Yves Jean - Molecular Orbitals of Transition Metal Complexes (793957), страница 2
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Characterization of the d block 692.5.2. Electronic structure 722.6. Trigonal-planar ML3 complexes 732.6.1. Characterization of the d block 732.6.2. 16-electron d10 complexes 742.7. Linear ML2 complexes 742.7.1. Characterization of the d block 752.7.2. Electronic structure 762.8. Other complexes or MLn fragments 762.8.1. Pyramidal ML3 complexes 772.8.2. ‘T-shaped’ ML3 complexes 792.8.3. ‘Butterfly’ ML4 complexes 812.8.4. Bent ML2 complexes 832.8.5. ML complexes 84Exercises 85Appendix A: polarization of the d orbitals 89Appendix B: Orbital energies 94Chapter 3π-type interactions 973.1.
π -donor ligands: general properties 983.1.1. The nature of the π orbital on the ligand 983.1.2. ‘Single-face’ and ‘double-face’ π -donors 993.1.3. Perturbation of the d orbitals: the generalinteraction diagram 1003.1.4. A first example: the octahedralcomplex [ML5 Cl] 1013.2. π -acceptor ligands: general properties 1043.2.1. The nature of the π orbital onthe ligand 1043.2.2. ‘Single-face’ and ‘double-face’π -acceptors 1053.2.3. Perturbation of the d orbitals: the generalinteraction diagram 107Contents3.2.4.
A first example: the octahedral complex[ML5 CO] 1083.3. Complexes with several π -donor orπ -acceptor ligands 1113.3.1. The trans-[ML4 Cl2 ] octahedralcomplex 1113.3.2. The trans-[ML4 (CO)2 ] octahedralcomplex 1163.3.3. Construction of the d-block orbitals‘by hand’ 1173.3.4. [MCl6 ] and [M(CO)6 ] octahedralcomplexes 1233.4. π complexes: the example of ethylene 1253.4.1. Orbital interactions: theDewar–Chatt–Duncanson model 1253.4.2. Electronic structure of a d6 complex[ML5 (η2 -C2 H4 )] 1263.4.3. Metallocenes Cp2 M 1293.4.4.
Cp2 MLn complexes 1303.5. π interactions and electron counting 133Exercises 135Appendix C: The carbonyl ligand, a double-faceπ -acceptor 138Chapter 4 Applications 1414.1. Conformational problems 1414.1.1. d8 -[ML4 (η2 -C2 H4 )] complexes 1414.1.2. d6 -[ML5 (η2 -C2 H4 )] complexes: staggered oreclipsed conformation? 1444.1.3.
d6 -[ML4 (η2 -C2 H4 )2 ] complexes: coupling of twoπ -acceptor ligands 1474.1.4. Orientation of H2 in the ‘Kubas complex’[W(CO)3 (PR 3 )2 (η2 -H2 )] 1524.2. ‘Abnormal’ bond angles 1564.2.1. Agostic interactions 1564.2.2. d6 ML5 complexes: a ‘T-shaped’ or ‘Y-shaped’geometry? 1604.3. Carbene complexes 1654.3.1. Ambiguity in the electron count for carbenecomplexes 1654.3.2.
Two limiting cases: Fischer carbenes and Schrockcarbenes 166Contents4.4. Bimetallic complexes: from a singleto a quadruple bond 1704.4.1. σ , π , and δ interactions 1714.4.2. M2 L10 complexes 1724.4.3. The [Re2 (Cl)8 ]2− complex: a staggered or aneclipsed conformation? 1744.5. The reductive elimination reaction 1764.5.1. Definition 1764.5.2. Simplified model for the reaction−R 176[Ln MR 2 ] → [Ln M] + R−4.5.3. An example:−R.
178d8 -[L2 MR 2 ] → d10 -[L2 M] + R −4.6. Principal references used 181Exercises 181Chapter 5 The isolobal analogy 1855.1. The analogy between fragments of octahedralML6 and of tetrahedral CH4 1855.1.1. Fragment orbitals by the valence-bondmethod 1875.1.2. Fragment molecular orbitals 1905.2. Other analogous fragments 1945.3. Applications 1955.3.1. Metal–metal bonds 1955.3.2. Conformational problems 1995.4. Limitations 200Exercises 202Chapter 6 Elements of group theory andapplications 2056.1. Symmetry elements and symmetry operations 2056.1.1. Reflection planes 2056.1.2. Inversion centre 2066.1.3. Rotation axes 2076.1.4. Improper rotation axes 2096.2. Symmetry groups 2106.2.1.
Definitions 2106.2.2. Determination of the symmetry pointgroup 2116.2.3. Basis of an irreducible representation 212Contents6.2.4. Characters 2156.2.5. Character tables 2176.3. The reduction formula 2206.3.1. The reduction formula 2206.3.2. Characters of a reduciblerepresentation 2216.3.3. Applications 2226.3.4. Direct products 2246.4. Symmetry-adapted orbitals 2256.4.1.
Projection operator 2256.4.2. Application 2256.5. Construction of MO: H2 O as an example 2296.5.1. Symmetry and overlap 2296.5.2. Molecular orbitals for H2 O 2306.6. Symmetry-adapted orbitals in several MLncomplexes 2316.6.1. Square-planar ML4 complexes 2316.6.2. Tetrahedral ML4 complexes 2346.6.3. Trigonal-planar ML3 complexes 2366.6.4. Trigonal-bipyramidal ML5 complexes 2386.6.5. Octahedral ML6 complexes 2406.6.6. Trigonal-planar ML3 complexes with a ‘πsystem’ on the ligands 242Exercises 247Answers to exercises 253Bibliography 271Index 273IntroductionThis book starts from the most elementary ideas of molecular orbitaltheory, and it leads the reader progressively towards an understandingof the electronic structure, of the molecular geometry and, in somecases, the reactivity of transition metal complexes.The use of simple notions, such as symmetry, overlap, and electronegativity, allows a qualitative method of analysis of the electronicstructure of complexes, and of the properties which follow from it suchas geometry or reactivity, to be developed.
Qualitative in the sense that,for example, it enables us to understand why the structure of a particularcomplex is tetrahedral rather than planar, without being able to providea reliable numerical value of the energy difference between these twostructures.
The quantitative level can be attained elsewhere—as is nowstandard practice in our laboratories—by more accurate methods suchas ab initio or density functional theories. But to interpret the resultsprovided by more complex calculations, it is often necessary to returnto the fundamental notions of symmetry, overlap, and electronegativity.The qualitative approach used here is mainly based on the analysisof orbital interactions (atomic or molecular).
Its application to transitionmetal complexes developed rapidly from about 1975, the leading exponent being Roald Hoffmann, winner of the Nobel prize for chemistry in1981 with Kenichi Fukui. As a result, many experimental results can berationalized, that is to say understood, on the basis of analyses and using alanguage that are accessible to every chemist. A colleague, Marc Bénard,spoke in the introduction to one of his lectures of the prodigious decade1975–85 .
. . Moreover, it has been possible to apply this approach to all ofchemistry (organic, inorganic, organometallic, and the solid state), whichis one of its strongest points. These are no doubt the main reasons forits success which has spread far beyond the realm of specialists: as RoaldHoffmann writes in the preface, it is a transferable theory which hasmarked our time.It is certainly transferable to students, and the aim of this book isto encourage that process. By learning this method for the theoretical analysis of molecular electronic structure, a method which hasso profoundly changed our approach to chemistry, the reader may beIntroductionencouraged to continue his exploration of the methods of quantumchemistry which nowadays are part of all chemical research.In the first chapter, we present the rules for electron counting intransition metal complexes, the different coordination modes adoptedby ligands and the essential properties of the orbitals that are involvedon the metal and on the ligands.
The main ligand fields are studied in thesecond chapter, where we limit ourselves to σ -type interactions betweenthe metal and the ligands. The structure of the d block is established;knowledge of this structure, which is essential for transiton metal complexes, enables us to explore the relationships between the electronicconfiguration of complexes and their geometry. In the third chapter, westudy the ways in which the analysis is changed when the ligands haveπ-type interactions with the metal (both π-donor and π -acceptor ligands). All these ideas are then used in the fourth chapter, which is a seriesof examples that illustrate how, starting from a knowledge of the orbitalstructure of complexes, we can understand their geometrical structureand, sometimes, their reactivity. The fifth chapter discusses the ‘isolobal analogy’ which shows how the electronic structures of transitionmetal complexes and of organic molecules can be related. A bridge isthus constructed between these two areas of chemistry that allows us tounderstand several resemblances (in particular, concerning structures)between species that appear to be very different.
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