NC6 H4 Research Articles

Convenient Synthesis of 3‐(1‐Carboxyalkyl)pyrido[2,3‐d]pyrimidine‐2,4‐diones

AbstractFor Abstract see ChemInform Abstract in Full Text.

Convenient synthesis of 3-(1-carboxyalkyl)pyrido-[2,3-d]pyrimidine-2,4-diones

A cheap and safe synthetic route to obtain 3-(1-carboxyalkyl)pyrido[2,3-d]pyrimidinediones (carboxyalkyl = -CHRCO2H; R = H; CH2; CH2Ph; Ph; CH2 (C3H3N2); (CH2)2CO2H; CH2CO2H) starting from 2,3-pyridinedicarboxylic acid is described. A process scheme consistent with empirical observations is proposed.

Kinetics and mechanism of the interaction of pentaammine(pyridine-2-carboxylato)cobalt(III) ions with hexaaquanickel(II) and nickel(II) complexes: the role of chelating ligands

The reversible complexation of the pentaammine(pyridine-2-carboxylato)cobalt(III) ion [N5Co{O2C-(2)-C5H4 N}]2+ [N5=5HN3 and tetraethylenepentaammine (tetren)] with NiIIL(OH2)6-n [L=H2O (N5=tetren); L=bipy, ida2- (iminodiacetate) and nta3- (nitrilotriacetate), N5=5NH3 and tetren] has been investigated by the stopped-flow technique at 20-40 degC, and I= 0.3mol dm-3. At 25degC, the rate constants, kf(dm3 mol-1s-1), DeltaH(kJmol-1) and DeltaS(JK-1mol-1) for the formation of the ternary complexes [(tetren)-CoIII{O2C-(2)-C5H4N} NiIIL(OH2)6-n] are as follows: L=H2O, 530+9, 53+2, -15+7, respectively; L=bipy, 640+30, 37+3, -65+9; L=ida2-, 3900+100, 47+3, -18+11; L=nta3-, 10200+400, 49+1, −2+2. Nickel(II), in the ternary complexes, is chelated by the free pyridyl-N and the carboxylato moiety of the pyridine-2-carboxylate bound to the cobalt centre. The formation rate constant (kf) and the associated activation parameters are relatively insensitive to the N5 moieties for a given ligand L; kf increased in the order: Ni(OH2)62+Ni(bipy)(OH2)42+ Ni(ida)(OH2)3 (nta)(OH2)2-. Data analysis indicated that the mechanism shifted from the dissociative interchange (Id) to the chelation-controlled one, with the decrease of the available sites for coordination in NiIIL(OH2)6−n. The rate constants (kr) for the dissociation of [N5CoIII{O2C-(2)-C5 H4N}NiIIL(OH2) 6-(n+2)] to the parent reactants indicated steric acceleration [krL(5NH3) kr Ni(ida) >krNi(bipy)2+ for both pentaammine substrates. The chelate ring opening rate constants for the ternary complexes were estimated, from which it was apparent that the tetren envelope of cobalt(III) exerted relatively greater steric pressure as compared with 5NH3 in favouring opening up of the chelate ring.

Valence-localised and valence-delocalised mixed-valence states; the effect of the substitution pattern of 1,2-, 1,3- and 1,4-[C6H4(NH)2]2 as bridging ligands

The mixed-valence complexes [{MoL(NO)X}2{µ-1, n-C6H4(NH)2}]–[L = tris(3,5-dimethylpyrazolyl)hydroborate; X = Cl, Br, I; n= 2,3,4] containing a 1,2-, 1,3- or 1,4-diamidobenzene bridge are prepared by electrochemical or chemical reduction of the diamagnetic neutral species; EPR spectroscopy shows that with 1,2- or 1,4-diamidobenzene as the bridge the mixed-valence state is delocalised on the EPR timescale, whereas with a 1,3-diamidobenzene bridge the mixed-valence state is valence-trapped.

Crystal structure of exo-1-(4-pyridyl)-1a,2,3,7b-tetrahydro-1H-cyclopropa[a]naphthalene, (C10H10)CH(C5H4N)

Article Crystal structure of exo-1-(4-pyridyl)-1a,2,3,7b-tetrahydro-1H-cyclopropa[a]naphthalene, (C10H10)CH(C5H4N) was published on February 1, 1993 in the journal Zeitschrift für Kristallographie - Crystalline Materials (volume 208, issue 2).

Substituent Effects of the1H and13C NMR Spectra of Substituted o-Hydroxyaromatic Schiff Basies (N-Salioylideneanilines and N-Benzylidene-2-Aminophenols)

Abstract 1H and 13C NMR spectra of para-substituted o-HOC6H4 CH[dbnd]NC 6H4 X and YC6H4 CH[dbnd]NC 6H4OH-o were determined in CDC13. Reasonable correlations between the azomethine proton and 13C chemical shifts and Hammett's σP constants were obtained. The observed through-resonance effect was attributed to intramolecular hydrogen bonding between the hydrogen at the phenolic group and the imine nitrogen in the molecule.

COMPLEXES OF BINUCLEATING LIGANDS. XIII. SOLUBLE COMPLEXES OF A LIGAND WITH A BRIDGING THIOPHENOXIDE COMPONENT AND PERIPHERAL n-OCTYL SUBSTITUENTS

Abstract The trianionic binucleating ligands formally derived from the condensation products of S-n-octyldithiocarbazate with either 2-hydroxy- or 2-mercapto-5-methylisophthalaldehyde (hereafter (L″)3- and L3- respectively) gave the binuclear complexes L″Ni2 (CH3 O), L″Ni2 (C6 H5 CH2 O), LNi2 (C3 H3 N2), LCu2 (C3 H3 N2) and LNi2 (SR) where R=C8H1 7 of CH3.C6 H4 and C3 H3 N2 −=the pyrazolate anion. These complexes were soluble in chloroform and 1H n.m.r. data for some of them are presented. There was no evidence for significant magnetic exchange within LCu2 (C3 H3 N2). Attempts to generate LNi2 (X) where X−=Cl−, Br− or I− gave L2 Ni3 in which L3- fails to impose the intended molecular arrangement. Attempts to generate L(Pd(II))2 (X) unexpectedly gave materials containing additional palladium, i.e. LPd4 (CH3 CO2) and LPd4 (C3 H3 N2).