New Ways towards the Cleavage of Non-activated Carbon-Carbon Bonds

• Applicant: Professor Dr. Gerhard Erker
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2011 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 197645375

• Final Report Year: 2020

Final Report Abstract

The (C6F5)2B-group acidifies C-H bonds in the α-position strongly. These systems can be viewed as borata-alkenes. We have used this dominant property to prepare and use a variety of such borata-alkenes, which are readily available by deprotonation reactions from the respective alkyl-B(C6F5)2 boranes with a suitable base. This has led to (C6F5)2B-substituted indenyl systems and the Ti or Zr complexes derived thereof. The Zr complex was used as a component in homogeneous metallocene olefin polymerization catalysis. A variety of our borata-alkenes were employed as reagents in borata-Wittig olefination reactions. This worked well with ketones, but these reagents could also be used in “abnormal Wittig reactions” of esters and amides. We were even able to isolate and structurally characterize the B=O Wittig co-product. It dimerized as a dianionic BOBO four-membered heterocycle, according to its X-ray crystal structure analysis. We generated a small group of conjugated iminium/borata-alkene systems. Some such systems are found to be responsible for E-/Z-isomerization reactions of the central olefinic moiety. Eventually, we used a methylene linked phosphane/borata-alkene as an anionic chelate ligand in coordination chemistry. The new ligand type was easily prepared (and isolated as the Li salt) by deprotonation of the respective ethylene-bridged P/B frustrated Lewis pair. We prepared two neutral Rh and one Ir complex with this new ligand type and investigated first catalytic applications.

Publications

• "Enamine/butadienylborane cycloaddition in the frustrated Lewis pair regime", Org. Biomol. Chem. 2015, 13, 10477-10486
  G.-Q. Chen, F. Türkyilmaz, C. G. Danliuc, C. Bannwarth, S. Grimme, G. Kehr, G. Erker
  
• "Borata-Alkene Derived Syntheses of (F5C6)2B-Substituted Bis(indenyl) Group 4 Metal Complexes", Organometallics 2016, 35, 2689-2693
  S. Kohrt, G. Kehr, C. G. Daniliuc, R. S. Rojas, B. Rieger, C. Troll, G. Erker
  
• "Borata-Wittig olefination reactions of ketones, carboxylic esters and amides with bis(pentafluorophenyl)-borata-alkene reagents", Org. Biomol. Chem. 2017, 15, 6223-6232
  T. Wang, S. Kohrt, C. G. Daniliuc, G. Kehr, G. Erker
  
• "Formation of borata-alkene/iminium zwitterions by ynamine hydroboration", Dalton Trans. 2018, 47, 10853-10856
  L. Wang, Z. Jian, C. G. Daniliuc, G. Kehr, G. Erker
  
• "Formation of Reactive π-Conjugated Frustrated N/B Pairs by Borane-Induced Propargyl Amine Rearrangement", J. Am. Chem. Soc. 2018, 140, 3635-3643
  T. Wang, C. G. Daniliuc, C. Mück-Lichtenfeld, G. Kehr, G. Erker