2000608 (1 of 7) © 2020 Wiley-VCH GmbH www.mrc-journal.de COMMUNICATION Synthesis of Tricyclic Laddersiloxane with Various Ring Sizes (Bat Siloxane) Thanawat Chaiprasert, Yujia Liu, Pa-kwan Intaraprecha, Rungthip Kunthom, Nobuhiro Takeda, and Masafumi Unno* T. Chaiprasert, Prof. Y. Liu, P.-k. Intaraprecha, Dr. R. Kunthom, Prof. N. Takeda, Prof. M. Unno Department of Chemistry and Chemical Biology Graduate School of Science and Technology Gunma University Kiryu 376–8515, Japan E-mail: unno@gunma-u.ac.jp The ORCID identifcation number(s) for the author(s) of this article can be found under https://doi.org/10.1002/marc.202000608. DOI: 10.1002/marc.202000608 example, catalyst support materials, [14,15] electronic materials, [16] and hybrid organic–inorganic semiconducting frag- ments. [17] Tricyclic laddersiloxanes with syn- and anti-structures, which are depend on the structure of starting pre- cursors, have typically been prepared through the base-catalyzed cleavage of cage hexasilsesquioxanes, [18] condensa- tion of cyclic silanols with dichlorosi- lane, [6,11,19,20] or isocyanate-substituted siloxanes with silanols, [21,22] and oxida- tion of ladder oligosilanes. [23] To the best of our knowledge, tricyclic laddersi- loxanes have been limited to 6-8-6- and 8-8-8-membered-ring systems. [3,11] According to earlier work, several studies indicated that siloxane bond can be formed by the coupling of silyl hydride in the presence of water mediated by B(C 6 F 5 ) 3 , [24] since B(C 6 F 5 ) 3 can coordinate with water. [25] Here we developed a new synthetic method for tricyclic lad- dersiloxanes involving B(C 6 F 5 ) 3 -catalyzed intramolecular cycli- zation of an extended Janus ring, as shown in Scheme 1A. By utilizing this method, we successfully obtained unprec- edented laddersiloxanes containing larger 12-membered rings (Scheme 1B). In this work, the products can be recognized as bat-shape siloxane, due to their rigid inorganic siloxane T 4 as core body with fexible oligosiloxane wings as side rings. Starting materials JP-01 to JP-04 (Table 1, entries 1 and 2) were successfully synthesized in three steps as shown in Scheme 1C. First, the siloxanolate salts ([RSi(O)OM] 4 ) (R = Ph, CHCH 2 ; M = Na, K) were prepared according to the alka- line-metal-directed hydrolytic condensation of alkoxysilanes according to Shchegolikhina and coworkers. [26–28] The impor- tant key for the all-cis structure formation is the metal-directed self-assembly strategy. [27] Among four possible stereoisomers, all-cis structure was obtained exclusively because of the sta- bilization of the intermediates in polar solvents. Next, these siloxanolate salts were carefully hydrolyzed using acetic acid to aford silanol products. [29] However, we found that hydrolysis of potassium siloxanolate [(CHCH 2 )Si(O)OK] 4 provided poly- meric products. Then, these silanol products (R = Me, Ph, i-Bu) or potassium siloxanolate salts (R = vinyl) were treated with chlorosilanes to aford extended Janus ring precursors JR-01 to JR-04 (Scheme S1 and Table S1, Supporting Information). Extended JR-05 could be prepared through the oxidation of JR-01 using meta-chloroperoxybenzoic acid (m-CPBA), followed by nucleophilic substitution with SiMe 2 HCl (Scheme S4, Sup- porting Information). [30] Examination of the reaction conditions A new synthetic method for tricyclic laddersiloxanes, ladder-type silses- quioxanes with defned structures, is developed based on intramolecular cyclization of hydrosilyl-functionalized cyclic siloxanes. This method enables the construction of unprecedented laddersiloxanes with various ring sizes. Herein, the preparation of tricyclic laddersiloxanes containing 6-8-6-, 8-8-8-, or 12-8-12-membered-ring systems is reported. These products can be consid- ered as bat-shape siloxanes, owing to their rigid inorganic siloxane body with fexible oligosiloxane “wings” as side rings. The synthesized compounds are potential building blocks for well-defned nanomaterials, porous materials, and host molecules. Recently, siloxane compounds have attracted signifcant research interest because of their potential for industrial application in cosmetics, body care products, lubricants, and nanofllers for thermal stability enhancement. [1,2] Laddersi- loxanes can be considered as hybrid molecules because of their ladder-shaped rigid inorganic fused siloxane rings that feature adaptable organic substituents. [3] Following the frst proposal of laddersiloxane structures by Brown et al., [4,5] we developed various tricyclic, [6] pentacyclic, [7] heptacyclic, [8] non- acyclic, [9] and polycyclic [10] laddersiloxanes as well as tricyclic laddersiloxanes with reactive organic substituents. [11] All of these laddersiloxanes have signifcant thermal stability, and the laddersiloxane structure has shown the highest refrac- tive index and Abbe number among linear, cyclic, and cage silsesquioxanes. [12] In addition, we recently reported the application of tricyclic laddersiloxanes to porous materials for the removal of dyes and heavy metal ions from water. [13] The syntheses, structures, and properties of laddersiloxanes, including those prepared by other groups, have been summa- rized in a review. [3] Owing to their unique properties, laddersiloxanes are becoming attractive precursors in countless applications, for Macromol. Rapid Commun. 2020, 2000608