1,8-Bis(tetramethylguanidino)naphthalene (TMGN): A New, Superbasic and Kinetically Active “Proton Sponge”

✍ Scribed by Volker Raab; Jennifer Kipke; Ruth M. Gschwind; Jörg Sundermeyer

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 399 KB
• Volume: 8
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20020402)8:7<1682::aid-chem1682>3.0.co;2-r

✦ Synopsis

1,8-Bis(tetramethylguanidino)naphthalene (TMGN, 1) is a new, readily accessible, and stable ™proton sponge∫ with an experimental pK 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. DG = values obtained by spectra simulation reveal a concerted mechanism of rotation about the CÀN bonds of the protonated forms of TMGN.