Cyclometalated
Iridium Complexes of Bis(Aryl) Phosphine
Ligands: Catalytic C–H/C–D Exchanges and C–C
Coupling Reactions
- Publication date
- Publisher
Abstract
This
work details the synthesis and structural identification of
a series of complexes of the (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine
ligands, PR′(Ar)<sub>2</sub>, for R′ = Me and Ar = 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>, <b>1b</b>; 2,6-Me<sub>2</sub>-4-OMe-C<sub>6</sub>H<sub>2</sub>, <b>1c</b>; 2,6-Me<sub>2</sub>-4-F-C<sub>6</sub>H<sub>2</sub>, <b>1d</b>; R′ = Et,
Ar = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, <b>1e</b>. Both chloride- and hydride-containing compounds, <b>2b</b>–<b>2e</b> and <b>3b</b>–<b>3e</b>, respectively, are described. Reactions of chlorides <b>2</b> with NaBAr<sub>F</sub> (BAr<sub>F</sub> = B(3,5-C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>)<sub>4</sub>) in the presence
of CO form cationic carbonyl complexes, <b>4</b><sup><b>+</b></sup>, with ν(CO) values in the narrow interval 2030–2040
cm<sup>–1</sup>, indicating similar π-basicity of the
Ir(III) center of these complexes. In the absence of CO, NaBAr<sub>F</sub> forces κ<sup>4</sup>-<i>P</i>,<i>C</i>,<i>C</i>′,<i>C</i>″ coordination
of the metalated arm (studied for the selected complexes <b>5b</b>, <b>5d</b>, and <b>5e</b>), 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 κ<sup>4</sup> species <b>5d</b> and <b>5e</b> into the corresponding hydrido phosphepine complexes <b>6d</b> and <b>6e</b>. Using CD<sub>3</sub>OD as the source of deuterium,
the chlorides <b>2</b> undergo deuteration of their 11 benzylic
positions whereas hydrides <b>3</b> experience only D incorporation
into the Ir–H and Ir–CH<sub>2</sub> sites. Mechanistic
schemes that explain this diversity have come to light thanks to experimental
and theoretical DFT studies that are also reported
