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  • 1

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -49- 333 2

    .

    Kinetic Chelate Effect

    - Chelate compounds polydentate ligands stable complex monodentate ligand rate of substitution chelate compounds

    1) polydentate ligand 2)

    - chelate bidentate ligand 2

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -50- 333 2

    .

    ..(19) bidentate ..(20) H2O ..(21) bidentate

    ligand ..(22) H2O

  • 2

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -51- 333 2

    .

    - 1 (19) NH3 NH2 ligand en (NH2CH2CH2NH2) H2O

    - 2 (21) ligand en

    - (20) (22)

    (Substitution reaction of square planar complex) - square planar complex d4, d8, d9 - d4 d9 weak bond z

    octahedral tetragonal octahedral distortion tetragonal

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -52- 333 2

    .

  • 3

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -53- 333 2

    .

    - square planar complex e- d8 Rh+, Ir+, Ni2+, Pt2+ Au3+

    Pt2+ - Pt2+ - complex Pt2+ C.N. = 4 square planar

    - Pt2+ Pt2+

    retention of configuration - rate of substitution ligand

    leaving ligand

    1) Kinetic and Stereochemistry of square-planar substitution - square planar complex

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -54- 333 2

    .

    [L3MX] + Y [L3MY] + X ..(23) rate

    rate = - []

    = k1 [L3MX] + k2 [L3MX] [Y]

    - 2

    - substitution 2 pathways

    (a) k2 pathway: associative mechanism

    L3MX + Y k2 L3MXY (intermediate C.N. = 5)

    L3MXY L3MY + X

    rate = k2 [L3MX] [Y}

  • 4

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -55- 333 2

    .

    (b) k1 pathway: solvent (s) association complex

    L3MX + S k1 L3MXS (intermediate C.N. = 5)

    L3MXS + Y L3MY + X + S

    rate 1st order ( [L3MX] [S]

    ) rate = k1 [L3MX]

    2) Experimental evidence in square-planar substitution

    (Association)

    - square-planar substitution 2

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -56- 333 2

    .

    (1) ligand Y [PtL2LX]

    - ligand Y Z - tbp intermediate (C.N. = 5) T, X, Y - X Y square planar product

    (2) (s) [PtL2LX] ligand Y

    2 :

    - polar solvent CH3OH Z

    - tbp intermediate (C.N. = 5) T, X, S

  • 5

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -57- 333 2

    .

    - X S square planar

    - ligand Y Z

    - S Y product

    Complex

    Product

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -58- 333 2

    .

    - intermediate C.N. = 5 (tbp) [Ni(CN)5]

    3-, [Pt(SnCl3)5]3-

    Rate of substitution

    rate factor 2 ligand (Y)

    - Pt2+ soft Lewis acid ligand soft Lewis base rate

    - rate of nucleophilic substitution square planar complex trans-[PtL2Cl2] + Y trans-[PtL2ClY] + Cl

    - (24) Rate of reaction = k1 [PtL2Cl2] + k2 [PtL2Cl2] [Y]

    CH3OH 30o C ligand Y

    rate ligand Y

  • 6

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -59- 333 2

    .

    - rate ligand Y PR3 > CN- > SCN- > I- > Br- > NO3

    - > NO2- > py >

    NH3 Cl- > CH3OH

    - 2 pathways ligand Y S ( CH3OH) complex

    k2 [Y] k1 [CH3OH] rate of nucleophilic substitution

    Pt = log {k2 (Y) / k1 (CH3OH)}

    Pt reactivity constant for the entering ligand

    complex [Pt(py)P(CH2CH3)3]2+

    entering ligand (Y) 4

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -60- 333 2

    .

    4 Pt entering ligands substitution [Pt(py)P(CH2CH3)3]2+

    Ligand Y Pt

    PPh3 SCN-

    I- Br- N3

    - NO2

    - NH3 Cl-

    8.93 5.75 5.46 4.18 3.58 3.22 3.07 3.04

    ( : Miessler & Tarr, 2004 : 436)

    Pt rate Pt rate

    ** rate 59

    ** complex rate

    square planar complex Pt(II)

  • 7

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -61- 333 2

    .

    ligand (X) - leaving ligand rate

    - entering ligand 59 ligand ( Cl-

    entering ligand leaving group ) - Cl-, NH3, NO3

    - hard ligand CN-, NO2

    - soft ligand -bond [Pt(dien)X]+ + py [Pt(dien)(py)]2+ + X- (25) rate = k1 [Pt(dien)X]

    + + k2 ([Pt(dien)X]+) [py]

    rate X = H2O 105 CN- NO2

    -

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -62- 333 2

    .

    5 rate constant (k2) leaving groups

    X- k2 (M-1 s-1)

    NO3-

    Cl- Br- I-

    N3-

    SCN- NO2

    - CN-

    very fast 5.3 x 10-3 3.5 x 10-3 1.5 x 10-3 1.3 x 10-4 4.8 x 10-5 3.8 x 10-6 2.8 x 10-6

    ligand-to-metal bonding weak -bond good leaving group rate of substitution

    metal-to-ligand bonding strong -bond bad leaving group ( : Miessler & Tarr, 2004 : 437)

  • 8

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -63- 333 2

    .

    trans ligand - square-planar Pt(II) complexes X leaving group

    ligand 3 cis trans leaving group - trans ligand -

    ligand isomers complex product rxn

    Step 1 Cl- .. Step 2 trans ligand

    Cl- > NH3

    Step 1 NH3 .. Step 2 trans ligand

    Cl- > NH3

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -64-

    - trans ligand

    Cl- > py > NH3 - isomers

    333 2 .

    d

    Cl

    Cl

    Cl

    Cl

    NH3 NH3 NH3

    NH3

    d

  • 9

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -65- 333 2

    .

    complex trans ligands

    Trans effect: CN- CO C2H4 > PH3 > NO2- > I- > Br- > Cl- > NH3 py > OH

    - > H2O

    Trans effect

    (1) -bonding effect Ea intermediate C.N. = 5

    (a)

    (b)

    -bonding (c)

    -bonding

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -66- 333 2

    .

    (1) -bonding effect

    Pt2+ px dx2-y2 -bond - ligand T -bond Pt2+ Pt-X (orbitals ) Ea ( b) Ea ( a)

    -bond effect trans ligand

    ** -bonding effect CO, CN-

    X = leaving ligand T = ligand trans X

  • 10

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -67-

    (2) -bonding effect

    - T -donor ligand Pt2+ dxz dyz -bond ligand T ligand X complex rate

    -donor trans ligand

    - T -acceptor ligand e- Pt2+ ligand orbitals -back bonding Pt2 -bonding Ea ( c) Ea ( a b)

    333 2 .

    1. Substitution Reactions Reaction and Mechanism in Inorganic Chemistry

    -68-

    trans ligand

    2. Oxidation-reduction Reactions - redox e- (reducer) (oxidizer) - e- transfer 2 complexes

    -acceptor ligands

    -donor, weak -bonding ligands

    strong -bonding ligands

    333 2 .

  • 11

    2. Oxidation-reduction Reactions Reaction and Mechanism in Inorganic Chemistry

    -69- 333 2

    .

    (1) inner-sphere reaction 2 complexes e- ligand bridging ligand

    (2) outer-sphere reaction 2 complexes e- bridging ligand Rate of e- transfer ligand, 2 reactants , solvation 2 reactants

    2.1) Inner- and outer-sphere reactions - ligands 2 reactants coordination sphere e- transfer outer-sphere mechanism [MnO4]

    - + [Mn*O4]2- [MnO4]

    2- + [Mn*O4]-

    oxidant reductant

    2. Oxidation-reduction Reactions Reaction and Mechanism in Inorganic Chemistry

    -70- 333 2

    .

    6 outer-sphere e- transfer reactions rate constants

    - rate e- potential barriers reductant oxidant

    oxidant Reductants

    [Cr(bipy)3]2+ [Ru(NH3)6]

    2+

    [Co(NH3)5(NH3)]3+

    [Co(NH3)5(F)]2+

    [Co(NH3)5(OH)]2+

    [Co(NH3)5(NO3)]2+

    [Co(NH3)5(H2O)]3+

    [Co(NH3)5(Cl)]2+

    [Co(NH3)5(Br)]2+

    [Co(NH3)5(I)]2+

    6.9 x 102

    1.8 x 103 3 x 104

    5 x 104 8 x 105 5 x 106

    1.1 x 10-2

    4 x 10-2 3.4 x 101

    3.0 2.6 x 102 1.6 x 103 6.7 x 103

  • 12

    2. Oxidation-reduction Reactions Reaction and Mechanism in Inorganic Chemistry

    -71- 333 2

    .

    - complexes -donor -acceptor ligands e- transfer - NH3 -donor ligand rate e

    - transfer - outer-sphere reaction ligand coordination sphere

    - complex - e- transfer eg orbital high spin Co(II) low spin Co(III) + e- t2g

    5 eg2 t2g

    6 labile inert