Synthesis and reactivity of closo -decaborate anion derivatives with multiple carbon–oxygen bonds

Some methods of functionalization of closo -borate anions on the example of the interaction with carboxylic acids are considered. Oxonium derivatives of closo -decaborate anion [2-B 10 H 9 OC(OR)CH 3 ] − (R = H, Et) were prepared and transformed upon subsequent heating into 2,6-disubstituted derivative [2,6-B 10 H 8 (O 2 CCH 3 )] − . The obtained compounds were characterized by IR and NMR ( 1 H, 11 B, 13 C) spectroscopies. The crystal structure of (Bu 4 N)[2,6-B 10 H 8 (O 2 CCH 3 )] was determined by X-ray diffraction. The interaction between the anion [B 10 H 11 ] − and carboxylic acids and esters has stepwise nature. The first step leads to monosubstituted products with equatorial located substituent, that forms as a result of nucleophilic attack of the carbonyl oxygen of reagent. The second stage is conducted at ca. 100 °C resulting in the formation of 2,6-disubstituted product [2,6-B 10 H 8 O 2 CCH 3 ] − . • New carbooxonium derivatives of closo -decaborate anion were discovered. • A novel method of the preparation of (Bu 4 N)[2,6-B 10 H 8 (O 2 CCH 3 )] was proposed. • The crystal structure of (Bu 4 N)[2,6-B 10 H 8 (O 2 CCH 3 )] was determined.