IV' Complexes of pbound Ligands

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IV. Complexes of p-bound Ligands
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Outline

• 1. Alkene complexes
• 2. Butadiene complexes
• 3. Alkyne complexes
• 4. Enyl Complexes
• 5. Complexes the cyclic p-perimeters CnHn
• 6. Metal p-complexes of Unsaturated ligands with
  heteroatoms
• 7. Characterization of organometallic compounds

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1. Alkene complexes
A. Structure and bonding of mono-olefin
complexes
Examples
Bonding
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Q1. Which interaction is dominant? High valent
metal (e- poor) systems Low valent metal (e-
rich) systems Q2. What are the effects of
complexation?

• d(C-C)
• bond angle at C
• n(CC)
• e- density on C

Q3. Do you expect that the complexed olefins be
more reactive or less reactive towards
nucleophiles?
(a) (b)
(c)
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Q4. Consider the fragment Pt(PPh3)2. Which of
the following olefins would you expect to form
the most stable olefin adduct A?
(a) CH2CH2 (b) CH3-CHCH2 c) CH2CHCN Q5.
Which of the following olefin complexes is more
stable?
Usual stability of olefin complexes
Q6. Which of the following olefin complexes is
more stable?
Release of ring strain
Q7. Which of the following olefin complexes is
more stable?
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B. Preparation of olefin complexes
1. From Substitution reactions LnM-L' olefin
----gt L' LnM-(olefin) Examples
3. From alkyl and related species
2. Metal salt olefin reducing agents. e.g.
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C. Reactivity of olefin complexes
1. Insertion reactions
Oxidative additon of C-H
Example
Example
Example
Examples
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3). Nucleophilic attack on coordinated olefins.
Examples
Summary Reactions of olefin complexes.
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2. Butadiene complexes
A. Most common structures of butadiene complexes
B. Synthesis of butadiene complexes 1. by
substitution reactions. e.g.
2. Reaction of coordinated ligands. e.g.
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(No Transcript)
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C. Reactions of butadiene complexes
Examples
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3. Alkyne complexes
A. Structure and bonding of alkyne
complexes R-C?C-R can be simple h2-ligand or
bridging ligand. As simple h2-ligand, they can
be 2e or 4e donors. e.g.
Q1. How can they be 2e or 4e donors?
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In terms of bonding
As bridging ligands


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Q2. For each pair of the following complexes,
which one is more stable?
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B. Preparation of alkyne complexes

• 1. By substitution reactions e.g.

2. By other methods e.g.
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C. Reactivity of alkyne complexes
Similar to olefins complexes, e.g.
Q1. Give the product for the following reaction.
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4. Enyl Complexes
Enyl Organic ligands with odd number of carbon
chains. Examples
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A. Allyl complexes
1. Structure of allyl complexes
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2. Preparation of allyl complexes a. Metal salt
main group organometallic reagents.
Examples
b). Low valent metal complexes allylhalide.
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c) Metal salts olefin base. A previously
mentioned example
Question. What is the product for the following
reaction?
Examples
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Reactivity of allyl complexes
a). With Nucleophiles
b). With electrophile (for h1-allyls)
c). Insertion reactions.
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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.
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b). Transfer of H or H-
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5. Complexes of the cyclic ?-perimeters CnHn
Common structural types a). Sandwich complexes,
e.g.
b) Half-sandwich complexes c) Multidecker
sandwich
d). Complexes with tilted sandwich structures.
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A. C3R3 as ligands
Examples and preparation.
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B. C4R4 as ligands
Q1. What are the common starting materials for
preparing M(h4-C4R4) complexes?
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Example and preparation.
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Important chemical properties
a. Show aromatic properties. e.g.
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C. C5R5 as ligands

• Common C5R5

Binding mode of C5R5
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A).How to prepare CpM complexes?

• Common starting materials

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Examples. 1). From a source of Cp- most common
route Cp- reagents NaCp, CpMgBr, TlCp, CpSnMe3
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2). From C5H6 or related ligands. e.g.
2). From C5H6 or related ligands. e.g.
c). From a source of Cp. e.g.
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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

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D. Arene complexes

• 1). Common structures

As simple ?n ligands.
As bridging ligands
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2). Common synthetic routes
a) From benzene
By substitution reactions
Benzene metal salts reducing agents
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b) From reactions of coordinated ligands
3). Common Chemical reactions
Effect of complexation
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Expected reactivity Less reactive toward E,
more reactive toward Nu-.
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E. C7H7 and C8H8 as ligands
Tropylium cation C7H7 Aromatic 6 e-. C7H7-
antiaromatic 8 e- for Electron counting and
oxidation state assignments

C7H7 can be a h1, h3, h5 and h7 ligand. e.g.
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C8H8 can be a h2, h4, h6 and h8 ligand. e.g.
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COT complexes can be made from

• The chemical properties of (h7-C7H7)M or
  (h8-C8H8)M are similar to
• other (hn-CnHn)M complexes.

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Metal ?-complexes of unsaturated ligands with
heteroatoms.
Many unsaturated ligands with heteroatoms can
form complexes.
Examples
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Synthesis similar to organic ones. e.g
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Characterization of Organometallic Compounds.
Common Organometallic Functionalities.

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How to characterized them?
Common spectroscopic methods
Chemical analysis Composition
Composition and functional groups
MS
NMR Functional
groups and stereochemistry
Functional groups
IR
Paramagnetic compounds
ESR
X-ray 3-D structures
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1). Characteristic IR frequencies of some common
organometallic groups.
2). NMR (1H, 13C) in characterization of
organometallics.
Chemical shifts gt functional groups. e.g.
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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
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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)