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Protonation of the Heterocyclic Cp‐Anion Equivalent [Pyrrolyl‐B(C 6 F 5 ) 3 ]Li − Formation of a Useful Neutral Brønsted Acid for the Generation of Homogeneous Metallocene Ziegler Catalysts
Author(s) -
Kehr Gerald,
Roesmann Rolf,
Fröhlich Roland,
Holst Christiane,
Erker Gerhard
Publication year - 2001
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200102)2001:2<535::aid-ejic535>3.0.co;2-6
Subject(s) - chemistry , metallocene , catalysis , protonation , medicinal chemistry , brønsted–lowry acid–base theory , yield (engineering) , lewis acids and bases , propene , moiety , polymer chemistry , polymerization , inorganic chemistry , organic chemistry , ion , materials science , metallurgy , polymer
N ‐pyrrolyllithium ( 1 ) adds to B(C 6 F 5 ) 3 to yield [(C 4 H 4 N)B(C 6 F 5 ) 3 ]Li ( 3 ). The corresponding monoetherate ( 3· OEt 2 ) was characterized by X‐ray diffraction and shows an η 5 coordination of the pyrrolyl moiety to the lithium cation. Treatment of 3 with HCl in ether leads to H + addition at a pyrrolyl α‐position to yield the neutral dipolar Brønsted acid system [(C 4 H 5 N)B(C 6 F 5 ) 3 ] ( 4 ). The reagent 4 can be used to protonate Cp 2 Zr(CH 3 ) 3 to yield [Cp 2 Zr(CH 3 ) + (C 4 H 4 N)B(C 6 F 5 ) 3 − ] ( 6 ) and methane. H + transfer from 4 to (butadiene)zirconocene results in the formation of the (π‐allyl)metallocene salt [(C 4 H 7 )ZrCp 2 + (C 4 H 4 N)B(C 6 F 5 ) 3 − ] (8) . In analogous reactions, the neutral Brønsted 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.