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 Ir I with the benzothiazolin-2-ylidene ligand could be achieved via precoordination of the allyl substituent of (H- 1 ) + to [Ir(cod)(MeCN) 2 ]BF 4 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 KO t Bu gave the five-coordinated Ir I complex [IrBr(cod)( η 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 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.