Density functional theory studies of the mechanistic aspects of olefin metathesis reactions

2010 ◽  
Vol 39 (32) ◽  
pp. 7575 ◽  
Author(s):  
Richard Tia ◽  
Evans Adei
Keyword(s):  
Density Functional Theory ◽  
Olefin Metathesis ◽  
Density Functional ◽  
Functional Theory ◽  
Metathesis Reactions

A theoretical study on the activation of hydrogen–hydrogen and hydrogen–alkyl bonds by electron-poor early transition metals

1992 ◽  
Vol 70 (2) ◽  
pp. 333-342 ◽  
Author(s):  
E. Folga ◽  
T. Ziegler
Keyword(s):  
Density Functional Theory ◽  
Transition State ◽  
Density Functional ◽  
Hydrogen Exchange ◽  
Theoretical Study ◽  
Experimental Studies ◽  
Functional Theory ◽  
Exchange Processes ◽  
Text Fragment ◽  
Metathesis Reactions

A theoretical study has been carried out on four σ-bond metathesis reactions mediated by the electron-poor lutetium metal centre. The four processes include hydrogen exchange, X2Lu-H + D2 → X2Lu-D + HD (1), and hydrogenolysis X2Lu-CH3 + H2 → Cl2Lu-H + CH4 (2), in which a H—H bond is activated, as well as methane exchange, X2Lu-CH3 + CH4 → X2Lu-CH3 + CH4 (3), and methylation, Cl2Lu-H + CH4 → X2Lu-CH3 + H2 (4), in which a C—H bond is activated. The [Formula: see text] fragment employed in a number of experimental studies was modelled by Cl2Lu and all calculations were based on approximate Density Functional Theory (DFT). The study combined methods from quantum mechanics and statistical mechanics to obtain enthalpies and entropies of activation as well as transition state structures. All four processes were found to have an ordered four-centre transition state with negative entropies of activation given by ΔS≠ = −109(1), −124(2), −131 (3), and −134(4)&nbspJ mol−1 K−1 at T = 298.15 K. The Gibb's free energies of activation, ΔG≠(= ΔH≠ − TΔS≠) were calculated as ΔG≠ = 81.6 (1), 126.0 (2), 136.7 (3), and 130.6 (4) kJ mol−1 at T = 298.15 K. The calculated trends in ΔG≠ are consistent with the observed order of reactivity for σ-bond metathesis reactions between R—H and M—R′ bonds: R = R′ = H >> R = H, R′ = CH3 > R = R′ = CH3. The decrease in the reaction rate is related to the different abilities of the 1s hydrogen orbital and the [Formula: see text] methyl orbital to stabilize the four-centre transition state. Thus, the spherical 1s hydrogen orbital is better able to overlap fully with orbitals on adjacent centres than the directional [Formula: see text] orbital. As a consequence, the electronic barrier is seen to increase from the hydrogen exchange reaction towards the hydrogenolysis and methane exchange processes as one or two hydrogens, respectively, are replaced by methyl groups in the four-centre transition state. Keywords: Density Functional Theory, C—H activation, metathesis, hydrogenolysis, H—H activation.

Doping effects on the geometric and electronic structure of tin clusters

2019 ◽  
Vol 21 (44) ◽  
pp. 24478-24488 ◽  
Author(s):  
Martin Gleditzsch ◽  
Marc Jäger ◽  
Lukáš F. Pašteka ◽  
Armin Shayeghi ◽  
Rolf Schäfer
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Beam Deflection ◽  
Functional Theory ◽  
Doping Effects ◽  
Depth Analysis ◽  
Trajectory Simulations

In depth analysis of doping effects on the geometric and electronic structure of tin clusters via electric beam deflection, numerical trajectory simulations and density functional theory.

What correlation effects are covered by density functional theory?

2000 ◽  
Vol 98 (20) ◽  
pp. 1639-1658 ◽  
Author(s):  
Yuan He, Jurgen Grafenstein, Elfi Kraka,
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Correlation Effects ◽  
Functional Theory
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