Chapter 4 Complexes of pbound Ligands - PowerPoint PPT Presentation

1 / 126
About This Presentation
Title:

Chapter 4 Complexes of pbound Ligands

Description:

The Organometallic Chemistry of the Transition Metals, Robert H. Crabtree, 3rd ... be more reactive or less reactive towards nucleophiles (compared with free ones) ... – PowerPoint PPT presentation

Number of Views:292
Avg rating:3.0/5.0
Slides: 127
Provided by: mcsy5
Category:

less

Transcript and Presenter's Notes

Title: Chapter 4 Complexes of pbound Ligands


1
Chapter 4
Complexes of p-bound Ligands
2
Outline
  • 1. Alkene complexes
  • 2. Butadiene complexes
  • 3. Alkyne complexes
  • 4. Enyl Complexes
  • 5. Complexes of the cyclic p-perimeters CnHn
  • Metal p-complexes of Unsaturated ligands with
    heteroatoms
  • 7. Characterization of organometallic compounds
  • References and suggested readings
  • The Organometallic Chemistry of the Transition
    Metals, Robert H. Crabtree, 3rd Edition, 2001,
    Chapters 5, 10.
  • Organometallic Chemistry, G. O. Spessard, G. L.
    G. L. Miessler, Prentice-Hall New Jersey, 1997,
    Chapter 5.
  • Organometallics, C. Elschenbrouch, A. Salzer,
    1989, Chapter 15.
  • Organotransition Metal Chemistry, Akio Yamamoto,
    1986. Chapters 3.4-3.9, 6.1d.

3
1. Alkene complexes
A. Structure and bonding of monoolefin complexes
Non-planar
Examples
4
X2-Type
L-Type
5
Bonding
  • Q1. Which interaction is dominant?
  • e- poor systems.
  • e- rich systems

Factors favoring X2-type binding - strong donor
ligands - a net negative charge on the complex -
low-oxidation state metals
X2-Type
L-Type
6
Bonding
  • Q1. Which interaction is dominant?
  • e- poor systems ?-donation is dominant.
  • e- rich systems ?-backdonation is dominant.

Factors favoring X2-type binding - strong donor
ligands - a net negative charge on the complex -
low-oxidation state metals
X2-Type
L-Type
7
Q2. What are the effects of complexation?
d(C-C) u(CC) e- density on
C
Q3. Do you expect that the complexed olefins be
more reactive or less reactive towards
nucleophiles (compared with free ones)?
(a) (b) (c)
8
Q2. What are the effects of complexation?
d(C-C) u(CC) e- density on
C
Q3. Do you expect that the complexed olefins be
more reactive or less reactive towards
nucleophiles (compared with free ones)?
(a) (b) (c) more reactive probably less
reactive
9
Q4. Consider the complexes A below. Which of the
following olefins would you expect to have the
strongest Pt- olefin bond?
(a) CH2CH2 (b) CH3-CHCH2 (c) CH2CHCN
For low valent metals, e.g. Pt(0), Ni(0), Pd(0),
backbonding is important. Electron-deficient
olefin forms the more stable olefin complexes.
Q5. Which of the following olefin complexes have
a stronger Pt- olefin bond?
Usual binding strength of olefins
10
Q4. Consider the complexes A below. Which of the
following olefins would you expect to have the
strongest Pt- olefin bond?
(a) CH2CH2 (b) CH3-CHCH2 (c) CH2CHCN
Answer (c) more backdonation
For low valent metals, e.g. Pt(0), Ni(0), Pd(0),
backbonding is important. Electron-deficient
olefin forms the more stable olefin complexes.
Q5. Which of the following olefin complexes have
a stronger Pt- olefin bond?
Answer A, Both electronic and steric
consideration
Usual binding strength of olefins
11
Q6. Which of the following olefin complexes have
a stronger Ni- olefin bond?
Q7. Which of the following olefin complexes is
more stable?
12
Q6. Which of the following olefin complexes have
a stronger Pt- olefin bond?
(b) Strained olefin binds more tightly, because
coordination can release ring strain.
Q7. Which of the following olefin complexes is
more stable?
(b) Chelating effect.
13
B. Preparation of olefin complexes
1. By addition of olefin to unsaturated complexes
2. From Substitution reactions LnM-L' olefin
----gt L' LnM-(olefin) Examples
precipitation
14
(No Transcript)
15
(No Transcript)
16
3. Metal salt olefin reducing agents. e.g.
Mechanism ?
17
3. Metal salt olefin reducing agents. e.g.
Mechanism ?
- HCl
18
Another example
19
4. From alkyl and related species
20
C. Reactivity of olefin complexes
1). Insertion reactions
Examples
21
(No Transcript)
22
(Less favored)
23
16e
16e
Examples
monomer
16e
16e
18e
16e
24
(No Transcript)
25
(No Transcript)
26
3). Nucleophilic attack on coordinated olefins.
Examples
27
Summary Reactions of olefin complexes.
28
2. Butadiene complexes
A. Most common structures of butadiene complexes
1,3-Dienes can act as L2-type or LX2-type ligands
29
Dienes have a relatively low-energy LUMO (p
orbital) and are better p-acceptors than
conventional alkene ligands. Metal?ligand
back-bonding is particularly strong in complexes
of early 4d and 5d transition metals which prefer
high oxidation states in organometallic compounds.
30
Bonding?
31
B. Synthesis of butadiene complexes
1. By substitution reactions. e.g.
2. Reaction of coordinated ligands. e.g.
32
B. Synthesis of butadiene complexes
1. By substitution reactions. e.g.
2. Reaction of coordinated ligands. e.g.
33
Other methods
34
C. Reactions of butadiene complexes
Examples
18e
18e
16e
35
18e
18e
36
18e
18e
37
3. Alkyne complexes
A. Structure and bonding of alkyne complexes
R-CC-R can be simple h2-ligand or bridging
ligand. As simple h2-ligand, they can be 2e or
4e donors. e.g.
18e
18e
Q1. How can they be 2e or 4e donors?
38
In terms of bonding
Alkynes are more electronegative, therefore are
better p-acceptors
39
As bridging ligands
40
Examples, structures of Alkyne complexes
41
Q2. For each pair of the following complexes,
which one is more stable?
42
Q2. For each pair of the following complexes,
which one is more stable?
(b). Acetylene complexes are usually more stable
than olefin ones.
(b). Complexation releases ring strain.
(b). Electron-withdrawing group enhances
backdonation, which increases the stability.
43
B. Preparation of alkyne complexes similar to
olefin complexes
1. By substitution reactions e.g.
44
Additional examples
45
2. By other methods e.g.
46
2. By other methods e.g.
47
Other methods
48
C. Reactivity of alkyne complexes
Similar to olefins complexes, e.g.
Q1. Give the product for the following reaction.
49
C. Reactivity of alkyne complexes
Similar to olefins complexes, e.g.
Q1. Give the product for the following reaction.
50
4. Enyl Complexes
Enyl Organic ligands with odd number of carbon
chains. Examples
51
A. Allyl complexes
1. Structure of allyl complexes
52
2. Preparation of allyl complexes
a. Metal salt main group organometallic
reagents.
Examples
53
2. Preparation of allyl complexes
a. Metal salt main group organometallic
reagents.
Examples
54
Examples
b). Low valent metal complexes allylhalide. E.g.
55
Examples
b). Low valent metal complexes allylhalide. E.g.
56
Exercise 1.
c) Metal salts olefin base.
A previously mentioned example
57
Exercise 1.
c) Metal salts olefin base.
A previously mentioned example
58
Question. What is the product for the following
reaction?
59
Question. What is the product for the following
reaction?
60
Examples
61
Examples
62
3. Reactivity of allyl complexes
a). With Nucleophiles
b). With electrophile (for h1-allyls)
c). Insertion reactions.
63
Exercise. Predict the product of following
reactions.
64
Exercise. Predict the product of following
reactions.
16e
14e
65
B. Examples of other enyl complexes and their
preparation
They can be prepared similar to allyl complexes.
Examples a). Metal salt main group
organometallic reagents.
66
B. Examples of other enyl complexes and their
preparation
They can be prepared similar to allyl complexes.
Examples a). Metal salt main group
organometallic reagents.
67
b). Transfer of H or H-
68
b). Transfer of H or H-
69
5. Complexes of the cyclic p-perimeters CnHn
Common complexes of cyclic p-perimeters CnHn
Common structural types
a). Sandwich complexes, e.g.
Cr Mn Fe Co Ni
70
c) Multidecker sandwich, e.g.
b) Half-sandwich complexes, e.g.
d). Complexes with tilted sandwich structures.
E.g.
71
A. C3R3 as ligands
Common starting materials for preparing h3-C3R3
complexes?
72
Examples and preparation.
73
Examples and preparation.
74
Examples and preparation.
75
B. C4R4 as ligands
Q1. What are the common starting materials for
preparing M(h4-C4R4) complexes?
76
Example and preparation.
77
Example and preparation.
78
Example and preparation.
79
(No Transcript)
80
(No Transcript)
81
Important chemical properties
a. Show aromatic properties. e.g.
b. Can be used as a source of C4R4.
82
C. C5R5 as ligands
Common C5R5
Other important Cp-type ligands
83
Binding mode of C5R5
84
Common Types of Cp complexes
Examples Metallocenes
85
(No Transcript)
86
Examples Bent Metallocenes
Metals of group 4 and the 2nd and 3rd rows of
groups 5-7 do not form stable Cp2M complexes.
However they do form stable metallocenes with
additional ligands attached to the metal center.
Examples Half-Sandwich Complexes
87
A).How to prepare CpM complexes?
Common starting materials
Examples. 1). From a source of Cp - most common
route Cp- reagents NaCp, CpMgBr, TlCp, CpSnMe3
88
(No Transcript)
89
(No Transcript)
90
2). From C5H6 or related ligands. e.g.
c). From a source of Cp. e.g.
91
Review questions. Give the product
92
Review questions. Give the product
93
B. What are the typical chemical properties of
h5-Cp ligand?
--- h5-Cp ligand is usually unreactive.
--- The following reactions may occur to h5-Cp.
Electrophilic substitution-like benzene
Metallation reactions
Nucleophilic attack on Cp
94
Examples.
95
D. Arene complexes
1). Common structures -----
  • As simple h6, h4, h2 ligands.

h6 - most common
18e
18e
18e
96
As bridging ligands
97
2). Common synthetic routes
a) From benzene
By substitution reactions
Benzene metal salts reducing agents

b) From reactions of coordinated ligands
98
Exercise. Provide the reagents or product for the
following reactions.
99
Exercise. Provide the reagents or product for the
following reactions.
Mo
Na
Ph3CBF4
100
Additional examples
101
Additional examples
102
(No Transcript)
103
(No Transcript)
104
3). Common Chemical reactions
Effect of complexation
Less reactive toward E, more reactive toward
Nu-.
Expected reactivity
105
Examples
106
(No Transcript)
107
E. C7H7 and C8H8 as ligands
C7H7 can be a h1, h3, h5 and h7 ligand. e.g.
18e
18e
18e
18e
C7H7 complexes can be made from
108
C8H8 can be h2, h4, h6 and h8 ligands. e.g.
COT complexes can be made from
109
Exercise Suggest the products or reagents for
the following reactions.
110
Exercise Suggest the products or reagents for
the following reactions.
uranium
Acetonitrile
111
(No Transcript)
112
(No Transcript)
113
6. Metal p-complexes of unsaturated ligands with
heteroatoms.
Many unsaturated ligands with heteroatoms can
form complexes. Examples
18e
18e
18e
114
5e donor
6e donor
4e donor
3e donor
115
6e
6e
6e
5e
4e
Donor
Donor
6e
6e
6e
116
Synthesis similar to organic ones. e.g.
Give the reagents or products for the following
preparations.
117
Synthesis similar to organic ones. e.g.
Give the reagents or products for the following
preparations.
18e
18e
18e
6e
118
7. Characterization of Organometallic Compounds.
Common Organometallic Functionalities.
How to characterize them?
119
Common spectroscopic
methods Chemical analysis Composition MS Comp
osition and functional groups IR Functional
groups NMR Functional groups and
stereochemistry ESR Paramagnetic
compounds X-ray 3-D structures
120
1). Characteristic IR frequencies of some common
organometallic groups.
2). NMR (1H, 13C) in characterization of
organometallics.
Chemical shifts gt functional groups. e.g.
121
Spin-spin coupling gt stereochemistry
The signal of C(or H) may be split by X or M if
they are also NMR active. e,g. when X is P, M is
Rh or Pt. J(C-X)cis lt J(C-X)trans J(H-X)cis lt
J(H-X)trans
Exercise. Based on the spectra data, propose
structures for the following reactions.
IR(cm-1) 2023, 1950, 1940 1H NMR (d) 0.4
(d, 3H), 2.5(m, 1H) 3.1(t, 2H), 4.6(t, 2H),
5.6(tt, 1H)
122
Spin-spin coupling gt stereochemistry
The signal of C(or H) may be split by X or M if
they are also NMR active. e,g. when X is P, M is
Rh or Pt. J(C-X)cis lt J(C-X)trans J(H-X)cis lt
J(H-X)trans
Exercise. Based on the spectra data, propose
structures for the following reactions.
IR(cm-1) 2023, 1950, 1940 1H NMR (d) 0.4
(d, 3H), 2.5(m, 1H) 3.1(t, 2H), 4.6(t, 2H),
5.6(tt, 1H)
123
IR(cm-1) 1965, 1915, 1630 1H NMR (d) 2.6
(br, 3H), 4.52 (s, 6H)
IR(cm-1) 1975, 1930 1H NMR (d) 0.17 (s, 3H),
4.40 (s, 6H)
124
IR(cm-1) 1965, 1915, 1630 1H NMR (d) 2.6
(br, 3H), 4.52 (s, 6H)
IR(cm-1) 1975, 1930 1H NMR (d) 0.17 (s, 3H),
4.40 (s, 6H)
125
(No Transcript)
126
Midterm Exam
Time 1630 1800, Friday, April 3, 2009 Place
RM2464
Contents Chapters 1-4 Bonding, electron
counting, Typical preparation, typical chemical
properties, reaction mechanism
Format MC Predict products Suggest
reagents Reaction mechanism
Write a Comment
User Comments (0)
About PowerShow.com