Synthesis and complexation of Cyclopentadienes

Abstract

The first part of chapter 1 gives a short general introduction to the importance of cyclopentadienyl complexes. This leads on to a presentation of the importance of chirality in cyclopentadienyl complexes with reference to their catalytic applications. The main bulk of the chapter then presents the subject of chirality in cyclopentadienyl complexes in terms of their molecular structure, with many important examples from the literature. There is also discussion of different methods of metallating cyclopentadienes and the influence of the choice of method on the ratio of stereoisomers produced. Chapter 2 is a selective review of methods of synthesising cyclopentadienes and cyclopentadiene precursors (i.e. cyclopentenones and cyclopentenois). The review is biased towards syntheses which have been (or have the potential to be) used for the production of multigram batches of cyclopentadienes (and cyclopentadiene precursors) with structures of interest to organometallic chemists. Chapter 3 presents the experimental work. The results are discussed first, after which the experimental procedures are presented. The aliphatic Friedel-Crafts/Nazarov reaction between crotonic acid and cyclohexene in warm polyphosphoric acid is an established method of synthesising 3-methyl-23.4,5,6,7-hexahydro-l//-inden-l-one (HKI). The technique has been improved by adding a semicarbazone formation-hydrolysis purification step to remove the inevitable cyclohexyl с ratónate by product.I-(3,5-dimethylphenyl)-3-methyl-4,5,6,7-telrahydro-2W-mdene (HCpl) was prepared from 3-melhyl-2,3,4,5,6,7- hexahydro-1 Я-inden-1 -one (HKl) by the use of 3,5-dimethylpheny! magnesium bromide in THF. HCpl was highly convenient on account of its crystallmity and was used to make metal complexes either by deprotonation and reaction with a metal chloride (FeCb) or through prior conversion to {R,ร)-1 -(3,5-dimethylphenyl)-2-(trimethylsiIyl)-3-methyl- 4,5,6,7-tetrahydro-2//-indene (TMSCpl). The latter compound reacted readily with ZrCİ4, TİCİ4 and NbCI.s, although only the reaction with TİCI4 lead to a isolable compound, η'՝-[l֊(3,5֊dimethylphenyl)-3-methyI-4,5,6,7-tetrahydro-2Я- indenyl]trichlorotiianium(IV) (CplTiCb). ： The reaction of deprotonated HCpl with FeCli produced two ferrocenes, a major product, հւտ-Վ-[[Հ?>,5֊ dimethyiphenyl)-3-methyl-4,5,6,7-tetrahydro-2//-inđenyl]iron(II) (СрІзРе), and a minor product, η'-[I-(3,5- dimethylphenyl)-3-methyl-4,5,6Jчetrahydro-2/ƒ-indenyI]-η^-[lЧЗ,5-dinไethylphenyl)-2-formyl-3-melhyl-4,5,6,7֊ tetrahydro-2/y-indenyl]iron(II) (CplCp2Fe). The minor product was thought to derive from some unknown impurity in the starling materials.Crystal structures of TMSCpl and CplCp2Fe were obtained. The molecular structure of the latter is discussed. To finish chapter 3, a proposal is outlined for a novel phosphonium salt/phosphorus ylid based approach to the synthesis of cyclopentadienes. The proposed reactions were not carried out, but it is hoped thai a future investigator will conduct experiments in this area.Appendix і gives some useful information on the naming of substituted hydroindenes.Appendix 2 presents information and calculations on the composition of polyphosphoric acid. It also gives a method of making polyphosphoric acid in the lab.Appendix 3 gives the crystal structure of TMSCpl ((;?,5)-l-{3,5-dimethylphenyl)-2-(trimethylsilyl)-3-methyl-4,5,6,7- tetranydro-2//-indene)Appendix 4 gives the crystal structure of CplCp2Fe (η^-[Ι -(3,5-dimethylphenyl)-3-methyl-4,5,6,7-tetrahydro-2^- indenyl]-n^4143,5-dimethyiphenyl)-2-formyl-3-methyl-4,5,6,7-tetrahydro-2//MndenyI]iron(ĪI))References for each chapter are collected together at the end of the chapter. References for the collected appendices are to be found at the very rear of the thesis. [brace not closed]