V­(CHSiMe3)­(NAd)­(CH2SiMe3)­(PMe3)2 (1, Ad = 1-adamantyl) has been isolated from V­(NAd)­(CH2SiMe3)3 in the presence of PMe3 (excess, 12 equiv) upon heating, and the reaction of 1 with 2,6-Me2C6H3OH in n-hexane afforded V­(CHSiMe3)­(NAd)­(O-2,6-Me2C6H3)­(PMe3)2 (2a); structures of 1 and 2a have been determined by X-ray crystallography. Reaction of 1 with C6F5OH in C6D6 afforded a mixture of V­(CHSiMe3)­(NAd)­(OC6F5)­(PMe3)2 (2b) and V­(NAd)­(CH2SiMe3)2­(OC6F5) (3b) and the PMe3 adduct (3b-PMe 3 ), and the consumption rate of 1 decreased upon addition of PMe3 or use of C6F5OD in place of C6F5OH, clearly suggesting that the reaction proceeds via coordination of C6F5OH and subsequent reaction with the alkylidene or the alkyl moiety. The catalytic activity in the ring-opening metathesis polymerization (ROMP) of norbornene by 1 increased upon addition of phenol; 1-C6F5OH catalyst showed a remarkable activity (TOF 20 000 h–1), affording high molecular weight polymer with a unimodal molecular weight distribution. Reactions with 2a,b with phenol afforded the bis­(phenoxy) complexes, and it has been suggested that these reactions proceed via coordination of phenol and subsequent reaction with the alkylidene accompanying phenoxy exchange on the vanadium.

A cationic complex [Ru{OC(O)CMeCH2‐κ2O,O′}(PMe3)4]+CH2CMeCO2− (5 a) and its related carboxylato complexes are newly prepared by the reaction of [cis‐RuH2(PMe3)4] (4) with carboxylic acids in methanol in 76–100 % yield. Complex 5 a reversibly transforms to the neutral form [cis‐Ru{OC(O)CMeCH2‐κ1O}2(PMe3)4] (2 a) in nonpolar solvents. Complex 2 a reversibly liberates a PMe3 group to give [Ru{OC(O)CMeCH2‐κ1O}{OC(O)CMeCH2‐κ2O,O′}(PMe3)3] (12 a) from which a stereoselective CH bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMeCH‐κ2O,C}(PMe3)4] (1 a) from the release of methacrylic acid. Complexes 2 a and 5 a also give 1 a but the prior dissociation of a PMe3 is indispensable for the CH bond cleavage reaction. Complex 1 a establishes an equilibrium with 2 a (or 5 a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the CH bond cleavage reaction as a proton acceptor, but neither the added carboxylato anion nor typical proton acceptors such as proton sponge assist the reaction. In [D4]MeOH, a catalytic stereospecific deuteration of carboxylic acids has been achieved by 4, in which the equilibrium between 5 a and 1 a plays a key role.