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

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)Cl-2(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 (mu-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 (mu-O)[{ReOCl2(dpa)}(2)] (3b). These compounds were characterised by common spectroscopic techniques, and the crystal structures of 2(.)3H(2)O, 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 180.0degrees about the Re-O-Re fragment away from an eclipsed conformation. In 3a, the two halves are only rotated by 61.4degrees.