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Theoretical investigation of the energy of olefin-and sila-olefin insertion/β-H elimination reactions of two late transition metals - DFT MO calculations
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Resumo(s)
The energetic of the olefin insertion/ -H elimination processes is going to be studied using density functional theory (B3LYP/SDD, Gaussian 03). The observed trends based on steric and electronic properties of two late transition metals (Co and Rh) and ligands (L) are reproduced.In a [L3M(C2H4)(H) (M=Co, Rh; L=PMe3, PF3) neutral complex the isomer with a -agostic metal-H-C interaction becomes stabilized when a rather less electron-donating ligand (e.g. PF3) is involved. Comparison of the activation parameters with those for other complexes suggests an increase of the barrier of migratory insertion with increasing electron richness of the metal center, which destabilizes species with agostic metal –H-C interactions.
The computed energy barriers obtained for the cationic [C5R5ML(H)(C2H4)]+ (R=H, CH3; M=Co, Rh; L=PF3) complexes compare very well with activation energies from previously reported NMR studies and confirm that the activation barriers are insensitive to L, but somewhat higher for R=H than R=Me.The study was extended to the cationic complexes of the type [C5R’5ML(H)(SiR2=CH2)]+ (M=Co, Rh; L=PH3, PF3, PMe3; R=H, Me), in which either C or Si atoms of the “sila-olefin” are involved in the "sila-olefin" insertion/-H elimination reaction. The "sila-olefin" conformation in which C is involved in the hydrogen migratory insertion is going to be deeply stabilized upon the formation of the "silyl-agostic" bond and the Eins barrier decreases to a greater extent comparing to the olefin isomer. In the course of these reactivity studies, subsequent rearrangements of the initially formed insertion products gave rise to a large number of different reaction pathways for the unsaturated “silyl” with a facile decomposition, including 1,2-migration to produce silylene.The study could not be extended the "sila-olefin" conformation in which Si is involved in the hydrogen migratory insertion owing to the role of the Si-H…M non classical interactions.The unsaturated “ethyl” isomers can be stabilized through a 1,3-migration reaction.
Descrição
Tese de doutoramento, Química (Química Inorgânica), Universidade de Lisboa, Faculdade de Ciências, 2013
Palavras-chave
Química inorgânica Teses de doutoramento - 2013