Synthesis, molecular and crystal structure of the zwitterionic Re(V)-oxo complex ReOCl3(L)(PPh3) with L=2-(diethylaminomethyl)-4-methylphenol

Ligand exchange between 2-(diethylaminomethyl)-4-methylphenol ((NOH)-O-o) and ReOCl3(PPh3)(2) yields green crystals of the zwitterionic complex ReOCl3((ONH)-N-o)(PPh3). The X-ray diffraction study reveals that the structure consists of monomeric units in which the distorted octahedral coordination around Re is provided by the oxo group, the three Cl atoms in a mer arrangement, the PPh3 ligand and the phenolate oxygen trans to the oxo group. The amino-phenol is monodentate via the phenolate oxygen, whereas the amine in the side-arm has been quaternized by migration of the phenol proton. The resulting ammonium group forms an intramolecular N-H ... Cl hydrogen bond with an adjacent Cl ligand, making the complex highly resistant to deprotonation. The H-1 NMR spectra indicate that the N-H proton is not labile in CDCl3. Electron delocalisation along the O=Re-O-C(phenolate) moiety via the sp-hybridised oxygen of the end-on coordinated phenolate would be consistent with the short Re-O(phenolate) distance of 1.915(3) Angstrom observed. (C) 1999 Elsevier Science S.A. All rights reserved.