User:Benjah-bmm27/degree/2/FCM

Transition metals 2, FCM
"Co-ordination Chemistry of the Transition Metals, Part 2"

Relevant textbooks

 * Richard A. Henderson, The Mechanisms of Reactions at Transition Metal Sites (Oxford Chemistry Primer) (1993) (on Amazon.co.uk)

Temperature dependence of rate constants

 * Over fairly narrow range of temps, rate constant varies according to Eyring equation:
 * $$ k_R = \left(\frac{k_\mathrm{B}T}{h}\right) \mathrm{exp}\left(\frac{\Delta S^\ddagger}{R}\right) \mathrm{exp}\left(-\frac{\Delta H^\ddagger}{RT}\right)$$,
 * where:
 * $$\ k_R $$ = rate coefficient
 * $$\ T $$ = temperature in kelvin
 * $$\ \Delta H^\ddagger $$ = enthalpy of activation
 * $$\ R $$ = gas constant
 * $$\ k_\mathrm{B} $$ = Boltzmann constant
 * $$\ h $$ = Planck's constant
 * $$\ \Delta S^\ddagger $$ = entropy of activation

Ligand substitution reactions

 * Associative, dissociative and interchange reaction mechanisms: Dissociative substitution, Associative substitution, Sn1CB mechanism

Effect of trans ligands



 * Trans series: F− < OH− < H2O < NH3 ≈ py < Cl− < Br− < I− ≈ SCN− ≈ NO2− < CH3− < H− ≈ PR3 < CN− ≈ CO


 * Trans influence (AKA thermodynamic trans effect): good σ donor trans ligand puts electron density on Pt, weakening and lengthening Pt-X bond in ground state
 * Trans-influence-Pt-5p-orbital-2D.png
 * Trans-influence-Pt-5d-orbital-2D.png


 * Trans effect (AKA kinetic trans effect): good π acceptor trans ligand stabilises five coordinate trigonal bipyramidal intermediate (removes electron density from 18e Pt)
 * Trans-effect-trigonal-bipyramidal-intermediate-pi-orbitals-2D.png

Substitution in octahedral complexes

 * Rate depends strongly of leaving group X but weakly or not at all on entering group Y (so D or Id mechanism)


 * at high [Y], rate = k[ML5X] (suggesting D mechanism)


 * at low [Y], rate = k[ML5X][Y] (suggesting A mechanism)


 * explained by Eigen-Wilkins mechanism (de:Eigen-Wilkins-Mechanismus, Manfred Eigen and R. G. Wilkins)


 * 1) ML5X and Y form a weakly-bound encounter complex, [ML5X···Y] (which forms and dissociates rapidly in a so-called pre-equilibrium with eqm. constant Ko)
 * 2) The encounter complex [ML5X···Y] rearranges to [ML5Y···X], i.e. breaking the M-X bond and forming an M-Y bond
 * 3) The rearranged complex [ML5Y···X] dissociates to the products ML5Y and X


 * {| class="wikitable" style="text-align:center; width:200px; height:200px"

! step !! equation !! symbol !! rate ! 1 ! 2 ! 3
 * ML5X + Y &#8652; [ML5X···Y] || Ko || fast
 * [ML5X···Y] &#8652; [ML5Y···X] || k || slow (RDS)
 * [ML5Y···X] &#8652; ML5Y + X || ? || fast
 * }

$${\text{rate}} = \frac$$

Electron transfer

 * Electron transfer: Oxford notes

Inner sphere ET

 * Inner sphere electron transfer: Housecroft p. 895, ET via a covalent linkage (a bridging ligand), IUPAC definition, Henry Taube, Creutz-Taube Complex

Outer sphere ET

 * Outer sphere electron transfer
 * Marcus theory:


 * Free energy of activation for self-exchange reactions:


 * $$\Delta G^{\ddagger}_{xx} = \Delta _{\text{w}} G^{\ddagger}  + \Delta _{\text{o}} G^{\ddagger}  + \Delta _{\text{s}} G^{\ddagger}  + RT\ln \left( {\frac} \right)$$


 * Rate of self exchange reactions:


 * $$k_{xx} = \kappa Ze^{ - \frac}$$


 * where Z ≈ 1011 dm3 mol−1 s−1 and the transmission coefficient κ ≈ 1


 * Marcus equation:


 * $$k_{12} = \left( {k_{11} k_{22} K_{12} f_{12} } \right)^{\tfrac{1}{2}}$$


 * $$\log f_{12} = \frac$$


 * $$\ln K_{12} = \frac

$$