Synthesis of Bifunctional Boron‐Lewis Acids – Thorough Investigation of the Adduct Formation with Pyrimidine

Abstract

Three bifunctional boron‐Lewis acids based on a 1,2‐diethynylbenzene backbone were synthesized using a tin‐boron exchange protocol in good to very good yields. Complexation experiments with pyrimidine were thoroughly investigated using the example of 1,2‐bis(benzo[d][1,3,2]dioxaborol‐2‐ylethynyl)benzene (3) in solution, in the solid phase and by quantum‐chemical calculations. Two adducts were structurally investigated by X‐ray diffraction experiments. DOSY‐/VT‐NMR experiments gave insight into the dynamic behaviour of the synthesized poly‐Lewis acids with pyrimidine.

Tridentate Lewis Acids Based on Tribenzotriquinacene Chalices

“…This suggests that the Lewis acidity of the aluminium atom attached to terminal alkynes is slightly higher, than that of the aluminium atom adjacent to vinyl functions, which is explicable by their different group electronegativities. It is noteworthy that the signal of the SiMe 3 groups of the Bis substituents of 5 ⋅ 3Py is split into two singlets (0.50 and 0.14 ppm), due to the increased hindrance of the rotation of the bulky substituents by complexation of pyridine [7a,b] . The chemical shift of −0.78 ppm of the methine hydrogen atoms (Al−C H ) is in agreement with similar compounds and indicates tetra‐coordination at the aluminium atom [11] .…”

Bidentate boron Lewis acids: synthesis by tin boron exchange reaction and host–guest complex formation

“…A rigid organic scaffold is required to ensure selective complexation of the guest molecule. To provide this rigidity, they are usually based on aromatic backbones such as phenylene, 22 naphthalene 13 or anthracene. 33 The element which serves as Lewis acid component in such systems as well as the distance between the functions is crucial for their host-guest chemistry, as it determines the selectivity towards potential guest molecules.…”

“…[1][2][3] Like their Lewis base counterparts, PLAs find applications in catalysis, [4][5][6][7][8] anion sensing [9][10][11][12][13][14][15][16][17][18][19][20] or small molecule recognition. [21][22][23] PLAs combine multiple Lewis acid functions via a mostly organic backbone. Although a wide variety of elements are used in PLAs, such as silicon, 24 tin, 25,26 antimony 11,27,28 or mercury, 29 a high percentage of PLAs contain group 13 elementsparticularly boron 12,21,[30][31][32][33] due to their natural electron deficiency.…”

Hexadentate poly-Lewis acids based on the bowl-shaped tribenzotriquinacene

“…Of course, there are also examples of PLAs with elements of the fifth group, such as the bidentate antimony-based system developed by Gabbaï et al 9 The synthesis of the Lewis acids is typically carried out by salt elimination, exchange reactions or hydrometallations. In addition to their applications in anion sensing 3 b ,5 a , b ,10 and catalysis, 5 g ,11 the complexation of small molecules in host–guest experiments, 7 d ,12 is the subject of current research. While early examples of PLAs were often based on small organic backbones such as alkyl 5 b ,6 d or phenyl derivatives, 7 a ,13 there is now a wide range of examples based on larger backbones, including derivatives of naphthalene, 5 a ,14 anthracene 5 c , d ,6 d ,9 b and even cyclic molecules.…”