Regioselectivity of Addition to the Azavinylidene Ligand in Tp′W(CO)(η2-HC≡CH)(N═CHMe): Electrophilic Addition versus Oxidation and Radical Coupling

详细信息    查看全文

• 作者：Ross J. Beattie ; Peter S. White ; Joseph L. Templeton
• 刊名：Organometallics
• 出版年：2016
• 出版时间：January 11, 2016
• 年：2016
• 卷：35
• 期：1
• 页码：32-38
• 全文大小：402K
• ISSN：1520-6041

文摘

The Tp′W(CO)(HCCH)(N═CHMe) (Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate) molecule contains an electron-rich 1-azavinylidene ligand where the preferred site for electrophile addition is the α-nitrogen. As is observed in other cases for electrophile addition to a 1-azavinylidene with a cis-alkyne ligand, this fragment will add small electrophiles such as H⁺, Me⁺, and Et⁺ to the α-nitrogen lone pair, maintaining a W^II metal center and forming the coordinated imine products [Tp′W(CO)(HCCH)(NH═CHMe)][BF₄], [Tp′W(CO)(HCCH)(N(Me)═CHMe)][OTf], and [Tp′W(CO)(HCCH)(N(Et)═CHMe)][OTf]. In contrast, when a one-electron oxidant is employed, net electrophile addition at the β-carbon can be achieved. Changing the nature of the electrophile to [CPh₃][BF₄] leads to a rapid one-electron oxidation and selective radical combination to form the imido product [Tp′W(CO)(HCCH)(NCH(CH₃)CPh₃)][BF₄]. This net addition of an electrophile at the 1-azavinylidene β-carbon concomitantly oxidizes the metal center to W^IV and raises the CO stretching frequency to 2109 cm^–1 versus 1946 cm^–1 for the W^II imine complex. This reactivity is also seen with [CPh₂(C₆H₄OMe)][BF₄]. This variable reactivity demonstrates the flexibility of the 1-azavinylidene ligand when it is paired with an adjacent alkyne ligand.