Macrocycles

Question 1

macrocyclic ligand

Answer 1

ring of at least 9 atoms of which at least 3 are able to donate a lone pair to a metal atom

Question 2

podand

Answer 2

non-cyclic, exists linearly and highly solvated

Question 3

macrocycle solvation

Answer 3

one point of solvation

Question 4

macrocyclic effect

Answer 4

macrocycle and podand have similar enthalpies, podand has linear form that’s not optimised for binding and must order itself around metal ion therefore has negative entropy, increased stability of macrocycles due to entropy

Question 5

kinetic stability of podands

Answer 5

one donor atom dissociates but held close to metal which increases prob of recombination, ligand can also unzip if donor rotates away from coord site, gives slower recombination or complete dissociation

Question 6

kinetic stability of macrocycles

Answer 6

dissociated donor held close by rigidity of macrocycle gives very high prob of recombination

Question 7

considerations for templatin

Answer 7

size of target macrocycle, metal ion size and types of donor atom present

Question 8

kinetic template effect

Answer 8

stabilises transition state by binding in geometry that favours product formation, gives lower Ea and holds reactive FG in position for sterically selective reactions

Question 9

thermodynamic template effect

Answer 9

acts on reversible reactions under thermo control, templating species binds to one member of equilibrium so POE shifts towards this species and stabilises specific structure

Question 10

metal ion dependence of templating

Answer 10

function of size and charge, more flexibility with podands than macrocycles

Question 11

hole size

Answer 11

radius of available binding cavity within ligand