Bidentate Lewis Acids Derived from o‐Diethynylbenzene with Group 13 and 14 Functions

Abstract

Starting from 1,2‐diethynylbenzene, a series of bidentate Lewis acids was prepared by means of hydrometalations, in particular hydrosilylation, hydroboration, hydroalumination and terminal metalation based on group 13 and 14 elements. In the case of terminal alkyne metalation, the Lewis‐acidic gallium function was introduced using triethylgallium under alkane elimination. A total of six different Lewis acids based on a semiflexible organic scaffold were prepared, bearing −SiClMe 2 , −SiCl 2 Me, −SiCl 3 , −B(C 6 F 5 ) 2 , −AlBis 2 (Bis=bis(trimethylsilyl)methyl) and −GaEt 2 as the corresponding functional units. In all cases, the Lewis acid functionalisation was carried out twice and the products were obtained in good to excellent yields. In the case of the twofold gallium Lewis acid, a different structural motif in the form of a polymer‐like chain was observed in the solid state. All new bidentate Lewis acids were characterised by multinuclear NMR spectroscopy, CHN analysis and X‐ray diffraction experiments.

Selectivity in Adduct Formation of a Bidentate Boron Lewis Acid

“…While a flexible backbone -as in the ethylenebased Lewis acid B of Shriver and Biallas [23] -should bind a wider range of guest molecules, a selective complexation requires a more rigid organic framework. Such frameworks are usually based on aromatic backbones (phenylene-, [24] naphthalene-, [25] biphenylene-, [1] anthracene- [26] ) and are sometimes substituted with alkynyl spacers. These spacers allow a certain degree of adaption of the cavity (semi-rigid) to the spatial requirements of the guest molecule and prevent a steric repulsion between the complexed guest molecule and the backbone.…”

Hydroalumination of 1,8-Diethynylanthracenes–Al-based Bis-Lewis-Acids and their Isomerization and Complexation Behavior

“…Within the field of main group chemistry, compounds such as frustrated Lewis pairs − or poly-Lewis acids (PLAs) containing main group elements as reactive sites–including octet compliant metallacyclo-compounds − along with systems of low-coordinate, electron-deficient Lewis centers anchored to organic backbones − –have been of special interest in the last decades, since most main group (semi-)metals are more abundant and the utilized compounds are often less toxic than analogous transition metal-based molecules. PLAs containing main group elements can be used in small molecule recognition, ,,,− anion sensing, ,,,,,,,− or in catalysis. ,− ,, This is why we focus on PLAs containing group 13 elements such as aluminum, boron, or gallium as active sites.…”

“…Hydroboration reactions have been reported for polyalkynyl-substituted phenylendiyl backbones 31,57 as well as for poly-alkynyl-substituted anthracene derivatives. 28 In the latter example, we obtained a fourfold boron-functionalized molecule from the twofold hydroboration of the two ethynyl units in 1,8diethynylanthracene.…”