High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo­(NAr)­(CHR)­(Me2Pyr)­(OTPP)
(Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide,
OTPP = O-2,3,5,6-Ph4C6H) and CH2CHX
where X = B­(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo­(NAr)­(CHX)­(Me2Pyr)­(OTPP) complexes in good yield. All have been characterized
through X-ray studies (as
an acetonitrile adduct in the case of X = PPh2). The efficiencies
of metathesis reactions initiated by Mo­(NAr)­(CHX)­(Me2Pyr)­(OTPP) complexes can be rationalized on the basis of steric
factors; electronic differences imposed as a consequence of X being
bound to the alkylidene carbon do not seem to play a major role. Side
reactions that promote catalyst decomposition do not appear to be
a serious limitation for MoCHX species.

配合物Mo(NAr)(CHR)(Me₂Pyr)(OTPP) [其中Ar为2,6-二异丙基苯基（2,6-i-Pr₂C₆H₃），R为氢原子或CHCMe₂Ph，Me₂Pyr为2,5-二甲基吡咯基（2,5-二甲基吡咯阴离子，即2,5-dimethylpyrrolide），OTPP为O-2,3,5,6-四苯基苯氧基（O-2,3,5,6-Ph₄C₆H）]与CH₂=CHX（X分别为频哪醇硼酸酯基B(pin)、三甲基硅基SiMe₃、N-咔唑基、N-吡咯烷酮基、二苯基膦基PPh₂、丙氧基OPr以及苯硫基SPh）发生反应，可高产率得到Mo(NAr)(CHX)(Me₂Pyr)(OTPP)类配合物。所有产物均通过X射线衍射完成结构表征，其中当X为PPh₂时，产物以乙腈加合物的形式完成表征。由Mo(NAr)(CHX)(Me₂Pyr)(OTPP)配合物引发的复分解反应效率，可基于空间位阻因素得到合理解释；X与亚烷基碳相连所引入的电子差异似乎并未发挥主要作用。而会促进催化剂分解的副反应，对于Mo=CHX物种而言似乎并未构成严重的局限性。