Eichenseher, Sandra Delacroix, Olivier Kromm, Klemenz Hampel, Frank Gladysz, J. A. Rhenium-Containing Phosphorus Donor Ligands for Palladium-Catalyzed Suzuki Cross-Coupling Reactions:  A New Strategy for High-Activity Systems The chiral racemic methyl complex (η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Re(NO)(PPh<sub>3</sub>)(CH<sub>3</sub>) is converted to the rhenium-containing phosphorus donor ligands (η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Re(NO)(PPh<sub>3</sub>)((CH<sub>2</sub>)<i><sub>n</sub></i>PR<sub>2</sub>) (<i>n</i>/R = <b>3a</b>, 0/Ph; <b>3b</b>, 0/<i>t</i>-Bu; <b>3c</b>, 0/Me; <b>5a</b>, 1/Ph; <b>5b</b>, 1/<i>t</i>-Bu) and (η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>PR<sub>2</sub>)Re(NO)(PPh<sub>3</sub>)(CH<sub>3</sub>) (<b>7</b>; R = <b>a</b>, Ph; <b>b</b>, <i>t</i>-Bu) via standard reactions (<b>3</b>, TfOH/CH<sub>2</sub>Cl<sub>2</sub> or HBF<sub>4</sub>/chlorobenzene, then PR<sub>2</sub>H, then <i>t</i>-BuOK; <b>5</b>, Ph<sub>3</sub>C<sup>+</sup>X<sup>-</sup>, then PR<sub>2</sub>H, then <i>t</i>-BuOK; <b>7</b>, <i>n</i>-BuLi, then PR<sub>2</sub>Cl). (η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>PR<sub>2</sub>)Re(CO)<sub>3</sub> (R = Ph, <i>t</i>-Bu) is prepared from (η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Re(CO)<sub>3</sub> analogously to <b>7</b>. Most of these species are effective ligands for palladium-catalyzed Suzuki couplings. Typical conditions involve toluene solvent, an aryl bromide (1.0 equiv), phenylboronic acid (1.5 equiv), K<sub>3</sub>PO<sub>4</sub> (2.0 equiv), Pd(OAc)<sub>2</sub> (1 mol %), the rhenium/PR<sub>2</sub> species (4 mol %), and 60−100 °C. In the cases of <b>3</b> and <b>5</b>, the rhenium/PR<sub>2</sub> species are generated in situ from indefinitely stable conjugate acids [rhenium/PR<sub>2</sub>H]<sup>+</sup> and <i>t</i>-BuOK (2 equiv or 8 mol %). The bulkier and more electron-rich rhenium/P(<i>t</i>-Bu)<sub>2</sub> systems generally give more active catalysts than the rhenium/PPh<sub>2</sub> analogues. Under many conditions, the activities of <b>3a</b> and <b>3b</b> approach (but do not exceed) those of the corresponding organophosphines PPh<sub>3</sub> and P(<i>t</i>-Bu)<sub>3</sub>, the latter being a benchmark ligand for Suzuki couplings. Turnover numbers of >1000 are easily realized. Chloroarenes can be coupled, but at much slower rates and in lower yields. The crystal structures of <b>5b</b> and <b>7b</b> are determined. The trigonal phosphorus atoms become increasingly pyramidalized in the series <b>5b</b> < <b>5a</b> < <b>7b</b>. 3 b approach;organophosphines PPh 3;HBF;equiv;series 5 b;Bu;Ph 3 C;chiral racemic methyl;PO;Suzuki;mol;C 5 H 5;ligand;PR 2 Cl;CH;PR 2 H;BuOK;Re;5 b;rhenium;n PR 2;7 b;species;C 5 H 4 PR 2 2005-01-17
    https://acs.figshare.com/articles/journal_contribution/Rhenium_Containing_Phosphorus_Donor_Ligands_for_Palladium_Catalyzed_Suzuki_Cross_Coupling_Reactions_A_New_Strategy_for_High_Activity_Systems/3304540
10.1021/om0492956.s002