New approaches to high-activity transition-metal catalysts for carbon–carbon bond forming reactions. Rhenium-containing phosphorus donor ligands for palladium-catalyzed Suzuki cross-couplings

Abstract

The rhenium complexes (η⁵-C₅H₅)Re(NO)(PPh₃)((CH₂)_nPR₂:) (n/R = 0/Ph, 0/t-Bu, 0/Me, 1/Ph, 1/t-Bu), which contain electron-rich and sterically congested phosphido moieties, give active catalysts for the title reaction; typical conditions (toluene, 60–100 °C): aryl bromide (1.0 equiv.), PhB(OH)₂ (1.5 equiv.), K₃PO₄ (2.0 equiv.), Pd(OAc)₂ (1 mol%), and a Re(CH₂)_nPR₂: species or a 1∶2 [Re(CH₂)_nPR₂H]⁺X⁻/t-BuOK mixture (4 mol% rhenium).