STERICALLY CONGESTED MOLECULES .5. TRIMERIC [ALPHA-(1,1,3,3-TETRAMETHYL-2-INDANYLIDENE)BENZYL]LITHIUM - STRUCTURAL EXAMPLE OF AN UNSOLVATED VINYLLITHIUM DERIVATIVE

The X-ray structure of [alpha-(1,1,3,3-tetramethyl-2-indanylidene)benzyl]lithium discloses the stabilization of a vinylic carbanion by two lithium cations in a hydrocarbon milieu. Each lithium cation is in turn coordinated to two carbanion centers and additionally to one aromatic CC bond as well as to one CH bond of a methyl group. These bonding interactions result in an unsolvated trimer with pseudo-C3 symmetry. Moderate strain along the CC double bond can be discerned for the phenyl substituent in front of the rigid 1,1,3,3-tetramethyl-2-indanylidene moiety within each one of the monomeric subunits. (C20H21Li)3 crystallizes triclinic with Z = 2, space group P1BAR (No. 2), a = 12.854 (4) angstrom, b = 13.010 (4) angstrom, c = 16.011 (5) angstrom, alpha = 109.21 (2)-degrees, beta = 94.73 (3)-degrees, gamma = 92.52 (3)-degrees.