Iridium and Rhodium Complexes Containing Fluorinated Phenyl Ligands and Their Transformation to η2-Benzyne Complexes, Including the Parent Benzyne Complex IrCp*(PMe3)(C6H4)

Abstract

Treatment of IrCp*(CO)2 (1) with C6F5I in benzene under reflux gives the oxidative addition product IrCp*(C6F5)(CO)I (2). Treatment of 2 with PMe3 gives IrCp*(C6F5)(PMe3)I (3), which, on treatment with AgO3SCF3 in the presence of traces of water, affords the cationic complex [IrCp*(C6F5)(PMe3)(OH2)]O3SCF3 (4). Treatment of 4 with 1,8-bis(dimethylamino)naphthalene (Proton Sponge) affords the hydride complex IrCp*(C6F5)(PMe3)H (5), which reacts with n-BuLi to give the tetrafluorobenzyne complex IrCp*(η2-C6F4)(PMe3) (6) in high yield. Similarly, treatment of RhCp*(CO)2 (7) with C6F5I in toluene at 80 °C affords a pentafluorophenyl complex of rhodium, RhCp*(C6F5)(CO)I (8). Treatment of 8 with PMe3 at room temperature affords RhCp*(C6F5)(PMe3)I (9), which reacts with NaBH4 to give RhCp*(C6F5)(PMe3)H (10). Treatment of 10 with n-BuLi gives the rhodium tetrafluorobenzyne complex RhCp*(η2-C6F4)(PMe3) (11) in high yield. Treatment of IrCp*(CO)2 with 1-fluoro-2-iodobenzene in toluene under reflux gives the oxidative addition product IrCp*(2-C6FH4)(CO)I (12), which is converted to IrCp*(2-C6FH4)(PMe3)I (13) by treatment with PMe3. Treatment of 13 with NaBH4 gives IrCp*(2-C6FH4)(PMe3)H (14), which, on treatment with n-BuLi, is converted to a mixture of the nonfluorinated benzyne complex IrCp*(η2-C6H4)(PMe3) (15) and the phenyl butyl complex IrCp*(C6H5)(n-Bu)(PMe3) (16). Treatment of Ir(C5Me4Et)(CO)2 with 2,3,4,5-tetrafluorobenzoyl chloride at 110 °C under reflux gives the oxidative addition product Ir(C5Me4Et)(2,3,4,5-C6F4H)(CO)Cl (17), which on treatment with PMe3 gives Ir(C5Me4Et)(C6F4H)(PMe3)Cl (18). Using analogous methodology this was converted to the unsymmetrical trifluorobenzyne complex Ir(C5Me4Et)(η2-3,4,5-C6F3H)(PMe3) (21), in which the benzyne ligand is shown to be stereochemically rigid on the NMR time scale, allowing a minimum value for the rotational barrier about the iridium−benzyne bond to be estimated at 20.3 kcal mol-1. The crystal structures of complexes 2, 3, 9, 11−15, 17, and 18 are reported and discussed, and the “through-space” nature of some coupling constants between 31P, 1H, and 19F is confirmed using heteronuclear Overhauser enhancement (HOESY) NMR spectroscopy.