Bipy ligands

Ag(4,4 -bipy)N03 has a three-dimensional structure with silver ions diagonally coordinated by two bipy ligands (N-Ag-N 173.7°) in extended infinite chains, the chains being cross-linked by Ag-Ag bonds (2.970 A) [45]. 

A combination of the Lewis acid zinc triflate and the bases NEt, or pyridine acted as an achiral catalyst for this reaction. Instead, using a chiral base which incorporates a bipy ligand to bind zinc gave 26% ee of the product (Scheme 5-42a). Alternatively, diethylzinc was an active precatalyst, but attempts to use chiral amino alcohols as ligands in this system gave low ees (Scheme 5-42b) [31]. 

Bis(bipyridyl)nickel(0) has been prepared by metal-vapor methods and electrochemical data were obtained for it. In these low-valence states, a significant proportion of the electron density lies on the bipy ligand.2469 Also, the crystal and molecular structure of 4,6-dimethyl-2,2 -dipyr-idyldicarbonylnickel(O) (1021) has been determined. The coordination geometry about Ni is tetrahedral.2470... 

Besides tris-chelates such as (58)-(63), Le Bozec and co-workers have also studied several tetrahedral complexes of 4,4 -disubstituted 2,2 -bipy ligands.129-131 1,340 nm EFISHG was applied... 

The 4,4 -bipy and bpe derivatives display a similar crystal structure to that of Cd(4,4 -bipy)2[Ag(CN)2]2 reported by Iwamoto et al. [89]. It consists of the interpenetration of two identical 3D networks. The knots of the networks are defined by the iron(II) and silver(I) atoms. Each iron(II) atom located on an inversion centre defines an elongated octahedron whose axial positions are occupied by the nitrogen atoms of two 4,4 -bipy ligands. In addition, each 4,4 -bipy ligand binds a silver atom so that it is three-coordinated. This is the reason why the [Ag(CN)2] group is bent (see Fig. 18). 

The [4+ 4]-homolog of the [4 + 2]-Alder-ene reaction (Equation (48)) is thermally forbidden. However, in the presence of iron(m) 2,4-pentanedioate (Fe(acac)3) and 2,2 -bipyridine (bipy) ligand, Takacs57 found that triene 77 cyclizes to form cyclopentane 78 (Equation (49)), constituting an unprecedented formal [4 + 4]-ene cycloisomerization. The proposed mechanism for this transformation involves oxidative cyclization followed by /3-hydride elimination and reductive elimination to yield the cyclized product (Scheme 18). 

It did not prove possible to synthesize a substituent-free Ga complex with formula Cp (CO)2Fe Fe(CO)4 Ga (Scheme 13).43 Addition of bipy to 30 resulted in halide elimation, but the main group element in the product 31 was coordinated by the bipy ligand. Upon addition of dppe, however, substitution of the carbonyl ligands occurred instead along with halide ion elimination to produce the substituent-free Ga complex 32. It has a linear coordination environment (Fe-Ga-Fe angle = 176.01(4)°), and the Ga-Fe bond distances are much shorter than in those related adducts where donor ligands are also bound to the Ga atom.43 The authors attributed the non-observation of the carbonyl derivative to a need for an electron-rich metal center to stabilize the Fe-Ga bond via 7r-backdonation. 

It undergoes an oxidation and a first reduction process, both of which involve a one-electron step and are chemically reversible. The more cathodic two-electron reduction is probably centred on the bipy ligand. 

Another type of complex in which Tc C bonds predominate is the seven-coordinate complex [Tc(CNR)gX] + (398) (R = variety of organic groups X = C1, Br). The compounds are easily prepared in good yield by reaction of the Tc complex [Tc(CNR)6] " with Br2 or CI2 in acetonitrile. Attempts to introduce a bipy ligand as well led to dealkylation of the isocyanide to give the seven-coordinate complex [Tc(CNR)5(CN)X]+ (399). Reductive coupling of the coordinated isocyanides was attempted, but the reduction of Tc to Tc was the only reaction." ... 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

Figure 89 The bonding of the bipy ligand in the trigonal pyramidal CuN4I chromophore of [Cu(bipy)2I]I1...

Both the cyanide, [Au(CN)2] , and fulminate, [Au(CNO)2] , ions contain linear gold(I) centres.387,388 A report that KAu(CN)2(2,2 -bipyridyl) contains square planar gold(I) has been disproved the bipy ligand is not coordinated to gold and the complex contains linear [Au(CN)2J ions. 390 AuCN is polymeric with a linear (—Au—CN—) Au— chain structure.391... 

Figure 4 Stabilization of Cu1 by steric effects in substituted bipy ligands, resulting in tetrahedral geometry...

Figure 21 Dinuclear Co 11 species with bipy ligands and with a peroxo and hydroxo bridge this compound shows interesting...

Triply bridged dinuclear Fe(n) complexes of a bis-N-hydroxy-pyridinone [9.82a] and of bis(bipy) ligands [9.61, 9.82b] possess triple-helical features. A triple-helical arrangement has been assigned to dinuclear Fe(lll) complexes of tripodal ligands on the basis of NMR and circular dichroism (CD) data [9.82c]. The self-assembly of well-defined triple-helical dinuclear cobalt(ll) [9.83] and lanthanide(lll) [9.84] complexes has been achieved. 

Using oligo-bipy ligands, the formation of triple helicates becomes possible through a modification of the steric instruction by shifting the 6,6 -disubstitution, as in 128-131, to a 5,5 -disubstitution, which should remove the hindrance towards binding of three bipy units to an octahedral metal centre. Indeed on reaction with... 

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