Reactions of Iridium and Rhodium Complexes Containing η2-Benzyne, η2-Tetrafluorobenzyne, and η2-Trifluorobenzyne Ligands. Differential Rates of Arene Elimination by Protonation of Isomeric Fluoroaryl Complexes and Restricted Rotation of PMe3 Ligands in ortho-Iodo and ortho-Bromoaryl Complexes

Treatment of the tetrafluorobenzyne complex Cp*Ir(η 2 -C 6 F 4 )(PMe 3 ) ( 1 ) with MeCO 2 H affords the tetrafluorophenyl complex Cp*Ir(2,3,4,5,-C 6 F 4 H)(PMe 3 )(O 2 CMe) ( 2 ), which, on treatment with NaBH 4, affords the hydride complex Cp*Ir(2,3,4,5,-C 6 F 4 H)(PMe 3 )H ( 3 ). Treatment of 3 with n- BuLi affords the trifluorobenzyne complex Cp*Ir(3,4,5-C 6 F 3 H)(PMe 3 ) ( 4 ). Treatment of 4 with MeCO 2 H gives a mixture of two protonation products, Cp*Ir(2,3,4-C 6 F 3 H 2 )(PMe 3 )(O 2 CMe) ( 5 ) and Cp*Ir(3,4,5-C 6 F 3 H 2 )(PMe 3 )(O 2 CMe) ( 6 ) in an 8:1 ratio. Treatment of the 5 / 6 mixture with CF 3 CO 2 H affords 1,2,3-C 6 F 3 H 3 and Cp*Ir(O 2 CCF 3 ) 2 (PMe 3 ) but at dramatically different rates, with 5 reacting significantly faster than 6 . Treatment of 1a with Br 2, I 2, or MeI gives the oxidative addition products Cp*Ir(2-C 6 BrF 4 )Br(PMe 3 ) ( 7 ), Cp*Ir(2-C 6 IF 4 )I(PMe 3 ) ( 8 ), or Cp*Ir(2-C 6 MeF 4 )I(PMe 3 ) ( 9 ), respectively. The variable-temperature proton NMR spectra of complexes 7 and 8 reveal an unusual restricted rotation about the Ir−PMe 3 bonds on the NMR time scale ( 7, Δ G ⧧ = 39 ± 2 kJ mol - 1; 8, Δ G ⧧ = 38 ± 2 kJ mol - 1 ). Similarly, treatment of Cp*Rh(η 2 -C 6 F 4 )(PMe 3 ) ( 1b ) with I 2 leads to formation of Cp*Rh(2-C 6 IF 4 )I(PMe 3 ) ( 10 ), which also exhibits restricted rotation about the metal−phosphorus bond (Δ G ⧧ = 44 ± 2 kJ mol - 1 ). While the tetrafluorobenzyne complex ( 1a ) is unreactive toward CO, the hydrocarbon analogue Cp*Ir(η 2 -C 6 H 4 )(PMe 3 ) ( 1c ) does react to give the CO monoinsertion product ( 11 ). Compound 1c also reacts with I 2 to afford Cp*Ir(2-C 6 IH 4 )I(PMe 3 ) ( 12 ), which also shows restricted rotation about the Ir−PMe 3 bond (Δ G ⧧ = 43 ± 2 kJ mol - 1 ). X-ray crystal structures of complexes 3, 4, 5, 7, 8, 10, and 11 are reported.