared with their monomeric counterparts [115]. 

Rh (172)]. These species merit comparison to the rhenium- and manganese-dicopper species 158 and 159, which have molecular mirror symmetry and a V-shaped trimetal unit that lacks a Cu-Cu bond. Although 171 and 172 appear symmetric in solution on the NMR time scale due to fluxional processes, in the solid state the two copper centers are clearly inequivalent and a Cu-Cu bond is present. The metal triangle is supported by two B-H Cu linkages, one to each Cu center, involving p- and y-B H vertexes in the M -bound CBBBBEi belt. 

The resulting triazoles can be N-alkylated by treatment with alkyl halides (0.25 mol/L, 30 equiv., DMF, NaOH), but mixtures of the 1-alkylated and 2-alkylated triazoles are obtained [255]. 1,2,4-Triazoles have also been prepared from N-amino-amidines (amidohydrazones Entry 4, Table 15.20), which were prepared from resin-bound thioamides by S-alkylation with methyl triflate followed by treatment with hydrazine [256]. 1,2,4-Tri azoles undergo Michael addition to polystyrene-bound a-acetamido acrylates to yield triazole-derived a-amino acids (Entry 7, Table 15.20). Benzotriazoles have been N-arylated on insoluble supports by treatment with aryl-boronic acids in the presence of catalytic amounts of copper salts (Entry 8, Table... 

Functionalized 1,2,3-triazoles 86 and 87 were prepared by [2 + 3] cycloadditions of resin-bound a-azido esters 85 with substituted alkynes <02TL4059>. Regiospecific copper(I)-catalyzed 1,3-dipolar cycloadditions of resin-bound alkynes 88 with azides afforded solid-supported 1,2,3-triazoles 89, which were ligated further to give 1,4-substituted-1,2,3-triazole peptide compounds <02JOC3057>. 

B) The metallic bonds allow for free movement of valence electrons within elemental copper. This allows greater conductivity. Copper chloride, on the other hand, is an ionic solid, where the electrons are all held tightly within the crystalline structure of the compound. Tightly bound electrons can t support the flow of electric current. 

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