BN cleavage of the azoniaboratacyclopropane ring by H 2O and by carbonyl and nitrile derivatives: crystal structure of (CF 3) 2B(OH)CH(SiMe 3)NHMe 2, (CF 3) 2[formula omitted] and (MeC(O)NH)(CF 3) 2BCH(SiMe 3)NHMe 2

Abstract

1,1-Dimethyl-2,2-bis(trifluoromethyl)azoniaboratacyclopropane derivatives (CF 3) 2 BCHRN Me 2 (R = H ( I), SiMe 3 ( II)) react with H 2O with cleavage of the NB bond to form (CF 3) 2B(OH)CHRNHMe 2 (R = H ( III), SiMe 3 ( IV)). Carbonyl compounds R 1R 2CO are inserted into the NB bond of I and II to yield the five-membered heterocycles (CF 3) 2 BCHRNMe 2CR 1R 2O (R = H, R 1 = R 2 = Et ( V); R = SiMe 3, R 1 = H, R 2 = Me ( VI), R 1 = R 2 = Me ( VII), Et ( VIII), R 1 = Me, R 2 = CH CMe 2 ( IX), CCMe(CH 2) 2C H 2) ( X). Similarly nitriles insert to form (CF 3) 2 BCHRNMe 2CR 1N (R = H, R 1 = CHClME ( XI); R = SiMe 3, R 1 = Me ( XII), CHClME ( XIII), Ph ( XIV)). The reaction of H 2CCHCH 2CN with II is accompanied by a shift in the CC bond whereby the substituent R 1 = trans-CHCHMe ( XV) is formed. Hydrogen cyanide combines with II to yield (CF 3) 2B(CN)CH(SiMe 3)NHMe 2 ( XVI). The nitrile derivatives XI–XIV are hydrolysed with formation of (R 1C(O)NHCF 3) 2BCHRNHMe 2 (R = H, R 1 = CHClME ( XVII; R = SiMe 3, R 1 = Me ( XVIII), CHClME ( XIX), Ph ( XX)). The novel boranes have been characterized by elemental analyses, multinuclear NMR, IR and mass spectra. The structures of IV and VII in a mixed crystal and of XVIII have been investigated crystallographically. In the solid state, IV and XVIII show intramolecular NH ⋯ O hydrogen bondings which leads to formation of five- and seven-membered rings respectively. Steric repulsion between the CF 3 and SiMe 3 groups leads to large BCSi bond angles (average, 124.1(8)°) and variable BCHSiN bond distances (1.604) Å in VII to 1.690(4) Å in IV).