日本語 /English
Specially Promoted Research of KAKENHI
(2010.4- 2015.3)
Title
Theoretical Study of Complex Electronic Systems Including d Electron: Fundamental Understanding and Prediction by New Electronic Structure Calculation Method for Large Systems
Co-I： Shigeru Nagase, Masahiro Ehara
Please also refer to pdf file in SPR page for abstract.
Project Description
1. Background of Research Project and Past-related Achievements of Applicants
In modern theoretical and computational chemistry, one of the important trends is to make new development for high quality electronic structure theory which can be applied to large systems. Another important trend is to present theoretical knowledge about large systems at molecular lever. Important target of modern theoretical and computational chemistry is biological system, as well known. Also, we believe that transition metal complexes are important research target of theoretical and computational chemistry. This is because the transition metal complexes possess in general complicated electronic structure, varieties of bonding nature, geometries, and reaction behavior. Besides those interesting issues from viewpoint of fundamental chemistry, transition metal complexes play key roles as catalysts and molecular devices which are very important from viewpoint of applied chemistry. These functions deeply relate to the electronic structure. To make new developments in chemistry of catalysis and molecular devices, we need correct and deep knowledge about their electronic structures. In many cases, theoretical calculations of transition-metal complexes require to consider correctly electron correlation effects. Thus, theoretical and computational studies of transition metal complexes need high quality of electronic structure theory for large systems, as described above.
S. Sakaki is theoretically investigating geometries, bonding natures, reaction behavior, catalyses of transition metal complexes for long. He successfully discussed bonding nature and geometries of various transition metal complexes, such as carbon dioxide complexes, dinitrogen complexes, and sulfur dioxide complexes in old days, and transition metal complexes of -conjugate systems including Si elements recently. He also successfully investigated several important reactions such as CO insertion into the metal-alkyl bond, ethylene insertion into the metal-hydride and metal-silyl bonds in old days, and -bond activation recently. In particular, it should be noted that he successfully carried out theoretical study of heterolytic -bond activation to present its characteristic features and new concept of heterolytic bond activation. Also, he investigated many catalytic reactions and elucidated those reaction mechanisms. For instance, he presented theoretical answers to the long question why the Pt-catalyzed hydrosilylation, one of important catalytic reactions, proceeds through Chalk-Harrod mechanism but the Rh-catalyzed one proceeds through different modified Chalk-Harrod mechanism. He also reported new reaction mechanism in Zr-catalytzed hydrosilylation.1 One of his important contributions is to present catalytic cycles of cross-coupling reactions. Recently, he clarified the reason why fluoride anion accelerates the Pd-catalyzed cross-coupling reaction of organic silicon compound. All his works clearly show the reaction mechanism with the clear reason why the catalytic cycle is favorable compared to other possible courses.2 Recently, he proposed frontier-orbital-consistent effective potential which was successfully applied to CCSD(T) calculations of large transition metal complexes.3
S. Nagase is theoretically investigating multiple bonds including Si for long. He succeeded in theoretically predicting how to synthesize the Si-Si triple bond. His another outstanding work is theoretical studies of fullerene. In particular, it is emphasized that he correctly elucidated the structures of many metal-encapsulated fullerenes which were incorrectly proposed by experimentalists. Also, his recent works about efficient MP2 procedure4 and new development of quantum Monte-Carlo method provide new developments about high quality compuational methods.5
M. Ehara is theoretically investigating excitation spectra of various compounds with SAC-CI method. He succeeded in theoretically presenting well understanding of many excitation spectra which experimentalist could not. He also succeeded in presenting new development in SAC-CI through including higher order excitation operators, which is called general-R method.6
In conclusion, I believe that collaboration of these three excellent theoreticians leads to new outstanding theoretical studies about complex systems including transition metal and heavy non-transition metal elements.
2. Importance and Necessity of this Project and its Expected Impact upon the Target Field of Research
Complex systems including transition metal elements are very important in both pure and applied chemistry. For instance, various new compounds including transition metal and heavy non-transition metal elements are synthesized recently, but their electronic structures and bonding natures can not be understood in classical way. We need non-classical understanding of them. Some of them is conjugate systems including multiple bonds which are completely different from carbon analogues. Also, transition metal-silaallyl and silapropargyl complexes, which are considered similar to the -allyl and -propargyl complexes, are very different from the carbon analogues. Again, we need new theoretical non-classical understanding. Also,
transition metal complexes including -conjugate systems are expected to be useful for molecular devises such as solar battery and organic luminescence materials. All those compounds need theoretical understanding because their functions arise from the complicated and flexible electronic structures. We never forget the fact that transition metal complexes play indispensable roles in many catalytic reactions which are necessary for chemical industry and organic syntheses. Experimentalists need theoretical knowledge to understand the catalytic cycle and catalyses.
Recently, DFT method is employed in almost all theoretical studies of large systems including transition metal elements. However, the DFT method with usual functionals can not present correct understanding about dispersion interaction. Also, we found new weak points in the DFT computational results of transition metal complexes; one of them is considerably large underestimation of binding energy. Though new efficient functionals are reported recently, we need post Hartree-Fock method which can be applied to large systems. We believe that collaboration of Sakaki, Nagase, and Ehara is very powerful to present such new method because each has original methodology and combination of them leads to new development of new efficient method. Also, all of them have correct knowledge about compounds and reactions. We believe that many experimentalists are waiting those theoretical knowledge to make new developments in molecular devices and catalytic reactions.
In conclusion, our project is able to present new development in both theoretical and experimental chemistry fields.
3. Research Objectives and Targeted Goals of this Project
(1) Development of Electronic Structure Theory for Large Systems: Nagase and his coworkwers presented recently new procedure for MP2 method. Sakaki and his coworkers recently proposed frontier-orbital-consistent effective potentials to incorporate electronic effects of substituent which can be applied to CCSD(T) calculations of large systems. Prof. K. Kitaura, who is our old colleague, proposed FMO recently. Combination of these three methods provides us high quality post Hartree-Fock computational method in which main part is calculated by CCSD(T) combined with FOC-EP and the other is calculated FMO-MP2. Ehara proposed SAC-CI General-R method, but it needs very high cost. We will carefully check what higher order excitation operator is necessary and propose SAC-CI General-R with reduced excitation operator which can be applied to transition metal system with FOC-EP method. This is also very powerful to investigate excited states of large transition metal complexes.
(2) Bonding Nature and Electronic Structure of Complex Systems including Transition Metal and heavy non-Transition-metal elements: Transition metal complexes including Si and heavier group 14 and 15 elements are one of most interesting and attractive compounds in recent chemistry, because they contain in many cases new non-classical geometries and bonding natures. We wish to present clear theoretical understanding of geometries and bonding natures of those compounds and also predict how to synthesize such new compounds.
(3) Electronic Structure and Excitation Spectra of Adsorped Molecules: Though excited state of the adsorpted molecule is one of important issues to investigate, their theoretical study is not easy. We can not perform SAC-CI calculation of metal-surface and adsorped molecule on the metal surface. However, the FOC-EP method allows us to apply the SAC-CI to adsorped molecule with realistic model of metal surface. Our theoretical study provides us new understanding of molecules on metal surface.
(4) Catalyses of Transition-Metal Complexes: Catalysis of transition metal complexes is one of important research targets in modern chemistry because various new organic syntheses are proposed with catalysis of transition metal complex. Catalysis is also indispensable in chemical industry; one good example is Kaminsky catalyst which efficiently catalyzes olefin polymerization. In our study, we plan to theoretically investigate catalytic reaction for CO2 fixation, cross-coupling reaction, and polymerization reaction. The first is important because CO2 can be converted to chemically useful material such as polymer, lactone, and similar compounds. The second is one of important synthetic reactions. In many cross-coupling reactions, palladium complexes are used as catalyst. We plan to substitute palladium to nickel, iron, and copper, because palladium is one of expensive metals. Many theoretical studies have been reported for polymerization of olefin. However, catalytic synthesis of functional polymer has not been theoretically investigated yet. We plan to elucidate the catalytic cycle first and then analyze catalytic function. Based on them, we wish to present theoretical prediction of new catalysts.
References
1) S. Sakaki, T. Takayama, M. Sumimoto, M. Sugimoto,J. Am. Chem. Soc., 126, 3332-3348 (2004).
2) A. Sugiyama, Y. –y. Ohnishi, M. Nakaoka, Y. Nakao, H. Sato, S. Sakaki, Y. Nakao, T. Hiyama, J. Am. Chem. Soc., 130, 12975-12985 (2008).
3) Y. –y. Ohnishi, Y. Nakao, H. Sato, S. Sakaki, J. Phys. Chem. A, 112, 1946-1955 (2008).
4) M. Katouda and S. Nagase, Int. J. Quant. Chem., 109, 2121-2130 (2009).
5) Y. Ohtsuka and S. Nagase, Chem. Phys. Lett., 463, 431-434 (2008).
6) M. Ehara, H. Nakatsuji, Chem. Phys. Lett. 282, 347 (1998).