Tethered pyrazolyl phosphinate: Pyrazolyl-N- and phosphoryl-O-metal coordination in Ph2P(O){OCH2CH2(3,5-Me2Pz)}

Article abstract of DOI:10.1021/ic010454c

Phosphorus pyrazolides, P(O)(3,5-Me₂Pz)₃ or RP(E)(3,5-Me₂Pz)₂ [E = S or O, R = Me or Ph], are hydrolytically sensitive particularly upon interaction with transition metal ions: In this paper, we report a new tethered pyrazolyl phosphinate, Ph₂P(O){OCH₂CH₂(3,5-Me₂Pz)} DPEP (1), where the pyrazolyl group is separated from the phosphorus by means of an ethyleneoxy spacer. 1 has two potential coordination sites in the form of a phosphoryl oxygen atom and a pyrazolyl nitrogen atom. 1 forms hydrolytically stable complexes, (DPEP·CoCl₂)_n (2), (DPEP)₂·CuCl₂ (3), (DPEP·ZnCl₂)_n (4), and (DPEP)₂·PdCl₂ (5). The cobalt(II) and the zinc(II) complexes 2 and 4 show a zigzag polymeric structure in the solid state with a tetrahedral coordination geometry around the metal ion; the ligand DPEP coordinates through its phosphoryl oxygen and the pyrazolyl nitrogen to two neighboring metal ions and functions as a bridging ligand to form the polymeric structure. In contrast to 2 and 4, the copper(II) and the palladium(II) complexes 3 and 5 show a square-planar geometry around the metal ion. Exclusive coordination through the pyrazolyl nitrogens of the ligand 1 is observed. An extensive supramolecular sheetlike two-dimensional polymeric network is observed in the solid-state structures of 3 and 5 as a result of two weak interactions: (a) an intermolecular C-H- - -O interaction involving the phosphoryl oxygen and an aromatic C-H and (b) a π-π face-to-face stacking interaction between the phenyl groups of two adjacent molecules.

Full text of DOI:10.1021/ic010454c

5890
Inorg. Chem. 2001, 40, 5890-5896
Tethered Pyrazolyl Phosphinate: Pyrazolyl-N- and Phosphoryl-O-Metal Coordination in
Ph2P(O){OCH2CH2(3,5-Me2Pz)}
Savariraj Kingsley,† Vadapalli Chandrasekhar,*,† Christopher D. Incarvito,‡
Matthew K. Lam,‡ and Arnold L. Rheingold‡
Department of Chemistry, Indian Institute of Technology, Kanpur-208016, India, and
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
ReceiVed April 30, 2001
Phosphorus pyrazolides, P(O)(3,5-Me2Pz)3 or RP(E)(3,5-Me2Pz)2 [E ) S or O, R ) Me or Ph], are hydrolytically
sensitive particularly upon interaction with transition metal ions. In this paper, we report a new tethered pyrazolyl
phosphinate, Ph2P(O){OCH2CH2(3,5-Me2Pz)} DPEP (1), where the pyrazolyl group is separated from the
phosphorus by means of an ethyleneoxy spacer. 1 has two potential coordination sites in the form of a phosphoryl
oxygen atom and a pyrazolyl nitrogen atom. 1 forms hydrolytically stable complexes, (DPEP‚CoCl2)n (2), (DPEP)2‚
CuCl2 (3), (DPEP‚ZnCl2)n (4), and (DPEP)2‚PdCl2 (5). The cobalt(II) and the zinc(II) complexes 2 and 4 show
a zigzag polymeric structure in the solid state with a tetrahedral coordination geometry around the metal ion; the
ligand DPEP coordinates through its phosphoryl oxygen and the pyrazolyl nitrogen to two neighboring metal
ions and functions as a bridging ligand to form the polymeric structure. In contrast to 2 and 4, the copper(II) and
the palladium(II) complexes 3 and 5 show a square-planar geometry around the metal ion. Exclusive coordination
through the pyrazolyl nitrogens of the ligand 1 is observed. An extensive supramolecular sheetlike two-dimensional
polymeric network is observed in the solid-state structures of 3 and 5 as a result of two weak interactions: (a) an
intermolecular C-H- - -O interaction involving the phosphoryl oxygen and an aromatic C-H and (b) a π-π
face-to-face stacking interaction between the phenyl groups of two adjacent molecules.
Introduction
copper(II) cluster, where the four copper atoms are held together
by an in situ formed methylphosphonate, MePO32-. This
reaction is triggered by a metal-assisted P-N bond hydrolysis
involving the phosphorus-pyrazole linkage.3 Partial hydrolysis
reactions involving these ligand systems are also known. Thus,
the reaction of tris(3,5-dimethylpyrazolyl)phosphine oxide,
P(O)(3,5-Me2Pz)3, with Cu(ClO4)2‚2H2O leads to the product
[{P(O)2(3,5-Me2Pz)2}2‚Cu], where one of the pyrazolyl groups
is hydrolyzed, and the in situ generated anionic phosphinate
ligand acts in a tridentate manner using a N2O coordination
mode.4 Such a partial hydrolysis also occurs in the reaction with
a molybdenum carbonyl derivative.2a Similarly, the reaction of
3-(2-pyridyl)pyrazole with POBr3 does not afford the expected
tris(pyrazolyl)phosphine oxide but affords the partially hydro-
lyzed product bis[3-(2-pyridyl)pyrazol-1-yl]phosphinate.2e Ex-
amples of partial P-N bond hydrolysis are also documented in
cyclic phosphazenes involving pyrazolyl derivatives such as
In contrast to the well-studied family of polypyrazolyl borate
ligands,1 the corresponding ligands based on phosphorus have
not received as much attention.2 One of the difficulties in the
use of the latter family, where the pyrazolyl group is attached
to the phosphorus through the nitrogen atom, is the susceptibility
of the resultant P-N bond toward hydrolysis particularly upon
interaction with transition metal ions.2a In this context, recently
we have reported an unusual desulfurization of bis(3,5-dimeth-
ylpyrazolyl)methylphosphine sulfide, MeP(S)(3,5-Me2Pz)2.3 This
ligand, upon interaction with CuCl2, affords a tetranuclear
† Indian Institute of Technology.
‡ University of Delaware.
(1) Review and representative examples: (a) Trofimenko, S. Chem. ReV.
1993, 93, 943. (b) Seino, H.; Arai, Y.; Iwata, N.; Nagao, S.; Mizobe,
Y.; Hidai, M. Inorg. Chem. 2001, 7, 1677. (c) Lopes, I.; Hillier, A.
C.; Liu, S. Y.; Domingos, A.; Ascenso, J.; Galva˜o, A.; Sella, A.;
Marques, N. Inorg. Chem. 2001, 6, 1116. (d) Hu, Z.; Gorun, S. M.
Inorg. Chem. 2001, 4, 667. (e) Rasika Dias, H. V.; Lu, H. L. Inorg.
Chem. 2000, 10, 2246. (f) Kimblin, C.; Bridgewater, B. M.; Churchill,
D. G.; Hascall, T.; Parkin, G. Inorg. Chem. 2000, 19, 4240. (g) Long,
D. P.; Chandrasekaran, A.; Day, R. O.; Bianconi, P. A.; Rheingold,
A. L. Inorg. Chem. 2000, 20, 4476. (h) Komatsuzaki, H.; Nagasu, Y.;
Suzuki, K.; Shibasaki, T.; Satoh, M.; Ebina, F.; Hikichi, S.; Akita,
M.; Moro-oka, Y. J. Chem. Soc., Dalton Trans. 1998, 511. (i) Akita,
M.; Ohta, K.; Takahashi, Y.; Hikichi, S.; Moro-oka, Y. Organome-
tallics 1997, 16, 4121. (j) Kitajima, N.; Fujisawa, K.; Moro-oka, Y.
J. Am. Chem. Soc. 1990, 8, 3210.
5
N3P3(3,5-Me2Pz)6 or aminocyclophosphazenes such as N3P3-
(HNCH2CH2NH)(NMe2)4.6 One of the ways of preparing robust
ligands of this family where the problem of P-N bond
hydrolysis is avoided is to incorporate a spacer between the
pyrazolyl substituent and the phosphorus. To test this idea, we
have synthesized P,P-diphenyl-2-{3,5-dimethylpyrazol-1-yl}-
ethylphosphinate, Ph2P(O){OCH2CH2(3,5-Me2Pz)}, hereafter
called DPEP (1), and studied its coordination behavior toward
(2) (a) Joshi, V. S.; Kale, V. K.; Sathe, K. M.; Sarkar, A.; Tavale, S. S.;
Suresh, C. G. Organometallics 1991, 10, 2898. (b) Tokar, C. J.; Kettler,
P. B.; Tolman, W. B. Organometallics 1992, 8, 2737. (c) Chowdhury,
S. K.; Joshi, V. S.; Samuel, A. G.; Puranik, V. G.; Tavale, S. S.; Sarkar,
A. Organometallics 1994, 13, 4092. (d) LeCloux, D. D.; Tokar, C. J.;
Osawa, M.; Houser, R. P.; Keyes, M. C.; Tolman, W. B. Organome-
tallics 1994, 13, 2855. (e) Psillakis, E.; Jeffery, J. C.; McCleverty, J.
A.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1997, 1645.
(3) Chandrasekhar, V.; Kingsley, S.; Vij, A.; Lam, K. C.; Rheingold, A.
L. Inorg. Chem. 2000, 39, 3238.
(4) Chandrasekhar, V.; Nagendran, S.; Kingsley, S.; Krishnan, V.;
Boomishankar, R. Proc.-Indian Acad. Sci., Chem. Sci. 2000, 112, 171.
(5) Thomas, K. R. J.; Chandrasekhar, V.; Scott, S. R.; Hallford, R.; Cordes,
A. W. J. Chem. Soc., Dalton Trans. 1993, 2589.
(6) Chandrasekaran, A.; Krishnamurthy, S. S.; Nethaji, M. Inorg. Chem.
1994, 33, 3085.
10.1021/ic010454c CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/05/2001

Tethered Pyrazolyl Phosphinate
Inorganic Chemistry, Vol. 40, No. 23, 2001 5891
(m), 732 (s), 696 (s), 562 (s), 534 (s), 505 (s) cm-1. UV-vis {CH2Cl2,
[λmax/nm (ꢀmax/M-1 cm-1)]}: 665 (334), 640 (sh, 300), 590 (191), 266
(1901), 246 (2263). Mass (ESMS, CH2Cl2): 905.1[(DPEP)2‚COCl2‚
CoCl]+. Anal. Calcd for C19H21Cl2CoN2O2P (470.18): C, 48.53; H,
4.50; N, 5.90. Found: C, 48.49; H, 4.55; N, 6.08. Solid-state room-
temperature magnetic susceptibility measurement gives µeff per Co as
4.20 µB.
Co(II), Cu(II), Zn(II), and Pd(II) chlorides. We describe here
the details of the above investigations involving the synthesis,
X-ray structural characterization, and spectroscopy of the
tethered pyrazolyl phosphinate 1 and its transition metal
complexes 2-5.
Experimental Section
Synthesis of (DPEP)2‚CuCl2 (3). Anhydrous CuCl2 (0.13 g, 0.96
mmol) was added to a solution of 1 (0.68 g, 1.99 mmol) in
dichloromethane (60 mL). The resulting green solution was stirred at
room temperature for 10 h. This was filtered, and the solvent was
removed from the filtrate to afford a green solid (0.75 g, 92.5%): mp
124 °C. IR (KBr): 3055 (m), 2960 (m), 1590 (m), 1552 (s), 1465 (s),
1438 (s), 1384 (s), 1312 (s), 1261 (s), 1226 (vs), 1129 (vs), 1110 (vs),
1038 (vs), 939 (s), 801 (s), 752 (s), 728 (s), 695 (s), 562 (s), 535 (s)
cm-1. IR (CH2Cl2): 3051 (m), 2961 (m), 2854 (m), 1592 (w), 1554
(m), 1438 (m), 1395 (m), 1310 (sh, w), 1265 (s), 1223 (s), 1130 (s),
1112 (s), 1038 (s), 939 (m), 864 (w), 797 (m), 736 (s), 698 (s), 560
(m), 532 (m), 499 (m) cm-1. UV-vis {CH2Cl2, [λmax/nm (ꢀmax/M-1
cm-1)]}: 883 (106), 377 (1264), 273 (5000), 239 (4754). EPR (CH2-
Cl2/toluene, 1:1, 300 K): broad isotropic signal with half line width of
195G and giso of 2.135. EPR (CH2Cl2/toluene, 1:1, 77 K): g|, 2.37; A|,
93.23 × 10-4 cm-1; g , 2.10. Anal. Calcd for C38H42Cl2CuN4O4P2
(815.15): C, 55.99; H, 5.19; N, 6.87. Found: C, 56.02; H, 5.26; N,
6.96. Solid-state room-temperature magnetic susceptibility measurement
gives a µeff per Cu as 1.92 µB. Solution magnetic susceptibility
measurement (Evans NMR method, chloroform as solvent) gave a value
of 1.90 µB.
Synthesis of (DPEP‚ZnCl2)n (4). Anhydrous ZnCl2 (0.14 g, 1.02
mmol) was added to a solution of 1 (0.34 g, 0.99 mmol) in
dichloromethane (50 mL). The resulting colorless solution was stirred
at room temperature for 10 h. This was filtered, and from the filtrate
the solvent was removed in vacuo to afford a white crystalline powder
(0.40 g, 84%): mp 240 °C. IR (KBr): 3056 (m), 2959 (m), 1590 (m),
1554 (s), 1466 (s), 1438 (s), 1389 (s), 1375 (sh, m), 1310 (w), 1273
(w), 1179 (vs), 1133 (s), 1112 (s), 1073 (s), 1040 (vs), 995 (sh, m),
945 (s), 796 (m), 752 (m), 733 (vs), 694 (s), 563 (s), 536 (s) cm-1. IR
(CH2Cl2): 3054 (m), 2925 (m), 1590 (m), 1554 (m), 1467 (sh, m),
1438 (s), 1374 (m), 1310 (w), 1268 (w), 1180 (s), 1133 (s), 1112 (s),
1073 (sh, m), 1040 (s), 945 (m), 796 (sh, m), 733 (s), 695 (s), 562 (s),
535 (s) cm-1. 1H NMR (CDCl3, ppm): δ 7.82-7.49 (m, 10H, Phenyl),
5.94 (s, 1H, 4H-Pyrazole), 4.28 (d, 4H, OCH2CH2N), 2.41 (s, 3H,
CH3), 2.26 (s, 3H, CH3). 31P NMR (CDCl3, ppm): δ 38.8 (s). Mass
(ESMS, CH2Cl2): 917[(DPEP)2‚ZnCl2‚ZnCl]+. Anal. Calcd for C19H21-
Cl2N2O2PZn (476.64): C, 47.88; H, 4.44; N, 5.88. Found: C, 47.96;
H, 4.33; N, 6.08.
Reagents and General Procedures. The solvents were purified and
were dried according to standard procedures.7 Anhydrous cobalt(II)
chloride, copper(II) chloride, zinc(II) chloride, palladium(II) chloride
bisbenzonitrile, diphenylphosphinic chloride, and 2-chloroethanol were
acquired from Fluka, Switzerland, and were used as such. Triethylamine
(Qualigens, India) was dried over KOH and was freshly distilled before
use. 3,5-Dimethylpyrazole7 and 1-(hydroxyethyl)-3,5-dimethylpyrazole8
were prepared according to literature procedures.
Instrumentation. Infrared spectra were recorded as KBr pellets using
a Bruker Vector 22 FTIR spectrophotometer. 1H and 31P NMR spectra
were recorded on a JEOL spectrometer operating at 400 and 135 MHz,
respectively. EPR spectra were recorded on a Varian spectrometer at
X-band frequency, and the magnetic field was calibrated with DPPH.
Optical absorption spectra were obtained by using 1-cm quartz cells in
a Shimadzu UV-160 spectrophotometer. Mass spectra were recorded
on a JEOL Sx 102/DA 6000 mass spectrometer using xenon (6 kV, 10
mA) as the FAB gas. Electron spray mass spectra were recorded on a
MICROMASS QUATTRO II triple quadrupole mass spectrometer in
dichloromethane solution. C, H, and N analysis were carried out at the
Central Drug Research Institute’s (Lucknow, India) regional instru-
mentation facility. Magnetic susceptibility data were obtained for
polycrystalline samples of 2 and 3 using a locally built magnetometer.
The setup consists of an electromagnet with constant gradient pole caps
(Polytronic Corp., Mumbai, India) and a Sartorius M25-D/S balance
(Germany). Hg[Co(NCS)4] was used as the calibrant. All of the
preparative procedures described in the following were carried out under
an inert gas atmosphere of dry N2.
Synthesis of DPEP (1). Diphenyl phosphinic chloride (7.57 g, 31.99
mmol) dissolved in 25 mL of THF was added dropwise to an ice cold
solution of 2-ethoxy-3,5-dimethylpyrazole (4.48 g, 31.95 mmol) and
triethylamine (3.24 g, 32.01 mmol) in 150 mL of dry THF. The reaction
mixture was allowed to attain room temperature and then was heated
under reflux for 24 h. It was again allowed to attain room temperature,
was filtered, and the solvent was removed from the filtrate in vacuo
affording a white solid. This was recrystallized from a mixture of
n-hexane and benzene (10:1) at 25 °C to afford white needles of DPEP
(9.20 g, 85%): mp 90 °C. IR (KBr): 3074 (s), 2969 (s), 2947 (s),
2919 (s), 1588 (s), 1553 (s), 1458 (s), 1438 (s), 1381 (s), 1311 (s),
1223 (vs), 1130 (vs), 1082 (vs), 1041 (vs), 934 (vs), 784 (s), 731 (vs),
695 (s), 562 (s) cm-1. IR (CH2Cl2): 3049 (m), 2949 (m), 1590 (w),
1553 (m), 1438 (m), 1385 (w), 1266 (m), 1226 (s), 1130 (s), 1072 (s),
1040 (s), 937 (m), 786 (w), 732 (s), 696 (s), 561 (s), 535 (s) cm-1. 1H
NMR (CDCl3, ppm): δ 7.68-7.35 (m, 10H, Phenyl), 5.84 (s, 1H, 4H-
Pyrazole), 4.33 (d, 4H, OCH2CH2N), 2.24 (s, 3H, CH3), 2.21 (s, 3H,
CH3). 31P NMR (CDCl3, ppm): δ 32.9 (s). Mass spectrum (FAB):
341.4 (M+). Anal. Calcd for C19H21N2O2P (340.35): C, 67.05; H, 6.22;
N, 8.23. Found: C, 66.82; H, 6.35; N, 8.03.
Synthesis of (DPEP‚CoCl2)n (2). Anhydrous CoCl2 (0.13 g, 1.0
mmol) was added to a solution of 1 (0.34 g, 0.99 mmol) in
dichloromethane (50 mL). The reaction mixture was stirred at room
temperature for 10 h. It was filtered, and the solvent was removed from
the filtrate to afford a blue crystalline powder (0.38 g, 81%): mp 168
°C. IR (KBr): 3441 (w), 3050 (m), 2966 (m), 1589 (m), 1551 (s),
1468 (s), 1437 (s), 1396 (s), 1379 (m), 1310 (m), 1262 (m), 1224 (s),
1191 (vs), 1130 (s), 1111 (s), 1077 (s), 1018 (s), 954 (s), 795 (s), 756
(s), 730 (m), 695 (s), 568 (s), 536 (s) cm-1. IR (CH2Cl2): 3055 (m),
2962 (m), 2926 (m), 1591 (w), 1553 (m), 1438 (s), 1374 (w), 1309
(w), 1262 (m), 1181 (s), 1112 (s), 1074 (s), 1038 (vs), 939 (s), 798
Synthesis of (DPEP)2‚PdCl2 (5). PdCl2(C6H5CN)2 (0.19 g, 0.49
mmol) was allowed to react with 1 (0.34 g, 0.99 mmol) taken in
dichloromethane (50 mL). A yellow solution was obtained. This was
stirred at room temperature for 10 h and was filtered. Removal of
solvent from the filtrate afforded a yellow powder (0.40 g, 92%): mp
262 °C. IR (KBr): 3056 (m), 2958 (m), 2921 (m), 1591 (m), 1553
(m), 1467 (sh, m), 1438 (s), 1313 (m), 1262 (sh, m), 1229 (vs), 1128
(s), 1040 (vs), 941 (s), 805 (s), 775 (s), 753 (s), 724 (s), 696 (s), 564
(s), 538 (s) cm-1. IR (CH2Cl2): 3053 (m), 1678 (m), 1555 (m), 1438
(m), 1273 (m), 1227 (s), 1130 (s), 1037 (s), 940 (m), 748 (vs), 696 (m,
1
sh), 560 (m), 533 (m) cm-1. H NMR (CDCl3, ppm): δ 7.78-7.68
(m, 5H, Phenyl), 7.52-7.43 (m, 5H, Phenyl), 5.88 (d, 1H, 4H-
Pyrazole), 5.18(t, 2H, OCH2), 4.99 (t, 2H, NCH2), 2.67 (s, 3H, CH3),
2.19 (s, 3H, CH3). 31P NMR (CDCl3, ppm): δ 34.0 (s). Mass (FAB):
859(M+). Anal. Calcd for C38H42Cl2N4O4P2Pd (858.02): C, 53.19; H,
4.93; N, 6.53. Found: C, 53.35; H, 5.52; N, 6.79.
The hydrolytic stability of compounds 1-5 was evaluated in the
following manner. The 31P NMR of 1, 4, and 5 were recorded in CDCl3
(vide supra). About 0.1 mL of D2O was added to these solutions, and
the 31P NMR was recorded after 24 h. There was no change in the
chemical shifts for any of the compounds. Also, no new peaks were
detected. Further, compounds 1-5 (0.10 g) were dissolved in about
20 mL of CH2Cl2 and were treated with 0.5 mL of water. These
solutions were stirred for 24 h at room temperature. Removal of solvent
(7) Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman:
London, 1989.
(8) Haanstra, W. G.; Driessen, W. L.; Reedijk, J.; Turpeinen, U.;
Hamalainen, R. J. Chem. Soc., Dalton Trans. 1989, 2309.

5892 Inorganic Chemistry, Vol. 40, No. 23, 2001
Kingsley et al.
a
Table 1
1b
2
3
4
5
empirical formula
fw
space group
color of crystal
crystal system
a (Å)
C38H48N4O7P2
734.74
C2/c
colorless
monoclinic
21.897(5)
10.009(2)
19.147(9)
90
111.40(3)
90
3907(2)
1.249
C19H21Cl2N2O2P1Co
470.18
P21/n
C38H42Cl2N4O4P2Cu
815.15
P1h
C19H21Cl2N2O2P1Zn
476.64
P21/n
colorless
monoclinic
9.7530(20)
18.0247(20)
11.9998(20)
90
95.5162(80)
90
2099.75(3)
1.508
C38H42Cl2N4O4P2Pd
858.02
P1h
yellow
triclinic
7.671(16)
11.487(2)
11.763(3)
97.551(18)
90.00(10)
106.87(8)
982(2)
1.450
1
0.734
0.71073
293(2)
blue
dark green
triclinic
7.6780(18)
11.455(3)
11.782(3)
97.525(16)
90.09(2)
106.96(3)
981.7(4)
1.379
monoclinic
9.751(6)
18.126(2)
11.946(3)
90
95.31(3)
90
2102.4(14)
1.485
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
F
Z
calcd (mg m-3
)
4
1
4
µ (mm-1
λ (Å)
T (K)
GOF
)
0.163
1.163
0.818
0.71073
253(2)
1.517
0.71073
193(2)
0.71073
253(2)
1.065
0.71069
293(2)
0.923
1.293
1.296
0.935
total reflections
independent reflns
Rint
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
3457
2836
0.0254
0.0436
0.1334
2414
2273
0.0557
0.0547
0.1817
3682
3000
0.0168
0.0373
9700
4533
0.0285
0.0451
3717
3433
0.0160
0.0284
0.1051
0.1528
0.0987
2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) {[∑w(|Fo| - |Fc| )2]/[∑w(|Fo| )2]}1/2
.
b 1 crystallizes with 1.5 molecules of H2O.
from these reaction mixtures in vacuo afforded the starting compounds
1-5 in quantitative yields.
Scheme 1
X-ray Crystallography. Crystals of 1-5 were obtained by the slow
diffusion of n-hexane into solutions of these compounds in dichlo-
romethane at room temperature in the absence of any precaution to
prevent ingress of moisture. The process of crystallization took about
one week. It was noticed that 1 crystallized with 1.5 molecules of water
(vide infra). Deliberate addition of 2 mol of water during the above
crystallization process of 1 also afforded the same crystals. The crystal
data, data collection methodology, and refinement parameters for 1, 2,
3, 4, and 5 are given in Table 1. The X-ray diffraction data for 1, 3,
and 4 were collected on a Bruker SMART diffractometer equipped
with a CCD area detector. The structure was solved by direct methods
using SHELXTL (5.10)9 program and was refined by the least-squares
method on F2. For compounds 2 and 5, X-ray diffraction data were
collected on an Enraf Nonius FR590 CAD-4 diffractometer. The
structure was solved by using the WINGX ver 1.63 crystallographic
collective package (L. J. Farrugia, WINGX ver 1.63, An Integrated
Systems of Windows programs for the solution, refinement and analysis
of single-crystal X-ray diffraction data, Department of Chemistry,
University of Glasgow). The structure was solved initially with SIR97
and was refined with the SHELX-9710 package incorporated in WINGX.
The structure was refined against F2 with a full-matrix least-squares
algorithm. All hydrogen atoms were included in idealized positions,
and a riding model was used.
possible modes of coordination are outlined in Scheme 2. Of
these, the chelating mode does not appear to be favorable as it
involves the formation of an eight-membered metallacycle.
Exclusive coordination through the phosphoryl oxygens also is
unlikely because of the presence of the strongly coordinating
pyrazolyl nitrogens.
Results and Discussion
Synthesis. The ligand DPEP was prepared in a nearly
quantitative yield by the reaction of diphenylphosphinic chloride
with 1-(2-hydroxyethyl)-3,5-dimethylpyrazole in the presence
of triethylamine as the hydrogen chloride scavenger (Scheme
1). DPEP shows a single phosphorus resonance at +32.9 ppm.
In the proton NMR, the chemical shifts of the N-CH2 and
O-CH2 protons are isochronous and resonate at +4.30 ppm.
The methyl substituents on the pyrazole are nonequivalent and
are seen as two singlets at 2.24 and 2.21 ppm, respectively.
The ligand DPEP has two potential coordination sites in the
form of the phosphoryl oxygen and the pyrazolyl nitrogen. The
The reactions of DPEP with transition metal salts are
insensitive to the stoichiometry of the reagents. Thus, in the
reactions of DPEP with ZnCl2 or CoCl2 involving various
stoichiometric combinations, only the 1:1 products are obtained.
Similarly in the reactions with CuCl2 or PdCl2(C6H5CN)2, only
the 2:1 products are obtained (Scheme 1). The complexes 2-5
are nonionic in solution as determined by conductivity measure-
ments, suggesting that the chlorides are bound to the metal ions
in the complexes. Also, unlike the hydrolytic sensitivity of the
metal complexes of phosphorus-based pyrazolyl ligands2a,3,4
where the pyrazolyl group is directly attached to the phosphorus
center, the complexes 2-5 are quite stable to moisture.
X-ray Crystal Structure of DPEP (1). The ligand crystal-
lizes in the space group C2/c and contains four molecules in
the unit cell. The molecular structure of 1 is shown in Figure
(9) Sheldrick, G. M. SHELXTL, An Integrated System for SolVing,
Refining, and Displaying Crystal Structures from Diffraction Data;
University of Gottingen: Gottingen, Germany, 1991.
(10) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Refine-
ment; University of Gottingen: Gottingen, Germany, 1997.

Tethered Pyrazolyl Phosphinate
Inorganic Chemistry, Vol. 40, No. 23, 2001 5893
Figure 2. ORTEP plot of two molecules of DPEP hydrogen bonded
through three water molecules. The phenyl rings and hydrogen atoms
from the ligand are omitted for clarity. Important bond lengths (Å)
and bond angles (°) are O(1)- - - -H(1) 1.996(42), O(3)- - - -H(3)
1.963(9), O(1)- - - -O(3) 2.786(58), O(3)- - - -O(4) 2.812(18), O(1)- - - -
O(4) 5.212(83), O(1)- - - -O(1A) 9.618(181), O(1)-H(1)-O(3)
171.03(2), O(3)-H(3)-O(4) 163.81(2), O(1)-O(3)-O(4) 137.23(1),
P(1)-O(1)-O(3) 128.47(1), O(3)-O(4)-O(3A) 119.32(1), and O(1)-
O(4)-O(1A) 134.66(1).
Figure 1. ORTEP plot of the ligand DPEP with thermal ellipsoids at
50% probability. Hydrogen atoms are omitted for clarity. Important
bond lengths (Å) and bond angles (°) are P(1)-O(1) 1.4735(18), P(1)-
O(2) 1.5874(19), O(1)-P(1)-O(2) 115.73(11), O(1)-P(1)-C(1)
113.47(11),
O(2)-P(1)-C(1)
100.99(10),
O(1)-P(1)-C(7)
111.15(12), O(2)-P(1)-C(7) 106.53(11), and C(1)-P(1)-C(7)
108.22(11).
Scheme 2
Figure 3. ORTEP plot of 2 showing the monomeric unit with thermal
ellipsoids at 50% probability. Hydrogen atoms were omitted for clarity.
Important bond lengths (Å) and bond angles (°) are Co(1)-Cl(1)
2.214(4), Co(1)-Cl(2) 2.229(4), Co(1)-O(1) 1.954(8), Co(1)-N(1)
2.031(11), P(1)-O(1) 1.490(9), P(1)-O(2) 1.578(9), O(1)-Co(1)-
Cl(2) 109.7(3), N(1)-Co(1)-Cl(1) 110.7(3), Cl(2)-Co(1)-Cl(1)
111.7(18), O(1)-Co(1)-Cl(1) 105.6(3), O(1)-Co(1)-N(1) 103.2(4),
N(1)-Co(1)-Cl(2) 115.2(3), and N(2)-N(1)-Co(1) 130.2(9).
water molecule. A water molecule that lies on a center of
inversion connects two DPEP‚H2O units affording a hydrogen-
bonded chain as shown in Figure 2. The hydrogen bond
distances O1-H1 [1.996(42) Å] and O3-H3 [1.963(9) Å] are
perfectly normal. Also, the bond angles observed for these
hydrogen bonds viz., O1-H1-O3 [171.03(2)°] and O3-H3-
O4 [163.81(2)°], are in keeping with the hydrogen bonding
trends known for O-H- - -O secondary interactions.12
X-ray Crystal Structures of (DPEP‚CoCl2)n (2) and
(DPEP‚ZnCl2)n (4). Both cobalt(II) and zinc(II) chlorides form
1:1 complexes 2 and 4 with the tethered pyrazolyl phosphinate
ligand DPEP. Compounds 2 and 4 are isostructural. The ORTEP
diagram of 2 is shown in Figure 3. The coordination environ-
ment in 2 and 4 consists of two chlorine, one oxygen, and one
nitrogen atoms arranged in a tetrahedral manner around the
metal ion. The ligand DPEP acts in a bidentate bridging mode
by linking two adjacent metal ions through its phosphoryl
oxygen atom and the pyrazolyl nitrogen atom. This leads to
the formation of a zigzag polymeric chain as shown in Figure
4A. The adjacent metal atoms within the polymeric chain are
arranged alternately on either side of an imaginary axis running
1. The two P-O bond lengths present in the molecule are not
equal; P1-O1 is 1.4735(18) and P1-O2 is 1.5874(19) Å. The
value of the PdO distance is sensitive to the substituents on
phosphorus; the shortest distance observed is for P(O)Br3 (1.44
Å).11 In compounds that are related to DPEP, such as (NH2)3Pd
O11 and (C6H5)2P(O)NMe2,11 these distances have been mea-
sured to be 1.51 and 1.47 Å, respectively. The latter value is
close to the one found in the present instance. The geometry
around the phosphorus in DPEP is nearly tetrahedral; the shortest
angle is the O2-P1-C1 angle of 100.99(10)°, and the largest
angle is 115.73(11)° observed for O1-P1-O2 (Figure 1).
Two molecules of DPEP are involved in hydrogen bonding
with three molecules of water of crystallization. The phosphoryl
oxygen O1 is involved in a hydrogen bond with the H1 of a
(11) Corbridge, D. E. C. The Structural Chemistry of Phosphorus; Elsevier
(12) Jeffrey, G. A.; Saenger, W. Hydrogen Bonding in Biological Structures;
Scientific Publishing Co.: Amsterdam, 1974.
Springer-Verlag: Heidelberg, 1991.

5894 Inorganic Chemistry, Vol. 40, No. 23, 2001
Kingsley et al.
Figure 5. ORTEP plot of 5 with thermal ellipsoids at 50% probability.
Hydrogen atoms were omitted for clarity. Important bond lengths (Å)
and bond angles (°) are Pd(1)-Cl(1) 2.2904(9), Pd(1)-N(2) 2.011(4),
Cl(1)-Pd(1)-Cl(1A) 180.00(4), N(2)-Pd(1)-N(2A) 180.00(8),
Cl(1)-Pd(1)-N(2A) 90.58(10), Cl(1)-Pd(1)-N(2) 89.42(10), and
N(1)-N(2)-Pd(1) 123.83(18).
Figure 4. (A) DIAMOND view showing the zigzag arrangement of
the polymer 4. Only the atoms involved in chain propagation have been
shown for clarity. The presence of two individual metal axis are marked
in dotted lines. Important bond lengths (Å) and bond angles (°) are
Zn(1)-Zn(2) 7.487, Zn(1)-Zn(3) 14.718, and Zn(1)-Zn(2)-Zn(3)
158.81. (B) DIAMOND view showing the rib-cage-like structural
arrangement for the complexes 2 and 4.
two phosphoryl oxygen atoms (O1 and O1A in 5) are in a
perfect trans disposition with respect to each other. The M-O
distances are 6.455 Å for 3 and 6.429 Å for 5, respectively.
The metric parameters found in the immediate coordination
environment of 5 are summarized in Figure 5, while those of 3
are given in the Supporting Information. These are comparable
to literature precedents.14,15 The P1-O1 distance (1. 470(3) Å)
for 5 and the analogous distance in 3 are completely unchanged
in comparison to the value found for the free ligand DPEP
consistent with the coordination situation found in these
complexes.
A closer examination of the structures of 3 and 5 reveals
extremely interesting intermolecular C-H- - -O secondary
interactions between the phosphoryl oxygen and an aromatic
C-H. This is shown for the copper complex 3 in Figure 6. Thus
the phosphoryl oxygen O2 is hydrogen bonded to H12a (the
meta hydrogen of the phenyl substituent on phosphorus of an
adjacent molecule). The O2- - - -H12a distance of 2.575 Å and
the C12a-H12a-O2 bond angle of 147.28° for 3 (and the
O1- - -H11 distance of 2.587 Å and the C11-H11-O1 angle
of 147.95° for 5) are quite reasonable for these kinds of
interactions.16 The effect of C-H- - -O interactions on the solid-
state structures of organic and in some organometallic com-
pounds has been recently reviewed.17
between the metal ions. This leads to an arrangement where
the alternate metal ions perfectly eclipse each other as shown
in Figure 4B and gives rise to an interesting situation where
the like atoms on either half of the imaginary axis running
between the polymer chain eclipse with each other to afford an
overall rib-cage-like structure. Although polymeric complexes
consisting of zinc and cobalt are previously known,13 the type
of polymeric architecture exhibited by 2 and 4 is unprecedented.
The adjacent metal separation in 2 (Co1-Co2) is 7.480 Å,
while in 4 (Zn1-Zn2) it is 7.487 Å. The distance between the
eclipsing metal atoms in 2 (Co1-Co3) is 14.705 Å, while in 4
(Zn1-Zn3) it is 14.718 Å. The metric parameters of 2 are
summarized in Figure 3, while those of 4 are given in the
Supporting Information. The P-O bond distance (P1-O1)
corresponding to the phosphoryl oxygen increases to 1.490(9)
Å in 2 and 1.496(2) Å in 4 and is consistent with the trends in
the PdO stretching frequency observed in the infrared spectra
of DPEP vis-a`-vis the complexes 2 and 4 (vide infra).
X-ray Crystal Structures of (DPEP)2‚CuCl2 (3) and
(DPEP)2‚PdCl2 (5). In contrast to the 1:1 complexes formed in
the reactions between DPEP and CoCl2 or ZnCl2, the corre-
sponding reactions with CuCl2 or PdCl2(C6H5CN)2 proceed to
afford exclusively 2:1 complexes 3 and 5 which are isostructural.
The ORTEP diagram of 5 is shown in Figure 5.
The metal ions in 3 and 5 adopt a perfect square-planar
geometry. The coordination environment around the metal ions
consists of two chlorine and two pyrazolyl nitrogen atoms
arranged in a trans configuration. Two DPEP ligands coordinate
to one metal ion exclusively through the pyrazolyl nitrogens.
The phosphoryl oxygen atoms are noncoordinating in contrast
to the situation found for 2 and 4. However, interestingly the
The consequence of C-H- - - -O interactions between two
adjacent molecules is the formation of a rectangular box-type
arrangement (Figure 6). In the absence of other effects, this
would have been the only structural manifestation. However,
as can be seen from Figure 7, a π-π, face-to-face, stacking
interaction occurs between the phenyl groups associated with
two immediate neighboring molecules leading to the formation
of a polymeric chain. The π-π centroid distance in the complex
3 is 3.883 Å, while in 5 it is 3.917 Å. The C-H- - -O
(14) Hathaway, B. J. In ComprehensiVe Coordination Chemistry, 1st ed.;
Wilkinson, G., Ed.; Pergamon Press: Great Britain, 1987; Vol. 5, p
533.
(15) Barnard, C. F. J.; Russell, M. J. H. In ComprehensiVe Coordination
Chemistry, 1st ed.; Wilkinson, G., Ed.; Pergamon Press: Great Britain,
1987; Vol. 5, p 1099.
(16) Forristal, I.; Lowman, J.; Afarinkia, K.; Steed, J. W. CrystEngComm
2001, 14, 1.
(17) (a) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290. (b) Braga, D.;
Grepioni, F.; Desiraju, G. R. Chem. ReV. 1998, 98, 1375.
(13) (a) Borisov, G.; Varbanov, S. G.; Venanzi, L. M.; Albinati, A.;
Demartin, F. Inorg. Chem. 1994, 33, 5430. (b) Ellis, W. W.; Schmitz,
M.; Arif, A. A.; Stang, P. J. Inorg. Chem. 2000, 39, 2547. (c) Lu, J.;
Paliwala, T.; Lim, S. C.; Lu, C.; Niu, T.; Jacobson, A. Inorg. Chem.
1997, 36, 923. (d) Lu, J.; Yu, C.; Niu, T.; Paliwala, T.; Crisci, G.;
Somosa, F.; Jacobson, A. Inorg. Chem. 1998, 37, 4637.

Tethered Pyrazolyl Phosphinate
Inorganic Chemistry, Vol. 40, No. 23, 2001 5895
PdO stretching frequency in cm-1
Table 2.
compound
in solid (KBr pellets)
in solution (DCM)
DPEP 1
1223 (vs)
1191 (vs)
1226 (vs)
1179 (vs)
1229 (vs)
1226 (s)
1181 (s)
1223 (s)
1180 (s)
1227 (s)
2
3
4
5
Scheme 3
Figure 6. DIAMOND view of 3 showing the box-type polymeric
network formed by the weak hydrogen bonds. Important bond lengths
(Å) and bond angles (°) are O(2)- - - -H(12A) 2.575, O(2)- - - - -C(12A)
3.395, Cu- - - -Cu 7.678(2), and C(12A)-H(12A)-O(2) 147.28(2).
Spectroscopic Aspects. The phosphorus chemical shifts of
the diamagnetic complexes 4 and 5 are slightly deshielded in
comparison to the ligand DPEP; the chemical shift of the zinc
complex 4 is observed at +38.8 ppm, while that of the palladium
derivative 5 is seen at +34.0 ppm. Also, in these metal
complexes the O-CH2 and the N-CH2 resonances are resolved,
and two distinct triplets are seen for each of these.
The PdO stretching frequency has been widely used as a
diagnostic probe in determining the involvement of the phos-
phoryl oxygen in coordination to the metal ions. The PdO
stretching frequency in the free ligand DPEP occurs at 1223
cm-1. This may be compared to the values of 1200 cm-1
observed for the triamidophosphine oxide, (NH2)3PdO,11 and
1165 cm-1 observed for dimethyl(aminomethyl)phosphine
oxide, (CH3)2P(O)CH2NH2.11 The PdO stretching frequency
of 1 is shifted to 1191 and 1179 cm-1 for the cobalt (2) and
zinc (4) complexes, respectively, corroborating the involvement
of the phosphoryl oxygen atom in coordination to the metal
ion in 2 and 4. In the copper and palladium complexes 3 and 5,
where such an interaction is absent, the PdO stretching
frequency remains almost unchanged in comparison to DPEP.
The IR stretching frequency values for 1-5 are summarized in
Table 2. As discussed vide supra these conclusions are borne
out by the results of the single-crystal X-ray structure investiga-
tions. Solution IR for all of the complexes in dichloromethane
shows that the PdO stretching frequency remains unchanged
for these complexes in comparison with the solid-state values.
This implies that the immediate coordination environment
around the metal ions remains undisturbed in solution. The
highest mass peaks observed in the electron-spray mass spectra
of the cobalt and zinc complexes 2 and 4 occur at 905 and 917,
respectively. These are due to singly charged ions of dimers
from which a chlorine loss has occurred viz., [(DPEP)2‚COCl2‚
CoCl]+ and [(DPEP)2‚ZnCl2‚ZnCl]+, respectively. The struc-
tures of the dimeric formulation for 2 and 4 are shown in
Scheme 3 and are consistent with the solution IR data for these
compounds (Table 2) which show that the PdO stretching
Figure 7. DIAMOND view of 5 showing the box-type polymeric
network and the π-π stacking arrangements. Only the hydrogen atoms
and phenyl rings involved in weak bonding and in π stacking are shown
for clarity. Important bond lengths (Å) and bond angles (°) are O(1)- - - -
H(11A) 2.587, O(1)- - - -C(11A) 3.411, Pd- - -Pd 7.671(16), and
C(11A)-H(11A)-O(1) 147.95(5); π-π(centroid-centroid) distance
is 3.917.
interactions between the parallel polymeric chains result in a
sheetlike two-dimensional polymeric network.

5896 Inorganic Chemistry, Vol. 40, No. 23, 2001
Kingsley et al.
frequency in solution also occurs at a lower value in comparison
to the ligand DPEP.
Acknowledgment. We are thankful to the Department of
Science and Technology (New Delhi) for financial support.
The EPR spectrum of the copper complex 3 as a glass in
dichloromethane/toluene at 77 K shows that the g| value occurs
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of DPEP (1), (DPEP‚
CoCl2)n (2), (DPEP)2‚CuCl2 (3), (DPEP‚ZnCl2)n (4), and (DPEP)2‚PdCl2
(5); ORTEP diagrams and metric parameters of the complexes 3 and
4. This material is available free of charge via the Internet at
http://pubs.acs.org.
at 2.370 with a corresponding A| value of 93.2 × 10-4 cm-1
.
This value corresponds to a tetrahedral geometry around the
copper. It is reasonable to suggest that the solid-state square-
planar geometry observed for Cu(II) in 3 is probably due to the
secondary interactions involving C-H- - -O hydrogen bonding
and the π-π stacking. Removal of these effects in solution or
in a glassy state leads to a change to a tetrahedral geometry.
IC010454C