Ligands 4,4 -dimethyl-2,2,-bipyridine

The use of a,P-unsaturated 2-acylimidazoles [151] as the dienophile increased the practicality of the approach, since the imidazole group can be removed readily from the product. The substrate scope is quite broad substituents at the alkene moiety (e.g., alkyl, aryl and 2-furanyl) were very well tolerated, hi all cases good to excellent enantioselectivies and diastereoselectivities were obtained, i.e., 80-98% ee for the endo isomer and endo. exo > 94 6, in the case of the 4,4 -dimethyl-2,2 -bipyridine ligand [152]. Moreover, the D-A reaction was successfully performed on a preparative scale (1 mmol), making it attractive from a synthetic point of view. 

These redox polymers were modified for reduced redox potential while maintaining activity with GOx. Replacement of the methyl groups (compound 4) with amines (compound 6) resulted in a redox potential decrease of 0.25 V, with only a 15% loss in GOx activity. More recently, further reductions in redox potential were achieved by replacing the bipyridine ligands to osmium by dimethylated bis-imidazole groups (compound 7). ... 

The complexes traTO-[ReO(OH)(N N)2] (N N = bipy or 4,4 -dimethyl-bipy) and trans-[Re02(N N)2]" (N N = 1,10-phenanthroline) are synthesized by reacting Rc207 with PPhs in the presence of the relevant ligands. Decomposition of the complexes occurs in aqueous media by slow oxidation of the coordinated bipyridine ligands to form the corresponding A-oxides." ... 

In a similar vein, self-assembly of the dimethyl derivative of the corresponding tris(bipyridine) ligand in the presence of bipyrimidine and copper(I) spontaneously generates the new ladder structure 49. A similar tetranuclear structure derived from the corresponding bis(bipyridine) ligand has also been reported. 

A mixed-valence complex of Ru(bpy)2 bridged by l,10-bis[4 -methyl(2,2 -bipyridyl)]-3,8-dimethyl-l,3,5,7,9-decapentene, i.e., with five double bonds constituting the spacer between 2,2 -bipyridine ligands, has been described by Lehn and co-workers [32b]. Hush s analysis of the intervalence transition gave = 0.018 eV for a 24 A metal-metal distance. 

Boron-substituted pyridine reagents can be used to construct the bipyridine ring system by coupling them with halopyridines in the presence of a Pd° catalyst and a base (Suzuki method). Various ligands have been made in this manner in moderate to high yields, including 2,3-bipyridine (85%)41 and 3,5-dimethyl bipyridine (60%) 42 One valuable feature of the Suzuki method is that it is compatible with stannanes. A pyridyl diethylborane has been coupled to a tributyl tin-functionalized pyridyl bromide.43 This compatibility is useful for polypyridine syntheses because subsequent Stille coupling of the bipyridyl stannane is possible. 

The vinyl derivative 4-methyl-4 -vinyl-bpy is valuable for chemical electrode modification because its ruthenium and osmium complexes can be polymerized to generate electroactive films with variable properties.86 This unsymmetric ligand was prepared in 35% overall yield from 4,4 -dimethyl bipyridine by first lithiating one methyl group and quenching the anion with (chloromethyl)methyl ether, then reacting with potassium t-butoxide to effect elimination.87,88... 

Reduction of ester functionalities with NaBH4 has furnished the corresponding alcohols. The 4- and 4,4 -substituted hydroxymethyl bipyridines have also been synthesized from halomethyl precursors, (23) and (26), respectively, by reaction with NaOAc followed by acetate hydrolysis.113 The 5,5 -dihydroxymethyl bipyridine ligand has been prepared (55%) by converting 5,5 -dimethyl bipyridine to the bis /V-oxide with hydrogen peroxide, followed by reaction with acetic anhydride in acetic acid,114 then hydrolysis with KCN in ethanol.115... 

In this communication we would like to report the synthesis and characterization of a new heteroleptic rutheni-um(II) complex with one of the bipyridine ligands replaced by a more conjugated ligand such as the 5,6-dimethyl-l,10-phenanthroline. Scheme 1 illustrates the molecular structure of the ruthenium(II) heteroleptic complex. Moreover, we have also carried out a study of the interfacial charge-transfer kinetics of the molecule when anchored onto the surface of nanocrystalline Ti02 semiconductor particles. 

Palladacyclo-2,4-pentadiene compounds containing a 2,2 -bipyridine ligand [Pd C(COOMe) = C(COOMe)-C(COOMe) = C(COOMe) (bipy)] have been prepared from [Pd(dba)2], 2,2 -bipyridine, and dimethyl 2-butynedioate or hexafluorobutyne (980M1812). The product oxidatively adds methyl iodide, benzyl bromide, or iodobenzene. 2,2 -Bipyridine or 1,10-phenanthroline reacts with [Pd(dba)2l and methyl phenylpropynoate to yield palladacyclopentadiene derivatives 52 (06ICA1773). 

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. 

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