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Theoretical (DFT) Insights Into The Mechanism Of Platinum Catalyzed Allyl Chloride Carbonylation And O-H Bond Insertion Reaction

Posted on:2011-12-07Degree:MasterType:Thesis
Country:ChinaCandidate:X J SunFull Text:PDF
GTID:2131330338477084Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
The decomposition of diazo compounds in the presence of transition metalcomplexes as catalysts has allowed the controlled transfer of carbene units intoorganic substrates. Usually these reactions formally consist of cyclopropanation or itsinsertion into an X-H bond(X= C, Si, N, P, O, S, Se, and halides). Particularlyinteresting is the case of the insertion into hydroxylic bonds, since it provides a newcarbon-oxygen bond, and the subsequent conversion of the alcohol into an ether.However, compared with the comprehensive studies of experiment aboutcyclopropanation and oxygen–hydrogen insertion reaction, the cyclopropanationreaction which catalyzed by many transition metal complexes have been studied intheoretical investigation at the DFT level, but there is little theoretical report about themechanism of O-H bond insertion reaction.In this paper, we chose several typical reactions that have been carefully studiedusing quantum methods, obtained some interesting results. On the basis of themolecular orbital theory, the tradition transition state theory as well as quantumchemistry theory, the systems (platinum complexes catalyzed) chose have beeninvestigated using Density Functional Theory (DFT) and the polarized continuummodel (PCM). The structures of the reagents, the reaction products and transitionstates along the reaction paths have been obtained, then obtained the potential energysurface, the dynamics datum and thermodynamic datum. The reaction mechanism hasbeen argued deeply using these data.The whole paper consists of four chapters. Chapter 1 mainly reviews the evolutionof the mechanism of allyl chloride carbonylation catalyzed by transition-metal. Thesecond chapter summarizes the theory of quantum chemistry and calculation methodsof this paper. The contents of two chapters were the basis and background of ourstudies and offer us with userful and reliable quantum methods.In chapter 3, theoretical study of the mechanism of allyl chloride carbonylationcatalyzed by platinum complexes is presented. The results indicate that the titlereaction has three possible channels, namely,πchannel,σchannel andπ+σchannel, and theπ+σchannel was the most major channel due to the lowest activation energybarrier. Furthermore, under the presence of high CO pressures, the complexesCl2Pt(CO)2 and Cl2Pt(CO) PH3, which are fromed by Cl2Pt(PH3)2, can behave as an"active"catalytic species, and the similarπ+σchannel is the most favorable channel.Chapter 4, In this paper we have carried out a theoretical investigation at theDFT (B3LYP) level of the mechanism of the O-H insertion reaction catalyzed byPtCl2 complex. The results obtained show that the active catalytic species is not aplatinum-carbene Cl2Pt=CH2 or a platinum-carbenoid ClPtCH2Cl, but the twocarbenoid-allyl alcohol complexes (IMA and IMB). Two similar reaction pathways,which are involve three main steps: coordination, hydrogen shift and reductiveelimination, has been found for the O-H insertion reaction. And the rate-determiningsteps are hydrogen shift process (20.56 and 19.00 kcal/mol, respectively, for path1and 2). But we discovered that cyclopropanation reaction can occur throughcarbometalation mechanism and the rate-determining step will be to overcome 29.34kcal/mol energy barrier, compared with the path1 and path2, the cyclopropanationreaction is more difficult than insertion reaction. Thus, we can conclude at this stagethat PtCl2 is an excellent chemoselective catalyst for the insertion of carbene into O-Hbonds of allyl alcohol.
Keywords/Search Tags:Density functional theory (DFT), Carbonylation, Insertion reaction, Carbenoid-allyl alcohol complexes
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