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

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.

V­(CHSiMe3)­(NAd)­(CH2SiMe3)­(PMe3)2 (1, 其中Ad代表1-金刚基) 已从V­(NAd)­(CH2SiMe3)3中分离出来，此过程在PMe3（过量，12摩尔当量）的存在下，通过加热完成。1与2,6-二甲基苯酚在正己烷中的反应，产生了V­(CHSiMe3)­(NAd)­(O-2,6-二甲基苯氧基)­(PMe3)2 (2a) 的结构；1和2a的结构已通过X射线晶体学确定。1与C6F5OH在C6D6中的反应，产生了V­(CHSiMe3)­(NAd)­(OC6F5)­(PMe3)2 (2b)、V­(NAd)­(CH2SiMe3)2­(OC6F5) (3b) 及其PMe3加合物(3b-PMe3)的混合物；在加入PMe3或以C6F5OD替代C6F5OH时，1的消耗速率降低，这明确表明反应是通过C6F5OH的配位及其随后与烯丙基或烷基部分的反应来进行的。1在开环共轭转移聚合反应（ROMP）中催化环戊二烯的聚合活性，在添加苯酚后得到增强；1-C6F5OH催化剂展现出卓越的活性（TOF 20,000 h–1），提供了具有单峰分子量分布的高分子量聚合物。1与2a、2b与苯酚的反应产生了双酚氧基复合物，并有人提出这些反应是通过苯酚的配位及其随后与伴随酚氧基交换的烯丙基的反应来进行的。