Deprotonated Amide Nitrogen Atoms Research Articles

The palladium(II) promoted hydrolysis of methyl, ethyl and isopropyl glycylglycylglycinate

The palladium(II) promoted hydrolysis of the ester function of methyl, ethyl and isopropyl glycylglycylglycinate has been studied in detail in the pH range 4–5. The tripeptide esters interact with [PdCl 4] 2− at a 1:1 metal-to-ligand ratio to give the complex I in which the α-amino group, two deprotonated amide nitrogen atoms and the alkoxy carbonyl group of the ester act as donors. Rate constants have been determined for hydrolysis of the ester function by water and hydroxide ion and activation parameters obtained for the hydrolysis of the methyl ester. At 25 °C base hydrolysis of the coordinated ester is 10 6 fold that of the free ester ligand. Mechanisms for the reactions are considered.

Studies on the metal—amide bond XV. The Molecular structure of chloro{[N-methyl-N-(2′-pyridinecarboxamide)N′-(2′-pyridinecarboxamido)]-1,2-ethane}palladium(II) determined by x-ray diffraction and high-resolution NMR studies

Chloro{[N-methyl-N-(2′-pyridinecarboxamide)-N′(2′-pyridinecarboxamido)]-1,2-ethane}palladium(II), C 15H 15N 4O 2ClPd, is tetragonal, space group I4 1/ a with a = 14.340(8), c = 31.226(10) Å, Z = 16. The crystal structure was refined to R = 0.078 for 1886 photographic reflexions by least-squares calculations The ligand acts as an N 3-tridentate to the Pd atoms via the two pyridine and one deprotonated amide nitrogen atoms [Pd-N(amide) 1.98(1) Å; average Pd- N(pyridine) 2.05(1) Å]. The N-methylated amide group is not coordinated but part of an unusual eight-membered chelate ring. A square-planar coordination is completed by the chlorine atoms [Pd-Cl 2.293(4) Å]. The coordinated picolinamide unit is almost co-planar with the coordination plane, whereas the N-methyl picolinamide unit is non-planar. The plane of this amide group is approximately perpendicular to the plane of the pyridine ring, the latter making an angle of 64.9° with the coordination plane. This unusual molecular geometry is shown to be retained in solution. The complex proton n.m.r. spectrum of the compound in CDCl 3 only may be stimulated a rigid structure similar to that found in the solid state. The hydrogen atoms of the central ethane link are closely eclipsed; observed vicinal coupling constants for the protons show a close correlation with those calculated using the HCCH torsion angles derived from the X-ray analysis. Observed chemical shifts are explained in terms of close intramolecular contacts in the structure as determined.

Stabilisation of high oxidation states by strong electron donors: the crystal structure of tetra-n-butylammonium o-phenylenebisbiuretatocuprate(III)–chloroform

The X-ray crystal structure of Bun4N[Cu-o-C6H4(NCONHCONH)2].CHCl3 shows that the Cu atom is formally tervalent and is co-ordinated by four deprotonated amide nitrogen atoms; the CuIII–N bonds (1·82–1·89 Å) are shorter than those found in related CuII complexes.

Copper(II)-promoted hydrolysis of ethyl glycylglycinate, ethyl glycyl-β-alaninate, and ethyl glycyl-L-leucinate

Copper(II)-promoted hydrolysis of the ethyl esters of glycylglycine, glycyl-β-alanine, and glycyl-L-leucine has been studied at 25 °C, I= 0·01M, and pH values >7·6. Under these conditions, and at a 1 : 1 metal to ligand ratio, the peptide esters act as tridentate ligands, donation occurring from the terminal amino·group and the deprotonated amide nitrogen atom, with a weak interaction between the metal ion and the carbonyl group of the ester. An aqua ⇌ hydroxo equilibrium occurs in these complexes, and rate constants are reported for base hydrolysis of the aqua- and hydroxo-complexes. Rate accelerations of the order of 103(compared with the unprotonated ligands) have been observed.

The bis(biuretato)cobaltate(III) ion: a paramagnetic planar CoN4 species

In the paramagnetic (3·5 B.M.) planar bis-(3-n-propylbiuretato)cobaltate(III) ion the cobalt is co-ordinated to four deprotonated amide nitrogen atoms, the u.v. spectrum being in accord with the assumption of a low-lying spin triplet term.

2-Acetamidothiazoles as ambidentate ligands. The coordination of a non deprotonated amide nitrogen atom

2-Acetamidothiazoles as ambidentate ligands. The coordination of a non deprotonated amide nitrogen atom