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Coordination Chemistry Reactions of Metal Complexes

Coordination Chemistry Reactions of Metal Complexes. Substitution reactions. Labile complexes <==> Fast substitution reactions (< few min) Inert complexes <==> Slow substitution reactions (>h) a kinetic concept. Not to be confused with

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Coordination Chemistry Reactions of Metal Complexes

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  1. Coordination Chemistry Reactions of Metal Complexes

  2. Substitution reactions Labile complexes <==> Fast substitution reactions (< few min) Inert complexes <==> Slow substitution reactions (>h) a kinetic concept Not to be confused with stable and unstable (a thermodynamic concept DGf <0)

  3. Dissociative (D) Associative (A) Interchange (I) Mechanisms of ligand exchange reactions in octahedral complexes Ia if association is more important Id if dissociation is more important

  4. Kinetics of dissociative reactions

  5. Fast equilibrium K1 = k1/k-1 k2 << k-1 Kinetics of interchange reactions For [Y] >> [ML5X]

  6. Kinetics of associative reactions

  7. Principal mechanisms of ligand exchange in octahedral complexes Dissociative Associative

  8. MOST COMMON Dissociative pathway (5-coordinated intermediate) Associative pathway (7-coordinated intermediate)

  9. Experimental evidence for dissociative mechanisms Rate is independent of the nature of L

  10. Experimental evidence for dissociative mechanisms Rate is dependent on the nature of L

  11. Inert and labile complexes Some common thermodynamic and kinetic profiles Exothermic (favored, large K) Large Ea, slow reaction Stable intermediate Exothermic (favored, large K) Large Ea, slow reaction Endothermic (disfavored, small K) Small Ea, fast reaction

  12. Labile or inert? LFAE = LFSE(sq pyr) - LFSE(oct)

  13. Inert ! Why are some configurations inert and some are labile?

  14. Substitution reactions in square-planar complexes the trans effect (the ability of T to labilize X)

  15. Synthetic applications of the trans effect

  16. Mechanisms of ligand exchange reactions in square planar complexes

  17. M1(x +1)+Ln + M2(y-1)+L’n M1(x+)Ln + M2(y+)L’n Electron transfer (redox) reactions -1e (oxidation) +1e (reduction) Very fast reactions (much faster than ligand exchange) May involve ligand exchange or not Very important in biological processes (metalloenzymes)

  18. Outer sphere mechanism [Fe(CN)6]3- + [IrCl6]3- [Fe(CN)6]4- + [IrCl6]2- [Co(NH3)5Cl]+ + [Ru(NH3)6]3+ [Co(NH3)5Cl]2+ + [Ru(NH3)6]2+ Reactions ca. 100 times faster than ligand exchange (coordination spheres remain the same) r = k [A][B] Tunneling mechanism

  19. Inner sphere mechanism [Co(NH3)5Cl)]2+:::[Çr(H2O)6]2+ [Co(NH3)5Cl)]2+ + [Çr(H2O)6]2+ [CoIII(NH3)5(m-Cl)ÇrII(H2O)6]4+ [Co(NH3)5Cl)]2+:::[Çr(H2O)6]2+ [CoII(NH3)5(m-Cl)ÇrIII(H2O)6]4+ [CoIII(NH3)5(m-Cl)ÇrII(H2O)6]4+ [CoII(NH3)5(m-Cl)ÇrIII(H2O)6]4+ [CoII(NH3)5(H2O)]2+ + [ÇrIII(H2O)5Cl]2+ [CoII(NH3)5(H2O)]2+ [Ço(H2O)6]2+ + 5NH4+

  20. Inner sphere mechanism Reactions much faster than outer sphere electron transfer (bridging ligand often exchanged) r = k’ [Ox-X][Red] k’ = (k1k3/k2 + k3) Tunneling through bridge mechanism

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