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1
Solubility Properties
X-ray crystal structure of :dicyclohexyl[18]crown-6 and potassium complex of [18]crown-6.
Structures are different:• In the solid state• In polar and apolar solvent• As a complex
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Solubility Properties
Structure a is unrealistic, why?
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Solution Applications
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Solution Applications
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Solution Applications
• Free, desolvated anions in organic solvents• All anions have a similar nucleophilicity
X A
K ACrown ether
Reaction of potassium salts with benzyl chloride in acetonitrile (X= Cl, A= anion,e.g.acetate).
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Solution Applications
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Selectivity of Cation Complexation
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Selectivity of Cation Complexation
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Selectivity of Cation Complexation
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The template Effect
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The template Effect
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High-Dilution Synthesis
Cyclization rate: rc = kc [X–Y]
Polymerization rate: rp = kp [X–Y]2
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High-Dilution Synthesis
OCl
C OCl
O
NH2
O
H2N
+High-dilution C
O OC O
HNNH
O O
NH
O O
HN
OO
O LiAlH4
High-dilution synthesis of diaza(18)crown-6.Note the use of acid chloride groups to enhance reaction rate.
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High-Dilution Synthesis
N
N
NH
N
N
HN
1+1
Fe
O
N
O
N
N
N
N
N
Fe
Cl
O
Cl
O Fe
NN
Fe
N N
O O
OO
N N
N NN N
N
N
N
N
N
N
N
N
N
N
N
NOO
O O
O OFe Fe
Fe
(3.56)
3+3
Simultaneous(1+1),(2+2) and (3+3) cyclococondensation in bipyridyl-based cryptands
2+2
(3.54)
(3.55)
+
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Kinetic and Dynamic Effects
X-ray crystal structures of free spherand 3.30 and its Li+ complex
K = k1/k-1k1 = 8*104 (M-1s-1) total desolvation leads to a high transition state
k-1 =<10-12 (s-1)
Cation receptor: slow kinetic, large stability constantCation carriers: fast kinetic, lower stability
One of the few kinetically stable complexes
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Soft Ligands for Soft Metal Ions
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Soft Ligands for Soft Metal Ions
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Soft Ligands for Soft Metal Ions
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Soft Ligands for Soft Metal Ions
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Soft Ligands for Soft Metal Ions
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Soft Ligands for Soft Metal Ions
X-Ray Crystal structures of the Ag+ complexes of [18]crown-6 and its sulfur analogue
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Soft Ligands for Soft Metal Ions
Macrocycle Synthesis through Schiff’s Bases
• Thermodynamic equilibrium
• Template effect
NH
NH2
HN
H2N+
OO
NH HN
NH HN
KCN NH
NH HN
HN
+
Ni(ClO4)2 Ni2+
Ni(Cn)42-
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Soft Ligands for Soft Metal Ions
NO O
+ H2N O O NH2
N NN
OO
NNN
O
O
NN N
O
O
Ba2+, Pb2+Mn2+, Mg2+
(a)(b)
M+M+
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Complexation of Organic Cations
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Complexation of Organic Cations
3.80
3.793.78
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Complexation of Organic Cations
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Recognition of NH 3+ (CH2)nNH3
+
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Calixarenes
Interconversion is slow on the NMR time sc ale
at r.t. (ca 150 s -1), but readily observed at 60 °C
p-tert-butylcalix[4]arene
Conformation
Cone conformer is most effectively stabilised by intramolecular hydrogen bonds
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OH
CH2*
CH2OH
OH
CH2O, H+*
n
+
OH
CH2*
CH2
*
nOH
* CH2
*
Bakelite
∆n
Calixarenes
R
OH
CH2
R
OH
CH2
R
OH
CH2
R
OH
CH2
OH
HOAc, HCl
OHOH HO
RR R R
OH
calix[4]arene
Bakelite
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Calixarenes
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Calixarenes
Conformational analysis by variable temperature NMR (VT NMR)
Suitable for energies in range from 20 to 1 00 kJ mol -1, typical error ±1 kJ mol -1
Lower temperatures: separate peaks (process is kinet ically slow on the NMR time scale),
broadening upon increase of temperature
Coalescence temperature: peaks merge to single broad signal
kc = rate, ∆ν∆ν∆ν∆ν = frequency separation between NMR peaks (at lower temperature)
kB = 1.3805 x 10-23 J K -1 (Boltzmann constant), h = 6.6256 x 10 -34 J s (Planck’s constant),
T = absolute temperature (K), R = 8.314 J mol -1 K-1 (molar gas constant)
Higher temperatures: single signal becomes sha rper
2
νπ ∆=ck
T R
GT#Λ
−= e
h
kk B
c
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Calixarenes
X- ray structures of a Na+ complex and a Cs+ complex of calix[4]arene
Two binding pockets:• an hydrophobic• And a spherand like
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Calixarenes
Fast intramolecular Ag + tunneling is observable by 1H NMR
(coalescence temperature about -70 °C)
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Calixarenes
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Calixarenes
BIS(CALIX)CROWNS
Conformational aspects of cation
inclusion
Extraction experiments with
picrates salts
2 days required for formation of the Na
komplex
Alkali metal intra- and intermolecular exchange pr ocesses
O
O
O
O
O
O
O
O
O
O
OO
O
O
O
O
O
O
BuBuBuBu
BuBu BuBu
1.Fast intramolecularcation exchange
2.Slow intermolecularcation exchange
O
O
O
O
O
O
O
O
O
O
OO
O
O
O
O
O
O
BuBuBuBu
BuBu BuBu
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Carbon Donor and ππππ-acid ligands
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Carbon Donor and ππππ-acid ligands
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Carbon Donor and ππππ-acid ligands
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Siderophores
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Siderophores
Bu2Sn(OC2H4O)
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Siderophores
