1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetrafluoridoborate

Abstract

The asymmetric unit of the title compound, C17H13N4 +·BF4 −, contains one half of the benzimidazolium cation and one half of the tetra­fluoridoborate anion, with crystallographic mirror planes bis­ecting the mol­ecules. One F atom of the tetra­fluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C—H⋯F inter­actions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F⋯π contacts involving the tetra­fluoridoborate anions and the five-membered rings [F⋯centroid = 2.811 (2) Å].

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

“…To avoid this complication 1,2-dibromobenzene had to be applied to eventually approach the preparation of 7 . For 8 a reported synthetic procedure was used [ 48 – 49 ] consisting of nucleophilic aromatic substitutions (S N Ar) of benzene-1,2-diamine at 2-chloropyridine ( Scheme 1 ). Once all the different N 1 , N 2 -diarylbenzene-1,2-diamines were prepared a method had to be developed to build up the imidazolium salts by ring closure.…”

“…3 -Cl and 4 -Cl could principally be obtained from the corresponding N 1 , N 2 -diarylbenzene-1,2-diamines via two different cyclization pathways leading to the benzimidazolium salts 3 -Cl [ 44 ] and 4 -BF 4 [ 48 ] ( Scheme 2 ). But we also planned to access the chloride compounds 1 -Cl, 3 -Cl and 4 -Cl reported previously as tetrafluoroborate [ 48 ] and chloride [ 45 ] salts for two reasons: we wished to find a faster way to access them and it seemed advantageous to aim preferentially at the synthesis of benzimidazolium chlorides than at [BF 4 ] − salts, since in case the carbene will be generated in “in situ” reactions in the presence of metal complexes, the lower stability of the [BF 4 ] − anion could lead to complications generating side-products [ 50 – 52 ]. The preparations of both 3 -Cl and 4 -Cl started along the given lines with the syntheses of the respective aryl-substituted diamines, which had to undergo ring closure in the presence of a C 1 component.…”

“…For 3 -Cl and 4 -Cl the synthetic procedures proceed without noticeable problems, while complications were faced in the synthesis for 1 -Cl and 2 -Cl, particularly during the benzimidazole ring closures. Excluding the procedure of Borguet [ 42 – 43 ] all the known procedures to accomplish imidazole ring formation [ 44 – 45 48 , 53 – 54 ] of either 6 and 7 failed.…”

“…The high resolution ESI were performed by the Mass Service of the University of Zurich using a Bruker maXis apparatus. The compounds 5 [ 44 ], 6 [ 52 ], 7 [ 46 ], 8 [ 47 – 48 ] were prepared according to literature with small modifications.…”

1,3-Bis(6-methylpyridin-2-yl)-1H-imidazol-3-ium hexafluorophosphate

“…For the isolation of an N-heterocyclic carbene, see: Arduengo et al (1991). For related structures, see: Huang et al (2011); Grieco et al (2011); Kim et al (2009). For applications of Nheterocyclic carbenes in catalytic processes, see: Enders et al (1996); Frenzel et al (1999); Scholl et al (1999).…”