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Characteristic Features of Neutral Cyclopropenylium‐Like Compounds: Synthesis, Structure, and Chemical Behavior of a Cyclopropenylioborate Betaine
Author(s) -
Ahlers Wolfgang,
Erker Gerhard,
Fröhlich Roland,
Zippel Frank
Publication year - 1997
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19971300809
Subject(s) - chemistry , betaine , isocyanide , ring (chemistry) , isomerization , crystal structure , stereochemistry , double bond , yield (engineering) , medicinal chemistry , molecule , x ray crystallography , crystallography , polymer chemistry , diffraction , organic chemistry , catalysis , materials science , physics , optics , metallurgy
Bis(propynyl)zirconocene was treated with B(C 6 F .5 ) 3 and then with two equivalents of tert‐butyl isocyanide to yield the organometallic three‐membered ring product 8 . Subsequent hydrolysis gives the substituted (2‐iminioethylidene)cyclopropeneborate betaine system 9 that exhibits a pronounced cyclopropenylioborate betaine character. This follows from its characteristic structural features (X‐ray crystal‐structure analysis of the isomer cis ‐ 9 ) and its chemical features. Complex 9 undergoes a very facile cis/trans isomerization by formal rotation around the exocyclic partial CC‐double bond (ΔG + ≈ 17 kcal mol −1 ). Compound 9 reacts cleanly in methanol solution with tert‐butyl isocyanide by insertion and ring enlargement to form the four‐membered ring system 12 . Compound 12 was also characterized by X‐ray diffraction.