Copper dendritic catalyst

Metallodendrimer Go-20 was used as a catalyst in the 1,4-addition reaction of diethylzinc to 2-cyclohexenone in a variety of solvents. The results obtained showed that this dendritic catalyst provides activities similar to or even higher than those observed for the unsupported aminoarenethiolato copper(I) complexes, depending on the solvent used. Applying Go-20, this reaction could also be performed using a solvent as apolar as hexane, whereas the unsupported complexes are not soluble in this medium. 

Chow H-F, Ching Mak C. Dendritic Bis(oxazoline)copper(ll) Catalysts. 2.1 Synthesis, Reactivity, and Substrate Selectivity. J Org Chem 1997 62 5116-27. 

Heuze et al. (34) synthesized three generations of bis(tert-butylphosphine)- and bis(cyclohexylphosphine)-functionalized Pd(II) DAB dendritic complexes that serve as copper-free recoverable catalysts for the Sonogashira coupling between aryl halides and alkynes (Scheme 9). 

The influence of Lewis acids on the 4 + 2-cycloaddition of (2ft,2/ft)-A,iV/-fumaro-ylbis[fenchane-8,2-sultam] with cyclopentadiene and cyclohexadiene was investigated by IR studies of the sultam compexes with various Lewis acids.101 The first enantios-elective silicon Lewis acid catalyst (91) catalysed the Diels-Alder cycloaddition of methacrolein and cyclopentadiene with 94% ee.102 [A1C13 + 2THF] is a new and efficient catalytic system for the Diels-Alder cycloaddition of a,/9-unsaturated carbonyl compounds with dienes under solvent-free conditions.103 Dendritic copper(II) triflate catalysts with a 2,2 -bipyridine core (92) increased the chemical yields of Diels-Alder adducts.104... 

In the case of the sintered mixture of dendritic copper and Cu/ZnO catalyst powder [35] forming the reactor walls, the final reactor design included vaporization, CAR of methanol and selective CO oxidation for CO reduction in the presence of hydrogen (Figure 25.6). For the vaporization and selective CO oxidation, the sintered metal was additionally coated with platinum. The outlet flow of the reactor consisted of 40% hydrogen, 20% CO2, 0.1% CO and residues of 1.2% methanol (dry basis, balance N2) at a steam to carbon ratio of 1. 

Figure 25.6 Cross-section, top and bottom views of a sintered mixture of dendritic copper and Cu/ZnO catalyst (35).

Given the utility of chiral Cu(II)/bisoxazoline complexes in enantioselective Mukaiyama aldol reactions, a number of reports detailing the development of polymer-bound or dendritic bisoxazoline copper (I I) complexes have been developed. Development of such catalyst systems provides the potential for easy recovery and reuse of the relatively expensive catalyst. To this end, Salvadori and CO workers reported Mukaiyama aldol addition of ketene thioacetal (57) to methyl pyruvate catalyzed by a Cu(OTf)2 complex of polystyrene-supported bisoxazoline (89) (Scheme 17.18) [23]. The enantioselectivity of the addition remained high over eight cycles of the catalyst, however, reactivity was gradually reduced over time. 

K. Heuze, D. Mery, D. Gaus, D. Astruc - Chem. Commun., 2274,2003 Copper-free Monomeric and Dendritic Pd Catalysts for the Sonogashira Reaction Substituent Effects, Synthetic Applications, and the Recovery and Re-use of the Catalysts, Chem. Eur. J. 10,3936, 2004 ... 

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