Organometallics

Question 1

What is hapticity?

Answer 1

How many atoms in the ligand are interacting with the metal

Question 2

What is bridging

Answer 2

How many metal atoms is the ligand bridging

Question 3

How to calculate O.S

Answer 3

Charge of complex - Charges of the ligands

Question 4

How to calculate valence electrons

Answer 4

Group number - O.S

Question 5

How to calculate TVEC

Answer 5

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

Question 6

σ donor ligands

Answer 6

Have lone pair e- to donate to metal

Question 7

𝜎 donor - 𝜋 acceptor ligands

Answer 7

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

Question 8

σ donor - π donor

Answer 8

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

Question 9

In terms of bond strength which type is more important?

Answer 9

𝜎 bonding due to better orbital overlap than 𝜋 bonding

Question 10

Synthesis of TM alkyls

Answer 10

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

Question 11

Reactivity of TM alkyls

Answer 11

β-elimination via agostic intermediate

Question 12

Synthesis of TM halides

Answer 12

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

Question 13

Reactivity of TM halides

Answer 13

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

Question 14

Synthesis of TM aryls

Answer 14

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

Question 15

Reactivity of TM carbonyls

Answer 15

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

Question 16

Bonding type of CO

Answer 16

𝜎 donor
𝜋 acceptor

Question 17

Bonding type of Phosphines

Answer 17

𝜎 donor
𝜋 acceptor

Question 18

Synthesis of alkene complex

Answer 18

1) Ligand substitution
2) Reduction
3) Hydride abstraction

Question 19

Reactivity of alkene TM complexes

Answer 19

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

Question 20

Alkyne TM bonding

Answer 20

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

Question 21

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

Answer 21

2 or 4

Question 22

TM carbenes bonding

Answer 22

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

Question 23

Carbene synthesis

Answer 23

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

Question 24

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

Answer 24

Loss of N2 drives reaction
CH2 binds to metal

Question 25

4 types of metathesis

Answer 25

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

Question 26

What catalyst is used for cross metathesis

Answer 26

Grubbs Catalyst

Question 27

Bonding mode of Allyl ligand [C3H5]-

Answer 27

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

Question 28

Bonding in the cyclopentadienyl ligand

Answer 28

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

Question 29

Synthesis of Allyls

Answer 29

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

Question 30

Reactivity of Allyls

Answer 30

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

Question 31

Synthesis of cyclopentadienyls

Answer 31

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

Question 32

Synthesis of Cp TM complexes

Answer 32

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

Question 33

2 different bonding modes for Cp

Answer 33

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

Question 34

Reactivity of Ferrocene

Question 35

Mechanisms in organometallic chemistry

Answer 35

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

Question 36

Elimination Reactions

Answer 36

𝛼 - elimination β - elimination 𝛾 - elimination

Question 36

What is Oxidative addition: concerted

Answer 36

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

Question 37

What is Oxidative addition: SN2

Answer 37

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

Question 38

Reductive elimination

Answer 38

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

Question 39

1,1 Migratory insertion

Answer 39

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

Question 40

1,2 migratory insertion

Answer 40

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

Question 41

𝛼 - elimination

Answer 41

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

Question 42

β - elimination

Answer 42

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

Question 43

𝛾 - elimination

Answer 43

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

Question 44

Dissociative ligand substitution

Answer 44

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

Question 45

Associative ligand substitution

Answer 45

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

Question 46

Why is ligand substitution faster with Indenyl ligand than Cp lignand

Answer 46

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

Question 47

Bonding of Dihydrogen ligand (H2)

Answer 47

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

Question 48

Characterisation of H2 dihydrogen ligand upon coordinating

Answer 48

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

Question 49

Agostic C-H 𝜎 - complexes

Answer 49

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

Question 50

Fluxionality

Answer 50

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

Question 51

What is a catalytic cycle

Answer 51

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

Question 52

Alkene hydrogenation steps

Answer 52

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)

Question 53

Alkene Hydroformylation

Answer 53

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

Question 54

Alkene isomerisation

Answer 54

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