Synthesis and coordination chemistry of an alkyne functionalised bis(pyrazolyl)methane ligand

Article abstract of DOI:10.1039/b613311h

The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl) bis(pyrazolyl)methane (L) was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl bromide in the presence of base. A series of transition-metal complexes including [MCl₂L] (M = Cu, Co, Ni, Zn, Pt), [ML₂](NO₃)₂ (M = Cu, Co, Ni, Zn), [AgL]NO₃ and [Pd(L)(dppe)](OTf)₂ were prepared and characterised by spectroscopic techniques. In addition, ligand L as well as the Co(ii) and Zn(ii) complexes [CoCl₂L]₂, [ZnCl ₂L] were structurally characterized by single-crystal X-ray diffraction. The organometallic gold(i) and platinum(ii) acetylide complexes [Pz₂CH(C₆H₄-2-OCH₂CCAuPPh ₃)] and trans-[{Pz₂CHC₆H₄-2-OCH ₂CC}₂Pt(PPh₃)₂] were prepared from L and [AuCl(PPh₃)] and trans-[PtCl₂(PPh₃) ₂], respectively. Treatment of these complexes with [Pd(OTf) ₂(dppe)] or [Cu(MeCN)₄]PF₆ results in formation of the cationic, mixed-metal complexes, which were isolated (Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu). The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b613311h

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and coordination chemistry of an alkyne functionalised
bis(pyrazolyl)methane ligand
Fabian Mohr,*a Elena Cerradab and Mariano Lagunab
Received 13th September 2006, Accepted 16th October 2006
First published as an Advance Article on the web 24th October 2006
DOI: 10.1039/b613311h
The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl)bis(pyrazolyl)methane (L)
was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl
bromide in the presence of base. A series of transition-metal complexes including [MCl2L] (M = Cu,
Co, Ni, Zn, Pt), [ML2](NO3)2 (M = Cu, Co, Ni, Zn), [AgL]NO3 and [Pd(L)(dppe)](OTf)2 were prepared
and characterised by spectroscopic techniques. In addition, ligand L as well as the Co(II) and Zn(II)
complexes [CoCl2L]2, [ZnCl2L] were structurally characterized by single-crystal X-ray diffraction. The
organometallic gold(I) and platinum(II) acetylide complexes [Pz2CH(C6H4-2-OCH2C≡CAuPPh3)] and
trans-[{Pz2CHC6H4-2-OCH2C≡C}2Pt(PPh3)2] were prepared from L and [AuCl(PPh3)] and
trans-[PtCl2(PPh3)2], respectively. Treatment of these complexes with [Pd(OTf)2(dppe)] or
[Cu(MeCN)4]PF6 results in formation of the cationic, mixed-metal complexes, which were isolated
(Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu).
Introduction
The large family of bis-and tris(pyrazolyl)borates, commonly
referred to as “scorpionate ligands”, that were pioneered by Trofin-
menko in the 1960s have seen extensive use in modern coordination
chemistry.1–5 A vast number of transition-metal and main-group
metal complexes containing these ligands and their substituted or
otherwise modified derivatives have been synthesised and struc-
turally characterised. In contrast, neutral analogues of the scor-
pionates such as bis- and tris(pyrazolyl)methanes have received
considerably less attention.6–8 More recently however, a variety
of “heteroscorpionate” ligands based on bis(pyrazolyl)methane
derivatives containing additional donor atoms such as O, N
and S have been reported; some examples are illustrated in
Fig 1.5,9
In our group with have developed heterometallic gold/silver
complexes and have also studied the chemistry of various phos-
phinegold(I) acetylide complexes.10–13 In pursuing our interest in
Fig. 1 Examples of heteroscorpionate pyrazolylmethane ligands.
this area of chemistry we wished to design a ligand possessing an
alkyne functionality as well as a bidentate N-donor site. Such a
ligand should form metal acetylide complexes via the alkyne unit
and, at the same time, could be coordinated to different metal
centres through the N-donor atoms. For this purpose, alkyne
functionalisation of a bis(pyrazolyl)methane derivative seemed
the most obvious choice so we began to explore the synthesis
and coordination chemistry of such a ligand. The results of our
endeavours are reported here.
Experimental
General
1
1
1H, 13C{ H} and 31P{ H} NMR spectra were recorded on a
400 MHz Bruker Avance spectrometer. Chemical shifts are quoted
relative to external TMS (1H, 13C) and 85% H3PO4 (31P); coupling
constants are reported in Hz. FAB mass spectra were measured on
a VG Autospec spectrometer using NBA as matrix. Electrospray
(ES) mass spectra were recorded on a Bruker Daltonics Microtof-
Q instrument as MeCN solutions. IR spectra were recorded
as KBr disks on a Perkin Elmer Spectrum One instrument.
Elemental analyses were obtained in-house using a Perkin Elmer
240B microanalyser. [AuCl(PPh3)],14 [Pd(OTf)2(dppe)]15 as well
as (2-hydroxyphenyl)bis(pyrazolyl)methane16 were prepared by
aFachbereich C, Anorganische Chemie, Bergische Universita¨t Wuppertal, D-
42119, Wuppertal, Germany. E-mail: fmohr@uni-wuppertal.de; Fax: 49 202
439 3053; Tel: 49 202 439 3641
bDepartamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales
de Arago´n, Universidad de Zaragoza-C.S.I.C., E-50009, Zaragoza, Spain
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published procedures. The precursor required for this phenol,
bis(pyrazolyl)methanone, was prepared by a modified litera-
ture procedure17 using bis(trichloromethyl) carbonate18 in order
to avoid handling and use of highly toxic phosgene. trans-
[PtCl2(PPh3)2] was prepared by the reaction of two equivalents
of PPh3 with [PtCl2(tht)2] (tht = tetrahydrothiophene). All other
reagents and solvents were sourced commercially and used as
received.
L − 2NO3]+. Anal. Calc. for C32H28N10O8Zn: C, 51.52; H, 3.78; N,
18.78. Found: C, 51.59; H, 3.82; N, 18.81%.
1
[AgL2]NO3 (5). Colourless solid 79% yield. H NMR (d in
acetone-d6): 3.09 (t, J = 2.5 Hz, 2 H, ≡CH), 4.74 (d, J = 1.8 Hz,
4 H, OCH2), 6.38 (t, J = 2.0 Hz, 4 H, Pz–H4), 6.98–7.01 (m, 4
H, H5ꢀ, H6ꢀ), 7.21 (d, J = 8.3 Hz, 2 H, H3ꢀ), 7.44 (dt, J = 8.8,
4.5 Hz, 2 H, H4ꢀ), 7.55 (d, J = 1.8 Hz, 4 H, Pz–H3), 7.87 (d,
J = 2.5 Hz, 4 H, Pz–H5), 8.18 (s, 2 H, CH). IR (cm−1 KBr): 3210
m(C≡C–H), 2124 m(C≡C). ES-MS m/z: 663 [M − NO3]+, 385 [M −
L − NO3]+. Anal. Calc. for C32H28N9O5Ag: C, 52.90; H, 3.88; N,
17.35. Found: C, 52.69; H, 3.78; N, 17.16%.
Preparations
(2-Propargyloxyphenyl)bis(pyrazolyl)methane (L). A mixture
of (2-hydroxyphenyl)bis(pyrazolyl)methane (2.5 g, 0.010 mol),
K2CO3 (4.3 g, 0.031 mol) and propargyl bromide (1.7 mL,
0.019 mol) in acetone (80 mL) was refluxed for 8 h. The solution
was filtered and the filtrate evaporated to dryness affording 2.7 g
(92%) of pale yellow microcrystalline solid. 1H NMR (d in acetone-
d6): 3.08 (t, J = 2.5 Hz, 1 H, ≡CH), 4.78 (d, J = 2.3 Hz, 2 H,
OCH2), 6.31 (dd, J = 2.7, 2.0 Hz, 2 H, Pz–H4), 6.98 (dt, J =
6.3, 0.5 Hz, 1 H, H5ꢀ), 7.03 (dd, J = 7.8, 0.5 Hz, 1 H, H6ꢀ), 7.21
(d, J = 8.3, 1 H, H3ꢀ), 7.43 (dt, J = 8.4, 2.0 Hz, 1 H, H4ꢀ), 7.54
(d, J = 1.8 Hz, 2 H, Pz–H3), 7.59 (d, J = 2.5 Hz, 2 H, Pz–H5),
[MCl2L] complexes. To a solution of the metal chloride in
EtOH (10 mL) was added an equimolar amount of L dissolved
in acetone (10 mL). The mixture was left to stand in an open
vessel and crystals of the complex deposited after a few days. In
the case of the Cu derivative, a greenish solid precipitated out
instantaneously. The solid was collected on a frit, washed with
small amounts of EtOH and Et2O and dried in vacuum.
[CuCl2L] (6). Light green solid 79% yield. IR (cm−1 KBr): 3238
m(C≡C–H), 2115 m(C≡C). FAB-MS m/z: 754 [M2]+, 376 [M − Cl]+,
341 [M − 2Cl]+. Anal. Calc. for C32H28N8O2Cl4Cu2: C, 46.56; H,
3.42; N, 13.57. Found: C, 46.68; H, 3.30; N, 13.46%.
1
8.03 (s, 1 H, CH). 13C{ H} NMR (d in acetone-d6): 57.91 (OCH2),
74.63 (CH), 78.42 (≡CH), 80.20 (C≡CH), 107.49 (Pz–C4), 114.59
(C3ꢀ), 123.07 (C5ꢀ), 127.22 (C1ꢀ), 129.94 (C6ꢀ), 131.31 (Pz–C5),
132.34 (C4ꢀ), 141.75 (Pz–C3), 156.65 (C2ꢀ). IR (cm−1 KBr): 3208
m(C≡C–H), 2124 m(C≡C). FAB-MS m/z: 279 [M]+, 223 [M −
OCH2C≡CH]+, 211 [M − Pz]+. Anal. Calc. for C16H14N4O: C,
69.05; H, 5.07; N, 20.13. Found: C, 68.88; H, 4.90; N, 20.37%.
X-Ray quality crystals were obtained by slow evaporation of an
EtOH solution of the compound.
[NiCl2L] (7). Green solid 63% yield. IR (cm−1 KBr): 2117
m(C≡C). FAB-MS m/z: 779 [M2 − Cl]+, 371 [M − Cl]+, 336 [M −
2Cl]+. Anal. Calc. for C32H28N8O2Cl4Ni2: C, 47.11; H, 3.46; N,
13.74. Found: C, 47.45; H, 3.27; N, 13.70%.
[CoCl2L]2 (8). Bright blue solid 81% yield. IR (cm−1
KBr): 3258 m(C≡C–H), 2116 m(C≡C). Anal. Calc. for
C32H28N8O2Cl4Co2: C, 47.08; H, 3.46; N, 13.73. Found: C, 46.91;
H, 3.20; N, 13.58%. An X-ray quality crystal was selected from
the bulk sample.
[ML2]X complexes. To a solution of the metal nitrate in EtOH
(10 mL) was added a solution of L in acetone (10 mL). The
mixture was left to stand in an open vessel and crystals of the
complex deposited after a few days. The solids were collected on a
frit, washed with small amounts of EtOH and Et2O and dried in
vacuum.
[ZnCl2L] (9). Colourless solid 70% yield. 1H NMR (d in
acetone-d6): 3.15 (t, J = 2.5 Hz, 1 H, ≡CH), 4.84 (d, J = 2.3 Hz,
2 H, OCH2), 6.57 (t, J = 2.5 Hz, 2 H, Pz–H4), 7.02 (dt, J = 7.8,
1.0 Hz, 1 H, H5ꢀ), 7.09 (dd, J = 7.8, 1.5 Hz, 1 H, H6ꢀ), 7.19 (dd,
J = 8.3, 0.5 Hz, 1 H, H3ꢀ), 7.45 (dt, J = 8.3, 1.8 Hz, 1 H, H4ꢀ),
7.91 (d, J = 1.8 Hz, 2 H, Pz–H3), 8.18 (br s, 2 H, Pz–H5), 8.48 (s,
2 H, CH). IR (cm−1 KBr): 3258 m(C≡C–H), 2114 m(C≡C). Anal.
Calc. for C32H28N8O2Cl4Zn2: C, 46.35; H, 3.40; N, 13.51. Found:
C, 46.20; H, 3.36; N, 13.27%. An X-ray quality crystal was selected
from the bulk sample.
[CuL2](NO3)2 (1). Blue solid 92% yield. IR (cm−1 KBr): 3242
m(C≡C–H), 2118 m(C≡C); ES-MS m/z: 619 [M − 2NO3]+, 341
[M − L − 2NO3]+. Anal. Calc. for C32H28N10O8Cu·2H2O: C, 49.26;
H, 4.13; N, 17.95. Found: C, 49.30; H, 3.83; N, 18.18%.
[NiL2](NO3)2 (2). Blue solid 83% yield. IR (cm−1 KBr): 3284
m(C≡C–H), 2119 m(C≡C); ES-MS m/z: 676 [M − NO3]+, 398 [M −
L − NO3]+. Anal. Calc. for C32H28N10O8Ni: C, 51.99; H, 3.82; N,
18.95. Found: C, 51.69; H, 3.79; N, 18.61%.
[Pd(L)(dppe)](OTf)2 (10). To
a
CH2Cl2 solution of
[Pd(OTf)2(dppe)] (0.144 g, 0.179 mmol) was added a solution of
L (0.050 g, 0.179 mmol) in the same solvent. After stirring for
4 h the mixture was passed through Celite and the filtrate was
concentrated in vacuum. Addition of pentane gave a pale-yellow
[CoL2](NO3)2 (3). Pink solid 86% yield. IR (cm−1 KBr): 3283
m(C≡C–H), 2119 m(C≡C). ES-MS m/z: 677 [M − NO3]+, 399 [M −
L − NO3]+. Anal. Calc. for C32H28N10O8Co: C, 51.97; H, 3.82; N,
18.94. Found: C, 51.70; H, 3.77; N, 18.53%.
1
solid which was isolated by filtration and dried. Yield 86%. H
NMR (d in CDCl3): 2.42 (t, J = 2.3 Hz, 1 H, ≡CH), 2.73 (br s,
2 H, PCH2CH2P), 3.16 (br s, 2 H, PCH2CH2P), 4.62 (d, J =
2.3 Hz, 2 H, OCH2), 6.05 (d, J = 7.3 Hz, 1 H, H6ꢀ), 6.28 (t, J =
2.3 Hz, 2 H, Pz–H4), 6.42 (t, J = 7.3 Hz, 1 H, H5ꢀ), 6.88 (d, J =
2.3 Hz, 2 H, Pz–H3), 7.15 (d, J = 8,1 Hz, 1 H, H3ꢀ), 7.25–7.32
(m, 4 H, Ph2P), 7.41 (dt, J = 8.6, 1.2 Hz, 1 H, H4ꢀ), 7.45–7.97
(m, 16 H, Ph2P), 8.64 (d, J = 1.2 Hz, 2 H, Pz–H5), 8.89 (s, 1
H, CH). 31P NMR (d in CDCl3): 68.54. IR (cm−1 KBr): 3245
[ZnL2](NO3)2 (4). Colourless solid 85% yield. 1H NMR (d in
acetone-d6): 3.13 (t, J = 2.3 Hz, 2 H, ≡CH), 4.80 (d, J = 2.3 Hz,
4 H, OCH2), 6.51 (br s, 4 H, Pz–H4), 6.83 (d, J = 7.8 Hz, 2 H,
H6ꢀ), 6.95 (t, J = 7.6 Hz, 2 H, H5ꢀ), 7.18 (d, J = 8.3 Hz, 2 H,
H3ꢀ), 7.42 (dt, J = 8.8, 1.8 Hz, 2 H, H4ꢀ), 7.78 (br s, 4 H, Pz–H3),
8.06 (br s, 4 H, Pz–H5), 8.36 (s, 2 H, CH). IR (cm−1 KBr): 3279
m(C≡C–H), 2119 m(C≡C). ES-MS m/z: 682 [M − NO3]+, 342 [M −
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m(C≡C–H), 2121 m(C≡C), 1264 m(SO3), 1157 m(CF3). FAB-MS
m/z: 782 [M]+, 653 [M − C6H4OCH2CCH]+, 504 [M − L]+. Anal.
Calc. for C44H38N4O7P2S2F6Pd: C, 48.87; H, 3.54; N, 5.18. Found:
C, 48.77; H, 3.43; N, 5.17%.
7.83 (m, 52 H, Ph2P, m-Ph3P), 7.86–7.94 (m, 6 H, p-PPh3), 8.26 (s,
2 H, CH), 8.27–8.33 (m, 16 H, o-Ph3P, Pz–H3). 31P NMR (d in
CDCl3): 73.88 (s, (Ph2PCH2CH2PPh2), 24.01 (JPt–P = 2620 Hz). IR
(cm−1 KBr): 2126 m(C≡C), 1259 m(SO3), 1155 m(CF3). Anal. Calc.
for C124H104N8O14P6F12S4Pd2Pt: C, 51.71; H, 3.64; N, 3.89. Found:
C, 51.91; H, 3.69; N, 3.86%.
[Pz2CH(C6H4-2-OCH2CCAuPPh3)] (11). A mixture of L
(0.309 g, 1.11 mmol), [AuCl(PPh3)] (0.500 g, 1.01 mmol) and KOH
(0.091 g, 1.62 mmol) in MeOH (50 mL) was stirred for ca. 18 h. The
orange solution was evaporated to dryness and the resulting solid
extracted into CH2Cl2. The CH2Cl2 extracts were passed through
Celite and concentrated in vacuum. Addition of Et2O precipitated
a pale yellow solid which was isolated by filtration and dried. Yield:
Copper(I) coordination of 11 and 12. Solutions of complexes
11 and 12 in MeCN (ca. 3 ml) were treated with [Cu(MeCN)4]PF6
and the resulting solutions were analysed by HR-ES mass
spectrometry.
1
0.682 g, 92%. H NMR (d in CDCl3): 4.81 (d, J = 1.5 Hz, 2 H,
X-Ray crystallography
OCH2), 6.26 (t, J = 2.0 Hz, 2 H, Pz–H4), 6.92–7.00 (m, 2 H, H5ꢀ,
H6ꢀ), 7.29 (d, J = 8.3 Hz, 1 H, H3ꢀ), 7.37 (dt, J = 8.6, 2.0 Hz,
1 H, H4ꢀ), 7.41–7.55 (m, 17 H, Ph3P, Pz–H5), 7.60 (d, J = 1.5 Hz,
2 H, Pz–H3), 8.04 (s, 1 H, CH). 31P NMR (d in CDCl3): 42.04. IR
(cm−1 KBr): 2135 m(C≡C). FAB-MS m/z: 737 [M]+. Anal. Calc.
for C34H28N4OPAu: C, 55.44; H, 3.83; N, 7.61. Found: C, 55.54;
H, 3.91; N, 7.77%.
Crystals of L, 8 and 9 were mounted in oil on a glass fibre and data
were collected at 100 K on either Oxford Diffraction XCalibur2
or Bruker APEX CCD diffractometers. Data were reduced and
absorption corrections applied using CrysalisRED,19 SAINT20
and SADABS.21 The structures were solved by direct methods and
refined to Fo using full-matrix least squares.22 Hydrogen atoms
2
were placed at calculated positions and refined as riding on their
respective carbon atoms. The hydrogen atoms in 8 were located on
the difference map and refined isotropically. The crystallographic
and refinement details are listed in Table 1.
CCDC reference numbers 620814–620816.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b613311h
trans-[{Pz2CHC6H4-2-OCH2CC}2Pt(PPh3)2] (12). A mixture
of L (0.089 g, 0.32 mmol), trans-[PtCl2(PPh3)2] (0.115 g,
0.15 mmol), CuI (5 mg), EtOH (10 mL) and Et2NH (10 mL)
was refluxed for 1 h. After cooling to room temperature, the
colourless solid was isolated by filtration and washed with EtOH
and Et2O. Yield: 0.141 g 76%. 1H NMR (d in CDCl3): 3.91 (s, 4 H,
OCH2), 6.15 (t, J = 2.3 Hz, 4 H, Pz–H4), 6.44 (d, J = 8.1 Hz, 2
H, H3ꢀ), 6.75–6.85 (m, 4 H, H5ꢀ, H6ꢀ), 6.90 (dt, J = 8.8, 1.8 Hz,
2 H, H4ꢀ), 7.19 (d, J = 2.3 Hz, 4 H, Pz–H3), 7.22–7.28 (m, 12 H,
m-Ph3P), 7.32–7.38 (m, 6 H, p-Ph3P), 7.56 (d, J = 1.8 Hz, 4 H, Pz–
H5), 7.61–7.68 (m, 12 H, o-Ph3P), 7.70 (s, 2 H, CH). 31P NMR (d
in CDCl3): 18.91 (JPt–P = 2636 Hz). IR (cm−1 KBr): 2132 m(C≡C).
FAB-MS m/z: 1206 [M − Pz]+. Anal. Calc. for C68H56N8O2P2Pt:
C, 64.09; H, 4.43; N, 8.79. Found: C, 64.32; H, 4.40; N, 8.81%.
Results and discussion
Ligand synthesis
The alkyne functionalised scorpionate ligand (2-propargyloxy-
phenyl)bis(pyrazolyl)methane (L) was easily prepared in
very high yields from the reaction of (2-hydroxyphenyl)bis-
(pyrazolyl)methane16 with propargyl bromide and K2CO3 in
refluxing acetone (Scheme 1). We wish to point out here that
ligand L should be considered a “true” scorpionate, since the three
donor sites (pyrazolyl and alkyne units) resemble the claws and the
stinger of a scorpion much closer than the tris(pyrazolyl)methanes
or borates.
[(dppe)PdPz2CH(C6H4-2-OCH2CCAuPPh3)](OTf)2 (13). To a
solution of 11 (0.025 g, 0.034 mmol) in CH2Cl2 (10 mL) was
added [Pd(OTf)2(dppe)] (0.027 g, 0.034 mmol). After stirring the
solution for 2 h most of the solvent was evaporated and pentane
was added. The resulting ochre–yellow precipitate was isolated
by filtration and washed with pentane and dried. Yield: 0.041 g,
1
79%. H NMR (d in CDCl3): 2.78 (br s, 2 H, PCH2CH2P), 3.17
(br s, 2 H, PCH2CH2P), 4.84 (s, 2 H, OCH2), 5.92 (d, J = 7.3 Hz,
1 H, H6ꢀ), 6.28 (br s, 2 H, Pz–H4), 6.36 (t, J = 7.3 Hz, 1 H,
H5ꢀ), 6.79 (br s, 1 H, Pz–H3), 7.12 (d, J = 8,1 Hz, 1 H, H3ꢀ),
7.31–8.08 (m, 36 H, Ph2P, Ph3P, H4ꢀ), 8.64 (br s, 2 H, Pz–H5),
8.81 (s, 1 H, CH). 31P NMR (d in CDCl3): 45.10 (s, PPh3), 67.63
(Ph2PCH2CH2PPh2). IR (cm−1 KBr): 2200 m(C≡C), 1259 m(SO3),
1156 m(CF3). Anal. Calc. for C62H52N4O7P3F6S2AuPd: C, 48.37;
H, 3.40; N, 3.64. Found: C, 48.54; H, 3.71; N, 3.77%.
Scheme 1
trans-[{(dppe)PdPz2CHC6H4 -2-OCH2CC}2Pt(PPh3)2 ](OTf)4
(14). To a solution of 12 (0.025 g, 0.0196 mmol) in CH2Cl2
(10 mL) was added [Pd(OTf)2(dppe)] (0.032 g, 0.0398 mmol). After
stirring the solution for 2 h most of the solvent was evaporated and
Et2O was added. The resulting pale-yellow precipitate was isolated
by filtration and washed with Et2O and dried. Yield: 0.052 g, 93%.
1H NMR (d in acetone-d6): 2.91 (br s, 4 H, PCH2CH2P), 3.31 (br s,
4 H, PCH2CH2P), 3.67 (s, 4 H, OCH2), 5.99 (d, J = 7.3 Hz, 2 H,
H3ꢀ), 6.38 (br s, 4 H, Pz–H4), 6.53–6.61 (m, 4 H, H5ꢀ, H6ꢀ), 7.37–
All spectroscopic and analytical data (see Experimental section)
are consistent with the proposed structure of the compound, which
was confirmed by a single-crystal X-ray diffraction study (Fig. 2).
The structure of L closely resembles that of its parent (2-
hydroxyphenyl)bis(pyrazolyl)methane.16 molecules of L consist
of two pyrazole rings, oriented in a roughly antiparallel man-
ner with respect to each other, N-bonded to the methine
carbon. The 2-propargyloxyphenyl group is attached to the
bis(pyrazolyl)methane unit and rotated by ca. 30◦ out of the
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Table 1 Crystallographic and refinement details for L, [CoCl2(L)]2 and [ZnCl2(L)]
L
[CoCl2(L)]2
[ZnCl2(L)].
Formula
Mr
C16H14N4O
278.31
Colourless block
0.07 × 0.12 × 0.15
Monoclinic
P21
9.2557(3)
7.5895(3)
9.8876(3)
90
95.411(3)
90
691.57(4)
2
1.337
292
0.088
7.88–64.30
6679
0.0171
3861
190/1
0.0328
0.0878
0.974
0.293, −0.269
C16H14Cl2CoN4O
408.14
Blue block
C16H14Cl2N4OZn
414.58
Colourless plate
0.09 × 0.13 × 0.37
Triclinic
¯
P1
8.1822(4)
9.1228(5)
11.7847(6)
96.5040(10)
95.6410(10)
103.3830(10)
843.18(8)
2
1.633
420
1.784
3.50–57.66
10612
Crystal colour, shape
Crystal size/mm
Crystal system
Space group
0.07 × 0.11 × 0.13
Triclinic
¯
P1
˚
a/A
8.2354(9)
9.3496(11)
11.5484(13)
95.643(2)
97.344(2)
108.028(2)
829.60(16)
2
1.634
414
1.367
3.60–56.50
7492
0.0387
3851
273/0
0.0462
0.0832
0.864
0.674, −0.481
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
U/A
Z
Dc/g cm3
F(000)
l/mm−1
2h Range/◦
No. of data collected
Rint
0.0173
4038
273/0
0.0251
0.0650
1.060
0.459, −0.228
No. obs. data [I > 2r(1)]
No. parameters/restraints
R1 (obs. data)
wR2 (all data)
S
−3
˚
Min., max. Dq/e A
Scheme 2
The compounds were characterised by IR spectroscopy, mass
spectrometry and, where possible, by 1H NMR spectroscopy. All of
the dichloro compounds, except the Zn(II) derivative, were poorly
soluble in common organic solvents, suggesting the possibility of
a dimeric or polymeric structure. This was indeed confirmed by
an X-ray diffraction study of [CoCl2L]2 (7) and [ZnCl2L] (9). The
structure of the bright blue, five-coordinate Co(II) complex (Fig. 3)
consists of a chloro-bridged dimer of MCl2L units.
The coordination about the metal atoms can be described
as distorted trigonal bipyramidal. The configuration of the six-
membered ring formed by the bis(pyrazolyl)methane and the
Co centre has a boat configuration with the methine proton
in an equatorial position. One of the ligand nitrogen atoms is
trans to one of the bridging chlorides, whilst the other nitrogen
is trans to the non-bridging Cl− ligand. The Co–N distances
Fig. 2 Molecular structure of L. Ellipsoids show 30% probability levels
and hydrogen atoms have been omitted for clarity.
plane perpendicular to that defined by the N–C–N fragment.
Unlike its phenolic precursor or the [CoCl2(L)]2 complex (see
below), molecules of L display no intramolecular hydrogen
bonding contacts or p-stacking interactions.
˚
[2.037(3) and 2.124(3) A] are quite asymmetric. In the structurally
related cobalt(II) dimer [CoCl2{di(2-pyridyl)methoxymethanol}]2,
Coordination compounds of L
obtained as a byproduct of ligand degradation, the Co–N
23
˚
Initially we examined the behaviour of L as a bidentate N-donor
ligand by preparing some Ag(I), Cu(II), Ni(II), Co(II), Zn(II) and
Pd(II) complexes. With exception of the Pd(II) derivatives (see
below), the M(II) complexes were easily prepared in good yields,
by simply mixing ethanolic solutions containing appropriate
amounts of L and the metal salts (Scheme 2).
distances are 2.119(3) and 2.124(3) A, respectively. Similarly,
the Co–Clbridging bond lengths in [CoCl2(L)]2 of 2.3303(9) and
˚
2.6343(9) A are much more asymmetric than those in [CoCl2{di(2-
˚
pyridyl)methoxymethanol}]2 [2.416(1) and 2.438(1) A]. Further-
more, the propargyloxyphenyl groups are rotated such a way
that the alkyne cannot interact with the metal centre. However,
5570 | Dalton Trans., 2006, 5567–5573
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Fig. 3 Molecular structure of [CoCl2L]2. Ellipsoids show 30% probability levels and hydrogen atoms omitted for clarity.
Fig. 4 Packing of [CoCl2L]2 showing the phenyl–phenyl interactions between adjacent dimmers.
˚
˚
there are p-stacking interactions of ca. 3.8 A between the
[2.2108(4) and 2.2448(4) A] are also similar to those reported for
˚
propargyloxyphenyl groups of adjacent dimer molecules resulting
in a polymeric chain as shown in Fig. 4.
The structure of the Zn(II) derivative (Fig. 5) contains only
monomeric [ZnCl2L] units; Cl atoms of adjacent molecules are
more than 3 A apart. Like the Co(II) derivative described above,
[ZnCl2L] contains the bis(pyrazolyl)methane ligand in a boat
conformation. The Zn–N distances [2.0515(13) and 2.0920(13)
A] are similar, but less symmetric, compared to those found
in the only other structurally authenticated Zn(II)Cl2 complex
[ZnCl2{Me2C(Pz)2}] [2.209(1) and 2.229(1) A].
Curiously, our attempts to prepare [PdCl2(L)] by displace-
ment of the weakly coordinated ligands from [PdCl2(cod)] or
[PdCl2(NCMe)2] failed; even after ca. 18 h reflux only unreacted
starting materials were recovered. However, the reaction of
[Pd(OTf)2(dppe)] with L gave high yields of the dicationic complex
[Pd(dppe)(L)](OTf)2 (10). The spectral data of 10 (see Experi-
mental section) are fully consistent with the proposed structure,
particularly informative is the ES mass spectrum, the isotopic
distribution of which matches perfectly with that computed for the
doubly charged [Pd(dppe)(L)]2+ cation. Attempts to deprotonate
the alkyne of the coordinated ligand to form alkynyl complexes
with other metals only led to decomposition or insoluble materials.
Furthermore, the poor solubility of many of the [ML] derivatives
described here hampered further reactions.
˚
˚
containing a bis(pyrazolyl)methane ligand [ZnCl2{Me2C(Pz)2}]
24
˚
[2.058(3) and 2.046(3) A]. The Zn–Cl distances in [ZnCl2L]
L as C-coordinating ligand
Treatment of L with [AuCl(PPh3)] in the presence of base
gives the organometallic gold(I) alkynyl complex [Pz2CH(C6H4-
2-OCH2CCAuPPh3)] (11) in high yield (Scheme 3).
The proton NMR spectrum of the compound shows a singlet
resonance due to the OCH2 group, indicating loss of the acetylenic
proton, which is further confirmed by the absence of a ≡C–H
band in the IR spectrum of the complex. The FAB mass spectrum
shows a weak signal for the molecular ion peak, the isotope
Fig. 5 Molecular structure of [ZnCl2L]. Ellipsoids show 40% probability
levels and hydrogen atoms omitted for clarity.
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still possess the vacant bis(pyrazolyl) unit, which should allow
coordination to other metals. To test this hypothesis we studied
the reaction of 11 and 12 with [Cu(MeCN)4]PF6 by electrospray
mass spectrometry. In both cases we observed signals, with isotope
patterns corresponding to the cationic mixed metal complexes
[11Cu]+ and [12Cu2]2+, respectively (Fig. 6).
Based on these findings, we then carried out the reac-
tion of complexes 11 and 12 with appropriate amounts of
[Pd(OTf)2(dppe)] and were able to isolate the mixed-metal com-
plexes [(dppe)PdPz2CH(C6H4-2-OCH2CCAuPPh3)](OTf)2 (13)
and trans-[{(dppe)PdPz2CHC6H4-2-OCH2CC}2Pt(PPh3)2](OTf)4
(14) ingood yields (Scheme 5). These complexes were characterised
by NMR spectroscopy and ES mass spectrometry. The former
clearly are consistent with the proposed structures, in particular
Scheme 3
pattern of which is in excellent agreement with the calculated
isotope distribution for the complex. Similarly, the reaction of
two equivalents of L with trans-[PtCl2(PPh3)2] in the presence of
Et2NH and a catalytic amount of CuI gives the bis(alkynyl)Pt(II)
complex in good yield (Scheme 4).
1
the 31P{ H} NMR spectra shows two distinct signals correspond-
ing to the dppe and PPh3 phosphorus atoms, respectively. In the
case of 14 platinum satellites (JPt–P = 2620 Hz), typical for trans
platinum(II) complexes, are observed. Unfortunately, the ES mass
spectra were not very informative as many unassignable fragments
containing Pd/Au and Pd/Pt with various charges could be
observed. No molecular ion peaks were detected under various
different instrument conditions.
Conclusions
We have shown here that the new scorpionate (2-propar-
gyloxyphenyl)bis(pyrazolyl)methane is a versatile ligand that can
form simple coordination compounds via the nitrogen atoms of the
bis(pyrazolyl) unit as well as organometallic complexes through
C-coordination of the alkyne functionality. Furthermore, we have
demonstrated that both of these coordination modes can operate
at the same time to form heterobimetallic Au/Pd, Cu/Pd and
Pt/Pd complexes.
Scheme 4
Again, the 1H NMR and IR spectra clearly indicate C-
coordination of the ligand since no signals due to the C≡CH
1
group are observed. The 31P{ H} NMR spectrum of the complex
shows a singlet resonance with Pt satellites of 2636 Hz, indicating
a trans geometry about the platinum. Complexes 11 and 12
Fig. 6 HR ES mass spectrum of [12Cu]2+ (top), computed isotope pattern (bottom).
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Scheme 5
13 F. Mohr, E. Cerrada and M. Laguna, Organometallics, 2006, 25, 644–
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