Reactivity of the triple ion and separated ion pair of tris(trimethylsilyl)methyllithium with aldehydes: a RINMR study.
Low-temperature rapid-injection NMR (RINMR) experiments were performed on tris(trimethylsilyl)methyllithium. In THF/Me2O solutions, the separated ion (1S) reacted faster than can be measured at -130 degrees C with MeI and substituted benzaldehydes (k >/= 2 s -1), whereas the contact ion (1C) dissociated to 1S before reacting. Unexpectedly, the triple ion reacted faster with electron-rich benzaldehydes relative to electron-deficient ones. The addition of HMPA had no effect on the rate of reaction of the triple ion with p-diethylaminobenzaldehyde, and the immediate product of the reaction was the HMPA-solvated separated ion 1S, with the Peterson product forming only slowly. Thus, the aldehyde is catalyzing the dissociation of the triple ion. HMPA greatly decelerated the reaction of 1S (<10 -10), providing an estimate of the Lewis acid activating effect of a THF-solvated lithium cation in an organolithium addition to an aldehyde.
Jones
Amanda C
AC
Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, USA.
Sanders
Aaron W
AW
Sikorski
William H
WH
Jansen
Kristin L
KL
Reich
Hans J
HJ
D000447:Aldehydes / Q000737:chemistry*; D006492:Hempa / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry*; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
D000447:Aldehydes; D009942:Organometallic Compounds; D014297:Trimethylsilyl Compounds; C520093:methyllithium; D006492:Hempa