Studies of the reactions of tripodal pyridine-containing ligands with Re(CO)5Br leading to rheniumtricarbonyl complexes with potential biomedical applications
Iron-Catalyzed Olefin cis-Dihydroxylation Using a Bio-Inspired N,N,O-Ligand
摘要:
Nature has evolved enzymes that carry out the cis-dihydroxylation of C=C bonds in the biodegradation of arenes in the environment. These enzymes, called Rieske dioxygenases, have mononuclear iron centers coordinated to a 2-His-1-carboxylate facial triad motif that has emerged as a common structural element among many nonheme iron enzymes. In contrast, olefin cis-dihydroxylation is conveniently carried out by OsO4 and related species in synthetic procedures. To develop more environmentally benign strategies for carrying out these transformations, we have designed Ph-DPAH [(di-(2-pyridyl)methyl)benzamide], a tridentate ligand that mimics the facial N,N,O site of the mononuclear iron center in the Rieske dioxygenases. Its iron(II) complex has been found to catalyze olefin cis-dihydroxylation almost exclusively and with high H2O2 conversion efficiency on a wide range of substrates. and 18O labeling experiments suggest the participation of an FeV oxidant.
Studies of rheniumtricarbonyl complexes of tripodal pyridyl-based ligands
作者:D. Vaughan Griffiths、Mohamad J. Al-Jeboori、Phillip J. Arnold、Yuen-Ki Cheong、Philip Duncanson、Majid Motevalli
DOI:10.1016/j.ica.2009.11.039
日期:2010.4
The reaction of N-benzoyl and N-acetyl tris(pyridin-2-yl) methylamine 1b and 1c (LH = tpmbaH and tpmaaH) with [Re(CO)(5)Br] has been investigated and shown to proceed via the initial formation of a cationic rheniumtricarbonyl complex [(LH)Re(CO)(3)]Br in which coordination of the ligand occurs via the three pyridine rings. For tpmbaH 1b, but not tpmaaH 1c, this initial complex 2b readily undergoes the loss of HBr to give a neutral octahedral complex 4b [(L)Re(CO)(3)] where coordination occurs via two of the pyridine rings and the deprotonated amide nitrogen. The H-1 NMR spectrum of the latter complex 4b is very unusual in that at room temperature the signals for the 3-H protons on the coordinated pyridine rings are not visible due to extreme broadening of these resonances. Comparison with the analogous complex 7 from N-benzoyl bis(pyridin-2-yl) methylamine 6b (bpmbaH) confirms that this is due to rotation of the uncoordinated pyridine ring. The structure of the cationic complex 3d [(LH)Re(CO)(3)]Br formed from N-benzyl tris(pyridin-2-yl) methylamine 1d (bz-tpmaH) is also discussed. The crystal structures of complexes [(tpmba)Re(CO)(3)] 4b, [(bz-tpmaH)Re(CO)(3)]Br 3d and [(bpmba)Re(CO)(3)] 7 have been determined. In all complexes the coordination geometry around Re is distorted octahedral with a facRe(CO)(3)}(+) core. (C) 2009 Elsevier B.V. All rights reserved.