ROMP using heterocyclic carbenes bearing a hydride ligand. An improved synthesis of RuCl2(PR3)2(CHMe)

Abstract

The cyclic, heteroatom-stabilized carbene complexes RuHCl(PR₃)₂[C(X)C₃H₆] (R = Prⁱ, Cy; X = O, NH) catalyze the ring-opening metathesis polymerization of 2-norbornene to give mainly (85%) trans-polynorbornene (M_w 1.1–2.0 × 10⁵ g mol⁻¹) in arene solvent at 30–80 °C. Initiation is slow, but not dependent on free phosphine concentration because the catalyst has an empty coordination site cis to the carbene. Protonation of RuHCl(PR₃)₂[C(OR)R′] species occurs at the hydride ligand, and the acidity of the resulting species leads to C–OR bond cleavage. This leads to facile conversion of RuHClL₂[C(OEt)Me] to RuCl₂L₂[CHMe] and EtOH by HCl and, thus, a convenient new synthesis of a traditional metathesis catalyst whose carbene source is H₂CC(OEt)H.