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CHM2911 > Organometallic Chemistry > Flashcards

Organometallic Chemistry Flashcards

1
Q

Alkene

A

any of the series of unsaturated hydrocarbons containing a double bond, including ethylene and propene.

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2
Q

Alkyne

A

any of the series of unsaturated hydrocarbons containing a triple bond, including acetylene

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3
Q

Allyl

A

of or denoting the unsaturated hydrocarbon radical —CH2CH=CH2.

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4
Q

Arene

A

a hydrocarbon with alternating double and single bonds between carbon atoms forming rings

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5
Q

Back bonding

A

a concept from chemistry in which electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a π-acceptor ligand

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6
Q

β-hydride elimination

A

a reaction in which an alkyl group bonded to a metal centre is converted into the corresponding metal-bonded hydride and an alkene

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7
Q

β-hydrogen transfer

A

the opposite of beta-hydride elimination

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8
Q

Bridging ligand

A

a ligand that connects two or more atoms, usually metal ions

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9
Q

Carbonyl

A

a coordination compound in which one or more carbon monoxide molecules are bonded as neutral ligands to a central metal atom.

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10
Q

Cyclopentadienyl

A

[C5H5]

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11
Q

EAN rule

A

the metal atom tends to surround itself with sufficient ligands that the resulting effective atomic number is numerically equal to the atomic number of the noble-gas element found in the same period in which the metal. Also known as the 18 electron rule

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12
Q

Ferrocene

A

an orange crystalline compound whose molecule has a sandwich structure in which two planar cyclic hydrocarbon ligands enclose an iron atom

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13
Q

Hapticity

A

the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η (‘eta’)

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14
Q

HOMO

A

a molecular orbital characterised by the highest occupied molecular orbital

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15
Q

Homogenous catalysis

A

catalytic reactions where the catalyst is in the same phase as the reactants

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16
Q

Homolytic fission

A

chemical bond dissociation of a molecule by a process where each of the fragments retains one of the originally bonded electrons

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17
Q

Hydroformylation

A

an industrial process for the production of aldehydes from alkenes

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18
Q

Infrared spectroscopy

A

a characterization tool chemists use to help determine the molecular structure. It capitalizes on the concept that functional groups absorb specific frequencies of energy based on their structure

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19
Q

Insertion reactions

A

a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity

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20
Q

LUMO

A

the lowest energy place to put or excite an electron

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21
Q

Metallation

A

a chemical reaction which involves the bonding of a metal atom to what is typically an organic molecule to form a new compound

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22
Q

Nucleophilic attack

A

a fundamental class of reactions in which an electron rich nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms to replace a leaving group

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23
Q

Organometallic compound

A

any member of a class of substances containing at least one metal-to-carbon bond in which the carbon is part of an organic group

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24
Q

Phosphine ligand

A

compound of the formula PRR’R” (R, R’, R” = H, alkyl, aryl, etc) that are used as ligands in metal complexes

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25
Q

π-acid ligand

A

a molecule that binds to a metal by accepting electrons through (antibonding) pi-orbitals

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26
Q

Redox transmetallation

A

a type of organometallic reaction that involves the transfer of ligands from one metal to another

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27
Q

Reductive elimination

A

an eliminatory step in organometallic chemistry in which the oxidation state of the metal center decreases while forming a new covalent bond between two ligands

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28
Q

σ-complex

A

The positively charged intermediate of an electrophilic aromatic substitution reaction

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29
Q

Synergism

A

An effect arising between two or more agents, entities, factors, or substances that produces an effect greater than the sum of their individual effects.

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30
Q

Define

Terminal ligand

A
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31
Q

Definition

any of the series of unsaturated hydrocarbons containing a double bond, including ethylene and propene.

A

Alkene

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32
Q

Definition

any of the series of unsaturated hydrocarbons containing a triple bond, including acetylene

A

Alkyne

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33
Q

Definition

of or denoting the unsaturated hydrocarbon radical —CH2CH=CH2.

A

Allyl

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34
Q

Definition

a hydrocarbon with alternating double and single bonds between carbon atoms forming rings

A

Arene

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35
Q

Definition

a concept from chemistry in which electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a π-acceptor ligand

A

Back bonding

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36
Q

Definition

a reaction in which an alkyl group bonded to a metal centre is converted into the corresponding metal-bonded hydride and an alkene

A

β-hydride elimination

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37
Q

Definition

the opposite of beta-hydride elimination

A

β-hydrogen transfer

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38
Q

Definition

a ligand that connects two or more atoms, usually metal ions

A

Bridging ligand

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39
Q

Definition

a coordination compound in which one or more carbon monoxide molecules are bonded as neutral ligands to a central metal atom.

A

Carbonyl

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40
Q

Definition

[C5H5]

A

Cyclopentadienyl

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41
Q

Definition

the metal atom tends to surround itself with sufficient ligands that the resulting effective atomic number is numerically equal to the atomic number of the noble-gas element found in the same period in which the metal. Also known as the 18 electron rule

A

EAN rule

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42
Q

Definition

an orange crystalline compound whose molecule has a sandwich structure in which two planar cyclic hydrocarbon ligands enclose an iron atom

A

Ferrocene

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43
Q

Definition

the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η (‘eta’)

A

Hapticity

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44
Q

Definition

a molecular orbital characterised by the highest occupied molecular orbital

A

HOMO

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45
Q

Definition

catalytic reactions where the catalyst is in the same phase as the reactants

A

Homogenous catalysis

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46
Q

Definition

chemical bond dissociation of a molecule by a process where each of the fragments retains one of the originally bonded electrons

A

Homolytic fission

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47
Q

Definition

an industrial process for the production of aldehydes from alkenes

A

Hydroformylation

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48
Q

Definition

a characterization tool chemists use to help determine the molecular structure. It capitalizes on the concept that functional groups absorb specific frequencies of energy based on their structure

A

Infrared spectroscopy

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49
Q

Definition

a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity

A

Insertion reactions

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50
Q

Definition

the lowest energy place to put or excite an electron

A

LUMO

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51
Q

Definition

a chemical reaction which involves the bonding of a metal atom to what is typically an organic molecule to form a new compound

A

Metallation

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52
Q

Definition

a fundamental class of reactions in which an electron rich nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms to replace a leaving group

A

Nucleophilic attack

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53
Q

Definition

any member of a class of substances containing at least one metal-to-carbon bond in which the carbon is part of an organic group

A

Organometallic compound

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54
Q

Definition

compound of the formula PRR’R” (R, R’, R” = H, alkyl, aryl, etc) that are used as ligands in metal complexes

A

Phosphine ligand

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55
Q

Definition

a molecule that binds to a metal by accepting electrons through (antibonding) pi-orbitals

A

π-acid ligand

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56
Q

Definition

a type of organometallic reaction that involves the transfer of ligands from one metal to another

A

Redox transmetallation

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57
Q

Definition

an eliminatory step in organometallic chemistry in which the oxidation state of the metal center decreases while forming a new covalent bond between two ligands

A

Reductive elimination

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58
Q

Definition

The positively charged intermediate of an electrophilic aromatic substitution reaction

A

σ-complex

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59
Q

Definition

An effect arising between two or more agents, entities, factors, or substances that produces an effect greater than the sum of their individual effects.

A

Synergism

60
Q
A

Terminal ligand

61
Q

Is Na4(CH3)4 an organometallic compound?

A

Yes

62
Q

Is N(CH3)3 an organometallic compound?

A

No

63
Q

Is CH3COONa an organometallic compound?

A

No

64
Q

Is [W(CO)6] an organometallic compound?

A

Yes

65
Q

What are the property differences between coordination and organometallic compunds?

A

Coordination compounds

  • Water soluble
  • Not air sensitive
  • High melting points (>250OC)

Organometallic compounds

  • Hydrocarbon soluble
  • Air sensitive
  • Low melting points or oils
66
Q

True or False:

CO is an important pi-base ligand

A

False

It is a pi-acid ligand

67
Q

a) Valence bond structure of CO shows ______ non-bonding electron pairs
b) Which electrons are the most available for donation to the metal on a CO

A

a) two
b) the electron pair on the carbon

68
Q

When is back bonding possible?

A

This type of bonding is possible between atoms in a compound in which one atom has lone pair of electron and the other has vacant orbital placed adjacent to each other.

69
Q

Back bonding results in a ________in bond length and ______-in bond order giving it partial double bond character

A

Back bonding results in a decrease in bond length and increase in bond order giving it partial double bond character

70
Q

What does the electron density in an anti-bonding orbital do to the C bond during back bonding?

A

Weakens the bond

71
Q

What happens during back bonding?

A

the electrons move from an atomic orbital on one atom to a π* anti-bonding orbital on another atom or ligand

72
Q

CO ligands are sigma _______ and pi _________

A

CO ligands are sigma donors and pi acceptors

73
Q

CO has much less of a dipole moment than expected. Explain this using your knowledge of back bonding

A

CO has much less dipole moment than expected due to back-donation from LONE PAIR ORBITAL OF Oxygen into vacant orbital of carbon

74
Q

BF3 < BCl3 < BBr3 < BI3 is order of lewis acidic character. Explain this observation using back bonding

A

BF3 < BCl3 < BBr3 < BI3 is order of lewis acidic character due to stronger 2pπ-2pπ back bonding in BF3 (LONE PAIR ORBITAL OF Fluorine into vacant orbital of boron) and gradually back bonding becomes weakest in BI3 (2pπ—5pπ) hence BF3 has stronger partial double bond character and consequently behaves as less electron deficient

75
Q

As the strength of a sigma bond increases, what happens to the back bond?

A

It also increases

76
Q

Is ligand-to-metal or metal-to-ligand bonding more energetically important?

A

Ligand-to-metal

77
Q

Why are some metal compounds stable in a 0 oxidation state?

A

Backbonding

78
Q

What are the two methods used to synthesise metal carbonyls?

A

Direct reaction

Reductive carbonylation

79
Q

M + nCO → [M(CO)n]

What is this type of reaction called?

A

Direct reaction

80
Q

What metals can undergo the direct reaction to synthesise metal carbonyls?

A

Iron (Fe) and Nickel (Ni)

81
Q

“M” + CO + reductant → [M(CO)n]

“M” = metal halide, metal oxide etc.

What is this type of reaction?

A

Reductive carbonylation synthesis of metal carbonyls

82
Q

How many electrons does a C5H5- ligand donate?

A

6

83
Q

How many electrons does a terminal CO donate?

A

2

84
Q

How many electrons does a bridging carbonyl donate to each metal?

A

1

85
Q

Does [Ni(CO)4] satisfy the 18-electron rule?

A

Yes

86
Q

Predict the formula of [Fe(CO)n]

A

n = 5

87
Q

What does the Greek symbol η indicate?

A

Hapticity or the number of carbons bonded to metal

88
Q

Explain how [Fe2(CO)9] has 18 electrons around each Fe?

A
89
Q
A
90
Q

What usually happens to complexes with 16e- or 14e-?

A

They are very reactive and will try and increase their coordination number

91
Q

What usually happens to 17e- compounds?

A

They will dimerise or form an anion to complete 18e-

92
Q

What are these reactions an example of?

A

Substitution reactions

93
Q

[Mn2(CO)10] + Cl2 →

A

[Mn2(CO)10] + Cl2 → 2 [Mn(CO)5Cl]

94
Q

[Fe(CO)5] + Br2 →

A

[Fe(CO)5] + Br2 → [Fe(CO)4Br2] + CO

95
Q

[Mo(CO)6] + excess MeCN →

A

[Mo(CO)6] + excess MeCN → [Mo(CO)3(NCMe)3] + 3CO

96
Q

[Mn2(CO)10] + H2 →

A

[Mn2(CO)10] + H2 → 2 [Mn(CO)5H]

97
Q

PIII ligands have a lone pair for ___-donation, as well as empty d-orbitals of ___-symmetry

A

PIII ligands have a lone pair for σ-donation, as well as empty d-orbitals of π-symmetry

98
Q

π-acidity of phosphine ligands is enhanced by what?

A

Electron withdrawing groups

99
Q

True or False:

Back bonding occurs for phosphine ligands

A

True

100
Q

List these ligands in order of increasing Tolan cone angle:

PPh3, PF3, P(tBu)3, P(CH3)3

A

PF3 < P(CH3)3 < PPh3 < P(tBu)3

101
Q

If the highly substituted complex [Mo(CO)3L3] is desired, which of the ligands P(CH3)3 or P(tBu)3 would be preferred?

A

P(CH3)3

Smaller Tolman cone angle

102
Q

What does the number of IR absorption bands of metal carbonyls relate to?

A

Symmetry

103
Q

What does an increase in back bonding do to IR frequency?

A

It lowers the wavenumber due to weaker bonding

104
Q

Predict which complex will exhibit the lower IR CO stretching frequency:

[Cr(CO)5(PEt3)] and [Cr(CO)5(PPh3)]

A

[Cr(CO)5(PEt3)]

It is a better Lewis base

Ethyl groups are more e- donating than phenyl groups

PEt3 is smaller than PPh3

105
Q

Predict which complex will exhibit the lower IR CO stretching frequency:

[Cr(CO)6] and [V(CO)6]-

A

[V(CO)6]-

Anion orbitals on metal center are bigger allowing more overlap with π* ligand orbitals

106
Q

How many electrons can an ethene ligand donate?

A

2

107
Q

How many electrons can cyclopentadienyl ligands donate?

A

6

108
Q

How many electrons can benzene ligands donate?

A

6

109
Q

What are the resonance structures of cyclopentadienyl?

A
110
Q

Why is ferrocene stable?

A

The sandwich conformation makes it hard for molecules to interact with the metal center

111
Q

Predict whether the following complex is stable:

[CrCp2]

A

Both stable and unstable are correct answers as long as explanations are valid:

Stable: due to sandwich conformation protecting the metal center

Unstable: due to 16e- complex, reactive when exposed to oxygen

112
Q

What ligand is Cp?

A

Cyclopentadienyl; [C5H5]-

113
Q

Draw the structure of [CpFe(CO)2]2

A
114
Q

Demonstrate that this complex satisfies the 18e rule

A
115
Q

Predict the product(s) of this reaction:

[CpFe(CO2)2 + Br2 →

A

[CpFe(CO2)2 + Br2 → 2[CpFe(CO)2Br] (oxidation)

116
Q

Why does ethene lose it planarity and its C-C bond lengths upon coordination to a Pt center?

A

Moves towards sp3 hybridisation

117
Q

How many sigma bonds is in a Zeise’s salt molecule?

A

8

The bond between the ethene and the Pt is not a pi or sigma bond due to back bonding effects

118
Q

Explain the bonding that occurs in Ziese’s salt

A

For the formation of bond between the metal and the ligand, electrons from filled π-bonding MO of ethene (πb) is donated to the vacant orbitals of Platinum. And electrons from the filled orbitals of Pt is back-donated to the vacant π∗ orbitals of ethene.

119
Q

Why are arenes more susceptible to deprotonation and nucleophilic substitution than free benzene?

A

Because electron density is sucked away from the coordinated benzene ring making it vulnerable to nucleophilic attack

120
Q

Why do alkynes tend to bind more tightly to transition metals than alkenes?

A

Because they are more more electropositive

121
Q

How many electrons does an alkyne ligand donate?

A

2 or 4

122
Q

How does alkyne donate 2 electron?

A

Only one out of 2 of its pi bond is involved

123
Q

Allyl ligands are sigma _______

A

Allyl ligands are sigma donors

124
Q

How many electrons is donated by allyl in this form?

A

2

125
Q

How many electrons are donated by allyl in this form?

A

4

126
Q

What is the reverse reaction of a β-hydride elimination?

A

β-hydrogen transfer

127
Q

β-hydride elimination involves the formation of a ___ bond and an M-__ bond

A

β-hydride elimination involves the formation of a π bond and an M-H bond

128
Q

What happens to metal alkyls that contain β-hydrogens?

A

Rapid elimination of the β hydrogens (provided a few conditions are met)

129
Q

What conditions must be met for β-hydride elimination to occur?

A
  • The complex must have an open coordination site and an accessible, empty orbital on the metal center
  • The leaving group (-H) needs a place to land
  • The M-Cα​ and Cβ-H must have the ability to align in a syn coplanar arrangement (all four atoms are in the same plane and the M-Cα​ and Cβ-H bonds are on the same side of the Cα-Cβ bond)
130
Q
A
131
Q

What is this reaction called? What will the unstable intermediate look like?

A

Beta-hydride reaction

132
Q

How do you prevent molecules from undergoing beta-hydride elimination reactions?

A
  • Coordinatively saturate the metal to tie up vacant orbitals
  • Use ligands without beta-hydrogen atoms
133
Q

True or False:

Both beta-hydrogen transfers and beta-hydride eliminations proceed through a 4-membered cyclic intermediate

A

True

134
Q

What is the reverse reaction of oxidative addition?

A

Reductive elimination

135
Q

What happens during reductive elimination?

A

The oxidation state of the metal decreases by 2 units and open coordination sites become available

136
Q

What reaction types would be occurring if the oxidation state of the metal decreases by 2 units and open coordination sites become available?

A

Reductive elimination

137
Q

Show how the following reaction is an example of reductive elimination

A
138
Q

What is homolytic fission?

A

The cleavage of M-R bond to give two reactive radicals

139
Q

What are the five methods of sigma complex synthesis?

A

Metallation

Redox Transmetallation

Metathesis

Salt formation

Oxidative addition

140
Q

Predict the products of this reaction:

CH3Li + Ph3CH ->

What is the reaction type?

A

CH3Li + Ph3CH -> Ph3CLi + CH4

Metallation

141
Q

Predict the products of this reaction:

2Al + 3Ph2Hg ->

What is the reaction type?

A

2Al + 3Ph2Hg​ -> 2AlPh3 + Hg

Redox Transmetallation

142
Q

Predict the products of this reaction:

HgX2 + 2PhMgX ->

What is the reaction type?

A

HgX2​ + 2PhMgX -> HgPh2 + MgX2

Metathesis

143
Q

Predict the products of this reaction:

Na+[Mn(CO)5]- + CH3I ->

What is the reaction type?

A

Na+[Mn(CO)5]- + CH3​I -> [CH3Mn(CO)5] + NaI

Salt formation

144
Q
A
145
Q
A
146
Q

What conditions are needed for oxidative addition to proceed?

A
  • Non-bonding electron density must be present on the metal
  • Two vacant coordination sites normally exist on M
  • Metal must have stable oxidation states separated by two units (sq planar -> octahedral)
147
Q

What are the two product types of hydroformylation?

A

Linear and a branched product

CHM2911 (4 decks)

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