Congested Ferrocenyl Polyphosphanes Bearing Electron-Donating or Electron-Withdrawing Phosphanyl Groups: Assessment of Metallocene Conformation from NMR Spin Couplings and Use in Palladium-Catalyzed C

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• 作者：Sophal Mom ; Matthieu Beaup茅rin ; David Roy ; Sylviane Royer ; R茅gine Amardeil ; H茅l猫ne Cattey ; Henri Doucet ; J.-C. Hierso
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：November 21, 2011
• 年：2011
• 卷：50
• 期：22
• 页码：11592-11603
• 全文大小：1083K
• 年卷期：v.50,no.22(November 21, 2011)
• ISSN：1520-510X

文摘

The synthesis of novel substituted cyclopentadienyl salts that incorporate both a congested branched alkyl group (tert-butyl, (triphenyl)methyl, or tri(4-tert-butyl)phenylmethyl) and a phosphanyl group is reported. The introduction of either electron-withdrawing or electron-donating substituents (furyl, i-propyl, cyclohexyl, tert-butyl) on P atoms was generally achieved in high yield. The modular synthesis of ferrocenyl polyphosphanes from an assembly of these cyclopentadienyl salts was investigated, leading to the formation of new triphosphanes (denoted as 9鈥?b>12) and diphosphanes (denoted as 14鈥?b>16). The resulting phosphanes are not sensitive to air or moisture, even when electron-rich substituents are present. This set of polyphosphanes displays varied conformational features, which are discussed in the light of their multinuclear NMR characterization in solution and of the X-ray solid state structure of the representative triphosphane 1,2-bis(diphenylphosphanyl)-1鈥?(diisopropylphosphanyl)-3鈥?(triphenyl)methyl-4-tert-butyl ferrocene, 11. In particular, the existence of a range of significantly different nonbonded (鈥渢hrough-space鈥? TS) spin鈥搒pin coupling constants between heteroannular P atoms, for the triphosphanes of this class, allowed their preferred conformation in solution to be appraised. The study evidences an unanticipated flexibility of the ferrocene platform, despite the presence of very congested tert-butyl and trityl groups. Herein, we show that, contrary to our first belief, the preferred conformation for the backbone of ferrocenyl polyphosphanes can not only depend on the hindrance of the groups decorating the cyclopentadienyl rings but is also a function of the substituents of the phosphanyl groups. The interest of these robust phosphanes as ligands was illustrated in palladium catalysis for the arylation of n-butyl furan with chloroarenes, using direct C鈥揌 activation of the heteroaromatic in the presence of low metal/ligand loadings (0.5鈥?.0 mol鈥?). Thus, 4-chlorobenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone, and 4-(trifluoromethyl)chlorobenzene were efficiently coupled to n-butyl furan, using Pd(OAc)₂ associated to the new diphosphane ligands 1,1鈥?bis(diisopropylphosphanyl)-3,3鈥?di(triphenyl)methyl ferrocene (15) or 1,1鈥?bis(dicyclohexylphosphanyl)-3,3鈥?di(triphenyl)methylferrocene (16), which respectively hold the electron-rich 鈭扨i-Pr₂ and 鈭扨Cy₂ groups.