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Organometallics > Webb Ligands > Flashcards

Webb Ligands Flashcards

1
Q

homo vs hetero catalysts

A

homo - active and (tailorable) selective

hetero - solid, low selectivity, easy product separation

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2
Q

what is an L-type ligand?

A

ionic - donates two electrons to the metal

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3
Q

what is an X-type ligand?

A

covalent - shared electrons in a dative bond

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4
Q

what is a lewis acid?

A

electron pair acceptor

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5
Q

what is a lewis base?

A

electron pair donor

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6
Q

what main compound is used in Friedel-crafts alkylation?

A

AlCl3

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7
Q

order soft to hard acids

A

I- < Br- < Cl- < F-

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8
Q

order soft to hard bases

A

R3P &laquo_space;R3N, R2S &laquo_space;R2O

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9
Q

how do sigma donor ligand affect electron density on metal?

A

increase

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10
Q

how does pi donation affect other bonds to the metal

A

weakens the M-C bonds (Tolman’s electronic parameter)

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11
Q

how does pi back-donation affect other bonds to the metal

A

strengthens the M-C bonds and weakens the C=O bond

because of donation into the sigma* orbital

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12
Q

what theory describes the molecular orbital adaptation of crystal field theory

A

ligand field theory

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13
Q

how does spin affect field strength

A

high spin = weak field (vice versa)

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14
Q

how does destructive overlap of orbitals affect the wave function?

A

makes an antibonding orbital

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15
Q

what sort of overlap of orbitals creates bonding orbitals

A

constructive

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16
Q

which end of the electrochemical series accounts for the high spin, weak field ligands

A

Br-

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17
Q

what size is delta O for a strong field ligand

A

big

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18
Q

how do you maximise delta O?

A

efficient orbital overlap

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19
Q

MO for a square planar complex is similar to what rule?

A

Jahn-Teller distortion

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20
Q

For the ionic method of the 18e rule, how many electrons are L ligands worth?

A

2

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21
Q

For the ionic method of the 18e rule, how many electrons are X ligands worth?

A

2

22
Q

what exceptions are there to the 18e rule?

A

square planar ==> 16e
steric hindrance could cause 16e
Class 1 could have 12-22e (3d metals have weak field)
Class 2 could have 12-18e (4d and 5d have strong field)

23
Q

what is synergic bonding?

A

combination of sigma donation and pi back-bonding

24
Q

three methods for synthesising M-CO bonds

A

reduction of metal halides under CO pressure; reaction between reactive metal and CO; ligand exchange

25
Q

reactions of M-CO complexes

A

nucleophilic attack; migratory insertion

26
Q

how do dinitrogen ligands complex with the metal?

A

end on // side on // bridging

27
Q

how does NO complex with a metal

A

NO+ linear or NO- bent

28
Q

in dihydrogen complexes, what effect does pi back donation have on the H-H bond length?

A

lengthens

29
Q

how would a hydride (H-) ligand bond to a metal centre?

A

single 2e- donation OR bridging

30
Q

how are metal hydrides stabilised? the more unstable the conjugate base, the less __ the compound is

A

with electron withdrawing ligands

acidic

31
Q

how do you synthesise a metal hydride complex?

A

oxidative addition of molecular H2 OR from oxidative addition of ‘active’ hydrogen sources (eg silanes or acids)

32
Q

What is the Drew-Chart-Duncanson model?

A

lengthening of the C=C bond distance by pi back-donation.

33
Q

Give examples of lewis base ligands

A

halides // oxygen (ethers, alkoxide, oxide, carboxylate) // sulfur (R2S, RS- S2-) // nitrogen (inorganic amides, chelating amines) // phosphines (PR3)

34
Q

what is a bite or cone angle?

A

optimum ligand bonding angles to relieve steric strain

35
Q

how does bite angle affect dissociation reactions?

A

angle increases - dissociation constant increases - easier dissociation

36
Q

definition of natural bite angle? what affects it?

A

preferred chelation angle.

ligand backbone contraints (not metal valence angles)

37
Q

examples of polydentate phosphines

A

dppm // dppe // dmpe // dppp

38
Q

benefits of phosphines as ligands?

A

very versatile soft donor ligands. Possible to fine-tune steric and electronic properties well described by ligand parameter.

39
Q

How do you find the oxidation state of a metal (in a complex)

A

subtract charges from negative ligands, add charges from positive ligands

40
Q

what charge on an acac ligand?

A

-1

41
Q

what does -ate ending mean on a ligand?

A

-

42
Q

how many electrons does a bridging CH2 give to each metal?

A

2e

43
Q

how many electrons does a bridging CH3 give to each metal?

A

1e

44
Q

In an M(CO)L complex, how does increasing electron density on M affect v(CO)?

A

increases (as its similar to decreasing back-bonding)

45
Q

How does an increase in back-bonding in an M(CO)L complex affect v(CO)

A

lowers

46
Q

Which out of 5d 4d and 3d transition metals has the lowest energy?

A

5d

47
Q

how does energy of a metal affect v(CO)

A

increase in energy, increase in v(CO)

48
Q

which would have a greater v(CO) based on numbers of d electrons: d0 or d2?

A

d0

49
Q

spectrochemical series for sigma donors

A

OH- < NH3 < Cl- < Br- < CN- < CO < CH3 < I- < SCN- < PR3 < H-
(Olivia never calls boys cos calling charlie is so preferred hehe)

50
Q

spectrochemical series for pi donors

A

Br- < I- < NCS- < NO2- < CN- < CO < C2H4

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Organometallics (7 decks)

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