One-step entry to olefin-tethered N,S-heterocyclic carbene complexes of ruthenium with mixed ligands

Abstract

A series of Ru(II) mixed-ligand complexes RuBr₂(PPh₃)₂(N-AyBzTh) (Ay = prop-2-enyl; BzTh = benzothiazol-2-ylidene) (4), RuBr(OAc)(PPh₃)(N-MeAyBzTh) (5), RuBr(OAc)(PPh₃)(N-MeBnBzTh)₂ (MeBn = 3-methylbut-2-enyl) (6) and RuCl(OAc)(PPh₃)(N-MeBnBzTh) (7) have been synthesized from Ru(OAc)₂(PPh₃)₂ in one-pot condensation and ligand exchange reactions. X-ray single-crystal diffraction analysis revealed that they are neutral octahedral Ru(II) complexes with one or two N,S-heterocyclic carbene (NSHC) ligands and a coordinated (4, 5 and 7) or dangling (6) olefin arm. The system displays a range of self-selecting structural variations. Entry of the hybrid olefin–NSHC and halide ligands ejects either one (5, 6 and 7) phosphine ligand or keeps both phosphines (4) by replacing the acetate. It is also possible to accommodate two NSHC ligands by keeping the olefin pendant (6). Complexes 5 and 7 are isostructural with all different ligands on the coordination sphere. Complexes 4–6 are active towards transfer hydrosilylation showing good β(Z) selectivity, with the Ru(II) bearing acetate giving higher yields.