Mesityl Alkyne Substituents for Control of Regiochemistry and Reversibility in Zirconocene Couplings: New Synthetic Strategies for Unsymmetrical Zirconacyclopentadienes and Conjugated Polymers

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• 作者：Adam D. Miller ; John F. Tannaci ; Samuel A. Johnson ; Hyuk Lee ; Jennifer L. McBee ; T. Don Tilley*
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：April 8, 2009
• 年：2009
• 卷：131
• 期：13
• 页码：4917-4927
• 全文大小：290K
• 年卷期：v.131,no.13(April 8, 2009)
• ISSN：1520-5126

文摘

Reaction of 2 equivs of MesCCPh with Cp₂Zr(η²-Me₃SiCCSiMe₃)(pyr) afforded the zirconacyclopentadiene Cp₂Zr[2,5-Ph₂-3,4-Mes₂C₄]. The regiochemistry of this isomer (ββ with respect to the mesityl substituents) was determined through single-crystal X-ray analysis and 2D (NOESY, HSQC, HMBC) NMR experiments. This selectivity is attributed largely to a steric-based directing effect of the o-methyl ring substituents since coupling of 1,3-dimethyl-2-(phenylethynyl)benzene with zirconocene gave a single regioisomer (o-xylyl groups in both β-positions) while coupling of 1,3-dimethyl-5-(phenylethynl)benzene gave a statistical distribution of zirconacyclopentadiene regioisomers. The coupling reaction of 2 equivs of MeCCMes or PrCCMes with Cp₂Zr(η²-Me₃SiCCSiMe₃)(pyr) at ambient temperature gave the ββ regioisomers, Cp₂Zr[2,5-Me₂-3,4-Mes₂C₄] and Cp₂Zr[2,5-Pr₂-3,4-Mes₂C₄], respectively, as the major products. Heating solutions of these zirconacycles at 80 °C for several hours resulted in an increase in the amount of the unsymmetrical product. For reaction mixtures of PrCCMes and Cp₂Zr(η²-Me₃SiCCSiMe₃)(pyr) the major (and apparently thermodynamic) product under these reaction conditions was Cp₂Zr[2,4-Mes₂-3,5-Pr₂C₄]. The steric strain in the mesityl-substituted zirconacycles allowed for facile substitution reactions of MesCCPh or PrCCMes by less bulky alkynes (i.e., tolan and 3-hexyne) to give the unsymmetrical ziconacyclopentadienes Cp₂Zr[2,4,5-Ph₃-3-MesC₄], Cp₂Zr[2-Ph-3-Mes-4,5-Et₂C₄], and Cp₂Zr[2-Pr-3-Mes-4,5-Ph₂C₄]. Reaction of a mesityl-terminated diyne containing a rigid dihexylfluorenylene spacer with zirconocene afforded poly(p-fluorenylenedienylene) after demetalation with benzoic acid.