Estudo da diastereoseletividade na interaÃÃo do β-pineno com catalisadores de rÃdio

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In this work, electronic structure calculations were carried out in order to study the spatial and electronic effects that drive the diastereoselectivity in the interaction of catalyst of Rhodium with monoterpenes, in particular with β-pinene. The interaction of the catalyst with the substrate, as well as, the insertion reaction of the monoterpene into the metal-hidride were analyzed using the compounds [HRh(CO)3] and [HRh(CO)2PMe3] as catalytic species. The density-functional theory (DFT) was used throughout, employing the GGA functional BP86. This functional was chosen after a systematic study on a model reaction where we evaluated the energetics involved in the insertion reaction of ethylene into the Rh-H bond of the compound [Rh(CO)3(H)(C2H2)]. Through this systematic study it was shown among several common used exchangecorrelation functionals, better energetic and structural results was obtained with the BP86, B3P86 and PBE, which were in good agreement with calculations performed at the CCSD(T)//CISD level of theory. It was also shown that the calculations using perturbation theory do not work well for this type of system, showing a great fluctuation along the perturbative series and showing results in complete disagreement with the DFT, CISD and CCSD(T) results. However, the MP2 and MP3 results are dramatically improved upon the application of the spin component scale method, with different scaling of the contributions of the same spin and opposite spins to the corrected energy. The calculations at the DFT level of theory presented in this work reveals that the diastereoseletivity found in the hydroformylation of β-pineno using the unmodified catalyst, [HRh(CO)3] , is due to the combination of two factors: (i) low activation energy for the catalyst attack through the top face, which is most sterically hindered face and (ii) the high stability of the metal-alkyl compound generated along this path. The analyze of nature of the metal-ligand interactions suggest that the π-complex formed through the top face is stronger than the π-complex formed along the bottom face. The substitution of a CO ligand by a phosphine (PMe3), which is a more basic ligand, does not change, appreciably, the results found for the unmodified catalyst.

ASSUNTO(S)

hidroformilaÃÃo de olefina, catalisador de rÃdio, dft. hydroformylation of olefin, rhodium catalyst, dft. quimica

ACESSO AO ARTIGO

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