Copper-diamine catalysts

Amines such as diethylamine, morpholine, pyridine, and /V, /V, /V, /V -tetramethylethylene-diamine are used to solubilize the metal salt and increase the pH of the reaction system so as to lower the oxidation potential of the phenol reactant. The polymerization does not proceed if one uses an amine that forms an insoluble metal complex. Some copper-amine catalysts are inactivated by hydrolysis via the water formed as a by-product of polymerization. The presence of a desiccant such as anhydrous magnesium sulfate or 4-A molecular sieve in the reaction mixture prevents this inactivation. Polymerization is terminated by sweeping the reaction system with nitrogen and the catalyst is inactivated and removed by using an aqueous chelating agent. 

Block copolymers may also be made by condensation polymerization. Elastomer fibers are produced in a three-step operation. A primary block of a polyether or polyester of a molecular weight of 1000-3000 is prepared, capped with an aromatic diisocyanate, and then expanded with a diamine or dihydroxy compound to a multiblock copolymer of a molecular weight of 20,000. The oxidative coupling of 2,6-disubstituted phenols to PPO is also a condensation polymerization. G. D. Cooper and coworkers report the manufacture of a block copolymer of 2,6-dimethyl-phenol with 2,6-diphenylphenol. In the first step, a homopolymer of diphenylphenol is preformed by copper-amine catalyst oxidation. In the second step, oxidation of dimethylphenol in the presence of the first polymer yields the block copolymer. 

The condensation of a,j8-diketones with 1,2-diamines is a classical route for the synthesis of alkyl- and arylpyrazines. For example, good yields of dihydropyrazines are obtained from reaction of 2,3-dioxo-alkanes andethylenediamine dehydrogenation over a copper chromite catalyst at 300° then gives 3-alkyl-2-methylpyrazines (Scheme 1). Attempts to carry out the dehydrogenation using a variety of milder and more convenient laboratory procedures were not successful.100,110... 

The nitrile can be converted to hexamethylene diamine by reduction in the presence of liquid ammonia at 125 C under 600 to 625 atmospheres pressure together with a copper-cobalt catalyst. 

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Enantioselective Mannich-type addition of enolate equivalents to imines continues to be an attractive strategy for the preparation of chiral p-amino carbonyl compounds. In the area of copper-catalyzed enantioselective Mannich reactions, a number of outstanding examples have appeared in this decade. In particular, work from Kobayashi s laboratories has led this field in recent years. Kobayashi and coworkers have developed a Cu(OTf) 2/diamine catalyst (121) for highly enantioselective addition of enolate equivalents to N-acylimino esters [36]. This methodology... 

Yeakey (55) described an improved method for preparation of polyoxyalkylene-polyamines that involved a reductive animation of polyoxyalkylene-polyols in the presence of a nickel-copper-chromium catalyst. When the poly(alkylene oxides)s in combination with ammonia and hydrogen were contacted with the catalyst at elevated temperatures (200-250°C) under pressure (2000-4000 psi 13.78 to 27.56 MPa), yields of the corresponding diamine, which was predominantly primary in nature, improved over that of other known processes. In addition, the process provided for the amination of higher molecular weight polyols than was possible before. Primary amines were the main reaction product when polyols with terminal, secondary hydroxyl groups were used. For this reason, it was preferred that poly-... 

In summary, for the most active of catalysts, the copper(II) ion, the diamine ligands that were investigated seriously hamper catalysis mainly by decreasing the efficiency of coordination of the dienophile. With exception of the somewhat deviant behaviour of N,N -dimethylethylenediamine, this conclusion also applies to catalysis by Ni" ions. Hence, significant ligand-accelerated catalysis using the diamine ligands appears not to be feasible. 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

It has been found that a number of bidentate ligands greatly expand the scope of copper catalysis. Copper(I) iodide used in conjunction with a chelating diamine is a good catalyst for amidation of aryl bromides. Of several diamines that were examined, rra s-yV,yV -dimethylcyclohexane-l,2-diamine was among the best. These conditions are applicable to aryl bromides and iodides with either ERG or EWG substituents, as well as to relatively hindered halides. The nucleophiles that are reactive under these conditions include acyclic and cyclic amides.149... 

Later, several other copper catalysts bearing dinitogen ligands [bipyridine derivatives (76),232,233 diamines (77),234 bis(azaferrocene) (78),235 bisferrocenyldiamine (79),159 and bis(oxazoyl) binaphthyl (80)236] have been introduced (Scheme 62), but asymmetric induction by them does not exceed that by complex (75). 

Kanemasa et al. (60) showed that chiral diamine-copper complexes are moderately effective catalysts for cyclopropanation. Phenylhydrazine reduction of the complex formed from Cu(OTf)2 and excess diamine afforded the active catalyst. Cyclopropanation of styrene proceeds in moderate diastereoselectivity and good enantioselectivity with these catalysts, Eq. 43. 

The basic study was performed on copper complexes with N,N,N, N1-tetramethylethane-1,2-diamine (TMED), which were known to be very effective oxidative coupling catalysts (7,12). From our first kinetic studies it appeared that binuclear copper complexes are the active species as in some copper-containing enzymes. By applying the very strongly chelating TMED we were able to isolate crystals of the catalyst and to determine its structure by X-ray diffraction (13). Figure 1 shows this structure for the TMED complex of basic copper chloride Cu(0H)Cl prepared from CuCl by oxidation in moist pyridine. 

At low ligand ratios using a mondentate amine, more than one species is probably present in solution and only at higher ligand ratios is most of the copper present in the active catalyst form. Since a bidentate amine like N,N,N, N -tetramethylethylene diamine forms a stable chelate in other systems, this may account for the reason that only a molar amount is necessary in this case. The first step in the reaction then appears to be (25), ... 

Among several chiral cyclic and acyclic diamines, (R,R)-cyclohexane-l,2-diamine-derived salen ligand (which can adopt the gauche conformation) was most effective in providing high enantioselectivity [38]. Further, the introduction of substituents at the 3,4, 5 and 6 positions on the aromatic ring of catalyst 39c was not advantageous, and resulted in low enantioselectivity [32,37,39]. The metal ions from first-row transition metals - particularly copper(II) and cobalt(II) - that could form square-planar complexes, produced catalytically active complexes for the asymmetric alkylation of amino ester enolates [38]. 

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