A new divalent organoeuropium(II) fluoride and serendipitous discovery of an alkoxide complex from pentaphenylcyclopentadiene precursors

Abstract

From the redox-transmetallation protolysis (RTP) reaction of europium metal, Hg(C6F5)2 and pentaphenylcyclopentadiene, we isolated and crystallographically characterised small amounts of the first divalent europium fluoride half-sandwich complex [Eu(C5Ph5)(μ-F)(thf)2]2 (1). Subsequently, a rational synthesis of this complex from in situ formed [EuF2(thf)n] and [Eu(C5Ph5)2] was carried out. In addition, the new divalent Eu alkoxide complex [Eu(OC5Ph5*)2(thf)4] (2) (OC5Ph5* = 2,3,4,5,5 pentaphenylcyclopenta-1,3-dienolate) was identified by X-ray diffraction analysis, in which an intriguing phenyl group migration in the cyclopentadiene ligand occurred. This complex was shown to be derived from small impurities of 1,2,3,4,5-pentaphenylcyclopenta-1,3-dienol (C5Ph5OH) in the C5Ph5H starting material and was then synthesised on a larger scale. Density functional theory calculations provided evidence for the facile phenyl group migration observed in the cyclopentadienolate ring.