Diastereoselective self-assembly of chiral diamine-chelated aryllithiums to dimeric aggregates

Aryllithium compounds [LiC6H4(CH2N(Et) CH2CH2NEt2)-2]2(2b), [LiC6H4(CH(Me)N(Me)CH2-CH2NMe2-(R))-2]2((R)-3b), and [LiC6H4(CH(Me)N(Me)CH2CH2NMe2-(rac))-2]2((rac)-3b) were synthesized and characterized in the solid state and in solution. X-ray crystallographic studies of 2b and (R)-3b and molecular weight determinations of 2b, (R)-3b, and (rac)-3b by cryoscopy in benzene showed that, both in the solid state and in apolar, noncoordinating solvents such as benzene, these compounds exist as discrete dimeric aggregates. For (R)-3b and (rac)-3b the aggregation process of two monomeric aryllithium units to one dimer is highly diastereoselective