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1,8‐Bis(tetramethylguanidino)naphthalene (TMGN): A New, Superbasic and Kinetically Active “Proton Sponge”
Author(s) -
Raab Volker,
Kipke Jennifer,
Gschwind Ruth M.,
Sundermeyer Jörg
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(20020402)8:7<1682::aid-chem1682>3.0.co;2-r
Subject(s) - chemistry , naphthalene , protonation , steric effects , proton , nucleophile , medicinal chemistry , stereochemistry , nmr spectra database , hydrolysis , proton nmr , crystallography , computational chemistry , spectral line , organic chemistry , catalysis , ion , physics , quantum mechanics , astronomy
1,8‐Bis(tetramethylguanidino)naphthalene (TMGN, 1 ) is a new, readily accessible, and stable “proton sponge” with an experimental p K BH +value of 25.1 in MeCN, which is nearly seven orders of magnitude higher in basicity than the classical proton sponge 1,8‐bis(dimethylamino)‐naphthalene (DMAN). Because of the sterically less crowded character of the proton‐accepting sp 2 ‐nitrogen atoms, TMGN also has a higher kinetic basicity than DMAN, which is shown by time‐resolved proton self‐exchange reactions. TMGN is more resistant to hydrolysis and is a weaker nucleophile towards the alkylating agent EtI in comparison to the commercially available guanidine 7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD). Crystal structures of the free base, of the mono‐ and bisprotonated base were determined. The dynamic behavior of all three species in solution was investigated by variable‐temperature 1 H NMR experiments. Δ G ≠ values obtained by spectra simulation reveal a concerted mechanism of rotation about the C−N bonds of the protonated forms of TMGN.