Bicyclo|3.2.1]octa-2,6-dienyllithium and -potassium Chemistry Solvation, Aggregation, and 119S n - 7Li Coupling of Stannylated Derivatives

The 13C N M R spectra o f bicyclo[3.2. l]octa-2,6-dienyl anion (1) as the lithium (ILi) and the potassium salt (1 K) were recorded at various tem peratures and in different solvents. The re­ sults show IK to exist as a contact ion pair (CIP), whereas for ILi solvent separated ions (SSIP) are also found as the tem perature is lowered and when the solvating pow er o f the sol­ vent is increased. In the 7Li N M R spectra a t very low tem perature the signals o f the SSIP dis­ appear and only those o f a m onom eric C IP and a triple ion (1 Li 1) consisting o f two carbanions and one lithium cation are present. F o r independent confirm ation, the h itherto unknow n 6-, 7-, and 3-trim ethylstannyl substituted bicyclo[3.2.1]octa-2,6-dienyllithium derivatives 2aLi, 2bLi, and 3Li were synthesized and also studied by u 9Sn, l3C, and 'H N M R . A ccording to the tem perature dependence o f the <5(13C)-values the C IP/SSIP-equilibrium o f 2 a Li in T H F / T M E D A is shifted to the C IP side. The observation o f a unique l|yS n 7Li coupling (6.2 Hz) shows tha t at 9 0 °C a species containing 2a and lithium exists under slow exchange condi­ tions. A sim ilar coupling o f 3.5 Hz can be estim ated for 3 Li. A m ixture o f the epim eric carbanions 2a and 2b yields two sets o f 13C N M R signals which are due to the diastereom eric triple ions 2 aLi 2 a and 2 aLi 2 b.