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Imidazole side chain of a single atom -bridged cyclopentadienyl ligands and the IV Vice ethnic transition metallocene Complexes

Author: WangXiaoWu
Tutor: Maxim.V.Borzov
School: Northwestern University
Course: Organic Chemistry
Keywords: cyclopentadienyl-imidazole ligands imidazole protection group lithiation Constrained-Geometry-Catalyst (CGC) titanium、zirconium complexes amine salt
CLC: O621.1
Type: Master's thesis
Year: 2009
Downloads: 50
Quote: 1
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Abstract


One novel type of imidazole one-atom bridged cyclopentadienyl ligands and its reaction withⅣB salts has been established,as well as the studies of their synthesis,structural and reactive activity.The synthetic route of this novel imidazole one-atom bridged cyclopentadienyl ligands has been thoroughly studied.Treatment 1-diethoxylmethylimidazole(1) and 1-dimethoxylmet hylimidazole(5) with 6,6-diphenyl fulvene(2),6-monopehylfulvene(11) has been shown to afford pure ligands C5H5CR2-(2-C3H3N2)(R2=Ph,Ph;Ph,H(4),(12) respectively).The novel bidentate ligands are finally characterized.Reaction of ligands(4),(12) with n-BuLi afford the corresponding dilithium salt,(7),(14).Dilithium salt LiC5H4CR2-(2-C3H2N2Li)(R2=Ph,Ph;7) has been isolated in pure state as an adduct with 2 molecules of THF.Crystal and molecular structure of 7·2THF has been established by X-ray diffraction analysis.For this compound, an interesting case of organolithium compound catenation provided byη5-Cp-Li(CN=2) -N(imidazolide) intermolecular interactions has been found.A brief quantum-chemical modeling for(7) revealed a good match of the observed and calculated structural parameters for theη5-Cp-Li(CN=2)-N(imidazolide) moiety and outlined considerableπ-interaction within this fragment.An interesting n-BuLi invoked rearrangement of 1-diethoxymethyl-1H-imidazole(1) or 1-dimethoxylmethyl-1H-imidazole(5) into their 2-isomers(17) and(20) has been observed. The suggested method allows to prepare 2-1H-imidazole carbaldehyde(18)(quantitative acidic hydrolysis of(17) and/or(20)) in a cheap and convenient way comparatively to the literature synthetic routines.Compound(18) is rather a useful pharmaceutical intermediate(20 $/g).Attempts to prepare the ligand(F) under various base conditions proved to be a failure.Under the gas chromatograph column conditions,compound(17) has been proved to undergo a quantitative conversion into 4,8-diethoxy-3a,4,7a,8-tetrahydro-1,3a,5,7a-tetraza-s-i ndacenes[19a(4RS,8RS)- and 19b(4R,8S)-diastereomers].Crystal and molecular structures of(17) and 19(b) have been established by X-ray diffraction analysis.For compound(13),NMR-time scale slow-limit tautomeric rearrangement has been observed.Crystal structure of(13) has been established by X-ray diffraction analysis.Attempts to develop an alternative route to the 1H-imidazol-2-yl side-chain functionalized cyclopentadienes(C) failed.Reaction of dilithium salt(7) with the Group 4 metal tetrahalides,ZrCl4·2THF and TiCl4, has been studied.Formation of supposedly polymeric products has been postulated in this case.Treatment of bidentate ligands(12 and 4) with Ti(NEt24(9) in toluene at 80-90℃has been shown to lead to pure {[2-η5-cyclopenta-2,4-dienyl]-mono(or di-) phenylmethyl] -1H-imidazole-κN]}bis(N,N-diehtylamido)titaniums(+4),C23H32N4Ti(15) and C39H37N4Ti (10) in 60 and 50%yields,respectively.Crystal structure of(15) has been established by X-ray diffraction analysis.The Ti-linked amido-nitrogen atoms of NEt2 and imidazole groups have been proved to possess planar environments what is indicative of an additionalπ-donation from all of the amido-type groups towards the Ti-center.Thus,the titanium atom in(15) formally possesses an 18e- shell,that presents a rather untypical phenomenon in Ti(Ⅳ) organochemistry.Generally,it possesses an 16 e- shell.

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