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

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)(mu-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.

Automated summary

In this study, the first divalent europium fluoride half-sandwich complex was isolated and crystallographically characterized through the redox-transmetallation protolysis reaction of europium metal, Hg(C6F5)(2), and pentaphenylcyclopentadiene. Additionally, a new divalent europium alkoxide complex was identified, and evidence for the potential phenyl group migration mechanism was provided.