AROMATICITY IN CHELATES. STUDY ON METALCOMPLEXES OF HYDROXYPYRONES AND RELATED COMPOUNDS....

AROMATICITY IN CHELATES.

STUDY ON METALCOMPLEXES OF HYDROXYPYRONES

AND RELATED COMPOUNDS.

Vibrational Spectroscopy Research Group,

Department of Chemical Physics,

Faculty of Chemistry,

Jagiellonian University, Kraków, Poland

Krzysztof Zborowski

Is the idea of aromaticity important?

H-Bond 387 817 Solvent 55 226

Water 314 874 Aromatic/aromaticity 46 859

DNA 260 914 AIDS 45 961

Cancer 204 036 Chiral/chirality 34 394

Virus 169 292 Substituent 12 449

Life 109 301 Nucleophilic 11 143

Death 72 337 Electrophilic 5 719

Frequencies of using chemical and biochemical terms in titles or as keywords retrieved from Institute of Scientific Information (1981- 1998). Krygowski et al, Tetrahedron, 56 (2000), 1783.

Before 1825 “aromatic” smell

1825 Faraday isolated benzene

Before 1865 high carbon:hydrogen ratios, unsaturated, high stable compounds

1865 benzene structure proposed by Kekule, aromatic are compounds containing a benzene ring

1866 Erlenmayer - aromatic are compounds with the reactivity similar to benzene, substitution is more favourable than addition

1911 Willstaetter showed that not all unsaturated compounds with cyclic conjugation are aromatic (i.e. similar to benzene).

1925 Annit – Robinson: electronic sextet and heteroaromaticity

1931 Hückel theory – aromatic are planar, cyclic systems with 4n+2 π electrons

1936 ring current theory – free π electrons circulation around the benzene ring (Pauling)

1951 bonds lenghts equalization in aromatic rings - Albert

1956 ring current effects on NMR chemical shifts

Milestones of development of the aromaticity concept

Compounds which exhibit significantly exalted diamagnetic susceptibility are aromatic. Cyclic electron delocalization also may result in bond length equalization, abnormal chemical shifts and magnetic anisotropies, as well as chemical and physical properties which reflect energetic stabilization. Those compounds with exalted paramagnetic susceptibility may be antiaromatic.

Paul von Ragué Schleyer, Haijun Jiao,

Pure & Appl. Chem., 68 (1996) 209

Modern attempts to aromaticity definition Modern attempts to aromaticity definition

Aromatic are cyclic compounds with high π electron delocalization

Simplified (and less magnetic) definitionSimplified (and less magnetic) definition

Several types of aromaticity can be considered:

•Carboaromaticity: aromatic rings are built from carbon atoms only,

•Heteroaromaticity: one or more carbon atom(s) are replaced by other elements (typically oxygen, sulphur and nitrogen),

•Quasiaromaticity: quasiaromatic can be pseudo-rings with hydrogen bond in which the C=C-C fragment (or analogical fragment including heteroatom(s) is replaced by the A...H-D group,

•Metalloaromaticity/Chelatoaromaticity: manifestation of aromatic properties in chelate rings where metal ion is essential part of the ring,

•All-Metal aromaticity: aromatic systems consisted of metal atoms only.

Several types of aromaticity can be considered:

•Carboaromaticity: aromatic rings are built from carbon atoms only,

•Heteroaromaticity: one or more carbon atom(s) are replaced by other elements (typically oxygen, sulphur and nitrogen),

•Quasiaromaticity: quasiaromatic can be pseudo-rings with hydrogen bond in which the C=C-C fragment (or analogical fragment including heteroatom(s) is replaced by the A...H-D group,

•Metalloaromaticity/Chelatoaromaticity: manifestation of aromatic properties in chelate rings where metal ion is essential part of the ring,

•All-Metal aromaticity: aromatic systems consisted of metal atoms only.

“Aromatic” compounds have some specific properties

• they are more stable than their analogues with localized double and single bonds – energetic criterion of aromaticity, resonance energy.

• their bonds lengths are between those typical for single and double bonds – geometric criterion of aromaticity.

• in aromatic compounds a π-electron ring current is induced by an external magnetic field – magnetic criterion of aromaticity.

• show higher energy UV spectrals bands – spectroscopic criterion of aromaticity.

• they usually undergo more easily substitution reactions (so-called aromatic substitution) than addition – reactivity criterion of aromaticity.

I6

1H NMR shifts

zz

11

On the base of mentioned previously criteria of aromaticity chemists defined a lot of aromaticity indices, that are used for quantitative measurements of aromaticity.

Energy based indices

For chemists, the most natural way to quantitative aromaticity determination is calculation the Resonance

Energy RE or Aromatic Stabilization Energy ASE (difference in energy between the energy of a compound

with cyclic π-electron delocalization and a model reference system without π-electron delocalization)

•selection of a proper and sufficiently well defined reference state•limite precision and accuracy of the energy determination (either experimentally or theretically)•the perturbation of derived energies by extraneous effects such as ring strain or change in hybridization.

•selection of a proper and sufficiently well defined reference state•limite precision and accuracy of the energy determination (either experimentally or theretically)•the perturbation of derived energies by extraneous effects such as ring strain or change in hybridization.

Problems connected with accurate RE/ASE calculation

A number of experimental or theoretical methods on semiempirical level used to be employed for RE calculations:

•calculations based on experimental heats of formation or atomization energies

•HRE -Hückel Resonance Energy

•DRE – Dewar Resonance Energy

•HSRE – Hess-Schaad Resonance Energy

and others

A number of experimental or theoretical methods on semiempirical level used to be employed for RE calculations:

•calculations based on experimental heats of formation or atomization energies

•HRE -Hückel Resonance Energy

•DRE – Dewar Resonance Energy

•HSRE – Hess-Schaad Resonance Energy

and others

Ab initio quantum mechanical calculations are a more general way of obtaining ASE values.

For calculations hypothetical, isodesmic (equal numbers of formal single and double bonds in products and reactants are required) and homodesmotic (the same number of bonds between given atoms in each state of hybridization, in addition the number of hydrogen bonds joined to the atoms in given hybridization must match, homodesmotic reactions are the subclass of isodesmic reactions) reactions are used.

Ab initio quantum mechanical calculations are a more general way of obtaining ASE values.

For calculations hypothetical, isodesmic (equal numbers of formal single and double bonds in products and reactants are required) and homodesmotic (the same number of bonds between given atoms in each state of hybridization, in addition the number of hydrogen bonds joined to the atoms in given hybridization must match, homodesmotic reactions are the subclass of isodesmic reactions) reactions are used.

example of the isodesmic reaction

example of a homodesmotic reaction

example of the isodesmic reaction

example of a homodesmotic reaction

YY +

YY2 CH3CH3+ 2 CH2CH2+

Stabilization energies for benzene calculated at different levels of theoryStabilization energies for benzene calculated at different levels of theory

Theory level Reaction Stabilization energy [kcal/mol]

MP2/RHF/SBK(d) A 74.7

RHF/SBK(d) A 61.4

MP2/6-31G/6-31G* A 67.2

MP4/6-31G B 24.3

MP2/6-311G** B 28.0

B3LYP/6-311G** B 23.3

HF/6-31G* C 23.4

MP4SDTQ/6-31G**/MP2(full)/6-31G** C 20.3

+ 3 CH3CHCHCH3 CH2CHCHCHCHCH2=

+ 3 CH2CH2 CH2CHCHCH2= 3(trans)

+ 6 CH4 CH3CH3= 3 CH2CH2+(A)(A)

(B)(B)

(C)(C)

Recently new, type of reaction scheme have been proposed for ASE calculations.

X2

YX1 X4

X3

YX4

X3X2

X1+ ++

X4

X3X2

YX1

X2

X1X4

X3

Y+ + +

Homodesmotic reaction with cyclic compounds onlyHomodesmotic reaction with cyclic compounds only

bR

aN

2

n

NN

NV

2)'(

'

100

kV

VI 11006

GEOEN

RRn

RRRRn

HOMA javeaveopt

jopt

1

)()([1)(1 222

Geometry based indices

HOMA (Harmonic Oscillator Model of Aromaticity) i I6

their values depends on the “aromatic system” bonds length

Kruszewski, Krygowski, Tetrahedron Lett. 3839 (1972) – HOMAKrygowski, Cyranski, Tetrahedron, 52, 10255 (1996) – EN, GEO

Kruszewski, Krygowski, Tetrahedron Lett. 3839 (1972) – HOMAKrygowski, Cyranski, Tetrahedron, 52, 10255 (1996) – EN, GEO

Bird, Tetrahedron, 42, 89 (1986)Bird, Tetrahedron, 42, 89 (1986)

Magnetic based index

NICS

(Nucleus Independent Chemical Shift)

Absolute magnetic shieldings, computed at ring center (nonweighted mean of the heavy atom coordinates) or at another interested point of molecule. To correspond to the familiar NMR chemical shift convention, the signs of the computed values are reversed: Negative “nucleus-independent chemical shifts” denote aromaticity; positive antiaromaticity

P. v. R. Schleyer et al, JACS, 118, 6317 (1996)P. v. R. Schleyer et al, JACS, 118, 6317 (1996)

Pyromeconic acid, Hpa (3-hydroxy-4H-pyran-4-one)

Investigated compounds. Pyromeconic acid and its derivatives

kojic acidmaltol ethylmaltol

azidokojic acidchlorokojic

acid

Studied derivatives of pyromeconic acidStudied derivatives of pyromeconic acid

O

S

O

CH3

H

H

H O

O

S

CH3

H

H

H S

O

O

CH3

H

H

H O

S

S

CH3

H

H

H

S

S

O

CH3

H

H

H S

S

S

CH3

H

H

HS

O

S

CH3

H

H

H

SOO OSO OOS

SOS OSS SSS

SSO

Maltol thio derivativesMaltol thio derivatives

Practical application of studied compounds

Maltol is an important compound in food chemistry. It was found in many

natural (milk, sweet potatoes) and processed (beer, wine, butter, ghee) food

products. It is also added to the food due to its flavour (bread, butter, green

tea, popcorn, flavour standard for whisky profiling) and antioxidant

properties.

Ethylmaltol is widely added to perfumes.

Maltol is an important compound in food chemistry. It was found in many

natural (milk, sweet potatoes) and processed (beer, wine, butter, ghee) food

products. It is also added to the food due to its flavour (bread, butter, green

tea, popcorn, flavour standard for whisky profiling) and antioxidant

properties.

Ethylmaltol is widely added to perfumes.

Kojic acid is a biologically important natural product. It is a fungal metabolite produced by many species of Aspergillus, Acetobacter and Penicillium. It was discovered during investigating on the fermentation of steamed rice (‘koji’). Kojic acid occurs in such traditional Japanese fermented food products as sake (rice wine), miso (soybean paste), shoyu (soy sauce) and many others. Thanks to its antibacterial and fungicidal properties, kojic acid is used as a food additive. It is also widely used as an antioxidant or antibrowning agent as well. Due to its properties of melatonin production inhibition it plays an important role in the cosmetic industry as a skin-whitening agent

Chlorokojic and azidokojic acids exhibit herbicidal and growth regulatory activity. Their antibacterial and fungicidal properties are stronger than kojic acid.

Kojic acid is a biologically important natural product. It is a fungal metabolite produced by many species of Aspergillus, Acetobacter and Penicillium. It was discovered during investigating on the fermentation of steamed rice (‘koji’). Kojic acid occurs in such traditional Japanese fermented food products as sake (rice wine), miso (soybean paste), shoyu (soy sauce) and many others. Thanks to its antibacterial and fungicidal properties, kojic acid is used as a food additive. It is also widely used as an antioxidant or antibrowning agent as well. Due to its properties of melatonin production inhibition it plays an important role in the cosmetic industry as a skin-whitening agent

Chlorokojic and azidokojic acids exhibit herbicidal and growth regulatory activity. Their antibacterial and fungicidal properties are stronger than kojic acid.

Investigated hydroxypyrones form cations and anions by protonation or deprotonation, respectively.

Investigated hydroxypyrones form cations and anions by protonation or deprotonation, respectively.

Maltol

cation neutral molecule anion

(H2ma+) (Hma) (ma-)

- H+

+ H+

- H+

+ H+

pKa1 = 2.28pKa1 = 2.28 pKa2 = 8.62pKa2 = 8.62

In coordination chemistry, studied hydroxypyrones are known as a potent monoanionic, bidendate metal chelators.

In coordination chemistry, studied hydroxypyrones are known as a potent monoanionic, bidendate metal chelators.

Their various complexes are extensively studied because of their catalytic, biochemical and farmacological properties.

Their various complexes are extensively studied because of their catalytic, biochemical and farmacological properties.

VO(ma)2

V(ma)3

VO2(ma)2-

Vanadium complexes of maltol, ethylmaltol and kojic acid are known as orally active insulin mimetics

Vanadium complexes of maltol, ethylmaltol and kojic acid are known as orally active insulin mimetics

Zn(ma)2*2H2O Zinc and molybdenum complexes have a similar property

MoO2(ma)2

Ferric complexes enable effective iron delivery in the iron deficiency anaemia.

Fe(ma)3 Fe(pa)3

Al(ma)3

Bismuth(III)-ethylmaltol complex acts as a antibacterial agent

Aluminium complexes exhibit a strong neurotoxical activity

Bi(ma)3

Indium and Gadolinum complexes were suggested as new radiopharmaceuticals

In(ema)3

Types of (potential) aromatic systems in studied hydroxypyrones an their complexes with metal ions

heteroaromatic

systemmetalloaromatic system

quasiaromatic systemelectron

delocalisation

Why chelatoaromaticity seems to be be important in coordination chemistry?

Stability of coordination compound.

Why chelatoaromaticity seems to be be important in coordination chemistry?

Stability of coordination compound.

•Thermodynamic stability

- R T lnK = G = H - T S

•Thermodynamic stability

- R T lnK = G = H - T S

CH2

CH2 OCH2

O

O

HO

O

HH

H O

-0,2

0,0

0,2

0,4

0,6

0,8

6-311++G(d,p) basis set HF SVWN B3LYP B1LYP

HO

MA


Changes of HOMA index for various maltol forms(heterocyclic ring)

0,0

0,2

0,4

0,6

0,8

1,0

1,2

B3LYP/6-311++G(d,p)GEO

HF SVWN B3LYP B1LYP

EN HF SVWN B3LYP B1LYP

GE

O, E

N


Pyromeconic acid. Dissection of the HOMA index into GEO and EN parts.

Dearomatization occurs mainly due to GEO part.

I6 values for cation, neutral molecule and anion of pyromeconid acid

(heterocyclic ring)

35

40

45

50

55

60


I6


-8

-7

-6

-5

-4

-3

-2

-1

NIC

S

6-311++G(d,p) basis set HF SVWN b3LYP B1LYP


NICS(0) values for cation, neutral molecule and anion of pyromeconid acid (heterocyclic ring)

Comparison of the aromaticity level of neutral molecules of pyromeconic acid, maltol and ethylmaltol.

-4

-3

-2

-1

0

1

35

40

45

50

55

HOMA

NICS

valu

e of

the

arom

atic

ity

inde

x


I6

pyromeconic acid maltol etylmaltol

Changes of HOMA index for various pyromeconic acid forms (OCCO spacer)


-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

HO

MA

6-311++G(d,p) HF SVWN B1LYP B3LYP

O

OOH

H H

H


(OCCO spacer)


(OCCO spacer)


0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

EN

, GE

O

6-311++G(d,p)EN

HF SVWN B1LYP B3LYP

GEO HF SVWN B1LYP B3LYP

For cations and neutral molecules again dearomatization occurs mainly due to EN part. For anion GEO is more important.

For cations and neutral molecules again dearomatization occurs mainly due to EN part. For anion GEO is more important.

NICS(0) values for cation, neutral molecule and anion of pyromeconid acid (OCCO fragment)

NICS(0) values for cation, neutral molecule and anion of pyromeconid acid (OCCO fragment)

cation neutral molecule anion-9

-8

-7

-6

-5

-4

-3

-2

-1

0

NIC

S

6-311++G(d,p) HF SVWN B1LYP B3LYP

Relative aromaticity in the heterocyclic rings of studied hydroxypyrones decreases in the order.

cation > neutral molecule > anion.

The same order of electron delocalization is observed for the OCCO spacer.

The data obtained show very low influence of the aliphatic substituents on the aromaticity level of studied hydroxypyrones.

Relative aromaticity in the heterocyclic rings of studied hydroxypyrones decreases in the order.

cation > neutral molecule > anion.

The same order of electron delocalization is observed for the OCCO spacer.

The data obtained show very low influence of the aliphatic substituents on the aromaticity level of studied hydroxypyrones.

Detailed investigations on the substituent influence on aromaticity of hydroxypyrones

Substituents involved: -CH3, -CN, -NO2, -COOH, -OH, -OCH3, -F, -Cl, -NH2, -CHO. Mono- , di- and tri- substitued derivatives

Substituents involved: -CH3, -CN, -NO2, -COOH, -OH, -OCH3, -F, -Cl, -NH2, -CHO. Mono- , di- and tri- substitued derivatives

O

O

R 1R 2

O

H.......

R3Conclusions:•Influence of substituents on aromaticity is not big.•The most significant aromaticity changes are observed for anions, moderate for neutral molecules and the smallest for cations.

Conclusions:•Influence of substituents on aromaticity is not big.•The most significant aromaticity changes are observed for anions, moderate for neutral molecules and the smallest for cations.

Obtained results support the tendency of the aromatic systems to conserve their aromaticity. Similar results were observed for monosubstitued benzene derivatives (Krygowski et al, J. Org. Chem. 69, 6634 (2004)

Obtained results support the tendency of the aromatic systems to conserve their aromaticity. Similar results were observed for monosubstitued benzene derivatives (Krygowski et al, J. Org. Chem. 69, 6634 (2004)

-0,3

0,0

0,3

0,6

0,9

HO

MA

Maltol SOO OSO OOS SSO SOS OSS SSS


HOMA values for cations, neutral molecules and anions of thiomalols (heterocyclic ring)

HOMA values for cations, neutral molecules and anions of thiomalols (heterocyclic ring)

HOMA values for cations, neutral molecules and anions of thiomalols (OCCO fragment)

HOMA values for cations, neutral molecules and anions of thiomalols (OCCO fragment)

-0,50

-0,25

0,00

0,25

0,50

HO

MA

B1LYP/6-311++G(d,p) Maltol SOO OSO OOS SSO SOS OSS SSS


NICS(0) values for cations, neutral molecules and anions of thiomalols (heterocyclc ring)

NICS(0) values for cations, neutral molecules and anions of thiomalols (heterocyclc ring)

-8

-6

-4

-2

0

NIC

S(0)

[pp

m] B1LYP/6-311++G(d,p)

Maltol SOO OSO OOS SSO SOS OSS SSS


NICS(0) values for cations, neutral molecules and anions of thiomalols (OCCO fragment)

NICS(0) values for cations, neutral molecules and anions of thiomalols (OCCO fragment)

-8

-6

-4

-2

0

2

NIC

S(0)

[pp

m]



ASE values for cations, neutral molecules and anions of thiomalolsASE values for cations, neutral molecules and anions of thiomalols

X

X

CH3

XH

X

X

CH3

XH

X

X

CH3

XH

X

X

CH3

XH

+ +

0

25

50

575

600

625

AS

E [

kJ/

mol

]



XM

Y

R1

R2

M

Y

X

R3

R4

R5

Metalloaromaticity

Metalloaromaticity is a manifestation of aromatic properties in chelate metalcomplexes where a metal ion is the essential part of the ring.

The concept of metalloaromaticity is very useful in that it unifies the reactivity, magnetic, spectroscopic and structural properties of chelates.

HF SVWN B3LYP

H2ma+ 0.220 0.351 0.116

Hma -0.195 0.068 -0.306

ma- -0.372 -0.080 -0.469

VO(ma)2 0.161 0.296 0.058

H3ka+ 0.202 0.329 0.116

H2ka -0.206 0.085 -0.288

Hka- -0.427 -0.114 -0.544

VO(Hka)2 0.111 0.274 0.040

Value of the HOMA index calculated for heterocyclic rings of maltol and kojic acid in their oxovanadium(IV) complexes

(geometries determined using LANL2DZ basis set).

VO(Hka)2

VO(ma)2

HF SVWN B3LYP

H2ma+ -7.37 -6.56 -6.98

Hma -2.38 -2.80 -2.57

VO(ma)2 -3.90 -3.37 -3.80 -3.74 -3.91 -3.81

VO(ma)2 (LANL2DZ) -2.96 -2.80 -3.47 -3.33 -3.56 -3.41

Aromaticity of heterocyclics rings of bis(maltolato)oxovanadium(IV), NICS(0) index.

B3LYP/(6-311++G(d.p), experimental structural data).

Aromaticity of heterocyclic hydroxypyrones´ rings in complexes with various metal ions

Compound HOMA

(exp. geometry - CSD)

NICS (0)

(B3LYP/LANL2DZ)

Fe(pa)3 0.63 0.60 0.63

Al(ma)3 0.15 0.17 0.15 -2.90 -2.90 -2.92

Sn(ma)2 0.07 0.07 -2.92 -2.99

Bi(ema)3 0.32 0.37 0.30 -2.53 -2.67 -2.75

In(ema)3 0.17 0.30 0.25 -2.97 -3.22 -3.15

Al(ema)3 0.36 0.30 0.33 -2.76 -2.74 -2.88

Fe(ema)3 0.35 0.21 0.22

MoO2(ka)2 0.28 0.49

H2ma+ 0.57 -5.78

Hma 0.21 -2.23

ma-

B3LYP/LANL2DZ-0.47 -1.24

Electron delocalization/aromaticity for chelates rings with metal ions.

Compound HOMA

(exp geometry - CSD)

NICS (0)

(B3LYP/LANL2DZ)

Fe(pa)3 0.58 0.58 0.58

Al(ma)3 0.74 0.62 0.62 -5.80 -6.15 -6.13

Sn(ma)2 0.48 0.48 -8.06 -8.08

Bi(ema)3 0.56 0.61 0.60 -8.81 -7.75 -8.10

In(ema)3 0.55 0.55 0.61 -7.39 -7.34 -7.22

Al(ema)3 0.59 0.61 0.75 -5.96 -5.90 -5.72

Fe(ema)3 0.49 0.65 0.65

MoO2(ka)2 0.49 0.57

H2ma+ 0.54 -11.56

Hma 0.31 -3.44

ma-

B3LYP/LANL2DZ-0.41 -3.36

For the heterocyclic ring the full order of aromaticity is as follow:

cation > metalcomplex > neutral molecule > anion

For the heterocyclic ring the full order of aromaticity is as follow:

cation > metalcomplex > neutral molecule > anion

In the case of metalocyclic ring, aromaticity/electron delocalisation is even more strengthened than in heterocyclic ring

metalcomplex ≈ cation > neutral molecule > anion

In the case of metalocyclic ring, aromaticity/electron delocalisation is even more strengthened than in heterocyclic ring

metalcomplex ≈ cation > neutral molecule > anion

On the basis of the presented data, existing of metalloaromaticity in both (heterocyclic and metalocyclic) rings of hydroxypyrones complexes is postulated

On the basis of the presented data, existing of metalloaromaticity in both (heterocyclic and metalocyclic) rings of hydroxypyrones complexes is postulated

What is the mechanism of aromaticity increasing in metalcomplexes of studied hydroxypyrones?

What is the mechanism of aromaticity increasing in metalcomplexes of studied hydroxypyrones?

Is there any correlation between Is there any correlation between the effective ligand charge and the effective ligand charge and aromaticity?aromaticity?

Is there any correlation between Is there any correlation between the effective ligand charge and the effective ligand charge and aromaticity?aromaticity?

- partial charge of the atom A

AzZ

AyY

AxXAQ

3

1

Q A

Analiza populacyjna GAPT (Generalized Atomic Polar Tensors)

Partial charge of the atom A is calculated according to the equation:

Cioslowski, JACS, 111, 8333 (1989)Cioslowski, JACS, 111, 8333 (1989)

A

Z

A

Y

A

X

zyx

- first derivatives of the dipol moment

of the molecule with respect to the cartesian coordinates of atom A

HOMA, GEO and EN values of heterocyclic ring as a fuction of the maltol unit charge

-1.00 -0.95 -0.90 -0.85 -0.80 -0.75 -0.70

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

LimaNamaKma

B3LYP/6-311++G(d,p) HOMA EN GEO

ma-

valu

e of

the

arom

atic

ity in

dex

charge of the maltol unit

Lima

Changes of HOMA, GEO i EN indices as a function of tha maltol unit charge (ring with metal ion involved).

Lima

-1.00 -0.95 -0.90 -0.85 -0.80 -0.75

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

LimaNamaKmama-


charge of the maltol unit

valu

e of

the

arom

atic

ity in

dex

Lima

-1.00 -0.95 -0.90 -0.85 -0.80 -0.75-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

LimaNamaKmama-

B3LYP/6-311++G(d,p) NICS - heterocyclic ring NICS - metalocyclic ring

NIC

S v

alue

Charge of the maltol unit

Changes of the NICS index as a function of tha maltol unit chargeChanges of the NICS index as a function of tha maltol unit charge

valu

e of

the

arom

atic

ity

inde

x

Charge of the maltol or ethylmalol unit in the complex

-0.95 -0.90 -0.85 -0.80 -0.75 -0.70

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Bi(ema)3

Sn(ma)2

In(ema)2

Al(ma)3

Al(ema)2

VO(ma)2

B3LYP/LANL2DZ HOMA EN GEO

Changes of HOMA, GEO i EN indices as a function of the maltol or ethylmaltol unit charge (heterocyclic ring).

Changes of HOMA, GEO i EN indices as a function of the maltol or ethylmaltol unit charge (heterocyclic ring).

-0.95 -0.90 -0.85 -0.80 -0.75 -0.700.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Bi(ema)3 Sn(ma)

2In(ema)

2

Al(ma)3

Al(ema)2

VO(ma)2

B3LYP/LANL2DZ HOMA EN GEO

Changes of HOMA, GEO i EN indices as a function of the maltol or ethylmaltol unit charge (ring with metal ion).

Changes of HOMA, GEO i EN indices as a function of the maltol or ethylmaltol unit charge (ring with metal ion).

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Charge of the maltol or ethylmaltol unit

It was observed for DNA and RNA bases that their aromaticity increases markedly along with the lenghtening of exocyclic C=X double bonds at the rings (Cyranski et al, J. Org. Chem., 68, 8607 (2003)).

It was observed for DNA and RNA bases that their aromaticity increases markedly along with the lenghtening of exocyclic C=X double bonds at the rings (Cyranski et al, J. Org. Chem., 68, 8607 (2003)).

N N

N N

O

N

N N

N N

NH

H

H

N

N

O

O

H

H

N

N

O

O

CH3

H

H

N

N

O

NH2

Is the same in the case of hydroxypyrones?Is the same in the case of hydroxypyrones?

1.2 1.4 1.6 1.8 2.0 2.2-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8


bond length

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Changes of HOMA, GEO i EN indices as a function of the “keto” C=O bond length of the maltol unit (heterocyclic ring).

Changes of HOMA, GEO i EN indices as a function of the “keto” C=O bond length of the maltol unit (heterocyclic ring).

1.2 1.4 1.6 1.8 2.0 2.2-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0


bond length

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xChanges of HOMA, GEO i EN indices as a function of the “hydroxy”

C-O bond length of the maltol unit (heterocyclic ring).

Changes of HOMA, GEO i EN indices as a function of the “hydroxy” C-O bond length of the maltol unit (heterocyclic ring).

1.24 1.25 1.26 1.27 1.28 1.29 1.30

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

B3LYP/LANL2DZ heterocyclic rings, metalcomplexes metalocyclic ring, metalcomplexes

B3LYP/6-311++G(d,p) heterocyclic rings, salts metalocyclic ring, salts

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xChanges of the HOMA index as a function of the “keto” C=O bond

length of the maltol or ethylmaltol unit in complexes and salts

Changes of the HOMA index as a function of the “keto” C=O bond length of the maltol or ethylmaltol unit in complexes and salts

bond length

1.26 1.28 1.30 1.32 1.34 1.36

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

B3LYP/LANL2DZ heterocyclic ring, metalcomplexes metalocyclic ring, metalcomplexes

B3LYP/6-311++G(d,p) heterocyclic ring, salts metalocyclic ring, salts

bond length

Changes of the HOMA index as a function of the “hydroxy” C-O bond length of the maltol or ethylmaltol unit in complexes and salts

Changes of the HOMA index as a function of the “hydroxy” C-O bond length of the maltol or ethylmaltol unit in complexes and salts

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arom

atic

ity

inde

x

Aromaticity increasing in the hydroxypyrones metalcomplexes is accelerated by the elongation of the interacted with metal ion double exocyclic C=O bond.

Additionally, electrons from the deprotonated ligand move toward the metal ion, with ligand acquiring some “cation” character.

Aromaticity increasing in the hydroxypyrones metalcomplexes is accelerated by the elongation of the interacted with metal ion double exocyclic C=O bond.

Additionally, electrons from the deprotonated ligand move toward the metal ion, with ligand acquiring some “cation” character.

Some general remarks on the metalloaromaticity of chelate complexes

1. There are a number of possible ligands similar to presented hydroxypyrones (they have rings with possible π electronic delocalization and exocyclic double bond(s) used for metal complexation).

2. During creation of the chelate complex exocyclic double bond(s) are elongated so ligands aromaticity should in general automatically increase.

3. Aromaticity stabilization seems to have important influence for such complexes creation and stability. Further studies of this problem are planning soon.

1. There are a number of possible ligands similar to presented hydroxypyrones (they have rings with possible π electronic delocalization and exocyclic double bond(s) used for metal complexation).

2. During creation of the chelate complex exocyclic double bond(s) are elongated so ligands aromaticity should in general automatically increase.

3. Aromaticity stabilization seems to have important influence for such complexes creation and stability. Further studies of this problem are planning soon.

Date post:	11-Jan-2016
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AROMATICITY IN CHELATES. STUDY ON METALCOMPLEXES OF HYDROXYPYRONES AND RELATED COMPOUNDS....

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