Akademik Veri Yönetim Sistemi
BORON2025 International Boron Symposium, Ankara, Türkiye, 3 - 05 Aralık 2025, ss.1, (Özet Bildiri)
A significant amount of research has been devoted to investigate stereogenism in compounds with tetra-coordinated main group elements other than carbon like nitrogen, phosphorus, silicon, and sulfur for decades. The study of compounds with tetra-coordinated boron as a stereogenic center has not been carried out at a much more intensive level, and stereomerism that relies solely on this element has been considered elusive for a long time. For the past few years, we have had a motive to better understand the reasons leading to the formation of different stereoisomers in boron compounds. Therefore, we have been interested in preparing multi-heterocyclic structures that have a skeleton consisting of two or three boron atoms. In this study, many series of dinuclear (2) and trinuclear (3) boron complexes based on boroxane and boroxine archhitectures, respectively, were synthesized from salenH2 type symmetrical bulky ligands [HOArCH=N-R-N=CHArOH (1)], arylboronic acids (phenylboronic acid, 4-formyl/hydroxy/mercaptophenylboronic acid, dibenzofuran-/dibenzothiophene-4-boronic acid), and boric acid for the investigation of their spectral and stereogenic properties (Scheme). The salen-boron complexes are the only examples of compounds in which the stereogenism is imparted exclusively by two equivalent boron centers, giving rise to diastereoisomers. These complexes were examined for their stereogenic properties, and the effects of the R bridge linking the two salicylidene groups on the stereogenic properties originating from the boron center were investigated using the combination of nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopies for the first time by our research group. It is possible to determine the number of stereoisomers present in boron complexes using NMR data. Hovewer, NMR data is not sufficient for identifying the stereoisomer type. The type of a stereoisomer was determined based on CD. In other words, CD spectroscopy was used to decide which diastereisomer was formed in boron complexes having 2 equivalent stereogenic boron centers or to determine whether the boron complex contained only a single diastereomer or a mixture of diastereomers. It is important to note that the most significant outcome is derived from the combination of CD and NMR spectra of the boron complexes. On the other hand, stereoisomers were compared with each other for two different architectural types, dinuclear complexes based on boroxane architecture (RB-O-BR) (2) and trinuclear complexes based on boroxine architecture [(B-O-B)-(O2BPh)] (3), with seven-, eight-, nine- and eleven-membered heterocycles [(B-O-B)-(N-CH2-R-CH2-N)]. It is concluded that the number of members in the heterocycles, and planar and bulky groups included in the structure of the bor-salen complex have been suggested to be a significant factor in the formation of stereoisomers. The knowledge obtained from this study is very important not only for boron complexes stereogenic only at the boron atom but also for the other systems containing stereogenic centers and/or groups.