11-Oxidative addition

b. Addition of X=Y or XY to LnM.
X Ln M + X Y Ln M Y X Ln M + X Y Ln M Y Ln M Ln M X Y X Y
Examples:
Cl Ph3P
Ir
PPh3 CO
+ O=O
Cl OC
PPh3 O Ir O PPh3
c. Binuclear oxidation reactions.
LnM: + R-X X Ln-1M R X or LnM R LnM R X #
+ LnM
R +X
*# of valence e- count of reactant LnM *S# > 0 or < 0? *Any solvent effect on reaction rate? e.g in benzene, acetone same reaction rate? Charge separation in TS, reaction is faster in polar solvent
LnM ML n + A-B 18e LnM A + LnM B 18e
O.S. = 1
18e A B ML n
Note: no change in valence electron count
LnM ML n + A-B
LnM
O.S. = 1
O O C C
Examples:
CO CO + H2 CO
R'OC
(RO)3Mo
Co CO
2 H Co CO CO CO
R'O (RO)3Mo OR' Mo(OR)3
Mo(OR)3
Q2. What types of complexes LnM can undergo oxidative addition reactions?
M
+ X Y
Y
M A
X
or
M B
X Y
Vaska et al.
OC Ir Me2PhP 11
Ir+1 d8, dsp2 Ha, Hb different in NMR 16e
PPhMe2 Cl
H2
PPhMe2 a H OC Ir b H Cl PPhMe2 12 Ir+3, d6, d2sp3
18 e
(a) Pt(PPh3)4 +
NC
CN
(b) Pt(PPh3)4 + (c) Pt(PPh3)4 + H3C CH3
Pt
Weak X-Y bond favors O.A. reaction. Stable M-X, M-Y bonds favor O.A. reaction.
Q4. What bonds can be oxidatively added?
LnM
18e
X Y
LnM
18e
X Y
X LnM Y
18e
Ln M 16e
+
X Y LnM
18e
X Y
LnM
18e
X Y
X LnM Y
18e
Q1. What are the most important features? *# of valence e- count of reactant LnM S# > 0 or < 0? Any solvent effect on reaction rate?
A). Pd(PR3)4 + CH3I a. PR3 = PPh3 b. PR3 = PMe3
B). Pd(PR3)4 + R-I R- = CH3-, CH3CH2-, CH3 C H CH3
I R3P
Pd
PR3 CH3
I R3P
Pd
PR3 R
C). Pd(PR3)4 + Et-X X = Cl, I, OTs
TiR4 WR6
Q3. In general, what are the factors affect the following equilibrium?
LnM
+
X Y
X LnM Y
bond strength
electron richness
bond strength
Q3A. Rank the order of Keq for the reactions below.
Cl L L CO L = PPh 3, PMe3, P(OPh)3 + H-Y Y L H Rh Cl L CO
Rh
Keq
Q3B. Which of the following reactions has a larger Keq?
Cl L Cl L Ir L CO L CO Cl + CH3I L Cl + CH3I L I Ir CH3 L CO (a)
X-X H2, Cl2, Br2, I2, RS-SR, RO-OR
L nM LnM
X X C C C X H X M' X
C-C
Ph3C-C-Ph3, NC-NC, Ph-CN
C-X
CH3I, Ph-I, CH2Cl2, CCl4 O O S R R R R R Cl HCl, HBr, HI, RO-H, RS-H, R2N-H, R2P-H, R2B-H Ph3PAu-Cl, Cl-Hg-Cl, R3Sn-Cl R3Si-Cl, Ph2B-X
Ln M + E +
+ Ln M
O.S. = 2 C.N. = 1
E
No change in total valence electrons count !
Examples:
Fe (CO)5 + H
+
[HFe (CO)5]+
CH3Mn(CO )5 + I -
[Mn(CO )5]- + CH 3I
importantrxncatalysislaststeptypicalreactionconditionsstrongpacceptingolefinligandweakenscnibondsfactorscontrollingreductiveeliminationelectrondeficientolefins联吡啶配位的二烷基镍络合物是对热相当稳定的但加入吸电子烯烃如丙烯睛等由于烯烃和金属配位金属向吸电子烯烃上的双键反馈成为主导地位造成nir键的电荷密度降低也即nir键被活化在常温下发生还原消除反应生成烷烃52及低价镍络合物
Q2. What is the character of substrate X-Y bonds? X-Y ---> H-H, R3Si-H, R3C-H, C-C H-X in nonpolar solvents.
Q3. Stereochemistry. If via concerted mechanism, which one should be the product?
Pt(PPh3)3 --------------> Pt(PPh3)2 + PPh3 Pt(PPh3)2 + R-X ---------> .PtR(PPh3)2 + X
X R3P
Pd
PR3 Et
b) Other non-concerted process (i) Radical mechanisms
Some possibilities: (a) Non-chain radical mechanism, e.g.
Pt(PPh 3)3 + R-I RX = MeI, EtI, PhC H2I I Ph 3P Pt PPh 3 R
A. Introduction to oxidative addition reactions Q1. What is an oxidative addition reaction?
Most common cases
X
Ln M + X Y Lm M Y
O.S. = 2
H Cl
Example:
L
Ir
Oxidative addition and Reductive elimination
Outline
A. Introduction to oxidative addition reactions B. Mechanism of oxidative addition reactions C. Examples of addition of specific molecules D. Reductive elimination E. Oxidative coupling of unsaturated hydrocarbons
Ph Pd(PPh3)4+ Br C H CH3 Br PPh3 Pd C H PPh3 A Ph CH3 PPh3 or Br Pd PPh3 B C Ph H CH3
Q5. Relative reaction rate. For the pair of oxidative addition reactions below, select the one with highest reaction rate. Assume that the reactions are though SN2 mechanism.
# + LnM
R C R R
+X
-
R X MLn C R R
16
# X
18
R . LnM. + R C X LnM R 18e complexes
R C R R
+ LnM
R C R R
+X
-
X MLn-1 L
C
R
R R
18
碳原子构型发生反转
18
18
Q1. What are the most important features?
LnM
H-X
LnM
M'-X
L nM
B. Mechanisms of oxidative addition reactions
1) Concerted pathway
Ln M 16e
+
X Y LnM
18e
X Y
LnM
18e
X Y
X LnM Y
18e
or:
Ln+1M 18e L LnM 16e
+
X Y
可能是协同机理： 1) 顺式产物，H－H断裂的同时，M－H生成 2) 室温反应，H－H键能430 KJ/mol-1，断H－H能量大，而生成M－H键能 也大，得到补偿。
Q4: If via concerted mechanism, which one should be the product?
R1 M + H Si R3 R2
Rh
I L (b) Rh CO CH3
In fact, for isostructural d8 complexes:
Fe (0)
Co(I)
Ni(II) Pd(II) Pt(II) increase tende ncy for O.A.
Ru(0) Rh(I) O s(0) Ir(I)
increase tende ncy for O.A.
LnM +
X Y
X LnM Y + LnM E
LnM + E +
* Higher oxidation state is accessible. * Availability of vacant site for newly formed bonds.
Exercise. Can the following complexes undergo O.A. reactions?
Q2. What kinds of substrates may undergo O.A. via an SN2 mechanism? e.g. X2: Cl2, Br2, I2 R-X: Ar-X, CH3X, PhCH2X, CH2=CH-CH2X Q3. Stereochemistry at M. If via SN2 mechanism, which product should one get?
H R1 M Si R2 R3 A H R1 Si or H R3 R2 R1 M C Si R3 R2 ?
or
M
B
2) Non-concerted mechanism
a) SN2 reactions
. LnM + .
R R R
16e or less complexes
R C X LnM C R R X
This is the trend for d orbital energy and ability for back-donation.
Q3C. Which of the following reaction is least likely?
Ph3P Ph3P Ph3P Ph3P Pt Ph3P Ph3P CH3 CH3 CN Pt CN
CH3 Cl L Ir L CO + CH3I Cl L Ir I A L CO or Cl L
CH3 Ir CO B L I
General cases:
M + R-X
R M + + X+X + R M
-
R M X R M + XX
Q4. Stereochemistry at R. If via SN2 mechanism, what would be the product?
L CO
H2
Cl L
Ir CO
L H
There are a few other types reactions that can be also regarded as oxidative addition reactions.
a. Electrophilic attack of metals. e.g.