New Ways towards the Cleavage of Non-activated Carbon-Carbon Bonds
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
(See online at https://doi.org/10.1039/c5ob01602a) - "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
(See online at https://doi.org/10.1021/acs.organomet.6b00427) - "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
(See online at https://doi.org/10.1039/c7ob01591g) - "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
(See online at https://doi.org/10.1039/c8dt02435a) - "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
(See online at https://doi.org/10.1021/jacs.7b11958)
