Copper complexes of superpodal amine ligands and reactivity studies towards dioxygen

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

FULL PAPER

DOI: 10.1002/ejic.201101265

Copper Complexes of “Superpodal” Amine Ligands and Reactivity Studies

towards Dioxygen

Anna Jozwiuk,^[a]E. Alper Ünal,^[a]Stefan Leopold,^[a]John P. Boyd,^[a]Marco Haryono,^[a]

Nadine Kurowski,^[a]Francisco Velazquez Escobar,^[b]Peter Hildebrandt,^[b]Jochen Lach,^[c]

Frank W. Heinemann,^[d]Dennis Wiedemann,^[a]Elisabeth Irran,^[a]and Andreas Grohmann*^[a]

Keywords: Tetrapodal pentadentate ligands / Copper / Dioxygen / Tyrosinase-like activity / N ligands / Density functional

calculations

The results of studies focussed on copper complexes of a vari- per(II) complexes (5 and 6) have been spectroscopically char-

ety of ligands with an NN₄donor set are reported. The per-

methylated tetrapodal ligand 2 forms a complex with cop-

per(I) which, upon reaction with dioxygen at –90 °C, yields

a product having a bis(μ-oxido)dicopper(III) core (“O-type”

product, 10), as inferred from UV/Vis and resonance-Raman

spectroscopic data. The UV/Vis spectrum of 10 has two

bands at 300 and 404 nm, with extinction coefficients of 9400

acterized. As ascertained by X-ray crystallography, 5 has the

Cu^IIion in a tetragonal-pyramidal environment, with almost

uniform Cu–N bond lengths (basal bonds: 2.052 Å and

2.070 Å; apical bond: 2.077 Å). No significant Jahn–Teller

distortion is observed here. In 6, the ligand acts as a multinu-

cleating donor, which leads to the formation of a ladder-like

cluster of [Cu(μ₃-OH)] units containing a total of two ligands,

six copper(II) ions, four hydroxido ligands and eight trifluo-

roacetate ions. Two of the trifluoroacetate ions are non-coor-

dinating. Variable-temperature magnetic susceptibility data

are reported for this hexanuclear copper(II) cluster. Copper(I)

complexes of 1 and 3 have been characterized and allowed

to react with molecular oxygen, which caused the decompo-

sition of the complexes. The IR spectra of the oxygenation

products have bands at 1652 and 1632 cm^–1, respectively,

which are absent in the spectra of 1 and 3, suggesting that

amine functions have been oxidized to imines.

and 10400 Lmol^–1cm^–1

,

respectively. Resonance-Raman

spectra display two ¹⁶O/¹⁸O-sensitive bands which, based on

the isotopic shifts and the absolute frequencies, are attrib-

uted to the Cu–O stretching modes of the O-type product.

Complex 10 shows tyrosinase-like activity, as its reaction

with sodium p-tert-butylphenolate at –90 °C in THF yields p-

tert-butylcatechol, in an ortho-hydroxylation reaction (yield:

30%). Two new rigid tetrapodal pentadentate ligands (the

“superpods” 3 and 4) can be synthesized by condensation of

the primary polyamine 1 with paraformaldehyde. Their cop-

ded in specialized polypeptides (e.g. plastocyanin in photo-

synthesis), or is the active-site ion (Cu^I/IIand possibly also

Cu^III) in proteins interacting with dioxygen and its metabo-

lites.^[4,5]Dinuclear examples where the two metal ions work

in concert with one molecule of dioxygen are the oxygen

carrier haemocyanin and oxidase or oxygenase enzymes

such as tyrosinase.^[6,7]The latter catalyzes the ortho-hydrox-

ylation of phenols to catechols (monophenolase reactivity),

as well as the oxidation of catechols to ortho-quinones (di-

phenolase activity). A functional catalytic tyrosinase model

has recently been described.^[8]Dinuclear dioxygen-activa-

ting enzymes in which the metal ions function largely inde-

pendently of each other include dopamine-β-monooxygen-

ase and peptidylglycine-α-hydroxylating monooxygenase.

Model complexes for these enzymes are difficult to synthe-

size but have been reported.^[9,10]Copper sites are often used

to illustrate the significance of an “entatic state” during

metalloprotein function: The highly specialized polypeptide

chain, which provides the metal coordination environment,

is so rigid that a change in the redox state of the copper

ion, as a consequence of electron transfer and/or substrate

Introduction

Copper has a particularly rich coordination chemistry,

owing to different structural preferences of the di- and

monovalent states (Cu^II: six-, five- or four-coordinate, often

tetragonal; Cu^I: four-coordinate, tetrahedral).^[1]Because of

the operation of the Jahn–Teller effect in its octahedral

complexes, copper(II) has been termed a coordination

chemical chameleon,^[2]with a “plasticity effect” in its

stereochemistry.^[3]The biological role of copper is essen-

tially twofold (with some parallels to that of iron): The

metal atom serves as an electron relay (Cu^I/II) when embed-

[a] Institut für Chemie, Technische Universität Berlin,

Straße des 17. Juni 135, 10623 Berlin, Germany

E-mail: andreas.grohmann@chem.tu-berlin.de

[b] Max-Volmer-Institut für Biophysikalische Chemie, Technische

Universität Berlin,

Straße des 17. Juni 135, 10623 Berlin, Germany

[c] Institut für Anorganische Chemie, Universität Leipzig,

Johannisallee 29, 04103 Leipzig, Germany

[d] Institut für Anorganische Chemie, Universität Erlangen-

Nürnberg,

Egerlandstraße 1, 91058 Erlangen, Germany

Eur. J. Inorg. Chem. 0000, 0–0

1

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

Scheme 1. Preparation of the ligands used in this study. Copper(II) complexes were obtained with ligands 3 and 4; the copper(II) complex

of ligand 1 is described in ref.^[13]The methyl groups in 2 make the ligand sterically too encumbered to give a complex with copper(II) in

which the NN₄ligand would act as a square-pyramidal coordination cap. Copper(I) complexes were obtained with ligands 1, 2 and 4.

The condensation reaction 3a Ǟ 3 is not amenable to copper(I) templating (see also text).

coordination, cannot lead to significant structural reorgani- state structure of [H₄2]⁴⁺is shown in Figure 1 (space group

zation. This produces an “energetically charged state” (a Pnma). The protons on all crystallographically independent

“rack” state) close to the transition state of the reaction, dimethylamino groups were located in difference Fourier

enabling fast electron transfer and/or efficient catalysis.^[11]

maps. Their charge is balanced by chloride counterions,

Against this background, we have investigated the cop- which leads to 4 equiv. of HCl in the structure. The pyridine

per(I) and copper(II) coordination chemistry of a series of nitrogen atom is unprotonated, reflecting the lower basicity

polypodal nitrogen donor ligands, based on the tetrapodal of pyridines when compared with aliphatic amines.^[16–18]

pentadentate motif

1

pioneered by our group Both 1,3-diaminoprop-2-yl moieties are in a W-like confor-

(Scheme 1).^[12,13]We have specifically studied the reactivity mation, and there is a C₂axis along the C1–N1 vector. Sol-

of the obtained copper(I) complexes towards dioxygen. De- vent water (one crystallographically independent molecule)

pending on whether the ligands are permethylated or con- was treated with fixed-distance and fixed-angle constraints.

tain primary or secondary amine functions, their copper(I) This molecule (O1) and a chloride ion (Cl3; on a general

complexes, upon reaction with dioxygen, produce a bis(μ- position) are in hydrogen-bonded contact, forming an infi-

oxido)dicopper(III) complex, or imine species. The series of nite zigzag chain throughout the structure. The other types

ligands encompasses coordination caps of variable rigidity, of chloride ions (Cl1 and Cl2; each positioned on a crystal-

or “juxtapositional fixedness”,^[14]which have been obtained lographic mirror plane) are each hydrogen-bonded in pincer

from the condensation of 1 with formaldehyde under a vari- fashion by pairs of ammonio substituents, above and below

ety of conditions. Ligands and complexes have been charac- the pyridine ring plane. There are no other intra- or inter-

terized by spectroscopic techniques (NMR, IR, UV/Vis,

resonance-Raman, as applicable), as well as X-ray structure

analysis.

Results and Discussion

Ligand Syntheses and Structures

The ligands were prepared as shown in Scheme 1. To the

best of our knowledge, the tertiary polyamine 2 has not

previously been employed in a coordination chemical study.

The ligand (systematic name: 2-{6-[1,3-bis(dimethylamino)-

propan-2-yl]pyridin-2-yl}-N¹,N¹,N³,N³-tetramethyl-

propane-1,3-diamine) may be obtained from 2,6-lutidine

(2,6-dimethylpyridine), paraformaldehyde and dimeth-

ylamine hydrochloride in a Mannich reaction,^[15]from

Figure 1. Crystal structure of 2·4HCl·2H₂O (ORTEP representa-

which it is isolated as the tetrahydrochloride dihydrate. Slow

cooling of a saturated aqueous solution yields single-crys-

atoms are given an arbitrary radius; other hydrogen atoms, chloride

talline material of composition 2·4HCl·2H₂O. The solid- ions and water molecules are omitted for clarity).

tion, ellipsoids at the 50% probability level; N-bonded hydrogen

2

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

molecular hydrogen-bonded contacts. Crystallographic data

are given in Table 3.

Both hexahydropyrimidine (hhp) rings are in the chair

conformation. There is a weak intramolecular hydrogen

For use in complexation studies, 2 is readily released bond between the aminal NH group (involving N35) of one

from its HCl adduct by treatment of the latter with 4 equiv. hhp ring and the pyridine nitrogen atom N10 [N35–

of sodium methoxide in methanol, and subsequent removal H35···N10 2.975(2) Å, 120.6(13)°]. The relative orientation

of insoluble NaCl. Ligand 2 is structurally related to the of the N–H bonds in both hhp rings is notable. While one

primary polyamine 1, whose attempted permethylation ring has both hydrogen atoms in axial positions (H33,

posed unexpected problems. Treatment of 1 with a mixture H35), the other has one hydrogen atom in an equatorial

of formaldehyde and formic acid (i.e. the attempted re- and the other in an axial position (H23 and H25, respec-

ductive methylation of 1 according to Eschweiler and tively). For hexahydropyrimidines, the theory predicts the

Clarke) invariably induced cleavage of one C–C bond at axial/axial (aa) and axial/equatorial (ae) conformations to

each quaternary carbon atom, in the sense of a retro-Man- be favoured over the ee conformation. The former two con-

nich reaction:^[19–21]The loss of two CH₂NH₂groups leads formers are of nearly the same energy, with

to the formation of a bis(dimethylamino) imine species.^[22]

n_N–σ*_(C–N)hyperconjugation favouring aa slightly over ea.

Ligand 3 {systematic name: hexahydro-5-[6-(hexahydro- The ee conformer is the least stable owing to 1,3-dipolar

1,3,5-trimethylpyrimidin-5-yl)pyridin-2-yl]-1,3,5-trimethyl- repulsion between the axial lone pairs on the nitrogen

pyrimidine} was generated in a sequence of reactions (in- atoms.^[25]In the case of 4, the availability of the pyridine

cluding metal-templated condensation) and has so far not nitrogen atom for hydrogen bonding is expected to have an

been isolated (Scheme 1). Monomethylation of all primary influence on the conformation of at least one of the hhp

amine functions in 1 is achieved by generating the tetrakis- rings. Both ligands 3 and 4 may be construed as rigidified

(carbamate) with ethyl chloroformate, and subsequent re- variants of the NN₄ligand 1, in which the 1,3-diami-

duction with lithium aluminium hydride.^[23]The purifica- noprop-2-yl side arms have been made into rings by the

tion of the crude product 3a (N¹,N³,2-trimethyl-2-{6-[2- introduction of methylene bridges, to counter the “plasticity

methyl-1,3-bis(methylamino)propan-2-yl]pyridin-2-yl}- effect” of copper(II) mentioned in the Introduction, and

propane-1,3-diamine) by distillation or column chromatog- thereby perhaps elicit unusual reactivity.

raphy proved impractical, and the material was therefore

used directly, in a copper(II)-templated condensation with

paraformaldehyde, to obtain the copper(II) complex of 3

Complex Syntheses and Properties

(see the following section).

[Cu^II(3)](ClO₄)₂(5)

Ligand

4 {hexahydro-5-[6-(hexahydro-5-methylpyrim-

Crude 3a was treated with paraformaldehyde in meth-

anol, in the presence of hexakis(dimethylformamide)-

copper(II) perchlorate. Two variants were tested: paraform-

aldehyde was added to a solution of preformed complex

{3a + [Cu(dmf)₆](ClO₄)₂}, or a solution of 3a and para-

formaldehyde was treated with the copper salt, added as a

solid. In both cases, and within minutes, the reaction mix-

ture deposited a blue precipitate, which was collected and

recrystallized from methanol to obtain single crystals of 5

suitable for an X-ray structure determination (Figure 3). A

selection of bond lengths and angles is given in Table 1, and

crystallographic data are listed in Table 3.

idin-5-yl)pyridin-2-yl]-5-methylpyrimidine} was obtained

by condensation of 1 with paraformaldehyde in methanol

(Scheme 1). It is necessary to control the amount of alde-

hyde used in this reaction as an excess leads to the forma-

tion of byproducts through the additional hydroxymethyl-

ation of one or two secondary amine functions in the de-

sired product.^[24]Under suitable conditions (see Experimen-

tal Section), we were able to obtain pure 4 as a crystalline

material. The solid-state structure of this bis(hexahydropyr-

imidine) derivative is shown in Figure 2 (see Table 3 for

crystallographic data).

Figure 2. Crystal structure of 4 (ORTEP representation, ellipsoids

at the 50% probability level; N-bonded hydrogen atoms are given

an arbitrary radius; other hydrogen atoms are omitted for clarity).

Figure 3. Crystal structure of 5 (ORTEP representation, ellipsoids

at the 50% probability level; hydrogen atoms and perchlorate coun-

terions are omitted for clarity).

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

3

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

Table 1. Selected bond lengths [Å] and bond angles [°] for 5.

Bond length or angle

Cu1–N1

Cu1–N2

Cu1–N3

N1–Cu1–N2

N1–Cu1–N2Ј

N1–Cu1–N3

N1–Cu1–N3Ј

2.077(4)

2.052(3)

2.070(3)

98.0(1)

98.4(1)

N2–Cu1–N2Ј

N2–Cu1–N3

N2–Cu1–N3Ј

N3–Cu1–N2Ј

N2Ј–Cu1–N3Ј

N3–Cu1–N3Ј

109.1(2)

66.9(1)

163.6(1)

66.9(1)

112.1(1)

The copper(II) ion in 5 is coordinated in a tetragonal-

pyramidal fashion, with five Cu1–N bonds of similar

lengths [Table 1; average: 2.064(3) Å]. The molecule has a

mirror plane orthogonal to the pyridine ring, containing the

atoms C1, N1 and Cu1. The hhp rings lock the NN₄donor

arrangement in place, resulting in symmetrical coordination

of the copper ion. The six-membered rings with their at-

tendant ring strain (chair conformation) apparently cause

the copper ion to move towards the pyridine nitrogen atom,

above the basal N₄plane. Consequently, no Jahn–Teller

elongation is observed here, in contrast to the complex

[Cu(1)](SCN)₂·H₂O, which contains the more flexible par-

ent tetraaminoimine 1 as a square-pyramidal capping li-

gand [Cu–N_ax2.207(2) Å vs. Cu–N_basav. 2.039(3) Å].^[13]

Figure 4. Crystal structure of 6 (MERCURY representation). The

Cu–O core is rendered in ellipsoid (90% probability level), N donor

ligands are in stick and all other ligands in wireframe representa-

tions (disordered groups in one representative position). Hydrogen

atoms, trifluoroacetate counterions and solvent molecules are omit-

ted for clarity.

[Cu^II₆(4)₂(μ-CF₃CO₂)₂(CF₃CO₂)₄(H₂O)₂(μ₃-OH)₄]-

(CF₃CO₂)₂·6MeOH·2H₂O (6)

Figure 5. Detail of the crystal structure of 6 in ORTEP representa-

tion (Cu–O coordination core, ellipsoids at the 50% probability

level).

None of the complexation reactions undertaken with 4

and a variety of copper(II) salts produced single crystals of

mononuclear complexes that would have enabled a struc-

tural comparison with the complexes of ligands 1 and 3. atom of each of its diazacyclohexyl rings (N20 and N30).

[Cu(dmf)₆](ClO₄)₂and CuCl₂in methanol were the first The other two nitrogen atoms of the ligand (one in each

salts used. The formation of complexes was indicated by diazacyclohexyl ring, N21 and N31) are coordinated to the

colour changes (typically to blue or green), the formation copper ions Cu2 and Cu3, respectively. Cu1 is six-coordi-

of precipitates and confirmed by mass spectrometry. Anion nate quasi-octahedral with the three N donors already men-

exchange was tried in order to obtain single crystals, and a tioned, one hydroxido, one trifluoroacetato-κ¹O and one

solution of a silver salt AgX (X = BF₄, SbF₆, CF₃SO₃, aqua ligand. The bond lengths (Table 2) range from

CF₃CO₂) in methanol added dropwise to a solution of the 1.963(1) to 2.230(1) Å, except for the bond Cu1–O3 which,

copper(II) chloride complex in the same solvent. The pre- at 2.472(1) Å, is considerably longer. Cu2 and Cu3 are each

cipitation of AgCl was spontaneous in all cases, the colour coordinated in a square-pyramidal fashion and together

of the solution changing from green to blue. AgCl was re- with the bridging hydroxido ligands (O1 and O2) create the

moved by filtration, and the filtrate was used for crystalli- ladder-like backbone. The lengths of the basal bonds are

zation by slow concentration, by diethyl ether diffusion or in the range 1.949(2)–2.016(2) Å (for Cu2) and 1.937(2)–

by layering of the methanol solution with diethyl ether. 2.028(2) Å (for Cu3), whereas the apical donors O1Ј (in the

Only in the case with trifluoroacetate as the counterion did case of Cu2) and O62 (Cu3) are bonded to Cu^IIat a greater

these procedures produce single crystals suitable for X-ray distance [2.289(2) and 2.279(2) Å, respectively], owing

diffraction. The structure (Figures 4 and 5) is oligonuclear, to the Jahn–Teller effect. Finally, the ions in the pairs

containing a ladder-like cluster of [Cu(μ₃-OH)] units with a Cu2/Cu3Ј and Cu2Ј/Cu3 are connected by bridging μ-tri-

total of two ligands, six copper(II) ions, four hydroxido li- fluoroacetato ligands.

gands and eight trifluoroacetate ions, as well as two water

Structures containing similar [Cu(μ₃-OH)] clusters have

and six methanol molecules per unit cell. As water was not been reported,^[26–29]with [Cu₂(OH)₂] repeating units mak-

purposely added to the mother liquor, the hydroxido li- ing up cube- or ladder-like entities. A complex described by

gands and solvate water molecules must derive from moist- Zheng and co-workers^[30,31]contains a zigzag chain whose

ure introduced through the solvents or the metal salts used. overall structural pattern, as well as bond lengths and

The structure of 6 is centrosymmetric. Each ligand coor- angles, are similar to that of 6. Complex 6 is different in

dinates to three copper ions (Cu1, Cu2 and Cu3). One of that it has extra copper atoms, Cu1 and Cu1Ј, which are

the metal ions, Cu1, is connected to the pyridine nitrogen joined to the rest of the cluster by only one Cu–(μ₃-OH)

atom N10 of one of the chelate ligands and to one nitrogen bond. The formation of 6 is reproducible, and its targeted

4

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

Table 2. Selected interatomic distances [Å] and bond angles [°] for susceptibility data to the isotropic HDvV exchange Hamil-

6.

tonian [Equation (1)] using a full-matrix diagonalization

approach.^[32]In a first attempt, we tried to simulate the ex-

Bond length or angle

perimental data on the basis of a tetranuclear unit with two

noncorrelated copper(II) ions, by assuming J₃= 0 cm^–1as

suggested for a similar complex by Li et al.^[30,31]This at-

tempt reproduced the experimental data reasonably well

over the temperature range 20–371 K for J₁= –27 cm^–1, J₂

= –25 cm^–1and g = 2.15, but failed at lower temperatures.

The introduction of a third exchange coupling constant (J₃

϶ 0 cm^–1) significantly improved the model, leading to a

Cu1–N10

Cu1–N20

Cu1–N30

Cu2–N21

Cu3–N31

Cu1–O2

Cu1–O3

Cu1–O50

Cu2–O1

2.230(1)

1.963(1)

1.964(1)

2.016(2)

2.028(2)

2.158(1)

2.472(1)

2.135(1)

1.949(2)

1.991(2)

2.289(2)

1.979(2)

1.937(2)

1.988(2)

1.972(2)

2.279(2)

92.6(1)

N10–Cu1–O2

N20–Cu1–O2

N30–Cu1–O2

N10–Cu1–O3

N20–Cu1–O3

N30–Cu1–O3

N10–Cu1–O50

N20–Cu1–O50

N30–Cu1–O50

O2–Cu1–O50

O3–Cu1–O50

O2–Cu1–O3

O1–Cu2–O2

O1–Cu2–O1Ј

O2–Cu2–O1Ј

O2–Cu3–O1

Cu2–O1–Cu3

Cu2–O2–Cu3

Cu2–O1–Cu2Ј

Cu1–O2–Cu3

83.8(1)

95.0(1)

99.2(1)

102.3(1)

86.4(1)

79.1(1)

178.1(1)

88.5(1)

85.6(1)

97.7(1)

Cu2–O2

good fit over the whole temperature range, with J₁

=

Cu2–O1Ј

Cu2–O40

Cu3–O1

76.1(1)

–23 cm^–1, J₂= –29 cm^–1, J₃= –5 cm^–1and g = 2.16 (Fig-

ure 7). The fact that J₃(at –5 cm^–1) is significantly smaller

than the other two exchange coupling constants, J₁and J₂,

can be rationalized by the fact that the distance of the Cu

spin centres giving rise to J₃is the largest, the distances

associated with J₁and J₂being shorter by 0.5 Å and 0.7 Å,

respectively.

173.7(1)

81.55(6)

85.72(6)

101.05(6)

81.93(6)

97.33(7)

94.33(6)

94.28(6)

121.75(7)

Cu3–O2

Cu3–O61

Cu3–O62

N10–Cu1–N20

N10–Cu1–N30

N20–Cu1–N30

Cu1–Cu3

Cu2–Cu3

Cu2–Cu2Ј

93.0(1)

165.3(1)

3.622(2)

2.918(2)

3.115(2)

ˆ

ˆ ˆ

H = –2J₁(S₂·S₃+ S₄·S₅) – 2J₂(S₃·S₄) – 2J₃(S₁·S₂+ S₅·S₆)

(1)

synthesis was accomplished as described in the Experimen-

tal Section.

Temperature-dependent susceptibility measurements on

a powdered sample of 6 were carried out by using a SQUID

Magnetometer (MPMS 7 XL, Quantum Design) over the

temperature range 2–371 K in an applied external field of

0.5 T. Figure 6 shows the variation of the molar suscep-

tibility χ_mand the effective magnetic moment μ_effwith tem-

perature. The value of μ_effdecreases slowly from 4.47 μ_Bat

371 K to 4.10 μ_Bat 100 K and then more steeply on further

cooling, reaching a minimum of 1.91 μ_Bat 2 K. The effec-

tive magnetic moment of 6 at room temperature (4.41 μ_B) is

much smaller than the theoretical spin-only value of 6.93 μ_B

calculated for six uncoupled Cu^IIions (S = 3, S_i= 1/2, g =

2.00), indicative of net antiferromagnetic exchange interac-

tions and an S = 0 ground state.

Figure 7. Core structure of 6 with exchange coupling pathways

(double arrows) J₁, J₂and J₃(see also Figure 5). In this model J₁

represents the sum of two coupling pathways (through the O1 and

O2 oxido bridges).

[Cu^I(1)](PF₆) (7)

Complex 7 is generated by the reaction of tetrakis(ace-

tonitrile)copper(I) hexafluorophosphate with 1 in THF, and

precipitates from solution as light-yellow prism-shaped

1

crystals upon diffusion of diethyl ether. In the H NMR

spectrum of 7 ([D₆]DMSO, room temp.), all resonances

show a complexation-induced shift to low field as compared

to the signals of the free ligand, while the overall appear-

ance of the NMR spectrum suggests a highly symmetrical

cation structure. Specifically, the methylene groups give rise

to an AB spin system, indicating the geminal protons to

be diastereotopic. This is compatible with either a square-

pyramidal coordination geometry (in which all five N do-

nors of the chelate ligand are bonded to Cu^I; C_2v) or a

tetrahedral set of N donors around Cu^I. The latter, which

reflects the coordination chemical preference of copper(I),

would involve a coordination/decoordination process that is

fast on the NMR timescale, in which the pyridine N atom

and three out of the four primary amine N atoms are coor-

dinated to the metal centre at any one time. The complex is

extremely sensitive towards dioxygen. Even the most exact-

ing precautions to exclude air during single-crystal X-ray

Figure 6. Plots of χ_m(squares) and μ_eff(circles) vs. T for the hexa-

nuclear copper(II) complex 6. The solid line represents the best fit.

The magnitude of the exchange interactions was deter- diffraction could not prevent the crystals from taking on

mined by least-squares fitting of the experimental magnetic a bluish hue in the process. The quality of the structure

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

5

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

determination is, however, acceptable. In the solid state, 7 [Cu^I(2)](PF₆) (8)

is a coordination polymer, with monovalent copper (Cu1)

Complex 8 was obtained by the reaction of ligand 2

with tetrakis(acetonitrile)copper(I) hexafluorophosphate in

THF. Combining the colourless reactants immediately pro-

duced a yellow-orange solution, with only very little pre-

cipitate after 3 h. Removal of the solvent in vacuo left a

green-brownish solid. Elemental analysis data are consis-

tent with the chemical formula of 8 (C₁₉H₃₇CuF₆N₅P), and

ESI-MS data indicate a mononuclear complex in the gas

phase (m/z = 398.2337 [Cu(2)]⁺). When compared to the ¹H

NMR spectrum of the free ligand, coordination shifts the

resonances to low field ([D₆]DMSO, room temp.). The pro-

tons on the pyridine ring give rise to an AB₂spin system

and show a triplet (δ = 7.84 ppm; 1 H, para) and a doublet

(δ = 7.27 ppm; 2 H, meta). The chemical shifts of the meth-

ylene protons (AB system; the geminal protons are dia-

stereotopic) are δ = 2.65 and 2.54 ppm, respectively. The

aliphatic methine protons (δ = 3.16 ppm) give rise o a

higher-order multiplet from the coupling to the adjoining

CH₂groups. The methyl groups on the nitrogen atoms are

magnetically equivalent as only one singlet is observed in

in a distorted tetrahedral environment (Figure 8). The metal

ion is coordinated by three nitrogen donors (N1, N3 and

N4) of one pentadentate ligand and a fourth donor (N2)

that belongs to a second ligand. One of the primary amine

functions of the first ligand (N5) remains uncoordinated.

The Cu1–N(amine) bond lengths lie in the range 2.0–2.1 Å

[Cu1–N4 1.999(5) Å, Cu1–N2 2.042(5) Å, Cu1–N3

2.105(5) Å], while the bond to the pyridine nitrogen atom

N1 is significantly longer [Cu1–N1 2.372(5) Å]. There are

weak intra- and intermolecular hydrogen-bonded contacts

between the primary amine nitrogen atoms N4 and N5 and

between N3/N4/N5 and the hexafluorophosphate counter-

ion. Crystallographic data for 7 are given in Table 3.

1

the H NMR spectrum. This suggests exchange (rapid on

the NMR timescale at room temperature) of the coordinat-

ing NMe₂residues. Structures of complexes with permethyl-

ated propane-1,3-diamine and related ligands have been dis-

cussed in the literature, with special consideration of the

Figure 8. Section of the 1D coordination polymer in 7 (ORTEP

representation; ellipsoids at the 50% probability level; hydrogen

atoms and hexafluorophosphate counterion are omitted for clar-

ity).

Table 3. Crystallographic data for compounds 2·4HCl·2H₂O, 4, 5, 6·6MeOH·2H₂O and 7.

2·4HCl·2H₂O

4

5

6·6MeOH·2H₂O

7

Empirical formula

M_r[gmol^–1]

Crystal system

Space group

a [Å]

b [Å]

c [Å]

α [°]

β [°]

C₁₉H₄₅Cl₄N₅O₂

517.40

orthorhombic

Pnma

12.0211(3)

21.5002(4)

10.4549(2)

90

C₁₅H₂₅N₅

275.40

C₁₉H₃₃Cl₂CuN₅O₈

593.94

orthorhombic

Pnma

22.9754(9)

12.2587(6)

8.6635(4)

90

C₅₂H₈₆Cu₆F₂₄N₁₀O₃₀C₁₃H₂₅CuF₆N₅P

2168.61

triclinic

P1

459.89

monoclinic

P2₁/c

triclinic

¯

P1

8.1936(5)

9.9327(6)

10.5803(5)

65.062(5)

80.856(4)

78.633(5)

2

762.69(7)

1.199

Oxford Xcalibur S

12.2860(4)

12.3193(3)

15.1404(4)

84.364(2)

80.382(2)

62.607(3)

1

6.3188(9)

22.669(2)

12.4931(4)

90

90.947(6)

90

4

90

4

γ [°]

Z

4

V [Å³]

2702.13(10)

1.272

Oxford Xcalibur S

2440.06(19)

1.617

Oxford Xcalibur S

2005.43(11)

1.796

1789.3(3)

1.707

ρ_calcd.[mgcm^–3]

Diffractometer

Oxford Xcalibur S

Bruker–Nonius Kap-

paCCD

0.71073

λ [Å]

0.71073

Crystal size [mm]

T [°C]

0.24ϫ0.15ϫ0.14

150(2)

0.25ϫ0.23ϫ0.13

150(2)

0.15ϫ0.12ϫ0.06

150(2)

0.24ϫ0.23ϫ0.21

150(2)

0.20ϫ0.16ϫ0.14

150(2)

Absorption correc-

tion

multi-scan

T_max/T_min

Scan

2θ range [°]

Measured reflections 12722

Unique reflections 2452

1.00000/0.93833

ω

3.20Յ2θՅ25.00

1.00000/0.95462

ω

3.11Յ2θՅ25.00

7378

2682

1.00000/0.93020

ω

3.01Յ2θՅ24.99

11427

1.00000/0.94096

ω

3.10Յ2θՅ30.00

24972

0.825/0.687

ω and φ

3.60Յ2θՅ27.10

31174

2259

11652

3918

Observed reflections 2066

2251

0.075

199

1759

1.169

175

8926

1.702

578

3334

1.378

238

μ(Mo-K_α) [mm^–1]

0.462

158

Refined parameters

Data/parameter ratio 15.5

13.5

12.9

20.2

16.5

wR₂(all data)

0.1772

0.0864

0.0859

0.0351

0.214/–0.146

0.0825

0.0467

0.376/–0.708

0.0813

0.0344

0.727/–0.622

0.1943

0.0678

1.053/–0.705

R₁(obsd. data)

ρ_fin(max/min) [eÅ^–3] 1.142/–0.376

6

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

steric bulk introduced by the dimethylamine donor requires the interconversion/enantiomerization of these

groups.^[33–35]In solution, at room temperature, the observa-

tion of one singlet in the H NMR spectrum for the N-

asymmetric (C₁) structures at room temperature. An inter-

mediate geometry is expected to exist (a stable geometry or

a transition state) that is achiral and lies sufficiently low in

energy. We located a possible tricoordinate transition state

that fulfils this requirement, as its approximate symmetry

group is C_s. This transition structure is only 7 kJmol^–1

higher in energy than the more favourable conformer, and

thus lower in energy than the less favourable conformer. We

conclude that, because of steric strain, coordination of three

out of four dimethylamino donors in 8 is not accompanied

by a significant energy gain in comparison to coordination

of two out of four dimethylamino donors, yet this may oc-

cur in the gas phase where no additional monodentate do-

nors (solvent molecules) are present. In a coordinating sol-

vent (such as DMSO, THF, acetonitrile), it appears reason-

able that 2 acts as a tridentate ligand with the remaining

coordination site on copper(I) occupied by a solvent mole-

cule.

1

bonded methyl groups leads us to presume fast averaging

of the four tertiary amine donors, of which three are coordi-

nated at any one time, resulting in a tetrahedral or trigonal-

pyramidal coordination geometry around copper(I). Single

crystals of 8 have not been obtained so far. DFT calcula-

tions for complex 8 are compatible with an overall trigonal-

pyramidal coordination geometry in the gas phase, as de-

picted in Figure 9.

To support the results obtained by DFT calculations, we

carried out variable-temperature (VT) ¹H NMR spectro-

scopic measurements (between room temperature and

180 K). Three solvents with sufficiently low melting points

were tested, [D₆]acetone, [D₄]methanol and [D₈]tetra-

hydrofuran. While complex 8 is stable in all of these sol-

vents (provided they are strictly oxygen-free), its solubility

is low in all cases. We specifically note that 8 is not per se

unstable in protic solvents, such as methanol. The best re-

sults were obtained with [D₈]tetrahydrofuran. Upon lower-

ing of the temperature, there is overall line broadening. The

position of the aromatic proton resonances is unaffected;

the resonances belonging to the NMe₂methyl groups split

at very low temperature, but overlap extensively; the methyl-

ene resonances move to higher field and start to overlap

with the broadened NMe₂methyl resonances. The only sig-

nal we found useful as a low-temperature probe of the mo-

Figure 9. Gas-phase structures of [Cu^I(2)]⁺(DFT). A similar aver-

aging process is suggested to operate in solution, explaining the

equivalence of the NMe₂groups as observed by ¹H NMR spec-

troscopy at room temperature.

To support our assumption, DFT calculations on the

RB3LYP/DGDZVP level were performed by using the

Gaussian 03 (C02) program package. There are two dif-

ferent stable conformations differing in energy by

13 kJmol^–1and arising from a subtle conformation change.

The more favourable conformer is characterized by a dis-

placement (0.1 Å) of the copper ion from the plane defined

by the three coordinating tertiary amine donors. The coor-

dination geometry around copper(I) is, therefore, best de-

scribed as distorted trigonal-pyramidal, not tetrahedral.

1

The high symmetry suggested by the H NMR spectrum

Figure 10. Partial VT NMR spectra of 8 in [D₈]THF (see text).

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

7

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

lecular dynamics is the methine signal belonging to the Reactivity of the Cu^IComplexes towards O₂

bridgehead CH moieties in the ligand side arms. This signal

splits into two clearly differentiated resonances at –93 °C

The reactivity of complexes 7–9 towards dioxygen was

(180 K) in spite of the observed line broadening. The fol- studied. All three compounds are sensitive to air. While the

lowing behaviour is to be expected on the basis of the DFT yellowish solutions of 7 and 9 in acetonitrile immediately

model: If two enantiomeric forms of the copper(I) complex turn green upon exposure to air, the colour change in solu-

are in rapid equilibrium, six of the eight NMe₂methyl tions of 8 in THF or acetonitrile (from greenish to blue)

groups (belonging to the three dimethylamino groups coor- is slow and takes about 5 min at room temperature. The

dinated to the copper ion) will be chemically inequivalent. spectroscopic characterization of the oxygenated products

Uncoordinated NMe₂will give rise to one additional signal. was performed as follows.

The methylene protons will give rise to eight different sig-

Dry dioxygen was passed through a solution of 7 in

nals (instead of two at room temperature), as each methyl- acetonitrile for several minutes, which induced a colour

ene group is on an arm of the ligand not symmetry-related change from light yellow to green. A high-resolution ESI

to any other (given that enantiomerization is slow on the mass spectrum of the resulting solution shows a peak at m/z

NMR timescale and the protons in each methylene group = 248.1864 that can be correlated with the uncomplexed,

are diastereotopic). The methyl and methylene proton sig- ligand-derived species [1–3H]⁺, a protonated diimine of 1.

nals overlap strongly in the experimental spectrum, as ex- The simulated isotope pattern of this ion has the same peak

pected for 15 different signals in that region. Most import- structure. The ion is not observed in the ESI mass spectrum

antly, the methine signals would also be differentiated, as of a solution of 7 under inert conditions. The IR spectra of

the two sides of the molecule are inequivalent in frozen complex 7 and of its oxidation product (after exposure to

equilibrium, just as the pendant arms are. This behaviour O₂; both as KBr discs) are very similar, but an additional

is in fact observed in the experimental spectrum (Fig- band appears at 1652 cm^–1after oxidation (a region typical

ure 10). In summary, while the room-temperature spectrum of imine vibrations). We conclude from this information

is compatible with pseudo-C_2vpoint group symmetry of the that the ligand in 7 is partially oxidized (primary amine to

complex, the spectrum recorded at –93 °C suggests C₁sym- imine) upon exposure to dioxygen, and probably decoordi-

1

metry. Thus, the VT H NMR spectroscopic data are fully nated at the same time. Future work will seek to provide

compatible with the density functional theory results de- conclusive evidence for this process, based on ¹H NMR

scribed above. The low energy barrier to enantiomerization spectroscopy. Similar reactions of copper(I) complexes con-

(as suggested by DFT calculations) is consistent with in- taining amine hydrogen atoms (primary and/or secondary

complete freezing of the equilibrium at –93 °C, as inferred amine functions) in the presence of dioxygen have been re-

from the observed line width.

ported in the literature.^[36,37]In a separate experiment, dry

dioxygen was passed through a solution of 9 in MeCN for

several minutes, which caused a colour change from light

[Cu^I(4)](PF₆) (9)

Complex 9 was obtained by treating a slight excess of yellow to green. ESI mass spectrometry and IR spec-

ligand 4 with tetrakis(acetonitrile)copper(I) hexafluoro- troscopy (the reaction with O₂causes the appearance of a

phosphate in THF. The combination of the colourless reac- new band at 1632 cm^–1) indicate the oxidation of complex

tants resulted in a yellow solution, which deposited a green- 9 to proceed with concomitant mono- and diimine forma-

yellowish precipitate. This was filtered, washed with THF tion and decoordination, similar to that of 7.

(to remove traces of the ligand) and dried in vacuo. The

Of the ligands studied in this work, 2 is special in that it

elemental analysis is consistent with a 1:1 complex of chem- contains only tertiary amine donors in its periphery, which

ical formula C₁₅H₂₅CuF₆N₅P (complex 9). ESI-MS data precludes imine formation in the course of oxidation. ESI

indicate a mononuclear complex in the gas phase (m/z = mass spectra of solutions of 8 in THF, measured a few min-

338.1407 [Cu(4)]⁺). The ¹H NMR spectrum of 9 ([D₆]- utes after exposure to air, still show a peak attributable to

DMSO, room temp.) shows proton resonances which, when the copper(I) complex [Cu(2)]⁺, suggesting that the oxi-

compared to those of the free ligand, are shifted to low dation of 8 proceeds relatively slowly. In order to check for

field. Similar to 8, the protons on the pyridine ring (AB₂dioxygen-derived products of 8, samples exposed to molec-

spin system) show a triplet (δ =7.89 ppm) and a doublet (δ ular dioxygen were monitored by low-temperature UV/Vis

=7.53 ppm). The methylene resonances (AB system) appear spectroscopy (solvent: THF). In the absence of dioxygen,

at δ = 3.68 and 2.83 ppm, respectively. The formaldehyde- the UV/Vis spectrum of 8 is characterized by two bands, at

derived methylene bridges (C₁linkers between the N atoms 330 nm (metal-to-ligand charge-transfer, MLCT) and

in the hexahydropyrimidine rings) show a broad singlet at 264 nm (ligand-centred transitions, π Ǟ π* or n Ǟ π*),

δ = 3.72 ppm, and the singlet at δ = 1.09 ppm is assigned with extinction coefficients of 5900 and 1200 Lmol^–1cm^–1,

to the exocyclic methyl groups. As judged from the NMR respectively. Upon passing dry oxygen through the cooled

spectra, the coordination of the metal ion in solution is solution (–90 °C), the colour changed from light yellow to

most likely similar to 8, with fast averaging of the four sec- brown. Two new bands, at 300 and 404 nm, with extinction

ondary amine N atoms, of which three are coordinated at coefficients of 9400 and 10400 Lmol^–1cm^–1, respectively,

any one time. No single crystals of compound 9 have been appeared, and their intensities increased while dioxygen was

obtained so far.

being added to the solution (Figure 11). No further change

8

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

could be observed after an addition time of ca. 4 min, and type core, reflected by slightly different frequencies of the

the addition of dioxygen was stopped. Purging the THF Cu–O stretching vibrations. Correlating the respective high-

solution with argon did not change any of the UV/Vis fea- and low-frequency components of the ¹⁶O- and ¹⁸O-derived

tures. The cooling bath was removed, and UV/Vis spectra products, one obtains very similar isotopic shifts for each

measured at 10 °C intervals while the solution was warmed conjugate band pair (31 and 35 cm^–1), confirming that the

to room temperature. The bands at 300 and 404 nm grad- nature of the underlying modes is the same. The absolute

ually disappeared, indicating that the absorbing species is frequencies and the ¹⁸O/¹⁶O shifts are in good agreement

very unstable at higher temperatures.

with literature values.^[6]

Figure 11. Spectral changes associated with the exposure of 8 to

O₂at –90 °C (the initial concentration of 8 is 2 mmolL^–1). Spectra

were measured before the addition of O₂(t = 0; lowest line, spec-

trum 1), immediately after addition of O₂(spectrum 2) and then at

60 s intervals (spectra 3–5).

The reaction of copper(I) complexes with dioxygen at

low temperature can produce different kinds of Cu^II/Cu^III

-

Figure 12. (A) RR spectra of the dioxygen-derived products 10,

prepared with ¹⁶O₂(grey) and ¹⁸O₂(black). Both spectra were nor-

malized to the solvent band (THF). (B) Simulated spectra obtained

from a fit of Lorentzian functions to the experimental spectra of

superoxido/peroxido/oxido complexes having different Cu/

O ratios, depending on the nature of the supporting ligands.

There is an extensive body of literature on complexes con- the ¹⁸O₂- and ¹⁶O₂-derived products; the spectral THF contribution

is displayed separately; bands insensitive to ¹⁸O₂labelling are de-

noted by numbers in italics. (C) Single Lorentzian functions, refer-

ring to the Cu–O stretching modes of the experimental spectra.

taining a Cu₂O₂core [bis(μ-oxido)dicopper(III) and peroxi-

dodicopper(II), classed as O-type and ^SP-type complexes,

respectively].^[6]O- and ^SP-type complexes are distinguish-

able from one another by their specific UV/Vis absorptions

and Raman vibrations. Examples of either species have

S

been isolated, and equilibria of interconverting O- and P-

Tyrosinase-Like Reactivity of the O-Type Species 10

type complexes are also well documented.^[38,39]In our case,

it is reasonable to assume that a single, well-defined species

On the basis of spectroscopic data, the oxygenated active

(10) is formed upon reaction of 8 with dioxygen, and the site of tyrosinase has been proposed to be a side-on peroxi-

UV/Vis features described above are characteristic of an O- dodicopper(II) core.^[40]Not all steps in the catalytic cycle

type copper/dioxygen product, containing a bis(μ-oxido)di- of the enzyme acting as a monophenolase have been under-

copper(III) core.^[6,40,41]The bands at 300 nm and 404 nm stood to date, and attempts to model the function of the

may be attributed to an oxide-to-Cu^IIIcharge transfer.^[42]active site are numerous. Several synthetic side-on peroxido-

In nonprotic solvents at –80 to –90 °C, what is presumably dicopper(II) complexes have shown monophenolase and

the complex [{Cu(2)}₂(O₂)] is stable for several hours. Since sometimes additional diphenolase activity, yielding cate-

purging with argon does not alter the spectroscopic charac- chols and quinones, respectively. These findings have been

teristics, dioxygen appears to be strongly bound. Its removal summarized recently.^[43]It was shown for the first time in

under vacuum was not attempted. At temperatures above 2005 that a bis(μ-oxido)dicopper(III) intermediate can acti-

–80 °C, compound 10 decomposes quickly.

vate phenolate to yield a catechol as well as a quinone.^[44]

The resonance-Raman (RR) bands of the Cu–O core are Subsequently, a bis(μ-oxido)dicopper(III) complex was iso-

highly diagnostic of O-type coordination of the O₂unit. lated and shown to react directly with the sodium salts of

Spectra of the products obtained with ¹⁶O₂and ¹⁸O₂were para-substituted phenolates, to give only the corresponding

measured in frozen THF solution (Figure 12). The RR catechol.^[45]Similar reactivity but higher product yields,

spectrum of the ¹⁶O-derived product shows bands at 620 using a different bis(μ-oxido)dicopper(III) complex, were

and 616 cm^–1that shift down to 589 and 581 cm^–1, respec- reported independently, and byproducts like quinone and in

tively, in the spectrum of the ¹⁸O-derived product. The two some cases bis(phenols) were also observed in this work.^[46]

closely spaced bands in each spectrum point to subtle struc- Selective phenolate ortho-hydroxylation was also shown

tural differences between the two μ-oxido bridges of the O- with an asymmetric dicopper μ-η¹:η¹-peroxido complex.^[47]

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

9

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

We investigated the behaviour of 10 in this context. So- (μ-oxido)dicopper(III) core has relevance as an active inter-

dium p-tert-butylphenolate (1 equiv.), dissolved in THF in mediate in the catalytic cycle of tyrosinase.

one portion, was added to a solution of freshly generated

10. UV/Vis monitoring showed the disappearance of the

Experimental Section

bands at 300 and 404 nm upon addition, indicating reaction

of the oxygen–copper complex with the substrate. Acidic

workup (quenching with 1 m HCl) of the warm reaction

solution and subsequent extraction with dichloromethane

yielded a yellow oil that was characterized by GC–MS and

¹H NMR spectroscopy. Two peaks were observed in the

GC, one generated by the reactant (p-tert-butylphenol) and

the other caused by a newly formed product. The mass

spectrum of the latter shows the highest mass at m/z = 166.

CAUTION! Although no problems were encountered in this work,

transition-metal perchlorate complexes with organic ligands are po-

tentially explosive and should be handled with precautions.

Materials and Instrumentation: Unless noted otherwise, all reac-

tions were carried out in dry solvents under dry dinitrogen using

standard Schlenk techniques, or in an MBraun inert-atmosphere

drybox containing purified dinitrogen. Solvents were dried by stan-

dard methods. The precursors [Cu(CH₃CN)₄]PF₆and 1 were syn-

This signal is assigned to p-tert-butylcatechol. The mass thesized according to published procedures.^[49,50]All other chemi-

cals were purchased from Aldrich or Acros and used without fur-

ther purification. NMR spectra were recorded with Bruker ARX

200, AV 400 or ARX 500 spectrometers (see also the section on

VT measurements below). IR spectra were measured by using KBr

disks with a Perkin–Elmer Spectrum 100 Series FTIR spectrometer.

Mass spectrometry was carried out by using a Finnigan MAT95S

instrument (EI) and an Orbitrap LTQ XL instrument (Thermo Sci-

entific. ESI). GC–MS measurements were carried out with a Shim-

adzu GC-2010 gas chromatograph (30 m Rxi-5ms column) linked

with a Shimadzu GCMA-QP 2010 Plus mass spectrometer. Ele-

spectrum of an authentic sample of this compound (as re-

trieved from the spectroscopic data base for organic com-

1

pounds)^[48]shows a similar fragmentation pattern. The H

NMR spectrum of the yellow oil supports the formation of

the ortho-dihydroxylated product. A yield of ca. 15% cate-

chol was determined from the integrated intensity ratio of

the tert-butyl proton signals in the mixture (reactant vs.

product). In a second experiment, 5 equiv. of the phenol

was used in a minimum amount of solvent. The same

workup procedure yielded 30% product. Overall, these fin- mental analyses were performed by combustion analysis using a

Thermo Finnigan EAGER 300 (Flash 1112) apparatus. UV/Vis

spectra were measured by using a Varian Cary 50 spectrometer

equipped with a UV/Vis quartz immersion probe (light path 1 mm,

Hellma), a home-built measuring cell and an immersion thermome-

ter. Resonance Raman spectra were measured at 90 K (Resultec/

Linkam cryostat) by using a confocal Raman microscope HR-800,

Jobin Yvon. Samples were excited with the 413 nm laser line of a

continuous-wave Kr⁺laser (Innova 300, Coherent). The scattered

light was collected over 180° through a lens (Olympus, 20ϫ, NA

0.35) of the microscope setup. Light detection was performed by a

dings substantiate tyrosinase-like activity of the O-type spe-

cies formed in the reaction of 8 with dioxygen.

Conclusions

This study describes the rich coordination chemistry of

pyridine-derived polypodal polyamine ligands towards cop-

per(I) and copper(II). All ligands have NN₄donor sets of

similar topology, but vary in terms of donor-set quality nitrogen-cooled CCD camera. Elastic scattering and laser plasma

lines were eliminated by means of a notch filter and an interference

filter. The spectrometer operation was performed with the LabSpec

software (v4.07, Dilor-Jobin Yvon-Spex). For the spectra cali-

bration, a standard mercury lamp was used. Spectral resolution

was better than Ϯ0.5 cm^–1. The samples were prepared as follows:

A droplet of the solution (freshly prepared at 193 K) was placed on

an aluminium or gold disc and shock-frozen by direct immersion

in liquid nitrogen. Photochemical degradation of the investigated

complex was observed within a few seconds under the resonance

conditions applied. For this reason, the working power of the laser

(primary vs. secondary vs. tertiary amines) and rigidity, or

juxtapositional fixedness (polypodal vs. polycyclic ligands).

The observed coordination geometries are determined by a

combination of factors: ligand flexibility, steric demand of

the donor-atom substituents and stereochemical preferences

of the metal ion [copper(I) vs. copper(II)]. Structural distor-

tions, typical of Cu^IIcomplexes with more accommodating

chelate ligands, are effectively suppressed in some cases, and

polynucleating coordination modes are observed in others

(both for Cu^Iand for Cu^II). Not unexpectedly, ligand oxi- was lowered considerably (500–600 μW). In addition to the low-

power conditions, rotation of the sample allowed the probing of

undamaged regions of the sample while the camera was open (2 s).

Around 10–20 single spectra were averaged to improve the signal/

noise ratio. The overall measuring time was between 20 and 40 s.

After accumulation, the recorded spectra were manipulated by

using the OPUS software (v5.5 or higher, Bruker Analytical Instru-

ments). A baseline correction was done by using a polynomial

function. In the case of the ¹⁸O₂-labelled sample, the signals of the

residual ¹⁶O₂species were subtracted manually before the baseline

correction.

dation occurs when the copper(I) complexes of primary and

secondary amine ligands used in this study are exposed to

dioxygen. By contrast, the copper(I) complex of a “su-

perpodal” Mannich base, which contains only tertiary

amine donors in addition to an apical pyridine nitrogen

atom, reacts with the formation of a dinuclear bis(μ-oxido)-

copper(III) species after exposure to dioxygen at –90 °C un-

der aprotic conditions, as indicated by its UV/Vis and reso-

nance-Raman spectral characteristics. This product shows

tyrosinase-like activity. We note that the present study has

produced what is only the second example described in the

literature of a bis(μ-oxido)dicopper(III) model complex that

is capable of converting phenolate to catechol as the only

X-ray Diffraction: Data collection for complex 7 was performed

with a Bruker Nonius KappaCCD diffractometer by using graph-

ite-monochromated Mo-K_αradiation with λ = 0.71073 Å. The

structure was solved by direct methods and refined by using the

product. Our findings further support the idea that a bis- program SHELXTL NT 6.12.^[51]All non-hydrogen atoms were re-

10

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

fined anisotropically. Data collection for the remaining structures

was performed with an Oxford Diffraction Xcalibur S instrument

equipped with a Sapphire CCD-detector by using graphite-mono-

chromated Mo-K_αradiation with λ = 0.71073 Å. Frames were inte-

grated by using the SCALE3 ABSPACK algorithm. Structures

were solved by direct methods using the program SHELXS-97.

The copper(I) complex had precipitated almost completely (yellow

solid) after the sealed tube had been allowed to stand for several

days. This ensured saturation of the solution with the copper(I)

complex and static conditions. NMR tubes were flame-sealed un-

der high vacuum after the contents had been cooled to –196 °C.

VT NMR spectra were measured by using a Bruker AvanceIII 500

spectrometer.

2

Subsequent full-matrix least-squares refinement of F_odata was

carried out by using SHELXL-97.^[52]All non-hydrogen atoms were

refined anisotropically. Molecular graphics were created by using

the software packages ORTEP-3 for Windows^[53]and MERCURY

2.3.^[54]Treatment of disorder: In complex 6, the trifluoro acetate

molecules show disorder in the CF₃unit. Three orientations could

be refined separately for each molecule [the occupancy factors are

27.2(4), 26.6(10) and 46.2(9) for atoms F(41)–F(43); 36.6(4), 34.8(9)

and 28.6(9) for atoms F(51)–F(53); 44.0(4), 18.1(8) and 37.9(9) for

atoms F61–F63; 45.1(4), 25.2(9) and 29.7(9) for atoms F(71)–

F(73)]. Treatment of hydrogen atoms: Unless otherwise noted, hy-

drogen atoms were located on the difference Fourier map and

placed in positions of optimized geometry. Isotropic displacement

parameters were tied to those of the corresponding carrier atoms.

For the refinement of the water hydrogen atoms [aqua ligand

H(3A)–O(3)–H(3B) and water molecule H(4A)–O(4)–H(4B)] in

compound 6, H–O–H-angle, O–H-distance restraints and aniso-

tropic displacement-factor constraints were used. The hydrogen

atom H(80) of a methanol molecule in 6 was refined by using O–

H-angle and O–H-distance restraints. The hydrogen atom positions

H(5A) and H(5B) in compound 7 were obtained from a difference

Fourier synthesis and refined with O–H-distance restraints. CCDC-

827107 (2·4HCl·2H₂O), -827108 (4), -827109 (5), -827110

(6·6MeOH·2H₂O), -827111 (7) contain the supplementary crystal-

lographic data for this paper. These data can be obtained free of

charge from The Cambridge Crystallographic Data Centre via

www.ccdc.cam.ac.uk/data_request/cif.

2-{6-[1,3-Bis(dimethylamino)propan-2-yl]pyridin-2-yl}-N¹,N¹,N³,N³-

tetramethylpropane-1,3-diamine (2): The ligand was prepared ac-

cording to a modified literature procedure.^[15]2,6-Lutidine (75 g,

0.7 mol), dimethylamine hydrochloride (460 g, 5.6 mol) and para-

formaldehyde (170 g, 5.6 mol) were suspended in water (500 mL)

and refluxed for 24 h, which resulted in a clear brown solution.

Water was distilled off (ca. 200 mL), and the remaining solution

left to stand at room temperature. The colourless crystalline solid,

which had precipitated after 4 weeks, was filtered, washed with a

small amount of cold methanol and dried in vacuo (colourless so-

lid, tetrahydrochloride dihydrate; 10.0 g; yield based on 2,6-luti-

dine: 3 %). C₁₉H₄₅Cl₄N₅O₂(515.23): calcd. C 44.11, H 8.77, N

13.54; found C 44.09, H 7.78, N 13.61. The free base was obtained

by dissolving the hydrochloride in dry methanol and treating the

solution with sodium methoxide (4 equiv.). The solvent was dis-

tilled off, the residue taken up in tetrahydrofuran and the suspen-

sion filtered. Evaporation of the solvent from the filtrate gave 2 as

a colourless, highly viscous oil. ¹H NMR (400MHz, [D₆]DMSO,

3

room temp.): δ = 7.47 [t, J(H,H) = 7.7 Hz, 1 H, py-H⁴], 6.99 [d,

³J(H,H) = 7.3 Hz, 2 H, py-H^3/5], 3.07 [m, (9 lines), ³J(H, H) = 8.5,

³J(H, H) = 6.0, ²J(H, H) = 12.0 Hz, 2 H, bridgehead CH], 2.53 (m,

4 H, C-CH₂-N), 2.41 (m, 4 H, C-CH₂-N), 2.05 (s, 24 H, CH₃) ppm.

{¹H}¹³C NMR (100.6 MHz, [D₆]DMSO, room temp.): δ = 162.05

(s, ortho-py-C), 135.65 (s, para-py-C), 120.47 (s, meta-py-C), 62.85

(s, CH₂), 45.47 (s, CH₃), 43.75 (s, CH) ppm. MS (ESI): m/z =

336.31154 [M + H]⁺.

Computational Details: Initial geometries were constructed by using

Avogadro^[55]and preoptimized by using the UFF method^[56]as im-

plemented in OpenBabel.^[57]Subsequent DFT calculations were

performed by using the programme Gaussian 03 (C02).^[58]The (re-

stricted) hybrid functional B3LYP as implemented in the Gaussian

package^[59]was used in combination with the DGauss basis set

DGDZVP for geometry optimizations as well as numerical fre-

quency calculations.^[60,61]This combination was chosen to provide

a reasonable geometric description of the rather large copper(I)

complex 8 at moderate computational cost.^[62,63]Geometries were

optimized without constraints by using the default SCF procedure

in Gaussian 03. Numerical frequency calculations were performed

to characterize the structures either as minima (Nimag = 0; Nimag:

number of imaginary frequencies) or saddle points (Nimag = 1).

The transition state shown in Figure 9 is characterized by an imagi-

nary frequency corresponding to a movement of all four pendant

amine arms, coordinated and uncoordinated, in a skeletal defor-

mation vibration. This vibration is antisymmetric with respect to

the C_ssymmetry plane present in the equilibrium geometry, which

appears reasonable when assuming an enantiomerization proceed-

ing through this saddle point.

N¹,N³,2-Trimethyl-2-{6-[2-methyl-1,3-bis(methylamino)propan-2-yl]-

pyridin-2-yl}propane-1,3-diamine (3a): 2·4HBr·MeOH (1.85 g,

3.04 mmol) was added to a saturated aqueous solution of K₂CO₃

(30 mL). The mixture was cooled to 0 °C, and ClCO₂Et (1.3 mL,

14.68 mmol) was added dropwise while stirring. Upon completion

of the addition, the cooling bath was removed and the mixture

stirred overnight. The mixture was extracted with ethyl acetate

(3ϫ30 mL), the organic phases were separated and dried with

Na₂SO₄, and the solvent was removed with a rotary evaporator to

1

obtain the crude carbamate intermediate (1.55 g, 94%). H NMR

3

(200 MHz, CDCl₃, room temp.): δ = 7.64 [t, J(H,H) = 7.9 Hz, 1

3

H, py-H], 7.26 [d, J(H,H) = 7.9 Hz, 2 H, py-H], 5.73 [s (br), 4 H,

3

NH], 4.09 [q, J(H,H) = 7.1 Hz, 8 H, O-CH₂-Me], 3.69–3.38 [ddd,

2

³J(H,H) = 7.6 Hz, J(H,H) = 5.8 Hz, 8 H, C-CH₂-N], 1.29 (s, 6 H,

CH₃), 1.19 [t, ³J(H,H) = 7.1 Hz, 12 H, O-CH₂-CH₃] ppm. {¹H}¹³C

NMR (50.3 MHz, CDCl₃, room temp.): δ = 162.4 (s, ortho-py-C),

157.4 (s, C=O), 137.1 (s, para-py-C), 118.9 (s, meta-py-C), 60.8 (s,

O-CH₂-Me), 46.5 (s, Py-C-Me), 46.3 (s, CH₂), 21.5 (s, CH₃), 14.5

(s, O-CH -CH ) ppm. IR (KBr): ν = 1036, 1139, 1249, 1463, 1540,

˜

2

3

1577, 1701 (C=O), 2935, 2980, 3336 cm^–1. MS (EI, 190 °C): m/z

(%) CH₂-

=

102 (8) [CH₂NHCOOEt]⁺, 438 (100) [M

–

VT NMR Measurements: Complex 8 was investigated in [D₈]THF

in the range from room temperature to 180 K. Oxygen-free condi-

tions were ensured by application of the freeze/pump technique un-

der high vacuum to a fresh solvent aliquot that had been stored

overnight over a freshly prepared potassium mirror. The solvent

was condensed onto the solid sample in a Schlenk tube attached

to a Schlenk line by using liquid nitrogen. After allowing the tube

to warm to room temperature, the sample was heated to reflux and

then transferred as a supersaturated solution to the NMR tube.

NHCOOEt]⁺, 450 (15) [M – 2 OEt]⁺, 495 (10) [M – OEt]⁺, 540 (5)

[M]⁺. C₂₅H₄₁N₅O₈(539.62): calcd. C 55.64, H 7.66, N 12.98; found

C 55.41, H 7.54, N 12.78. Reduction to 3a: A solution of the carb-

amate (740 mg, 1.37 mmol) in THF (10 mL) was added dropwise

to a suspension of lithium aluminium hydride (418 mg, 11 mmol)

in THF (10 mL) over 10 min. The resulting suspension was re-

fluxed for 17 h, during which time its colour changed from colour-

less through yellow to greenish. The mixture was allowed to cool

and then carefully hydrolyzed at 0 °C by addition of water (2 mL)

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

11

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

and concd. aqueous NaOH (10 mL), to give an aqueous phase of

strongly basic pH. The aqueous phase was extracted with THF

(3ϫ15 mL), and the combined organic phases were dried with

Na₂SO₄. The crude product was isolated after solvent evaporation

as a light yellowish oil (400 mg, 95%). ¹H NMR (400 MHz, CDCl₃,

from colourless to dark green. In order to exchange the counterion,

silver(I) trifluoroacetate (172 mg, 78 mmol) in methanol (1 mL)

was added. This caused the colour of the solution to change to

dark blue instantaneously, and silver chloride started to precipitate.

The suspension was filtered and the filtrate concentrated by slow

solvent evaporation. Dark blue crystals of 6 had formed after 3 d.

Method B: The reproducibility of the formation of 6 was ascer-

tained by a directed synthesis. A solution of copper(II) trifluo-

roacetate was prepared by mixing solutions of trifluoroacetic acid

(5.1 mL, 66.4 mmol, 98%) in water (50 mL) and basic copper car-

bonate (3.67 g, 16.6 mmol) in water (10 mL). The concentration

of copper(II) in the resulting solution was 0.56 molL^–1. Ligand 4

(330 mg, 1.2 mmol) was then dissolved in methanol (5 mL), and an

aliquot of the copper(II) trifluoroacetate solution (6.4 mL,

3.6 mmol, 0.56 m in water) was added dropwise to give a dark-blue

solution. The pH value was adjusted to ca. 7–8 with aqueous so-

dium hydroxide (1 m) and the precipitate removed by filtration. The

filtrate was set aside, and crystals of 6 formed by slow evaporation

of the solvent after 2 d. Washing with cold methanol and hexane

3

room temp.): δ = 7.56 [t, J(H,H) = 7.9 Hz, 1 H, py-H⁴], 7.13 [d,

2

³J(H,H) = 7.8 Hz, 2 H, py-H^3/5], 2.91 [dd, J(H,H) = 12.3 Hz, 8 H

CH₂], 2.34 (s, 12 H, NH-CH₃), 1.34 (s, 6 H, CH₃) ppm.

Hexahydro-5-[6-(hexahydro-5-methylpyrimidin-5-yl)pyridin-2-yl]-

5-methylpyrimidine (4): Paraformaldehyde (0.73 g, 22 mmol, 90–

92%) was added in one portion to a stirred solution of 1 (2.77 g,

11 mmol) in methanol (15 mL). The colour of the solution immedi-

ately changed from yellow to colourless, and the aldehyde dis-

solved. The mixture was refluxed for 24 h. After cooling to room

temperature, the solvent was removed in vacuo to yield a highly

viscous yellowish oil. The crude product was recrystallized from

toluene by diffusion of pentane to give 4 as colourless crystals

1

(2.42 g, 80%). H NMR (200 MHz, [D₆]DMSO, room temp.): δ =

3

7.69 [t, J(H,H) = 7.9 Hz, 1 H, py-H⁴], 7.24 [d, J(H,H) = 7.9 Hz,

gave the pure product (390 mg, 34%). IR (KBr): ν = 520, 609, 669,

˜

2 H, py-H^3/5], 3.53 (s, 4 H, N-CH₂-N), 3.40 [d, ²J(H,H) = 13.3 Hz,

709, 725, 762, 799, 818, 838, 901, 918, 981, 1001, 1044, 1137, 1204,

1277, 1327, 1360, 1390, 1436, 1579, 1596, 1675, 2891, 2980, 3153,

3286, 3406, 3562, 3671 cm^–1. MS (ESI): m/z = 276.2193 [4 + H]⁺.

C₄₆H₅₄Cu₆F₂₄N₁₀O₂₀(1903.80): calcd. C 29.01, H 2.86, N 7.36;

found C 29.34, H 2.47, N 7.11.

2

4 H, C-CH₂-N], 2.75 [d, J(H,H) = 13.3 Hz, 4 H, C-CH₂-N], 1.89

[t, J(H,H) = 6.5 Hz, 4 H, NH], 1.10 (s, 6 H, CH₃) ppm. {¹H}¹³C

3

NMR (50.3 MHz, [D₆]DMSO, room temp.): δ = 164.9 (s, ortho-py-

C), 137.5 (s, para-py-C), 118.2 (s, meta-py-C), 62.3 (s, CH₂), 55.5

(s, CH ), 39.3 (s, CMe), 24.9 (s, py-CH ) ppm. IR (KBr): ν = 755,

˜

2

3

[Cu(1)](PF₆) (7): A suspension of tetrakis(acetonitrile)copper(I)

hexafluorophosphate (473.7 mg, 1.27 mmol) in THF (3 mL) was

added dropwise to a stirred solution of 1 (320 mg, 1.27 mmol) in

THF (3 mL). A yellow colour appeared immediately and the mix-

ture deposited a yellow solid. The suspension was stirred for an

additional 3 h, the solid collected by filtration, washed with THF

and dried in vacuo (480 mg, 82 %). ¹H NMR (500 MHz,

815, 892, 941, 994, 1068, 1084, 1001, 1134, 1170, 1210, 1260, 1300,

1376, 1420, 1466, 1576, 1635, 2868, 2931, 2961, 3306, 3402 cm^–1.

MS (EI, 70 eV): m/z (%) = 275 (10) [M]^·+. C₁₅H₂₅N₅(275.40):

calcd. C 65.42, H 9.15, N 25.43; found C 65.21, H 9.19, N 25.43.

[Cu(3)](ClO₄)₂(5): Method a: A solution of hexakis(dimethylform-

amide)copper(II) perchlorate (406 mg, 0.58 mmol) in methanol

(1 mL) was added dropwise to a solution of 3a (180 mg, 0.58 mmol)

in methanol (2 mL). The colour of the solution changed from

colourless to dark blue, and it began to deposit a precipitate. Para-

formaldehyde (38 mg, 1.16 mmol) was added in one portion and

the reaction mixture stirred at room temperature for 14 h, during

which time the colour turned to turquoise. Crude 5 (110 mg, 32%)

was collected by filtration, washed with cold methanol and dried

in vacuo. Slow concentration of a solution of 5 in acetonitrile

yielded dark blue single crystals. Method b: Crystals of 5 were also

obtained when the reaction sequence was inverted. Paraformalde-

hyde (47 mg, 0.71 mmol) was added in one portion to a solution of

4 (220 mg, 0.71 mmol) in methanol (2 mL). As the solid dissolved,

hexakis(dimethylformamide)copper(II) perchlorate (500 mg,

1.43 mmol) in methanol (1 mL) was added dropwise. The reaction

mixture was stirred at room temperature for 14 h, during which

time the colour turned to turquoise. The crude product 5 (180 mg,

43%) was collected by filtration as a light blue solid, washed with

cold methanol and dried in vacuo. Slow evaporation of the solvent

from a solution of 5 in acetonitrile yielded dark-blue single crystals

3

[D₆]DMSO, room temp.): δ = 7.82 [t, J(H,H) = 7.9 Hz, 1 H, py-

3

2

H⁴], 7.38 [d, J(H,H) = 8.0 Hz, 2 H, py-H^3/5], 3.00 [d, J(H,H) =

12.8 Hz, 4 H, C-CH₂-N], 2.88 [d, ²J(H,H) = 12.8 Hz, 4 H, C-CH₂-

N], 2.70 [s (br), 8 H, NH₂], 1.26 (s, 6 H, CH₃) ppm. {¹H}¹³C NMR

(125.8 MHz, [D₆]DMSO, room temp.): δ = 162.7 (s, ortho-py-C),

138.2 (s, para-py-C), 119.4 (s, meta-py-C), 49.7 (s, CH₂), 44.2 (s, C-

Me), 22.2 (s, CH ) ppm. IR (KBr): ν = 559, 741, 749, 833, 915,

˜

3

1004, 1018, 1074, 1446, 1466, 1567, 1577, 1615, 1980, 2838, 2884,

2951, 2974, 3052, 3341, 3379, 3383 cm^–1. MS (ESI): m/z (%) =

314.1400 [Cu(1)]⁺. C₁₃H₂₅CuF₆N₅P (459.88): calcd. C 33.95, H

5.48, N 15.23; found C 34.37, H 5.26, N 14.75.

[Cu(2)](PF₆) (8): A suspension of tetrakis(acetonitrile)copper(I)

hexafluorophosphate (225 mg, 0.6 mmol) in THF (1 mL) was

added dropwise to a stirred solution of 2 (202 mg, 0.6 mmol) in

THF (3 mL). The colour of the solution turned to yellow-orange

immediately, and stirring was continued for 2 h. The solvent was

then removed in vacuo, and complex 8 was obtained as a yellow-

brownish solid (300 mg, 98%). ¹H NMR (200 MHz, [D₆]DMSO,

3

room temp.): δ = 7.84 [t, J(H,H) = 7.8 Hz, 1 H, py-H⁴], 7.27 [d,

suitable for X-ray structure determination. IR (KBr): ν = 523, 563,

˜

³J(H,H) = 7.8 Hz, 2 H, py-H^3/5], 3.16 (m, 2 H, CH), 2.65 (m, 4 H,

C-CH₂-N), 2.54 (m, 4 H, C-CH₂-N), 2.34 (s, 24 H, CH₃) ppm.

{¹H}¹³C NMR (100.6 MHz, [D₆]DMSO, room temp.): δ = 161.1

(s, ortho-py-C), 137.2 (m, para-py-C), 120.5 (s, meta-py-C), 63.1 (s,

623, 702, 769, 825, 858, 905, 931, 981, 1021, 1091, 1194, 1217, 1240,

1250, 1303, 1333, 1373, 1396, 1420, 1469, 1582, 1596, 1645, 2017,

2745, 2868, 2884, 2921, 2947, 2980, 3249, 3442 cm^–1. MS (ESI):

m/z (%) = 197.1016 [Cu(3)]²⁺, 332.2817 [3 + H]⁺, 493.1517 [Cu(3)-

ClO₄]⁺. C₁₉H₃₃Cl₂CuN₅O₈(593.88): calcd. C 38.42, H 5.60, N

11.79; found C 38.65, H 3.65, N 11.51.

CH ), 46.7 (s, CH ), 42.1 (s, CH) ppm. IR (KBr): ν = 559, 619,

˜

2

3

636, 755, 842, 991, 1038, 1101, 1144, 1164, 1190, 1244, 1267, 1293,

1373, 1413, 1466, 1576, 1596, 1655, 2731, 2775, 2824, 2844, 2868,

2901, 2947, 2974 cm^–1. MS (ESI): m/z (%) = 398.2337 [Cu(2)]⁺.

C₁₉H₃₇CuF₆N₅P (544.04): calcd. C 41.95, H 6.85, N 12.87; found

C 42.36, H 6.65, N 12.93.

[Cu₆(4)₂(μ-CF₃CO₂)₂(CF₃CO₂)₄(H₂O)₂(μ₃-OH)₄](CF₃-

CO₂)₂·6MeOH·2H₂O (6): Method A: Compound 4 (98 mg,

0.36 mmol) was dissolved in methanol (3 mL), and a solution of

copper(II) chloride (52 mg, 0.39 mmol) in methanol (1 mL) was

added dropwise. The addition was accompanied by a colour change

[Cu(4)](PF₆) (9): A suspension of tetrakis(acetonitrile)copper(I)

hexafluorophosphate (268 mg, 0.72 mmol) in THF (1 mL) was

12

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

added dropwise to a stirred solution of 4 (220 mg, 0.79 mmol) in

THF (2 mL). A yellow colour immediately appeared, and the solu-

tion deposited a yellow-greenish solid. Stirring was continued for

3 h, and the solid was then collected by filtration. Product 8 was

washed with THF and dried in vacuo (260 mg, 75%). ¹H NMR

(500 MHz, [D₆]DMSO, room temp.): δ = 7.89 [t, ³J(H,H) = 7.9 Hz,

1 H, py-H⁴], 7.53 [d, ³J(H,H) = 7.8 Hz, 2 H, py-H^3/5], 3.72 (s, 4 H,

N-CH₂-N), 3.68 [dd, ²J(H,H) = 11.3 Hz, 4 H, C-CH₂-N], 2.83 [dd,

²J(H,H) = 11.3 Hz, 4 H, C-CH₂-N], 1.09 (s, 6 H, CH₃) ppm.

{¹H}¹³C NMR (100.6 MHz, [D₆]DMSO, room temp.): δ = 163.8

(s, ortho-py-C), 138.6 (s, para-py-C), 120.8 (m, meta-py-C), 63.7 (m,

CH₂), 56.0 (m, CH₂), 39.5 (s, C-Me), 27.3 (m, CH₃) ppm. IR (KBr):

[1]

B. Murphy, B. Hathaway, Coord. Chem. Rev. 2003, 243, 237–

262.

[2]

[3]

[4]

D. Reinen, Comments Inorg. Chem. 1983, 2, 227–246.

B. J. Hathaway, Struct. Bonding (Berlin) 1984, 57, 55–118.

E. I. Solomon, J. W. Ginsbach, D. E. Heppner, M. T. Kieber-

Emmons, C. H. Kjaergaard, P. J. Smeets, L. Tian, J. S. Woert-

ink, J. Chem. Soc. Faraday Trans. 2011, 148, 11–39.

R. A. Himes, K. D. Karlin, Curr. Opin. Chem. Biol. 2009, 13,

119–131.

[5]

[6]

L. M. Mirica, X. Ottenwaelder, T. D. P. Stack, Chem. Rev.

2004, 104, 1013–1046.

[7]

[8]

E. A. Lewis, W. B. Tolman, Chem. Rev. 2004, 104, 1047–1076.

M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem.

2010, 122, 6583; Angew. Chem. Int. Ed. 2010, 49, 6438–6422.

R. L. Peterson, R. A. Himes, H. Kotani, T. Suenobu, L. Tian,

M. A. Siegler, E. I. Solomon, S. Fukuzumi, K. D. Karlin, J.

Am. Chem. Soc. 2011, 133, 1702–1705.

ν = 559, 652, 739, 755, 842, 971, 998, 1064, 1104, 1170, 1244, 1297,

˜

1333, 1356, 1383, 1463, 1576, 2871, 2934, 2961, 3070, 3283 cm^–1.

MS (ESI): m/z (%) = 338.1407 [Cu(4)]⁺. C₁₅H₂₅CuF₆N₅P (483.85):

calcd. C 37.23, H 5.21, N 14.47; found C 37.69, H 4.97, N 14.30.

[9]

Reaction of Complex 8 with Dioxygen To Produce 10: A Schlenk

flask was charged with a solution of 8 in THF (1 mL), capped with

a rubber septum and cooled to –90 °C by immersion in a liquid

N₂/methanol bath. Dioxygen from an O₂cylinder was then passed

through the solution with a cannula. This caused the colour of the

solution to change from yellowish green to a deep brown green.

The oxygen flow was stopped after ca. 5 min. When using ¹⁸O₂a

three-way valve was employed to enable evacuation of the system

before starting the oxygen flow, which was admitted into a pre-

viously set up static vacuum. Complex 10 may be stored for several

hours at –90 °C under aprotic conditions. Upon warming to room

temperature the solution undergoes a colour change to dark green,

and 10 decomposes.

[10]

J. Woertink, L. Tian, D. Maiti, H. R. Lucas, R. A. Himes,

K. D. Karlin, F. Neese, C. Würtele, M. C. Holthausen, E. Bill,

J. Sundermeyer, S. Schindler, E. Solomon, Inorg. Chem. 2010,

49, 9450–9459.

G. Chaka, J. L. Sonnenberg, H. B. Schlegel, M. J. Heeg, G. Jae-

ger, T. J. Nelson, L. A. Ochrymowycz, D. B. Rorabacher, J. Am.

Chem. Soc. 2007, 129, 5217–5227.

A. Grohmann, Dalton Trans. 2010, 39, 1432–1440.

C. Zimmermann, F. W. Heinemann, A. Grohmann, Eur. J. In-

org. Chem. 2001, 547–555.

D. H. Busch, Chem. Rev. 1993, 93, 847–860.

J. L. Hughes, Dissertation, University of Michigan, Ann Arbor,

USA, 1961.

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

H. A. Bent, Chem. Rev. 1961, 61, 275–311.

D. W. Gruenwedel, Inorg. Chem. 1968, 7, 495–501.

S.-D. Kim, J.-K. Kim, W.-S. Jung, Bull. Korean Chem. Soc.

1997, 18, 653–656.

H. Möhrle, M. Pycior, J. Lessel, Sci. Pharm. 1996, 64, 569–575.

Möhrle, M. Pycior, Arch. Pharm. 1995, 328, 293–296.

G. L. Buchanan, A. C. W. Curran, Chem. Commun. (London)

1966, 773.

H. Kämpf, Dissertation, Technische Universität Berlin 2007.

L. H. Gade, N. Mahr, J. Chem. Soc., Dalton Trans. 1993, 489–

494.

P. C. Bansal, I. H. Pitman, J. N. S. Tam, M. Martes, J. J. Kam-

inski, J. Pharm. Sci. 1981, 70, 850–854.

U. Salzner, J. Org. Chem. 1995, 60, 986–995.

Y.-Q. Zheng, D.-Y. Cheng, B.-B. Liu, W.-X. Huang, Dalton

Trans. 2011, 40, 277–286.

F. Bramsen, A. D. Bond, C. J. McKenzie, R. G. Hazell, B.

Moubaraki, K. S. Murray, Chem. Eur. J. 2005, 11, 825–831.

S. Triki, F. Thétiot, J. S. Pala, S. Golhen, J. M. Clemente-Juan,

C. J. Gómez-García, E. Coronado, Chem. Commun. 2001,

2172–2173.

J. A. Real, G. De Munno, R. Chiappetta, M. Julve, F. Lloret,

Y. Journaux, J. C. Colin, G. Blondin, Angew. Chem. 1994, 106,

1223; Angew. Chem. Int. Ed. Engl. 1994, 33, 1184–1186; Angew.

Chem. 1994, 106, 1223–1225.

Reaction of Sodium p-tert-Butylphenolate: p-tert-Butylphenol

(500 mg, 3.33 mmol) was dissolved in THF (5 mL), and a slight

excess of sodium sand (80 mg, 3.48 mmol) was added in one por-

tion. The mixture evolved gas, and its colour changed from colour-

less to light pink. The solution was separated from unreacted so-

dium with a cannula, and the solvent was removed in vacuo. So-

dium p-tert-butylphenolate was obtained as a light-pink powder

(567 mg, 99%). Method a: Complex 8 (75 mg, 0.14 mmol) in THF

(30 mL) was exposed to O₂as described above. Sodium p-tert-but-

ylphenolate (24 mg, 0.14 mmol) dissolved in THF (1 mL) was

added to the cooled solution of 10, which caused an instantaneous

colour change from yellow green to dark green. The reaction mix-

ture was warmed to room temperature and subsequently quenched

with aqueous HCl (30 mL, 1 m), resulting in a yellow solution.

THF was removed in vacuo and the aqueous phase extracted with

DCM (4ϫ20 mL). The organic phases were combined, and the

solvent was removed in vacuo to leave a yellow oil. GC–MS and

¹H NMR spectroscopy indicated the material to be a mixture of p-

tert-butylphenol and p-tert-butylcatechol (in an approximate ratio

of 85:15). Method b: The reaction was repeated by using a fivefold

excess of sodium p-tert-butylphenolate. Complex 10 was prepared

in the minimum amount of THF (3 mL). After acidic workup, the

p-tert-butylphenol-derived mixture was again isolated as an oil. The

conversion of the starting material was 30%, as concluded from ¹H

NMR spectroscopic data.

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

X. Li, D. Cheng, J. Lin, Z. Li, Y. Zheng, Cryst. Growth Des.

2008, 8, 2853–2861.

X. Li, D. Cheng, J. Lin, Z. Li, Y. Zheng, Cryst. Growth Des.

2008, 8, 4602.

R. T. Azuah, L. R. Kneller, Y. Qiu, P. L. W. Tregenna-Piggott,

C. M. Brown, J. R. D. Copley, R. M. Dimeo, J. Res. Natl. Inst.

Stand. Technol. 2009, 114, 341.

Acknowledgments

[33]

[34]

[35]

W. J. Kasowski, J. C. Bailar Jr., Polyhedron 1994, 13, 1989–

Support of this work by the Deutsche Forschungsgemeinschaft

(GR 1247/7-1) is gratefully acknowledged. We thank Dr. Anna

Company for fruitful discussions, Ralf Reichert and Wiebke

Matthes for assistance with NMR glassware, and Sebastian

Kemper for technical assistance with the VT NMR spectroscopy.

1996.

W. J. Kasowski, J. C. Bailar Jr., Polyhedron 1994, 13, 1997–

2003.

D. A. Handley, P. B. Hitchcock, T. H. Lee, G. J. Leigh, Inorg.

Chim. Acta 2001, 314, 14–21.

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

13

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

A. Grohmann et al.

FULL PAPER

[36]

[37]

[38]

[54] C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P.

McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J.

van de Streek, P. A. Wood, J. Appl. Crystallogr. 2008, 41, 466–

470.

[55] Avogadro: an open-source molecular builder and visualization

tool, version 1.0, http://avogadro.openmolecules.net/.

[56] A. K. Rappe, C. J. Casewit, K. S. Colwell, W. A. Goddard III,

W. M. Skiff, J. Am. Chem. Soc. 1992, 114, 10024–10035.

[57] N. M. O’Boyle, M. Banck, C. A. James, C. Morley, T. Vander-

meersch, G. R. Hutchison, J. Cheminf. 2011, 3:33, DOI:

10.1186/1758-2946-3-33.

[58] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,

M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.

Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,

J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.

Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.

Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.

Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.

Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,

R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-

elli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.

Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,

A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D.

Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,

A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,

A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.

Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,

M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.

Wong, C. Gonzalez, and J. A. Pople, Gaussian 03, re-

vision C.02, Gaussian, Inc., Wallingford, CT, USA, 2004.

[59] R. H. Hertwig, W. Koch, Chem. Phys. Lett. 1997, 268, 345–

351.

A. De la Lande, O. Parisel, H. Gerard, V. Moliner, O. Reinaud,

Chem. Eur. J. 2008, 14, 6465–6473.

D. Utz, S. Kisslinger, F. Hampel, S. Schindler, J. Inorg. Bio-

chem. 2008, 102, 1236–1245.

J. A. Halfen, S. Mahapatra, E. C. Wilkinson, S. Kaderli, V. G.

Young Jr., L. Que Jr., A. D. Zuberbühler, W. B. Tolman, Sci-

ence 1996, 271, 1393–1395.

L. Q. Hatcher, M. A. Vance, A. A. Narducci Sarjeant, E. I. Sol-

omon, K. D. Karlin, Inorg. Chem. 2006, 45, 3004–3013.

E. I. Solomon, U. M. Sundaram, T. E. Machonkin, Chem. Rev.

1996, 96, 2563–2605.

A. P. Cole, V. Mahadevan, L. M. Mirica, X. Ottenwaelder,

T. D. P. Stack, Inorg. Chem. 2005, 44, 7345–7364.

M. J. Henson, P. Mukherjee, D. E. Root, T. D. P. Stack, E. I.

Solomon, J. Am. Chem. Soc. 1999, 121, 10332–10345.

M. Rolff, J. Schottenheim, H. Decker, F. Tuczek, Chem. Soc.

Rev. 2011, 40, 4077–4098.

L. M. Mirica, M. Vance, D. J. Rudd, B. Hedman, K. O. Hodg-

son, E. I. Solomon, T. D. P. Stack, Science 2005, 308, 1890–

1892.

[39]

[40]

[41]

[42]

[43]

[44]

[45] A. Company, S. Palavicini, I. Garcia Bosch, R. Mas-Ballesté,

L. Que Jr., E. V. Rybak-Akimova, L. Casella, X. Ribas, M. Co-

stas, Chem. Eur. J. 2008, 14, 3535–3538.

[46] S. Herres-Pawlis, P. Verma, R. Haase, P. Kang, C. T. Lyons,

E. C. Wasinger, U. Flörke, G. Henkel, T. D. P. Stack, J. Am.

Chem. Soc. 2009, 131, 1154–1169.

[47] I. Garcia-Bosch, A. Company, J. R. Frisch, M. Torrent-Sucar-

rat, M. Cardellach, I. Gamba, M. Güell, L. Casella, L. Que Jr.,

X. Ribas, J. M. Luis, M. Costas, Angew. Chem. 2010, 122, 2456;

Angew. Chem. Int. Ed. 2010, 49, 2406–2409.

[48] SDBSWeb, http://riodb01.ibase.aist.go.jp/sdbs/; National Insti-

tute of Advanced Industrial Science and Technology, viewed

March 2011.

[60] J. Andzelm, E. Wimmer, J. Chem. Phys. 1992, 96, 1280–1303.

[61] C. Sosa, J. Andzelm, B. C. Elkin, E. Wimmer, K. D. Dobbs,

D. A. Dixon, J. Phys. Chem. 1992, 96, 6630–6636.

[49] G. J. Kubas, Inorg. Synth. 1990, 28, 68–70.

[50] A. Grohmann, F. Knoch, Inorg. Chem. 1996, 35, 7932–7934.

[51] Bruker Analytical X-ray Systems, SHELXTL NT, version 6.12,

Bruker AXS GmbH, Karlsruhe, Germany, 2002.

[52] G. M. Sheldrick, SHELXL-97, Universität zu Göttingen,

Göttingen, Germany, 1997.

[53] L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.

[62] P. Aslanidis, P. J. Cox, A. Kaltzoglou, A. C. Tsipis, Eur. J. Inorg.

Chem. 2006, 334–344.

[63] S. K. Hadijikakou, C. D. Antoniadis, P. Aslanidis, P. J. Cox,

A. C. Tsipis, Eur. J. Inorg. Chem. 2005, 1442–1452.

Received: November 11, 2011

Published Online: ᭿

14

www.eurjic.org

Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: A11265

/KAP1

Date: 02-05-12 18:07:28

Pages: 15

Copper Complexes of “Superpodal” Amine Ligands

Copper Complexes

Copper(I/II) complexes of varying nu-

clearity have been obtained with a series of

tetrapodal pentadentate N-donor ligands.

A. Jozwiuk, E. A. Ünal, S. Leopold,

J. P. Boyd, M. Haryono, N. Kurowski,

F. V. Escobar, P. Hildebrandt, J. Lach,

F. W. Heinemann, D. Wiedemann, E. Irran,

A. Grohmann* ................................. 1–15

Copper Complexes of “Superpodal”

Amine Ligands and Reactivity Studies

towards Dioxygen

Keywords: Tetrapodal pentadentate li-

gands / Copper / Dioxygen / Tyrosinase-

like activity / N ligands / Density functional

calculations

Eur. J. Inorg. Chem. 0000, 0–0

www.eurjic.org

15

Article Doi

Copper complexes of superpodal amine ligands and reactivity studies towards dioxygen

DOI: 10.1002/ejic.201101265

Source and publish data:

Authors:

Article abstract of DOI:10.1002/ejic.201101265

Full text of DOI:10.1002/ejic.201101265

Products guided by the article

R&D Labs maybe for 5787-50-8

Relevant to this article

Hot Product