Dicopper complex

The stoichiometric selective oxidation of the benzyhc alcohol function in (di)hydroxy-substituted benzylalcohols (Eq. 14) has been demonstrated by Nolte et al., using host-guest chemistry to steer the regiospecificity in the reaction [167-170]. The host-receptor used to construct dicopper complex 21 is based on the building block diphenylglycoluril, which was functionahzed... 

Scheme 11 Intramolecular oxo-transfer to an amine with a dicopper complex [171]...

The first of two conversions catalyzed by the metalloenzyme tyrosinase is the selective ortho-hydroxylation of a phenol moiety, yielding catechol. Few synthetic systems exist that are capable of selectively performing the same monooxygenase reaction [172-178]. The group of Casella has studied a series of dicopper complexes based on 2,6-disubstituted benzene hgands providing two N3 compartments [179-181] (26a,b) as well as the asymmetrically substituted tripodal amine-based ligand (27) [182]. 

Pyrazolate-based dinucleating hgands have proven useful to control crucial characteristics of the dicopper core, such as the Cu - Cu separation and the electronic properties of the metal ions, by variation of the chelate side arms attached to the heterocycle (31). This leads to greatly differing activities in the catalytic oxidation of DTBC mediated by those dicopper complexes [133,135]. While most of the pyrazolate-derived complexes 31 display an enzyme-hke Michaehs-Menten type kinetic behavior, it is apparent that both the Cu - Cu separation as well as the redox potential play an important... 

The dicopper(I) complex with dinucleating bisamino-bispyridine ligand 37 as well as the dicopper complex 38 were shown to couple 2,4-di-ferf-butylphenol to the corresponding bisphenol derivative (Eq. 22), while with 2,6-substituted phenols, oxidative coupling at the para-position was observed to yield the diphenoquinone derivatives (Eq. 23) [256,257]. Similar reactivity is observed for various other dicopper systems. 

Figure 13.3 A bis(/i,-oxo)dicopper complex represented using Eq. (13.6) where each boxed R group is H for the small QM system and benzyl for the large MM system. The structure on the right is a TS structure for H-atom transfer from C to O found by optimization at the hybrid level of theory. All other H atoms have been removed for clarity...

Besides the knot, the major cyclization product (24%) obtained in the latter reaction could be identified as a dicopper complex consisting of two 43-membered rings arranged around the metallic centers in an approximate face-to-face geometry [94]. This unknotted compound originates from a non-helical precursor which is in equilibrium with the expected double helix. Figure 18 describes in a schematic way the alternative cyclization reaction leading to the unknotted face-to-face complex and the equilibrium which interconverts the helical and the non-helical precursors. 

A further extension of m-xylyl dicopper complexation and xylyl hydroxy la-tion is seen in a Schiff-base macrocycle [175], When dicopper(I) complex 38 is reacted with 02, one of the two arene rings is hydroxylated, again producing a phenoxo-bridged dicopper(II) species a peroxo-dicopper(II) intermediate is suggested as the actual oxidant. 

In 1988, the author s group reported the formation of a fx-peroxo dicopper complex by low-temperature treatment of the p-oxo di-... 

An important precursor of such studies is the investigation of model compounds that are fully characterized. For instance, the end-on mode of dioxygen binding in dicopper complexes has been investigated by molecular mechanics 3961. The successful reproduction of the structures of such model compounds provides a sound basis for the modeling of similar sites in metalloenzymes13971. 

Thus, the dicopper complexes with the PD or PD-O" ligand provide very novel chemistry, clearly exhibiting cases of dinuclear metal-promoted hydrolytic processes. The range of possible substrates for this complex has yet to be studied and one wonders if similar chemistry can be observed for zinc or other metal analogues. A variety of mechanistic... 

Unlike in the polypyridyl system, where oxo-dicopper(II) complex formation accompanies N-N bond formation (48), a third NO accepts the oxygen atom in our case [the known (68) complex TpMe2Cu-(/x-0)-CuTpMe2 was not observed for the case R = Me]. We hypothesize that in the initial stages of the disproportionation reaction the adduct TpMe2Cu(I)-(NO)2 forms and either dimerizes to yield a dibridged dicopper complex analogous to intermediates postulated by Paul and Karlin (48) or adds a second NO to afford a mononuclear species with cis... 

Fe(CsH4CR R"OH)2] have been reported <07OL4769>. With a dicarboxylate linker, macrocyclic dicopper complexes were formed generating supramolecular [2+2] self-assembled nanoscopic rectangles <07CC4410>. 

Oxidative decomposition of bis(p-oxo)dicopper complexes of trisubstituted triazonanes 139 resulted in the dealkylation products 141 along with recovered ligand 140 (Equation 5) <1996JA11575>. In the case of tribenzyl-substituted ligand (R = R1 = Bn), equivalent amounts of benzaldehyde were formed and detected as side products of the oxidative process. Ligands with isopropyl moiety (R = R1 = /-Pr or R z -Pr, R = Bn) produced acetone in the similar manner. 

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