2,2 -Bipyridinium complexes

S. Sortino, S. Petralia, S. Conoci, and S. Di Bella, Novel self-assembled Monolayers of dipolar ruthe-nium(III/II) pentaammine(4,4/-bipyridinium) complexes on ultrathin platinum films as redox molecular switches, J. Am. Chem. Soc. 125, 1122—1123 (2003). 

Wilber, I., Eichen, Y, Doron, A., and Marx, S. Effects of electrostatic and 7t-jt-intcractions on the stabilities of xantene dye-4,4 -bipyridinium complexes - Structural design of a geared supramolecular machine. Isr. J. Chem. 1992, 32, 53-59. 

The redox-switching of the linear optical absorption of self-assembled mono-layers and Langmuir-Schafer films of [Ru(NH3)5(4,4 -bipyridinium)] complexes [52-54] and a redox-switching of the NLO response of Langmuir-Blodgett thin films based on 5 were recently reported. Oxidation to Ru causes ca. 50% decrease of the intensity of the SHG, which is almost completely restored by reduction to Ru [55]. 

Bipyridiniums. The bipyridinium herbicides (Table 2), paraquat and diquat, ate nonselective contact herbicides and crop desiccants. Diquat is also used as a general aquatic herbicide (2,296). Bipyridinium herbicides are organic cations and are retained ia the soil complex via cation exchange. They are strongly sorbed to most soils and are not readily desorbed (332). Both paraquat and diquat are not readily leached (293). 

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

More recently, Kim et al. synthesized dendritic [n] pseudorotaxane based on the stable charge-transfer complex formation inside cucurbit[8]uril (CB[8j) (Fig. 17) [59]. Reaction of triply branched molecule 47 containing an electron deficient bipyridinium unit on each branch, and three equiv of CB[8] forms branched [4] pseudorotaxane 48 which has been characterized by NMR and ESI mass spectrometry. Addition of three equivalents of electron-rich dihydrox-ynaphthalene 49 produces branched [4]rotaxane 50, which is stabilized by charge-transfer interactions between the bipyridinium unit and dihydroxy-naphthalene inside CB[8]. No dethreading of CB[8] is observed in solution. Reaction of [4] pseudorotaxane 48 with three equiv of triply branched molecule 51 having an electron donor unit on one arm and CB[6] threaded on a diaminobutane unit on each of two remaining arms produced dendritic [ 10] pseudorotaxane 52 which may be considered to be a second generation dendritic pseudorotaxane. 

By introducing redox-active N-methyl-4,4/-bipyridinium ion (mbpy+) to the oxo-centered triruthenium cores, a series of triruthenium derivatives bearing two or three axially coordinated mbpy+ were prepared by Abe et al. [12, 13]. Electrochemical studies indicated that these mbpy+-containing triruthenium complexes afforded a total of seven to nine reversible or quasi-reversible redox waves in acetonitrile solutions at ambient temperature. Of these redox waves, four or five one-electron redox processes arise from RU3 -based oxidations or reductions involving five or six formal oxidation states, including... 

The molecule [ReI(MQ+)(CO)3(dmb)]2+ has been a model system for studying intramolecular electron transfer over the last two decades. Here, MQ+ is the monodentate ligand Af-methyl-4,4/-bipyridinium, dmb is the bidentate ligand 4,4r-dimethyl-2,2r-bipyridine, and the three CO ligands are facially coordinated. Irradiation of this complex at room temperature in solution with near-UV light leads to a sequence of intramolecular electron-transfer events as shown in Fig. 7. 

In a very special system, the photoelectrochemical regeneration of NAD(P)+ has been performed and applied to the oxidation of the model system cyclohexanol using the enzymes HLADH and TBADH. In this case, tris(2,2 -bipyridyl)ruthenium(II) is photochemically excited by visible light [43]. The excited Ru(II) complex acts as electron donor for AT,AT -dimethyl-4,4 -bipyridinium sulfate (MV2+) forming tris(2,2 -bipyridyl)ruthenium(III) and the MV-cation radical. The Ru(III) complex oxidizes NAD(P)H effectively thus... 

Bipyridinium crown receptors designed to exhibit conformationally induced electrochemical perturbations on cation complexation... 

Upon addition of Ba2+ cations, the 2+/l+ bipyridinium redox couple is shifted anodically by 45 mV and the l+/0 couple is shifted cathodically by 10 mV. K+ and NH4 produce similar effects (Table 15). However, addition of Na+ cations causes a small cathodic shift to the 2+/l+ couple and an anodic perturbation to the l+/0 couple. This is in agreement with the proposed conformational change pathway for coupling the complexation and redox reactions. 

The article by Kim et al. (2002) give an opportunity to compare the cations depicted in Scheme 2.45 and iV,iV -dimethyl-4,4 -bipyridinium as guests to cucurbituril. The inclusion complex of N,N -... 

The high affinity of ammonium cations for tetra-bridged phosphorus(IV) P=0 cavitands was used to complex bis-ammonium guests. The highly insoluble NjAT-dimethyl-bipyridinium dication [paraquat " ] was readily dissolved in chloroform solution in presence of 12b in a 2 1 host-guest ratio. 

The X-ray crystal structures (Figure 7) of 6-[Diquat] and 9-[Paraquat] demonstrate that complex formation is aided not only by [C—H O] hydrogen bonding and [N O] electrostatic interactions but also by charge transfer stabilization between the ir electron rich aromatic rings in the molecular receptors and the ir electron deficient bipyridinium rings in the substrates. 

Although the high resolution X-ray crystal analysis of 4,4 -bipyridine has not been reported, the crystal structure of 4,4 -bipyridinium chlorocuprate (22) has been discussed. Whereas the dimensions of the 4,4 -bipyridinium dication may have been distorted because of the influence of the bulky metal cation, it is interesting to note that the 4,4 -bipyridinium dication is planar with both pyridine rings lying in the same plane. In metal complexes of the parent 4,4 -bipyridine, however, the pyridine rings may be coplanar or rotated up to 40° with respect to one other. 

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