Complexation with pyridine

X-ray crystallography, 3, 623 Ruscodibenzofuran synthesis, 4, 698, 709 Ruthenacyclobutane, 3-cyano-synthesis, 1, 667 Ruthenium complexes with pyridines, 2, 124 triazenido, 5, 675 Rutin... 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

RATES OF REACTIONS OF ANALOGUES OF Pt(ll) COMPLEXES WITH PYRIDINE... 

Probably the solubility of C02 and CS2 can be explained by the formation of a Lewis complex with pyridine, so that the titration equation must be written as an exchange reaction with OH-. 

Complexes with pyridine-2,6-diimine ligands, five-coordinate [NiX2(174)] (X = C1, Br) or six-coordinate [Ni(174)2]X2, were usually assumed to have innocent neutral ligands. The X-ray structure and spectroscopic characteristics of [Ni(174)2](PF6) confirm that the complex contains the neutral ligand ([174] ) and a divalent nickel ion.579 The cyclic voltamogram of this complex in CH2C12 shows three reversible one-electron-transfer processes at = 1.19 V, —1.30 V, and — 1.82V (vs. Fc+/Fc), of which the first is a one-electron oxidation, while the other two correspond to two successive one-electron reductions. The spectroscopic data allow one to assign these processes as follows ([174]1 is a one-electron reduced radical form of [174] ) [Nini(174)°2]3+ [NiII(174)02]21 - " [NiI(174)°2]+ = " [NiI(174)°(174)1 ]°. 

Table 6. Trans-effect on the rates of reaction of some Pt( II) complexes with Pyridine (12)...

Eley, D. D., and H. Watts Aluminium Halide Complexes with Pyridine, Trimethylamine and Triethylamine, Part I. J. chem. Soc. [London] 1952, 1914. 

This intramolecular interaction of heteroatoms may be distorted by introducing different substituents onto the 4,6-positions of the ring. In the case of acceptor substituents, (CC13) dioxaboraphosphorinane (97) is not alkylated at the phosphorus atom and is inert to sulfur at the same time it forms a stable complex with pyridine [Eq. (96)]. In the case of donor substituents (Aik) (93)—(94), by contrast, the corresponding sulfides have been obtained and the pyridine complex is formed only with four-coordinated phosphorus derivatives. 

Compounds with the E14=C multiple bonds are polar and form complexes with pyridine. According to our estimations, the complex formation energies are 3.9-7.5kcal/mol. The formation of such complexes allows an additional stabilization of products of their Wittig type decomposition. 

Figure 11. Crystal structure of morellic add, 15 in its 1 1 complex with pyridine. Hydrogen bonds a (strong) and b through g (weak) are marked. The pyridine molecule assists in assembling the structure.

These results have been rationalized74 by Heasley and coworkers by assuming that the primary function of the complexes is to limit the concentration of free halogen. In the reaction of free bromine where the reaction is second order in bromine, two or more molecules of halogen participate in the transition state while the halogen complexes with pyridine or amines impose a first-order mechanism by limiting the availability of free halogen (equation 40). 

Boratetrahedrane (121) that has the triplet A2 ground state and the carbene Cs structure (122) possess higher energies than that of structure (119e). Similar to borabenzene, the stabilization of boracyclobutadiene (119e) can be achieved through the formation of a complex with pyridine. 

Co(II)salen complex with pyridine, in toluene, at 15 °C, percentage of oxygen... 

Citrate forms a yellow complex with pyridine (which is carcinogenic) in the presence of acetic anhydride the complex may be quantified spectrophotometrically. Alternatively, citrate can be determined by an enzymatic assay. 

Optically active ds.vic-diofa.1 It is known that pyridine catalyzes the hydroxyl-ation of alkenes with Os04 and that the osmate ester intermediates form an isolable complex with pyridine (1, 760-761). Hentges and Sharpless reasoned that a similar chiral amine could induce chirality in the diol. And indeed addition of 1 equivalent of 1 or of the C8-diastereoisomer, dihydroquinidine acetate (2), does result in vic-diols in fair to high enantiomeric excess, particularly in reactions performed in toluene at —78°. Opposite stereoselectivities are exhibited by 1 and 2. Optical yields range from 25 to 85%. Use of an amine in which the chiral center is two carbon atoms removed from the coordination site lowers the optical yield to 3 18%. 

V(py)4Cl2 has a trans structure with a mean V—N of 2.189 A.74 On heating it at 170 °C under vacuum, red-brown V(py)2Cl2 was detected and finally V(py)Cl2 is formed. The formulae of complexes with pyridine, jS-picoline and y-picoline are listed in Table 4 with magnetic moments and thermal decomposition data. 

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

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

Complexes with Pyridine and Other Heterocyclic Ligands 880... 

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