Osmium-mediated C-H and C-C bond cleavage of a phenolic substrate: P-Quinone methide and methylene arenium pincer complexes

Regis M. Gauvin, Haim Rozenberg, Linda J.W. Shimon, Yehoshoa Ben-David, David Milstein

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Abstract

The diphosphine 2,4,6-(CH3)3-3,5-(iPr 2PCH2)2C6OH (1) reacts with [OsCl2(PPh3)3] in presence of an excess of triethylamine to yield the isomeric para-quinone methide derivatives [Os{4-(CH2)-1-(O)-2,6-(CH3)2-3,5-(iPr 2PCH2)2C6}(Cl)(H)(PPh3)] (2 and 3), which differ in the positions of the mutually trans hydride and chloride ligands. Complex 2 reacts with CO to afford the dicarbonyl species [Os{1-(O)-2,4,6-(CH3)3-3,5-(iPr2PCH 2)2C6}(Cl)(CO)2] (4), which results from hydride insertion into the quinonic double bond. Protonation of 2 and 3 leads to the formation of the methylene arenium derivative [Os{4-(CH 2)-1-(OH)-2,6-(CH3)2-3,5-(iPr 2PCH2)2C6}(Cl)(H)(PPh 3)]-[OSO2CF3] (5a). The diphosphine 1 reacts with [OsCl2(PPh3)3] at 100°C under H 2 to afford [Os{1-(OH)-2,6-(CH3)2-3,5-(iPr 2PCH2)2C6}(Cl)(H2)- (PPh3)] (6), a PCP pincer complex resulting formally from C(sp 2) - C(sp3) cleavage of the C-CH3 group in 1. C-C hydrogenolysis resulting in the same complex is achieved by heating 2 under H2 pressure. Reaction of the diphosphine substrate with [OsCl 2(PPh3)3] under H2 at lower temperature allows the observation of a methylene arenium derivative resulting from C-H activation, [Os{4-(CH2)-1-(OH)-2,6-(CH3) 2-3,5-(iPr2PCH2)2C 6}(Cl)2(H)] (7). This compound reacts with PPh3 in toluene to afford the ionic derivative [Os(4-(CH2)-1-(OH)-2,6- (CH3)2-3,5-(iPr2PCH2)2C 6)(Cl)(H)(PPh3)]Cl (5b). X-ray diffraction studies have been carried out on compounds 2, 3, 4, 5b, 6, and 7, which allows the study of the structural variations when going from methylene arenium to quinone methide derivatives.

Original languageEnglish
Pages (from-to)1382-1393
Number of pages12
JournalChemistry - A European Journal
Volume13
Issue number5
DOIs
Publication statusPublished - Jun 21 2007

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Keywords

  • C-C activation
  • C-H activation
  • Osmium
  • P ligands
  • Quinone methides

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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