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The CBC Method of electron counting

Five slides about…. The CBC Method of electron counting. Consider…. The ‘ionic’ method says. 2 Cp - 6e - each (-1 each) 2 Me - 2e - each (-1 each) Ligand total 16e - -4 So Ti +4 (d 0 ) since it is neutral 16e - exception?

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The CBC Method of electron counting

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  1. Five slides about… The CBC Method of electron counting

  2. Consider…

  3. The ‘ionic’ method says • 2 Cp- 6e- each (-1 each) • 2 Me- 2e- each (-1 each) • Ligand total 16e- -4 • So Ti+4 (d0) since it is neutral • 16e- exception? • Problem…is this really a +4 metal interacting with four anions?

  4. The ‘covalent’ method says • 2 Cp 5e- each • 2 Me 1e- each • Ligand total 12e- • So Ti0 (d4) since it is neutral • 16e- exception? • Problem…assuming the d-electrons are non-bonding how is this diamagnetic?

  5. CBC ligand classification • L • Ligand donates two electrons • CO, phosphines, alkenes • X • Ligand donates one electron • H, halides, alkyl • Z • Ligand donates zero electrons • boranes

  6. How to count? [MLlXxZz] • Total electron count • From ligands: 2l + x • From metal: m • m + 2l + x • Valence number (VN) for the metal = x + 2z • Ligand bond number (LBN) for the metal = l + x + z • dn count for metal = m - VN

  7. Current example X H3C• L L2X X

  8. Counting • Metal is classified as ML4X4 • Electron count: 4 + 10 + 2 = 16 • VN: 4 • LBN: 8 • dn: 0

  9. What have we learned? • Electrons: 16 • VN: 4 • Classification: ML4X4 http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm

  10. A different view Ti http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm

  11. What about valence? • VN: 4 is not saying it is +4 • Gives the d0 count Ti http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm

  12. What is LBN? • Not coordination number • Number of sites on the metal • LBN: 8 while CN: 12 Ti http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm

  13. Further readings • M.L.H. Green J. Organomet. Chem. 1995, 500, 127-148. • G. Parkin, in Comprehensive Organometallic Chemistry III, Volume 1, Chapter 1; R.H. Crabtree and D.M.P. Mingos(Eds), Elsevier, Oxford, 2006. • http://www.columbia.edu/cu/chemistry/groups/parkin/cbc.htm

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