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Year 3 - Chemistry > TM Catalysis of Organic > Flashcards

TM Catalysis of Organic Flashcards

1
Q

What is the oxn state of a metal?

A

Charge left on metal after all ligands have been removed in their normal closed shell config

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2
Q

What is the 18e- rule?

A

Total no of e- in shell never exceeds 18
In mononuclear diamagnetic complexes

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3
Q

What is the formal charge of a ligand?

A

number of electrons required from metal required for bonding

i.e. -1 for when requires one e- and 0 if 2 are donated to the M

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3
Q

What is the formal charge of a ligand?

A

number of electrons required from metal required for bonding

i.e. -1 for when requires one e- and 0 if 2 are donated to the M

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4
Q

What is oxidative addition?

A

X-Y added to coordinatively unsaturated metal centre
M increases oxn state by 2

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5
Q

Name examples of things added in oxidative addition

A

alkenyl-X
aryl-X
RCO-X
RSO2-X
H-H, etc.

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6
Q

How is X-Y added in oxidative addition?

A

Added in cis fashion
Can rearrange to trans

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7
Q

How do Pd complexes become active?

A
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8
Q

What promotes oxidative addition (OA)?

A

Bulkyl and good donor ligand -> stabilises oxn+2 state

Reactivity: I > OTf > Br > Cl

e- defficient substrates react faster

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9
Q

Does inversion of config occur for OA?

A

Vinyl halides - retention

Allyl, benzyl, alkyl halides - inversion

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10
Q

What is the rate of OA for Pd(0) and alkyl halides?

A

Slow as no pre-coordination event is possible

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11
Q

What is the mechanism for oxidative addition?

A
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12
Q

What is reductive elimination (RE)?

A

Loss of 2xligands of cis-config to give single product
Unimolecular pathway
Oxn state of M reduced by 2

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13
Q

What is the oxn state of Pd during OA/RE?

A

Pd(0) <-> Pd(2)

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14
Q

What type of ligand encourages RE?

A

e- poor ligands, so reduced e- density of M (more electrophilic)
π-acceptors and bulkyl ligands also increase rate of RE

e.g. PPh3 > PPh2Me

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15
Q

How does RE occur wrt retention?

A

Retention of stereochem in both fragments

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16
Q

What is the bite angle of a ligand?

A

Angle between two ligand atoms in a bidentate

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17
Q

How does bite angle effect RE?

A

Increased bite angle (larger bidentate rings) increase RE by bringing two departing ligands closer together

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18
Q

What is transmettalation?

A

M-R of main group metal react with Pd, organic group/H is transferred to Pd

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19
Q

What is the driving force of transmetallation?

A

Difference in electronegativity of two metals
Main group is more electropositive than Pd

M = Mg, Zn, B, Al, Sn, Si, Hg

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20
Q

What is the driving force of transmetallation?

A

Difference in electronegativity of two metals
Main group is more electropositive than Pd

This is often RDS in a process

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21
Q

What is the change of oxn state in transmetallation?

A

No change

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22
Q

What increases the rate of transmetallation?

A

Ligands increasing nucleophilicity of R of Pd and increasing electrophilicity of Main group metal

e.g. Zn > Sn > B&raquo_space; Li
Transfer faster with alkyne > alkene > aryl > allyl > Benzyl&raquo_space; alkyl

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23
Q

Name some examples of complexes for transmettalation

A

LiR, XMgR, RZrClCp2, RZnCl, RCuLn
RSnR’3, RB(OR’)2m, R-9BBN, RSiR’3

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24
Q

What is 1,1-migratory insertion of CO?

A

R groups undergo migratory insertion to CO ligand
Rapid and reversible

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25
Q

What is the retention of config for 1,1-migratory insertion of CO?

A

Retention of config

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26
Q

What is 1,2-migratory insertion of alkenes?

A

Addition of alkene/alkyne to sigma-bonded Pd complex
Syn fashion and can happen multiple times

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27
Q

What is β-hydride elimination?

A

Syn-elim of H from C at β-position to metal centre to give a H-Pd-X and an alkene
Reversible and requires coord unsaturated Pd complexes
Resulting H-Pd complex then gives Pd[0] by reductive elim in presence of base

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28
Q

What is required for β-hydride elim?

A

cis to alkyl group is site of coord unstaturation - corresponds to site of elec unsaturation (empty metal orbital)

M-C-C-H unit can take coplanar conformation which brings β-H in close proxim to metal to form an agostic interaction

M is electrophilic resulting in agostic interaction primarily e- donation (σ donation&raquo_space; π-backbonding)

29
Q

How does Ni and Pd compare for β-hydride elim?

A

Higher energy Ni(II) vacant d-orbtial means weaker agostic interaction with β CH sigma bond
Shown by greater lengthening of this bond in Pd complex

Ni alkyl more stable towards β-elim in line with greater electronegativity of Pd(II) than Ni(II)

30
Q

What is the Mizoroki-Heck reaction?

A

R-X + monosub-alkene -> E-geometry alkene

Cat: Pd(OAc)2 or Pd2(dba)3
Ligands: phosphines
Solvents: aprotic
Base: PMP, Et3N, K2CO3

31
Q

Why is the Mizoroki-Heck reaction E-stereoselective?

A

TS leading to cis-olefin complex involvewd is energetically unfavourable eclipsing interactions between CO2Me and Ph

32
Q

What is the mechansim cycle for the Mizoroki-Heck reaction?

33
Q

What 3 ways can you do in situ reduction of Pd(II) to Pd(0)?

A

Transmetalation
Tertiary alpiphatic amines
e- rich phosphines and base

34
Q

How can Pd(II) be reduced in situ to Pd(0) via transmetallation?

35
Q

How can Pd(II) be reduced in situ to Pd(0) by 3° aliphatic amines?

A

Is via a β-hydride elim

36
Q

How can Pd(II) be reduced in situ to Pd(0) by e- rich phosphines and bases?

37
Q

What are the conditions and result of the cationic Mizoroki-Heck reaction?

A

Pd(OAc)2, PPh3, base, AND AgNO3

Reduces double-bond isomeration

38
Q

How does the cationic Mizoroki-Heck reaction reduce isomerisation?

A

Reduces reversibility of the β-H elim so less isomerism

e.g.

39
Q

What is the mechanism of the cationic mizoroki-heck reaction mechanism

40
Q

What is the regioselectivity of the Mizoroki-Heck reaction when e- poor or rich alkene and PhX?

A

e- poor (EWG): Ph attached to β-C, further from EWG

e- rich (EDG): Ph attached to α-C, closer to EDG

41
Q

What is a consideration for the intramolecular heck reaction?

A

Endo vs exo ring closure
exo - double bodn outside the new cycle

Large rings - endo
Small rings - exo for 5,6,7 membered ring closures

42
Q

What is the Heck-Tandem reaction?

43
Q

What is the stereochemn of carbopalladation and β-hydride elim?

A

syn processes

44
Q

What is the enantionselective heck reaction?

A

Asymmetric, uses chiral phosphine BINAP

45
Q

What are the hybridisations are C which can be connected by cross-coupling reactions?

A

Csp-Csp2
Csp2-Csp2
Csp2-Csp3
Csp3-Csp3

46
Q

Name all the cross-coupling reactions

A

Kumada coupling
Stille reaction
Suzuki reaction
Negishi coupling
Hiyama coupling
Sonogashira

47
Q

What is the general cross-coupling cycle?

A

Overall: R1-X + R2-M -> R1-2
Uses [TM] and grignard reagent

48
Q

What is the Kumada cross-coupling reaction?

A

C-C bond forming cross-coupling reaction

Ni or Pd Catalysis

49
Q

Why are Ni catalysts advantageous?

A

More economical

Aryl&vinyl chlorides are more reactive unlike normal

50
Q

Why is the Kamada coupling reaction advantageous?

A

Direct coupling of Grignard reagents - avoids additional steps scuhsuch as conversion to Zn

51
Q

What is the mechanism of the kumada coupling?

52
Q

What is the advantage of using Pd over Ni catalyst?

A

Transmetallation is stereospecific

53
Q

What is the issue in the kumada coupling?

A

Grignard reagent used - not functional group tolerant

54
Q

How do bidentate phosphine ligands change the activity of a catalyst?

A

Higher catalytic activity for a wide range of aryl & vinyl halides

55
Q

What is the Negishi coupling?

A

R1-X + R2ZnX -> R1R2
Using MLn, usually M = Pd

56
Q

How are the Zn reagents prepared for the Negishi coupling?

A

alkyne hydroalumination then ZnCl2
or
iodide + ZnCl2

57
Q

What is the Stille reaction?

A

Cross-coupling using organotin reagent

58
Q

What are the benefits of organotin reagents?

A

Easily accessible
Group tolerant
Air/moisture stable, and to large range of organic reagents

59
Q

What is the ease of ligand transfer for the stille reaction?

A

alkynyl > alkenyl > aryl > ally or benzyl > alkyl
where alkyl is most difficult to transfer

60
Q

What is the rate of the Stille reaction?

A

Rate = k[Pd][Sn][R-I]0

61
Q

What does Cu added in the Stille reaction do?

A

Rate enhancement - promote ligand dissociation and transmetallation by binding to free PPh3
Increased group transfer selectivity

61
Q

What does Cu added in the Stille reaction do?

A

Rate enhancement - promote ligand dissociation and transmetallation by binding to free PPh3
Increased group transfer selectivity

62
Q

What is the retention for the Stille reaction?

A

Retention: E->E, and Z->Z

63
Q

How can you make organostannanes for the Stille reaction?

A

tBuLi and Bu3SnCl

OTf on alkyl/allyl, Pd and Me3SnSnMe3

or radical:
alkyne + AIBN (cat) + Bu3SnH

or do a Stille

64
Q

How can you perform carboalumination?

65
Q

What is the mechanism for carboalumination?

66
Q

What happens when a carboaluminate reacts with BuLi and an epoxide?

67
Q

What can an alkene bonded to a copper grignard reagent make?

68
Q

How can you perform a carbocupration?

Year 3 - Chemistry (12 decks)

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