Theoretical Elucidation of the Mechanism of Cleavage of the Aromatic C[BOND]C Bond in Quinoxaline by a Tungsten-Based Complex [W(PMe3)42-CH2PMe2)H]

Authors

  • Dr. Yuxia Liu,

    1. Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100 (P.R. China), Fax: (+86) 531-88564464
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  • Prof. Dongju Zhang,

    Corresponding author
    1. Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100 (P.R. China), Fax: (+86) 531-88564464
    • Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100 (P.R. China), Fax: (+86) 531-88564464
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  • Dr. Jun Gao,

    1. Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100 (P.R. China), Fax: (+86) 531-88564464
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  • Prof. Chengbu Liu

    1. Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100 (P.R. China), Fax: (+86) 531-88564464
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Abstract

The aromatic C[BOND]C bond cleavage by a tungsten complex reported recently by Sattler and Parkin15 offers fresh opportunities for the functionalization of organic molecules. The mechanism of such a process has not yet been determined, which appeals to computational assistance to understand how the unstrained C[BOND]C bond is activated at the molecular level.16, 17 In this work, by performing density functional theory calculations, we studied various possible mechanisms of cleavage of the aromatic C[BOND]C bond in quinoxaline (QoxH) by the W-based complex [W(PMe3)42-CH2PMe2)H]. The calculated results show that the mechanism proposed by Sattler and Parkin involves an overall barrier of as high as 42.0 kcal mol−1 and thus does not seem to be consistent with the experimental observation. Alternatively, an improved mechanism has been presented in detail, which involves the removal and recoordination of a second PMe3 ligand on the tungsten center. In our new mechanism, it is proposed that the C[BOND]C cleavage occurs prior to the second C[BOND]H bond addition, in contrast to Sattler and Parkin’s mechanism in which the C[BOND]C bond is broken after the second C[BOND]H bond addition. We find that the rate-determining step of the reaction is the ring-opening process of the tungsten complex with an activation barrier of 28.5 kcal mol−1 after the first PMe3 ligand dissociation from the metal center. The mono-hydrido species is located as the global minimum on the potential-energy surface, which is in agreement with the experimental observation for this species. The present theoretical results provide new insight into the mechanism of the remarkable C[BOND]C bond cleavage.

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