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CHEM 522 Chapter 02

CHEM 522 Chapter 02. General Properties of Organometallic Complexes. Types of Ligands. Table 2.2 Me, Cl, Ph, η 1 allyl, NO (bent) CO, CN-, NH 3 , PR 3 C 2 H 4 H 2 η 3 allyl, NO (linear) η 4 butadiene η 5 Cp. Electron Count. One electron donors (X· type): M-X M· + ·X

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CHEM 522 Chapter 02

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  1. CHEM 522Chapter 02 General Properties of Organometallic Complexes

  2. Types of Ligands • Table 2.2 • Me, Cl, Ph, η1allyl, NO (bent) • CO, CN-, NH3, PR3 • C2H4 • H2 • η3allyl, • NO (linear) • η4butadiene • η5Cp

  3. Electron Count • One electron donors (X· type): M-X M· + ·X "normal covalent" bond • X· = ·H, ·CH3, ·CH=CHR, ·C6H5, ·CΞN, ·CΞCR, ·C(=O)R, ·COOR, ·F, ·Cl, ·Br, ·I, etc. (always) • X·= ·NR2, ·PR2, ·OR, ·SR, ·NO (rarely)

  4. Electron Count • Two electron donor (L: type): M-L M + :L, "dative" or "coordinate covalent" bond • L: = :CO, :PR3, :NR3, :AsR3, :CR2, R2C=CR2, etc. (always), • RCΞCR, :OR2, :SR2 (nearly always) • = :O, :NR, :PR (rarely) • = σ adducts, e. g. H-H, H-R, H-SiR3, H-M • note: generally the strength of interaction with M decreases in order

  5. Electron Count • Three electron donor (LX type):

  6. Electron Count • Four electron donor:

  7. Electron Count • Five electron donor (L2X type):

  8. Electron Count • >5 electron donors:

  9. The 18 electron Rule • The metals in organometallic complexes like to have eighteen electrons around it • Where the electrons of the metal + the electrons that are donated by the ligands is considered • How to count electrons?

  10. The 18 electron Rule • There are two methods • Neutral ligand formalism • The metal is considered at neutral state and the ligand as well MLnXx M + nL + xX • To count the electrons add for M (the 4s+3d electrons) + two electrons for each L and one electron for X • If there is a formal charge do not forget to consider it

  11. Examples • Table 2.1 • How many electrons are in • V(CO)6 • V(CO)6- • Cr(CO)6 • Fe(CO)5 • Ni(CO)4

  12. Examples • See Fig 2.1 • Both ionic method and covelant method is presented

  13. Examples • Table 2.1 • How many electrons are in • (CO)5Mn-Mn(CO)5 • (CO)3Co(μ-CO)2Co(CO)3

  14. Examples (a) [Cp*Ru(PPh2CH2PPh2)(η2-O2)][BF4] (b) [Ru(PPh3)2Cl(NO)2]+ (c) Mo(CO)3(C6H6) (d) Cp*Os(CH3CO2)(PMe3) (e) [{η2-(Me2CH)2NCH2CH2N(CHMe2)2}PtMe2(CH3CN)2][PtCl6] (f) [CpFe(CO)2]2

  15. Examples (g) (PPh3)2(CF3CO2)2Ru(CH2) (h) Cp*Ta(CyNCH=CHNCy)(η4-CH2-CH=CH-CH2) (i) (η4-C6H6)Fe[(PMe2CH2)3SiMe] (j) Cp*Rh[(η2-CH2=CH)2Si(η5-C5H2-2,4-Me2)2]ZrCl2 (k) Os(η2-(2-(2’-pyridyl)phenyl))Cl(CO)(PPh3)2

  16. The 18 electron Rule • There are two methods • Oxidation state formalism • The metal is considered at its oxidation state and the ligand as well MLnXx Mx+ + nL + xX- • To count the electrons add for Mx+ (the 3d electrons) + two electrons for each L and two electron for X- • If there is a formal charge do not forget to consider it

  17. Examples • For each transition metal in the following molecules, indicate the valence shell, electron count, the formal oxidation state, and the d-electron count.

  18. 16-Electrons • As an exception • Always d8 square planar complexes prefer to have only 16 electrons around the central metal • Examples • PdCl2L2 • [PtCl4]2- • [AuMe4]-

  19. Coordination Number and Geometry • Table 2.5 2 linear 3 triangle or T-shape 4 tetrahedral or square 5 trigonal bipyramid or square pyramid 6 octahedral 7 capped octahedral or pentagonal bipyramid

  20. Coordination Number and Geometry • Table 2.6 • Square planar (d8 or d9) vs. Td (d0,d5,d10) • Oh usually low d occupancy • High coordination number usually with very small ligands

  21. Effect of Ligands Because both Cp and dpe are electron donor ligands, the reaction is enhanced

  22. Effect of Ligands • Co(III) is a strong oxidizing agent however Co(NH3)63+ lack the tendency • Mo is strongly reducing, Mo(CO)6 is an air stable compound

  23. Effect of Metals • Early transition metals like d2 Zr(II), and Ta(III) are easily oxidized because of the two electrons being in relatively high energy orbital. Usually bind to π ligands strongly. • Later transition metals tend to prefer lower oxidation state, back donation is not as early metals

  24. CO Stretching • Complex v(CO) (cm-1) V(CO)6 1979 Cr(CO)6 2000 Cr(CO)4 1938 Fe(CO)5 2023 Fe(CO)4 1995

  25. CO Stretching • Complex v(CO) (cm-1) V(CO)6- 1860 Cr(CO)6 2000 Mn(CO)6+ 2090

  26. Basic Transformations in Organotransition Metal Chemistry 1. ligand substitution

  27. 2. external attack at ligands by nucleophiles and electrophiles

  28. 3. oxidative addition/reductive elimination

  29. 4. sigma bond metathesis

  30. 5. α migratory insertion/elimination

  31. 6. 1,2 addition/elimination

  32. 7. reversible 2 + 2 addition

  33. 8. β migratory insertion/elimination

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