333334-62-6Relevant articles and documents
Synthesis and reactivity of (C6F5)3B-N-heterocycle complexes. 1. Generation of highly acidic sp3 carbons in pyrroles and indoles
Guidotti, Simona,Camurati, Isabella,Focante, Francesca,Angellini, Luca,Moscardi, Gilberto,Resconi, Luigi,Leardini, Rino,Nanni, Daniele,Mercandelli, Pierluigi,Sironi, Angelo,Beringhelli, Tiziana,Maggioni, Daniela
, p. 5445 - 5465 (2003)
The reaction of pyrroles and indoles with B(C6F5)3 and BCl3 produces 1:1 B-N complexes containing highly acidic sp3 carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp3 carbons in these complexes is shown by their ability to protonate NEt3, with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.
Protonation of the heterocyclic cp-anion equivalent [pyrrolyl-B(C6F5)3]Li - Formation of a useful neutral bronsted acid for the generation of homogeneous metallocene ziegler catalysts
Kehr, Gerald,Roesmann, Rolf,Froehlich, Roland,Holst, Christiane,Erker, Gerhard
, p. 535 - 538 (2007/10/03)
N-pyrrolyllithium (1) adds to B(C6F5)3 to yield [(C4H4N)B(C6F5)3 ] Li (3). The corresponding monoetherate (3·OEt2) was characterized by X-ray diffraction and shows an η5 coordination of the pyrrolyl moiety to the lithium cation. Treatment of 3 with HC1 in ether leads to H+ addition at a pyrrolyl α-position to yield the neutral dipolar Bronsted acid system [(C4H5N)B(C6F5)3 ] (4). The reagent 4 can be used to protonate Cp2Zr(CH3)3 to yield [Cp2Zr(CH3)+(C4H4N)B- (C6F5)3-] (6) and methane. H+ transfer from 4 to (butadiene)-zirconocene results in the formation of the (π-allyl)metallocene salt [(C4H7)ZrCp2+(C4 H4 (C6F5)3-] (8). In analogous reactions, the neutral Bronsted acid was employed as a protonating activator component for the generation of homogeneous Ziegler catalysts derived from a variety of (butadiene)-or (dimethyl)ansa-metallocenes. The systems generated by treatment with 4 show comparable activities in ethene or propene polymerization reactions as conventionally generated Group 4 metallocene Ziegler catalysts.
