Paul Jensen's research while affiliated with The University of Sydney and other places

Coupling picolinic acid (pyridine-2-carboxylic acid) and pyridine-2,6-dicarboxylic acid with N-alkylanilines affords a range of mono- and bis-amides in good to moderate yields. These amides are of interest for potential applications in catalysis, coordination chemistry and molecular devices. The reaction of picolinic acid with thionyl chloride to generate the acid chloride in situ leads not only to the N-alkyl-N-phenylpicolinamides as expected but also the corresponding 4-chloro-N-alkyl-N-phenylpicolinamides in the one pot. The two products are readily separated by column chromatography. Chlorinated products are not observed from the corresponding reactions of pyridine-2,6-dicarboxylic acid. X-Ray crystal structures for six of these compounds are described. These structures reveal a general preference for cis amide geometry in which the aromatic groups (N-phenyl and pyridyl) are cis to each other and the pyridine nitrogen anti to the carbonyl oxygen. Variable temperature 1H NMR experiments provide a window on amide bond isomerisation in solution.

Four ZnII 5,10,15-triphenylporphyrin (TriPP) complexes meso–meso linked by two-atom bridges, namely, C2H2 (2), C2 (3), CH=N (4), and N2 (5), were prepared, for comparison of ground-state inter-porphyrin conjugation. The X-ray crystal structure of azoporphyrin 5·py2 (py = pyridine) was determined: it exhibits a stepped-offset shape and a porphyrin–azo torsion angle of 34.8°. Some new monoporphyrin starting materials were prepared, and ZnTriPPNH2 (27), ZnTriPPCHO (23), NiTriPPCHO (7), and ZnTriPPCH2CH2Ph (18), as well as the byproduct butadiyne-linked dimer 26 were characterized by single-crystal X-ray crystallography. The conjugation in the dimers was assessed by electronic absorption and steady-state fluorescence spectroscopy. All show variously split B bands: azoporphyrin 5 clearly has the strongest ground-state inter-porphyrin interactions. Imine 4 and azo 5 show strongly quenched fluorescence emission, which indicates the presence of efficient relaxation pathways afforded by the N-containing linkers.

Nitrile hydratase (NHase, EC 4.2.1.84) is a metalloenzyme which catalyses the conversion of nitriles to amides. The high efficiency and broad substrate range of NHase have led to the successful application of this enzyme as a biocatalyst in the industrial syntheses of acrylamide and nicotinamide and in the bioremediation of nitrile waste. Crystal structures of both cobalt(III)- and iron(III)-dependent NHases reveal an unusual metal binding motif made up from six sequential amino acids and comprising two amide nitrogens from the peptide backbone and three cysteine-derived sulfur ligands, each at a different oxidation state (thiolate, sulfenate and sulfinate). Based on the active site geometry revealed by these crystal structures, we have designed a series of small-molecule ligands which integrate essential features of the NHase metal binding motif into a readily accessible peptide environment. We report the synthesis of ligands based on a pyridine-2,6-dicarboxylic acid scaffold and L-cysteine, L-S-methylcysteine, L-methionine or L-penicillamine. These ligands have been combined with cobalt(III) and iron(III) and tested as catalysts for biomimetic nitrile hydration. The highest levels of activity are observed with the L-penicillamine ligand which, in combination with cobalt(III), converts acetonitrile to acetamide at 1.25 turnovers and benzonitrile to benzamide at 1.20 turnovers.

The new complex Cu[L1]Cr2O7has been synthesised with the N,N′-bis(2-pyridylmethylene) butane-1,4-diamine Schiff base L1, [NC5H4CH=N(CH2) 4N=CHC5H4N], and characterised with elemental analyses and different spectroscopic and electrochemical studies. The structure of the new complex has been established by single crystal X-ray diffraction. The complex crystallises in the monoclinic system with space group P21/c having cell parameters a = 14.7(5), b = 9.22(2), c = 16.2(5) Å, β= 116.9(1)°, and Z = 4. The Cr2O72- unit is bonded through one terminal oxygen donor end to the central Cu(II) chelated by the Schiff base ligand.

We compare the results from the oxidation of two unusual "enediamide" motifs (3,4-dihydropyrazin-2(1H)-ones), where a double bond is flanked by two amides. In one case the oxidation led to a ring-opened product arising from the cleavage of the double bond, and in the other a rare cis-dioxygenated compound was obtained. Both products have been characterized by X-ray crystallography. The outcomes of the key reactions are rationalized based on calculated free energies of intermediates.

B3-LYP/6-31G(d)-optimized structures and M06-2X/6-311+G(3df,2p) electronic energies for various species. (DOC)

13C NMR Spectrum of N-formyl-N-(2-oxo-2-(1-oxo-3,4-dihydroisoquinoline-2(1yl)ethyl)cyclohexanecarboxamide, (6). (TIFF)

13C NMR spectrum of 2-(cyclohexanecarbonyl)-6,7-dihydro-2H-pyrazino[2,1-a]isoquinolin-4(3H)-one, (5). (TIFF)

1H NMR spectrum of 2-(cyclohexanecarbonyl)-6,7-dihydro-2H-pyrazino[2,1-a]isoquinolin-4(3H)-one, (5). (TIFF)