Affiliations: Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA | Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
Abstract: The structures of unsolvated {Li[1,1′,3-(SiMe3)3C3H2]}2 ([LiA″]2) and {K[1,3-(SiMe3)2C3H3]}∞ ([KA′]∞) are reported. The base-free complex LiA″ is a dinuclear species in the solid state in which the two Li atoms are bridged by the allyls in a µ2-η1, η2 fashion. The Li—C σ-bonded distance is 2.232(7) Å; the Li—C η2-interaction occurs at distances of 2.230(7) Å and 2.241(6) Å. Density functional theory calculations on [Li(C3H5)]2 and {Li[1,1′,3-(SiH3)3C3H2]}2 indicate that inclusion of the silyl groups is critical to reproducing the distortions observed in [LiA″]. The structure of the solvated Li(C3H5)(thf)2 complex is calculated to be stable as a dimer, consistent with previous measurements on allyllithium in THF solution. Like related DME and THF solvates, [KA′]∞ is a coordination polymer with potassium ions linked by bridging π-allyl ligands; in [KA′]∞ the polymer takes the form of helical chains with a broad range of K–C distances (2.87–3.15 Å).
Keywords: lithium, potassium, allyl, crystal structure, bulky ligands, trimethylsilyl group
