Alkali Metal Complexes of Silyl-Substituted ansa-(Tris)allyl Ligands:Metal-, Co-Ligand- and Substituent-Dependent Stereochemistry

摘要

The structures of alkali metal complexes of silyl-substitutedansa-tris(allyl) ligands [RSi(C_3H_3SiMe_3)_3]~(3-) (R = Me, L~1; orPh, L~2)are discussed. Triple deprotonation ofL1H3bynBuNa/tmeda affords [L~1{Na(tmeda)}_3)(4) in which the so-dium cations are complexed by η~n-allyl ligands and the silylsubstituents adopt [exo,exo][endo,exo]_2stereochemistries inone crystallographically disordered form and [endo,exo]_3inanother. Triple deprotonation of L~2H_3with nBuLi/tmeda re-sults in the formation of [L~2{Li(tmeda)}_3](5),the structureofwhich features silyl substituents with [exo,exo]_2[endo,exo]stereochemistries. The trisodium complex [L~2Na{Na-(tmeda)}_2]_2(6) consists of a hexa(allylsodium) macrocyclethat aggregates as a result of cation-it interactions betweenthe phenyl substituents and the sodium cations. An attemptto prepare the tripotassium complex of L~1resulted in the for-mation of the bimetallic potassium/lithium complex [L~2{K(OEt_2)_2}_2KLi(μ_4-O/Bu)]_2(7), in which the lithiumtert-butoxide by-product is incorporated into a hexa(allylpotas-sium) macrocycle. Triple deprotonation of L~1H)3with nBuLiand the terdentate Lewis base pmdeta results in [L~1Li-(pmdeta)}_3] (8), in which the three allyl. groups do not μ-bridge between lithium cations, resulting in an [exo,exo]_3stereochemistry of the silyl substituents. NMR spectroscopicstudies reveal complicated solution-phase behaviour for 4, 6and 7, whereas the solid-state structures of 5 and 8 are pre-served in solution. Further insight into the structures andstereochemical preference of the ansa-tris(allyl) ligands in 4and 5 is provided by detailed density functional theory calcu-lations.