Benzothiazolin-2-ylidene Complexes of Iridium(I)

The reaction of allyl bromide with benzothiazole under neat conditions furnished 3-(2-propenyl)benzothiazolium bromide, (H-1)Br, in high yield. Attempts to synthesize the corresponding carbene dimer by deprotonation of (H-1)+ led to the isolation of the rearrangement product 2,3-di(2-propenyl)-2‘,3‘-dihydro-2,2‘-bisbenzothiazole (2). The reaction of [Ir(μ-OMe)(cod)]2 with the salt (H-1)Br unexpectedly afforded [IrBr(cod)(benzothiazole)] (3) (cod = 1,5-cyclooctadiene), which contained an N-coordinated unsubstituted benzothiazole ligand. The formation of carbene complexes of IrI with the benzothiazolin-2-ylidene ligand could be achieved via precoordination of the allyl substituent of (H-1)+ to [Ir(cod)(MeCN)2]BF4 and subsequent deprotonation at the C2 position of (H-1)+ by addition of base. The use of NaH as external base yielded the square planar IrI complex 4 with an N-propyl-substituted carbene ligand, while deprotonation with KOtBu gave the five-coordinated IrI complex [IrBr(cod)(η2-1)], 5. Displacement of the cod ligand in complex 4 by two CO ligands afforded the complex [IrBr(CO)2(NHC)] (NHC = 3-propylbenzothiazolin-2-ylidene), 6, which allowed an estimation of the σ-donor capabilities of benzothiazolin-2-ylidene ligands. Compounds 1−6 have been characterized spectroscopically, and the molecular structures of (H-1)Br and 2−5 were determined by X-ray diffraction.