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Transition Metal Complexes with P-Acid Ligands P-bonding Organometallic Systems

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Transition Metal Complexes with P-Acid Ligands P-bonding Organometallic Systems

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    1. Transition Metal Complexes with P-Acid Ligands P-bonding Organometallic Systems P-Acid Ligands accept electrons from metal t2g orbitals (of P symmetry) into empty ligand t2g orbitals (e.g. P- and S- donors) or empty P* antibonding orbitals of unsaturated ligand systems (e.g. carbonyls, alkenes, aromatics). P-Acid Ligands form complexes with non-traditional geometries and unusual metal oxidation states. P-Acid Ligands stabilize metals in low oxidation states.

    2. Metal Carbonyls

    3. P-Alkenes, Allyls and Aromatic Complexes

    8. 18-electron rule

    13. 16/18-electron counts for d-block organometallic compounds Usually less Usually 16 or 18 than 18 electrons 18 electrons electrons Sc Ti V Cr Mn Fe Co Ni Y Zr Nb Mo Tc Ru Rh Pd La Hf Ta W Re Os Ir Pt

    14. Metal Clusters

    20. Rationalization of Cluster Structures Polyhedral Skeletal Electron Pair Theory

    21. Bonding in Boranes and Metal Clusters Parallels between main group (p-block) and organometallic chemistry, boranes and transition metal clusters Boranes Classification of boranes: closo- (cage-like) boranes BnHn2-. Closed polyhedra with n corners and all triangular faces (i.e. deltahedra). Each corner is occupied by a BH group (e.g. B6H62- with Oh symmetry, B12H122- with icosohedral symmetry). nido- boranes. Polyhedra with one corner removed from a closo framework (nest-like). e.g. B5H9 (from B6H62- - BH + 2H+ + 2H) B10H14 (from B11H112- - BH + 2H+ + 2H) arachno- boranes. Polyhedra with two corners removed. (spider-like). e.g. B4H10 (from B6H62- - 2B + 2H+ + 2H). hypho- boranes. Polyhedra with three corners removed. (net-like) e.g. B5H12 (from B8H82- - 3B + 2H+ + 2H).

    22. Bonding in boranes

    23. Wade's "2n + 2" rule for electron- deficient borane clusters Valence electrons - external (B-H) electrons = cluster framework electrons

    24. Delocalized Metal Cluster Electrons V = 14n + 2 ______________________________________________________ Total valence electrons (V) - external cluster electrons (n x 2) - metal core electrons ( n x 10) = cluster framework electrons (2n + (2)) __________________________________________________________ ______________________________________________________ V = 14 n + (2)

    28. Polyhedral Fragments Isolobal Principle

    29. Fragment Donor Electrons

    31. Isolobal Fragments

    32. The number of electrons provided for cluster bonding by selected fragments

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