Coordination of Nickel(II) by 3-(2-(Diphenylphosphanyl)phenyl)-1H-pyrazole

Article abstract of DOI:10.1002/zaac.201500579

Starting from easily accessible 3-[2-(diphenylphosphanyl)phenyl]-1H-pyrazole a series of four- and five-coordinate diamagnetic nickel(II) complexes were synthesized and structurally characterized. The resulting complexes show dynamic NMR spectra reflecting a high degree of flexibility in the ligand backbone. Protonation and deprotonation of the pyrazole moiety allows interconversion of the nickel(II) complexes.

Full text of DOI:10.1002/zaac.201500579

Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500579
Coordination of Nickel(II) by 3-(2-(Diphenylphosphanyl)phenyl)-1H-pyrazole
Alexandra D. Schmidt,[a] Yu Sun,[a] and Werner R. Thiel*[a]
Dedicated to Professor F. Ekkehardt Hahn on the Occasion of his 60th Birthday
Keywords: Phosphine; Pyrazole; Nickel; X-ray structure
Abstract. Starting from easily accessible 3-[2-(diphenylphosphanyl)- degree of flexibility in the ligand backbone. Protonation and deproton-
phenyl]-1H-pyrazole a series of four- and five-coordinate diamagnetic ation of the pyrazole moiety allows interconversion of the nickel(II)
nickel(II) complexes were synthesized and structurally characterized. complexes.
The resulting complexes show dynamic NMR spectra reflecting a high
Introduction
While nature uses nickel(II) sites in a series of enzymes such
as urease, CO dehydrogenase, or hydrogen hydrogenase,[1]
man-made nickel catalysts are widely employed in chemical
industry as well as in laboratory scale synthesis. Raney nickel,
the probably most prominent example for a heterogeneous
nickel catalyst, has found broad applications in hydrogenation
reactions.[2] Aside to heterogeneous systems an impressive
number of nickel based homogeneous catalysts has been devel-
oped during the last three decades. The oligomerization of ole-
fins catalyzed by nickel complexes has found industrial appli-
cation in the so-called Shell Higher Olefins Process (SHOP).[3]
Herein hemilabile chelating phosphines stabilize and activate
the catalytically active nickel site. Furthermore nickel com-
plexes catalyze cycloaddition reactions,[4] C–C-coupling reac-
tions,[5] the Karash reaction,[6] help functionalizing C–H
Scheme 1. Synthesis of aryl phosphines functionalized with heterocy-
cles. The corresponding trans substituted derivatives are accessible by
the same route.
bonds,[7] and perform the addition of Ph2S2 to hexynes.[8]
Recently, Standley et al. summarized the latest developments
especially in nickel catalyzed cross coupling reactions in a
review article.[9]
Palladium(II) complexes derived from ligands bearing an
Since some years we are interested in aryl phosphines bear-
aminopyrimidine group show catalytic activities, that strongly
ing additional heterocyclic groups.[10] Such ligands are rapidly
depend on the amino group attached to the pyrimidine ring:
accessible by a route that combines the fluoride mediated for-
Tertiary amines give rise to a cyclopalladation reaction (P,C
mation of P–C bonds with (aryl)2P(SiMe3) and 1- or 4-fluoro-
coordination) that takes place at the 6-position of the pyrimid-
phenyl-3-dimethylaminoprop-2-en-1-one as the precursors and
ine ring and finally results in highly active Suzuki catalysts,
a subsequent ring closure reaction with either hydrazine, lead-
while primary and secondary amines, leading to the expected
ing to pyrazoles or guanidines, giving aminopyrimidines
(Scheme 1).[11]
P,N coordination, do not show this feature.[12] Interestingly, the
reaction of Ni(ClO4)2 with the same type of ligand leads to a
splitting of the central P–C bond leaving a phenyl carbanion
stabilized by coordination to the central nickel(II) cation and
formally a Ph2P+ fragment, that is stabilized by formation of a
P–N bond with the amino group attached to the pyrimidine
ring.[13] From the according pyrazole derivatives being coordi-
nated to palladium dichloride, catalysts for the Heck reaction
are accessible. The chelating ligand 1 allows the activation of
* Prof. Dr. W. R. Thiel
Fax: +49-631-2054676
E-Mail: thiel@chemie.uni-kl.de
[a] Fachbereich Chemie
Technische Universität Kaiserslautern
Erwin-Schrödinger-Str. 54
67663 Kaiserslautern, Germany
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aryl chlorides.[14] We herein present the coordination chemistry
At +7 °C a small broad signal appears, which already be-
of ligand 1 to nickel(II) that led, depending on the synthesis comes sharpened at –13 °C. The chemical shift of this phos-
procedure (e.g. presence/absence of a base) to up to now four phorus resonance changes only slightly with the variation of
new nickel(II) complexes.
the temperature (–13 °C: 20.35; –53 °C: 21.23 ppm). At lower
temperatures, the association of the chloride anion giving an
octahedral nickel(II) complex should be favored over the
dissociation of the chlorido ligand resulting in a square-planar
complex. However, both steps should lead to stronger shifts of
the phosphorus resonance with the temperature, which is not
observed, making a ligand association or dissociation implaus-
ible and thus some dynamic processes in the ligand backbone
Results and Discussion
Reacting anhydrous nickel(II) chloride with two equivalents
of 3-(2-(diphenylphosphanyl)phenyl)-1H-pyrazole (1)[10,11] in
methanol gave the dark purple, pentacoordinate nickel(II)
complex 2 in good yields (Scheme 2).
1
supposable. This explanation is further confirmed by the H
NMR spectra of 2 recorded at lower temperatures (Figure 2).
Scheme 2. Synthesis of the nickel(II) complex 2.
Compound 2 was structurally characterized by means of
spectroscopic methods, elemental analysis, and single-crystal
X-ray crystallography. A first comparison of the 1H NMR
spectroscopic data of the 18 VE complex 2 with those of the
free ligand 1 shows that the resonances of the phenylpyrazole
core are generally shifted to lower field reflecting the electron
donation of the pyrazole and the phosphine units to the
nickel(II) cation. However, the spectrum is dominated by a
series of broad peaks showing different half-widths. H,H-
COSY measurements clarified that the protons of the ortho-
phenylene unit and two of the para-phenyl protons give quite
sharp resonances, while the resonances of the pyrazole site
already appear as broadened and the ortho- and meta-phenyl
protons are severely broadened. This spectroscopic behavior
excludes paramagnetism as the reason for the line broadening.
Astonishingly, there is no resonance for the triarylphosphino
unit in the 31P{1H} NMR spectrum of compound 2 at room
temperature. To get a deeper insight on whether association/
dissociation of either the chloride anion or the chlorido ligand
or some dynamics in the ligand backbone would be responsible
for these phenomena, NMR experiments at variable tempera-
tures were carried out. Figure 1 shows the changes in the
31P{1H} NMR spectra caused by cooling the sample from
room temperature to –53 °C.
Figure 2. Temperature dependent 1H NMR spectra of compound 2.
The resonances of the central phenylpyrazole core are not
temperature dependent at all, but the number of visible phenyl
resonances strongly increases by lowering the temperature.
While there is e.g. a very broad signal at approx. 6.88 ppm at
room temperature, for which a point of coalescence is observed
at +7 °C, this resonance is split into two triplets at δ = 7.12
and 6.65 ppm at lower temperatures. Another resonance (δ =
8.06 ppm), being broad at room temperature further broadens
by cooling and is at its point of coalescence at –53 °C. Two
resonances at 8.43 and 5.71 ppm, that can also be assigned to
phenyl protons show a parallel temperature behavior and ap-
pear at lower temperatures. The chemical shifts of these two
resonances are quite extreme which might be explained by aro-
matic shielding effects. At –53 °C there are overall twelve aro-
matic signals being well resolved and there is still a broad
1
resonance at δ = 7.35 ppm. The analysis of the H NMR spec-
troscopic data clearly speaks for a ligand dynamics, wherein
the bent six-membered chelate rings flip up and down with
respect to the position of the chlorido ligand, leading to four
different phenyl units, which might further be hindered in rota-
tion around the P–C bonds. The whole process might be trig-
gered by an increasing association of the chloride anion to the
N–H bonds, resulting in a pronounced shift of the N–H reso-
nance towards higher field. Long et al. reported the square
planar palladium complex [Pd(1)2]2+ with chloride or perchlo-
rate as the counterion and observed similar dynamic behavior
in their systems.[15] As the dynamic behavior is limited exclu-
sively to the Ph2P phenyl groups, they explain this special fea-
Figure 1. Temperature dependent 31P{1H} NMR spectra of compound 2. ture by hindered rotations around P–C bonds.
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Having a look to the solid-state structure of 2 can help to served by Nishikawa et al. for bis[2-(diphenylphosphi-
clarify the situation. Compound 2 crystallizes in the triclinic nomethyl)-1-methylimidazolyl]nickel(II) bis(tetrafluoroborate)
¯
space group P1 with two molecules in the unit cell. Further- and by Braunstein et al. for bis(10-(diphenylphosphanyl)-
more, there are two equivalents of dichloromethane found per 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine)nickel(II)
molecule of 2. Figure 3 (top) shows the structure of the cation tetrachloronickelate(II).[16] However, while the angle P2–Ni1–
2+ in the solid state.
N2 (173.29°) is close to a linear arrangement that would be
expected for an ideal square pyramid, the angle P1–Ni1–N4
(153.85°) is strongly reduced. Due to the bulkiness of the two
Ph2P units, the angle P1–Ni1–P2 is expanded to 101.12°. The
two six-membered chelate rings are bent as found in other
complexes carrying this type of ligand:[12] one is directing
towards the chlorido ligand, the other one in the opposite di-
rection. This feature allows avoiding a repulsion of the two
pyrazole N–H units. In the solid-state structure of 2, two of
the cations 2+ are linked via centrosymmetric hydrogen bonds
that include one proton of an N–H unit and the chlorido ligand,
resulting in a four-membered H2Cl2 ring (Figure 3 bottom).
The non-coordinating chloride anion undergoes a hydrogen
bond with the second N–H unit. To the best of our knowledge,
there is no similar five-coordinate nickel(II) complex of the
type [(P–N)2NiCl]+ that has structurally been characterized be-
fore. Solely bis(2-(diphenylphosphinomethyl)pyridine)iodi-
donickel(II) iodide possesses a structure similar to 2.[17] Kamer
et al. reacted (dme)NiCl2 with a series of P,N-donors in a 1:1
ratio and obtained tetrahedrally coordinated, neutral complexes
of the type (P-N)NiCl2.[18] For 2-(2-(diphenylphosphanyl)-
phenyl)pyridinenickel(II) dichloride, they found slightly longer
distances (Ni–P: 2.2548; Ni–N: 2.0001 Å) which can be ex-
plained by the differences in charge between their compound
and 2+.
To elucidate, whether by deprotonation of the pyrazole site,
nickel(II) pyrazolato complexes can be accessible, nickel(II)
chloride was reacted with 1 in ethanol in the presence of KOH
or in acetonitrile in the presence of NaOMe (Scheme 3). For
both routes the orange colored, neutral compound 3 was the
only species that could be isolated. The reaction with KOH in
ethanol gave a little lower yields, probably due to the forma-
tion of insoluble Ni(OH)2.
Figure 3. Top: Structure of the cation 2+ in the solid state. The counter
anion and the two solvent molecules are omitted for clarity. Characteristic
bond lengths /Å and bond angles /°: Ni1–Cl1 2.6120(6), Ni1–P1
2.1889(7), Ni1–P2 2.1822(7), Ni1–N2 1.929(2), Ni1–N4 1.959(2), Cl1–
Ni1–P1 111.60(3), Cl1–Ni1–P2 88.98(2), Cl1–Ni1–N2 88.60(6), Cl1–
Ni1–N4 94.29(6), P1–Ni1–P2 101.12(3), P1–Ni1–N2 85.60(6), P1–Ni1–
N4 153.85(7), P2–Ni1–N2 173.29(6), P2–Ni1–N4 82.35(7), N2–Ni1–N4
91.59(8). Bottom: Structure of the hydrogen bound, centrosymmetric di-
mer in the solid state. All hydrogen atoms, except those involved in the
hydrogen bonds and the solvent molecules are omitted for clarity. Charac-
teristic hydrogen bond parameters: N1–H1N 0.88, H1N···Cl1 2.54,
N1···Cl1 3.042(2), N1–H1N···Cl1 117.0, H1N_a···Cl1 2.51, N1_a···Cl1
3.176(2), N1_a–H1N_a···Cl1 133.00, N3–H3N 0.8800, H3N···Cl2 2.26,
N3···Cl2 3.002(2), N3–H3N···Cl2 142.00.
The coordination environment of the nickel(II) site can be
described best as a distorted square pyramid with the chlorido
ligand occupying the apical position. The four phenyl units are
structurally inequivalent being in accordance to the results of
1
the low temperature H NMR measurements. While the Ni–P
distances are found to be almost identical, the Ni–N distances
differ slightly by about 0.03 Å. As predicted by the trans influ-
ence of phosphane and pyrazole, the phosphane and pyrazole
units of the two chelating ligands are found in cis orientation.
Similar orientations of P- versus N-donor sites have been ob- Scheme 3. Synthesis of the nickel(II) complexes 3 and 4.
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Compound 3 could completely be characterized by NMR
As expected from the synthesis of compound 3 and its spec-
spectroscopy although the compound shows dynamics in the
ligand sphere at room temperature. The assignment of the reso-
nances was possible by a combination of 1D and 2D NMR
methods. The phosphorus resonance was observed at δ =
12.77 ppm in the 31P{1H} NMR spectrum, and is thus shifted
by about 8 ppm towards higher field compared to compound
2, reflecting the anionic nature of the pyrazolato ligands. In
troscopic characterization, the pyrazole moieties of ligand 1
are found to be deprotonated. They are now located in trans
orientation, since the trans influence of the pyrazolate sites
is stronger than the trans influence of the pyrazole donors in
compound 2. This allows the structure of compound 3 to be
determined by steric reasons. A comparison of the bond
lengths at the nickel(II) site shows, that the Ni–N distances in
3 are slightly shorter and the Ni–P distances are slightly longer
than those found for compound 2. The coordination environ-
ment of the central nickel(II) cation is almost square planar and
close to C2 symmetry. While the N1–Ni1–N3 angle (172.03°)
suggests an almost linear arrangement of the two pyrazolato
ligands with respect to the nickel(II) site, the P1–Ni1–P2 angle
(164.13°) is much more bent. This bending arises from the
envelope-like structure of the two chelate rings, which are
folded into the same direction to minimize the interference be-
tween the pyrazole ring of one and the Ph2P unit of the neigh-
boring ligand. Alternatively, the two envelope-like chelate
rings could have been folded into opposite directions resulting
in a structure possessing a center of inversion at the nickel(II)
site. To elucidate the energetic values of the three possible
orientations of the chelate ligand, quantum chemical calcula-
tions (DFT) were carried out. The three calculated structures
are shown in Figure 5. Obviously the stereoisomer trans1, be-
ing present in the solid-state structure of compound 3 is the
thermodynamically most favored one.
1
the H and the 13C{1H} NMR spectra, all phenyl resonances
are broad at room temperature, while the resonances of the
ortho-phenylene moiety and the pyrazolato donor are well re-
solved. The latter (6.01 and 6.95 ppm) are shifted to higher
field by 0.5 and 0.7 ppm, respectively, compared to compound
2.
By gas diffusion of ethyl ether into a saturated solution of
3 in chloroform, crystals being suitable for a single-crystal X-
ray analysis could be obtained. Compound 3 crystallizes in the
monoclinic space group P21/n with four molecules in the unit
cell. Figure 4 shows the structure of compound 3 in the solid
state.
To elucidate, whether protonation of the pyrazolato moieties
of the nickel(II) complex 3 is possible, the compound was re-
acted with two equivalents of methanesulfonic acid resulting
in the formation of the dicationic complex 4 in good yields.
Since the nucleophilicity of the methanesulfonate anion is
lower than of chloride, being present in the five-coordinate
complex 2, the nickel(II) site in compound 4 is four-coordinate
showing a distorted square-planar environment, with the phos-
phane and pyrazole sites in cis orientation as observed for
compound 2 (see structural discussion below).
Figure 4. Structure of the nickel(II) complex 3 in the solid state. Charac-
teristic bond lengths /Å and bond angles /°: Ni1–P1 2.2106(4), Ni1–P2
2.2186(4), Ni1–N1 1.8649(12), Ni1–N3 1.8728(12), P1–Ni1–P2
164.13(2), P1–Ni1–N1 89.47(4), P1–Ni1–N3 91.94(4), P2–Ni1–N1
96.52(4), P2–Ni1–N3 84.17(4), N1–Ni1–N3 172.03(5).
As already observed for the nickel(II) complexes 2 and 3,
there are a series of broad resonances in the room temperature
1H NMR spectrum of 4. Since the resonance of the methane-
sulfonate anions is sharp, a dynamic association/dissociation
Figure 5. Calculated structures and Gibbs energies of three possible isomers of compound 3. Characteristic bond lengths /Å and bond angles
/° (for trans1 the mean values from the solid-state structure are given in parentheses): trans1: Ni–P 2.223/2.223 (2.215), Ni–N 1.866/1.866 (1.866), P–
Ni1–P 166.8 (164.1), N1–Ni1–N3 169.4 (172.0); trans2: Ni–P 2.260/2.224, Ni–N 1.858/1.875, P–Ni1–P 154.8, N1–Ni1–N3 157.5; cis: Ni–P 2.238/
2.238, Ni–N 1.867/1.867, P–Ni1–P 109.2, N1–Ni1–N3 92.2.
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of these ions can be excluded. In contrast to the spectra of 2 nor sites. The Ni–P and the Ni–N distances are close to those
and 3, not all phenyl resonances are broadened, which makes found for compound 2.
plausible some hindered rotations around P–C bonds of the
In the past, a series of nickel(II) complexes bearing bridging
Ph2P moieties. The N–H resonance appears at δ = 14.43 ppm pyrazolato ligands have been reported (for the discussion: see
thus shifted by about 0.9 ppm towards lower field compared below). To access a similar structure containing the deproton-
to compound 2. The 31P resonance (δ = 24.42 ppm) is broad ated ligand 1–, the nickel complex 2 was treated with an equi-
at room temperature but clearly detectable. It is shifted to molar amount of KOtBu in acetonitrile according to Scheme 4,
lower field compared to the data of compounds 2 (δ = resulting in the formation of the homodinucler nickel com-
21.23 ppm, –53 °C) and 3 (δ = 12.77 ppm, 25 °C), reflecting pound 5.
the dicationic character of 4. As for compound 2 (3164,
3151 cm–1) there are two NH-absorptions in the IR spectrum
(3134, 3113 cm–1), which are slightly shifted to lower energies.
This implies slightly weaker NH and thus slightly stronger
Ni–N bonds.
By gas diffusion of ethyl ether into a saturated solution of
4 in chloroform, ruby-red crystals being suitable for a single-
crystal X-ray analysis could be obtained. Compound 4 crys-
tallizes in the triclinic space group P1 with two molecules in
Scheme 4. Synthesis of the homodinuclear nickel(II) complex 5.
¯
the unit cell. Furthermore, there are two equivalents of dichlo-
romethane found per molecule of 4. Figure 6 shows the struc-
ture of compound 4 in the solid state.
The NMR spectra of the recrystallized sample measured at
room temperature showed solely weak resonances of com-
pound 2, probably due to severe dynamic and/or paramagnetic
broadening of the resonances. To prove the structure, an X-ray
crystal structure analysis was carried out. By gas diffusion of
ethyl ether into a saturated solution of 5 in dichloromethane,
orange colored crystals being suitable for a single-crystal X-
ray analysis could be obtained. Compound 5 crystallizes in the
¯
triclinic space group P1 with two crystallographically indepen-
dent molecules (overall four molecules) in the unit cell. Fig-
ure 7 shows the structure of compound 5 in the solid state and
typical bond parameters for one of the two crystallographically
independent molecules. The data for the second one are almost
identical.
Figure 6. Structure of the nickel(II) complex 4 in the solid state. The two
solvent molecules are omitted for clarity. Characteristic bond lengths /Å
and bond angles /°: and hydrogen bond parameters: Ni1–P1 2.1898(5),
Ni1–P2 2.1874(6), Ni1–N1 1.9268(18), Ni1–N3 1.9273(16), P1–Ni1–P2
98.85(2), P1–Ni1–N1 87.43(5), P1–Ni1–N3 168.65(5), P2–Ni1–N1
167.13(6), P2–Ni1–N3 84.60(5), N1–Ni1–N3 91.42(7), N2–H2N
0.862(18), H2N···O5 1.864(19), N2···O5 2.695(2), N2–H2N···O5 162(2),
N2–H2N 0.862(18), H2N···N3 2.62(2), N2···N3 2.934(3), N2–H2N···N3
103(2), N4–H4N 0.867(18), H4N···O1 2.55(2), N4···O1 3.129(2), N4–
H4N···O1 125(2), N4–H4N 0.867(18), H4N···O2 1.884(19), N4···O2
2.708(2), N4–H4N···O2 158(2).
Figure 7. Structure of the nickel(II) complex 5 in the solid state. The draw-
ing of the second crystallographically independent molecule in the unit
cell is omitted for clarity. Characteristic bond lengths /Å and bond angles /
°: Ni1–Cl1 2.166(5), Ni1–P1 2.159(4), Ni1–N1 1.898(11), Ni1–N3
1.949(12), Ni2–Cl2 2.155(4), Ni2–P2 2.146(4), Ni2–N2 1.924(12), Ni2–
N4 1.880(11), Cl1–Ni1–P1 90.31(17), Cl1–Ni1–N1 171.9(3), Cl1–Ni1–
N3 90.6(4), P1–Ni1–N1 88.1(3), P1–Ni1–N3 174.4(4), N1–Ni1–N3
91.8(5), Cl2–Ni2–P2 92.16(17), Cl2–Ni2–N2 90.7(4), Cl2–Ni2–N4
170.7(3), P2–Ni2–N2 173.7(4), P2–Ni2–N4 86.6(3), N2–Ni2–N4
91.5(5).
The solid-state structure analysis of compound 4 shows the
nickel(II) cation coordinated in a distorted square-planar fash-
ion by two P,N-chelating ligands. The two methane sulfonate
counter anions perform hydrogen bonds to the NH protons. As
for compound 2, the chelating ligands are found in cis orienta-
Although the quality of the single crystal and accordingly
tion, which can be explained by the trans influence of the do- the quality of the resulting arrangement is not excellent, a few
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phosphanyl)phenyl]-1H-pyrazole was prepared according to a pub-
structural features of compound 5 can be extracted. As docu-
lished procedure.[10] 1H, 13C, and 31P NMR spectra were recorded with
BRUKER Spectrospin Avance 400 and Avance 600 devices. The
chemical shifts are referenced to internal solvent resonances and are
reported relative to tetramethylsilane, the resonances were assigned to
the numbering presented in Scheme 5. ESI MS data were recorded
with a Bruker Esquire 6000 device. For recording the IR spectra a
Perkin-Elmer FT-ATR IR 100 spectrometer equipped with a diamond-
coated ZnSe window was used. Elemental analyses were carried out
at the Fachbereich Chemie with an Elementar Analysentechnik vario
mented by the according bond angles, the nickel(II) sites are
coordinated in an almost perfect square-planar environment.
The distances between the nickel sites and the chlorido ligands
are found to be close to the values observed in compound 2,
whereas the Ni–P distances are slightly shorter. Having a
closer look to the nickel(II) nitrogen distances, it becomes
clear that the nitrogen atoms in the 2-position of the pyrazolato
group (N1, N4), being embedded in the chelate ring are found
closer to the nickel(II) sites than the nitrogen atoms in the 1- Micro cube.
position of the pyrazolato moieties (N2, N3). The two bridging
pyrazolato ligands and the two central nickel(II) cations form
a six-membered ring that occupies a boat conformation with a
Ni1–Ni2 distance of 3.421 Å. There is a whole bunch of nickel
complexes with bridging pyrazolato ligands in the literature,
mainly bi- and some trinuclear[19] compounds. The ligand sys-
tems used for the synthesis of dinuclear complexes in most
cases bear additional donor units to prevent the formation of
polymeric structures such as catena-(bis(μ2-pyrazolato)-
nickel(II) and MOF-type solids.[20] While capping the other
Scheme 5. Labeling scheme for the assignment of the NMR reso-
nances.
coordination sites with appropriate donor ligands allows intro-
ducing simple, unfunctionalized bridging pyrazolates,[21]
mostly symmetrically donor-functionalized pyrazoles have
been invented to access dinuclear pyrazolato-bridged nickel(II)
complexes.[22] A few examples of unsymmetrically donor-
functionalized pyrazoles have found application in this con-
text,[23] but to the best of our knowledge, functionalization
with a phosphorus donor has not been reported yet. The Ni–N
distances we found in the pyrazolato-bridges complex 5 are in
complete agreement with the data from the literature.
Bis[2-(pyrazol-3-yl)phenyldiphenylphosphine]chloridonickel(II)
chloride (2): In a 100 mL two-necked flask equipped with a reflux
condenser anhydrous nickel(II) chloride (103 mg, 0.79 mmol) were
added to dry methanol (20 mL). After heating the mixture to reflux for
5 min, a hot solution of 3-(2-(diphenylphosphanyl)phenyl)-1H-pyr-
azole (2.70 g, 8.30 mmol) in dry methanol (20 mL) was added. An
intensely purple colored solution formed, which was heated to reflux
for 8 h. Subsequently the solvent was evaporated under vacuum, the
residue was dissolved in dry dichloromethane (30 mL) and was fil-
tered. The solvent was removed from the solution under vacuum giv-
ing 456 mg (0.58 mmol, 74%) of 2 as a dark purple colored solid.
Conclusions
C
42H34N4Cl2NiP2·(CH2Cl2)0.7 (786.29 g·mol–1): calcd. C 60.64, H
Reacting nickel(II) chloride with 3-[2-(diphenylphosphan-
yl)phenyl]-1H-pyrazole results in the formation of a five-coor-
dinate, monocationic nickel(II) complex. Doing the same reac-
tion in the presence of a strong base gives a homoleptic, neu-
tral nickel(II) complex bearing two deprotonated pyrzolato
1
4.22, N 6.62%; found C 60.58, H 4.51, N 6.76%. H NMR (CDCl3,
600 MHz, –53 °C): δ = 13.53 (br., 2 H, NH), 8.43 (br., 2 H, HPh), 7.96
(d, 2 H, JHH = 7.2 Hz, H5), 7.72 (s, 2 H, H1), 7.66 (t, 2 H, JHH
7.5 Hz, H6), 7.40 (m, 2 H, HPh), 7.35 (br., 4 H, HPh), 7.31 (t, JHH
7.7 Hz, H7), 7.22 (t, 2 H, JHH = 7.5 Hz, HPh), 7.12 (t, 2 H, JHH
3
3
=
=
=
=
3
3
3
3
3
units. Subsequent protonation of this compound with meth- 7.5 Hz, HPh), 6.87 (dd, 2 H, JPH = 12.0 Hz, H8), 6.65 (t, 2 H, JHH
7.5 Hz, HPh), 6.51 (s, 2 H, H2), 5.71 (dt, 2 H, HPh). 13C{1H} NMR
(CDCl3, 600 MHz, –53 °C): δ = 149.5 (C3), 136.2 (C1), 133.8 (CPh),
132.6 (CPh), 132.4 (C6), 132.2 (CPh), 133.2 (CPh), 131.3 (C8), 130.7
(CPh), 130.6 (C5), 129.3 (C7), 129.2 (CPh), 128.9 (C9), 128.8 (CPh),
125.5 (CPh), 124.2 (C4), 106.2 (C2). 31P{1H} NMR (CDCl3, 162 MHz,
–53 °C): δ = 21.23. IR (ATR): ν˜ = 3164 m, 3151 m, 3051 m, 1586 w,
1571 w, 1526 w, 1499 w, 1482 w, 1465 m, 1435 s, 1365 w, 1299 w,
1276 w, 1262 w, 1197 m, 1183 m, 1170 w, 1131 m, 1094 s, 1070 m,
1026 w, 998 w, 968 w, 922 w, 890 w, 850 w, 787 m, 758 s, 748 s, 724
s, 692 s cm–1.
anesulfonic acid makes a nickel(II) complex accessible, where
both pyrazoles are again protonated but the nickel(II) site re-
mains four-coordinate due to the weakly donating methane-
sulfonato anions. Deprotonation of the above mentioned five-
coordinate, monocationic nickel(II) complex by KOtBu results
in the cleavage of one chelating ligand and in the formnation
of a pyratolato-bridged dinuclear nickel(II) complex. This
series shows the large flexibility in the coordination arrange-
ments of 3-[2-(diphenylphosphanyl)phenyl]-1H-pyrazole
nickel(II) complexes. We are presently investigating the cleav-
age of the pyratolato-bridged dinuclear nickel(II) complex by
a series of strongly σ-donating ligands.
Bis[2-(pyrazol-3-yl-2-ido)phenyldiphenylphosphine]nickel(II) (3):
Anhydrous nickel(II) chloride (546 mg, 4.21 mmol) was suspended in
dry acetonitrile (40 mL) in a 100 mL two-necked flask equipped with
a reflux condenser. The mixture was heated to reflux for 5 min, re-
sulting in the formation of a blue solution and a yellowish solid. To
this was added a heated suspension of 3-(2-(diphenylphosphanyl)
Experimental Section
General Information: All reactions were carried out in an atmosphere phenyl)-1H-pyrazole (2.70 g, 8.30 mmol) and sodium methoxide
of argon using Schlenk techniques. The solvents were dried and de-
gassed before use according to standard techniques. 3-[2-(Diphenyl-
(444 mg, 8.22 mmol) in dry acetonitrile (10 mL). The resulting orange
colored mixture was heated to reflux for 2 h whereby the color changed
Z. Anorg. Allg. Chem. 2015, 2093–2101
2098
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
to deep red. After heating, the solvent was removed under vacuum and
the remaining residue was dissolved in dry dichloromethane (20 mL)
and filtered to remove sodium chloride. The filtrate was evaporated H, JHH = 7.3 Hz, H5), 7.78 (s, 2 H, H1), 7.64 (t, 2 H, JHH = 7.3 Hz,
NMR (CDCl3, 400 MHz, 25 °C): δ = 14.43 (s, 2 H, NH), 8.44 (d, 2
3
3
H, JHH = 7.5 Hz, HPh), 8.13 (d, 4 H, JHH = 6.4 Hz, HPh), 7.85 (d, 2
3
3
3
and the residue was suspended under ultrasonication (30 min) in dry H6), 7.50–7.37 (m, 6 H, HPh), 7.32 (t, 2 H, JHH = 7.7 Hz, H7), 7.21
3
3
diethyl ether (20 mL) to dissolve residual ligand. The solid was filtered
off and dried under vacuum. Yield after recrystallization: 1.09 g
(1.53 mmol, 36 %) of 3 as an orange-colored solid. C42H32N4NiP2
(t, 2 H, JHH = 7.4 Hz, HPh), 7.10 (br., 2 H, HPh), 6.89 (d, 2 H, JH,H
= 7.6 Hz, H8), 6.72 (br., 2 H, HPh), 6.45 (s, 2 H, H2), 5.87 (br., 2 H,
HPh), 2.45 (s, 6 H, CH3SO3 ). 13C{1H} NMR (CDCl3, 101 MHz,
–
(713.38 g·mol–1): calcd. C 70.71; H, 4.52; N, 7.85%; found C 70.49; 25 °C): δ = 150.5 (C3), 137.3 (C1), 135.9 (CPh), 135.9 (CPh), 134.7
H, 4.60; N, 7.91%. 1H NMR (CDCl3, 400 MHz, 20 °C): δ = 7.93
(CPh), 133.4 (CPh), 132.6 (CPh), 132.4 (C6), 132.0 (C8), 130.8 (CPh),
130.1 (C9), 129.9 (C5), 129.4 (CPh), 129.4 (CPh), 129.2 (C7), 125.3
3
3
(br.,4 H, HPh), 7.57 (d, 2 H, JHH = 6.7 Hz, H5), 7.48 (t, 2 H, JHH
=
(C4), 105.8 (C2), 39.0 (CH3SO3 ). 31P{1H} NMR (CDCl3, 162 MHz,
–
7.4 Hz, H6), 7.33 (br., 6 H, HPh), 7.24 (br., 10 H, HPh), 7.09 (t, 2 H,
3
3JHH = 7.4 Hz, H7), 6.95 (d, 2 H, JHH = 1.6 Hz, H1), 6.84–6.73 (m, 25 °C): δ = 24.4 (br). IR (ATR): ν˜ = 3134 w, 3113 w, 3059 w, 1588
2 H, H8), 6.02 (d, 2 H, H2). 13C{1H} NMR (CDCl3, 101 MHz, 20 °C):
w, 1574 w, 1538 w, 1509 w, 1482 w, 1435 s, 1368 m, 1342 w, 1326
w, 1311 w, 1245 s, 1215 s, 1188 m, 1189 m, 1145 s, 1098 s, 1078 m,
1028 s, 998 m, 967 w, 926 w, 909 w, 849 w, 815 m, 761 s, 747 s, 727
s, 713 m, 690 s cm–1.
2
δ = 147.0 (s, C3), 144.3 (s, C1), 139.6 (d, JPC = 7.3 Hz, C4), 134.0
(br., CPh), 133.4 (s, C8), 131.4 (s, C6), 130.1 (br., CPh), 128.3 (br.,
1
2ϫCPh), 127.1 (s, C5), 126.3 (s, C7), 123.1 (d, JPC = 20.1 Hz, C9),
104.6 (s, C2). 31P{1H} NMR (CDCl3, 162 MHz, 20 °C): δ = 12.77.
ESI MS (CH3CN): m/z = 713.0 ([NiLPN(LPN–H)]+, theor: 713.15). IR
(ATR): ν˜ = 3071 w, 3056 w, 3015 w, 1587 w, 1572 w, 1562 w, 1514
w, 1481 w, 1445 m, 1435 m, 1343 m, 1311 w, 1256 w, 1183 w, 1164
w, 1136 w, 1120 w, 1098 s, 1062 w, 1038 w, 1028 w, 999 w, 966 w,
925 w, 880 w, 873 w, 848 w, 778 w, 756 s, 748 s, 728 m, 708 m, 693
s, 654 m cm–1.
Bis(chlorido(μ2-(2-(pyrazol-3-ylato)phenyldiphenylphosphine)-
nickel(II)) (5): 2 (63.1 mg, 80.2 μmol) was dissolved in dry aceto-
nitrile (50 mL) in a Schlenk tube. KOtBu (9.0 mg, 80.2 μmol) was
added. The resulting a dark purple solution was stirred for 18 h at
room temperature whereby the color changed to orange. The solvent
was removed under vacuum. The orange residue was dissolved
in dry dichloromethane (30 mL) and filtered to remove KCl.
Red prisms, yield after recrystallization: 10.2 mg (30%).
C42H32N4Cl2Ni2P2·(CH2Cl2)1.5 (920.26 g·mol–1): calcd. C 53.84, H
3.64, N 5.77%; found C 54.20, H 3.64, N 5.43%.
Bis[2-(pyrazol-3-yl)phenyldiphenylphosphine]nickel(II) dimethan-
sulfonate (4): In a Schlenk tube, 3 (503 mg, 0.705 mmol) was dis-
solved in dry dichloromethane (50 mL). A solution of methanesulfonic
acid (135 mg, 93 μL, 1.40 mmol) in dry dichloromethane (20 mL) was
added. The resulting reddish-brown solution was stirred for 48 h at
room temperature. The solvent was removed under vacuum, the dark
red residue was suspended in dry diethyl ether (30 mL) by ultra-
X-ray Structure Determination: Crystals suitable for X-ray structure
analysis were obtained by dissolving 2–5 in a minimum of amount of
dichloromethane or chloroform followed by slow diffusion of diethyl
sonication (3ϫ10 min), filtered off and dried under vacuum. ether into these solutions. Crystal data and refinement parameters for
Ruby colored crystals, 486 mg (72%) after recrystallization.
compounds 2–5 are collected in Table 1. The structures were solved
by direct methods (SIR92 [24] and SHELXS97 [25]), completed by sub-
sequent difference Fourier syntheses, and refined by full-matrix least-
C44H40N4NiO6P2S2·(CH2Cl2)2 (1075.47 g·mol–1): calcd. C 51.37, H
1
4.12, N 5.21, S 5.96%; found C 51.67, H 4.26, N 5.20, S 5.92%. H
Table 1. Crystallographic data, data collection, and refinement.
2
3
4
5
Emp. formula
Formula weight
Crystal size /mm
T /K
C44H38Cl6N4NiP2
956.13
0.54ϫ0.40ϫ0.30
150(2)
C42H32N4NiP2
713.37
0.26ϫ0.13ϫ0.09
150(2)
C46H42Cl6N4NiO6P2S2
1144.31
0.20ϫ0.14ϫ0.07
150(2)
C42H32Cl2N4Ni2P2
842.97
0.590ϫ0.150ϫ0.140
150(2)
l /Å
1.54184
1.54184
1.54184
1.54184
Crystal system
Space group
a /Å
b /Å
c /Å
triclinic
P1
monoclinic
P21/n
18.7683(2)
9.4299(1)
19.9831(2)
90
103.876(1)
90
3433.46(6)
4
triclinic
P1
triclinic
P1
¯
¯
¯
12.0464(5)
12.3039(4)
15.8631(5)
74.337(3)
80.638(3)
72.247(3)
2147.79(13)
2
11.4985(3)
14.7651(6)
15.3422(5)
96.469(3)
96.759(2)
104.830(3)
2472.66(14)
2
14.8372(5)
15.6920(4)
16.6635(8)
103.274(3)
104.970(4)
90.113(2)
3640.1(2)
4
α /°
β /°
γ /°
V /Å3
Z
ρcalcd. /g·cm–3
1.478
5.087
1.380
1.982
1.537
5.385
1.538
3.763
μ /mm–1
θ Range /°
Refl. coll.
Indep. refl.
Data/restr./param.
Final R indices [I Ͼ 2σ(I)]a)
R indices (all data)
GooFb)
3.87–62.74
14318
3.71–62.80
23375
3.13–62.73
16933
3.535–62.674
25324
6811 [Rint = 0.0187]
6811/0/514
0.0401, 0.1012
0.0413, 0.1022
1.062
5483 [Rint = 0.0209]
5483/0/442
0.0270, 0.0697
0.0280, 0.0706
1.050
7859 [Rint = 0.0248]
7859/2/612
0.0333, 0.0866
0.0357, 0.0889
1.037
11421 [Rint = 0.0461]
11421/6/938
0.1576, 0.4498
0.1632, 0.4585
2.236
Δρmax min
/
/e·Å–3
1.869/–1.151
0.287/–0.260
0.507/–0.604
3.083/–1.116
a) R1 = Σ||Fo|–|Fc||/Σ|Fo|, wR2 = [Σw(Fo –Fc ) /ΣwFo2]1/2. b) GooF = [Σw(Fo –Fc ) /(n–p)]1/2
.
2
2 2
2
2 2
Z. Anorg. Allg. Chem. 2015, 2093–2101
2099
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
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of complex 4, the hydrogen atoms H2N and H4N, which are bound to
the nitrogen atoms N2 and N4, respectively, were located in the differ-
ence Fourier synthesis, and were refined semi-freely with the help of
a distance restraint, while constraining their U values to 1.2 times the
U(eq) values of N2 and N4, respectively. All the other hydrogen atoms
were placed in calculated positions and refined by using a riding
model.
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Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1409101 (2), CCDC-1409102 (3), CCDC-1409103
(4), and CCDC-1410919 (5) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
DFT Calculations: Quantum chemical calculations on the possible
stereoisomers of compound 3 were performed with the program
[27]
Gaussian09
using the B3LYP gradient corrected exchange-corre-
lation functional[28] in combination with the 6-31G* basis set for C,
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C1 symmetry using analytical gradient techniques and the resulting
structures were confirmed to be true minima by diagonalization of the
analytical Hessian Matrix.
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Acknowledgements
We thank Dr. H. Kelm for measuring the temperature dependent NMR
spectra. Financial support by the Deutsche Forschungsgemeinschaft
(DFG-funded transregional collaborative research center, SFB/TRR 88
3MET, Cooperative effects in homo- and heterometallic complexes) is
gratefully acknowledged.
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Zeitschrift für anorganische und allgemeine Chemie
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