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Synthesis of (Adamantylmido)vanadium(V)-Alkyl, Alkylidene Complex Trapped with PMe3: Reactions of the Alkylidene Complexes with Phenols

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posted on 17.12.2015, 05:58 by Kohei Hatagami, Kotohiro Nomura
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-PMe3), 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.