Synthesis and coordination chemistry of 4‐azabenzimidazole derivatives

Abstract

ABSTRACT:A facile method for the preparation of N1-(1a-6a) and N3-alkylated (1b-6b)

Synthesis of complexes bearing NH,NMe-substituted NHCs by oxidative addition of 2-halogenato-N-methylbenzimidazoles to Ni0

“…The 13 C{ 1 H} NMR spectrum showed the characteristic resonance for the C2 carbon atom at d = 104.2 ppm in the range previously observed for C2-I substituted 4-azabenzimidazoles. 16 The reaction of 1 equiv. of 1 with 1 equiv.…”

Synthesis of NHC Complexes with an N‐(2‐Oxopropyl) Group

“…[23] The C1À MÀ N3 bite angles of the chelate ligands were determined as 83.72(6) and 83.33(8)°for [2]BF 4 and [3]BF 4 , slightly smaller than 90°and in accord with previous reports on [Ir(Cp*)(C NHC^Npyridine )X] + complex cations. [23] The removal of the N-(2-oxopropyl) protecting group from Ir III coordinated imidazolin-2-ylidene [16] or 4-azabenzimidazolin-2-ylidene NHC ligands [18] has been demonstrated previously. The N-deprotection was achieved in both cases by column chromatography of the neutral NPG,N'R-NHC iridium complexes on silica gel with CH 2 Cl 2 /acetone as eluent.…”

“…However, cleavage of the NÀ PG bond proved previously impossible with the gold(I) complex bearing an N-butyl,N'-(2-oxopropyl)-4azabenzimidazolin-2-ylidene ligand. [18] Treatment of complex [4] with silver tetrafluoroborate led to abstraction of the chlorido ligand. The vacant coordination site was then occupied by the pyridine donor of a second complex molecule.…”

“…Removal of the protecting group from the coordinated NPG,N'R-NHC gave access to pNHC complexes of type B (method e, Figure 1). Benzoyl, [17] 2-oxopropyl [16,18] or diethoxymethyl [19] groups have been described as suitable protecting groups.…”

Silver and gold

“…1 The synthesis of 4-azabenzimidazole silver derivatives and transmetallation to Ir and Au has been published. 54 The synthesis of [Au(NHC)] bromides followed by oxidation to the gold(III) compounds was reported. 55,56 The reaction of imidazolium nitrates with Ag 2 O and transmetallation to [AuCl(SMe 2 )] was reported to give cationic bis-NHC metal complexes.…”