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Substituted cyclopentadienyl chemistry of the alkaline earth and rare earth elements
thesisposted on 09.02.2017, 05:11 authored by Daniels, Daisy Parveena
This thesis explores the synthesis and characterisation of substituted cyclopentadienyl complexes of the alkaline earth and rare earth metals and exemplifies the similarities between the two groups of elements. Chapter 2 describes a series of alkaline earth metallocene complexes carrying the (diphenylphosphano)cyclopentadienyl ligand, [Ae(L)x(η5-C5H4PPh2)2] (Ae = Ca, Sr or Ba; L = thf or dme) which were prepared by redox transmetallation/protolysis from the free metals, diphenylmercury and (diphenylphosphano)cyclopentadiene. This chapter also describes the syntheses of alkaline earth and lanthanoid 1,3-bis(diphenylphosphano)metallocene complexes, [Ln(or Ae)(L)(η5-C5H3(PPh2)2-1,3)2].(solv) (L = dme or thf; solv = dme or PhMe; Ln = Yb and Eu; Ae = Ca, Sr and Ba) by redox transmetallation/protolysis. This work provides a major advance by extending the structural library to include lanthanoid and alkaline earth metal derivatives of the phosphano-substituted cyclopentadienyl ligand. Chapter 3 describes the isolation of the bimetallic complexes, [Ae(thf)x(η5-C5H4PPh2)2Pt(Me)2].(thf)y (Ae = Ca, Sr or Ba), obtained by reaction of the homometallic complexes [Ae(thf)(η5-C5H4PPh2)2] (Ae = Ca, Sr or Ba) with [Pt(cod)(Me)2]. The crystal structures of [Ca(thf)2(η5-C5H4PPh2)2Pt(Me)2].1.5thf, [Sr(thf)3(η5-C5H4PPh2)2Pt(Me)2].1.5thf and [Ba(thf)3(η5-C5H4PPh2)2Pt(Me)2].thf show the eight (calcium) and nine coordinate (strontium and barium) fragments acting as a chelating metalloligands attached to the square planar platinum through the phosphorus donor atoms. The solution chemistry of these bimetallic complexes has been investigated by NMR spectroscopy, electro-spray ionisation mass spectrometry and conductivity experiments which indicate that the bimetallic compounds stay associated in solution. Also, the bimetallic complexes [Ln/Ae(L)x(η5-C5H4PPh2)2Pt(R)2] (Ln = Yb; Ae = Ca, Sr, Ba; R = Ph or C6H4But-p) were synthesised using the platinum complexes [Pt(cod)(Ph)2] and [Pt(cod)(C6H4But-p)2]. In Chapter 4, the intended direction towards the synthesis of divalent metallocene complexes using (diphenylphosphano)tetraphenylcyclopentadiene for further use in the formation of bimetallic complexes was diverted due to the formation of an unexpected divalent europium-phosphanido complex, [Eu(dme)2(µ-1,2-(PPh)2(C6H4))]2 via redox transmetallation/protolysis. The isolation of this complex was supported by X-ray crystallographic evidence. Investigations into the synthetic formation of this complex led to the surprising isolation of the tetraphenylcyclopentadienyl sandwich complex [Eu(dme)(η5-C5Ph4H)2] via P−C bond cleavage using (C5Ph4H(PPh2)). This result drew attention to the possibility of synthesising more soluble polyarylcyclopentadienyl complexes which was achieved using the redox transmetallation/protolysis method. Both divalent complexes, [Eu(dme)(η5-C5Ph4H)2] and the solvent separated ion pair [Yb(dme)4][C5Ph4H]2 were isolated and characterised using 1H NMR spectroscopy as well as X-ray crystallography.