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.