Nonorthogonal Dilithium-1,3-biborataallenes Containing Planar-Tetracoordinate Carbon Atoms.

Deviations of up to 36° from the orthogonality of the planes of the terminal B atoms of the allene skeleton and their neighbors (ipso-C atoms) are observed in tetraaryl-1,3-diborataallenes of contact-ion triples 1. The unusual geometries are caused by steric hindrance between ortho-methyl groups, which is induced by interactions of the lithium counterions with the π electrons of the aryl substituents, as well as by small barriers to planarization of 1,3-diborataallenes. Ar=for example, 2,3,5,6-tetramethylphenyl.