Preparation and Crystal Structures of Benzoylhydrazido‐ and‐diazenidorhenium Complexes with N,O‐Ligands and Their Catalytic Activity Towards Peroxidative Oxidation of Cycloalkanes

Abstract

AbstractThe η2‐(benzoylhydrazido)rhenium(V) complex [Re{(OCH2CH2)2N(CH2CH2OH)}{N=NC(O)Ph}(PPh3)] (2) and the η1‐(benzoyldiazenido)rhenium(III) compounds [ReCl{N(CH2COO)(CH2CH2OH)(CH2CH2OH)}{N=NC(O)Ph}(PPh3)] (3) and [ReCl(O,N‐L){N=NC(O)Ph}(PPh3)2] [O,N‐L = N(=O)CH2COO (4), HN=C(Me)COO (5), C5H4N(COO) (6)], withchelating N,O‐ligands (amino alkoxides, amino‐, oxyamino‐,imino‐ and pyridinocarboxylates) have been prepared by treatment of [ReCl2{N=NC(O)Ph}(PPh3)2] (1) with triethanolamine [N(CH2CH2OH)3], N,N‐bis(2‐hydroxyethyl)glycine [N(CH2CH2OH)2(CH2COOH)], N‐hydroxyiminodiacetic acid [HON(CH2COOH)2], N‐hydroxy‐2,2'‐iminodipropionic acid [HON{CH(Me)COOH}2] and picolinic acid (NC5H4COOH‐2), respectively. The N,O‐ligands in 4 and 5 result from fragmentation of the N‐hydroxyiminodicarboxylic acids. All the complexes have been characterized by IR, 1H and 13C NMR spectroscopy, FAB+‐MS, elemental analysis and X‐ray diffraction structural analysis, which indicate a π‐delocalized chelated benzoylhydrazidorhenium ring in 1 and 2, and, in the other complexes, an essentially linear η1‐diazenido ligand that is always trans to the O‐coordinated carboxylate moiety of the N,O‐ligand. The complexes act as catalysts (TON values up to about 45) for peroxidative oxidation, by radical mechanisms, of cyclohexane and cyclopentane to the corresponding alcohols and ketones, under mild conditions (room temperature, use of aqueous H2O2 and without added acid). This is an unprecedented use of inorganic Re coordination compounds as catalysts in alkane functionalization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)