2,2′-dipyridylamine complexes of rhenium(V)

Abstract

The reactivity of oxorhenium(V) precursors with the potentially N,N-donor ligand 2,2′-dipyridylamine (dpa) has been investigated. Reaction of a two-fold molar excess of dpa with trans-[ReO(OEt)Cl2(PPh3)2] in ethanol led to the isolation of [ReOCl2(OEt)(dpa)] (1). Spectroscopic measurements indicate that dpa is coordinated as a bidentate in the equatorial plane cis to the oxo group, with the ethoxide in the trans position. Treatment of trans-[ReOCl3(PPh3)2] with a tenfold molar excess of dpa in ethanol at reflux yielded the trans-dioxo complex [ReO2(dpa)2]Cl (2), but with a twofold molar excess (μ-O)[{ReOCl2(dpa)}2] (3a) was isolated. The latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature led to a dark green product, also with the formulation (μ-O)[{ReOCl2(dpa)}2] (3b). These compounds were characterised by common spectroscopic techniques, and the crystal structures of 2·3H2O, 3a and 3b·2DMSO were determined. The structure of 3b presents a nearly linear O=Re–O–Re=O group, with the two [ReOCl2(dpa)] halves of the dimer rotated by 180.0° about the Re–O–Re fragment away from an eclipsed conformation. In 3a, the two halves are only rotated by 61.4°.