Webb Ligands

Question 1

homo vs hetero catalysts

Answer 1

homo - active and (tailorable) selective

hetero - solid, low selectivity, easy product separation

Question 2

what is an L-type ligand?

Answer 2

ionic - donates two electrons to the metal

Question 3

what is an X-type ligand?

Answer 3

covalent - shared electrons in a dative bond

Question 4

what is a lewis acid?

Answer 4

electron pair acceptor

Question 5

what is a lewis base?

Answer 5

electron pair donor

Question 6

what main compound is used in Friedel-crafts alkylation?

Answer 6

AlCl3

Question 7

order soft to hard acids

Answer 7

I- < Br- < Cl- < F-

Question 8

order soft to hard bases

Answer 8

R3P &laquo_space;R3N, R2S &laquo_space;R2O

Question 9

how do sigma donor ligand affect electron density on metal?

Answer 9

increase

Question 10

how does pi donation affect other bonds to the metal

Answer 10

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

Question 11

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

Answer 11

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

because of donation into the sigma* orbital

Question 12

what theory describes the molecular orbital adaptation of crystal field theory

Answer 12

ligand field theory

Question 13

how does spin affect field strength

Answer 13

high spin = weak field (vice versa)

Question 14

how does destructive overlap of orbitals affect the wave function?

Answer 14

makes an antibonding orbital

Question 15

what sort of overlap of orbitals creates bonding orbitals

Answer 15

constructive

Question 16

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

Answer 16

Br-

Question 17

what size is delta O for a strong field ligand

Answer 17

big

Question 18

how do you maximise delta O?

Answer 18

efficient orbital overlap

Question 19

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

Answer 19

Jahn-Teller distortion

Question 20

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

Answer 20

2

Question 21

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

Answer 21

2

Question 22

what exceptions are there to the 18e rule?

Answer 22

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)

Question 23

what is synergic bonding?

Answer 23

combination of sigma donation and pi back-bonding

Question 24

three methods for synthesising M-CO bonds

Answer 24

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

Question 25

reactions of M-CO complexes

Answer 25

nucleophilic attack; migratory insertion

Question 26

how do dinitrogen ligands complex with the metal?

Answer 26

end on // side on // bridging

Question 27

how does NO complex with a metal

Answer 27

NO+ linear or NO- bent

Question 28

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

Answer 28

lengthens

Question 29

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

Answer 29

single 2e- donation OR bridging

Question 30

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

Answer 30

with electron withdrawing ligands acidic

Question 31

how do you synthesise a metal hydride complex?

Answer 31

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

Question 32

What is the Drew-Chart-Duncanson model?

Answer 32

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

Question 33

Give examples of lewis base ligands

Answer 33

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

Question 34

what is a bite or cone angle?

Answer 34

optimum ligand bonding angles to relieve steric strain

Question 35

how does bite angle affect dissociation reactions?

Answer 35

angle increases - dissociation constant increases - easier dissociation

Question 36

definition of natural bite angle? what affects it?

Answer 36

preferred chelation angle. | ligand backbone contraints (not metal valence angles)

Question 37

examples of polydentate phosphines

Answer 37

dppm // dppe // dmpe // dppp

Question 38

benefits of phosphines as ligands?

Answer 38

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

Question 39

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

Answer 39

subtract charges from negative ligands, add charges from positive ligands

Question 40

what charge on an acac ligand?

Answer 40

-1

Question 41

what does -ate ending mean on a ligand?

Answer 41

-

Question 42

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

Answer 42

2e

Question 43

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

Answer 43

1e

Question 44

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

Answer 44

increases (as its similar to decreasing back-bonding)

Question 45

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

Answer 45

lowers

Question 46

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

Answer 46

5d

Question 47

how does energy of a metal affect v(CO)

Answer 47

increase in energy, increase in v(CO)

Question 48

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

Answer 48

d0

Question 49

spectrochemical series for sigma donors

Answer 49

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

Question 50

spectrochemical series for pi donors

Answer 50

Br- < I- < NCS- < NO2- < CN- < CO < C2H4 | Boys in NYC kNow canadians cooperate cheerfully