Synthesis of (Adamantylmido)vanadium(V)-Alkyl, Alkylidene Complex Trapped with PMe<sub>3</sub>: Reactions of the Alkylidene Complexes with Phenols

2015-12-17T05:58:51Z (GMT) by Kohei Hatagami Kotohiro Nomura
V­(CHSiMe<sub>3</sub>)­(NAd)­(CH<sub>2</sub>SiMe<sub>3</sub>)­(PMe<sub>3</sub>)<sub>2</sub> (<b>1</b>, Ad = 1-adamantyl) has been isolated from V­(NAd)­(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub> in the presence of PMe<sub>3</sub> (excess, 12 equiv) upon heating, and the reaction of <b>1</b> with 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>OH in <i>n</i>-hexane afforded V­(CHSiMe<sub>3</sub>)­(NAd)­(O-2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)­(PMe<sub>3</sub>)<sub>2</sub> (<b>2a</b>); structures of <b>1</b> and <b>2a</b> have been determined by X-ray crystallography. Reaction of <b>1</b> with C<sub>6</sub>F<sub>5</sub>OH in C<sub>6</sub>D<sub>6</sub> afforded a mixture of V­(CHSiMe<sub>3</sub>)­(NAd)­(OC<sub>6</sub>F<sub>5</sub>)­(PMe<sub>3</sub>)<sub>2</sub> (<b>2b</b>) and V­(NAd)­(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>­(OC<sub>6</sub>F<sub>5</sub>) (<b>3b</b>) and the PMe<sub>3</sub> adduct (<b>3b</b>-<b>PMe</b><sub><b>3</b></sub>), and the consumption rate of <b>1</b> decreased upon addition of PMe<sub>3</sub> or use of C<sub>6</sub>F<sub>5</sub>OD in place of C<sub>6</sub>F<sub>5</sub>OH, clearly suggesting that the reaction proceeds via coordination of C<sub>6</sub>F<sub>5</sub>OH and subsequent reaction with the alkylidene or the alkyl moiety. The catalytic activity in the ring-opening metathesis polymerization (ROMP) of norbornene by <b>1</b> increased upon addition of phenol; <b>1</b>-C<sub>6</sub>F<sub>5</sub>OH catalyst showed a remarkable activity (TOF 20 000 h<sup>–1</sup>), affording high molecular weight polymer with a unimodal molecular weight distribution. Reactions with <b>2a</b>,<b>b</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.