From pyrazolate-based binuclear copper(I) complexes to octanuclear θ-mesityl-bridged μ4-oxo-cuprocuprates: Controlled dioxygen splitting by organocopper scaffolds

ARTICLE

pubs.acs.org/Organometallics

From Pyrazolate-Based Binuclear Copper(I) Complexes to Octanuclear

σ-Mesityl-Bridged μ₄-Oxo-Cuprocuprates:

Controlled Dioxygen Splitting by Organocopper Scaffolds

Michael Stollenz,*^,†Henrike Gehring, Vera Konstanzer, Stefan Fischer, Sebastian Dechert,

Christian Grosse, and Franc Meyer*

Institut f€ur Anorganische Chemie, Georg-August-Universit€at G€ottingen, Tammannstrasse 4, D-37077 G€ottingen, Germany

S Supporting Information

b

ABSTRACT: The synthesis of a series of new pyrazole-based binucleating compartmental

ligands, 3,5-bis(R²R³N)-(4-R¹)-pyrazoles L¹HꢀL⁶H (L¹H, R¹= H, R²= Me, R³= 2-py-

(CH₂); L²H, R¹= Ph, R²= Me, R³= 2-py(CH₂); L³H, R¹= H, R²= Cy, R³= 2-py(CH₂); L⁴H,

R¹= Ph, R²= Cy, R³= 2-py(CH₂); L⁵H, R¹= Ph, R², R³= 2-py(CH₂), L⁶H, R¹= Ph, R²= Me,

R³= 8-quin), together with the X-ray crystal structure of L³H is reported. After deprotonation

and subsequent reaction with 2 equiv of [Cu^I(CH₃CN)₄](BF₄) and PMe₃, L³H forms the

stable binuclear Cu^Icomplex [L³{Cu(PMe₃)}₂](BF₄) (1). The analogous reaction with L⁶H

and 2 equiv of tert-butyl isonitrile aﬀords [L⁶{Cu(CNtBu)}₂](BF₄) (2). 1 and 2 represent the

ﬁrst examples of binuclear Cu^Iꢀpyrazolate complexes of the type [LCu^I₂]X that have been

characterized by their X-ray crystal structures. With respect to the planes spanned by the

pyrazolate backbone, 1 shows a cis orientation of the PMe₃ligands, whereas 2 exhibits a trans

arrangement of the tBuNC ligands. L¹HꢀL⁶H are shown to react with 4 equiv of

mesitylcopper and stoichiometric amounts of dioxygen, leading to the formation of the

unusually stable organocopper frameworks 3ꢀ8. These complexes follow a general structural

principle that is best described by the heteroleptic O-centered cuprate anion [(MesCu^I)₄

(μ₄-O)]^2ꢀlinked via four trans-oriented σ-mesityl bridges to two ﬂanking binuclear

Cu^I-pyrazolates [(L¹ꢀL⁶)Cu^I₂]^þ. Thus, 1 and 2 can also be viewed as capping binuclear

Cu^I-complex units that are concealed by two ancillary PMe₃and tBuNC ligands, respectively. The exemplary reaction of 4 with an

excess of dimethyl acetylenedicarboxylate (DMDAC) supports the observed cuprate features of 3ꢀ8, since after hydrolysis the

corresponding (syn-)addition product MesC(CO₂Me)dC(CO₂Me)H (9) and the free ligand L²H are found as major products.

’ INTRODUCTION

intermediates in cuprate-involving reactions. This has been

demonstrated earlier for the unique cuprocuprate [(DPPE)₂Cu]-

[CuMes₂] (DPPE = 1,2-bis(diphenylphosphino)ethane) by

Leoni, Pasquali, and Ghilardi,⁷and later for magnesium organo-

cuprates bearing arenethiolate coligands by van Koten et al.,^1,8

and recently again for several intriguing lithium and magnesium

organocuprates by Davies et al.⁹A real breakthrough en route to a

deeper insight into oxidative copper-mediated CꢀC couplings

was also achieved with mesitylcopper, namely its controlled oxy-

genation resulting in the formation of bimesityl and the unusual

complex array [Cu₁₀O₂Mes₆] (Chart 1).¹⁰According to an X-ray

structure determination, this remarkable compound consists of

ten Cu^Icenters which are held together by two μ₄-O bridges and

six μ-σ-mesityl linkers. Further spectroscopic investigations of

this highly sensitive framework still remain a challenging goal and

have not been reported so far.

Organocopper chemistry has attracted considerable interest

over the last few decades, which is attributed to its high and

versatile potential in synthetic chemistry.¹This is, for instance,

reﬂected by the unique role of copper in the activation of dioxy-

gen, as demonstrated by important transformations such as the

catalytic oxidation of ethylene to ethylene glycol, the Wacker

process, and the oxidative coupling of acetylenes and of biaryls.^2ꢀ4

Another large area of importance is represented by organo-

cuprates and their stoichiometric and catalytic applications as

selective transfer reagents that generate valuable organic building

blocks.^1,5

Although organocopper reagents provide this broad range of

useful synthetic methodologies, relatively little is known about

the speciﬁc role of such species in oxidatively induced CꢀC

coupling reactions and cuprate-type transformations. To eluci-

date the structural role of organocuprates in the latter types of

reactions, valuable approaches were made by employing mesityl-

copper⁶as a well-deﬁned and well-characterized precursor. Its

use is convenient for the synthesis of a variety of unusual yet

relatively stable organocopper frameworks which serve as potential

We have recently communicated an exceptionally stable

octanuclear σ-mesitylcopper complex with a related structure

Received: August 27, 2010

Published: April 13, 2011

r

2011 American Chemical Society

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Organometallics

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Chart 1. Cu^IComplex Framework Obtained from Mesityl-

copper and Dioxygen

Scheme 1. Synthesis of L¹HꢀL⁶H

consisting of a complex cuprate anion, [(MesCu^I)₄(μ₄-O)]^2ꢀ

,

that is encapsulated by two ﬂanking, and thus stabilizing, bi-

nuclear Cu^I-pyrazolates [(L²)Cu^I₂]^þ; it was obtained from the

reaction of two chelating ligands, 8 equiv of mesitylcopper, and

¹/₂equiv of dioxygen.¹¹Multinucleating pyrazolate-based com-

partmental ligands have attracted considerable interest over the

course of the past decade, since they allow the positioning of two

metal centers in close proximity, thus resulting in bi- or oligo-

meric frameworks with unique structural features and syner-

getic electronic or magnetic properties, using Cu^IIand other

metals.^2b,12,13Fine-tuning of the bimetallic arrangement is

achieved by combining the negatively charged pyrazolate back-

bone, which acts as the bridging core of the ligand system to hold

two metal centers at a distance of around 3.0ꢀ4.5 Å to each

other, with suitable appended donor side groups at the 3,5-

positions of the central heterocyclic ring providing variable

binding pockets. Since mesitylcopper is known to form tetra-

meric or pentameric cyclic arrays [CuMes]_nin the solid state

with interatomic distances between next but one neighboring Cu

atoms in the range of about 3.40ꢀ4.15 Å,^6bꢀdwe reasoned that

pyrazolate-based compartmental ligand systems should oﬀer the

right premise to host two terminal Cu^Icenters of a tailored

fragment of mesitylcopper such as [Cu(μ₂-Mes)Cu(μ₂-

Mes)Cu]^þor [Cu(μ₂-Mes)Cu(μ₂-Mes)Cu(μ₂-Mes)Cu]^þ; this

has indeed been supported by our recent preliminary results.¹¹

In this context we have now been interested in gaining deeper

insight into the various structural features of those complex

frameworks, in particular those features that are related to their

cuprate character and the resulting reactivity in dependence of

diﬀerent stabilizing pyrazolate scaﬀolds. This requires the initial

synthesis of smaller Cu^Ibuilding blocks of the type [LCu₂]^þ,

which represent the stabilizing capping units in the previously

reported [(L²)Cu^I₂(μ₂-MesCu^I)₂(μ₄-O)(μ₂-MesCu^I)₂(L²)Cu^I₂].

It has also previously been demonstrated that the nuclearity of

usually trimeric or tetrameric Cu^Iand Ag^Ipyrazolates^14ꢀ16can

be controlled by using ancillary strong σ-donor or π-acceptor

ligands such as phosphines, isonitriles, and CO.¹⁷However, it has

remained a great challenge to ﬁnd appropriate methods for syn-

thesizing binuclear Cu^Ispecies with compartmental pyrazolate

scaﬀolds that are structurally related to the established binuclear

Cu^IIpyrazolate complexes. Prerequisite for the targeted prepara-

tion of binuclear Cu^Ipyrazolate species is a well-adjusted com-

bination of the donor/acceptor strengths of the coligands and

the presence of two suitable binding pockets at the central pyra-

zolate bridging unit. Otherwise, alternative binding modes and

nuclearities are obviously favored over the desired binuclear

arrangement (vide infra).

Herein, we describe the synthesis of four new compartmental

pyrazole ligands and the ﬁrst X-ray crystal structure determina-

tion of a pyrazole derivative with {N₂} ligating chelate arms at the

3,5-positions of the heteroaromatic core. Second, the synthesis

and structural characterization of the ﬁrst two examples of

binuclear Cu^Ipyrazolate complexes of the type [L(Cu^I)₂]X are

reported. Finally, we report on a series of unusual organocopper

oligomeric frameworks of the general composition [(L¹ꢀL⁶)

Cu^I₂(μ₂-MesCu^I)₂(μ₄-O)(μ₂-MesCu^I)₂(L¹ꢀL⁶)Cu^I₂], which

bear close structural relation to the binuclear complexes; we

describe their spectroscopic properties together with some

remarkable structural features, and we also give an example

for the reactivity of those organocopper assemblies toward

activated alkynes.

’ RESULTS AND DISCUSSION

Synthesis of the Ligands and X-ray Crystal Structure

Determination of L³H. The new ligands L¹H and L³HꢀL⁵H

are accessible by a proven multistep synthetic sequence that was

described earlier for L²H and L⁶H (Scheme 1).^11,15They all can

be readily prepared from the starting materials 3,5-bis-

(hydroxymethyl)-1H-pyrazole¹⁸and 3,5-bis(hydroxymethyl)-4-

phenyl-1H-pyrazole¹⁹and the respective secondary amines; the

products are isolated as viscous oils (L¹H and L⁵H) or powders

(L³H and L⁴H) in reasonable to good overall yields (37ꢀ85%).

L¹H is readily soluble in polar solvents such as THF and

acetonitrile as well as in CH₂Cl₂and CDCl₃, whereas its solubility in

benzene or toluene is rather low. All other new ligands bearing

nonpolar side groups such as phenyl and cyclohexyl can be

dissolved also in the less polar solvents without restrictions. The

HR-ESI(þ) spectra of all four new ligands L¹H and L³HꢀL⁵H

exhibit the expected [M þ H]^þpeaks, which are in good

agreement with their calculated isotopic distribution patterns

(see Experimental Section). Slow evaporation of a saturated

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Figure 2. Molecular structure of the complex cation of one (A) of the

two independent molecules of 1. The BF₄^ꢀcounterion and hydrogen

atoms have been omitted for clarity. Selected interatomic distances (Å)

and bond angles (deg): N1ꢀN2 = 1.355(4), Cu1ꢀP1 = 2.1499(11),

Cu1ꢀN1 = 1.983(3), Cu1ꢀN3 =2.249(3), Cu1ꢀN4 =2.067(3), Cu2ꢀP2

= 2.1771(12), Cu2ꢀN2 = 1.981(3), Cu2ꢀN5 = 2.394(3), Cu2ꢀN6 =

2.094(3), Cu1 Cu2 = 4.2778(16); P1ꢀCu1ꢀN1 = 126.11(8),

3 3 3

P1ꢀCu1ꢀN3 = 127.51(8), P1ꢀCu1ꢀN4 = 119.72(9), N1ꢀCu1ꢀN3 =

80.87(10), N1ꢀCu1ꢀN4 = 108.28(12), N3ꢀCu1ꢀN4 = 80.94(11),

P2ꢀCu2ꢀN2 = 143.69(9), P2ꢀCu2ꢀN5 = 124.54(7), P2ꢀCu2ꢀN6 =

110.58(8), N2ꢀCu2ꢀN5 = 77.31(11), N2ꢀCu2ꢀN6 = 101.53(11),

N5ꢀCu2ꢀN6 = 78.70(10).

Figure 1. Representation of two hydrogen-bridged molecules of L³H.

Hydrogen atoms, except those forming hydrogen bridges, have been

omitted for clarity. Selected interatomic distances (Å) and bond angles

(deg): N1ꢀN2 = 1.3449(16), N1ꢀC2 = 1.319(2), N2ꢀC3 = 1.362(3),

L³H to L⁴H, indicating a limited free rotation of the cyclohexyl,

pyridyl, and even phenyl substituents around their CꢀC and

CꢀN bonds. Again, this eﬀect of steric hindrance occurs in the

¹H NMR spectrum of L⁵H (benzene-d₆at room temperature),

whose CH₂resonance is clearly broadened, whereas the aromatic

signals are sharp and display four pyridyl groups that appear to be

equivalent in solution.

Synthesis, Properties, and X-ray Crystal Structure Deter-

minations of Complexes 1 and 2. Dicopper(I) complexes

could be isolated and structurally characterized in two cases.

Deprotonation of L³H or L⁶H with a strong base (NaN(SiMe₃)₂

or KOtBu) and subsequent reaction with 2 equiv of [Cu^I(CH₃-

CN)₄](BF₄) and 2 equiv of a coligand (PMe₃or tBuNC) afforded

the complexes [L³{Cu(PMe₃)}₂]BF₄(1) and [L⁶{Cu(CNtBu)}₂]

BF₄(2) as pale yellow and beige solids, respectively. Elemental

analyses and characteristic fragments of the ESI(þ) mass spectra

confirm the proposed compositions (see the Experimental Section

for details).

1 is readily soluble in THF and reasonably in toluene, but only

sparingly in diethyl ether. Both in solution and in the solid state

this complex is moderately air stable, but it can be stored under

an atmosphere of argon for a longer time period. Decomposition

takes place in air, presumably by releasing PMe₃, thus resulting in

a green compound, which is very likely a Cu^IIspecies. The

solubility of 2 is more restricted to polar solvents such as CH₂Cl₂,

THF, and acetonitrile, since the complex is poorly soluble in

toluene. 2 is also moderately air stable and can be stored under

inert conditions for several months.

C1ꢀC2 = 1.401(2), C1ꢀC3 = 1.379(2), N2 N1⁰⁰= 2.8994(17);

3 3 3

N1ꢀN2ꢀC3 = 113.52(13), N2ꢀN1ꢀC2 = 104.90(13). Symmetry

operations used to generate equivalent atoms: (⁰) 1 ꢀ x, 1 ꢀ y, 1 ꢀ z; (⁰⁰)

1 ꢀ x, ꢀy, 1 ꢀ z; (⁰⁰⁰) x, ꢀ1 þ y, z.

solution of L³H in diethyl ether at room temperature aﬀorded

colorless crystals suitable for an X-ray crystal structure determi-

nation. L³H crystallizes in the monoclinic space group P2₁/c. Its

molecular structure is shown in Figure 1, together with selected

bond distances and angles.

The solid-state structure of L³H conﬁrms the expected

symmetrical arrangement of the side arms at the 3,5-positions

of the pyrazole backbone. As reported earlier for only a few

pyrazoles,²⁰in the crystal lattice of L³H two molecules are

arranged in NH N bridged dimeric pairs, as indicated by

3 3 3

close intermolecular donorꢀacceptor distances between the

pyrazole N atoms (N2 N1⁰⁰= 2.8994(17) Å). However, since

3 3 3

the pyrazole units in L³H are disordered, these distances should

be considered with care. The planes spanned by each of the two

pyrazole heterocyclic rings connected by hydrogen bridges are

almost parallel but not coplanar, as shown by their distance of

approximately 0.28 Å. This dimeric arrangement is rarely ob-

served, since generally more common structural motifs for

pyrazoles forming Nꢀhydrogen bridges are cyclic trimers, tetra-

mers, or catemers.^20a,21

1

Both the H and ¹³C NMR spectra of L¹H, monitored in

CDCl₃at room temperature, display only one set of signals

attributed to the ꢀCH₂N(CH₃)(2-pyridyl) side arms, thus

suggesting fast rotation around the CꢀC and CꢀN bonds of

these groups as well as a fast proton exchange due to the pyrazole

NꢀH tautomerism. A characteristic singlet at δ 6.16 ppm (¹³C

105.1 ppm) reﬂects the 4-pyrazole proton (CH) of L¹H; the

corresponding resonances of L³H appear at δ 6.33 and 103.2

Single crystals of 1 suitable for an X-ray crystal structure deter-

mination were grown by slow diﬀusion of diethyl ether into a

THF solution at þ4 °C. 1 crystallizes in the triclinic space group

P1 with two independent molecules in the asymmetric unit and

two disordered BF₄^ꢀcounterions (see the Supporting Informa-

tion). The molecular structure of one complex cation (A), whose

bond distances and angles of the chelating backbone only slightly

diﬀer from those of the second cation (B), is depicted in Figure 2.

As anticipated from the analytical results, the X-ray molecular

structure of 1 shows a binuclear, cationic copper(I) pyrazolate

complex with distorted-tetrahedral coordination of the two

metal centers, each bearing one ancillary PMe₃as a coligand.

1

ppm in the H and ¹³C NMR spectra recorded in benzene-d₆.

Also in the case of L³H and L⁴H only one set of signals related to

the considerably bulkier ꢀCH₂N(Cy)(2-pyridyl) side groups is

observed. However, line broadening of the signals of the hinge

CH₂groups and of the R-CH^Cyproton signal increases from

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Chart 2. Isomers of 1 and 2

ꢀ

Figure 3. Molecular structure of the complex cation of 2. The BF₄

counterion and hydrogen atoms have been omitted for clarity. Selected

interatomic distances (Å) and bond angles (deg): N1ꢀN2 = 1.368(4),

Cu1ꢀC1 = 1.827(4), Cu1ꢀN1 = 2.014(2), Cu1ꢀN3 = 2.232(3),

Cu1ꢀN4 = 2.042(3), Cu2ꢀC2 = 1.867(3), Cu2ꢀN2 = 1.949(3),

Cu2ꢀN5 = 2.691(3), Cu2ꢀN6 = 2.093(3), Cu1 Cu2 = 4.0552(6);

3 3 3

C1ꢀCu1ꢀN1 = 130.74(13), C1ꢀCu1ꢀN3 = 119.95(13), C1ꢀCu1ꢀ

N4 = 125.42(12), N1ꢀCu1ꢀN3 = 79.49(10), N1ꢀCu1ꢀN4 =

100.83(10), N3ꢀCu1ꢀN4 = 81.04(10), C2ꢀCu2ꢀN2 = 132.72(13),

C2ꢀCu2ꢀN5 = 137.99(13), C2ꢀCu2ꢀN6 = 108.08(13), N2ꢀCu2ꢀ

N5 = 74.97(9), N2ꢀCu2ꢀN6 = 116.78(10), N5ꢀCu2ꢀN6 = 69.35(9).

The BF₄^ꢀcounterion is found to be separated from the cationic

complex unit. The distortion of both Cu^Icenters is reﬂected by

the angles PꢀCuꢀN and NꢀCuꢀN⁰, which range from

77.31(11) to 143.69(9)° and clearly deviate from an ideal

tetrahedral angle. The CuꢀP bonds are slightly diﬀerent

(2.1499(11) and 2.1771(12) Å) but lie in the range observed

for other Cu^I(PMe₃) complexes involving chelating ligands.^22,23

Due to the anionic character of the pyrazolate bridge, the

CuꢀN^pzbonding distances are signiﬁcantly shorter (1.981(3)

and 1.983(3) Å) than those between the copper ions and the

pyridyl donor atoms (2.067(3) and 2.094(3) Å). As expected, the

aliphatic (Cy)N(CH₂) hinges that lack any back-bonding cap-

ability show even longer CuꢀN distances (2.249(3) and

2.394(3) Å). If only the three stronger donor atoms of each

binding pocket are considered, coordination of the Cu^Iions can

be described as almost trigonal, as revealed by the sums of the

corresponding binding angles at Cu1 (354.11(12)°) and Cu2

(355.80(11)°). These values are much closer to the sum of the

binding angles expected for an ideal trigonal-planar coordination

geometry (360°) than the sum of three angles of an ideal

tetrahedron (328.5°). Another Cu^Icomplex with a related

multinucleating scaﬀold and ancillary PMe₃ligands was recently

reported by our group.²³This complex of the composition

[L₂Cu₄(PMe₃)₂](PF₆) (L = (Me-imidazolyl)₂(CꢀOMe)(3,5-

pz)(CꢀOMe)(Me-imidazolyl)₂) indeed bears four Cu^Icenters

with distorted-trigonal coordination arranged in a more compli-

cated fashion than in 1, however, with very similar CuꢀP and

CuꢀN^pzbonding distances. This conﬁrms the general tendency of

Cu^Ito form complexes with coordination numbers lower than 4,

especially in these types of multinuclear complexes based on

compartmental pyrazolate scaﬀolds, which overall behave as

comparatively strong donors toward the embedded metal centers.

With respect to the plane spanned by the pyrazolate backbone,

the two PMe₃ligands in 1 are oriented to the same side of this

plane with distances P1 Pz = 1.052(1) Å and P2 Pz =

3 3 3

0.467(1) Å (Pz = plane of the pyrazolate ring).²⁴This is best

described as a cis arrangement of the ancillary phosphine ligands

and, at the opposite side of the Pz plane, also of the chelating

pyridyl side groups (Figure S3, Supporting Information).²⁵

¹H NMR spectra of 1 (recorded in benzene-d₆as well as in

THF-d₈) show one set of signals related to the chelating ꢀCH₂N-

(Cy)(2-pyridyl) side groups, as observed also for the free ligand

L³H. One additional sharp doublet at δ 1.27 ppm (²J_HP= 5.9 Hz)

in the benzene-d₆spectrum and at δ 1.28 ppm (²J_HP= 5.8 Hz) in

the spectrum recorded in THF-d₈shows the presence of two

equivalent PMe₃ligands, which suggests that the 2-fold symme-

try of the molecular structure of 1 found in the solid state is

1

retained in solution. Comparison of the H NMR benzene-d₆

spectra of L³H and 1 reveals considerable downﬁeld shifts of the

signals assigned to the 5- and 6-pyridyl protons by about 0.89 and

0.74 ppm, which can be attributed to the two coordinated Cu^I

centers. The 3-pyridyl protons and the 4-pyrazolate proton are

shifted to higher ﬁeld by around 0.98 and 0.33 ppm, whereas the

resonance signals related to the 4-pyridyl proton and the aliphatic

cyclohexyl protons show no substantial changes. The proton

signals of the hinge CH₂groups are clearly shifted and become

somewhat broadened. A similar trend of chemical shift changes

between L³H and 1 is also observed in the corresponding ¹³C

NMR spectra (see the Experimental Section). When a solution of

1 in benzene-d₆is stored at room temperature for longer times, in

1

the H NMR spectrum a remarkable high-ﬁeld shift of the

6-pyridyl proton signal of 0.14 ppm and downﬁeld shifts of

the 3- and 4-pyridyl proton signals of 0.17 and 0.14 ppm are

observed, while the remaining resonance signals show no

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signiﬁcant alterations. Since these aromatic protons may be

strongly aﬀected by conformational and electronic changes at

the coordination spheres of the two Cu^Iions, we believe that a

slow isomerization process of 1 occurs in solution, presumably

from the cis to the trans isomer (Chart 2). This interpretation is

supported by the solid-state structure of the related complex 2,

which indeed shows a trans disposition of the ancillary ligands.

Slow diﬀusion of diethyl ether into a solution of 2 in CH₂Cl₂

at þ4 °C aﬀorded light yellow crystals suitable for an X-ray

crystal structure determination. 2 was found to crystallize in the

triclinic space group P1 (like complex 1) with the cationic

complex unit, the BF₄^ꢀcounterion, and one CH₂Cl₂molecule

in the asymmetric unit. As also observed for 1, the BF₄^ꢀanion is

clearly separated from the cationic complex unit. Figure 3 shows

the binuclear complex cation, together with selected interatomic

distances and bond angles.

In agreement with the spectroscopic results, the molecular

structure of the complex cation of 2 in the solid state displays the

expected bimetallic arrangement with one ancillary tBuNC

ligand per metal ion. Similar to the case for 1, both Cu^Iatoms

are found in distorted-tetrahedral environments. Again, the sum

of the binding angles related to the more strongly binding donor

atoms C1, N1, and N4 (356.99(13)° at Cu1) as well as C2, N2,

and N6 (357.58(13)° at Cu2) reﬂects the tendency of both

cuprous ions in 2 to prefer a trigonal-planar over a tetrahedral

coordination sphere. Interestingly, the aliphatic N donors N3

and N5 of the chelating ꢀCH₂N(Me)(8-quinolyl) side groups

show very diﬀerent CuꢀN bond lengths. The interatomic

separation between N5 and Cu2 of 2.691(3) Å is quite large,

albeit below the sum of the van der Waals radii of N and Cu of

2.95 Å.²⁶In fact, one may expect a relatively weak σ-donor

strength of N3 and N5 because of the electron-withdrawing

quinolyl rings. In the case of N3, however, a remarkable close

bonding distance (Cu1ꢀN3 = 2.232(3) Å) is observed that is

equal or even shorter than the corresponding CuꢀN(Cy) bonds

in 1. This is somewhat surprising, since in the solid-state structure

Figure 4. Representation of four complex molecule cations of the

crystal structure of 2. Intermolecular πꢀπ stacking is highlighted by

the closest C C distances shown.

3 3 3

observed for the corresponding distances between the N-quinolyl

donors and the pyrazolate plane (1.859(3) and 0.593(3) Å).²⁴

The observed trans orientation of the coligands (and of the

peripheral donor groups) in 2 supports our assumption that 1

may undergo slow conversion in solution from the cis (C_s) to the

trans (C₂) isomers according to Chart 2. As indicated by the

inversion center in space group P1, both enantiomers of 2 (with

its idealized noncrystallographic C₂symmetry) are present in the

crystal lattice. These two enantiomers formally interconvert by

changing the positions of the ancillary isonitrile ligands with

respect to the chelating quinolyl side arms at both copper centers.

of the homoleptic complex [L⁶Cu]₄the Cu N distances

15

3 3 3

involving the hinge N(Me) groups are clearly out of the range of

any bonding interaction. As the ¹H and ¹³C NMR spectra (THF-

d₈at room temperature) indicate, complex 2 adopts a highly

symmetric structure in solution or is highly ﬂuxional. Therefore,

the (Me)N donor functions in the chelating side groups are

anticipated to act as hemilabile ligands, and the close Cu1ꢀN3

bonding distance is presumably forced by packing eﬀects as well

as particularly by πꢀπ stacking interactions in the crystal

structure of 2. Such stacking mainly involves the peripheral

quinolyl groups, as displayed in Figure 4. Similar πꢀπ contacts

have been reported recently also for the homoleptic Cu^Icomplex

[L⁶Cu]₄, which shows an extended network of πꢀπ stacking in

its crystal lattice.¹⁵This additional driving force seems to

dominate the orientation of these weakly coordinating, hemi-

labile side arm donor groups in the solid state.

1

As is the case for 1, the H NMR spectrum of complex 2,

monitored in THF-d₈at room temperature, shows only one set

of signals for the chelating side groups as well as for the phenyl

group attached to the pyrazolate heterocycle. Additionally, a

slightly broadened singlet at δ 1.56 ppm is assigned to the two

tBuNC coligands and shows that 2 has 2-fold symmetry on the

NMR time scale. Signiﬁcant shifts of the aromatic proton signals

(that also appear as only one set) of 2 in comparison to its free

ligand L⁶H conﬁrm that both Cu^Iions remain coordinated in

solution. For example, the quinolyl H²protons, which are the

closest atoms to the coordinating quinolyl-N donor groups, show

a downﬁeld shift of about þ0.45 ppm. In the ¹³C NMR spectrum

of 2 the corresponding quinolyl C²resonance signal is shifted by

þ4.3 ppm.

Considering the orientation of both tBuNC coligands relative

to the plane spanned by the pyrazolate backbone, the solid-state

molecular structure of 2 represents a trans isomer, in contrast to

the corresponding cis arrangement that is observed in 1 (Figures

S3 and S6, Supporting Information).

Thus, in 2 the ancillary tBuNC ligands are oriented to opposite

sides of the pyrazolate plane. Distortion of the coordination

spheres at both copper centers is considerably more pronounced

than in 1, as reﬂected by the diﬀerent distances of the isonitrile C

(1.513(4) and 0.979(4) Å) to the plane. Similar diﬀerences are

Synthesis, Properties, and X-ray Crystal Structure Deter-

minations of the Organocopper Complexes 3ꢀ8. Com-

pounds 3ꢀ8 can be obtained from the reactions of L¹HꢀL⁶H

with mesitylcopper in a molar ratio of 1:4 in THF or toluene

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Scheme 2. Synthesis of Complexes 3ꢀ8

Figure 5. Molecular structure of 5. Hydrogen atoms have been omitted

for clarity. Cu Cu contacts are represented as dashed lines.

3 3 3

Crystallography and the Supporting Information). Similarly, 6

also contains two independent complex molecules in the asym-

metric unit of the crystal lattice. Since in both 3 and 6 the

complex molecules are similar, only the data of one molecule are

discussed herein. The corresponding data for complex 4 were

previously communicated.¹¹Complexes 5 and 6 show disorder

for some of the cyclohexyl rings which are not displayed in

Figures 5 and Figures S10ꢀS13 (see the Supporting Infor-

mation), respectively. The X-ray crystal structure determination

for 7 reveals disordered noncoordinating pyridyl groups and a

disordered phenyl substituent at the pyrazolate scaﬀold embed-

ding Cu7 and Cu8 as well. This is, however, not shown in

Figure 6 (and Figure S15).

At ﬁrst glance, all organocopper complexes adopt very similar

structures. Each of them features a distorted pseudo tetrahedral

(μ₄-O)Cu^I₄core with tethered σ-mesityl bridging ligands that

are linked to two binuclear Cu^I-pyrazolato scaﬀolds in a three-

centerꢀtwo-electron bonding mode; such a bonding situation is

well-known from homoleptic σ-organocopper compounds such

as [Cu₄Mes₄], [Cu₅Mes₅], and [Cu₄(CH₂SiMe₃)₄].^6bꢀd,28Over-

all, 3ꢀ8 represent octanuclear organocopper frameworks with

two distinct sets of Cu^Icenters that are shielded by two pyra-

zolate chelating scaﬀolds. However, in the case of complex 8, the

hemilabile character of ligand L⁶leads to some remarkable struc-

tural deviations from this general motif (vide infra).

solutions at ꢀ78 °C and subsequent treatment with stoichio-

metric amounts of dioxygen at room temperature; they are

isolated as yellow to beige solids in yields of 48ꢀ87%. Excess

dioxygen results in decomposition, as evidenced by the forma-

tion of insoluble brownish solids and mesitylene. The byproducts

mesitylene and bimesityl resulting from the stoichiometric reac-

tion, which both strongly support the reaction pathway sketched

1

in Scheme 2, were identified by H NMR (in a 1:2.6 ratio of

bimesityl to mesitylene).^11,27

Elemental analyses of 3ꢀ8 conﬁrm the composition

[(L³ꢀL⁶)(Cu₄Mes₂O_0.5)]. Their ESI(þ) spectra show several

representative fragments of oligonuclear organocopper species

such as [LCu₂Mes þ1]^þfor 4¹¹or [LCu₂Mes₂Cu₂]^þ(3 and

5ꢀ7) and even [LCu₂Mes₂CuO þ1]^þin the case of 8 (see also

the Experimental Section). Complexes 3ꢀ8 are sensitive to air

and moisture both in solution and in the solid state. However,

under argon, they are stable at room temperature for several

months. All organocopper compounds are readily soluble in

THF, toluene, and C₆D₆, whereas their solubility in diethyl ether

is considerably lower. Complex 6 represents an exception, since

this compound bears six large, nonpolar substituents (two

phenyl, four cyclohexyl) and is therefore also readily soluble in

diethyl ether and even slightly in n-pentane.

Single crystals suitable for X-ray crystal structure analyses were

grown from THF (3 and 4), toluene (5, 7, and 8) or diethyl ether

(6) by slow diﬀusion of diethyl ether (3ꢀ5, 7, and 8) or n-

pentane (6) into the respective solutions at þ4 °C (3, 4, and

6ꢀ8) or ꢀ18 °C (5). The result of the structure determination

of 5 is depicted in Figure 5; selected atom distances and bond

angles of 3ꢀ8 are collected in Tables 1 and 2 (for further

information about the X-ray molecular structures of 3 and 6 see

also the Supporting Information). In the case of complex 3,

two complex molecules—one with disorder in the pyrazolate

backbone—were found in the asymmetric unit (see also X-ray

Peripheral copper ions hosted by the {N₃} binding pockets of

the pyrazolate ligands are all found in distorted-tetrahedral

environments (except for 8), even in the presence of additional

donor functions such as in complex 7. Drastic distortion of the

tetrahedral coordination sphere may arise not only from the

constraints of the binding framework of the chelating ligand but

also from contributions by cuprophilic d¹⁰

d

¹⁰contacts with

3 3 3

the central metal ions. If one considers such interactions, coor-

dination polyeders might be best described as pseudo trigonal

bipyramidal. This is conclusive by τ values ranging from 0.52 to

0.70 for 3ꢀ7, although one (in 4A) or two (in 5) coordination

polyeders are slightly closer to the square-pyramidal coordina-

tion mode (τ = 0.48ꢀ0.50, Table 3).²⁹

The situation for complex 8 is clearly diﬀerent, since only three

peripheral copper centers show pentacoordination at all. The

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Table 1. Selected Bond Lengths (Å) of 3ꢀ8

3A

4A

5

6A

7

8

Cu1ꢀN1

Cu2ꢀN2

Cu7ꢀN11

Cu8ꢀN12

Cu1ꢀN3

Cu2ꢀN5

Cu7ꢀN13

Cu8ꢀN15

Cu1ꢀN4

Cu2ꢀN6

Cu7ꢀN14

Cu8ꢀN16

Cu1ꢀC1

Cu2ꢀC2

Cu7ꢀC3

Cu8ꢀC4

Cu3ꢀC1

Cu4ꢀC2

Cu5ꢀC3

Cu6ꢀC4

Cu3ꢀO1

Cu4ꢀO1

Cu5ꢀO1

Cu6ꢀO1

1.981(9)

2.009(9)

2.026(15)

1.972(15)

2.412(9)

2.322(9)

2.374(12)

2.368(11)

2.045(9)

2.069(9)

2.121(13)

2.084(11)

2.141(11)

2.137(11)

2.171(12)

2.167(12)

1.923(11)

1.937(11)

1.934(12)

1.935(11)

1.850(7)

1.848(7)

1.853(7)

1.847(7)

1.986(5)

1.962(6)

2.018(5)

1.982(6)

2.387(5)

2.323(5)

2.370(5)

2.323(5)

2.039(5)

2.090(6)

2.082(6)

2.072(5)

2.115(7)

2.104(7)

2.157(7)

2.149(7)

1.924(7)

1.913(8)

1.918(6)

1.854(5)

1.843(5)

1.848(5)

1.860(4)

2.000(4)

1.971(4)

1.992(4)

1.989(4)

2.408(4)

2.419(4)

2.452(4)

2.411(5)

2.038(4)

2.077(4)

2.046(4)

2.056(4)

2.147(5)

2.124(5)

2.120(5)

2.155(5)

1.907(5)

1.920(5)

1.928(5)

1.909(5)

1.855(4)

1.834(4)

1.843(3)

1.853(4)

1.9998(15)

1.9944(15)

2.0079(14)

2.0142(14)

2.4751(15)

2.4529(16)

2.4224(14)

2.4774(15)

2.0294(15)

2.1167(16)

2.0619(14)

2.1012(15)

2.1223(19)

2.1462(18)

2.1737(18)

2.1361(17)

1.9072(19)

1.9265(18)

1.9152(18)

1.9187(17)

1.8426(13)

1.8355(13)

1.8372(13)

1.8413(12)

1.981(4)

1.992(4)

2.008(5)

1.969(5)

2.409(4)

2.375(3)

2.313(4)

2.321(4)

2.031(4)

2.038(4)

2.062(5)

2.073(5)

2.146(4)

2.138(4)

2.159(6)

2.150(5)

1.915(4)

1.909(5)

1.909(6)

1.933(6)

1.841(3)

1.839(3)

1.833(3)

1.829(3)

1.928(4)

2.003(4)

2.021(5)

1.892(4)

2.589(6)

2.401(4)

2.381(4)

2.711(6)

2.454(5)

2.096(5)

2.048(5)

3.034(6)

2.047(5)

2.131(6)

2.083(5)

1.984(5)

1.953(6)

1.947(6)

1.935(6)

1.968(6)

1.863(4)

1.851(4)

1.845(4)

1.863(4)

very small τ value at Cu1 is indicative of a square-pyramidal

coordination sphere, while the coordination polyeders of the

Cu2 and Cu7 ions are closer to a trigonal-bipyramidal geometry

(Figure 7). One peripheral copper ion (Cu8) is only threefold

coordinated and adopts a distorted “T-shape”, as evidenced by

the bond angles C4ꢀCu8ꢀN12 (172.1(2)°) and C4ꢀCu8ꢀ

N15 (112.3(3)°; see Table S7). The N15ꢀCu8 bond is, as

expected from the poor donor character of the N(CH₃)(quinolyl)

group, very weak if present at all (2.711(6) Å; Table 2). If the

(μ₄-O)Cu^I₄core. As the CuꢀOꢀCu bond angles reveal, these

central units deviate considerably from an ideal tetrahedral

geometry. The largest diﬀerences are found in complex 4, where

those angles vary from 94.75(19) to 124.6(3)°.¹¹Similar distor-

tion is also observed for the two (μ₄-O)Cu^I₄centers in [Cu₁₀-

O₂Mes₆],¹⁰whereas in Cu^IIcomplexes of the type [L₄Cu^II-

4

(μ-O)X₆] (L = monodentate ligand, X = halide), bearing an

isostructural core, the CuꢀOꢀCu bond angles are closer to the

value expected for an ideal tetrahedron. This may be explained by

the presence of the halide capping ligands in the Cu^IIcomplexes,

which additionally stabilize the tetrahedral coordination sphere.³⁰

Other Cu^IIcomplexes of this type, which involve a tridentate

phenolate bridging ligand instead of a monoligating donor group,

Cu6 Cu8 binding contact (2.427(1) Å) is taken into account,

3 3 3

a distorted-square-planar or tetrahedral environment is observed

for this copper center. Closer inspection of the crystal packing of

8 reveals πꢀπ interactions similar to those previously observed

for 2 and [L⁶Cu]₄, which are, however, exceptional in this case.

One noncoordinating quinolyl substituent of each complex

molecule undergoes intramolecular πꢀπ stacking with the

adjacent mesityl group that also exhibits a weak intermolecular

πꢀπ contact with one coordinating quinolyl substituent of a

second molecule of 8. Remarkably, these interactions clearly

aﬀect the N-donor abilities of the quinolyl groups, thus resulting

in very long Cu1ꢀN4 bonding distances (2.454(5) Å) and

nonbonding distances between Cu8 and N16 (3.034(6) Å).

Overall, this gives rise to a dimeric arrangement which is held

together by weak πꢀπ stacking interactions in a molecular “gear

rack” fashion (Figure 8). Again, L⁶is responsible for the unusual

structural features of 8 that originate from the combination of

πꢀπ stacking yet weakly coordinating donor side groups and the

presence of aromatic organometallic ligands that are capable of

supporting such πꢀπ contacts.

also show a considerably distorted (μ₄-O)Cu^IIunit (even

4

though less distorted than that observed in 3ꢀ8), which is

inﬂuenced by the steric constraints of the chelating ligand. As a

consequence, the CuꢀOꢀCu angles opposite to the phenolate

bridges are signiﬁcantly smaller (about 103°), whereas the

corresponding angles close to the halide bridges are substan-

tially enlarged (110.1(2)ꢀ114.6(2)°).³¹A similar observation

was made for the molecular structures of the complexes

[(μ₄-O)Cu^I₄X₂(TMTCH)₄] (X = Cl, Br; TMTCH = 3,3,6,6-

tetramethyl-1-thia-4-cycloheptyne). Herein, the two halide bridges

cause the distortion by pulling two copper centers together.³²

Although two pyrazolate capping ligands are present in 3ꢀ8,

they do not aﬀect the central (μ₄-O)Cu^I₄core in a similar way,

since the mesityl bridges act as ﬂexible “chain linkers” between

the core and the peripheral binuclear pyrazolate frameworks.

This is apparent from the bond angles Cu3ꢀO1ꢀCu4 and

Cu5ꢀO1ꢀCu6 of 3ꢀ8, which lie opposite to the pyrazolate

complex units, compared with the remaining “non-bridged”

A common structural feature and part of the general struc-

tural motif of 3ꢀ8 is represented by the pseudo tetrahedral

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Table 2. Selected Cu Cu Distances (Å) and Bond Angles (deg) of 3ꢀ8

3 3 3

3A

4A

5

6A

7

8

Cu1 Cu2

4.0000(22)

4.0418(32)

2.896(2)

2.939(2)

74.8(4)

4.0121(15)

4.0145(9)

2.9164(6)

2.9106(14)

74.5(2)

4.1671(9)

4.051(1)

3.9982(7)

4.0759(6)

2.8644(7)

2.9105(5)

75.57(7)

4.0598(7)

4.1776(10)

3.0226(7)

3.0790(7)

74.60(16)

74.29(16)

71.32(19)

71.31(19)

112.8(2)

4.0420(11)

3.783(1)

2.8322(10)

2.818(1)

75.1(2)

3 3 3

Cu7 Cu8

3 3 3

Cu3 Cu4

3.0149(9)

2.9129(9)

74.21(17)

73.85(17)

75.44(18)

73.53(17)

116.0(3)

3 3 3

Cu5 Cu6

3 3 3

Cu1ꢀC1ꢀCu3

Cu2ꢀC2ꢀCu4

Cu5ꢀC3ꢀCu7

Cu6ꢀC4ꢀCu8

Cu1ꢀC1ꢀC_p

Cu2ꢀC2ꢀC_p

Cu7ꢀC3ꢀC_p

Cu8ꢀC4ꢀC_p

Cu3ꢀC1ꢀC_p

Cu4ꢀC2ꢀC_p

Cu5ꢀC3ꢀC_p

Cu6ꢀC4ꢀC_p

C1ꢀCu3ꢀO1

C2ꢀCu4ꢀO1

C3ꢀCu5ꢀO1

C4ꢀCu6ꢀO1

Cu3ꢀO1ꢀCu4

Cu3ꢀO1ꢀCu5

Cu3ꢀO1ꢀCu6

Cu4ꢀO1ꢀCu5

Cu4ꢀO1ꢀCu6

Cu5ꢀO1ꢀCu6

72.9(4)

73.2(2)

72.19(6)

73.7(2)

72.2(4)

72.8(3)

72.44(6)

74.94(19)

75.8(2)

72.6(4)

73.3(2)

73.86(6)

113.18(44)

129.36(46)

129.49(49)

116.09(44)

171.88(52)

157.74(52)

161.28(57)

171.28(52)

177.5(4)

174.2(4)

173.2(4)

177.7(4)

103.1(4)

106.8(4)

106.7(3)

117.8(4)

116.4(4)

105.2(4)

121.46(2)

124.44(2)

127.82(1)

116.77(1)

163.88(1)

162.33(1)

165.08(1)

165.11(1)

174.0(3)

175.3(3)

175.6(2)

176.4(3)

104.2(2)

124.6(3)

94.75(19)

120.0(2)

105.2(2)

103.4(2)

116.13(8)

137.82(9)

122.64(7)

133.05(7)

168.28(9)

149.95(8)

164.87(9)

153.07(8)

173.17(7)

170.82(7)

172.39(7)

168.85(6)

102.30(6)

115.49(7)

113.99(7)

116.92(7)

103.23(6)

104.60(6)

128.8(3)

130.8(4)

128.8(3)

136.1(3)

156.2(4)

155.4(4)

157.7(3)

148.1(3)

168.2(2)

168.4(2)

170.4(2)

166.02(19)

99.40(17)

109.7(2)

100.86(18)

107.83(19)

138.4(2)

98.92(17)

117.7(3)

115.5(2)

119.7(2)

128.2(3)

120.2(2)

127.7(2)

169.7(3)

172.4(2)

168.4(3)

170.2(2)

164.9(3)

160.4(3)

166.2(3)

159.6(3)

175.92(19)

177.44(19)

172.7(2)

176.90(16)

177.01(16)

175.16(19)

173.19(18)

110.41(15)

103.71(15)

115.52(18)

111.61(18)

101.36(15)

114.46(15)

176.99(19)

109.62(17)

107.18(18)

98.13(17)

117.6(2)

118.18(19)

104.02(17)

CuꢀOꢀCu angles (Table 2). There is indeed a clear tendency of

smaller angles in the ﬁrst case for 6A (with the exception of

Cu4ꢀO1ꢀCu6) and 8, while in 3A, 4A, 5, and 7 the diﬀerences

are only small or exhibit no clear trend. Thus, the distortion of the

(μ₄-O)Cu^I₄tetrahedron seems to depend on packing eﬀects in

the crystal structures rather than on the inﬂuence of the

respective capping ligand. The CuꢀO bond distances of 3ꢀ8

are not signiﬁcantly diﬀerent from each other and lie in a range

similar to that observed for [Cu₁₀O₂Mes₆].¹⁰They are, however,

slightly shorter than in the complexes of the type [(μ₄-O)

Cu^I₄X₂(TMTCH)₄] (averaged CuꢀO bonding distances

1.908(3) Å) and also in comparison with the CuꢀO bonds of

Cu(O)ꢀC(1ꢀ4)ꢀC_pthat are related to the (μ₄-O)Cu^I₄core

(Table 2). They diﬀer in the range of about 40ꢀ50° for 3ꢀ5 and

7. Notable exceptions are complex 6 and again 8 (up to 30°).

Generally, all complexes 3ꢀ8 can thus be viewed as heteroleptic

cuprate anions [(MesCu^I)₄(μ₄-O)]^2ꢀthat are ﬂanked and

stabilized by two capping [(L¹ꢀL⁶)Cu^I₂]^þcations. This struc-

tural motif is very rare and is only known for few organocopper

compounds such as the homoleptic 8-(dimethylamino)naph-

thylcopper(I).³⁴It should also be noted that a heteroleptic cuprate

anion involving oxygen as a coligand has not been reported in the

literature so far. In principle, it might seem feasible to separate

this anionic complex part from the attached [(L¹ꢀL⁶)Cu^I₂]^þ

clamps. This was tried by employing ligand L⁵H with the

intention to obtain two separated [(L⁵)Cu^I₂]^þcations, in which

both copper centers are tetrahedrally coordinated, and the free

cuprate anion [(MesCu^I)₄(μ₄-O)]^2ꢀ. Inspiration for this ap-

proach comes from the preparation method for [(DPPE)₂-

Cu][CuMes₂], which was simply obtained by treating mesityl-

copper with DPPE in an equimolar ratio in toluene. The X-ray

structure determination indeed revealed separated [(DPPE)₂-

Cu]^þand [CuMes₂]^ꢀions.⁷Also, more complex cuprate anions

such as [Cu₅Ph₆]^ꢀand the recently reported tetrasilicide tetra-

anion [(MesCu)₂Si₄]^4ꢀare known to be stable without contact

ion pairing.^35,36As conﬁrmed by the X-ray structure analysis of 7,

however, in the solid state the two additional pyridyl side arms of

the pyrazolate ligands do not participate in coordination at all.

Attempts to separate the binuclear pyrazolate-based complex

cations from the central [(MesCu^I)₄(μ₄-O)]^2ꢀcore by slow

heating of a solution of 7 in benzene-d₆up to 70 °C, which was

cupric compounds [(μ₄-O)Cu^IIX₆L₄].^30,32This may be due to

4

the higher coordination numbers at the copper centers in those

latter complexes, since in the crystal structure of cuprite (Cu₂O),

which consists of linear OꢀCuꢀO units, short (1.848 Å) CuꢀO

bonding distances are also observed.³³The linking Cu(μ-

Mes)Cu units of all these complexes 3ꢀ8 show typical CuꢀC

bond lengths and CuꢀC_iꢀCu angles as well as Cu Cu

3 3 3

separations (Tables 1 and 2), which are also observed in the

molecular structures of the parent [Cu₁₀O₂Mes₆] and [Cu₅Mes₅].

In contrast to what is expected from these two examples, the

bridging σ-mesityl ligands in 3ꢀ8 are rather asymmetric. This is

evident from the considerably diﬀering Cu(pz)ꢀC(1ꢀ4) and

Cu(O)ꢀC(1ꢀ4) bond lengths. These diﬀerences lie in the

range of 0.2ꢀ0.3 Å for 3ꢀ7 (but less than 0.2 Å in the case of

8). Consequently, the mesityl groups lean toward the pyrazolate-

ligated, peripheral Cu^Icenters, as reﬂected by the relatively small

Cu(pz)ꢀC(1ꢀ4)ꢀC_pangles and the substantially larger angles

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Figure 7. Molecular structure of 8. Hydrogen atoms have been omitted

Figure 6. Molecular structure of 7. Hydrogen atoms have been omitted

for clarity. Cu Cu contacts are represented as dashed lines.

3 3 3

Table 3. τ Values of the {N₃}Cu(μ₂-Mes) Cu Coordina-

3 3 3

tion Polyeders of 3ꢀ8

3A

4A

5

6A

7

8

{N₃}Cu1(μ₂-Mes) Cu3 0.65 0.60 0.50 0.56 0.63 0.02

3 3 3

{N₃}Cu2(μ₂-Mes) Cu4 0.58 0.48 0.48 0.61 0.60 0.50

3 3 3

{N₃}Cu7(μ₂-Mes) Cu5 0.60 0.70 0.59 0.59 0.52 0.40

3 3 3

{N₃}Cu8(μ₂-Mes) Cu6 0.69 0.63 0.57 0.62 0.50

ꢀ

3 3 3

monitored by ¹H NMR, resulted in decomposition, as indicated

by the presence of free ligand L⁵H, a considerable amount of

mesitylene, and unknown byproduct.

¹H NMR spectra of organocopper complexes 3ꢀ6 in benzene-

d₆are very similar: All compounds show only one set of the

expected proton signals, thus supporting the presence of a

symmetric arrangement in solution on the NMR time scale

(see Table 4 and the Experimental Section). In comparison with

their free ligands L¹HꢀL⁶H, some characteristic groups show

signiﬁcant shifts, especially those that are inﬂuenced by the

coordinated metal centers, such as the pyridyl or quinolyl donor

substituents. The most striking eﬀects are the downﬁeld shifts of

the py H⁶protons by about 1.4ꢀ1.7 ppm. Similar observations

are also made for the corresponding ¹³C NMR data of 3ꢀ6. The

spectra of complexes 7 and 8 exhibit basically the same trends,

although the typical downﬁeld shift for the py H⁶and quin H²

protons, respectively, is smaller than for 3ꢀ6 (around 0.9 ppm).

7 also shows some broad resonances in the ¹H NMR spectrum

that can be related to the pyridyl side arms which are only weakly

coordinating at the Cu^Iions of the compartmental ligand

backbones or, as the molecular structure of 7 suggests, are not

Figure 8. Representation of two complex molecules of the crystal

structure of 8. Inter- and intramolecular πꢀπ stacking is highlighted

by selected close C C distances.

3 3 3

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Table 4. Selected ¹H and ¹³C NMR Data for 3ꢀ8 (298 K, Benzene-d₆)

group

3

4

5

6

7

8

¹H NMR (δ)

o-CH₃

2.60 (s)

2.20 (s)

6.78 (s)

3.32 (s)

3.15 (s)

5.95 (s)

6.39 (d)

(³J_HH= 7.7 Hz)

6.89 (dt) (⁴J_HH= 1.7,

³J_HH= 7.6 Hz)

6.74ꢀ6.76 (m)

9.89 (d)

2.60 (s)

2.25 (s)

6.83 (s)

3.49 (s)

2.97 (s)

ꢀ

2.57 (s)

2.60 (s)

2.28 (s)

6.85(s)

3.74 (s)

3.29 (s)

ꢀ

2.72 (s)

2.22 (s)

6.88(s)

3.90 (s)

3.52 (s)

ꢀ

2.52 (s)

2.08 (s)

6.48 (s)

4.16 (s)

p-CH₃

m-Mes

pz CH₂

py CH₂

pz H⁴

2.25 (s)

6.79 (s)

3.44, 3.54 (s)

5.98 (s)

ꢀ

py H³

6.31 (d)

6.38ꢀ6.40 (m)

6.29ꢀ6.31 (m)

6.61 (d)

(³J_HH= 7.6 Hz)

6.89 (dt) (⁴J_HH= 1.7,

³J_HH= 7.6 Hz)

6.77ꢀ6.80 (m)

10.07 (d)

(³J_HH= 7.7 Hz)

6.92 (dt) (⁴J_HH= 1.8,

³J_HH= 7.6 Hz)

py H⁴/quin H⁴

6.90ꢀ6.95 (m)

6.91ꢀ6.96 (m)

7.43 (dd) (⁴J_HH= 1.2,

³J_HH= 8.3 Hz)

py H⁵/quin H³

py H⁶/quin H²

6.90ꢀ6.95 (m)

9.98ꢀ9.99 (m)

6.91ꢀ6.96 (m)

10.05ꢀ10.06 (m)

6.67ꢀ6.72 (m)

9.23ꢀ9.25 (m)

6.72ꢀ6.76 (m)

9.27ꢀ9.28 (m)

(³J_HH= 4.4 Hz)

(³J_HH= 4.3 Hz)

¹³C NMR (δ)

29.6

o-CH₃

29.6

29.7

29.8

21.5

124.6

57.3

p-CH₃

21.5

21.6

21.7

21.5

m-Mes

124.4

56.2

124.4

55.6

124.7

124.8

50.7

124.8

51.2

pz CH₂

51.5, 54.8

97.8

py CH₂

pz C⁴

py C³

py C⁴/quin C⁴

py C⁵/quin C³

py C⁶/quin C²

61.2

61.1

54.6

57.2

97.7

115.2

122.2

135.8

123.1

152.3

115.4

121.5

136.0

122.7

151.8

115.6

123.6

135.7

122.4

150.8

115.0

122.3

135.8

123.0

147.1

121.6

135.9

135.7

122.7

119.5 or 122.0

150.1

151.7

involved in coordination at all. Extreme line broadening prevents

detection of a complete signal set of one of those groups or an

exact assignment of corresponding single resonance signals (see

the Experimental Section). It might be expected that elevated

temperatures should result in a higher population of noncoordi-

nating pyridyl side groups in solution, which would also lead to

decreasing line broadening of the corresponding ¹H NMR

resonances. As already mentioned, under these conditions,

however, only decomposition of complex 7 could be observed.

Complex 8 represents again an exception from this series of

organocopper frameworks, since a minor product (or a mixture

of diﬀerent species) is observed both in the ¹H and the ¹³C NMR

spectra. The overall amount of this (these) side product(s) lie(s)

in the range of about 5ꢀ10%, related to the major species. Since

the additional resonance signals were observed in spectra from

diﬀerent samples obtained under altered conditions—even from

single-crystal material—and since no free pyrazolate ligand is

observed, simple decomposition of 8 in solution can be ruled out.

Due to the fact that the intensities of the additional signals are

very low, at this stage the identity of this (these) minor species

remain(s) unknown. It seems likely, however, that the hemilabile

character of L⁶is responsible for the formation of diﬀerent

isomers of 8, which diﬀer only by the number of CH₂N(CH₃)(8-

quinolyl) side arms that are either coordinating or dangling. This

is supported not only by the known ﬂuxional behavior of these

side groups¹⁵but also by the unusual structural characteristics of

8 in the solid state (vide supra).

exhibit different stereochemical arrangements in the solid state

which can be viewed as cis/trans isomers, if the position of the

ancillary ligands PMe₃and tBuNC relative to the plane defined

by the central pyrazolate heterocycle is considered (Figures S3

and S6, Supporting Information). This can also be analyzed for

the binuclear Cu^Ipyrazolate scaffolds of the organocopper

species 3ꢀ8. The most informative examples are 5 and 8, since

these complexes can be directly compared with their binuclear

counterparts 1 and 2, which contain the same pyrazolate com-

partmental ligands. In all examples with the exception of 8, the

positions of the ipso carbon atoms of the two mesityl bridges at

each binuclear complex unit relative to the pyrazolate plane

confirm a trans orientation of both σ-organo ligands (shown for

5 in Figure S11).

Such a trans orientation of the σ-mesityl ligands is observed at

both binuclear Cu^Ipyrazolate units within each complex, which

represent a pair of the two enantiomers trans and trans⁰. This

arrangement is determined by the pseudotetrahedral (μ₄-O)Cu^I₄

cluster, which obviously allows no structural alternatives that

could provide less steric hindrance. In the solid-state molecular

structure of complex 8 only one binuclear cap of the molecule

exhibits the trans conﬁguration of the σ-mesityl groups (the

alternative trans⁰form is shown in Figure S17). As a result of

extended πꢀπ-stacking interactions and the hemilabile charac-

ter of the quinolyl groups, one such group does not coordinate at

the second L⁶Cu₂cap and therefore no cis/trans isomerism is

observed there.

More striking is a comparison of the structural features

regarding the cuprocuprate character of 3ꢀ8 with those of their

Structural Features of 1 and 2 Compared with Those of 5

and 8. As described above, the binuclear Cu^Icomplexes 1 and 2

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ARTICLE

related binuclear complexes. For example, if both the mono-

formally substituted by [(MesCu^I)₄(μ₄-O)]^2ꢀ, the organocop-

per complexes 5 and 8 are obtained (Scheme 3).

dentate coligands and the anionic counterion BF₄^ꢀof 1 or 2 are

Thus, the complex cations [L³Cu^I₂]^þand [L⁶Cu^I₂]^þ, which

are isolable as their ionic complexes 1 and 2, are clearly suppor-

tive of the cuprate features particularly of 5 and 8, but also

generally for the complete series 3ꢀ8 of this type of organo-

copper complexes that follow a common structural motif.

Reaction of Complex 4 with Dimethyl Acetylenedicarbox-

ylate (DMADC). The structural characteristics of 3ꢀ8 give rise to

the question whether these complexes would undergo transfor-

mations typical for organocuprates. It has been earlier demon-

strated by van Koten et al. that 8-(dimethylamino)naphthyl-

copper(I) exhibits remarkable cuprate features, since its reaction

with the activated alkyne DMADC results in the syn-addition

product Me₂N(naphtyl)C(CO₂Me)dC(CO₂Me)H after hydro-

lysis.³⁴This is quite unusual, since typically only lithium and

magnesium cuprates show similar reactivity. Complex 4 was thus

chosen as a representative example and was reacted with an

excess (8 equiv) of DMADC, as outlined in Scheme 4.

Scheme 3. Structural Relation between 1 and 5 as well as 2

and 8

After workup, a viscous yellow oil was obtained and was

analyzed by ¹H NMR spectroscopy as a mixture of the addition

product 9 (1.2 equiv) and the liberated pyrazole ligand L²H

(1 equiv), as well as traces of unidentiﬁed byproduct. 9 is

1

characterized by two singlets in the H NMR spectrum in d₆-

benzene at δ 2.05 and 2.33 ppm for the mesityl CH₃protons, two

OCH₃signals at δ 3.33 and 3.41 ppm, the oleﬁnic proton

resonance at δ 5.77 ppm, and a multiplet between δ 6.69 and 6.70

ppm for the mesityl CH groups. Its presence is also conﬁrmed by an

EI mass spectrum of the product mixture, which shows fragments of 9

as well as its molecular ion peak at m/z 262. This shows that 4 (and

presumably all other complexes 3ꢀ8) can transfer a σ-mesityl group

onto activated alkynes. The considerable amount of L²Hsuggeststhat

the original complex framework of 4 is completely degraded during

this reaction, at least in the organic phase after hydrolytic workup.

’ CONCLUSIONS

In conclusion, we have elaborated a convenient method to

synthesize the two new Cu^Icomplexes 1 and 2 with pyrazolate-based

Scheme 4. Reaction of Complex 4 with DMADC

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compartmental ligands. Together with the X-ray crystal struc-

ture determination of such a ligand system bearing {N₂} side

arms, 1 and 2 have been presented as the ﬁrst examples of

binuclear Cu^Ipyrazolates of the type [LCu^I₂]X. In solution

these complexes interconvert between diﬀerent isomers,

and in the case of 2 remarkable structural features originate

from the hemilabile character of the ꢀCH₂N(Me)(8-quinolyl)

side groups and their capability to undergo πꢀπ stacking

interactions.

L⁶H,¹⁵and 4¹¹were described previously. Mesitylcopper was synthe-

sized according to a known procedure.^6c

Elemental analyses were performed by the Analytical Laboratory of the

Institute for Inorganic Chemistry at the University of G€ottingen

(Elementar Vario EL III). Melting points for L³H and L⁴H were

determined with an SRS (Stanford Research Systems) Opti Melt instru-

ment; values are uncorrected. NMR measurements were performed at 300

K on a Bruker AC 200 at 200.13 MHz (¹H) and 50.33 MHz (¹³C), a

Bruker Avance 300 at 300.13 MHz (¹H) and 75.47 MHz (¹³C), and a

Bruker Avance 500 at 500.13 (¹H), 125.77 (¹³C), and 202.46 MHz (³¹P),

respectively. ¹³C NMR resonances were obtained with proton broad-band

decoupling and referenced to the solvent signals of benzene-d₆at 128.0

ppm, THF-d₈at 25.3 ppm, and chloroform at 77.0 ppm (¹H NMR residual

nondeuterated and partially deuterated solvent signals, 7.15 (benzene-d₆),

1.73 (THF-d₈), and 7.24 ppm (CDCl₃), respectively). Most assignments

are based on H,H and C,H correlation experiments. EI-MS spectra were

recorded on a Finnigan MAT 8200 instrument and ESI-MS spectra on an

Applied Biosystems API 2000 as well as on a Thermo Finnigan Ion Trap

LCQ spectrometer. ESI-HRMS, performed by using a Bruker FTICR

APEX IV instrument, was applied for compounds whose accurate ele-

mental analyses were diﬃcult to obtain or as supplemental data.

Second, it could be shown that L¹HꢀL⁶H, 4 equiv of

1

mesitylcopper and

/ equiv of dioxygen form a series of

4

unusually stable organocopper assemblies 3ꢀ8 of general compo-

sition [(L¹ꢀL⁶)Cu^I₂(μ₂-MesCu^I)₂(μ₄-O)(μ₂-MesCu^I)₂(L¹ꢀL⁶)

Cu^I₂], all with the same basic structural motif. Structural details

of the peripheral {(L¹ꢀL⁶)Cu^I₂} fragments of 3ꢀ8 are closely

related to those of complexes 1 and 2. Indeed, the observation of

diﬀering CuꢀC_ipsobonding distances within the organocopper

core of 3ꢀ8 is strong evidence for a cuprocuprate arrangement

consisting of two [(L¹ꢀL⁶)Cu^I₂]^þcations that serve as capping

(thus stabilizing) units for the complex heteroleptic O-centered

cuprate anion [(MesCu^I)₄(μ₄-O)]^2ꢀ. Subtle diﬀerences in the

solid-state structures of 3ꢀ8 are induced by the diﬀerent chelate

arms of the peripheral ligand scaﬀolds L¹ꢀL⁶, and intriguing

L¹H.⁴¹A suspension of anhydrous Na₂CO₃(3.973 g, 37.48 mmol),

3,5-bis(chloromethyl)-1-(tetrahydropyran-2-yl)pyrazole (0.935 g, 3.75 mmol),

and N-(2-picolyl)methylamine (0.919 g, 7.52 mmol) in acetonitrile

(80 mL) was heated to reflux for 36 h, then cooled to room temperature

and subsequently filtered. Evaporation of the solvent gave an oily orange

residue that was treated dropwise with ethanolic HCl

(40 wt %, 6 mL) and diethyl ether (50 mL). The resulting suspension

was stirred for 2 h. The precipitate was separated by filtration, washed

with diethyl ether (6 ꢁ 60 mL), and dried in vacuo for 1 h. After addition

of aqueous KOH (pH 12, 80 mL) the product was extracted with

CH₂Cl₂(5 ꢁ 40 mL). The combined organic phases were dried with

MgSO₄. Filtration and evaporation of the solvent afforded a golden

viscous oil which was dried in vacuo overnight. Yield: 0.973 g

structural relations between the cap groups [(L¹ꢀL⁶)Cu ]^þand

2

the analogous complexes 1 and 2 are apparent; these features are

strongly inﬂuenced by the hemilabile nature of the quinolyl side

arms and their ability to undergo extended πꢀπ stacking inter-

actions in the solid state.

Finally, as demonstrated in the case of 4, these organocopper

assemblies show unusual reactivity toward activated alkynes such

as DMADC. Their σ-mesityl groups are predominantly trans-

ferred to the activated alkyne, resulting in the addition product 9,

which is believed to be formed via a syn addition.

1

(2.89 mmol, 77%). H NMR (300.13 MHz, CDCl₃): δ 2.28 (s, 6 H,

Interesting chemistry obviously arises from the combination

of established organometallic synthons and compartmental ligand

scaﬀolds originally developed for biomimetic/bioinspired metal

complexes. To explore other useful transformations with the

versatile cuprate frameworks reported here and to generate other

oligonuclear copper species by activating small molecules apart

from dioxygen are of ongoing interest in our current and future

research projects.

CH₃), 3.63, 3.66 (2 ꢁ s, 8 H, py and pz CH₂), 6.16 (s, 1 H, pz H⁴), 7.15

(ddd, ⁴J_HH= 1.1 Hz, ³J_HH= 4.9 Hz, ³J_HH= 7.5 Hz, 2 H, py H⁵), 7.40 (d,

³J_HH= 7.8 Hz, 2 H, py H³), 7.63 (dt, ⁴J_HH= 1.8 Hz, ³J_HH= 7.7 Hz, 2 H,

py H⁴), 8.54 (ddd, ⁵J_HH= 0.9 Hz, ⁴J_HH= 1.7 Hz, ³J_HH= 4.9 Hz, 2 H, py

H⁶). ¹³C NMR (125.77 MHz, CDCl₃): δ 42.5 (CH₃), 52.9 (broad), 62.2

(CH₂), 105.1 (CH, pz C⁴), 122.1 (CH, py C⁵), 123.6 (CH, py C³), 136.5

(CH, py C⁴), ∼145.0 (br, C, pz C^3,5), 149.0 (CH, py C⁶), 158.7 (C, py

C²). MS (ESI(þ) in MeOH): m/z (relative intensity) 337.21 (100)

[M þ H]^þ. HRMS (ESI(þ) in MeOH): m/z calcd for C₁₉H₂₅N₆

[M þ H]^þ337.214 07, found 337.213 53.

L³H. This compound was prepared according to the method des-

cribed for L¹H by the use of Na₂CO₃(5.560 g, 52.46 mmol), 3,5-

bis(chloromethyl)-1-(tetrahydropyran-2-yl)pyrazole (1.310 g, 5.26 mmol),

and N-(2-picolyl)cyclohexylamine (2.000 g, 10.51 mmol), which were

heated in solution to reflux for 48 h. The crude product was purified by

column chromatography (basic alumina, 1:0 to 10:1 v/v ethyl acetate/

methanol). A colorless solid was obtained and dried in vacuo for 24 h.

Yield: 1.172 g (2.48 mmol, 47%). Mp: 112 °C. Anal. Calcd for

C₂₉H₄₀N₆: C, 73.69; H, 8.53; N, 17.78. Found: C, 73.08; H, 8.80; N,

17.45. ¹H NMR (300.13 MHz, C₆D₆): δ 0.83ꢀ1.20 (m, 10 H, cy

H^2aꢀ4a), 1.39ꢀ1.44 (m, 2 H, cy H^4e), 1.57ꢀ1.61 (m, 4 H, cy H^3e),

1.80ꢀ1.84 (m, 4 H, cy H^2e), 2.53ꢀ2.62 (m, 2 H, cy H¹), 3.81, 3.91 (2 ꢁ

s, 8 H, py and pz CH₂), 6.33 (s, 1 H, pz H⁴), 6.61 (ddd, ⁴J_HH= 1.1 Hz,

’ EXPERIMENTAL SECTION

General Procedures. All manipulations involving Cu^Icompounds

were carried out by using Schlenk techniques under an atmosphere of

dry argon. Glassware and NMR tubes were heat-sealed with a heat gun

under vacuum. Prior to use, tetrahydrofuran (THF), diethyl ether,

toluene, and pentane were freshly distilled from sodium/benzophenone.

Benzene-d₆and tetrahydrofuran-d₈were distilled from sodium. Dichloro-

methane was dried over calcium hydride and distilled. Acetonitrile and

propionitrile were dried over phosphorus pentoxide and distilled.

Ethanol was dried according to the established method via sodium/

diethyl phthalate.³⁷KOtBu (Acros), NaN(SiMe₃)₂(2 M solution in

THF, Alfa Aesar), tBuNC (Aldrich), PMe₃(1 M in THF, Aldrich),

N-(2-picolyl)cyclohexylamine (ABCR), and dimethyl acetylenedicar-

boxylate (DMADC, Aldrich) were used as purchased. [Cu(CH₃CN)₄]

BF₄,³⁸N-(2-picolyl)methylamine,^11,39and N-bis(2-picolyl)amine⁴⁰were

prepared according to the literature procedures. The syntheses of

3,5-bis(chloromethyl)-1-(tetrahydropyran-2-yl)pyrazole,^18,20b3,5-bis-

(chloromethyl)-1-(tetrahydropyran-2-yl)-4-phenylpyrazole,¹¹L²H,¹¹

3

³J_HH= 4.9 Hz, J_HH= 7.4 Hz, py H⁵), 7.10ꢀ7.14 (m, 2 H, py H⁴),

∼7.39ꢀ7.42 (m, broad, 2 H, py H³), 8.39ꢀ8.41 (m, 2 H, py H⁶). ¹H

NMR (500.13 MHz, THF-d₈): δ 1.03ꢀ1.18 (m, 6 H, cy H^3a,4a), 1.30

2a

(dq, ³J_HaHe= 2.8 Hz, ²J_HaHe, ³J_HaHa= 11.9 Hz, 4 H, cy H ), 1.54ꢀ1.56

0

(m, 2 H, cy H^4e), 1.71ꢀ1.72 (m, 4 H, cy H^3e), 1.84ꢀ1.87 (m, 4 H, cy

H^2e), 2.50 (tt, ³J_HaHa= 3.4 Hz, ³J_HaHa'= 11.5 Hz, 2 H, cy H¹), 3.68, 3.78

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(2 ꢁ s, 8 H, py and pz CH₂), 6.11 (s, 1 H, pz H⁴), 7.05 (ddd, ⁴J_HH

=

L⁶H.¹⁵¹H NMR (500.13 MHz, C₆D₆): δ 2.84 (s, broad, 6 H, CH₃),

4.82 (s, broad, 4 H, CH₂), 6.73 (dd, ³J_HH= 4.1 Hz, ³J_HH= 8.2 Hz, 2 H,

quin H³), 6.81 (d, broad, ³J_HH= 7.2 Hz, 2 H, quin H⁷), 6.91ꢀ6.94 (m,

1.6 Hz, ³J_HH= 4.8 Hz, ³J_HH= 6.7 Hz, 2 H, py H⁵), 7.53ꢀ7.58 (m, 4 H, py

H

^3,4), 8.39ꢀ8.40 (m, 2 H, py H⁶). ¹³C NMR (75.47 MHz, C₆D₆):

δ 26.3 (CH₂, cy C³), 26.5 (CH₂, cy C⁴), 29.4 (CH₂, cy C²), 47.6

(broad), 56.3 (py and pz CH₂), 60.0 (CH, cy C¹), 103.2 (CH, pz C⁴),

121.6 (CH, py C⁵), 122.6 (CH, py C³), 136.0 (CH, py C⁴), 149.1 (CH,

py C⁶), 162.2 (C, py C²). The signal of pz C^3,5is too broad to be

detected. ¹³C NMR (125.77 MHz, THF-d₈): δ 27.0 (CH₂, cy C³), 27.3

(CH₂, cy C⁴), 29.8 (CH₂, cy C²), 47.8 (broad), 56.7 (py and pz CH₂),

60.3 (CH, cy C¹), 103.9 (CH, pz C⁴), 122.1 (CH, py C⁵), 123.0 (CH, py

C³), 136.6 (CH, py C⁴), ∼147 (br, C, pz C^3,5), 149.4 (CH, py C⁶), 162.8

(C, py C²). MS (EI): m/z (relative intensity) 472 (1) [M]^þ, 380 (100)

[M ꢀ (C₆H₆N)]^þ, 284 (19) [M ꢀ (C₆H₆N)(C₆H₁₁N) þ H]^þ, 283

(14) [Mꢀ (C₆H₆N)(C₆H₁₁N)]^þ, 191 (32) [M ꢀ (C₆H₆N)(C₆H₁₁N) ꢀ

(C₆H₆N)]^þ, 93 (21) [C₆H₇N]^þ. HRMS (ESI(þ) in MeOH): m/z

calcd for C₂₉H₄₁N₆[M þ H]^þ473.339 27, found 473.339 07.

1 H, p-Ph), 6.96ꢀ7.00 (m, 2 H, m-Ph), 7.02 (dd, ⁴J_HH= 1.2 Hz, ³J_HH

=

8.1 Hz, 2 H, quin H⁵), 7.12ꢀ7.15 (m, overlaid by the benzene signal,

2 H, quin H⁶), 7.25ꢀ7.27 (m, 2 H, o-Ph), 7.52 (dd, ⁴J_HH= 1.8 Hz, ³J_HH

= 8.3 Hz, 2 H, quin H⁴), ∼8.41 (m, broad, 2 H, quin H²). ¹³C NMR

(125.77 MHz, C₆D₆): δ 40.1 (broad, CH₃), 51.6 (CH₂), 116.2 (CH,

quin C⁷), 120.0 (CH, quin C⁵), 120.7 (C, pz C⁴), 120.7 (CH, quin C³),

126.1 (CH, p-Ph), 126.9 (CH, quin C⁶), ∼128.0 (CH, overlaid by

benzene signal, m-Ph), 130.0 (C, quin C^4a), 130.3 (CH, o-Ph), 133.9

(C, i-Ph), 136.3 (CH, quin C⁴), 143.1 (C, quin C^8a), 147.3 (CH, quin

C²), 149.5 (C, quin C⁸). The signal of pz C^3,5is too broad to be

detected.

1. A solution of L³H (199 mg, 0.42 mmol) in THF (10 mL) was

treated dropwise with a 2 M solution of Na(N(SiMe₃)₂) in THF

(0.21 mL, 0.42 mmol). After it was stirred for 5 min, this solution was

added to a suspension of [Cu(CH₃CN)₄]BF₄(264 mg, 0.84 mmol) in

THF (20 mL). After this mixture was stirred for 22 h, a 1 M solution of

PMe₃in THF (0.84 mL, 0.84 mmol) was added. The suspension was

stirred for 6 days, then filtered over Kieselgur, and the resulting clear

yellow to orange solution was concentrated in vacuo to 5 mL. Slow

diffusion of diethyl ether (15 mL) into the solution at 4 °C over the

course of 11 days afforded small pale yellow crystals. The orange

solution was decanted, and the crystalline solid was washed with cold

diethyl ether and then dried in vacuo for 18 h. Yield: 150 mg (0.18 mmol,

43%). Anal. Calcd for C₃₅H₅₇N₆P₂Cu₂BF₄: C, 50.18; H, 6.86; N, 10.03.

L⁴H. This compound was prepared according to the method

described for L¹H by the use of Na₂CO₃(5.315 g, 50.15 mmol), 3,5-

bis(chloromethyl)-1-(tetrahydropyran-2-yl)-4-phenylpyrazole (1.608 g,

4.94 mmol), and N-(2-picolyl)cyclohexylamine (1.885 g, 9.91 mmol),

which were heated in solution to reflux for 90 h. Recrystallization from

diethyl ether and drying in vacuo for 15 h gave a beige powder. Yield:

1.010 g (1.84 mmol, 37%). Mp: 127 °C. Anal. Calcd for C₃₅H₄₄N₆: C,

76.60; H, 8.08; N, 15.31. Found: C, 75.93; H, 8.13; N, 15.00. ¹H NMR

(500.13 MHz, C₆D₆): δ 0.81ꢀ0.88 (m, 2 H, cy H^4a), 0.92ꢀ1.12 (m,

8 H, cy H^3a,2a), 1.39 (d, J_HH= 12.3 Hz, 2 H, cy H^4e), 1.54 (d, J_HH

=

12.3 Hz, 2 H, cy H^3e), ∼1.71ꢀ1.72 (m, broad, 4 H, cy H^2e),

∼2.50ꢀ2.55 (m, broad, 2 H, cy H¹), 3.92 (broad), 3.94 (2 ꢁ s, 8 H,

py and pz CH₂), 6.56 (dd, ³J_HH= 4.9 Hz, ³J_HH= 8.2 Hz, 2H, py H⁵), 7.04

(t, ³J_HH= 6.4 Hz, 2 H, py H⁴), ∼7.15 (m, broad, overlaid by the benzene

signal, 2 H, py H³), 7.15ꢀ7.19 (m, overlaid by the benzene signal, 1 H,

p-Ph), 7.29ꢀ7.33 (m, 2 H, m-Ph), 7.61ꢀ7.63 (m, 2 H, o-Ph), 8.36ꢀ8.37

(m, 2 H, py H⁶). ¹³C NMR (125.77 MHz, C₆D₆): δ 26.4 (CH₂, cy C³),

26.5 (CH₂, cy C⁴), 29.2 (CH₂, cy C²), 46.8 (broad), 56.2 (py and pz

CH₂), 60.5 (CH, cy C¹), 118.7 (C, pz C⁴), 121.5 (CH, py C⁵), 122.7

(CH, py C³), 126.3 (CH, p-Ph), 128.5 (CH, m-Ph), 130.3 (CH, o-Ph),

135.2 (C, i-Ph), 135.9 (CH, py C⁴), 149.1 (CH, py C⁶), 162.1 (C, py C²).

The signal of pz C^3,5is too broad to be detected. MS (EI): m/z (relative

intensity) 548 (1) [M]^þ, 456 (100) [M ꢀ (C₆H₆N)]^þ, 360 (24) [M ꢀ

(C₆H₆N)(C₆H₁₁N) þ H]^þ, 359 (17) [M ꢀ (C₆H₆N)(C₆H₁₁N)]^þ, 267

(12) [Mꢀ (C₆H₆N)(C₆H₁₁N) ꢀ (C₆H₆N)]^þ, 266 (51) [M ꢀ (C₆H₆N)

(C₆H₁₁N) ꢀ (C₆H₆N) ꢀ H]^þ, 191 (25) [M ꢀ (C₆H₆N)(C₆H₁₁N) ꢀ

(C₆H₆N) ꢀ (C₆H₅) þ H]^þ, 93 (31) [C₆H₇N]^þ. HRMS (ESI(þ) in

MeOH): m/zcalcd for C₃₅H₄₅N₆[Mþ H]^þ549.370 57, found 549.370 13.

L⁵H. This compound was prepared according to the method des-

cribed for L¹H by the use of Na₂CO₃(4.410 g, 41.61 mmol), 3,5-

bis(chloromethyl)-1-(tetrahydropyran-2-yl)-4-phenylpyrazole (1.350 g,

4.15 mmol), and N-bis(2-picolyl)amine (1.650 g, 8.28 mmol), which

were heated in solution to reflux for 48 h. The resulting oily residue was

dried in vacuo (5 ꢁ 10^ꢀ4mbar, 100 °C). A beige to brownish resin was

1

Found: C, 49.74; H, 6.98; N, 9.78. H NMR (500.13 MHz, C₆D₆):

δ 0.77ꢀ1.02 (m, 10 H, cy H^2aꢀ4a), 1.27 (d, ²J_HP= 5.9 Hz, 18 H, PMe₃),

1.38ꢀ1.42 (m, 2 H, cy H^4e), 1.48ꢀ1.50 (m, 4 H, cy H^3e), 1.72ꢀ1.75 (m,

4 H, cy H^2e), 2.41ꢀ2.45 (m, 2 H, cy H¹), 3.37, 3.65 (2 ꢁ s, broad, 8 H, py

and pz CH₂), 6.00 (s, 1 H, pz H⁴), 6.43 (d, ³J_HH= 7.8 Hz, 2 H, py H³),

7.12ꢀ7.15 (m, overlaid by the benzene signal, 2 H, py H⁴), 7.49ꢀ7.51 (m,

2 H, py H⁵), 9.14 (d, ³J_HH= 4.8 Hz, 2 H, py H⁶). ¹H NMR (after 8 weeks,

500.13 MHz, C₆D₆): δ 0.80ꢀ1.07 (m, 10 H, cy H^2aꢀ4a), 1.26 (d, ²J_HP

=

5.8 Hz, 18 H, PMe₃), 1.37ꢀ1.42 (m, 2 H, cy H^4e), 1.50ꢀ1.52 (m, 4 H, cy

H^3e), 1.76ꢀ1.78 (m, 4 H, cy H^2e), 2.43ꢀ2.48 (m, 2 H, cy H¹), 3.43, 3.65

(2 ꢁ s, broad, 8 H, py and pz CH₂), 5.98 (s, 1 H, pz H⁴), 6.60 (d, ³J_HH

=

7.7 Hz, 2 H, py H³), 7.27 (t, ³J_HH= 7.4 Hz, 2 H, pyH⁴), 7.49ꢀ7.52 (m, 2 H,

py H⁵), 9.00ꢀ9.01 (m, 2 H, py H⁶). ¹H NMR (500.13 MHz, THF-d₈):

δ 1.05ꢀ1.41 (m, 10 H, cy H^2aꢀ4a), 1.28 (d, ²J_HP= 5.8 Hz, 18 H, PMe₃),

1.57ꢀ1.60 (m, 2 H, cy H^4e), 1.73ꢀ1.76 (m, overlaid by the THF signal,

4 H, cy H^3e), 2.00ꢀ2.03 (m, 4 H, cy H^2e), 2.67ꢀ2.72 (m, 2 H, cy H¹), 3.77,

3.83 (2 ꢁ s, broad, 8 H, py and pz CH₂), 5.71 (s, 1 H, pz H⁴), 7.29 (d, ³J_HH

= 7.5 Hz, 2 H, py H³), 7.38ꢀ7.41 (m, 2 H, py H⁵), 7.72 (t, ³J_HH= 7.4 Hz, 2

H, py H⁴), 8.66ꢀ8.67 (m, 2 H, py H⁶). ¹³C NMR (125.77 MHz, C₆D₆): δ

16.5 (d, ¹J_CP= 20.9 Hz, CH₃, PMe₃), 26.0 (CH₂, cyC³), 26.2 (CH₂, cyC⁴),

29.9 (broad, CH₂, cy C²), 52.5, 55.2 (py and pz CH₂), 64.4 (CH, cy C¹),

98.3 (CH, pz C⁴), 121.7 (CH, py C³), 124.6 (CH, py C⁵), 137.2 (CH, py

C⁴), 149.2 (C, pz C^3,5), 151.2 (CH, py C⁶), 158.5 (C, py C²). ¹³C NMR

(after 8 weeks, 125.77 MHz, C₆D₆):δ16.5 (d, ¹J_CP= 20.7 Hz, CH₃, PMe₃),

26.1 (CH₂, cy C³), 26.2 (CH₂, cy C⁴), 29.7 (broad, CH₂, cy C²), 52.3, 55.4

(py and pz CH₂), 64.4 (CH, cy C¹), 98.3 (CH, pz C⁴), 122.2 (CH, py C³),

124.6 (CH, py C⁵), 137.5 (CH, py C⁴), 149.3 (C, pz C^3,5), 150.8 (CH, py

1

obtained. Yield: 1.354 g (2.39 mmol, 58%). H NMR (500.13 MHz,

C₆D₆): δ 3.91 (s, broad, 12 H, CH₂), 6.55 (ddd, ⁴J_HH= 0.9 Hz, ³J_HH

=

4.9 Hz, ³J_HH= 7.4 Hz, 4 H, py H⁵), 7.02 (dt, ⁴J_HH= 1.5 Hz, ³J_HH= 7.6

Hz, 4 H, py H⁴), 7.11ꢀ7.14 (m, 1 H, p-Ph), 7.18ꢀ7.21 (m and overlaid

broad band, 6 H, py H³, m-Ph), 7.45ꢀ7.48 (m, 2 H, o-Ph), 8.35 (d,

³J_HH= 4.3 Hz, 4 H, py H⁶). ¹³C NMR (125.77 MHz, C₆D₆): δ 49.7

(broad), 59.8 (CH₂), 120.0 (C, pz C⁴), 121.7 (CH, py C⁵), 123.4 (CH,

py C³), 126.2 (CH, p-Ph), 128.5 (CH, m-Ph), 130.3 (CH, o-Ph), 134.6

(C, i-Ph), 135.9 (CH, py C⁴), 149.2 (CH, py C⁶), 159.8 (C, py C²). The

signal of pz C^3,5is too broad to be detected. MS (EI): m/z (relative

intensity) 566.3 (1) [M]^þ, 474.2 (37) [M ꢀ (C₆H₆N)]^þ, 369.1 (12)

[M ꢀ (C₁₂H₁₂N₃) þ H]^þ, 275.0 (12) [M ꢀ (C₁₂H₁₂N₃) ꢀ (C₆H₆N) ꢀ

H]^þ, 92.9 (100) [C₆H₇N]^þ. HRMS (ESI(þ) in MeOH): m/z calcd for

C₃₅H₃₅N₈[M þ H]^þ567.298 47, found 567.298 08.

C⁶), 158.7 (C, py C²). ¹³C NMR (125.77 MHz, THF-d₈): δ 16.7 (d, ¹J_CP

=

20.4 Hz, CH₃, PMe₃), 26.8 (CH₂, cy C³), 26.9 (CH₂, cy C⁴), 30.5 (broad,

CH₂, cy C²), 52.6, 56.1 (py and pz CH₂), 65.2 (CH, cy C¹), 98.4 (CH, pz

C⁴), 123.3 (CH, py C³), 124.5 (CH, py C⁵), 138.3 (CH, py C⁴), 149.8 (C,

pz C^3,5), 150.7 (CH, py C⁶), 160.3 (C, py C²). ³¹P NMR (202.46 MHz,

C₆D₆): δ ꢀ51.1 (s). ³¹P NMR (202.46 MHz, THF-d₈): δ ꢀ50.9 (s). MS

(ESI(þ) in CH₃CN): m/z (relative intensity) 837.4 (3) [M þ H]^þ, 749.3

(10) [L³Cu₂(PMe₃)₂]^þ, 673.2 (55) [L³Cu₂(PMe₃)]^þ, 611.3 (71)

[L³Cu(PMe₃) þ H]^þ, 597.2 (89) [L³Cu₂]^þ, 535.5 (100) [L³Cu þ

H]^þ, 215.1 (93) [Cu(PMe₃)₂]^þ.

3720

dx.doi.org/10.1021/om100836j |Organometallics 2011, 30, 3708–3725

Organometallics

ARTICLE

2. To a solution of L⁶H (291 mg, 0.60 mmol) in THF (10 mL) was

added a solution of KOtBu (67 mg, 0.60 mmol) in THF (10 mL). After

the mixture was stirred for 30 min, the solvent was removed in vacuo.

The resulting brownish solid residue was dissolved in propionitrile

(10 mL) and a solution of [Cu(CH₃CN)₄]BF₄(376 mg, 1.20 mmol) in

propionitrile (10 mL) was added. A deep red solution had formed ,which

was treated with a solution of tBuNC (100 mg, 1.20 mmol) in

acetonitrile (4.8 mL) via a syringe. After this mixture was stirred for

18 h, the solvents were removed in vacuo. The residue was then dried in

vacuo for 2 h and extracted with CH₂Cl₂(10 mL), and the obtained

suspension was filtered. The clear solution was stored for 8 days

at ꢀ32 °C to form a small amount of a colorless precipitate that was

filtered off. Slow diffusion of diethyl ether (20 mL) into the solution at

þ4 °C over the course of 3 days afforded pale yellow crystals. The yellow

solution was decanted; the solid was washed with diethyl ether (20 mL)

and finally dried for 12 h in vacuo. 2 was obtained as a beige powder that

contained 1.4 equiv of CH₂Cl₂. Yield: 296 mg (0.30 mmol, 50%). Anal.

Table 5. Crystal Data and Reﬁnement Details for L³H, 1,

and 2

L³H

1

2

formula

C₂₉H₄₀N₆

C₃₅H₅₇N₆-

P₂Cu₂BF₄

837.71

C₄₁H₄₅N₈-

Cu₂BF₄CH₂Cl₂

3

M_r

472.67

948.68

cryst size

(mm)

0.14 ꢁ 0.11

ꢁ 0.10

monoclinic

P2₁/c

0.25 ꢁ 0.20

ꢁ 0.20

0.48 ꢁ 0.29

ꢁ 0.18

cryst syst

space group

a (Å), R (deg)

triclinic

P1

triclinic

P1

11.9534(8),

90

11.157(2),

91.60(3)

11.544(2),

97.93(3)

31.350(6),

92.49(3)

3993.0(14)

4

13.0195(8),

70.774(5)

13.2270(8),

75.933(5)

14.2430(8),

72.910(5)

2184.4(2)

2

b (Å), β (deg)

c (Å), γ (deg)

6.1044(4),

101.041(6)

18.5872(15),

90

Calcd for C₄₁H₄₅N₈Cu₂BF₄1.4CH₂Cl₂: C, 51.82; H, 4.90; N, 11.40.

3

Found: C, 51.82; H, 4.97; N, 11.63. ¹H NMR (500.13 MHz, THF-d₈): δ

1.56 (s, 18 H, tBuNC), 3.06 (s, 6 H, CH₃), 4.19 (s, 4 H, CH₂),

6.83ꢀ6.85 (m, 2 H, o-Ph), 7.01ꢀ7.05 (m, 1 H, p-Ph), 7.17 (t, ³J_HH= 7.7

Hz, 2 H, m-Ph), 7.50 (t, ³J_HH= 7.9 Hz, 2 H, quin H⁶), 7.72 (d, ³J_HH= 7.9

Hz, 2 H, quin H^5,7), 7.83ꢀ7.85 (m, 2 H, quin H^5,7), 7.88ꢀ7.91 (m, 2 H,

V (Å³)

1331.17(16)

2

Z

F

_calcd.(g cm^ꢀ3

)

1.174

1.393

1.442

F(000)

512

1752

976

quin H³), 8.33ꢀ8.35 (m, 2 H, quin H⁴), 9.23 (dd, ⁴J_HH= 1.5 Hz, ³J_HH

=

μ (mm^ꢀ1

)

0.072

2.500

1.153

4.5 Hz, 2 H, quin H²). ¹³C NMR (125.77 MHz, THF-d₈): δ 30.5 (CH₃,

tBuNC), 47.1 (NꢀCH₃), 57.3 (C, tBuNC), 60.3 (CH₂), 114.2 (C, pz

C⁴), 124.2 (CH, broad, quin C^5,7), 124.4 (CH, broad, quin C³), 125.3

(CH, p-Ph), 126.9 (CH, quin C^5,7), 127.8 (CH, quin C⁶), 128.8 (CH, m-

Ph), 129.0 (CH, o-Ph), 130.6 (C, quin C^4a), 136.1 (C, i-Ph, tBuNC),

138.1 (CH, quin C⁴), 143.6 (C, quin C^8a), 145.9 (C, pz C^3,5), 150.9 (C,

quinC⁸), 152.1 (CH, broad, quin C²). Onesignalofaquaternary aromatic

carbon atom is not observed but is likely hidden by another resonance in

the aromatic region of the spectrum. MS (ESI(þ) in CH₃CN): m/z

(relative intensity) 609.0 (27) [L⁶Cu₂]^þ, 483.2 (6) [L⁶]^þ, 453.0 (11)

[L⁶Cu₂ꢀ (C₁₀H₉N₂) þ H]^þ, 389.1 (100) [L⁶Cu ꢀ (C₁₀H₉N₂)]^þ,

T_max/T_min

0.6347/

0.5738

0.8558/0.6325

hkl range

(14, (7,

ꢀ22 to þ19

1.74ꢀ26.08

19 477

(12, (13,

0ꢀ36

1.42ꢀ64.79

32 969

ꢀ14 to þ16,

(16, (18

1.53ꢀ26.98

40 954

θ range (deg)

no. of

measd rﬂns

no. of unique

19 477 (0)

11 796

9463 (0.0808)

9463/0/540

rﬂns (R_int

)

(0.0374)

11 798/

1206/996

no. of data/

19 477/

1/183

219.1 (69) [(C₁₀H₈N₂)Cu]^þ. IR (KBr): ν_NC2155 cm^ꢀ1

.

restraints/

params

General Procedure for the Preparation of 3ꢀ8. A solution of

mesitylcopper (including varying amounts of toluene, determined by ¹H

NMR) in toluene or THF was treated with a solution of the correspond-

ing ligand L¹HꢀL⁶H in toluene or THF at ꢀ78 °C by means of a

cannula. After the mixture was stirred at room temperature overnight,

the solvent was concentrated to 5 mL and the reaction mixture was

filtered. A 5 mL portion of toluene or THF was added. Oxygen (dried

with P₂O₅) was slowly bubbled into the solution via a syringe. Depend-

ing on the ligand used, the golden orange to brown solution immediately

became dark red to brown. After it was stirred for 2 h, the clear solution

was layered with diethyl ether (or pentane for a solution of 6 in diethyl

ether, 10 mL) and stored for about 1 week at ꢀ18 °C. The first

crystalline crop of the complex was isolated by filtration. In the case of 3

and 7 the filtrate was concentrated to a volume of ca. 2 mL and treated

with pentane (20 mL) to give more of the beige precipitate, which was

then removed by filtration. The remaining clear solution was again

concentrated to a volume of ca. 2 mL, treated with pentane (20 mL), and

filtered. The unified solid fractions were washed with pentane (3 ꢁ

5 mL) and dried in vacuo for 14 h.

goodness of ﬁt

R1 (I > 2σ(I))

wR2 (all data)

resid electron

1.017

1.044

1.016

0.0481

0.1126

0.290/

ꢀ0.149

0.0329

0.0472

0.0928

0.1206

0.699/ꢀ0.572

0.885/ꢀ1.406

density (e Å^ꢀ3

)

⁴J_HH= 1.7 Hz, ³J_HH= 7.6 Hz, 4 H, py H⁴), 9.89 (d, ³J_HH= 4.4 Hz, 4 H, py

H⁶). ¹³C NMR (125.77 MHz, C₆D₆): δ 21.5 (CH₃, p-CH₃), 29.6 (CH₃,

o-CH₃), 43.1 (CH₃, N-CH₃), 56.2 (CH₂, pz CH₂), 61.2 (CH₂, py CH₂),

97.7 (CH, pz C⁴), 122.3 (CH, py C³), 123.0 (CH, py C⁵), 124.4 (CH, m-

Mes), 135.5 (C, Mes), 135.8 (CH, py C⁴), 137.3 (C, Mes), 147.1 (C, pz

C

^3,5, Mes, py C²), 152.0 (CH, py C⁶), 153.4 (C, pz C^3,5, Mes, py C²),

157.8 (C, pz C^3,5, Mes, py C²). MS (ESI(þ) in THF): m/z (relative

intensity) 1222.9 (7) [L¹Cu₄Mes₃Cu(C₁₂H₁₆N₄)]^þ, 1006.9 (5) [L¹Cu₄-

Mes₃Cu]^þ, 825.0 (18) [L¹Cu₂Mes₂Cu₂]^þ, 643.1 (36) [L¹Cu₃Mes]^þ,

461.2 (100) [L¹Cu₂]^þ.

5. This complex was prepared from a solution of L³H (199 mg,

3. This complex was prepared from a solution of L¹H (164 mg, 0.49

0.42 mmol) in toluene (10 mL) and a solution of CuMes 0.09(toluene)

mmol) in THF (10 mL) and a solution of CuMes 0.14(toluene) (390

3

(323 mg, 1.69 mmol) in toluene (10 mL) as well as oxygen (2.6 mL,

0.11 mmol). A yellow to beige crystalline solid was obtained directly

from layering the reaction solution with diethyl ether. Yield: 194 mg

(0.10 mmol, 48%). Anal. Calcd for C₉₄H₁₂₂N₁₂OCu₈: C, 58.06; H, 6.32;

mg, 1.99 mmol) in THF (10 mL) as well as oxygen (2.8 mL, 0.12 mmol).

An orange powder was obtained. Yield: 278 mg (0.17 mmol, 69%). Anal.

Calcd for C₇₄H₉₀N₁₂OCu₈: C, 53.16; H, 5.43; N, 10.05. Found: C,

52.90; H, 5.39; N, 9.80. ¹H NMR (500.13 MHz, C₆D₆): δ 1.73 (s, 12 H,

N-CH₃), 2.20 (s, 12 H, p-CH₃), 2.60 (s, 24 H, o-CH₃), 3.15 (s, 8 H, py

CH₂), 3.32 (s, 8 H, pz CH₂), 5.95 (s, 2 H, pz H⁴), 6.39 (d, ³J_HH= 7.7 Hz,

4H, py H³), 6.74ꢀ6.76 (m, 4 H, py H⁵), 6.78 (s, 8 H, m-Mes), 6.89 (dt,

1

N, 8.64. Found: C, 58.07; H, 6.36; N, 8.32. H NMR (500.13 MHz,

C₆D₆): δ 0.67ꢀ0.74, 0.88ꢀ0.96 (m, 12 H, cy H^2a,4a), 1.00ꢀ1.08 (m,

8 H, cy H^3a), 1.38ꢀ1.40 (m, 8 H, cy H^2e), 1.47ꢀ1.50 (m, 4 H, cy H^4e),

3721

dx.doi.org/10.1021/om100836j |Organometallics 2011, 30, 3708–3725

Organometallics

ARTICLE

Table 6. Crystal Data and Reﬁnement Details for 3, 5, and 6

3

5

6

formula

1.5C₇₄H₉₀N₁₂OCu₈

C₄H₈O

C

₉₄H₁₂₂N₁₂OCu₈

1.25C₁₀₆H₁₃₀N₁₂OCu₈

3

2C₄H₁₀O C₇H₈

5C₄H₁₀O

3

M_r

2580.04

2184.80

2991.38

cryst size (mm)

cryst syst

0.20 ꢁ 0.10 ꢁ 0.10

monoclinic

0.30 ꢁ 0.11 ꢁ 0.04

0.30 ꢁ 0.20 ꢁ 0.15

tetragonal

I4₁/a

triclinic

space group

a (Å), R (deg)

b (Å), β (deg)

c (Å), γ (deg)

V (Å³)

C2/c

P1

h

64.988(13), 90

17.4933(7), 112.961(3)

18.5505(7), 93.578(3)

19.8633(7), 111.651(3)

5353.7(3)

42.615(6), 90

32.935(7), 90

59 812(17)

16

17.154(3), 100.91(3)

21.229(4), 90

23 238(8)

Z

8

2

F

_calcd.(g cm^ꢀ3

)

1.475

1.355

1.329

F(000)

10 616

2288

25 160

μ (mm^ꢀ1

)

2.752

1.611

1.954

T_max/T_min

hkl range

0.7704/0.6090

ꢀ32 to þ64, (17, ꢀ20 to þ19

2.67ꢀ50.43

49 878

0.8404/0.6501

ꢀ22 to þ21, (23, (25

1.31ꢀ26.84

51 169

0.7582/0.5917

(33, 0 to 47, 0 to 36

1.70ꢀ60.01

22 216

θ range (deg)

no. of measd rﬂns

no. of unique rﬂns (R_int

)

11 778 (0.0470)

11 778/1992/1598

3.206

22 690 (0.0832)

22 690/11/1153

1.002

22 216

no. of data/restraints/params

goodness of ﬁt

22 216/2210/1851

1.278

R1 (I > 2σ(I))

0.0916

0.0637

0.0667

wR2 (all data)

0.3082

0.1112

0.2227

resid electron density (e Å^ꢀ3

)

0.878/ꢀ0.744

0.699/ꢀ0.745

0.922/ꢀ0.903

1.53ꢀ1.56 (m, 8 H, cy H^3e), 1.76ꢀ1.82 (m, 4 H, cy H¹), 2.25 (s, 12 H,

p-CH₃), 2.57 (s, 24 H, o-CH₃), 3.44 (broad), 3.54 (2 ꢁ s, 16 H, py and

pz CH₂), 5.98 (s, 2 H, pz H⁴), 6.38ꢀ6.40 (m, 4H, py H³), 6.79 (s, 8 H,

(CH, m-Mes), 128.5, 129.4 (CH, o-, m-Ph), 135.7 (C, i-Ph, Mes), 136.0

(CH, py C⁴), 137.2, 137.3 (C, i-Ph, Mes), 145.5 (C, pz C^3,5, Mes, py C²),

151.8 (CH, broad, py C⁶), ∼154.0 (broad), 160.1 (C, pz C^3,5, Mes, py

C²). The CH₂resonance signal of cy C²is too broad to be detected. MS

(ESI(þ) in THF): m/z (relative intensity) 1970.9 (7) [M ꢀ Mes]^þ,

1465.2 (17) [L⁴Cu₂MesCu₂L⁴]^þ, 1219.2 (4) [L⁴Cu₂Mes₂Cu₂MesCu]^þ,

1037.2 (49) [L⁴Cu₂Mes₂Cu₂]^þ, 855.2 (12) [L⁴Cu₂MesCu]^þ, 673.4

(36) [L⁴Cu₂]^þ, 421.3 (26) [L⁴Cu ꢀ (N(C₆H₁₁)CH₂(C₅H₄N)]^þ,

360.3 (100) [L⁴H ꢀ (N(C₆H₁₁)CH₂(C₅H₄N)]^þ, 359.3 (100) [L⁴H ꢀ

(N(C₆H₁₁)CH₂(C₅H₄N)]^þ.

m-Mes), 6.90ꢀ6.95 (m, 8 H, py H^4,5), 9.98ꢀ9.99 (m, 4 H, py H⁶). ¹³

C

NMR (125.77 MHz, C₆D₆): δ 21.7 (CH₃, p-CH₃), 26.4 (CH₂, cy C³),

26.5 (CH₂, cy C⁴), 28.7 (CH₂, broad, cy C²), 29.6 (CH₃, o-CH₃), 51.5,

54.8 (py and pz CH₂), 63.3 (CH, cy C¹), 97.8 (CH, pz C⁴), 121.6 (CH,

py C³), 122.7 (CH, py C⁵), 124.7 (CH, m-Mes), 135.6 (C, Mes), 135.9

(CH, py C⁴), 137.1 (C, Mes), 148.2 (C, pz C^3,5, Mes, py C²), 151.7 (CH,

py C⁶), 153.9, 160.0 (C, pz C^3,5, Mes, py C²). MS (ESI(þ) in THF): m/

z (relative intensity) 1818.9 (1) [M ꢀ Mes]^þ, 1495.0 (3) [L³Cu₂-

Mes₂Cu₃L³]^þ, 1313.2 (9) [L³Cu₂MesCu₂L³]^þ, 1143.0 (2) [L³Cu₂-

Mes₂Cu₂MesCu]^þ, 961.2 (56) [L³Cu₂Mes₂Cu₂]^þ, 779.2 (11) [L³Cu₂-

MesCu]^þ, 597.4 (26) [L³Cu₂]^þ.

7. This complex was prepared from a solution of L⁵H (272 mg,

0.48 mmol) in toluene (10 mL) and a solution of CuMes 0.14(toluene)

3

(374 mg, 1.91 mmol) in toluene (10 mL) as well as oxygen (2.7 mL,

0.11 mmol). A beige powder was obtained. Yield: 394 mg (0.18 mmol,

75%). Anal. Calcd for C₁₀₆H₁₁₀N₁₆OCu₈: C, 59.70; H, 5.20; N, 10.51.

6. This complex was prepared from a solution of L⁴H (236 mg,

1

Found: C, 59.21; H, 5.24; N, 10.35. H NMR (300.13 MHz, C₆D₆,

0.43 mmol) in toluene (10 mL) and a solution of CuMes 0.09(toluene)

3

signals attributed to the labile or noncoordinating pyridyl side groups are

denoted with asterisks): δ 2.22 (s, 12 H, p-CH₃), 2.72 (s, 24 H, o-CH₃),

3.52 (s, 16 H, py CH₂), 3.90 (s, 8 H, pz CH₂), 3.99 (broad, CH₂*), 6.61

(d, ³J_HH= 7.7 Hz, 8 H, py H³), 6.67ꢀ6.72 (m, 8 H, py H⁵), 6.88 (s, 8 H,

m-Mes), 6.92 (dt, ⁴J_HH= 1.8 Hz, ³J_HH= 7.6 Hz, 8 H, py H⁴), 6.96ꢀ6.97

(m, 2 H, p-Ph), 7.12ꢀ7.17 (m, 4 H, m-Ph), 7.22ꢀ7.25 (m, broad,

py*),7.30ꢀ7.33 (m, 4 H, o-Ph), 7.41ꢀ7.47, 7.84, 8.24ꢀ8.26, 9.07

(4 ꢁ m, broad, py*), 9.23ꢀ9.25 (m, 8 H, py H⁶). ¹³C NMR (75.47

MHz, C₆D₆): δ 21.5 (CH₃, p-CH₃), 29.8 (CH₃, o-CH₃), 51.2 (pz CH₂),

57.2 (py CH₂), 115.6 (C, pz C⁴), 121.8, 122.0 (py*), 122.4 (CH, py C⁵),

123.6 (CH, py C³), 124.4 (CH, p-Ph), 124.8 (CH, m-Mes), ∼128.0

(CH, m-Ph, overlaid by the benzene signal), 129.2 (CH, o-Ph), 135.6

(332 mg, 1.74 mmol) in toluene (10 mL) as well as oxygen (2.7 mL,

0.11 mmol). A yellow to beige crystalline solid was obtained directly

from layering a solution of the product in diethyl ether (10 mL) with

pentane. Yield: 276 mg (0.13 mmol, 60%). Anal. Calcd for C₁₀₆H₁₃₀

-

N₁₂OCu₈: C, 60.72; H, 6.25; N, 8.02. Found: C, 60.22; H, 6.82; N, 7.79.

¹H NMR (500.13 MHz, C₆D₆): δ ∼0.63 (s, broad, 8 H, cy H^2a),

0.88ꢀ0.93 (m, 4 H, cy H^4a), 0.99ꢀ1.07 (m, 8 H, cy H^3a), 1.37ꢀ1.39 (m,

8 H, cy H^2e), 1.46ꢀ1.48 (m, 4 H, cy H^4e), 1.51ꢀ1.53 (m, 8 H, cy H^3e),

1.80ꢀ1.86 (m, 4 H, cy H¹), 2.28 (s, 12 H, p-CH₃), 2.60 (s, broad, 24 H,

o-CH₃), ∼3.29 (s, broad, 8 H, py CH₂), 3.74 (s, 8 H, pz CH₂),

6.29ꢀ6.31 (m, 4H, py H³), 6.85 (s, 8 H, m-Mes), 6.91ꢀ6.96 (m, 8 H,

py H^4,5), 7.09ꢀ7.13 (m, 2 H, p-Ph), 7.32ꢀ7.33 (m, 8 H, o-, m-Ph),

10.05ꢀ10.06 (m, 4 H, py H⁶). ¹³C NMR (125.77 MHz, C₆D₆): δ 21.7

(CH₃, p-CH₃), 26.4 (CH₂, cy C³), 26.5 (CH₂, cy C⁴), 29.7 (CH₃,

o-CH₃), 50.7 (pz CH₂), 54.6 (py CH₂), 63.5 (CH, cy C¹), 115.4 (C, pz

C⁴), 121.5 (CH, py C³), 122.7 (CH, py C⁵), 124.6 (CH, p-Ph), 124.8

(C, i-Ph, Mes), 135.7 (CH, py C⁴), 137.1, 138.2 (C), 144.9 (C, pz C^3,5

,

Mes, py C²), 150.8 (CH, py C⁶), 153.7, 158.0 (C, pz C^3,5, Mes, py C²).

MS (ESI(þ) in THF): m/z (relative intensity) 1319.1 (4) [(L⁵)₂Cu₃]^þ,

1055.0 (18) [L⁵Cu₂Mes₂Cu₂]^þ, 873.1 (16) [L⁵Cu₂MesCu]^þ, 691.3

3722

dx.doi.org/10.1021/om100836j |Organometallics 2011, 30, 3708–3725

Organometallics

ARTICLE

(57) [L⁵Cu₂]^þ, 430.3 (27) [L⁵Cu ꢀ (N(CH₂(C₅H₄N))₂)]^þ, 369.3

(86) [L⁵Hꢀ (N(CH₂(C₅H₄N))₂) þ H]^þ, 368.3 (100) [L⁵Hꢀ (N(CH₂-

(C₅H₄N))₂)]^þ.

Table 7. Crystal Data and Reﬁnement Details for 7 and 8

7

8

8. This complex was prepared from a solution of L⁶H (147 mg,

formula

C

₁₀₆H₁₁₀

-

C₉₈H₉₈N₁₂OCu₈

3

0.30 mmol) in toluene (10 mL) and a solution of CuMes 0.06(toluene)

3

N₁₆OCu₈

C₄H₁₀O 0.5 C₇H₈

3

(263 mg, 1.40 mmol) in toluene (10 mL) as well as oxygen (2.0 mL,

0.08 mmol). A precipitate was formed from the stirred reaction mixture

that was collected by filtration after cooling for 10 days. This solid was

washed with diethyl ether (5 ꢁ 2 mL) and dried in vacuo for 14 h. Yield:

174 mg (0.09 mmol, 60%). Anal. Calcd for C₉₈H₉₈N₁₂OCu₈: C, 59.80;

H, 5.02; N, 8.54. Found: C, 59.77; H, 5.48; N, 8.47. ¹H NMR

(500.13 MHz, C₆D₆): δ 2.08 (s, 12 H, p-CH₃), 2.17 (s, 12 H, N-CH₃),

2.52 (s, 24 H, o-CH₃), 4.16 (s, 8 H, CH₂), 6.48 (s, 8 H, m-Mes),

6.72ꢀ6.76 (m, 8 H, quin H³, quin H^5,7or o-Ph), 6.89ꢀ6.92 (m, 4 H,

quin H⁶or m-Ph), 6.96ꢀ6.97 (m, 4 H, quin H^5,7or o-Ph), 7.03ꢀ7.05,

M_r

2132.48

2088.47

cryst size (mm)

cryst syst

0.29 ꢁ 0.19 ꢁ 0.16

monoclinic

C2/c

0.36 ꢁ 0.24 ꢁ 0.14

triclinic

space group

a (Å), R (deg)

b (Å), β (deg)

c (Å), γ (deg)

V (Å³)

P1

25.1096(6), 90

50.2683(11), 91.799(2)

18.3179(5), 90

23109.8(10)

8

15.6032(7), 67.364(3)

18.6504(7), 86.560(3)

19.8654(8), 66.561(3)

4865.7(3)

Z

2

7.18ꢀ7.19 (2 ꢁ m, 10 H, quin H, Ph), 7.43 (dd, ⁴J_HH= 1.2 Hz, ³J_HH

=

F

_calcd.(g cm^ꢀ3

)

1.226

1.425

8.3 Hz, 4 H, quin H⁴), 9.27ꢀ9.28 (m, 4 H, quin H²). ¹³C NMR

(125.77 MHz, C₆D₆): δ 21.5 (CH₃, p-CH₃), 29.8 (CH₃, o-CH₃), 42.1

(CH₃, N-CH₃), 57.3 (CH₂), 115.0 (C, pz C⁴), 119.5, 122.0 (CH, quin

C³, quin C^5,7, or o-Ph), 122.8 (CH, quin C^5,7or o-Ph), 124.6 (CH, m-

Mes), 124.8 (CH, p-Ph), 126.5 (CH, quin C⁶, or m-Ph), 128.3, 129.4

(CH, quin C, Ph), 129.8, 134.5 (C), 135.7 (CH, quin C⁴), 136.4, 136.5,

143.1, 145.9 (C), 150.1 (CH, quin C²), 150.2, 154.5 (C). MS (ESI in

CH₃CN): m/z (relative intensity) 927.1 (16) [L⁶Cu₂Mes₂CuO þ H]^þ,

847.1 (15) [L⁶Cu₂Mes₂]^þ, 609.2 (95) [L⁶Cu₂]^þ, 545.3 (58) [L⁶Cu ꢀ H]^þ.

9. The reaction was performed according to the procedure described

for 8-(dimethylamino)naphthylcopper(I)^34aby using a solution of 4

(109 mg, 0.06 mmol) in toluene (30 mL) and a 0.5 M solution of

DMADC in toluene (0.96 mL, 0.48 mmol). Instead of a chromato-

graphic workup, filtration was used to separate the insoluble reaction

products. A yellow oil was obtained. ¹H NMR data reveal the formation

F(000)

8784

2154

μ (mm^ꢀ1

)

1.491

1.768

T_max/T_min

hkl range

0.8216/0.6789

ꢀ30 to þ27,

(61, (22

1.38ꢀ26.00

120 104

0.7951/0.5641

(18, (21,

ꢀ22 to þ23

1.43ꢀ24.79

104 897

θ range (deg)

no. of measd rﬂns

no. of unique

22 614 (0.0624)

16 639 (0.1150)

rﬂns (R_int

)

no. of data/

22 614/128/1152

16 639/16/1140

restraints/params

goodness of ﬁt

R1 (I > 2σ(I))

wR2 (all data)

resid electron

1.019

1.008

0.0589

0.0563

1

of 9 and L²H in a molar ratio of 1.2:1 (expected ratio 2:1). H NMR

0.1572

0.1602

(500.13 MHz, C₆D₆): δ 2.05 (s, 3 H, p-CH₃), 2.33 (s, 6 H, o-CH₃), 3.33,

3.41 (2 ꢁ s, 6 H, OCH₃,), 5.77 (s, 1 H, HC=C), 6.69ꢀ6.70 (m, 2 H,

m-Mes). MS (EI): m/z (relative intensity) 262 (2) [M]^þ, 247 (3) [M ꢀ

CH₃]^þ, 231 (16) [M ꢀ OCH₃]^þ, 230 (40) [M ꢀ OCH₃ꢀ H]^þ, 203

(40) [M ꢀ (CO)OCH₃]^þ, 202 (100) [M ꢀ (CO)OCH₃ꢀ H]^þ, 143

(57) [M ꢀ Mes]^þ, 128 (26) [M ꢀ Mes ꢀ CH₃]^þ.

0.983/ꢀ0.802

1.679/ꢀ0.555

density (e Å^ꢀ3

)

solvent molecules (4734.3 Å³, electron count 937) was subtracted from

the reflection data by the SQUEEZE⁴³routine of the PLATON⁴⁴

program. Face-indexed absorption corrections for 2, 5, 7, and 8 were

performed numerically with the program X-RED.⁴⁵

X-ray Crystallography. X-ray data for L³H and 2, 5, 7, and 8 were

collected on a STOE IPDS II diffractometer (graphite-monochromated

Mo KR radiation, λ = 0.710 73 Å) by use of ω scans at ꢀ140 °C

(Tables 5ꢀ7). The structures were solved by direct methods and refined

by full-matrix least-squares procedures on F²using all reflections with

SHELX-97.⁴²Non-hydrogen atoms were refined anisotropically. Hy-

drogen atoms were placed in calculated positions (riding model) and

assigned to an isotropic displacement parameter of 0.08 Å². In the case of

L³H the crystal under investigation was found to be nonmerohedrally

twinned (twin law: ꢀ1,0,0.25, 0,ꢀ1,0, 0,0,1). An HKLF 5 format file was

used for the refinement of the structure. The twin ratio was refined to

0.4535(5)/0.5465(5). Additionally the central pyrazole moiety is dis-

ordered about a center of inversion and was refined at half-occupancy.

SADI restraints (d_CꢀC) were used to model the disorder. Parts of the

ligand are also disordered in 5 and 7. For the disordered cyclohexyl

moiety in 5 no constraints or restraints were applied (occupancy factors

0.848(8)/0.152(8)), whereas in 7 SADI (d_CꢀC/N) and FLAT restraints

and EADP (N18A/B) constraints were used to model the disorder of

two pyridyl groups (occupancy factors 0.733(13)/0.267(13) and

0.612(17)/0.388(17)). The AFIX 66 instruction was used to model

the disorder of one of the phenyl rings bound to the pyrazole moiety in 7

(occupancy factors 0.562(7)/0.438(7)). Furthermore, disordered toluene

and diethyl ether molecules are present in 5, 7, and 8. DFIX and SADI

restraints and EADP constraints were applied in the case of 5 and 8. For

the solvent molecules in 7 no satisfactory model for the disorder could

be found, and for further refinement the contribution of the missing

X-ray data for 1, 3, and 6 were collected on a Bruker three-circle

diﬀractometer with a SMART 6000 detector and Cu KR radiation (λ =

1.541 78 Å) at ꢀ178 °C. The crystal of compound 1 that was used was a

nonmerohedral twin, and two domains (0.529/0.471) could be identi-

ﬁed with the program CELL_NOW.⁴⁶Both domains were used for

integration. Absorption and intensity data were corrected with the

TWINABS program.⁴⁷The structure was solved using direct methods

and reﬁned by full-matrix least-squares procedures against F²using all

reﬂections with SHELX-97.⁴²Non-hydrogen atoms were reﬁned aniso-

tropically, and hydrogen atoms were placed in calculated positions using

the riding model. In the asymmetric unit two independent complex

molecules and two BF₄^ꢀcounterions could be reﬁned. Since all BF₄

counterion molecules are disordered through a symmetry center, SADI

restraints were used to equal bond lengths and angles.

ꢀ

In the case of compound 3 a multidomain split crystal was used, but

single domains could be identiﬁed. The structure was solved using direct

methods and reﬁned by full-matrix least-squares procedures against

F²using all reﬂections with SHELX-97.⁴²Two possible space groups

(C2/c and Cc) could be found that gave equal results and disorder. Thus,

the higher symmetric space group C2/c was chosen. Non-hydrogen

atoms were reﬁned anisotropically, and hydrogen atoms were placed in

calculated positions using the riding model. In the asymmetric unit two

independent complex molecules and one disordered THF solvent

molecule could be reﬁned. Because of complex and solvent disorder,

3723

dx.doi.org/10.1021/om100836j |Organometallics 2011, 30, 3708–3725

Organometallics

ARTICLE

FLAT, DFIX, and DANG as well as SIMU and DELU restraints

were used.

D. R. Chem. Soc. Rev. 2006, 35, 218–225. (i) Temma, T.; Hatano, B.;

Habaue, S. Tetrahedron 2006, 62, 8559–8563.

(5) See for example: (a) Rossiter, B. E.; Swingle, N. M. Chem. Rev. 1992,

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(c) Woodward, S. Angew. Chem. 2005, 117, 5696–5698; Angew. Chem., Int.

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Knochel, P. Angew. Chem. 2007, 119, 9251–9255; Angew. Chem., Int. Ed.

2007, 46, 9093–9096. (f) Alexakis, A.; B€ackvall, J. E.;Krause, N.;Pꢁamies, O.;

Diꢀeguez, M. Chem. Rev. 2008, 108, 2796–2823.

(6) (a) Tsuda, T.; Yazawa, T.; Watanabe, K.; Fujii, T.; Saegusa, T.

J. Org. Chem. 1981, 46, 192–194. (b) Gambarotta, S.; Floriani, C.;

Chiesi-Villa, A.; Guastini, C. J. Chem. Soc., Chem Commun. 1983,

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A._ꢂ; Guastini, C. Organometallics 1989, 8, 1067–1079. (d) Eriksson, H.;

Hakansson, M. Organometallics 1997, 16, 4243–4244.

Absorption and intensity data of compound 6 were corrected with the

SADABS program. The structure was solved in the tetragonal space

group I4₁/a using direct methods and reﬁned by full-matrix least-squares

procedures against F². Non-hydrogen atoms were reﬁned anisotropi-

cally, and hydrogen atoms were placed in calculated positions using the

riding model. In the asymmetric unit two independent complex

molecules and ﬁve partially disordered ether molecules could be reﬁned.

Since the cyclohexyl groups in the complex as well as the solvent

molecules are disordered, SADI, DFIX, DANG, SIMU, and DELU

restraints were used.

’ ASSOCIATED CONTENT

S

Supporting Information. CIF ﬁles giving crystallo-

b

(7) Leoni, P.; Pasquali, M.; Ghilardi, C. A. J. Chem. Soc., Chem.

Commun. 1983, 240–241.

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with anisotropic displacement factors, and tables giving selected

interatomic distances and angles of 5ꢀ8 as well as of all inde-

pendent molecules in the asymmetric unit of the crystal struc-

tures of 3 and 6. This material is available free of charge via the

Internet at http://pubs.acs.org.

(8) (a) Knotter, D. M.; Smeets, W. J. J.; Spek, A. L.; van Koten, G.

J. Am. Chem. Soc. 1990, 112, 5895–5896. (b) Knotter, D. M.; Grove,

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Chem. 2007, 119, 5283–5286; Angew. Chem., Int. Ed. 2007, 46

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’ AUTHOR INFORMATION

Corresponding Author

*M.S.: tel, þ1 979 845 5978; fax, þ1 979 845 5629; e-mail,

mstollenz@mail.chem.tamu.edu. F.M.: tel., þ49 551 393012;

fax, þ49 551 393063; e-mail, franc.meyer@chemie.uni-goettingen.de.

Present Addresses

^†Department of Chemistry, Texas A&M University, 580 Ross

Street, P.O. Box 30012, College Station, Texas 77842ꢀ3012.

€

(10) Hakansson, M.; Ortendahl, M.; Jagner, S.; Sigalas, M. P.;

Eisenstein, O. Inorg. Chem. 1993, 32, 2018–2024.

(11) Stollenz, M.; Grosse, C.; Meyer, F. Chem. Commun. 2008,

1744–1746.

(12) (a) Garilova, A. L.; Bosnich, B. Chem. Rev. 2004, 104, 349–383.

(b) Klingele, J.; Dechert, S.; Meyer, F. Coord. Chem. Rev. 2009, 253

2698–2741.

’ ACKNOWLEDGMENT

(13) (a) Meyer, F.; Pritzkow, H. Angew. Chem. 2000, 112

2199–2202; Angew. Chem., Int. Ed. 2000, 39, 2112–2115. (b) Ackermann,

J.; Meyer, F.; Kaifer, E.; Pritzkow, H. Chem. Eur. J. 2002, 8, 247–258.

(c) Prokoﬁeva, A.; Prikhod’ko, A. I.; Enyedy, E. A.; Farkas, E.; Maringgele,

W.; Demeshko, S.; Dechert, S.; Meyer, F. Inorg. Chem. 2007, 46,

4298–4307. (d) Ackermann, J.; Buchler, S.; Meyer, F. C. R. Chim.

2007, 10, 421–432. (e) Prokoﬁeva, A.; Prikhod’ko, A. I.; Dechert,

S.; Meyer, F. Chem. Commun. 2008, 1005–1007. (f) Prokoﬁeva, A.;

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We thank Prof. G. M. Sheldrick for providing X-ray data

collection facilities, Dr. Michael John (Institute for Inorganic

Chemistry at the University of G€ottingen) for helpful discus-

sions, Dr. Holm Frauendorf (Institute for Organic and Biomo-

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HR mass spectra, and the Fonds der Chemischen Industrie for

ﬁnancial support.

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dx.doi.org/10.1021/om100836j |Organometallics 2011, 30, 3708–3725

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From pyrazolate-based binuclear copper(I) complexes to octanuclear θ-mesityl-bridged μ4-oxo-cuprocuprates: Controlled dioxygen splitting by organocopper scaffolds

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