Highly tunable fluorinated trispyrazolylborates [HB(3-CF3-5-{4-RPh}pz)3]- (R = NO2, CF3, Cl, F, H, OMe and NMe2) and their copper(i) complexes

Article abstract of DOI:10.1039/c5dt04006j

The ethene and carbon monoxide adducts of copper(i) with seven trispyrazolylborate ligands ([HB(3-CF₃-5-{4-RPh}pz)₃]^-; R = NO₂ (4a), CF₃ (4b), Cl (4c), F (4d), H (4e), OMe (4f) and NMe₂ (4g)) were synthesized and characterized. The ligands were synthesized from their corresponding pyrazoles and sodium tetrahydridoborate and were obtained as solvent adducts of their sodium salts after workup. When the pyrazole with the most electron-withdrawing substituent (R = NO₂) is used the asymmetric ligand [HB(3-CF₃-5-{4-NO₂Ph}pz)₂(3-{4-NO₂Ph}-5-CF₃pz)]^- (4a′) is formed as the major product. Copper(i) complexes with ethene or CO as a co-ligand were prepared in good yields and were structurally characterized using ¹H NMR, ¹³C NMR and infrared spectroscopy. Single crystal X-ray crystallography analyses revealed the structures of Na4a′, Na4b, four copper ethene complexes and four copper carbonyl complexes. The structures of the copper(i) complexes show Cu^I ions in pseudo-tetrahedral coordination environments consisting of three nitrogen atoms of the trispyrazolylborate ligand and the carbonyl or η²-coordinated ethene ligands, with nearly identical coordination environments around the Cu^I ion. The compound [Na(4a′)(H₂O)]_n crystallizes as one-dimensional chains with intermolecular Na...O₂N interactions. The sodium ions were found in severely distorted octahedral geometries with three nitrogen atoms from the trispyrazolylborate ligand, one aqua ligand and two oxygen atoms from the nitro group of an adjacent molecule. The compound [Na₂(4b)₂(μ-H₂O)₂] crystallizes as a centrosymmetric water-bridged dimer: two five-coordinate square-pyramidal sodium ions each are coordinated facially by three nitrogen atoms from a trispyrazolylborate ligand and two bridging water ligands. Below the base of the pyramidal structure one intermolecular and two intramolecular Na...F short contacts are present. The ¹H and ¹³C NMR spectra of the copper-ethene complexes show signals for the ethene ligands in the range of 4.84-4.96 ppm and 84.9-86.8 ppm respectively. The infrared spectra of the carbonyl complexes show CO stretching frequencies in the range of 2096-2120 cm^-1. Both the NMR signals for the ethene ligands and infrared signals for the carbonyl ligands were found to show good correlations with the Hammett σ_p parameters of the substituents on the phenyl rings of the ligands.

Full text of DOI:10.1039/c5dt04006j

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PAPER
Highly tunable fluorinated trispyrazolylborates
[HB(3-CF3-5-{4-RPh}pz)3]− (R = NO2, CF3, Cl, F, H,
OMe and NMe2) and their copper(I) complexes†
Cite this: Dalton Trans., 2015, 44,
21109
Thomas F. van Dijkman,a Maxime A. Sieglerb and Elisabeth Bouwman*a
The ethene and carbon monoxide adducts of copper(I) with seven trispyrazolylborate ligands ([HB(3-CF3-
5-{4-RPh}pz)3]−; R = NO2 (4a), CF3 (4b), Cl (4c), F (4d), H (4e), OMe (4f) and NMe2 (4g)) were synthesized
and characterized. The ligands were synthesized from their corresponding pyrazoles and sodium tetra-
hydridoborate and were obtained as solvent adducts of their sodium salts after workup. When the pyrazole
with the most electron-withdrawing substituent (R = NO2) is used the asymmetric ligand [HB(3-CF3-5-
{4-NO2Ph}pz)2(3-{4-NO2Ph}-5-CF3pz)]− (4a’) is formed as the major product. Copper(I) complexes with
ethene or CO as a co-ligand were prepared in good yields and were structurally characterized using 1H
NMR, 13C NMR and infrared spectroscopy. Single crystal X-ray crystallography analyses revealed the struc-
tures of Na4a’, Na4b, four copper ethene complexes and four copper carbonyl complexes. The structures
of the copper(I) complexes show CuI ions in pseudo-tetrahedral coordination environments consisting of
three nitrogen atoms of the trispyrazolylborate ligand and the carbonyl or η2-coordinated ethene ligands,
with nearly identical coordination environments around the CuI ion. The compound [Na(4a’)(H2O)]n crys-
tallizes as one-dimensional chains with intermolecular Na⋯O2N interactions. The sodium ions were
found in severely distorted octahedral geometries with three nitrogen atoms from the trispyrazolylborate
ligand, one aqua ligand and two oxygen atoms from the nitro group of an adjacent molecule. The com-
pound [Na2(4b)2(µ-H2O)2] crystallizes as a centrosymmetric water-bridged dimer: two five-coordinate
square-pyramidal sodium ions each are coordinated facially by three nitrogen atoms from a trispyrazolyl-
borate ligand and two bridging water ligands. Below the base of the pyramidal structure one inter-
1
molecular and two intramolecular Na⋯F short contacts are present. The H and 13C NMR spectra of the
copper–ethene complexes show signals for the ethene ligands in the range of 4.84–4.96 ppm and
84.9–86.8 ppm respectively. The infrared spectra of the carbonyl complexes show CO stretching fre-
quencies in the range of 2096–2120 cm−1. Both the NMR signals for the ethene ligands and infrared
signals for the carbonyl ligands were found to show good correlations with the Hammett σp parameters
of the substituents on the phenyl rings of the ligands.
Received 13th October 2015,
Accepted 12th November 2015
DOI: 10.1039/c5dt04006j
www.rsc.org/dalton
ligands allows for the optimization of complexes for specific
purposes such as catalysis and biomimetic structural and func-
Introduction
Trispyrazolylborates (commonly referred to as scorpionate tional models. The properties of trispyrazolylborate ligands
ligands1) form a highly versatile class of ligands that were pio- can be changed by systematic modification of the substituents
neered by Trofimenko in the 1960s. They have since been deve- on the pyrazolyl groups or, though much less common, on the
loped from the simple unsubstituted Tp− into ligands of central boron atom. At present a wide variety of the facially
increasing complexity and scope.2–7 The great diversity in coordinating tridentate ligands is known with substituents
steric and electronic properties available in trispyrazolylborate ranging from alkyl groups to aryl groups (both aromatic like
phenyl groups and heteroaromatic such as the thienyl group)
as well as phosphines, esters and amides.8–13 Due to the struc-
turally and electronically similar properties of the pyrazole and
aLeiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA, Leiden,
the Netherlands. E-mail: bouwman@chem.leidenuniv.nl
imidazole rings trispyrazolylborate ligands offer an interesting
bDepartment of Chemistry, Johns Hopkins University, MD 21218 Baltimore, USA
avenue towards the modelling of biological systems that in-
†Electronic supplementary information (ESI) available. CCDC 1430362–1430371.
corporate multiple histidine residues coordinating facially to
For ESI and crystallographic data in CIF or other electronic format see DOI:
the metal center in the active site. A metal that is encountered
10.1039/c5dt04006j
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often in such sites is copper, in enzymes and proteins such as
hemocyanin, cytochrome-c oxidase, ceruloplasmin, superoxide
dismutase, laccase and many others.14 Copper offers advan-
tages besides being biologically relevant; the ethene and carbo-
nyl complexes of copper(I) offer relatively simple systems to
characterize the steric and electronic properties of novel tris-
pyrazolylborate ligands. Such complexes have a (pseudo) tetra-
hedral coordination environment in which a single copper(I)
ion is facially coordinated by a single trispyrazolylborate
ligand and one ethene or carbonyl ligand which allows for
unambiguous characterization of the steric and electronic pro-
perties of the trispyrazolylborate ligand. Unfortunately com-
parison of the properties of trispyrazolylborate ligands
typically results in their differences being ascribed to a combi-
nation of steric and electronic factors without detailed knowl-
edge of the contributions of each factor. To facilitate the
Table 1 Schematic representation of the ligands and complexes
described in this paper, including the Hammett σp values of the substitu-
ents on the para-positions of the phenyl groupsa
[TpCF ,4-RPhCuL]
3
b
R
σp
Ligand L = C2H4 L = CO
c
NO2
CF3
Cl
F
H
0.78 4a/4a′
5a′
5b
5c
5d
5e
5f
6a′
6b
6c
6d
6e
6f
0.54 4b
0.23 4c
0.06 4d
0
4e
−0.27 4f
NMe2 −0.83 4g
OMe
5g
6g
a The third pyrazole ring is schematically shown as [NvN]. b Taken from
ref. 18. c The major product is an asymmetric isomer, indicated with a′, see
comparison of the steric and electronic factors a series of iso- text.
steric, purely electronically varied trispyrazolylborates would be
useful. By keeping the steric properties of the binding pocket
around the metal center constant and varying only the elec-
for chemical modification of the phenyl rings while retaining
tronic properties of the trispyrazolylborate ligands a spectro-
chemical series of isosteric trispyrazolylborate ligands could
be created. Such a spectrochemical series of trispyrazolylborate
ligands could be used to separately estimate the optimal elec-
tronic properties of a trispyrazolylborate ligand in a catalytic or
biomimetic system prior to optimization of the steric factors.
To create a spectrochemical trispyrazolylborate ligand series
strict regiochemical control during ligand synthesis is
required. The coordination environment around the metal
must vary as little as possible while the electronic properties of
the ligand are varied. In this regard trispyrazolylborate ligand
synthesis offers a convenient handle in that the 3-positions of
the pyrazolyl rings are typically occupied by the bulkiest substi-
tuent. Exceptions to this situation occur if the pyrazole also
carries a particularly electron-withdrawing substituent like a
trifluoridomethyl group, in which case the electron-withdraw-
ing group assumes the 3-position instead. The resulting elec-
tron-withdrawing trispyrazolylborate ligands have a special
place in copper(I) chemistry because they allow for the syn-
thesis and isolation of otherwise thermally and oxidatively
unstable copper(I) complexes with ligands like ethene and
the structure of the binding pocket surrounding the copper(I)
center. Delocalization in the aromatic rings allows for efficient
charge transfer from substituents on the distal phenyl rings to
the copper(I) ion while conformational differences between the
resulting complexes are limited by the steric bulk of the
crowded phenyl groups. Particularly substitution on the para-
position of the phenyl rings would result charge transfer
without significant structural modification to the ligands.
Even though the substituents would be placed relatively far
away from the copper(I) ions the charges of the substituents
could be transferred quite effectively by resonance effects in
the conjoined aromatic rings. In this work the effect of para-
substitution on the phenyl rings of [TpCF ,Ph −
]
was examined;
3
by judicious selection of electron donating and withdrawing
substituents a spectroscopic series was created (Table 1). Sub-
stituents were chosen that offer a broad range of electronic
properties (based on their Hammett σp parameters) and are
tolerant to the strongly reducing conditions required for the
synthesis of these trispyrazolylborate ligands.19 To study the
upper limit of electron withdrawing effects the particularly
electron withdrawing nitro substituent was also included
despite its sensitivity to reducing conditions.
carbon monoxide. Examples of such ligands include
− 15–18
[Tp(CF )2]−, [Tp(CF )3]−, [TpCF ,Ph]−, [Ttz(CF )2 −
]
and [TpCF ] .
3
3
3
3
3
The [TpCF ,RCu(C2H4)] complexes of these ligands are air stable
as are the corresponding carbonyl complexes which have infra-
red CO stretching frequencies close to that of free CO indicat-
ing particularly electron-poor copper(I) centers. Both effects
are unusual for copper(I) trispyrazolylborate complexes and
3
Results
Synthesis
can be ascribed to the electron-withdrawing effects of the The ligands used in this work were synthesized from 4′-substi-
fluorinated substituents on the pyrazole moieties. The trifluor- tuted acetophenones (1a–g) in a multistep procedure (see
idomethyl groups thus tune the electronic properties of the Scheme 1). The 4-substituted acetophenones were converted
ligand to a great extent while adding only a limited amount of into 4′-substituted benzoyltrifluoridoacetates (2a–g) in
a
steric bulk and a chemically inert binding pocket around the Claisen condensation with ethyl trifluoridoacetate in THF or
copper(I) center. With the aim of synthesizing isosteric, elec- diethyl ether. Typically the use of diethyl ether gave higher yields
tronically different trispyrazolylborate ligands the ligand and less side products but the more polar THF was sometimes
[TpCF ,Ph −
]
in particular is interesting because of its potential required to keep reaction mixtures from becoming too viscous.
3
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Scheme 1 (a) CF3COOEt, KOtBu/NaOEt, Et2O, rt; (b) N2H4·H2O, EtOH, reflux; (c) 3 N HCl, reflux; (d) NaBH4, Ar either at 180 °C (melt reaction) or in
refluxing 4-methylanisole.
The 4′-substituted benzoyltrifluoridoacetates were then con-
verted into the corresponding pyrazoles (3a–g) by a two-step
condensation reaction with hydrazine hydrate which resulted
in product mixtures comprising the desired pyrazole and (par-
tially) hydrated intermediates which were dehydrated by reflux-
ing in dilute hydrochloric acid; without the additional
dehydration step the reaction is typically incomplete. Alterna-
tive methods were less successful; reflux in toluene under
Dean–Stark conditions required much longer reaction times
Scheme 2 The asymmetric structure of the major fraction [4a’]−.
and vacuum thermolysis frequently led to co-sublimation of
incompletely dehydrated products. The pyrazoles can be puri-
fied readily by means of vacuum sublimation to yield pure and
dry products that can be used immediately for ligand
synthesis.
The pyrazoles were converted into the trispyrazolylborate
mixtures thereof. All ligand salts exchanged some solvent with
adventitious water upon standing in air.
ligands by heating in the presence of NaBH4 (Scheme 1). A
reaction temperature of 180 °C was used in a solvent-free reac-
tion as reported for the synthesis of Na4e except in the cases
of Na4a and Na4f for which 4-methylanisole was used as a
solvent.16 In the case of Na4f the solvent was used because the
melting point of 3g is too high to let the reaction proceed
smoothly at 180 °C and higher temperatures led to excessive
scorching. For Na4a the solvent-free synthesis resulted in the
formation of large amounts of byproducts, whereas stepwise
heating in 4-methylanisole facilitated the formation of the
monopyrazolylborate and bispyrazolylborate intermediates at
lower reaction temperatures before raising the reaction temp-
erature to 180 °C. This was not possible without the use of a
solvent as the melting point of 3a is too high (171 °C). As
The ethene and carbonyl copper(I) complexes (respectively
5a′, 5b–g and 6a′, 6b–g, see Table 1) were synthesized by stir-
ring the sodium salts of the trispyrazolylborate ligands Na4a′,
Na4b–g and CuI in DCM in an atmosphere of ethene or
carbon monoxide. It was found that if CuI was added to an
ethene or carbon monoxide saturated solution of the ligand in
DCM the synthesis could be performed with minimal further
use of Schlenk techniques. Workup consisted of filtration to
remove NaI and evaporation of the solvent in vacuo to yield the
complexes as white powders which were recrystallized from
DCM/pentane to yield the pure products. Most of the isolated
ethene or carbonyl copper(I) complexes are air stable for at
least six months in the solid state. In solution in dichloro-
methane 5a′, 6a′, 5g and 6g slowly turn green over the course
of hours with associated loss of the ethene or carbonyl ligands
(as evident from their NMR spectra) if exposed to air. Com-
plexes 5b–g and 6b–g show good stability in the presence of
air, light and moisture and can be manipulated without
special precautions. The complexes 5a′ and 6a′ were found to
be less stable over time and had to be kept under argon to
avoid decomposition. Aside from DCM the complexes were
found to be slightly soluble in n-pentane, n-hexane and cyclo-
hexane and to have good solubility in benzene, toluene, THF,
1,4-dioxane, chloroform and acetonitrile. A general trend
appears to be that the more polar complexes (those incorporat-
ing methoxy and dimethylamino substituents) are less soluble
in the more apolar solvents although even 5g and 6g are some-
what soluble in n-hexane. Coordinating solvents (acetonitrile,
acetone and THF) cause decomposition of the complexes over
1
evident from the H and 13C NMR spectra of the sodium salt
and the complexes of [4a]− the nitro-substituted ligand formed
almost exclusively as the asymmetric species in which two of
the pyrazole rings have the trifluoridomethyl group in the
3-position and one pyrazole ring is attached “in reverse” with
the trifluoridomethyl group in the 5-position (see Scheme 2).
This asymmetric isomer will be referred to as 4a′.
All trispyrazolylborate ligands were isolated as solvent
adducts of their sodium salts, typically incorporating solvents
such as acetone, THF or diethyl ether in stoichiometric ratios.
Instances of mixed solvent adducts were also observed such as
in Na4d·(Et2O)0.5(acetone)0.5
. Examples of similar solvent
adducts in other fluorinated trispyrazolylborate ligands have
been described.17,20,21 Na4b formed as the water adduct even
when recrystallized in the presence of suitable solvents or
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Table 2 Selected bond distances (Å) and angles (°) for Na4a’ and Na4b
Bond
distances (Å)
Bond
angles (°)
Na4a′
Na4b
Na4a′
Na4b
Na1–N12
Na1–N22
Na1–N32
Na1–O1W
Na1–O1W′
N11–N12
N21–N22
N31–N32
Na1⋯F12
Na1⋯F13′
Na1⋯F21′
Na1⋯F23
Na1⋯F33
2.4731(15)
2.4351(15)
2.5737(15)
2.2581(16)
2.4595(12)
2.4440(12)
2.4355(12)
2.4512(12)
2.4274(12)
1.3605(14)
1.3589(15)
1.3590(15)
O1W–Na1–O1W′
O1W–Na1–N12
O1W–Na1–O231′
O1W–Na1–O232′
O1W′–Na1–N12
O1W′–Na1–N32
O1W–Na1–N22
N22–Na–N32
82.03(4)
104.30(4)
99.18(6)
86.28(6)
67.35(5)
100.89(4)
99.69(4)
104.57(4)
73.79(4)
162.1(3)
1.3566(19)
1.3603(18)
1.3551(19)
3.625(2)
103.78(6)
81.30(5)
N12–Na–F13′
O231′–Na1–O231′
2.930(12)
46.64(4)
4.144(1)
3.197(4)
3.116(2)
the course of hours to days; decomposition is slowest for the
most Lewis acidic complexes.
Table 3 Selected bond distances (Å) and angles (°) for complexes 5b,
5c, 5d and 5fa
Bond distances (Å)
Single crystal X-ray crystallography
5b
5c
5d
5f
Colorless single crystals of Na4a′, Na4b, 5b, 5c, 5d, 5f, 6b, 6c,
6d and 6f were obtained by slow evaporation of DCM solutions
at −20 °C and were characterized by single crystal X-ray crystallo-
graphy. Crystallographic data are given in Tables S1–S3.†
Selected distances and bond angles are given in Table 2 for the
sodium salts of 4a′ and 4b, in Table 3 for the ethene com-
plexes, and in Table 4 for the carbonyl complexes. Projections
of the structures of Na4a′ and Na4b are shown in Fig. 1 and 2.
As representative examples of the copper(I) complexes projec-
tions of the structures of 5b and 6b are shown in Fig. 3; projec-
tions of the other structures are provided in the ESI.†
Na4a′ crystallized as a coordination polymer with bridging
NO2⋯Na+ interactions (with bidentate κ2-O,O′ coordination).
The sodium ions are in a severely distorted octahedral coordi-
nation sphere comprising three nitrogen atoms from the
ligand 4a′, two oxygen atoms from a nitro group of an adjacent
complex and a water molecule, which is stabilized by hydrogen N12–Cu1–N22
bridges to the nearby nitro group oxygen atoms. The Na–N dis-
tances range from 2.4351(15) to 2.5737(15) Å, the Na–Oaqua dis-
tance is 2.25581(16) Å and the Na–O2N distances are 2.5291 C1–Cu1–N22
(14) and 2.8633(14) Å. The severely distorted octahedral coordi-
nation sphere on the sodium ion in Na4a′ appears to be com-
plemented by an intramolecular Na⋯FC contact between the C2–Cu1–N32
CvCethene
Cu–Cethene
1.357(4)
2.034(2)
2.051(5)
2.0450(15)
2.0369(15)
2.2465(16)
1.3626(19)
1.3619(19)
1.3631(19)
1.553(2)
1.311(14)
2.019(9)
2.035(9)
2.094(3)
2.070(3)
2.137(4)
1.356(5)
1.355(5)
1.363(5)
1.558(5)
1.561(5)
1.537(6)
1.350(3)
1.351(8)
2.054(5)
2.046(5)
2.026(4)
2.046(4)
2.224(4)
1.360(5)
1.363(6)
1.358(5)
1.564(5)
1.539(6)
1.551(6)
2.0428(16)
2.0455(16)
2.0255(14)
2.0164(13)
2.2964(13)
1.3685(17)
1.3648(17)
1.3682(17)
1.553(2)
Cu–N12
Cu–N22
Cu–N32
N11–N12
N21–N22
N31–N32
N11–B1
N21–B1
N31–B1
1.554(2)
1.545(2)
1.552(2)
1.545(2)
Bond angles (°)
5b
5c
5d
5f
C–Cu–C
Cu–CvC
38.79(11)
71.3(2)
69.9(2)
37.7(4)
70.5(5)
71.8(5)
38.55(7)
70.83(10)
70.62(10)
90.77(5)
90.77(5)
85.68(5)
115.04(7)
147.96(7)
108.95(7)
151.13(6)
111.15(6)
111.57(7)
38.5(2)
70.5(3)
71.1(3)
92.55(6)
87.03(6)
89.81(5)
149.26(9)
112.92(9)
107.70(9)
111.18(9)
147.41(11)
114.02(12)
89.58(14)
90.60(13)
90.17(13)
126.2(4)
111.5(3)
135.8(4)
111.8(3)
148.9(3)
110.8(3)
94.64(15)
88.25(14)
87.01(14)
148.49(18)
110.75(18)
111.30(18)
110.68(18)
144.25(19)
116.93(18)
N22–Cu1–N32
N12–Cu1–N32
C1–Cu1–N12
C1–Cu1–N32
C2–Cu1–N12
C2–Cu1–N22
sodium ion and a nearby trifluoridomethyl group. The upper
a Bond distances and bond angles are only provided for one of the two
crystallographically independent molecules.
limit to what may be considered as short contacts (and thus
potentially dative bonds) between a hard donor/acceptor pair
such as sodium ions and fluorine atoms in fluoridocarbons is
somewhat vague as it depends on the ionic and covalent radii
that are used. Using the ionic radius of six-coordinate Na+ ions
reported by Shannon et al. (1.02 Å) Plenio et al. suggested an
upper limit to the interatomic distance between Na+ ions and
fluorine atoms in fluoridocarbons at 3.07 Å.22,23 It was further
pointed out that Na⋯FC contacts typically have shallow poten-
tial wells, which means small outside forces such as those
present in crystals because of packing can cause significant
changes to the interatomic distance between the sodium ion
and the fluorine atom. The distances observed for the Na⋯FC
contacts in Na4a′ are 3.625(2) Å and 4.144(1) Å, considerably
longer than the upper limit of 3.07 Å even when crystal
packing effects are taken into account. The proximity of the tri-
fluoridomethyl groups is therefore not considered to constitute
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2.4355(12) Å to 2.4595(12) Å and the Na–Oaqua distances are
2.4274(12) Å and 2.4512(12) Å. trans to the apical position are
one intermolecular and two intramolecular Na⋯FC short con-
tacts, at distances of respectively 2.930(12), 3.197(4) and
3.116(2) Å. With the foregoing considerations regarding
Na⋯FC short contacts in mind it appears reasonable to con-
sider both the intermolecular and intramolecular Na⋯FC dis-
tances in the structure of Na4b as short contacts.
Table 4 Selected bond distances (Å) and angles (°) for complexes 6b,
6c, 6d and 6f a
Bond distances (Å)
6b
6c
6d
6f
C1–O11
Cu1–C1
Cu–N12
Cu–N22
Cu–N32
N11–N12
N21–N22
N31–N32
N11–B1
N21–B1
N31–B1
1.124(2)
1.126(4)
1.800(3)
2.069(2)
2.056(2)
2.057(3)
1.354(3)
1.358(3)
1.360(3)
1.553(3)
1.549(3)
1.546(4)
1.123(8)
1.791(6)
2.0552(19)
1.130(4)
1.793(3)
2.038(2)
2.062(2)
2.075(2)
1.353(3)
1.367(3)
1.358(3)
1.560(3)
1.554(3)
1.554(3)
1.7998(19)
2.0642(15)
2.0496(15)
2.0505(15)
1.3571(19)
1.3623(19)
1.3625(19)
1.548(2)
The crystal structures of Na4a′ and [Na(4e)(H2O)]n contain
non-bridging water ligands while the crystal structures of Na4b
1.364(2)
1.553(2)
and [Na2(TpCF ,CH )2(µ-H2O)2] are dinuclear and contain bridg-
ing water molecules. The Na–Oaqua distance in the crystal
structure of Na4a′ of 2.2558(16) Å is comparable to the dis-
tance observed in [Na(4e)(H2O)]n (2.245(2) Å) but shorter than
3
3
1.557(2)
1.553(2)
the distance in [Na2(TpCF ,CH )2(µ-H2O)2] (2.417(2) Å), which is
closer to the Na–Oaqua distance found in Na4b (2.4274(12) Å
and 2.4512(12) Å).16
3
3
Bond angles (°)
6b
6c
6d
6f
Complexes 5b, 5c, 5d, 5f, 6b, 6c, 6d and 6f all have highly
similar coordination environments around the copper(I)
center. In every case the copper(I) center is coordinated by
three nitrogen atoms from the trispyrazolylborate ligand and
either the carbon atom of the carbonyl ligand or the ethene
ligand in the typical η2 coordination. Bond lengthening or con-
traction in the carbonyl and ethene ligands as a result of
π-backbonding interactions are not evident from the bond
lengths observed in the crystal structures and are assumed to
be obscured by crystal packing effects. The Cu–N distances in
the ethene complexes (5b, 5c, 5d and 5f) range from
2.0164(13) to 2.2964(13) Å with in all cases two shorter bonds
(2.0164(13)–2.094(3) Å) and one longer bond (2.173(4)–
2.2964(13) Å); such asymmetry in the Cu–N bond lengths was
also observed in other [CuI(TpR,R′)(C2H4)] complexes.24,25 The
Cu–N bond lengths in the carbonyl complexes (6b, 6c, 6d and
6f) fall in the range 2.038(2) Å–2.075(2) Å and do not feature
the two ranges of Cu–N bond lengths observed in the ethene
complexes. The unequal Cu–N bond lengths in the ethene
complexes are attributed to the symmetry of ethene. Ethene
ligands have a two-fold symmetry while the carbonyl ligands
have full rotational symmetry. This means that while the carb-
onyl copper complexes can retain the approximate threefold
symmetry of the trispyrazolylborate ligand, whereas the ethene
complexes cannot. The resulting pseudo-twofold symmetry
Cu1–C1–O11
C1–Cu1–N12
C1–Cu1–N22
C1–Cu1–N32
N12–Cu1–N22
N22–Cu1–N32
N32–Cu1–N12
176.0(2)
118.66(8)
129.95(8)
126.11(7)
90.60(6)
88.85(6)
91.85(6)
177.4(3)
180.0
125.13(5)
178.3(3)
122.17(11)
127.99(11)
124.75(13)
90.14(9)
90.58(8)
90.37(8)
126.66(11)
121.77(12)
125.74(11)
91.65(8)
90.23(7)
90.31(8)
90.19(7)
a Bond distances and bond angles are only provided for one of the two
crystallographically independent molecules.
Fig. 1 Projection of part of the structure of [Na(4a’)(H2O)]n with dis- observed in the solid state of the ethene complexes means that
placement ellipsoids plotted at the 50% probability level at 110(2) K. For
clarity major parts of the ligand are shown in wireframe and hydrogen
π-backbonding into the π* orbitals of the ethene ligands can
not occur with equal contributions from all of the pyrazole
1
2
2
3
atoms have been omitted. Symmetry operations ’ = [23 − x, y −
,
− z],
rings but mostly from two of the three rings. The resulting dis-
crepancy in charge transfer from the rings to the π*-orbitals of
the ethene ligand explains the presence of two short Cu–N
bonds and one long Cu–N bond in complexes 5b–g. The com-
pounds 6b, 6c and 6f crystallized with pseudo threefold
rotational symmetry with Cu–C–O angles ranging from
176.0(2) to 178.3(3)°. Complex 6d crystallized with proper
threefold rotational symmetry. The elongated thermal ellipsoid
for the oxygen atom of the carbonyl ligand suggests that this
ligand is most likely disordered as the CuO bond may not be
perfectly aligned along the threefold axis. The deviation from
1
’’ = [23 − x, y + 2
,
23 − z].
actual bonding between the sodium ion and the fluorine
atoms but merely dipolar interactions.
Na4b crystallized as a dimer comprising two sodium ions
in distorted square-pyramidal coordination geometries. The
sodium ions are each coordinated facially by three nitrogen
atoms of the trispyrazolylborate ligand and by two bridging
water molecules (Oaqua). The Na–N distances range from
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Fig. 2 Projection of the structure of [Na2(4b)2(µ-H2O)2] with displacement ellipsoids plotted at the 50% probability level at 150(2) K. For clarity
major parts of the ligand are shown in wireframe and hydrogen atoms have been omitted. Symmetry operation ’ = [−x, 1 − y, −z].
Fig. 3 Projections of the structures of 5b (left) and 6b (right) with displacement ellipsoids plotted at the 50% probability level at 110(2) K. For clarity
hydrogen atoms have been omitted. Projections of the structures of the other ethene and carbonyl complexes are available in the ESI.†
rotational symmetry in 6b, 6c and 6f is small and might be the such effects appears to indicate fluxional behavior of the
result of crystal packing effects.
ethene ligand within the NMR timescale. In the NMR spectra
of 5b–g the ethene ligands were detected as sharp singlets
with chemical shifts between 4.81 and 4.96 ppm which are
upfield from the chemical shift of free ethene (5.40 ppm in
DCM-d2) but not as far upfield as the signals observed in com-
NMR spectroscopy
1
The H and 13C-NMR spectra of compounds 5a′, 5b–g and 6a′,
6b–g were recorded in deuterated DCM as it was found to be
the only solvent in which the ethene complexes are all soluble
and air-stable over longer periods of time (more than
30 minutes). CDCl3, acetone-d6, THF-d8, benzene-d6 and DMSO-
d6 caused solutions of the copper ethene compounds to turn
green after some time. The coordinating solvents DMSO-d6,
acetone-d6, THF-d8 and benzene-d6 (a π-donor solvent) all
appeared to be competing with the ethene ligands as peaks for
free ethene grow over time on 1H NMR. The complexes with the
less Lewis basic trispyrazolylborate ligands are more stable in
solution. Complexes 5b–g gave very similar spectra with no evi-
dence of anisotropy in the signal for the ethene ligand at room
temperature. Considering the asymmetry observed in the crystal
structures of complexes 5b–g splitting of the ethene peaks or at
least some peak broadening could be expected. The absence of
plexes of non-fluorinated trispyrazolylborate ligands like
26
[TpMe Cu(C2H4)] (4.41 ppm in DCM-d2). The ethene protons
2
of 5a′ showed as a singlet at 4.44 ppm which was assigned to
the asymmetric isomer; a small singlet at 4.99 ppm in the
same spectrum was tentatively assigned to the ethene protons
of the complex 5a incorporating the symmetric isomer [4a]−.
The ratio of the integrals of the ethene protons of the sym-
metric 5a vs. the asymmetric species 5a′ was approximately
1 : 20. In all ethene complexes peak broadening in the pres-
ence of free ethene was not observed, indicating that the
exchange of coordinated ethene, if at all, does not occur
within the NMR time scale. Solutions of all ethene complexes
in DCM-d2 show no peak for free ethene even upon prolonged
standing. The 1H-NMR signals for the borohydrides were
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Fig. 4 1H chemical shifts (squares, red trend line. 5a’ was not included in the trend line) and 13C chemical shifts (triangles, blue trend line) of the
ethene ligands vs. the Hammett σp parameters of the substituents on the trispyrazolylborate ligands in complexes 5a–g and 5a’.
observed in the sodium compounds Na4a–g as well as the analogy with the ethene resonances in the NMR spectra of
carbonyl and ethene complexes as broadened singlets with compound 5a′. The CO stretching frequency observed in
chemical shifts in the range 4.3–4.9 ppm. In principal the reso- complex 6g is significantly higher than the value predicted
nances of the borohydrides should be present as overlapping based on the trend line in Fig. 5 (approximately 2076 cm−1) for
quartets and smaller septets as a result of splitting by 10B which no obvious explanation is available. Possibly unusual
(I = 3) and 11B (I = 3/2). Typically, however, these resonances crystal packing effects cause the CO stretching frequency to be
are observed as (broadened) quartets only in relatively sym- different than predicted, but as all attempts to grow crystals
metric environments. In less symmetric environments the failed this hypothesis remains untested. Unfortunately infra-
quadrupoles of the boron nuclei are more pronounced and the red measurements on a sample of 6g in DCM were inconclu-
borohydride resonances broaden to broad singlets without dis- sive as no clear signal was observed until evaporation caused
tinguishable splitting as is the case in this work.27
solid 6g to precipitate. CO stretching typically shows itself in
In the 13C-NMR spectra of complexes 6a′ and 6b–g no signals infrared spectroscopy as sharp absorptions due to the sym-
were observed for the CO ligands even after increasing the relax- metry of the vibration. One possible explanation for the
ation delay; we ascribe the lack of signals for CO to the low absence of an obvious CO stretching peak in solution is a low-
natural abundance of 13CO and peak broadening.28,29 The shifts ering of the symmetry of the bonding environment surround-
of the resonances trispyrazolylborate ligands show only small ing the carbonyl ligand. Such lowering of local symmetry
differences between the ethene and the carbonyl complexes. For could be the result of out-of-axis vibrations of the carbonyl
complexes 5b–g the change in the 1H-NMR and 13C-NMR shifts ligand, somewhat similar to motion of the ethene ligands
of the ethene protons and carbon atoms respectively is linearly in the NMR experiments and presumably have similarly low
correlated with the σp values of the para-substituents on the barriers. We surmise that liberation of the carbonyl ligand
phenyl groups (R2 = 96% for 1H and R2 = 97% for 13C; see from the copper ion is considerably more pronounced in solu-
Fig. 4).
tion compared to the solid state and that as a result peak
broadening causes the weak signal to be drowned out by
noise.
Infrared spectroscopy
The B–H moieties of the trispyrazolylborate ligands feature
IR stretching frequencies that are typically found as small,
broad peaks around 2600 cm−1 (see Table 5 and Fig. 5) in
Lewis-basic trispyrazolylborate complexes. In order to compare
the B–H stretching frequencies of ligands 4a–g the carbonyl
complexes 6a′ and 6b–g and other, structurally similar, carbo-
nyl complexes were compared. The pseudo-threefold axial sym-
metries observed in such carbonyl complexes mean that the
comparison is not likely to be distorted by local asymmetry.
The B–H stretching frequencies of complexes 6a′ and 6b–g
were observed in the region 2611–2647 cm−1. The B–H stretch-
ing frequencies show considerably less linearity vs. the σp para-
meters of the substituents of the trispyrazolylborate ligands
The IR spectra of complexes 5a′, 5b–g and 6a′, 6b–g were
recorded in the solid state at 1 cm−1 resolution. Complexes
6a′, 6b–g have CO stretching frequencies in the range
2096–2120 cm−1, close to that of free CO (2143 cm−1). This
indicates that the compounds have relatively Lewis-acidic
copper(I) ions compared to other, similar, copper(I) carbonyl
complexes like [TpMe CuCO] (2066 cm−1) and [TpPh CuCO]
(2080 cm−1, see Table 5 for more examples). The CO stretching
frequencies correlate linearly (R2 = 95%) with the σp values of
the substituents on the phenyl rings for compounds, with the
exception of 6a′ and 6g (see Fig. 5). For complex 6a′ this is
likely because the structure of [4a′]− is asymmetric and thus
poorly comparable to the other ligands in the series, in
2
2
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Table 5 Selected 1H and 13C chemical shifts and bond lengths for the compounds 5a–g and 6a–g, L = C2H4 or CO
C2H4 a (ppm)
Compound
13C
1H
νCO (cm−1
)
νBH f (cm−1
)
CvC (Å)
CuO (Å)
Ref.
Free C2H4/CO
123.2
89.1b
86.4
86.8
86.4
5.40
2143
2137
2105
2120
2113
2107
2103
2101
2100
2096
2096
2066
2080
1.3384(10)
1.325(9)
1.13078(9)
1.110(5)
30, 31
[Tp(CF )2CuL]
4.96b
2634
2611
2620
2616
2575
2616
2639
2507
2636
2647
2500
2635
18, 20, 32
This work
This work
This work
33
This work
This work, 16
18,20
3
[Cu(4a′)L]d
[Cu(4b)L]
[Cu(4c)L]
4.44 (4.99e)
4.96
4.91
1.342(3)
1.340(9)
1.124(2)
1.126(4)
1.122(3)
1.123(8)
1.113(5)
1.126(5)
1.130(4)
[TpCF ,MeCuL]
3
[Cu(4d)L]
86.1
85.8
85.8c
85.6
84.9
4.91
4.91
4.89c
4.81
4.84
4.41
3.53
1.350(3)
1.30(1)
1.34(1)
1.351(8)
[TpCF ,PhCuL]
3
[TpCF CuL]
3
[Cu(4f)L]
[Cu(4g)L]
This work
This work
26,34
[TpMe CuL]
1.329(9)
1.381(19)
2
[TpPh2CuL]
81.6b
1.08(1)
8,35
a DCM-d2. b CDCl3. c C6D6. d Asymmetric isomer. e Symmetric isomer. f As observed in the Cu(I) CO complexes.
Fig. 5 Infrared CO stretching frequencies (red squares) and BH stretching frequencies (blue triangles) of complexes 6a’, 6b–g vs. the Hammett
σp parameters of the substituents on the trispyrazolylborate ligands. The red linear trend line was calculated including all points except 6a’ and 6g
(R2 = 0.95). The blue linear trend line was calculated including all complexes 6a’, 6b–g (R2 = 0.74).
4a′ and 4b–g (R2 = 0.74) than the CO stretching frequencies. 3a–g were readily prepared from ethyl trifluoridoacetate and
Intriguingly, compared to the unexpectedly high CO stretching 4′-substituted acetophenones using a Claisen condensation,
frequency the B–H stretching frequencies of 6a′ and 6g appear followed by cyclization with hydrazine. The synthesis of the
almost exactly on the trend line in Fig. 5. The most Lewis-basic trispyrazolylborate ligands requires fine-tuning of the con-
trispyrazolylborate ligands have the highest B–H stretching fre- ditions depending on the specific pyrazole using solventless
quencies as donation of electron density towards the boro- reactions whenever possible; 4-methylanisole was used as a
hydride increase the strength of the hydridic bond.
solvent if temperature control was required or the melting
point of the pyrazole was too high. To the best of our knowl-
edge [4a′]− is only the second example in the literature of a tris-
pyrazolylborate ligand to include the synthetically challenging
Discussion
− 36
nitro group, the first being [TpNO ] .
2
The trispyrazolylborate ligands studied in this work all
formed as their symmetric isomers with the trifluoridomethyl
groups in the 3-positions of the pyrazole rings, except [4a′]−
which formed as a mixture of symmetric and asymmetric
species. The major product was the asymmetric species in
which one of the pyrazole rings is connected to the boron
In this work seven new fluorinated trispyrazolylborate ligands
([TpCF ,4-RPh]−, R = NO2, CF3, Cl, F, H, MeO and NMe2) and
3
their copper(I) complexes with carbon monoxide and ethene
were prepared. The ligands form an isosteric spectrochemical
series based on the electronic properties of the substituents
placed on the 4-position of the phenyl rings. The pyrazoles
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center with the nitrogen atom adjacent to the phenyl ring. The rings in the trispyrazolylborate ligands is excellent. The ability
regioselectivity usually observed in the synthesis of trispyrazo- of the ligands to propagate the electron donating or withdraw-
lylborate ligands is a result of the relative steric and electronic ing effects of the substituents on the phenyl rings over as
properties of the substituents on the 3 and 5 positions of the many as eight bonds and almost one nanometer, is remark-
pyrazole, which influence the nucleophilicity of the nitrogen able. The explanation for these long range effects is found in
atoms. Typically the bulkiest substituent assumes the 3 posi- the ability of the ligands to propagate charges by means of
tions of the pyrazole rings in the trispyrazolylborate anion. resonance structures. Further underscoring the importance of
However, if one of the substituents is considerably more elec- resonance effects is the observation that the B–H stretching
tron withdrawing than the other it will assume the 3 position frequencies observed in the carbonyl complexes 6a′ and 6b–g
even if the other substituent is bulkier. This regioselectivity is are much less predictable than the CO stretching frequencies
pronounced in ligands with clearly sterically or electronically because the nitrogen atom adjacent to the borohydride is not
differentiated substituents like [TpPh,Me]−, [TpCF ,Me −
]
and part of these resonance structures. We conclude that indeed
3
[TpCF
]
− but breaks down when the steric and electronic differ- the π-backbonding ability of the copper(I) centers can be modi-
3
ences are small such as in [TpiPr,Me −
which formed a fied extensively through substitution of the trispyrazolylborate
]
4 : 1 mixture of symmetric and the asymmetric isomers.37 Evi- ligands without significantly affecting the steric properties of
dently the strongly electron withdrawing nitro group in [4a′]− the binding pocket surrounding the metal center.
causes the electronic disparity between the trifluoridomethyl
groups and phenyl rings to diminish sufficiently to shift the
thermodynamic equilibrium of the system so that the asym-
metric isomer is favored over the symmetric isomer. The
Conclusions
absence of the formation of asymmetric isomers in the other In this work the synthesis and characterization of copper(I)
ligands in the series puts an upper limit on the σp parameter complexes comprising a spectrochemical series of trispyrazo-
of the substituents that can be used to synthesize symmetric lylborate ligands and ethene or carbon monoxide have been
[TpCF ,4R-Ph]− ligands between +0.54 (CF3) and +0.78 (NO2).
described. The ethene and carbonyl complexes described in
3
The good correlation between the chemical shifts of the this work are essentially isostructural around their copper(I)
ethene protons in complexes 5b–g vs. σp of the substituents on centers while their electronic properties vary significantly and
the phenyl rings of the ligands was used to predict the chemi- predictably based on the Hammett σp parameters of the substi-
cal shift of the ethene protons of the symmetric complex 5a. tuents placed on the trispyrazolylborate ligands. The spectro-
Based on the trend line in Fig. 4 and the σp parameter of the scopic data reveal good correlations between the chemical
nitro group the signal for the symmetric complex 5a was pre- shifts of the ethene protons and CO stretching frequencies vs.
dicted to be around 4.98 ppm and indeed a weak singlet was the Hammett σp parameters. Notable exceptions to the, other-
found at 4.99 ppm. Comparison of the integrals of the ethene wise predictable, compounds in this work were the ligand
protons in the symmetric and asymmetric complexes gave an [4a′]− and the carbonyl complex 6g. The ligand [4a′]− formed
approximate 1 : 20 ratio. Unfortunately attempts to locate the almost exclusively as an asymmetric isomer with one of the
infrared CO stretching frequency of the symmetric isomer of pyrazole rings counter-rotated so as to have its 4′-nitrophenyl
6a using the σp parameter of the nitro group and the trend line substituent in the 3-position instead of the trifluoridomethyl
in Fig. 5 were unsuccessful as the predicted CO stretching fre- group. We attribute the asymmetry of [4a′]− to the strongly
quency for the symmetric isomer 6a at 2128 cm−1 would be electron withdrawing properties of the nitro group. Copper
obscured by the much stronger absorption at 2105 cm−1 of the complex 6g shows a surprisingly high CO stretching frequency.
asymmetric isomer 6a′.
That this aberrant result is not due to trend-breaking pro-
More difficult to explain is the unexpectedly high CO perties of the ligand is evident from the good correlation
stretching frequency observed for 6g, which was predicted to between the predicted and found values in the corresponding
be at 2076 cm−1 but instead was found at 2096 cm−1, the same ethene complex 5g. The results presented in this work under-
value as found for 6f. It appears implausible that the CO score the usefulness of combining the use of more than a
stretching frequencies of 6f and 6g are equal as an effect of single ancillary ligand probe with the systematic study of this
equal amounts of π-backbonding interactions as the 1H and promising and important class of ligands.
13C chemical shifts of the ethene ligands in 5f and 5g almost
exactly conform to the predicted values. Unfortunately the
higher than expected CO stretching frequency of 6g cannot be
conclusively explained by crystal packing effects as infrared
spectroscopy on 6g in solution was inconclusive and all
Experimental
General information
attempts at crystallization failed.
All manipulations of air-sensitive compounds were performed
With the exceptions of 6a and 6g the predictability of the in an atmosphere of purified argon gas using standard
chemical shifts of the ethene protons in the ethene complexes Schlenk techniques. All solvents were purchased from com-
and CO stretching frequencies in the carbonyl complexes with mercial sources and reagent grade. Solvents used for air-
respect to the σp parameters of the substituents of the phenyl sensitive manipulations were dried and deaerated using a
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PureSolv MD 5 Solvent Purification System and stored on 3 Å crystal shattered (most likely due to a solid–solid phase tran-
molecular sieves under argon. When appropriate, glassware sition), resulting to poor quality diffraction. When crystals
1
was flame dried in vacuo immediately prior to use. H and 13C were cooled from RT to 150 K, the crystals remained stable.
NMR spectra were recorded on a Bruker DPX300 spectrometer CCDC 1430371 contains the supplementary crystallographic
(300 MHz for 1H and 75.44 MHz for 13C); Bruker DMX400 data for Na4b.
1
spectrometer (400 MHz for H and 100.6 MHz for 13C); Bruker
[Cu(4b)(C2H4)] (5b). The structure is mostly ordered. The
Avance AV500 spectrometer (500 MHz for H, 160 MHz for 11B asymmetric unit contains two crystallographically independent
1
and 126 MHz for 13C) or Bruker Avance 600 (600 MHz for H, molecules. One of the two crystallographically independent
1
193 MHz for 11B and 151 MHz for 13C). Chemical shifts are ethene molecules is found to be disordered over two orien-
given in ppm and referenced using the deuterated solvents as tations, and the occupancy factor of the major component of
internal references for H and 13C.38 13C spectra were recorded the disorder refines to 0.849(5). As the H atoms of the minor
1
using 1H-decoupling. Elemental analyses were performed component could not be retrieved via difference Fourier map,
using a Perkin Elmer 2400 series II CHNS/O analyzer or by the the H atoms of the major component were constrained to have
Microanalytical laboratory Kolbe in Germany. IR spectra were full occupancies. CCDC 1430362 contains the supplementary
recorded on a Perkin Elmer UATR Two FT-IR spectrometer set crystallographic data for 5b.
to a resolution of 1 cm−1. HRMS spectra were recorded on a
[Cu(4c)(C2H4)] (5c). The structure is mostly ordered. The
Thermo Scientific LTQ Orbitrap XL high resolution FT-MS asymmetric unit contains two crystallographically independent
system in MeCN. Intermediates 2a, 2b, 2d and 2f were syn- molecules. One of the two crystallographically independent
thesized according to a literature procedure using KOt-Bu in ethene molecules is found to be disordered over two orien-
THF instead of sodium in methanol.39 2d was purified by con- tations, and the occupancy factor of the major component of
version to the copper(II) diketonate instead of column the disorder refines to 0.502(7). The crystal is racemically
chromatography as described below.
twinned, and the BASF scale factor refines to 0.510(14). CCDC
1430363 contains the supplementary crystallographic data
for 5c.
Single crystal X-ray crystallography
All reflection intensities were measured at 110(2) K or 150(2) K
[Cu(4d)(C2H4)] (5d). The structure is ordered. CCDC
(only for Na4b) using a SuperNova diffractometer (equipped 1430364 contains the supplementary crystallographic data
with Atlas detector) with Cu Kα radiation (λ = 1.54178 Å) under for 5d.
the program CrysAlisPro (Versions 1.171.36.32/1.171.37.31
[Cu(4f)C2H4] (5f). The structure is mostly ordered. The
Agilent Technologies, 2013/2014). The same program CrysAlis- asymmetric unit contains two crystallographically independent
Pro was used to refine the cell dimensions and for data molecules. One of the two crystallographically independent
reduction. All structures were solved with the program ethene molecules is found to be disordered over two orien-
SHELXS-2013/2014 (Sheldrick, 2008) and were refined on tations, and the occupancy factor of the major component of
F2 with SHELXL-2013/2014.40 Analytical numeric absorption the disorder refines to 0.56(3). The positions of the H atoms
corrections based on a multifaceted crystal model were for the disordered ethene molecule are most likely smeared
applied using CrysAlisPro. The temperature of the data collec- out, and cannot be retrieved reliably from the data collected.
tion was controlled using the system Cryojet (manufactured The crystal is racemically twinned, and the BASF scale factor
by Oxford Instruments). The H atoms were placed at calculated refines to 0.43(3). The riding model AFIX 93 could not be used
positions (unless otherwise specified) using the instructions as this will put the H atoms along the plane defined by Cu2,
AFIX 43 with isotropic displacement parameters having C3 and C4, which is chemically impossible (the H atoms must
values 1.2 times Ueq of the attached C atoms. The H atoms be approximately located in the plane perpendicular to the
attached to C1/C2, C3/C4 (ethene), and to B1 and B2 were plane defined by Cu2, C3 and C4). CCDC 1430365 contains the
found from difference Fourier maps, and their atomic coordi- supplementary crystallographic data for 5f.
nates were refined freely. The H atoms attached to the water
[Cu(4b)CO] (6b). The structure is mostly ordered. One –CF3
molecules (only for Na4a′ and Na4b) and to the B atoms were group is disordered over two orientations. The occupancy
found from difference Fourier maps, and their coordinates factor of the major component of the disorder refines to
were refined freely using the DFIX instructions. For 5b, 5c, 5d 0.742(15). CCDC 1430366 contains the supplementary
and 5f, the C–H and H⋯H distances of the ethene molecules crystallographic data for 6b.
were restrained using the DFIX instructions. Their isotropic
temperature factors were fixed for the ethene molecules (1.2 pseudo-merohedrally twinned. The twin relationship is
times Ueq of the attached C atoms). defined by (101/0−10/00−1), which corresponds to a twofold
Na4a′. The structure is ordered. CCDC 1430370 contains the axis along a*. The BASF scale factor refines to 0.3341(9). CCDC
supplementary crystallographic data for Na4a′. 1430367 contains the supplementary crystallographic data
Na4b. The structure is partly disordered. The six −CF3 for 6c.
[Cu(4c)CO] (6c). The structure is ordered. The structure was
groups are found disordered over two or three orientations. All
[Cu(4d)CO] (6d). The structure is ordered. The Cu complex
occupancies factors can be retrieved from the cif file. When is found at sites of threefold axial symmetry, and only one
crystals of Na4b were flash cooled from RT to 110 K, the third of the complex is crystallographically independent. The
21118 | Dalton Trans., 2015, 44, 21109–21123
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absolute configuration was established by anomalous-dis- pension was cooled to 0 °C on an ice bath and ethyl
persion effects in diffraction measurements on the crystal. The trifluoridoacetate (14.2 mL, 119 mmol) was then added drop-
Flack and Hooft parameters refine to −0.009(6) and −0.010(6), wise. 4′-Chloridoacetophenone (13 mL, 100 mmol) in 125 mL
respectively. CCDC 1430368 contains the supplementary crys- dry Et2O was then slowly dropped into the first suspension
tallographic data for 6d.
with vigorous stirring. The ice bath was removed and the reac-
[Cu(4f)CO] (6f). The structure is mostly ordered. One –CF3 tion was stirred at room temperature for 30 minutes, the reac-
group is disordered over two orientations. The occupancy tion was then warmed to 50 °C and stirred overnight. The
factor of the major component of the disorder refines to mixture was added to 250 mL 0.5 M HCl and separated. The
0.879(14). The crystal that was mounted on the diffractometer aqueous fraction was extracted twice with Et2O (2 × 125 mL).
was non-merohedrally twinned. The twin relationship corres- The combined organic fraction was then washed with water
ponds to a twofold axis around 0.9995a* + 0.0115b* + (1 × 200 mL) and brine (1 × 200 mL) and dried over Na2SO4.
0.0288c*. The BASF scale factor refines to 0.5073(14). CCDC The solvent was removed in vacuo to yield 2c as a yellow solid.
1430369 contains the supplementary crystallographic data Yield 23.4 g (93%).1H NMR (400 MHz, CDCl3) δ 14.57 (s, 1H,
for 6f.
enol-OH), 7.87 (d, J = 8.8 Hz, 2H), 7.47 (d, J = 8.8 Hz, 2H), 6.53
(s, 1H). 13C NMR (100 MHz, CDCl3) δ 185.00, 177.42 (q, J = 36.6
Hz), 140.75, 131.39, 129.50, 129.02, 117.22 (q, J = 283.5 Hz),
Ligand and complex synthesis
5-(4-Nitrophenyl)-3-(trifluoridomethyl)-1H-pyrazole (3a). 2a 92.39 (q, J = 2.1 Hz).
(19.6 g, 75 mmol) was suspended in 250 mL EtOH and the sus-
2c (23.0 g, 93.4 mmol) was dissolved in 100 mL n-PrOH and
pension was cooled to 0 °C using an ice bath. Hydrazine hydrazine hydrate (5.0 mL, 103 mmol) was added dropwise.
hydrate (3.9 mL, 80 mmol) was added dropwise with vigorous The reaction was heated to reflux for 2 hours. The reaction was
stirring. After stirring at 0 °C for 10 minutes the ice bath was then cooled to 0 °C in an ice bath. 10.5 mL 37% HCl was
removed and the reaction was stirred at room temperature for added after which the ice bath was removed and the reaction
approx. 30 minutes, the reaction was then heated to reflux for was heated to 100 °C for 30 minutes. The reaction was cooled
approx. 17 hours. The EtOH was then evaporated in vacuo to a down to room temperature and the mixture was diluted with
volume of approx. 100 mL. The solution was cooled in an ice 600 mL cold water. The product was collected by filtration and
bath to 0 °C and 20 mL 37% HCl was added dropwise with vig- washed with water (approx. 1 L). The product was dried
orous stirring. The solution was left to stir for 1 hour and then in vacuo and purified by vacuum sublimation (160 °C, 10−4
poured into 600 mL cold water, the resulting suspension was atm) to yield the product as a white solid. Yield 20.4 g (88%).
1
filtered and the residue was washed on the filter with 1 L M.p. 151–153 °C. H NMR (300 MHz, CDCl3) δ 13.09 (s, 1H),
water. The solids were dried in vacuo and then purified by 7.46 (d, J = 8.6 Hz, 2H), 7.38 (d, J = 8.5 Hz, 2H), 6.64 (s, 1H).
vacuum sublimation (215 °C, 10−4 atm) to yield the product as 13C NMR (75 MHz, CDCl3) δ 144.55, 143.45 (q, J = 37.2 Hz),
yellow needles. Yield 14.0 g (73%). M.p. darkened around 135.62, 129.59, 126.87, 126.26, 120.97 (q, J = 268.9 Hz), 101.23
1
150 °C, melted 169–171 °C. H NMR (400 MHz, Acetone-d6) δ (q, J = 1.6 Hz).
13.53 (s, 1H), 8.35 (d, J = 8.6 Hz, 2H), 8.12 (d, J = 8.6 Hz, 2H),
5-(4-Fluoridophenyl)-3-(trifluoridomethyl)-1H-pyrazole (3d).
7.31 (s, 1H). 13C NMR (75 MHz, Acetone-d6) δ 148.71, 144.53 2d (13.25g, 56.6 mmol) was dissolved in 100 mL EtOH and
(q, J = 37.6 Hz), 143.30, 135.14, 127.47, 125.27, 122.56 (q, J = cooled in an ice bath to 0 °C. Hydrazine hydrate (3.25 mL,
267.7 Hz), 103.70.
67 mmol) was added dropwise. When the addition was com-
3-(Trifluoridomethyl)-5-[4-(trifluoridomethyl)phenyl]-1H-pyr- plete the ice bath was removed and the reaction was stirred at
azole (3b). 2b (13.3 g, 56 mmol) was dissolved in 26 mL EtOH room temperature for 1 hour and then heated to reflux over-
and 2.2 mL 37% HCl and the solution was cooled to 0 °C with night. The solvent was removed in vacuo to approx. 25 mL. The
an ice bath. Hydrazine hydrate (1.35 mL, 27.9 mmol) was then solution was cooled to 0 °C in an ice bath and slowly 20 mL
slowly added. When the addition was complete the ice bath 37% HCl was added. The ice bath was removed and the reac-
was removed and the reaction was allowed to stir at room tion was heated to reflux for 1 hour after which the reaction
temperature for 20 minutes, it was then heated to reflux for mixture was poured into 150 mL cold water. The product was
approximately 20 hours. The solvent was removed in vacuo and filtered off, dried in vacuo and purified by vacuum sublimation
the resulting solids were purified by vacuum sublimation (100 °C, 10−4 atm) to yield the product as an off-white solid.
(140 °C, 10−4 atm) to yield the product as a white solid. Yield Yield 10.95 g (85%). M.p. 115–118 °C. 1H NMR (300 MHz,
1
5.73 g (77%). M.p. 143–145 °C. H NMR (300 MHz, DMSO-d6) CDCl3) δ 11.32 (s, 1H), 7.53 (dd, J = 8.8, 5.1 Hz, 2H), 7.13 (t, J =
δ 13.58 (s, 1H), 7.82–7.55 (m, 4H), 6.74 (s, 1H). 13C NMR 8.6 Hz, 2H), 6.67 (s, 1H). 13C NMR (100 MHz, aceton-d6)
(100 MHz, Acetone-d6) δ 149.24, 143.44 (q, J = 38.1 Hz), 134.36, δ 163.45 (d, J = 250.1 Hz), 144.64, 143.53 (q, J = 38.6 Hz),
131.37 (q, J = 34.6), 130.48, 125.12, 124.07 (q, J = 272.5 Hz), 127.65 (d, J = 8.4 Hz), 124.18, 121.05 (q, J = 268.7 Hz), 116.51
121.36 (q, J = 269.3 Hz), 106.38 (q, J = 2.3 Hz), 86.82.
(d, J = 22.1 Hz), 101.01 (q, J = 1.8 Hz).
5-(4-Chloridophenyl)-3-(trifluoridomethyl)-1H-pyrazole (3c).
5-(4-Methoxyphenyl)-3-(trifluoridomethyl)-1H-pyrazole (3f).
In a flame-dried 500 mL round bottom flask (kept under 2f (22.0 g, 89.3 mmol) was dissolved in 250 mL EtOH and
argon) potassium tert-butoxide (13.5 g, 120 mmol) was sus- cooled to 0 °C in an ice bath. Hydrazine hydrate (5.0 mL,
pended in 125 mL dry Et2O under a dry atmosphere. The sus- 103 mmol) was added dropwise with vigorous stirring. The
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Dalton Transactions
reaction was stirred at 0 °C for 30 minutes and then heated to 9.1 Hz, 2H), 6.85–6.78 (m, 3H), 3.00 (d, J = 1.6 Hz, 6H).
reflux overnight. The EtOH was removed in vacuo to a volume 13C NMR (75 MHz, CDCl3) δ 151.07, 145.70, 143.79 (q, J =
of approx. 100 mL and the solution was cooled to 0 °C in an 35.7 Hz), 126.79, 121.54 (q, J = 268.9 Hz), 115.91, 112.44, 99.50,
ice bath. 10 mL 37% HCl was slowly added and the reaction 40.35.
was heated to reflux for 1 hour after which the mixture was
Sodium hydridobis[3-(trifluoridomethyl)-5-(4-nitrophenyl)-
poured into 500 mL cold water. The product was collected by pyrazol-1-yl][3-(4-nitrophenyl)-5-(trifluoridomethyl)-pyrazol-1-
filtration and was recrystallized from EtOH/water at −20 °C to yl]borate (Na4a′). 3a (3.00 g, 11.67 mmol) and NaBH4 (126 mg,
yield transparent needles. Yield 19.66
g (91%). M.p. 3.33 mmol) are mixed in 10 mL 4-methylanisole and were
134–136 °C. 1H NMR (400 MHz, CDCl3) δ 11.55 (s, 1H), 7.49 (d, placed under argon in a flame-dried Schlenk vessel fitted with
J = 8.7 Hz, 2H), 6.95 (d, J = 8.7 Hz, 2H), 6.63 (s, 1H), 3.85 (s, a flame dried glass tube (30 cm). The mixture was heated to
3H). 13C NMR (100 MHz, CDCl3) δ 160.50, 145.04, 143.62 (q, 120 °C for 2 hours to form the di-substituted borate species,
J = 38.4 Hz), 127.20, 121.36 (q, J = 268.9 Hz), 120.83, 114.71, bubbling was observed using an oil bubbler and became
100.36 (q, J = 2.0 Hz), 55.50.
sporadic after approx. 90 minutes. The temperature was then
N,N-Dimethyl-4-[3-(trifluoridomethyl)-1H-pyrazol-5-yl]aniline raised to 180 °C for three hours. After approx. 1.5 hours bub-
(3g). In a flame-dried 250 mL round bottom flask (kept under bling stopped but BH4 was still observed on 1H NMR, after
−
−
argon) potassium tert-butoxide (8.5 g, 75.8 mmol) was sus- 3 hours BH4 was no longer observed. The solvent was then
pended in 70 mL dry Et2O. The suspension was cooled to 0 °C removed in vacuo to yield the product as a brown oil. The
on an ice bath and ethyl trifluoridoacetate (9.0 mL, product was purified by extensive trituration with Et2O to yield
75.6 mmol) was slowly added. 4-Acetyl-N,N-dimethylaniline the product as an off-white solid which was recrystallized from
(8.16 g, 50 mmol) was then added in small scoops with vigor- DCM/pentane. Yield 1.11 g (40%). M.p. 225 °C (decompo-
1
ous stirring resulting in a clear solution after the last scoop sition). H NMR (500 MHz, CD2Cl2) δ 8.19 (d, J = 8.4 Hz, 2H),
was added. When the addition was complete the reaction was 8.05 (d, J = 8.3 Hz, 4H), 7.77 (d, J = 8.4 Hz, 2H), 7.32 (d, J =
stirred at 0 °C for 45 minutes, the ice bath was then removed 8.3 Hz, 4H), 6.97 (s, 1H), 6.66 (s, 2H), 4.59 (bs, 1H). 13C NMR
and the reaction was allowed to warm to room temperature (75 MHz, acetone-d6) δ 150.17, 148.75, 148.06, 147.82, 143.21
and stirred until TLC (silica, 5% MeOH in DCM) showed com- (q, J = 36.8 Hz), 140.64, 139.37, 138.63 (q, J = 38.1 Hz), 130.98,
plete consumption of the starting material (approx. 127.09, 124.57, 123.50, 123.15 (q, J = 267.6 Hz), 121.73 (q, J =
90 minutes). The reaction mixture was then diluted with 269.0 Hz), 106.79 (q, J = 3.0 Hz), 105.73 (q, J = 1.8 Hz). HRMS
30 mL Et2O and 100 mL 1 M HCl and the layers were separ- (ESI neg.) m/z calcd For [M−] (vC30H16BF9N9O6−) 780.11674
ated. The aqueous layer was extracted with Et2O (1 × 50 mL, found 780.11778.
2 × 25 mL) and the combined organic layers were washed with
water (2 × 25 mL) and brine (1 × 25 mL). The organic fraction methyl}phenyl)pyrazol-1-yl]borate
Sodium
hydrotris[3-(trifluoridomethyl)-5-(4-{trifluorido-
(Na4b). 3b (7.75 g,
was then dried over Na2SO4 and evaporated to dryness in vacuo 27.7 mmol) and NaBH4 (0.202 g, 5.35 mmol) were mixed and
resulting in a red oil that crystallized upon standing to yield 2g placed under argon in a flame-dried Schlenk vessel fitted with
1
as red needles. Yield 12.7 g (98%). H NMR (400 MHz, CDCl3) a flame-dried condenser (not cooled with water). The mixture
δ 15.27 (s, 1H, enol-OH), 7.86 (d, J = 9.1 Hz, 2H), 6.71 (d, J = 9.1 was heated 200 °C for 4 hours, 3b subliming in the glassware
Hz, 2H), 6.43 (s, 1H), 3.11 (s, 6H). 13C NMR (75 MHz, Acetone- was occasionally molten using a heat gun to return it to the
d6) δ 187.41, 174.47 (q, J = 35.1 Hz), 155.7, 131.24, 119.50, reaction mixture. The remaining pyrazole was removed from
118.84 (q, J = 281.8 Hz), 112.12, 91.15 (q, J = 2.3 Hz), 40.08.
the product by extensive vacuum sublimation at 160 °C. The
2g (12.7 g, 50 mmol) was dissolved in 125 mL EtOH and product was dissolved in DCM and filtered over celite to
cooled to 0 °C in an ice bath. Hydrazine hydrate (2.7 mL, remove insoluble byproducts. The solvent was removed
56 mmol) was added dropwise, when the addition was com- in vacuo to yield the product as a white powder. Yield 3.59 g
1
plete the ice bath was removed and the reaction was stirred at (77%). M.p. 212–214 °C. H NMR (300 MHz, acetone-d6) δ 7.37
room temperature for 30 minutes before the reaction was (d, J = 8.4 Hz, 6H), 7.23 (d, J = 8.4 Hz, 6H), 6.74 (s, 3H), 4.47
heated to reflux for approx. 17 hours. The solvent was evapor- (bs, 1H). 13C NMR (75 MHz, acetone-d6) δ 150.38, 143.75 (q, J =
ated in vacuo and 100 mL 3 M HCl was added. The solution 36.7 Hz), 136.43, 131.05, 125.36 (m), 122.97 (q, J = 267.7 Hz),
was heated to reflux for 5 minutes, cooled to room temperature 125.25 (q, J = 271.8 Hz), 105.34 (q, J = 1.9 Hz). HRMS (ESI neg.)
and diluted with 500 mL aqueous saturated NaHCO3 solution m/z calcd For [M−] (vC33H16BF18N6
) 849.12366 found
−
and 100 mL DCM. The layers were separated and the aqueous 849.12078.
fraction was extracted with DCM (2 × 50 mL). The combined
Sodium hydrotris[3-(trifluoridomethyl)-5-(4-chloridophenyl)-
organic fractions were washed with water (2 × 100 mL) and pyrazol-1-yl]borate (Na4c). 3c (5.00 g, 20.3 mmol) and NaBH4
brine (1 × 100 mL) and dried over Na2SO4. The solvent was (0.247 g, 6.53 mmol) were placed in a flame-dried Schlenk
removed in vacuo and the product was recrystallized from hot vessel fitted with a flame-dried glass tube (30 cm) and placed
MeOH/water to yield a white solid. Yield (10.2 g, 80%). M.p. under argon. The mixture was heated at once to 180 °C and
179–181 °C. 1H NMR (300 MHz, DMSO) δ 12.03 (s, 1H), 7.45 held at this temperature for 2.5 hours. The condenser was
(d, J = 8.9 Hz, 2H), 6.73 (d, J = 8.9 Hz, 2H), 6.62 (s, 1H), 3.00 (s, then replaced with a cold finger and vacuum was applied (10−4
6H). 1H NMR (300 MHz, Acetone-d6) δ 12.86 (s, 1H), 7.66 (d, J = atm). The pyrazole was left to sublime out of the product over-
21120 | Dalton Trans., 2015, 44, 21109–21123
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night. When no more of the pyrazole deposited on the cold
Sodium hydrotris[3-(trifluoridomethyl)-5-(4-{N,N-dimethyl-
finger the cold finger was removed and the product was dis- amino}phenyl)pyrazol-1-yl]borate
(Na4g). 3g
(6.00
g,
solved in THF (approx. 50 mL) and filtered over celite to 23.5 mmol) and NaBH4 (0.286 g, 7.56 mmol) were suspended
remove insoluble byproducts. The THF was evaporated in 20 mL 4-methylanisole in a flame dried Schlenk flask fitted
in vacuo and the resulting solids were washed with boiling with a flame-dried glass tube (30 cm) and placed under argon.
heptane (4 × 20 mL) and Et2O (1 × 20 mL) on a glass frit The mixture was heated to reflux for 4 hours. The mixture was
leaving the pure product as a 1 : 1 mixture of the Et2O and THF allowed to cool to room temperature and 200 mL petroleum
adducts. Yield 3.2 g (62%). M.p. 192 °C (decomposition). 1H ether was added. The diluted mixture was stirred in an ice
NMR (400 MHz, CDCl3) δ 7.00 (d, J = 8.4 Hz, 6H), 6.77 (d, J = bath for approx. 30 minutes and then filtered. The filtrate was
8.4 Hz, 6H), 6.44 (s, 3H), 4.57 (bs, 1H), 3.92 (ddd, J = 6.5, 4.2, washed with MeCN (6 × 25 mL) and then dissolved in acetone
2.7 Hz, 2H, coord. THF), 3.55 (q, J = 7.0 Hz, 2H, coord. Et2O), (50 mL). The acetone was removed in vacuo to yield the
2.02–1.96 (m, 2H, coord. THF), 1.24 (t, J = 7.0 Hz, 3H, coord. product as a white powder. The product formed was the
Et2O). 13C NMR (100 MHz, Acetone-d6) δ 150.38, 143.25, acetone adduct. Yield 1.80 g (28%). Decomposed around
1
134.56, 131.69, 131.07, 128.52, 121.44, 104.67. HRMS (ESI 230 °C. H NMR (300 MHz, Acetone-d6) δ 6.82 (d, J = 8.9 Hz,
neg.) m/z calcd For [M−] (vC30H16BCl3F9N6−) 747.04459 found 6H), 6.46 (s, 3H), 6.33 (d, J = 8.9 Hz, 6H), 4.93 (bs, 1H), 2.93 (s,
747.04770.
18H). 13C NMR (75 MHz, CDCl3) δ 152.86, 150.81, 142.83 (q,
Sodium hydrotris[3-(trifluoridomethyl)-5-(4-fluoridophenyl)- J = 36.1 Hz), 131.28, 123.37 (q, J = 267.4 Hz), 120.35, 112.07,
pyrazol-1-yl]borate (Na4d). 3d (5.00 g, 21.7 mmol) and NaBH4 103.18 (q, J = 1.8 Hz), 40.22. HRMS (ESI neg.) m/z calcd for
(0.267 g, 7.06 mmol) were placed in a flame-dried Schlenk [M−] (vC36H34BF9N9−) 774.28810 found 774.28907.
vessel fitted with a flame dried glass tube (30 cm) and placed
General method for synthesis of the copper(I) ethene
complexes (5a′, 5b–g)
under argon. The mixture was heated to 180 °C for 3 hours
and 20 minutes. The temperature was lowered to 140 °C and
the condenser was replaced with a cold finger, leftover pyrazole Na4a′ or Na4b–g (50 mg) was dissolved in 5 mL dry, degassed
was removed by vacuum sublimation. When no more pyrazole DCM. The solution was bubbled with ethene for 2 minutes.
deposited on the cold finger the residue was dissolved in CuI (1.05 eq.) was then added and the solution was saturated/
toluene (50 mL) and filtered over celite to remove insoluble bubbled with ethene for another 2 minutes. The flask was
byproducts. The toluene was evaporated in vacuo and the then stoppered and left to stir at medium speed overnight to
remaining solids were dissolved in acetone and evaporated to form a white suspension. The suspension was filtered using a
1
dryness. Yield 1.72 g (53%). M.p. 190 °C (decomposition). H syringe filter (0.45 µm PTFE) and the solvent was removed
NMR (400 MHz, CDCl3) δ 6.88 (dd, J = 8.6, 5.4 Hz, 6H), 6.72 (t, in vacuo to yield the products as white powders. The complexes
J = 8.6 Hz, 6H), 6.44 (s, 3H), 4.61 (bs, 1H), 2.34 (s, 6H, coord. could be further purified by recrystallization from DCM/
acetone). 13C NMR (100 MHz, CDCl3)
δ
220.47 (coord. pentane at −20 °C under an ethene atmosphere to yield color-
acetone), 162.75 (d, J = 248.1 Hz), 150.18, 142.70 (q, J = less blocks except for 5a′ which was brown.
36.6 Hz), 131.60 (d, J = 8.3 Hz), 127.79 (d, J = 3.3 Hz), 122.20
[Cu(4a′)(C2H4)] (5a′). Yield 42 mg (83%), yellow solid. 1H
(d, J = 267.8 Hz), 114.74 (d, J = 21.7 Hz), 103.84 (q, J = 1.5 Hz), NMR (300 MHz, CD2Cl2) δ 8.37 (d, J = 8.9 Hz, 2H), 8.07 (d, J =
65.98 (coord. THF), 31.31 (coord. acetone), 23.06 (coord. THF). 8.9 Hz, 4H), 7.76 (d, J = 8.9 Hz, 2H), 7.36 (d, J = 8.9 Hz, 4H),
−
HRMS (ESI neg.) m/z calcd for [M−] (vC30H16BF12N6
)
6.87 (s, 1H), 6.72 (s, 2H), 4.54 (bs, 1H), 4.44 (s, 4H). 13C NMR
699.13324 found 699.13033.
(126 MHz, CD2Cl2) δ 152.46, 148.84, 148.67, 148.42, 143.52 (q,
Sodium hydrotris[3-(trifluoridomethyl)-5-(4-methoxyphenyl)- J = 38.4 Hz), 139.00 (q, J = 39.1 Hz), 138.60, 136.99, 131.11,
pyrazol-1-yl]borate (Na4f). 3f (6.867 g, 28.35 mmol) and 129.57, 124.32, 123.36, 121.23 (q, J = 269.3 Hz), 120.05 (q, J =
NaBH4 (0.346 g, 9.15 mmol) were placed in a flame-dried 269.7 Hz), 106.76 (q, J = 2.5 Hz), 86.37. Elemental analysis calc.
Schlenk vessel fitted with a flame-dried glass tube (30 cm) and (%) for C32H20BCuF9N9O6·1.5H2O·1.0DCM (found): C 40.29
placed under argon. The mixture was heated to 180 °C for (41.20), H 2.56 (2.8), N 12.81 (12.32).
1
3 hours. The product was dissolved in boiling toluene (50 mL)
[Cu(4b)(C2H4)] (5b). Yield 49 mg (91%). H NMR (400 MHz,
and filtered, the filtrate was diluted with 200 mL heptane and CD2Cl2) δ 7.22 (d, J = 8.4 Hz, 6H), 7.00 (d, J = 8.3 Hz, 6H), 6.69
left to stand while the product crystallized. Filtration yielded a (s, 3H), 4.96 (s, 4H), 4.43 (bs, 1H). 13C NMR (100 MHz, CD2Cl2)
white powder. Recrystallization from acetone yielded the δ 149.24, 143.44 (q, J = 38.2 Hz), 134.36, 131.37 (q, J = 33.8 Hz),
product as its acetone adduct. Yield 3.75 g (53%). M.p. 206 °C 130.48, 125.12, 124.07 (q, J = 272.4 Hz), 121.36 (q, J = 269.3
(decomposition). 1H NMR (300 MHz, CDCl3) δ 6.85 (d, J = Hz), 106.38 (q, J = 2.4 Hz), 86.82. Elemental analysis calc. (%)
8.6 Hz, 6H), 6.52 (d, J = 8.6 Hz, 6H), 6.42 (s, 3H), 4.69 (bs, 1H), for C35H20BCuF18N6 (found): C 44.68 (44.63), H 2.14 (2.01),
3.79 (s, 9H), 2.33 (s, coord. acetone). 13C NMR (75 MHz, N 8.93 (8.91).
1
CDCl3) δ 212.24 (coord. Acetone), 159.40, 151.06, 142.34 (q, J =
[Cu(4c)(C2H4)] (5c). Yield 47 mg (94%). H NMR (600 MHz,
36.2 Hz), 131.26, 122.37 (q, J = 268.0 Hz), 113.08, 103.10 (q, J = CD2Cl2) δ 7.02 (d, J = 8.5 Hz, 6H), 6.80 (d, J = 8.5 Hz, 6H), 6.61
1.6 Hz), 55.14, 31.27 (coord. acetone). HRMS (ESI neg.) (s, 3H), 4.92 (s, 4H), 4.47 (bs, 1H). 13C NMR (151 MHz, CD2Cl2)
m/z calcd for [M−] (vC33H25BF9N6O3
735.19424.
)
735.19320 found δ 149.57, 143.14 (q, J = 38.0 Hz), 135.49, 131.41, 129.26, 128.49,
121.45 (q, J = 269.0 Hz), 105.93 (q, J = 2.5 Hz), 86.35. Elemental
−
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Dalton Transactions
analysis calc. (%) for C32H20BCl3CuF9N6 (found): C 45.74 J = 269.3), 105.24 (q, J = 1.8 Hz). IR (cm−1): 2620 (w, BH stretch-
(46.37), H 2.40 (2.77), N 10.00 (9.87).
ing), 2120 (s, CO stretching). Elemental analysis calc. (%) for
[Cu(4d)(C2H4)] (5d). Yield 36.6 mg (73%). 1H NMR C34H16BCuF18N6O (found): C 43.40 (43.20), H 1.71 (1.79),
(300 MHz, CD2Cl2) δ 6.95–6.83 (m, 6H), 6.74 (t, J = 8.5 Hz, 6H), N 8.93 (8.83).
6.60 (s, 3H), 4.91 (s, 4H), 4.54 (bs, 1H). 13C NMR (126 MHz,
[Cu(4c)(CO)] (6c). Yield 45 mg (90%). 1H NMR (300 MHz,
CD2Cl2) δ 163.24 (d, J = 249.8 Hz), 149.65, 142.95 (q, J = 37.9 CD2Cl2) δ 7.04 (d, J = 8.3 Hz, 6H), 6.79 (d, J = 8.5 Hz, 6H), 6.61
Hz), 131.86 (d, J = 8.3 Hz), 126.88 (d, J = 3.4 Hz), 121.41 (q, J = (s, 3H), 4.33 (bs, 1H). 13C NMR (75 MHz, CD2Cl2) δ 149.71,
268.7 Hz), 115.13 (d, J = 21.6 Hz), 105.92 (q, J = 2.4 Hz), 86.07. 143.06 (q, J = 37.8 Hz), 135.66, 131.38, 128.85, 128.54, 121.31
Elemental analysis calc. (%) for C32H20BCuF12N6·H2O (found): (q, J = 269.2 Hz), 105.17 (q, J = 2.0 Hz). IR (cm−1): 2616 (w, BH
C 47.52 (47.48), H 2.74 (2.57), N 10.39 (10.23).
stretching), 2113 (s, CO stretching). Elemental analysis calc.
[Cu(4f)(C2H4)] (5f). Yield 43.5 mg (86%). 1H NMR (%) for C31H16BCl3CuF9N6O (found): C 44.31 (44.43), H 1.92
(400 MHz, CD2Cl2) δ 6.81 (d, J = 8.7 Hz, 6H), 6.56 (s, 3H), 6.51 (1.99), N 10.00 (9.95).
(d, J = 8.7 Hz, 6H), 4.88 (s, 4H), 4.62 (bs, 1H), 3.78 (s, 9H). 13C
[Cu(4d)(CO)] (6d). Yield 34 mg (72%). 1H NMR (300 MHz,
NMR (100 MHz, CD2Cl2) δ 160.29, 150.69, 142.51 (q, J = 37.6 CD2Cl2) δ 6.89 (dd, J = 8.9, 5.3 Hz, 6H), 6.76 (dd, J = 9.0, 8.5 Hz,
Hz), 131.47, 123.22, 121.67 (q, J = 268.8 Hz), 113.55, 105.25 (q, 6H), 6.59 (s, 3H), 4.45 (bs, 1H). 13C NMR (75 MHz, CD2Cl2)
J = 2.5 Hz), 85.57, 55.47. Elemental analysis calc. (%) for δ 163.41 (d, J = 247.5 Hz), 149.86, 142.92 (q, J = 37.8 Hz),
C35H29BCuF9N6O3 (found): C 51.01 (50.83), H 3.47 (3.53), 131.93 (d, J = 8.5 Hz), 126.54 (d, J = 3.5 Hz), 121.34 (q, J = 268.9
N 10.12 (10.16).
Hz), 115.28 (d, J = 21.8 Hz), 105.25 (q, J = 1.8 Hz). IR (cm−1):
1
[Cu(4g)(C2H4)] (5g). Yield 40 mg (79%). H NMR (500 MHz, 2616 (w, BH stretching), 2103 (s, CO stretching). Elemental
CD2Cl2) δ 6.75 (d, J = 8.7 Hz, 6H), 6.51 (s, 3H), 6.26 (d, J = 8.7 analysis calc. (%) for C31H16BCuF12N6O·0.2C5H12 (found):
Hz, 6H), 4.84 (s, 4H), 4.77 (bs,1H), 2.92 (s, 18H). 13C NMR C 47.73 (48.03), H 2.30 (2.30), N 10.44 (10.65).
(126 MHz, CD2Cl2) δ 151.56, 150.56, 142.41 (q, J = 37.5 Hz),
[Cu(4f)(CO)] (6f). Yield 45 mg (89%). 1H NMR (300 MHz,
130.98, 121.82 (q, J = 268.6 Hz), 118.42, 111.46, 104.57 (q, J = CD2Cl2) δ 6.79 (d, J = 8.6 Hz, 6H), 6.55 (s, 3H), 6.52 (d, J = 8.7
2.6 Hz), 84.94, 40.12. Elemental analysis calc. (%) for Hz, 6H), 4.50 (bs, 1H), 3.79 (s, 9H). 13C NMR (75 MHz, CD2Cl2)
C38H38BCuF9N9·0.2C5H12 (found): C 53.20 (53.40), H 4.62 δ 160.07, 150.46, 142.24 (q, J = 37.3 Hz), 131.11, 122.45, 121.18
(4.61), N 14.32 (14.07).
(q, J = 269.0 Hz), 113.23, 104.12 (q, J = 1.8 Hz), 55.17. IR
(cm−1): 2636 (w, BH stretching), 2096 (s, CO stretching).
Elemental analysis calc. (%) for C34H25BCuF9N6O4 (found): C
49.38 (49.11), H 3.05 (3.14), N 10.16 (9.99).
General method for the synthesis of the copper(I)–CO
complexes (6a′, 6b–g)
Na4a′ or Na4b–g (50 mg) was dissolved in dry, degassed DCM.
[Cu(4g)(CO)] (6g). Yield 51 mg (86%). 1H NMR (300 MHz,
The solution was bubbled with argon for 2 minutes and placed CD2Cl2) δ 6.74 (d, J = 8.8 Hz, 6H), 6.50 (s, 3H), 6.28 (d, J = 8.8
in a glass-lined autoclave (volume 12 mL). CuI (1.05 eq.) was Hz, 6H), 4.66 (bs, 1H), 2.92 (s, 18H). 13C NMR (75 MHz,
added and the autoclave was closed and purged with dry nitro- CD2Cl2) δ 151.32, 150.34, 142.14, 130.62, 117.65, 111.12,
gen gas. The autoclave was then pressurized with carbon mon- 103.41 (q, J = 1.8 Hz), 40.15. CO and CF3 could not resolved
oxide to at least 5 atm and left to stir at room temperature for due to the low solubility of the complex. IR (cm−1): 2647 (w,
20 hours. The autoclave was then bubbled with dry nitrogen BH stretching), 2096 (s, CO stretching). Elemental analysis
gas to remove unreacted carbon monoxide. The resulting white calc. (%) for C37H34BCuF9N9O·H2O (found): C 50.27 (50.63), H
suspension was filtered using a syringe filter (0.45 µm, PTFE) 4.10 (4.24), N 14.26 (13.90).
and the solvent was removed in vacuo to leave behind the
product as a white powder except in the case of 6a′ which was
brown.
Acknowledgements
1
[Cu(4a′)(CO)] (6a′). Yield 36 mg (56%). H NMR (300 MHz,
CD2Cl2) δ 8.40 (d, J = 8.5 Hz, 2H), 8.09 (d, J = 8.5 Hz, 4H), 7.91 This work is supported by NanoNextNL, a micro and nano-
(d, J = 8.4 Hz, 2H), 7.35 (d, J = 8.4 Hz, 4H), 6.91 (s, 1H), 6.72 (s, technology consortium of the Government of the Netherlands
2H), 4.40 (bs, 1H). 13C NMR (100 MHz, CD2Cl2) δ 151.85, and 130 partners. We thank Jos van Brussel for CHN analysis;
149.09, 148.89, 148.66, 143.50 (q, J = 38.1 Hz), 139.41 (q, J = Gerwin Spijksma for HRMS and Fons Lefeber and Karthick Sai
39.5 Hz), 138.09, 136.57, 131.11, 129.05, 124.53, 123.49, 121.12 Sankar Gupta are acknowledged for assistance with the NMR
(q, J = 269.2 Hz), 119.97 (q, J = 269.5 Hz), 107.27, 106.33. IR experiments.
(cm−1): 2611 (w, BH stretching), 2105 (s, CO stretching).
Elemental analysis calc. (%) for C31H16BCuF9N9O7 (found):
C 42.71 (42.88), H 1.85 (1.97), N 14.46 (14.34).
References
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124.82 (tt, J = 3.9, 1.9 Hz), 123.70 (q, J = 277.1 Hz), 120.87 (q,
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