Oxidative additions of amides to an iridium(I) metal center

Abstract

Carboxylic amides will add oxidatively via N-H activation to the complex [(COD)Ir(PMe3h]CI (where COD 1,5-cyclooctadiene) in organic solvents at 80°C to form stable iridium hydrides with the hydride arranged cis to nitrogen and trans to chloride. Acetamide will add to form the complex mer-(MeC(O)HN)IrH(PMe3)3CI which is isolable as a sticky yellow solid and soluble in all common solvents. The reaction with benzamide in toluene at 80°C produces the complex mer( PhC(O)HN)IrH(PMe3)3CI which is stabilized by a hydrogen bonding interaction with one equivalent of excess benzamide. All attempts to isolate the organometallic failed as the organometallic degraded quickly in the absence of amide. FTIR experiments indicated a significant hydrogen bonding interaction between the benzamide and mer(PhC(O)HN)IrH(PMe3)3Cl. NMR scale reactions with acrylamide and benzanalide showed that oxidative N-H addition could occur despite the presence of an unsaturate or an N-substituent. The attempts to form the thioamide analogues of the acetamide and benzamide complexes failed to produce stable iridium hydrides. Thioacetamide will add to [(COD)Ir(PMe3)3]CI in chloroform or methylene chloride; however~ any hydrido species which formed subsequently reacted with the solvent to produce fac( MeC(S)HN)Ir(PMe3)3Ch. All attempts at adding thiobenzamide to [(COD)Ir(PMe3)3)CI produced an uncharacterizable mixture of products. The reactivity ofmer-(PhC(O)HN)IrH(PMe3)3CI was probed with regard to its potential for catalytic amination. Reaction with TIPF6 in methylene chloride showed evidence for the formation of the bidentate amide mer-[(PhC(O)HN)IrH(PMe3)3]CI where the amide is chelated through the nitrogen and the oxygen; however, the species was not stable and could not be isolated. Refluxing mer-(PhC(O)HN)IrH(PMe3)3CI in water produces a rearrangement to form another isomer of mer( PhC(O)HN)IrH(PMe3)3CI in which the hydride is trans to nitrogen and cis to chloride. Reactions with unsaturates in benzene, chloroform, and water at elevated temperatures produced evidence for the formation of insertion products. The reaction of mer( PhC(O)HN)IrH(PMe3)3CI with t-butyl acetylene in water shows evidence for the formation of an amidated elimination product, though it was not shown to be catalytic.