A Quest for Ligand‐Unsupported Li⁺–π Interactions in Mono‐, Di‐, and Tritopic Lithium Arylborates

Abstract

Abstract The lithium salts of selected mono‐, di‐, and tritopic arylborates have been synthesized and their solid‐state structures have been analyzed by X‐ray crystallography with focus on the occurrence of Li + –aryl π interactions. The solvated salts of the monotopic arylborate [Li(thf) 4 ][( p ‐BrC 6 H 4 )BPh 3 ] as well as the ditopic borates [Li(12‐crown‐4) 2 ] 2 [ p ‐C 6 H 4 (BMe 3 ) 2 ] and [Li(tetraglyme)] 2 [ p ‐C 6 H 4 (BPh 3 ) 2 ] exist as solvent‐separated ion pairs in the crystal lattice. The attachment of two moderately coordinating monohydridoborate functionalities on a benzene ring leads to Li + –hydride interactions. In the case of [Li(thf) 3 ] 2 [ p ‐C 6 H 4 {9‐BBN(H)} 2 ] [9‐BBN(H) = 9‐borabicyclo[3.3.1]nonane], this additional attractive force is not sufficient to promote Li + –aryl π interactions, however, the 1,2‐dimethoxyethane (DME) solvate [Li(dme) 2 ] 2 [ p ‐C 6 H 4 {9‐BBN(H)} 2 ] shows a remarkably short contact between the Li + cation and the adjacent phenylene ipso carbon atom [Li–C 2.366(2) Å]. The targeted structural motif ofLi + –arene η 6 coordination was finally observed in the solid‐state structures of the tritopic borates [{Li(12‐crown‐4) 2 } 2 Li(thf)][1,3,5‐C 6 H 3 (BMe 3 ) 3 ] and [{Li(thf) 2 } 2 Li][1,3,5‐C 6 H 3 (BH 3 ) 3 ]. In the latter complex, an extensive network of Li–H–B bonds is observed in addition to the Li + –π interaction.