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

The cyclic, heteroatom-stabilized carbene complexes RuHCl(PR3)(2)[=C(X)C3H6](R = Pr-i, 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 x 10(5) g mol(-1)) in arene solvent at 30-80 degreesC. Initiation is slow, but not dependent on free phosphine concentration because the catalyst has an empty coordination site cis to the carbene. Protonation of 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 H2C=C(OEt)H.