4-Aminopyridines complexes

The reaction of [Rh2Cl2(CgHi4)4] with 2-aminopyridine led to a species believed to be a cationic solvated rhodium(I)-aminopyridine complex. This was more active than [RhCl(PPh3)3] or [RuH(Cl)(PPh3)3] for the hydrogenation of cyclohexene. The mechanism was thought to involve oxidative addition of hydrogen to rhodium(I) prior to alkene coordination.143... 

Finally, the synthesis of hexaruthenium derivatives of Hampy has been achieved. The triruthenium aminopyridine complexes have been the subject of a recent review. This chemistry has been extended to other nitrogen ligands triruthenium and triosmium complexes of deprotonated di(2-pyridyl)amine have been obtained.In addition, a number of triruthenium derivatives of 2-amino-7,8-benzoquinoline have been synthesized. I24,i24a... 

A number of recent papers have also focussed on the identification of paramagnetic transient reactive intermediates in bio-inspired non-heme iron catalysed oxidations. Makhlynets and Rybak-Akimova investigated the mechanism of the substrate oxidation, using H2O2 as oxidant, in an iron aminopyridine complex for aromatic hydro qrlation (Scheme 1). EPR with stopped-flow kinetic measurements, was used to identify the formation of the key Fe" (OOH) intermediate, with rhombic g... 

In this experiment the method of continuous variations is used to determine the stoichiometry and equilibrium constant for the organic complex of 3-aminopyridine with picric acid in CHCI3, and the inorganic complex of Fe +with salicylic acid. 

The authors claim that these associations, which are destroyed in fixed compounds, play an important role in the calculation of Ty.The cases of 1,2,4-triazole-5-thiones 74 [97SA(A)699] and of pyridone dimers 15a-15a and 15a-15b were also studied [96MI(13)65]. (3) The recording of IR spectra in solution at different temperatures to determine the effect of the temperature on Kj-, for instance, in pyrazolinones [83JPR(325)238] and in cytosine-guanine base pairs [92MI(9)881]. (4) The determination of the equilibrium 2-aminopyridine/acetic acid 2-aminopyridinium acetate (see Section III.E) in the acid-base complex was carried out by IR (97NKK100). 

Treatment of a residue, obtained after the evaporation of the reaction mixtures of 2-aminopyridines and enone Mannich bases 344 with 70% HCIO4 gave 3-aroyl-l,2,3,4-tetrahydropyrido[l,2-n]pyrimidinium perchlorates 345 (98SL263). Reactions in AcOH afforded a complex reaction mixture with lower overall yields. 

Aminopyridines can be perfluoroalkylated in a photoinduced electron transfer process. A charge transfer complex between the heterocycle and polyfluoroalkyl iodide, observable by NMR, is photolytically stimulated... 

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

In a similar way, 1,3-dinitrogen systems such as diamines, amidines, guanidines, aminothiazoles, aminopyridines, ureas and thioureas react with alkynyl-carbene complexes generating the corresponding heterocycles. Of particular interest is the reaction with ureas, as the process can be applied to the easy synthesis of pyrimidine derivatives [88] (Scheme 41). 

Alkali metal derivatives of 2-(trimethylsilyl)aminopyridines can be further derivatized by insertion of 1,3-dicyclohexylcarbodiimide. Functionalized guani-dinates are formed in this reaction via a 1,3-silyl shift. Scheme 170 illustrates the reaction sequence as well as the preparation of an aluminum complex of the modified ligand, which exhibits pseudo jS-diketiminate binding of the metal center, thus exemplifying the coordinative versatility of this new multi-N-donor system. ... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

In addition to complexes of the type, trans-[Tc02(pyr)2]+ (pyr pyridine or imidazole), various species, such as Jrans-[TcO(RO)X2(pyr)2] (R CH3 or CH3CH2 X Cl or Br) were detected in alcohol. Further complicated mixed-valence species, [X2(pyr)3Tc-0-Tc(pyr)2X3] and [X(pyr)4TcO Tc(pyr)X4], appeared on long standing or heating in pyridine [44,45]. Rather peculiar features were found in the substitution reaction of trans-[Tc02(py)4] + with 4-aminopyridine (apy) in mixtures of methanol and toluene in the presence of excess pyridine ([py] — 0.14 M) [46]. Its rate was expressed as... 

AJC287>. From a complex reaction mixture of BuCH(COCl)2 and 2- 4-[(4-hydroxy-3-carboxyphenyl)hydrazi-no]phenylsulfonylamino pyridine at elevated temperature, tf yr/r >-(3-butyl-2-hydroxy-4-oxo-4//-pyrido[l,2-tf]pyrimi-din-3-ylium)hydroxide was isolated <2001MI53>. Reaction of 2-aminopyridines and diethyl alkylidenemalonates at 175 °C yielded 3-(2,2-disubstituted vinyl)-2-hydroxy-4//-pyrido[l,2-tf]pyrimidin-4-ones from the initially formed... 

While the aforementioned reaction works well for aminopyridines and alkoxypyridines, it is not operative for most electron-deficient pyridines as well as 2- and 4-bromopyridines. One of the possible reasons for its failure with 2-halopyridines is the formation of an unreactive dimer complex from the oxidative addition intermediate [130]. 

The unusual structure 125 displays an acylborane group the latter was formed from carboxyborane as a complex with secondary or tertiary amines, imidazole, or pyridine derivatives. The synthetic pathway (Scheme 31) consisted in an oxidation with NBS, substitution with cyanide, then treatment with 2-aminopyridine <2004JOM3567>. 

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