Green synthesis and structural characterisation of a novel tetraoxadisiladiborocane-bridged thiadiazole oligomer and its transformation into a hydrogen-bonded 1D polymer

Abstract

This study reports on the synthesis and characterization of novel cyclodiboradisiloxane derivatives. A one-pot 2+2 cyclo-condensation reaction of diphenylsilanediol and phenylboronic acid produced an eight-membered 2,2,4,6,6,8-hexaphenyl-1,3,5,7,2,6,4,8-tetraoxadisiladiborocane (Ph₆B₂Si₂O₄) (3). The reaction of compound 3 with 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L) and phenylboronic acid produced an oligomer (4) and a hydrogen-bonded-induced 1D polymer (5), respectively. Products (4 and 5) have been characterized by melting point, FT-IR spectroscopy, nuclear magnetic resonance, and single-crystal X-ray diffraction. Single-crystal X-ray diffraction revealed triclinic crystal systems with centrosymmetric space group for compounds 4 and 5. On the other hand, the hydrogen-bonded induced 1D polymer [Ph₆B₂Si₂O₄]·2L·2[PhB(OH)₂] is colourless blocky cocrystals which also crystallized in the triclinic crystal system with a centrosymmetric space group of P-1. These two novel products (4 and 5) exhibit various intermolecular and intramolecular π-π non-covalent interactions and hydrogen bonds in their crystal packing. Compound 4 shows intramolecular non-covalent C-H···π (3.427 Å), C-H···N (2.601 and 2.684 Å), C-H···O (2.360 and 2.684 Å), C-H···S (2.601 Å and 2.701 Å) interactions in its crystal packings. In addition, compound 4 also displays some intermolecular short distance non-covalent interactions in its crystal packing such as π centroid···π centroid (3.805 Å) and C-H17A···π centroid (3.112 Å). On the other hand, the crystal packing of compound 5 also shows intra-molecular non-covalent C-H···π 3.440 Å, C-H···N 2.563 Å, C-H···O 2.654 Å, C-H···S 2.876 Å and H···B 2.939 Å interactions. Furthermore, compound 5 also exhibits short noncovalent intermolecular interactions in its crystal packing such as π···π, (3.362 Å, C14-C3 and 3.243, C11-C37), CH···π (2.587 Å, CH37A···πC38 and 2.452 Å, H7A···O42). The individual molecules of compounds 4 and 5 interact intermolecularly via C-H···N, C-H···O, C-H···S and N-B. Therefore, this study demonstrates the potential for the production of novel materials via the combination of cyclodiboradisiloxane (a Lewis acid) and a nitrogen-, oxygen-, and sulphur-containing ligand (a Lewis bases).