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ACCA 3 > Organometallics > Flashcards

Organometallics Flashcards

1
Q

What is hapticity?

A

How many atoms in the ligand are interacting with the metal

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2
Q

What is bridging

A

How many metal atoms is the ligand bridging

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3
Q

How to calculate O.S

A

Charge of complex - Charges of the ligands

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4
Q

How to calculate valence electrons

A

Group number - O.S

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5
Q

How to calculate TVEC

A

d electrons + electrons from ligands + number of M-M bonds

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6
Q

σ donor ligands

A

Have lone pair e- to donate to metal

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7
Q

𝜎 donor - 𝜋 acceptor ligands

A

Have lone pair of e- to donate to metal and also empty 𝜋 orbital to accept electrons from metal

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8
Q

σ donor - π donor

A

Have lone pair to donate as well as additional 𝜋 electrons to donate

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9
Q

In terms of bond strength which type is more important?

A

𝜎 bonding due to better orbital overlap than 𝜋 bonding

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10
Q

Synthesis of TM alkyls

A

Nucleophilic substitution of Me- group
(oxidative addition) Electrophilic attack of Me at nucleophilic metal centre
Alkene insertion into M-H bond

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11
Q

Reactivity of TM alkyls

A

β-elimination via agostic intermediate

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12
Q

Synthesis of TM halides

A

Protonation of e- rich metal centre
Reaction with a hydride (H-) source
Oxidative addition of H2 = cis dihydride
β- elimination from alkyl to form M-H bond

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13
Q

Reactivity of TM halides

A

Insertion into an alkene = alkyl chain
Reductive elimination (remove H2)
Bridging between metal centres

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14
Q

Synthesis of TM aryls

A

Nucleophilic subs of Nu Aryl group
Oxidative addition to e- rich late TM e.g. Pd
Orthometallation
Transmetallation from main group compound

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15
Q

Reactivity of TM carbonyls

A

Thermal or photochemical dissociative substitution
Addition of nucleophiles (e.g. H- or HO-)
1,1 Migratory insertion (e.g CH3)

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16
Q

Bonding type of CO

A

𝜎 donor
𝜋 acceptor

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17
Q

Bonding type of Phosphines

A

𝜎 donor
𝜋 acceptor

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18
Q

Synthesis of alkene complex

A

1) Ligand substitution
2) Reduction
3) Hydride abstraction

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19
Q

Reactivity of alkene TM complexes

A

1) 1,2 migratory insertion into M-C bond
2) Nucleophilic attack at one end of C=C bond and break C=C bond to form alkane chain instead

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20
Q

Alkyne TM bonding

A

𝜎 donation into metal vacant 𝜎 orbital
𝜋 donation into metal vacant 𝜋 orbital
𝜋 back bonding from metal into alkyne

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21
Q

Alkynes can be flexible in the number of electrons it donates, how many can it donate?

A

2 or 4

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22
Q

TM carbenes bonding

A

:C-R2
has 2 e to do 𝜎 donation to metal
and also p orbitals to do 𝜋 donation to metal
4e donor

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23
Q

Carbene synthesis

A

1) Hydride abstraction by strong cation from e.g. a methyl group to make a formal M=CH2 double bond
2) 𝛼- elimination of H onto metal to form M-H bond and M=CH2

24
Q

Synthesis of Carbene TM complex from diazoalkanes
H2C=N+=N-
driving force

A

Loss of N2 drives reaction
CH2 binds to metal

25
Q

4 types of metathesis

A

1) Alkene Metathesis
2) Cross metathesis (joining)
3) Ring closing metathesis
4) Ring opening metathesis polymerisation

26
Q

What catalyst is used for cross metathesis

A

Grubbs Catalyst

27
Q

Bonding mode of Allyl ligand
[C3H5]-

A

2 different bonding modes
1) 𝜼1 2e bonding through 1 Carbon atom
2) 𝜼3 4e bonding through 3 carbon atoms

28
Q

Bonding in the cyclopentadienyl ligand

A

6 𝜋 electrons
-1 charge
𝜼5
𝜎 donor 𝜋 donor
𝜋 acceptor

29
Q

Synthesis of Allyls

A

Nucleophilic attack of Metal centre to 𝛿+ Br-CH2-CH-CH2
forms 𝜼1 allyl bond through single carbon
loss of a different ligand means allyl can bond 𝜼3 through C=C

30
Q

Reactivity of Allyls

A

1) Nucleophile can attack C-C-C neg charge delocalised area of allyl and break so only C=C bond coordinated to Metal centre rather than 𝜼3

31
Q

Synthesis of cyclopentadienyls

A

Crack dicyclopentadiene then reduce with NaH to eliminate H2 and form (Na+)(Cp-)

32
Q

Synthesis of Cp TM complexes

A

Reaction of NaCp with electrophilic metal centre eg with M-Cl bond

33
Q

2 different bonding modes for Cp

A

1) 𝜼1 where electron rich metal attacks 𝛿+ carbon on Cp eg C-Br
2) 𝜼5

34
Q

Reactivity of Ferrocene

A
35
Q

Mechanisms in organometallic chemistry

A

1) Oxidative addition: concerted
2) Oxidative addition: SN2
3) Reductive elimination
4) 1,1 Migratory insertion
5) 1,2 Migratory insertion

36
Q

Elimination Reactions

A

𝛼 - elimination
β - elimination
𝛾 - elimination

36
Q

What is Oxidative addition: concerted

A

Addition of A-B to metal centre - coordinate at same time giving cis product

37
Q

What is Oxidative addition: SN2

A

Addition of A-B to Nu- metal centre, with Metal SN2 nucleophilic attack at A+, inverting stereochemistry and kicking out B- group which then attacks pos metal centre either giving cis or trans product

38
Q

Reductive elimination

A

2 groups must be Cis to each other, both dissociate from metal centre at same time. Often proceeded by loss of ligand to form 5 coord w flexible geometry to arrange into cis conformation

39
Q

1,1 Migratory insertion

A

X migrates from metal centre onto C atom of CO ligand forming an acyl group and leaving vacant site on metal

40
Q

1,2 migratory insertion

A

R (H, Alkyl or aryl) group migrates onto alkene cis to R forming an akyl chain and leaving a vacant site on metal

41
Q

𝛼 - elimination

A

Loss of Hydride from methyl group coordinated to metal to form Carbene ligand M=CH2 and hydride ligand M-H

42
Q

β - elimination

A

Loss of Hydride from β Carbon (2 carbons away from metal) in alkyl chain to form an alkene ligand and a hydride ligand

43
Q

𝛾 - elimination

A

Loss of hydride from 𝛾 Carbon (3 carbons from metal) to form a alkyl 𝜼2 ligand, coordinated at both ends of chain and a hydride ligand M-H

44
Q

Dissociative ligand substitution

A

First loss of ligand from 6 coord or 18e complex to create vacant site
Then new ligand can coordinate

45
Q

Associative ligand substitution

A

First Coordination of new ligand onto 4 coordinate or 16e complex
Then loss of old ligand

46
Q

Why is ligand substitution faster with Indenyl ligand than Cp lignand

A

Indenyl ligand allows ring slip to occur changing 𝜼 from 5 to 3 and electron donation from 6 to 4 so allows for associative ligand substitution which is much faster than dissociative

47
Q

Bonding of Dihydrogen ligand (H2)

A

𝜎 donation into vacant metal orbital and 𝜋 acceptor into H-H 𝜎* antibonding orbital which weakens the H-H bond

48
Q

Characterisation of H2 dihydrogen ligand upon coordinating

A

Dihydrogen bond length increases upon coordinating to M = weakened H-H bond
HD coupling constant decreases upon coordinating = weakened H-D bond
Frequency of HH bond decreases upon bonding = weaker H-H bond

49
Q

Agostic C-H 𝜎 - complexes

A

e.g β-H Coordinating with metal centre weakens C-H bond
NMR coupling constant decreases

50
Q

Fluxionality

A

Some ligands undergo dynamic processes on the NMR timescale
e.g. 𝜼5 Cp ligand rotates with all H environments are equivalent so 1 HNMR peak with integral of 5
e.g 𝜼1 Cp ligand also rotates but has 3 different proton environments.
At high temp only 1 peak of H5 seen but at lower temp see 3 different peaks for the 3 different environments

51
Q

What is a catalytic cycle

A

Catalytic cycle is a set of sequential reactions mediated by a catalyst that leads to product formation from reactants

52
Q

Alkene hydrogenation steps

A

1) pre catalyst dissociation of ligand (e.g. PPh3) to make vacant coord site + activate catalyst
2) CIs oxidative addition of H2
3) Coordination of the alkene
4) 1,2 migratory insertion
5) Isomerisation to move 2nd H and alkyl chain cis
6) Irreversible reductive elimination (loss of cis A and B group from metal)

53
Q

Alkene Hydroformylation

A

1) Dissociation of ligand from pre catalyst to active
2) Coordination of propene
3) 1,2 Migratory insertion of H onto alkene
4) Coordination of CO ligand
5) 1,1 migratory insertion of alkyl onto CO
6) Cis oxidative addition of H2
7) reductive elimination

54
Q

Alkene isomerisation

A

1) dissociation of phosphite ligand
2) Coordination of alkene
3) 1,2 migratory insertion of H onto alkene
4) β elimination of H from alkyl chain
5) Dissociation of alkene

55
Q
A

ACCA 3 (4 decks)

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