Cyclometalated Iridium Complexes of Bis(Aryl) Phosphine Ligands: Catalytic C–H/C–D Exchanges and C–C Coupling Reactions

This work details the synthesis and structural identification of a series of complexes of the (η5-C5Me5)­Ir­(III) unit coordinated to cyclometalated bis­(aryl)­phosphine ligands, PR′(Ar)2, for R′ = Me and Ar = 2,4,6-Me3C6H2, 1b; 2,6-Me2-4-OMe-C6H2, 1c; 2,6-Me2-4-F-C6H2, 1d; R′ = Et, Ar = 2,6-Me2C6H3, 1e. Both chloride- and hydride-containing compounds, 2b–2e and 3b–3e, respectively, are described. Reactions of chlorides 2 with NaBArF (BArF = B­(3,5-C6H3(CF3)2)4) in the presence of CO form cationic carbonyl complexes, 4+, with ν­(CO) values in the narrow interval 2030–2040 cm–1, indicating similar π-basicity of the Ir­(III) center of these complexes. In the absence of CO, NaBArF forces κ4-P,C,C′,C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C–C coupling reaction converts the κ4 species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD3OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir–H and Ir–CH2 sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported.