Topics in organometallic chemistry vol 12 theorectical aspects of transition metal catalysis 2005 springer

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12 Topics in Organometallic Chemistry Editorial Board: J.M Brown · P.H Dixneuf · A Fürstner · L.S Hegedus P Hofmann · P Knochel · S Murai · M Reetz · G van Koten Topics in Organometallic Chemistry Recently Published and Forthcoming Volumes Palladium in Organic Synthesis Volume Editor: J Tsuji Vol 14, 2005 Metal Carbenes in Organic Synthesis Volume Editor: K H Dötz Vol 13, 2004 Theoretical Aspects of Transition Metal Catalysis Volume Editor: G Frenking Vol 12, 2005 Transition Metal Arene p -Complexes in Organic Synthesis and Catalysis Volume Editor: E.P Kündig Vol 7, 2004 Organometallics in Process Chemistry Volume Editor: R.D Larsen Vol 6, 2004 Organolithiums in Enantioselective Synthesis Volume Editor: D.M Hodgson Vol 5, 2003 Ruthenium Catalysts and Fine Chemistry Volume Editors: C Bruneau, P.H Dixneuf Vol 11, 2004 Organometallic Bonding and Reactivity: Fundamental Studies Volume Editors: J.M Brown, P Hofmann Vol 4, 1999 New Aspects of Zirconium Containing Organic Compounds Volume Editor: I Marek Vol 10, 2005 Activation of Unreactive Bonds and Organic Synthesis Volume Editor: S Murai Vol 3, 1999 CVD Precursors Volume Editor: R Fischer Vol 9, 2005 Lanthanides: Chemistry and Use in Organic Synthesis Volume Editor: S Kobayashi Vol 2, 1999 Metallocenes in Regio- and Stereoselective Synthesis Volume Editor: T Takahashi Vol 8, 2005 Alkene Metathesis in Organic Synthesis Volume Editor: A Fürstner Vol 1, 1998 Theorectical Aspects of Transition Metal Catalysis Volume Editor : G Frenking With contributions by D V Deubel · G Drudis-Sole · G Frenking · A Lledos · C Loschen F Maseras · A Michalak · K Morokuma · G Musaev S Sakaki · V Staemmler · S Tobisch · G Ujaque · T Ziegler The series Topics in Organometallic Chemistry presents critical overviews of research results in organometallic chemistry, where new developments are having a significant influence on such diverse areas as organic synthesis, pharmaceutical research, biology, polymer research and materials science Thus the scope of coverage includes a broad range of topics of pure and applied organometallic chemistry Coverage is designed for a broad academic and industrial scientific readership starting at the graduate level, who want to be informed about new developments of progress and trends in this increasinly interdisciplinary field Where appropriate, theoretical and mechanistic aspects are included in order to help the reader understand the underlying principles involved The individual volumes are thematic and the contributions are invited by the volumes editors In references Topics in Organometallic Chemistry is abbreviated Top Organomet Chem and is cited as a journal Springer WWW home page: springeronline.com Visit the Top Organomet Chem contents at springerlink.com Library of Congress Control Number: 2004116518 ISSN 1436-6002 ISBN-10 3-540-23510-8 Springer Berlin Heidelberg New York ISBN-13 978-3-540-23510-8 DOI 10.1007/b94252 Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available in the Internet at This work is subject to copyright All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Violations are liable to prosecution under the German Copyright Law Springer is a part of Springer Science+Business Media springeronline.com © Springer-Verlag Berlin Heidelberg 2005 Printed in Germany The use of registered names, trademarks, etc in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use Typesetting: Fotosatz-Service Köhler GmbH, Würzburg Production editor: Christiane Messerschmidt, Rheinau Cover: design & production GmbH, Heidelberg Printed on acid-free paper 02/3141 me – Volume Editor Professor Dr Gernot Frenking Philipps-Universität Marburg Fachbereich Chemie Lahnberge 35032 Marburg, Germany frenking@chemie.uni-marburg.de Editorial Board Prof John M Brown Prof Pierre H Dixneuf Dyson Perrins Laboratory South Parks Road Oxford OX1 3QY john.brown@chem.ox.ac.uk Campus de Beaulieu Université de Rennes Av du Gl Leclerc 35042 Rennes Cedex, France Pierre.Dixneuf@univ-rennes1.fr Prof Alois Fürstner Prof Louis S Hegedus Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 45470 Mühlheim an der Ruhr, Germany fuerstner@mpi-muelheim.mpg.de Department of Chemistry Colorado State University Fort Collins, Colorado 80523-1872, USA hegedus@lamar colostate.edu Prof Peter Hofmann Prof Paul Knochel Organisch-Chemisches Institut Universität Heidelberg Im Neuenheimer Feld 270 69120 Heidelberg, Germany ph@phindigo.oci.uni-heidelberg.de Fachbereich Chemie Ludwig-Maximilians-Universität Butenandstr 5–13 Gebäude F 81377 München, Germany knoch@cup.uni-muenchen.de Prof Gerard van Koten Prof Shinji Murai Department of Metal-Mediated Synthesis Debye Research Institute Utrecht University Padualaan 3584 CA Utrecht, The Netherlands vankoten@xray.chem.ruu.nl Faculty of Engineering Department of Applied Chemistry Osaka University Yamadaoka 2-1, Suita-shi Osaka 565, Japan murai@chem.eng.osaka-u.ac.jp Prof Manfred Reetz Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 45470 Mülheim an der Ruhr, Germany reetz@mpi.muelheim.mpg.de Topics in Organometallic Chemistry is also Available Electronically For all customers who have a standing order to Topics in Organometallic Chemistry, we offer the electronic version via SpringerLink free of charge Please contact your librarian who can receive a password for free access to the full articles by registration at: springerlink.com If you not have a subscription, you can still view the tables of contents of the volumes and the abstract of each article by going to the SpringerLink Homepage, clicking on “Browse by Online Libraries”, then “Chemical Sciences”, and finally choose Topics in Organometallic Chemistry You will find information about the – Editorial Board – Aims and Scope – Instructions for Authors – Sample Contribution at springeronline.com using the search function Preface It has been stated in the past that the search for new catalysts has more the character of an art than a science discipline This is because there was usually more speculation than true knowledge about the reaction mechanisms of catalytic processes Even the identity of the catalytically active species was frequently not known, which is the reason that systematic testing of all possibly interesting compounds for catalytic reactions was carried out This is costly and time consuming The situation has changed in the last decade because much progress has been made in understanding the mechanisms of many catalytic reactions Besides sophisticated experimental tools, quantum chemical calculations of transition states and reaction intermediates played a prominent role in gaining much better insight into the fundamentals of transition metal catalysis Estimating solvent effects and the calculation of spectroscopic data are now routinely included in many theoretical studies Although the design of new catalytically active species is still largely a trialand-error process, modern research is guided by theoretical calculations in the search for new catalysts, which helps researchers to focus on more promising compounds The progress in quantum chemical method development has led to the present situation where theory and experiment are synergistically used in an unprecedented manner In particular, the calculation of transition metal compounds is no longer a too-difficult task for quantum chemistry because efficient methods are available for dealing with many-electron atoms and with relativistic effects The seven articles in this volume not provide a comprehensive view of theoretical investigations of catalytic reactions, because the field has expanded already beyond the scope that can be covered in one book The contributions written by experts in the field exemplarily demonstrate the strength but also the present limitations of quantum chemical methods for giving insights into the mechanism of transition-metal mediated reactions Because the development of new theoretical methods is still a very active research area, much progress can be expected in the coming years Marburg, Germany, February 2005 Gernot Frenking Preface Contents Transition Metal Catalyzed s -Bond Activation and Formation Reactions D G Musaev · K Morokuma Theoretical Studies of C-H s -Bond Activation and Related Reactions by Transition-Metal Complexes S Sakaki 31 Enantioselectivity in the Dihydroxylation of Alkenes by Osmium Complexes G Drudis-Solé · G Ujaque · F Maseras · A Lledós 79 Organometallacycles as Intermediates in Oxygen-Transfer Reactions Reality or Fiction? D V Deubel · C.Loschen · G Frenking 109 Late Transition Metals as Homo- and Co-Polymerization Catalysts A Michalak · T Ziegler 145 Co-Oligomerization of 1,3-Butadiene and Ethylene Promoted by Zerovalent ‘Bare’ Nickel Complexes S Tobisch 187 The Cluster Approach for the Adsorption of Small Molecules on Oxide Surfaces V Staemmler 219 Author Index Volume 1-14 257 Subject Index 263 Topics Organomet Chem (2005) 12: 1– 30 DOI 10.1007/b104397 © Springer-Verlag Berlin Heidelberg 2005 Transition Metal Catalyzed s -Bond Activation and Formation Reactions Djamaladdin G Musaev ( ) · Keiji Morokuma Cherry L Emerson Center for Scientific Computation and Department of Chemistry, Emory University, 1515 Dickey Dr., Atlanta GA 30322, USA dmusaev@emory.edu, morokuma@emory.edu Introduction 2 The Role of the Lower-Lying Electron States of Transition Metal Cations in Oxidative Addition of the s -Bonds (such as H-H, C-H and C-C) 3.1 3.2 Role of Cooperative Effects in the Transition Metal Clusters Reaction of Pt and Pd Metal Atoms with H2/CH4 Molecules Reaction of Pd2 and Pt2 Dimers with H2/CH4 Molecules s -Bond Activation via Nucleophilic Mechanism: the Role of Redox Activity of the Transition Metal Center – Hydrocarbon Hydroxylation by Methanemonooxygenase (MMO) 10 Vinyl-Vinyl Coupling on Late Transition Metals Through C-C Reductive Elimination Mechanism 5.1 Reductive Elimination from PtIV Halogen Complexes [Pt(CH=CH2)2X4]2– (X=Cl, Br, I) 5.2 Reductive Elimination from Mixed PtIV Complexes [Pt{cis-/trans-(CH=CH2)2(PH3)2}Cl2] 5.3 Reductive Elimination from PtII Halogen Complexes [Pt(CH=CH2)2X2]2– (X=Cl, Br, I) 5.4 Reductive Elimination from PtII Complexes with Amine and Phosphine Ligands [Pt(CH=CH2)2X2] (X=NH3, PH3) 5.5 Reductive Elimination from PdIV Complexes [Pd(CH=CH2)2X4]2– (X=Cl, Br, I) 5.6 Reductive Elimination from Mixed PdIV Complex [Pd{trans-(CH=CH2)2(PH3)2}Cl2] 5.7 Reductive Elimination from PdII Halogen Complexes [Pd(CH=CH2)2X2]2– (X=Cl, Br, I) 5.8 Reductive Elimination from PdII Complexes with Nitrogen and Phosphine Ligands [Pd(CH=CH2)2X2] (X=NH3, PH3) 5.9 Reductive Elimination from RhIII, IrIII, RuII and OsII Complexes 5.10 General Discussion 5.11 Comparison of the Vinyl-Vinyl (Csp2-Csp2) and Alkyl-Alkyl (Csp3-Csp3) Reductive Elimination 17 18 19 21 21 23 23 23 23 24 24 26 Concluding Remarks 27 27 References D G Musaev · K Morokuma Abstract The factors controlling the transition metal catalyzed s-bond (including H-H, C-H and C-C) activation and formation, the fundamental steps of many chemical transformations, were analyzed It was demonstrated that in the mono-nuclear transition metal systems the (1) availability of the lower lying s1dn–1 and s0dn states of the transition metal atoms, and (2) nature of the ligands facilitating the reduction of the energy gap between the different oxidative states of the transition metal centers are very crucial Meanwhile, in the transition metal clusters the “cooperative” (or “cluster”) effects play important roles in the catalytic activities of these clusters Another important factor affecting the catalytic activity of the transition metal systems shown to be their redox activity Keywords s-Bond activation and formation · Transition metal systems · Catalytic activity Introduction Sigma-bond (including H-H, C-H and C-C) activation and formation are fundamental steps of many chemical transformations and have been subject of numerous review articles [1] It is well accepted that certain transition metal complexes significantly facilitate the s-bond activation/formation steps, which may occur via various mechanisms, including oxidative addition/reductive elimination, metathesis and nucleophilic attack However, the factors affecting H-H, C-H and C-C activation/formation still need to be clarified in detail In this chapter we intend to analyze some factors that control the catalytic activity of transition metal complexes toward H-H, C-H and C-C bond activation/ formation Namely, we elucidate the role of (a) lower-lying electronic states of transition metal cations/atoms, (b) cooperative effects in transition metal clusters, (c) redox activity of the transition metal centers, and (d) the role of metal and ligand effects in vinyl-vinyl coupling The Role of the Lower-Lying Electron States of Transition Metal Cations in Oxidative Addition of the s -Bonds (such as H-H, C-H and C-C) The study of gas-phase activation of H-H, C-H and C-C bonds of the hydrogen molecule and saturated hydrocarbons, respectively, by bare transition metal atoms and cations is very attractive for getting insight to the mechanisms and factors (such as nature of metal atoms and their lower-lying electronic states) controlling catalytic activities of transition metal complexes Such studies, which are free from the ligand and solvent effects, have been subject of many experimental [2] and theoretical [3] papers in the past 10–15 years Experimental studies indicate that reaction of some transition metal cations (such as Fe+, Co+, and Rh+) with methane exclusively leads to the ion-molecule complex M+(CH4), while others (such as Sc+ and Ir+) pro- 242 V Staemmler probably attributable to adsorption on defects rather than on regular terrace positions on the MgO(100) surface plane The number of theoretical treatments of the CO/MgO(100) adsorption is so large that we could not include all of them in the table, but quote only the most important ones (More details can be found in [9].) We also not include experimental and calculated results for the adsorption geometry and for the shift of the C-O vibration frequency upon adsorption The reader is referred to the references given in Table All calculations, irrespective of their character, agree that the CO molecule is adsorbed at a Mg2+ cation on the MgO(100) terrace, it is oriented perpendicular to the surface with the C atom towards the surface (normal adsorption, C-down) However, there are large differences as far as the calculated adsorption energies are concerned The early SCF cluster result of Pacchioni et al from 1992 [78], 0.20 eV, seems to be very close to the best experimental value of 0.14 eV (which was not known in 1992), but the binding energy was certainly overestimated in this calculation, since the basis set superposition error (BSSE) was not corrected At the same time, Neyman and Rösch obtained a very large adsorption energy of 0.97 eV by means of DFT cluster calculations using the LDA functional [79]; in this study, the overbinding typical for the LDA functional was responsible for the strong adsorption.As soon as the LDA functional is replaced with a gradient corrected functional, the binding energy is greatly reduced, e.g., to about 0.10 eV in the calculations of Rösch and coworkers using the BLYP functional [80, 81] This effect has been confirmed by Vulliermet et al [82] who employed a DFT scheme particularly developed for treating weakly interacting systems (denoted by “Kohn-Sham equations with constrained electron density”, KSCE) together with the gradient corrected PW91 functional and found a moderate overbinding of 0.288 eV for CO adsorbed on an embedded Mg9O9 cluster Similarly, if the counterpoise correction is applied in the SCF calculations, the artificial overbinding due to the BSSE is avoided and rather small adsorption energies are obtained as well, e.g., a value of only 0.02 eV in the study of Nygren et al [83] using a small MgO58– cluster embedded in a large point charge array with ab initio model potentials (AIMP) Of course, the size of the quantum cluster and the embedding scheme will also have some influence on the calculated adsorption energy This was investigated by Neyman et al [81] who systematically varied the cluster size for the CO/MgO(100) adsorption The result of this and related studies can be briefly summarized as follows: as long as the cluster is too small, the calculated binding energy is too large, but it converges rapidly with increasing cluster size In the favorable case of MgO with its cubic structure, a Mg25O25 cluster can be safely regarded as large enough Too large binding energies are also obtained if small hydrogen saturated or small free clusters are used Or, even worse, if a small quantum cluster is embedded in unscreened point charges (PCs) and is not surrounded by a coordination shell of point charges carrying pseudo potentials The reason is easily understood: In all these cases, the 2p orbitals of the O2– anions adjacent to the Mg2+ adsorption site extend too much into the The Cluster Approach for the Adsorption of Small Molecules on Oxide Surfaces 243 bulk crystal or towards the hydrogen atoms or the positive point charges of the embedding PC field This reduces the Pauli repulsion with the approaching CO molecule and leads to a too strong bond Stated differently, the presence of a larger number of coordination shells “squeezes” the electrons of the spatially extended O2– anions immediately adjacent to the adsorption site out of the surface and leads to a larger Pauli repulsion and a smaller adsorption energy The next question is, how important are correlation effects for the CO/MgO(100) adsorption? Nygren et al [83] applied the modified coupled pair functional method (MCPF, an approximation to CCSD, see Table 3) in their calculations with the embedded MgO58– cluster When all the 50 valence electrons of CO and the quantum cluster were correlated, an increase in the calculated adsorption energy from 0.014 eV at the SCF level to 0.066 eV was found (BSSE corrected) This indicates a correlation contribution of about 0.05 eV Certainly, this is a lower bound, since only part of the semi-infinite MgO(100) surface could be included in the correlation treatment A similar estimate has been obtained by Ugliengo and Damin [72, 84] These authors used a periodic “supercell” model with a (1¥4) coverage of CO on MgO(100) The BSSE corrected DFT calculations with the B3LYP functional and a basis set of polarized triple zeta quality yielded an adsorption energy of only 0.034 eV [72] An ONIOM-MP2 type estimate of the correlation contribution performed with the help of a free Mg9O9 cluster increased the adsorption energy to 0.137 eV, very close to the best experimental value A further analysis of the intra- and intersystem correlation contributions gave a value of 0.068 eV as due to the Van der Waals interaction between CO and MgO(100) [84] Several authors have also performed a detailed analysis of the different components to the total binding energy [72, 78] The results obtained at the SCF [78] and DFT [72] levels are very similar There is a delicate balance between Pauli repulsion and electrostatic attraction, the contributions of induction and chemical bonding (covalent bond and charge transfer) are nearly negligible However, the electrostatic interaction is not only caused by the attraction of the dipole moment of CO by the Mg2+ ions at the surface, the contribution of the quadrupole moment is even more important The multipole expansion of the electrostatic interaction, as given in Eq (1), is only useful for large molecule/ surface separations, in the vicinity of the equilibrium geometry it is too slowly convergent As indicated by the data in Table 4, the delicate balance between Pauli repulsion and electrostatic interaction can be greatly perturbed if too small clusters, bad embeddings, inflexible basis sets or inappropriate functionals are used in the calculations A summary of these and several more theoretical treatments yields the following picture: At the SCF level one obtains only a small part of the experimental adsorption energy, between about 0.01 and 0.02 eV The same is true for DFT calculations with hybrid functionals (e.g., 0.04 eV with the B3LYP functional) while local and semi-local gradient corrected functionals overestimate the binding energy Inclusion of correlation effects on top of SCF largely enhances the binding energy and improves the agreement with experiment 244 V Staemmler Electron correlation is needed for three reasons: The inter-system correlation, contained neither in the SCF nor in the DFT approach, describes the Van der Waals interaction; it amounts to about 0.05–0.08 eV in the case of CO/MgO The intra-system correlation, also not included in the SCF approximation, but partly so in the DFT functionals, is mainly necessary to improve the electronic densities and to correct wrong SCF or DFT values of the permanent multipole moments of the fragments For the CO/MgO adsorption this effect contributes also about 0.05 eV to the total adsorption energy And finally, there is another contribution to the intra-system correlation which is generally slightly reduced in the supermolecule as compared to the isolated fragments [14, 85], but this effect is probably very small for CO/MgO(100) To conclude, it can be safely stated that the mechanism of the interaction between CO and the MgO(100) surface is well understood The difficulties connected with a reliable calculation of adsorption energies as well as adsorption geometries, vibration frequency shifts and so forth are also well understood Therefore it seems straightforward, though it might be quite tedious, to proceed from this simple prototype system to more complex cases 5.2 Small Molecules on NiO(100) Since NiO has the same crystal structure as MgO, with nearly the same lattice constant (4.21 Å in MgO and 4.17 Å in NiO [86]) and is a good insulator as well (the band gap of NiO is about 3.5 eV [87]) it can be expected that the adsorption of small molecules on its (100) surface plane is very similar to that on MgO(100) However, there are two differences between the electronic structures of MgO and NiO While the Mg2+ cations in MgO have a closed shell structure with a fully occupied 2p shell, the Ni2+ cations have a d8 configuration with two unpaired electrons and a 3A2g ground state in the octahedral environment in NiO Further, the spins at the Ni2+ cations are antiferromagnetically coupled This raises two immediate questions: first, is there the possibility of a covalent chemical bond between the partially occupied orbitals at the Ni adsorption site and the adsorbed molecule, and second, are the d-orbitals at the Ni2+ cations completely localized or they form delocalized, metal-like bands and how does this affect the adsorption properties? Most of the cluster treatments for the adsorption of CO, NH3, NO and other small molecules on NiO(100) simply ignored the second problem They used very small clusters containing just one Ni atom, either the hydrogen-saturated NiO5H8 cluster of Pöhlchen and Staemmler [36, 37, 88] or MgO clusters doped with one Ni atom [89–94] Only in a few more recent papers was the attempt made to use larger NiO clusters: an embedded Ni5O5 cluster by Klüner and Staemmler [95], Ni9O9 clusters and NiO slabs by Bredow [96] and by Pacchioni and coworkers [92–94] and the recent periodic DFT slab calculation with a LSDA+U functional by Rohrbach et al [97] The use of larger NiO clusters is severely hampered by the fact that NiO is antiferromagnetic, therefore all The Cluster Approach for the Adsorption of Small Molecules on Oxide Surfaces 245 cluster treatments are forced to use the spin-contaminated unrestricted Hartree-Fock approximation or to work with the high-spin state of the cluster which is not its electronic ground state The adsorption of the closed shell molecules CO and NH3 on NiO(100) shows similar characteristics as on MgO(100), though the adsorption energies are a little larger, 0.30±0.04 eV for CO [98] and 0.80 eV for NH3 [12, 13] At the SCF level only very small binding energies of 0.15 eV or even less can be obtained [92–96]; DFT treatments show the same qualitative behavior as for MgO: local density functionals exhibit strong overbinding, gradient corrected functionals a little overbinding, while the hybrid functional B3LYP is again quite close to the SCF results [92–94, 96, 97] Correlation effects on a wave function based level have not been treated so far for these systems Of course, the same care with basis sets and counterpoise corrections has to be applied as in the simpler CO/MgO case The adsorption of NO on NiO(100) is quite different Since NO has an open shell structure with a singly occupied 2p* orbital, there is the possibility of a covalent bond between this orbital and the partially occupied 3d orbitals on Ni A detailed analysis has shown [36] that the two singly occupied 3d orbitals at Ni, 3dz2 and 3dx2–y , and the two components of the 2p* orbital at NO have different symmetries and cannot form a covalent chemical bond as long as NO is adsorbed normal to the NiO(100) surface In a tilted adsorption geometry, however, the symmetries match and a covalent bond can be formed This is in complete agreement with experiment: NO adsorbs tilted on NiO(100), with a tilt angle of about 50° [12, 36, 98] However, this bond is still rather weak, since the Pauli repulsion between the fully occupied 2p orbitals of the O2– ions adjacent to the Ni2+ adsorption site and the doubly occupied orbitals of NO prevents NO from approaching the surface so closely that the short-range chemical bonding becomes effective Therefore, the system NO/NiO(100) exhibits a “weak chemisorption” The experimental adsorption energy of 0.57±0.04 eV [99] is substantially larger than that for the adsorption of CO on MgO(100) or NiO(100) As stated by Hoeft et al [12, 13], the calculation of accurate adsorption geometries and energies for NO/NiO(100) is still far from being satisfactory It follows from the above discussion that NO/NiO(100) is not a “single reference” case, i.e., the chemical bond cannot be properly described by a wave function in the form of a single determinant The consequence for wave function based approaches is that one has to start from a multi-configuration SCF method (MC-SCF or complete active space SCF, CASSCF) and has to include correlation effects on top of this reference wave function This can again be done by perturbation theory (CASPT2) or by multi-reference coupled cluster theory (e.g., the MC-CEPA approach mentioned in Table 3) On the other hand, its is not clear whether DFT can properly describe such a situation at all Indeed, all previous attempts to calculate reasonable adsorption energies for NO/NiO(100) by DFT failed [93] The conclusions obtained in a recent study, reported by Pacchioni et al [94], can be summarized as follows: DFT is inappropriate for 246 V Staemmler such cases; the results are either seriously in error or depend so sensitively on the functional and the model (cluster or slab) that they are completely useless At the CASSCF level, there is only very weak bonding,
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