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Schlenk's Early “Free” Carbanions
Author(s) -
Harder Sjoerd
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020715)8:14<3229::aid-chem3229>3.0.co;2-3
Subject(s) - carbanion , delocalized electron , chemistry , crystallography , crystal (programming language) , ion , carbon atom , atom (system on chip) , crystal structure , stereochemistry , ring (chemistry) , organic chemistry , computer science , embedded system , programming language
Nearly a century ago, Schlenk published the syntheses and isolation of two most remarkable and unstable complexes: crystalline [Ph 3 C − ][Me 4 N + ] and [PhCH 2 − ][Me 4 N + ]. The crystal structure of the first complex contains a “free” Ph 3 C − ion, which displays the expected planar trigonal geometry at its central carbon atom. The phenyl groups are not orientated in the typical propeller arrangement, but instead display various orientations with respect to the molecular plane. These orientations can be directly related to the extent of charge delocalization and correlate well with other structural characteristics related to charge delocalization. The crystal structure also shows a network of CH δ + ⋅⋅⋅C δ − and CH⋅⋅⋅π interactions. Only CH⋅⋅⋅π interactions to the most negative charged phenyl rings are observed. The absolute Brønsted acidity of Me 4 N + is calculated by the G2(MP2) method (287.7 kcal mol −1 ) and is compared to the calculated acidity of Me 4 P + (268.4 kcal mol −1 ). On this basis, the p K a value for Me 4 N + is estimated at 29.6. This makes the existence, and especially Schlenk's early isolation, of the “free” carbanions [Ph 3 C − ][Me 4 N + ] and [PhCH 2 − ][Me 4 N + ] quite noteworthy.