Abstract
A series of novel cobalt bis(dicarbollide) based amidines were synthesized by the nucleophilic addition of primary and secondary amines to highly activated B-N+≡C–R triple bond of the propionitrilium derivative [8-EtC≡N-3,3′-Co(1,2-C2B9H10)(1′,2′-C2B9H11)]. The reactions with primary amines result in the formation of mixtures of E and Z isomers of amidines, whereas the reactions with secondary amines lead selectively to the E-isomers. The crystal molecular structures of E-[8-EtC(NMe2)=HN-3,3′-Co(1,2-C2B9H10)(1′,2′-C2B9H11)], E-[8-EtC(NEt2)=HN-3,3′-Co(1,2- C2B9H10)(1′,2′-C2B9H11)] and E-[8-EtC(NC5H10)=HN-3,3′-Co(1,2-C2B9H10)(1′,2′-C2B9H11)] were determined by single crystal X-ray diffraction.
Highlights
Nucleophilic addition reactions to the highly polarized –N+≡CR triple bonds in aryl- and alkylnitrilium salts [30] and nitrile complexes of transition metals [31,32,33,34,35] are widely used in organic synthesis and have large potential in the modification of polyhedral boron hydrides [36]
We report on the synthesis of boronated amidines by nucleophilic addition of primary and secondary amines to the propionitrilium derivative of cobalt bis(dicarbollide)
Amidine derivatives are commonly used for the synthesis of many important heterocycles such as imidazoles, triazoles, thiazoles, oxadiazoles, pyrimidines, pyridines and triazines
Summary
Cobalt bis(dicarbollide) [3,3 -Co(1,2-C2B9H11)2]− is the most available and the most stable of metallacarboranes [1,2,3,4], which attracts considerable attention of researchers due to possibility of its use in a variety of fields, from the development of new materials [5,6,7,8,9,10,11,12] to medicine [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. The development of new convenient methods for the functionalization of cobalt bis(dicarbollide) cobalt is an important task [3,4]. One of the convenient methods for the functionalization of the cobalt bis(dicarbollide) anion is the ring opening of its cyclic oxonium derivatives with various nucleophiles [29]. Another promising method is the addition of nucleophiles to the nitrilium derivatives of cobalt bis(dicarbollide). Nucleophilic addition reactions to the highly polarized –N+≡CR triple bonds in aryl- and alkylnitrilium salts [30] and nitrile complexes of transition metals [31,32,33,34,35] are widely used in organic synthesis and have large potential in the modification of polyhedral boron hydrides [36].
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