Nucleophilic Addition Reactions to 10-Acetonitrilium Derivative of <i>nido</i>-Carborane and Intramolecular NH⋯HB Interactions in <i>N</i>-Alkyl Amidines 10-RNHC(Me)=NH-7,8-C₂B₉H₁₁

Abstract

The addition reactions of water, alcohols, and primary and secondary amines to the 10-acetonitrilium derivative of nido-carborane were studied. Hydrolysis of 10-MeC≡N-7,8-C2B9H11 results in iminol 10-MeC(OH)=HN-7,8-C2B9H11, which, on treatment with a base, gives amide [10-MeC(=O)HN-7,8-C2B9H11]−. The reactions of 10-MeC≡N-7,8-C2B9H11 with alcohols lead to imidates 10-ROC(Me)=HN-7,8-C2B9H11 (R = Me, Et) as mixtures of E- and Z-isomers. In the solid state, 10-MeOC(Me)=HN-7,8-C2B9H11 adopts E-configuration. The reactions of 10-MeC≡N-7,8-C2B9H11 with primary amines result in amidines 10-RNHC(Me)=HN-7,8-C2B9H11 (R = Me, Et) as mixtures of E- and Z-isomers. In the solid state 10-EtNHC(Me)=HN-7,8-C2B9H11 was found to have the Z-configuration, which is stabilized by intramolecular N-H⋯H-B interactions between the NH group originating from the primary amine and the BH group of the carborane cage. These interactions are rather strong (3.7 kcal/mol) and are likely to persist in solution. The reactions of 10-MeC≡N-7,8-C2B9H11 with secondary acyclic (Me2NH, Et2NH) and cyclic (piperidine, morpholine) amines result in amidines 10-R2NC(Me)=HN-7,8-C2B9H11 (R = Me, Et; R2 = N(CH2)5, N(CH2CH2)2O) as single isomers, which, according to single crystal X-ray diffraction data, have the E-configuration.

Keywords

• <i>nido</i>-carborane
• acetonitrilium derivative
• amide
• iminol
• imidates
• amidines