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CHEM411 > Module 7 > Flashcards

Module 7 Flashcards

1
Q

what bonding is most prominent in Ln organometallic chemistry

A

ionic bonding

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2
Q

why can oxidative addition now occur for Ln elements

A

cannot go up or down 2 oxidation states

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3
Q

because organo Ln complexes contain vacant orbitals what reactions can they take part in

A

B-hydride elemination
B-alkyl elimination
agostic interaction
insertions

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4
Q

what is the charge on an alkyl group

A

-1

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5
Q

give an example of an organoLn ate complex

A

[Lu(tBu)4]

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6
Q

give an example of an Lnorgano complex with an Li complex cation

A

[Li(tmeda)]3 [LuMe6]

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7
Q

give an example of an organoLn with a chelating ligand

A

[Lu(C6H4(H2NMe2)3]

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8
Q

what are available to form [Ln(C6H4(H2NMe2)3]

A

Er, Yb, Lu

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9
Q

give an example of an organoLn with bulky ligands

A

[La(CH(SiMe3)2)3]

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10
Q

give an example of a bulky ligand that fills the coordination sphere of an Ln2+ ion

A

Yb(C(SiMe3)3)2

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11
Q

what is the reaction equation for salt metathesis

A

LnCl3 + n(XLi) —-> LnXn + nLiCl

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12
Q

what happens if only 3 ligands are reacted with LnCl in salt metathesis, and how can it be avoided

A

Ln will form an adduct with LiCl

Can be avoided by using Ln(OAr)3 not LnCl3

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13
Q

describe the reactivity of alkyl Lns

A

very reactive

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14
Q

how can the reactivity of alkyl Lns be moderated

A

with spectator ligands

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15
Q

what are some required properties of spectator ligands

A

must increase coordinative saturation
pKa of protonated ligand < pKa protonated alkyl
must be tunable
must stabilise against redistribution

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16
Q

what is redistribution

A

3LnRL2-> LnR3 + 2LnL3

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17
Q

how can Cp be tuned as a spectator ligands

A

solubility
bulk
can be linked to chelate

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18
Q

what complexes do neutral ligands form

A

cationic complexes

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19
Q

what are the properties of cationic complexes

A

highly electrophilic

enhanced reactivity

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20
Q

what is a rough value for strength of Ln-C bond

A

200 kJmol-1

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21
Q

for which Ln is activation energy of sigma bond metathesis highest

A

late (small) Ln

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22
Q

describe the regioselectivity of alkene insertion to Ln complexes

A

least hindered end bonds to Ln

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23
Q

what are the 2 types of degradation reaction

A

b alkyl elimination

b hydride elimination

24
Q

how can 1e- Ox. addition occur in organoactinides

A

bimetallic ox. addition

25
Q

how does the strength of An-C compare to Ln-C

A

stronger

26
Q

what are reactions of organoactinoids governed by

A

sterics

27
Q

how is LnCp3 made

A

LnCl3 + 3NaCp –THF–> 3NaCl + Cp3Ln(THF) –> Cp3Ln

28
Q

how is LnCp*2 made

A

LnI2 + 2NaCp* –THF-> LnCp2(THF) + 2NaI —> LnCp

29
Q

what properties does a ligand need to stabilies Ln2+

A

bulky

30
Q

how can Cp complex with An

A

AnCp*3 - bulky

AnCp4 - for Th,U,Pa,Np

31
Q

how is UCp*3 made

A

UCl3 + 3KCp* -> 3KCl + Cp*3U

32
Q

how is ThCp4 made

A

ThCl4 + 4KCp -> ThCp4 + 4KCl

33
Q

what is the main bonding interaction in Cp complexes

A

interaction of of An-Cp is via 6d orbitals excluding 6dz^2

34
Q

how does isocyanide react with Cp3Ln/An

A

forms adduct - Cp complexes are lewis acidic

35
Q

which Cp complex does isocyanide back-bond with

A

U

36
Q

how is COT made negative

A

Addition of 2e-

37
Q

what can be said about the symmetry of the HOMO in COT

A

has the correct symmetry to interact with f orbitals

38
Q

how many COT ligands and be accommodated by Ln/An

A

2 Ligands

39
Q

what elements can form [An(COT)2]

A

Th, U, Np, Pu

40
Q

what elements can form K[Ln(COT)2]

A

all Ln

41
Q

how are the 2 COTs arranged in a Uranium complex

A

eclipsed -D8H

42
Q

how are the 2 COTs arranged in a cerium complex

A

staggered

43
Q

describe the bonding in uranocene

A

bonding orbitals in ligand can donate into U f-orbitals

Uf4+ f orbital can donate into pi* on COT

44
Q

what is the stability of uranocene

A

thermally stable

45
Q

compare the reactivity of K[Ln(COT)2] and [U(COT)2]

A

K[Ln(COT)2] is more reactive

46
Q

describe [Ce(COT)2]

A

Ce(III) with 2 cot ligands is less reactive than would be expected though

47
Q

what happens to a carbonyl when it is bonded to Ln

A

C atom is activated

48
Q

why are Ln good at activating carbonyls

A 
high affinity for O
labile Ln-L bond
Large radii - can handle many substrates
flexible coordination geometry
contraction across series allows for tuning
49
Q

how does lewis acidity change across the group

A

increase with decreasing radius

Yb3+>Lu3+ due to partly filled shell

50
Q

which Ln ions favour enantiometeric selectivity

A

large ions

51
Q

what factors affect the rate of alkene insertion

A

accessibility of binding site
preferible monomeric
non-coordinating solvent

52
Q

what is the regioselectivity of alkene insertion

A

Ln usually goes to least hindered end

53
Q

what is the optimum Ln for insertion of butadiene

A

Nd

54
Q

which Ln ions cannot be used in butadiene insertion and why

A

Sm and Eu are reduced

55
Q

why is C-H activation in hydrocarbons so difficult

A 
No lone pairs
no low lying vacant orbitals
C-H bonds are not acidic
strong bonds
hard to be selective
56
Q

what metal properties does sigma bond metathesis require

A

electrophilic metal centre

57
Q

why could Ox. addition be possible for U

A

can go up 2 oxidation state

CHEM411 (5 decks)

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