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(A-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 Ir-I with the benzothiazolin- 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 Ir-I complex 4 with an N-propyl-substituted carbene ligand, while deprotonation with (KOBu)-Bu-t gave the five-coordinated IrI complex [IrBr(cod)(eta(2)-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 sigma-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.