Copper complexes bipyridine ligands

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

These authors further described the synthesis and resolution (by chiral HPLC) of a new C2-symmetric planar-chiral bipyridine ligand [43] (see structure 35 in Scheme 18). They obtained an X-ray crystal structure of the corresponding copper complex proving a bidentate complexation. This system led to high diastereo- (up to 94%) and enantioselectivity (up to 94%) in the... 

Despite numerous studies involving copper catalysts, only a few isolated copper complexes have been examined, including complexes (155)-(157). Bipyridine,397 phenanthroline,398 and pyridyli-mine cationic complexes399 all exhibit tetrahedral geometries, in which the copper center is bound to two ligands. 

Asymmetric cyclopropanations of alkenes and alkynes with a-diazocarbonyl compounds have been extensively explored in recent years and a number of very effective chiral catalysts have been developed2. Copper complexes modified with such chiral ligands as salicy-laldimines 38202,203, semicorrins 39204 208, bis(oxazolines) 40209-2" and bipyridines 41212 have... 

Similarly, when a mixture of the two tris-bipyridine ligands 129 and 148 is allowed to react simultaneously with copper(l) and nickel(il) ions, only the double helicate 132 and the triple helicate 149 are formed (Figure 49). Thus, parallel operation of two programmed molecular systems leads to the clean self-assembly of two well-defined helical complexes from a mixture of their four components in a process involving the assembly of altogether 11 particles of four different types into two supramolecular species. 

Thus one can expect that the copper complexes with 2,2 -bipyridine, 1,10-phenanthroline, and their derivatives are successfully applied to asymmetric photoreactions, as with chiral ruthenium(II) complexes, if the optically active moiety is introduced to the ligand, as discussed above (see introduction). 

Since the copper complexes, [Cu(NN)2]+ and [Cu(NN)(PR3)2]+ (NN = 1,10-phenanthroline, 2,2 -bipyridine, and their derivatives) were applied to stoichiometric and catalytic photoreduction of cobalt(III) complexes [8a,b,e,9a,d], one can expect to perform the asymmetric photoreduction system with the similar copper(l) complexes if the optically active center is introduced into the copper(I) complex. To construct such an asymmetric photoreaction system, we need chiral copper(I) complex. Copper complex, however, takes a four-coordinate structure. This means that the molecular asymmetry around the metal center cannot exist in the copper complex, unlike in six-coordinate octahedral ruthenium(II) complexes. Thus we need to synthesize some chiral ligand in the copper complexes. 

The ligands 6,6 -bis(2-hydroxyphenyl)-bpy, (44), and 6,6 -bis(2"-thienyl)-bpy, (45), each have two additional groups that may chelate. Ligand (44) has been shown to be tetradentate in some copper complexes, and was prepared from 6,6 -diacetyl bipyridine in 90% yield.237 The mono-substituted phenolic bipyridine is also known.238 The dithienyl substituted bipyridine was synthesized via Negishi coupling of 6,6 -dibromo bipyridine and 2-thienylzinc chloride.235... 

A novel soluble complex, (t/ -ethene)hydrotris(3,5-dimethylpyrazol-l-yl)boratocopper(I) (3) mediates the cyclopropanation of styrene, hex-1 -ene, and cyclooctene with ethyl diazoacetate in 76 96% yield (25 C, 1 mol% of catalyst).Copper complexes with the tridentate 2,6-bis[(5-oxo-2,5-dihydropyrrol-2-ylidene)methyl]pyridine ligand or homologous tetradentate l,T-bipyridine and l,T-biisoquinoline ligands are also suited to cyclopropanation of styrene with ethyl diazoacetate. 

Pasternack and co-workers have reported a series of detailed temperature-jump studies on mixed ligand complexes involved in the copper(ll) + bipyridine + glycine system [142], the copper(ll) + bipyridine + ethylene-diamine, of-alanine, and j3-alanine systems, and the cobalt(ll) + bipyridine + glycine system [143]. 

---