Pyridine and Substituted Pyridines

Complexes of pyridine and substituted pyridines, mainly in the +2 state, have been made [134] ... 

Our attempts at using the pyridine and substituted-pyridine based bromonium ions to induce chirality were not encouraging. As exemplified by the process shown in Figure 4, the enantiomeric excesses (e.e.) in the bromocyclized products formed on reaction of the to(2-(-)-menthylpyridine) bromonium ion 6 with both 4-penten-l-ol and 4-pentenoic acid were only 2.4% and 4.8% respectively (27). The exact reasons for the poor e.e. s observed could be... 

Pyridine and substituted pyridine species such as trans- u 0) y) f, Ru(0)2(py)2X2 and Ru3(0)g(py) are covered here. The pyridine species are unusual in that some are aerobic catalysts (albeit inefficient ones) for the oxidation of alcohols. The oxoruthenate(Vl) complexes so far considered are two electron oxidants, the metal being reduced to Ru(IV) the (py) complexes however, and probably those of (bpy) and (phen), are effectively four electron oxidants, being reduced to Ru(II). This probably arises from the strong 71-acceptor properties of these N-donor ligands, which will prefer a d" metal configuration to maximise metal-to-ligand back bonding. 

Primary Aliphatic Amines and Diamines Hexylamine Monomethylamine Primary Aliphatic Amines Pyridine and Substituted Pyridines Paraquat... 

Pyridine and Substituted Pyridines Pyrrole and Fused-Ring Derivatives of Pyrrole Captan... 

To measure the equilibrium in low-dielectric medium requires quite a strong base. Unless this condition is met, measurable fractions of the octahedral form are not seen. Thus, for example, CoCl2 in quinoline shows only the spectrum of the tetrahedral configuration, although pyridine solvent shows both octahedral and tetrahedral CoCl2 spectra (6). Primarily for this reason, the bases most used have been pyridine and substituted pyridines. The equilibrium has been studied in pyridine as a function of temperature for CoCl2 (8, 39). In pure pyridine the octahedral form predominates at room temperature, and only at temperatures approximating 60°C are the two forms equally abundant (8). 

Cationic indium(III) complexes could not be prepared with pyridine, but species such as [In(bipy)3]3+ and [In(phen)3]3+ are known as the perchlorate62 or nitrate64 salts, and [In(terpy)2](C104)3 has also been reported.67 Stability constants have been measured in the In3+/bipy and In3+/phen systems71,72 and for some substituted pyridines.9 The adducts of indium(III) halides and pseudohalides with pyridine and substituted pyridines have been... 

A considerable number of nickel(II) complexes with pyridine and substituted pyridines have been reported so far. Selected examples are reported in Table 44. 

The most common stoichiometries found in nickel(H) pyridine and substituted pyridine complexes are NiX2L4 and NiX2L2 where X is a mononegative ion and L is pyridine or a substituted pyridine. Complexes of formula NipysX2 have been found to correspond to either [NiX2py4]-2py (X = NCS, NCO)818 or [Ni(N03)2py3]-3py.819... 

Table 44 Selected Complexes with Pyridine and Substituted Pyridines... 

The complexes HgNi(NCS)4, HgNi(NCSe)4 and HgNi(NCS)2(NCSe)2 are supposed to contain six-coordinate nickel(II) in a polynuclear structure.1082 1089 All of the complexes with the general formula HgNi(NCX)4 behave as Lewis acids towards a number of bases such as alcohols, pyridine and substituted pyridines, PPh3, bipy, phen, DMSO, etc., giving in most cases polynuclear species.1084,1089... 

Ni(acac)2 reacts with a variety of monodentate donors giving mono and bis adducts Ni(acac)2B (n = 1,2 B = H20, primary and secondary amines, pyridine and substituted pyridines, pyridine iV-oxide, alcohols, dioxane, substituted benzaldehydes).1558,1563-1570 Details of the structures of some complexes are reported in Table 78. The chelate ring of the coordinated /3-diketones is nearly planar, and, in thl mononuclear complexes, the Ni—O bond distances (as well as the C—O and C—C bond distances within the chelate ring) are substantially similar. Two different dinuclear structures have been found in the two complexes Ni2(acac)4B [B = py (197),1540,1571,1530 Ph3AsO (198)1542,1572]. 

Even if the C104 ion is commonly believed to experience a scarce tendency to act as a ligand, nonetheless coordination of perchlorate as a monodentate ligand through an oxygen atom has been proposed in a number of nickel complexes containing alkylamines,1676 pyridine and substituted pyridines,1677-1680 arylamines such as aniline and substituted anilines,1681 phosphine and arsine oxides1682,1683 (Table 84). 

Solution studies on the adducts formed by various heterocyclic bases with some nickel porphyrins have been reported.2899-2902 From these studies one can conclude that pyridine and substituted pyridines form predominantly 1 1 adducts while piperidine, imidazole and substituted imidazoles also form 1 2 complexes or a mixture of both 1 1 and 1 2 complexes. Electrochemical redox reactions of nickel porphyrins have been investigated.2903,2904... 

The addition and dissociation of pyridine and substituted pyridine molecules to a planar nickel(II) complex with a quadridentate N202 ligand have been studied by the microwave temperature-jump technique in chlorobenzene solvent (38). The data were interpreted with the assumption of mechanism C (Fig. 7), i.e., that k65 is the smallest rate constant. Subsequently, however, 14N NMR was used to measure the rate of pyridine exchange from the octahedral complex (138). The rates are the same for the two different experiments within a factor of two. This observation excludes mechanism B and is consistent with either mechanism A or C. The rate constants have consequently been presented in Table VI as k64. 

Table 3 Nitration of pyridine and substituted pyridine with N2O5/SO2...

Table 4 Nitration of pyridine and substituted pyridines with nitric acid/TFAA and sodium metabisulfite...

Pyridines and substituted pyridines (9.1), and their protonated derivatives (9.2). 

Acetaldehyde once was widely used as raw material for a variety of large-volume chemical products such as acetic acid and butanol. U.S. usage peaked in 1969 at 1.65 billion lb. Today, most of the former uses have been superseded by routes based on C, or other chemistry such as methanol carbonylation to acetic acid and butanol from propylene by oxo chemistry. Of the remaining uses, which totaled about 400 million lb in the United States in 2000, pyridine and substituted pyridines are the major consumers at 40 percent. It is also used as a raw material for peracetic acid, pentaery-thritol, and 1,3-butylene glycol. 

Numerous Rh111 complexes containing coordinated pyridine and substituted pyridines are known, but this area is dominated by the chemistry of the /raHS-[Rhpy4Cl2]+ cation. First characterized by Jorgensen,780 its chemistry has been studied extensively by Gillard, Wilkinson and co-workers, and it has served as the parent for a host of derivatives. 

The hydrogen cyanide complex,28 [HC=NXeF] [AsF6], is made by interaction of XeF+ or Xe2F cations with HCN in anhydrous HF. The cation is linear with a weak Xe—N bond and solutions in HF are extensively solvolyzed to give XeF2 and HC=NH+. [C6FsXe][AsF6] has been shown to form compounds with pyridine and substituted pyridines.29... 

The solubility of AgCl is therefore sufficient to give [Ag(NH3)2]Cl on treatment with aqueous ammonium carbonate, while AgBr dissolves only in aqueous ammonia, in which Agl is poorly soluble. Aqueous pyridine and substituted pyridines form [Ag(py)]+ and [Ag(py)2]+ ions, but in non-aqueous conditions tetrahedral complexes, such as [Ag(py)4]C104, may be obtained. The tetrahedral acetonitrile adduct [Ag(NCMe)4]+ is also known and is quite stable. There are a number of argen-tate(I) complexes, such as [Ag(NCO)2] and [Ag(ON02)2]- they are linear, with 2-coordinate Ag+.4 Linear coordination is also found in the tetrameric silver amide [Ag N(SiMe3)2 ]4.5... 

The reactions of DPAt and radical cations of other aromatic hydrocarbons with pyridine and substituted pyridines are among the most intensively studied electrode reactions of positive ions. The first definitive study of the mechanism of the reaction employed the rotating disk electrode (Manning et al 1969). Data were found to fit ECE working curves (Fig. 21) for the reactions of DPA7 with 4-cyanopyridine, 4-acetoxypyridine, pyridine and 4-methylpyridine. Pseudo first order rate constants of about 3, 10, 30, 300... 

Dippel s oil. (bone oil). Dark-brown oil obtained from distillation of bones. Contains pyridine and substituted pyridines. 

Pyridine and substituted pyridine derivatives were shown to react with spiro-activated electrophilic cyclopropanes to give ring-opened zwitterions. 11 ss -157 jjjgjg reactions were mainly studied for theoretical reasons. 

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