Generality and Strength of Transition Metal β-Effects
Generality and Strength of Transition Metal β-Effects
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DOI：
10.1021/jacs.8b06817
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发表时间：
2018-08-22
影响因子：
15
通讯作者：
Musaev, Djamaladdin G.
中科院分区：
文献类型：
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作者：
Haines, Brandon E.;Sarpong, Richmond;Musaev, Djamaladdin G.
通过计算，我们检验了过渡金属中心对β消除的β效应的普遍性和强度。特别是，我们发现- pd （II）取代基对碳正离子的稳定性是硅取代基的两倍以上，这是众所周知的-硅效应的代表。我们建立了有效和实用的计算参数来研究sigma共轭在实验相关的体系：N，N-吡啶酰胺乙烯基金属环，可以被消除。我们发现β -Pd效应取决于c - β取代基(X)的性质：对于X = H、Me、OH和F，这种效应可以忽略不计，但对于X = Cl、Br和i，这种效应是显著的。我们还将这些研究扩展到具有其他过渡金属- fe （II）、Ru（II）、Os（II）、Co（III）、Rh（III）、Ir（III）、Ni（II）、Pd（II）、Pt（II）、Cu（III）、Ag（III）和Au(III) -取代基的N，N-吡啶酰胺乙烯基金属环中的β效应。我们发现金属的电负性与相对的β效应有相当好的相关性，第一行过渡金属的影响最大。总的来说，我们预计对过渡金属β效应的更深刻的认识将有助于设计新的反应，包括过渡金属催化的碳氢官能化的新变体。
Using computation, we examine the generality and strength of beta-effects from transition metal centers on beta-elimination. In particular, we find that a beta-Pd(II) substituent imparts over twice the stabilization to a carbocation as a Si substituent, representative of the well-known beta-silicon effect. We established efficient and practical computational parameters to investigate the sigma sigma conjugation in an experimentally relevant system: N,N-picolinamide vinyl metalacycles with fisubstituents that can undergo elimination. We have found that the beta-Pd effect depends on the nature of the C-beta substituent (X): This effect is negligible for X = H, Me, OH, and F, but is significant for X = Cl, Br, and I. We have also extended these studies to the beta-effect in N,N-picolinamide vinyl metalacycles with beta-substituents of other transition metals-Fe(II), Ru(II), Os(II), Co(III), Rh(III), Ir(III), Ni(II), Pd(II), Pt(II), Cu(III), Ag(III), and Au(III). We found that the electronegativity of the metals correlates reasonably well with the relative beta-effects, with first-row transition metals exerting the strongest influence. Overall, it is our anticipation that a more profound appreciation of transition metal beta effects will facilitate the design of novel reactions, including new variants of transition metal catalyzed C-H functionalization.