B(C6F5)3-Mediated Transformations and Hydrogenation of Carbodiimides

• Published in: Chemistry : a European journal 2015-01, Vol.21 (5), p.2193-2199
• Main Authors: Holthausen, Michael H., Colussi, Mariah, Stephan, Douglas W.
• Format: Article
• Language: English
• Subjects: amidines; carbodiimides; Chemistry; cyanamides; frustrated Lewis pairs; hydrogenation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201405014

The reactivity of a series of carbodiimides RNCNR (R=tBu (1 a), iPr (1 b), SiMe3 (1 c), and Dipp (2,6‐di‐iso‐propylphenyl (1 d)) with B(C6F5)3 was investigated. After initial adduct formation, several distinct reaction pathways were identified. These pathways involve either isomerization of the carbodiimide to cyanamide derivatives or insertion of a carbodiimide into a BC bond of B(C6F5)3 to yield four‐membered heterocycles. In the presence of dihydrogen, stepwise hydrogenation of the heteroallene moiety in the carbodiimides was achieved, which yielded the respective amidine–B(C6F5)3 adducts and amidinium borate salts upon reaction with one or two equivalents of H2, respectively. Frustrated Lewis pairs: Reactions of carbodiimides (RNCNR) with B(C6F5)3 yield either four‐membered boron amidinate heterocycles or cyanamide derivatives depending on the nature of the substituents. In the presence of dihydrogen, mixtures of RNCNR and B(C6F5)3 are amenable to stepwise hydrogenation. The reaction with one or two equivalents of H2 yields amidine or amidinium borate‐type products, respectively (see scheme).