Novel reactivity mode of hydroxamic acids: A metalla-pinner reaction

Article abstract of DOI:10.1021/ic025554c

The reaction between the nitrile complex trans-[PtCl₄(EtCN)₂] and benzohydroxamic acids RC₆H₄C(=O)NHOH (R = p-MeO, p-Me, H, p-Cl, o-HO) proceeds smoothly in CH₂Cl₂ at ～45°C for 2-3 h (sealed tube) or under focused 300 W microwave irradiation for ～15 min at 50°C giving, after workup, good yields of the imino complexes [PtCl₄{NH=C(Et)ON=C(OH)(C₆H₄R)}₂] which derived from a novel metalla-Pinner reaction. The complexes [PtCl_4- {NH=C(Et)ON=C(OH)(C₆H₄R)}₂] were characterized by elemental analyses (C, H, N), FAB mass spectrometry, and IR and ¹H and ¹³C{¹H} spectroscopies, and [PtCl₄{NH=C(Et)ON=C(OH)(Ph)}₂] (as the bis-dimethyl sulfoxide solvate), by X-ray single-crystal diffraction. The latter disclosed its overall trans-configuration with the iminoacyl species in the hydroximic tautomeric form in E-configuration which is held by N-H···N hydrogen bond between the imine =NH atom and the hydroximic N atom.

Full text of DOI:10.1021/ic025554c

Inorg. Chem. 2002, 41, 2981−2986
Novel Reactivity Mode of Hydroxamic Acids: A Metalla-Pinner Reaction
,†
Konstantin V. Luzyanin,† Vadim Yu. Kukushkin,* Maxim L. Kuznetsov,‡ Dmitrii A. Garnovskii,‡
,‡
Matti Haukka,§ and Armando J. L. Pombeiro*
St. Petersburg State UniVersity, 198504 Stary Petergof, Russian Federation, Centro de Qu´ımica
Estrutural, Complexo I, Instituto Superior Te´cnico, AV. RoVisco Pais, 1049-001 Lisbon, Portugal,
and Department of Chemistry, UniVersity of Joensuu, P.O. Box 111, FIN-8010 Joensuu, Finland
Received February 21, 2002
The reaction between the nitrile complex trans-[PtCl4(EtCN)2] and benzohydroxamic acids RC H C(dO)NHOH (R
6
4
) p-MeO, p-Me, H, p-Cl, o-HO) proceeds smoothly in CH Cl2 at ∼45 °C for 2−3 h (sealed tube) or under focused
2
300 W microwave irradiation for ∼15 min at 50 °C giving, after workup, good yields of the imino complexes
[PtCl4{NHdC(Et)ONdC(OH)(C H R)}2] which derived from a novel metalla-Pinner reaction. The complexes [PtCl4-
6
4
{NHdC(Et)ONdC(OH)(C H R)}2] were characterized by elemental analyses (C, H, N), FAB mass spectrometry,
6
4
and IR and 1H and 13C{1H} spectroscopies, and [PtCl4{NHdC(Et)ONdC(OH)(Ph)}2] (as the bis-dimethyl sulfoxide
solvate), by X-ray single-crystal diffraction. The latter disclosed its overall trans-configuration with the iminoacyl
species in the hydroximic tautomeric form in E-configuration which is held by NsH‚‚‚N hydrogen bond between
the imine dNH atom and the hydroximic N atom.
Introduction
they play an important role in the chemical defense of cereals
against pests such as insects and pathogenic fungi and
bacteria12 and as plant growth regulators.13 Some other
Hydroxamic acids and metal hydroxamates are among the
most studied compounds owing to their high applicability
in diverse areas and significance in life processes. In
bioinorganic chemistry, they are the subject of rapt attention
as inhibitors of enzymes, for example, peroxidases,1 ureases,2
and matrix metalloproteinase,3 and siderophores for iron-
(III).4 In medicine, these acids have recently been widely
used as key functional groups of potential therapeutics
targeting cardiovascular diseases, HIV, and Alzheimer’s
disease.5 Hydroxamic acid based chelation therapy is useful
for the treatment of cancer,6 metal poisoning,7 iron-overload,8
malaria,9 allergic diseases,10 and tuberculosis.11 In agriculture,
(3) Porter, J. R.; Millican, T. A.; Morphy, J. R. Expert Opin. Ther. Pat.
1995, 5, 1287; Chem. Abstr. 1996, 124, 80174. (b) Hidalgo, M.;
Eckhardt, S. G. J. Natl. Cancer Inst. 2001, 93, 178. (c) Yamamoto,
M.; Hirayama, R.; Naruse, K.; Yoshino, K.; Shimada, A.; Inoue, S.;
Kayagaki, N.; Yagita, H.; Okumura, K.; Ikeda, S. Drug Des. DiscoVery
1999, 16, 119. (d) Steinman, D. H.; Curtin, M. L.; Garland, R. B.;
Davidsen, S. K.; Heyman, H. R.; Holms, J. H.; Albert, D. H.; Magoc,
T. J.; Nagy, I. B.; Marcotte, P. A.; Li, J.; Morgan, D. W.; Hutchins,
C.; Summers, J. B. Bioorg. Med. Chem. Lett. 1998, 8, 2087. (e)
Hooper, N. M.; Turner, A. J. Biochem. Soc. Trans. 2000, 28, 441-6.
(4) Albrecht-Gary, A. M.; Libman, J.; Shanzer, A. Pure Appl. Chem. 1996,
68, 1243. (b) Crumbliss, A. L. Coord. Chem. ReV. 1990, 105, 155.
(c) Hara, Y.; Shen, L.; Tsubouchi, A.; Akiyama, M.; Umemoto, K.
Inorg. Chem. 2000, 39, 5074.
(5) El Yazal, J.; Pang, Y.-P. J. Phys. Chem. B 2000, 104, 6499. (b) El
Yazal, J.; Pang, Y.-P. J. Phys. Chem. A 1999, 103, 8346.
(6) Steward, W. P.; Thomas, A. L. Expert Opin. InVest. Drugs 2000, 9,
2913. (b) Steward, W. P. Cancer Chemother. Pharmacol. 1999, 43,
Suppl. S56-60. (c) Brammer, R.; Buckels, J.; Bramhall, S. Int. J.
Clin. Pract. 2000, 54, 373-381.
* To whom correspondence should be addressed. E-mail: kukushkin@
vk2100.spb.edu (V.Yu.K.); pombeiro@ist.utl.pt (A.J.L.P.).
† St. Petersburg State University.
‡ Instituto Superior Te´cnico.
§ University of Joensuu.
(1) O’Brien, E. C.; Farkas, E.; Gil, M. J.; Fitzgerald, D.; Castineras, A.;
Nolan, K. B. J. Inorg. Biochem. 2000, 79, 47. (b) Tsukamoto, K.;
Itakura, H.; Sato, K.; Fukuyama, K.; Miura, S.; Takahashi, S.; Ikezawa,
H.; Hosoya, T. Biochemistry 1999, 38, 12558.
(2) Benini, S.; Rypniewski, W. R.; Wilson, K. S.; Miletti, S.; Ciurli, S.;
Mangani, S. J. Biol. Inorg. Chem. 2000, 5, 110. (b) Zhang, Y.; Li,
D.; Houtman, J. C.; Witiak, D. T.; Seltzer, J.; Bertics, P. J.; Lauhon,
C. T. Bioorg. Med. Chem. Lett. 1999, 9, 2823. (c) Brown, D. A.; Cuffe,
L. P.; Fitzpatrick, N. J.; Glass, W. K.; Herlihy, K.; Nimir, H.; Deeg,
O.; Errington, W.; Kemp, T. J. Chem. Commun. 1998, 2433. (d)
Arnold, M.; Brown, D. A.; Deeg, O.; Errington, W.; Haase, W.;
Herlihy, K.; Kemp, T. J.; Nimir, H.; Werner, R. Inorg. Chem. 1998,
37, 2920.
(7) Domingo, J. L. Reprod. Toxicol. 1998, 12, 499-510; Chem. Abstr.
1998, 129, 311786.
(8) Turcot, I.; Stintzi, A.; Xu, J.; Raymond, K. N. J. Biol. Inorg. Chem.
2000, 5, 634. (b) Richardson, D. R.; Ponka, P. J. Lab. Clin. Med.
1998, 131, 306.
(9) Cabantchik, Z. I. Parasitol. Today 1995, 11, 74; Chem. Abstr. 1995,
122, 229826. (b) Tsafack, A.; Golenser, J.; Libman, J.; Shanzer, A.;
Cabantchik, Z. I. Mol. Pharmacol. 1995, 47, 403; Chem. Abstr. 1995,
122, 230213.
(10) Igeta, K.; Tobetto, K.; Saiki, I.; Odake, S.; Fujisawa, T.; Matsuo, T.;
Oku, T. PCT Int. Appl. WO 00 03,703, 2000; Chem. Abstr. 2000,
132, 117536.
(11) Miller, M. J. Chem. ReV. 1989, 89, 1563 and references therein.
10.1021/ic025554c CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/04/2002
Inorganic Chemistry, Vol. 41, No. 11, 2002 2981

Luzyanin et al.
practical areas involving hydroxamic acids and their com-
plexes include removal of toxic elements by solvent extrac-
tion,14 usage as efficient and environmentally friendly
corrosion inhibitors,15 applications as collectors for flotation
of minerals,16 antioxidant acivity,17 and their potential as
redox switches for electronic devices.18
has recently been reviewed by two of us.28 In particular, the
reaction between platinum(IV) complexes [PtCl4(RCN)2] (R
) alkyl, benzyl, phenyl),29-31 and also nitrile complexes of
Pt(II),32 Rh(III),33 and Re(IV),34 with such NOH nucleophiles
as oximes, RR′CdNOH, and dialkyl hydroxylamines, R2-
NOH, giving a CsO bond upon addition of the OH group
across the nitrile group of metal-activated RCN, have been
observed. As a continuation of this project, we focused our
attention on hydroxamic acids as potential NOH nucleophiles
(where the N amide atom in the sp2 hybridization35 is
different of the sp3 amine nitrogen in hydroxylamines) and
found, instead of the conventional chelation, a novel reactiv-
ity pattern for those species, that is, their involvement in a
new metalla-Pinner type reaction leading to their O-addition
to the nitrile carbon. In organic chemistry, the Pinner
reaction,28 interaction between an organonitrile and an alcohol
which is typically performed in the presence of substantial
amounts of hydrogen chloride, is widely applicable for the
preparation of imino esters which are, in turn, useful as
synthons for further versatile conversions. We have now
extended this type of reaction to hydroxamic acids in a novel
metal-mediated process.
Amazingly, such a broad spectrum of activity of hydrox-
amic acids is almost exclusively associated with only one
type of chemical reactions; that is, their ability to bind a
large variety of metal ions forms, in the vast majority of
cases, O,O five-membered chelate rings19-21 (bridging22,23
and monodentate24 coordination modes are also known,
although scarce), and these complexes are often characterized
by very high stability constants.21 Although hydroxamic acids
have been known for over a century,25 their reactivity modes
involving metal centers, besides the complex forming
properties, are practically unexplored; among the rare excep-
tions are the recently described deoxygenation of the N-OH
group occurring at Os(III) and Rh(I) centers,26 Ni(II)-assisted
hydroxylamine elimination,23 and reductive cleavage of the
N-O bond with SmI2.27
In recent years, our group has been involved in investiga-
tions of the reactivity of metal-activated nitriles, a topic that
Experimental Section
(12) Gierl, A.; Frey, M. NoVartis Found. Symp. 1999, 223, 150; Chem.
Abstr. 2000, 133, 263823.
Materials and Instrumentation. Hydroxamic acids were syn-
thesized in accord with the published method.20 Solvents were
obtained from commercial sources and used as received while
dichloromethane was conventionally dried. The complex [PtCl4-
(EtCN)2] was prepared as previously described.36 C, H, and N
elemental analyses were carried out by the Microanalytical Service
of the Instituto Superior Te´cnico. For TLC, Merck UV 254 SiO2
plates have been used. Positive-ion FAB mass spectra were obtained
on a Trio 2000 instrument by bombarding 3-nitrobenzyl alcohol
(NBA) matrixes of the samples with 8 keV (∼1.28 × 1015 J) Xe
atoms. Mass calibration for data system acquisition was achieved
using CsI. Infrared spectra (4000-400 cm-1) were recorded on a
(13) Rentzea, C.; Rademacher, W.; Harreus, A.; Jung, J. Eur. Pat. Appl.
EP 350,693, 1990; Chem. Abstr. 1990, 113, 40433. (b) Moser, H.;
Schurter, R. Ger. Offen. 2,709,854, 1977; Chem. Abstr. 1977, 87,
201125.
(14) Szymanowski, J. Miner. Process. Extr. Metall. ReV. 1998, 18, 389;
Chem. Abstr. 2000, 133, 284426. (b) Szymanowski, J. Pol. J. Appl.
Chem. 1996, 40, 3; Chem. Abstr. 1997, 126, 146462.
(15) Kalman, E.; Felhosi, I.; Karman, F. H.; Lukovits, I.; Telegdi, J.;
Palinkas, G. Mater. Sci. Technol. 2000, 19 (Pt. 1), 471; Chem. Abstr.
2000, 134, 20007.
(16) Willis, M. J.; Mathur, S.; Young, R. H. AdV. Flotation Technol.,
Proceedings of Symposium of Society for Mining, Metallurgy, and
Exploration, Littleton, CO, 1999; Parekh, B. K., Miller, J. D., Eds.; p
219; Chem. Abstr. 1999, 132, 95954. (b) Lee, J. S.; Nagaraj, D. R.;
Coe, J. E. Miner. Eng. 1998, 11, 929; Chem. Abstr. 1998, 129, 292133.
(17) Collis, C. S.; Rice-Evans, C. A. Antioxid. Health Dis. 1997, 4, 409;
Chem. Abstr. 1997, 127, 185242.
1
BIO-RAD FTS 3000MX instrument in KBr pellets. H and 13C-
{1H} NMR spectra were measured on a Varian UNITY 300
(18) Inouye, M. Kagaku (Kyoto) 1995, 50, 512; Chem. Abstr. 1995, 123,
157215.
spectrometer at ambient temperature. The microwave experiments
(19) Larin, G. M. Russ. J. Coord. Chem. 1999, 25, 750. (b) Kurzak, B.;
Kozlowski, H.; Farkas, E. Coord. Chem. ReV. 1992, 114, 169. (c)
Agraval, I. K. Usp. Khim. 1979, 48, 1773-1803. (d) Mizukami, S.;
Nagata, K. Coord. Chem. ReV. 1968, 3, 267.
(20) Chatterjee, B. Coord. Chem. ReV. 1978, 26, 281.
(21) For general compilation of stability constants see: Menon, S. K.;
Agrawal, Y. K. ReV. Inorg. Chem. 1996, 16, 1. (b) For metal complex
formation properties of the naturally occurring hydroxamate-type
siderophore desferrioxamine B see: Kiss, T.; Farkas, E. J. Inclusion
Phenom. Mol. Recognit. Chem. 1998, 32, 385. (c) For stability
constants of Al complexes see: Yokel, R. A. J. Toxicol. EnViron.
Health 1994, 41, 131.
(22) Benini, S.; Rypniewski, K. S.; Wilson, K. S.; Miletti, S.; Ciurli, S.;
Mangani, S. J. Biol. Inorg. Chem. 2000, 5, 110.
(23) Brown, D. A.; Cuffe, L. P.; Fitzpatrick, N. J.; Glass, W. K.; Herlihy,
K.; Nimir, H.; Deeg, O.; Errington, W.; Kemp, T. J. Chem. Commun.
1998, 2433.
(24) Scolnick, L. R.; Clements, A. M.; Liao, J.; Crenshaw, L.; Helberg,
M.; May, J.; Dean, T. R.; Christianson, D. W. J. Am. Chem. Soc.
1997, 119, 850.
(25) Kikugawa, Y. ReV. Heteroat. Chem. 1996, 15, 263; Chem. Abstr. 1997,
126, 59462. (b) Kikugawa Y. Yakugaku Zasshi 1995, 115, 909.
(26) Das, A.; Basuli, F.; Falvello, L. R.; Bhattacharya, S. Inorg. Chem.
2001, 40, 4085. (b) Das, A.; Basuli, F.; Peng, S.-M.; Bhattacharya, S.
Inorg. Chem. 2002, 41, 440.
(28) Kukushkin, V. Yu.; Pombeiro, A. J. L. Chem. ReV., in press.
(29) Kukushkin, V. Yu.; Pakhomova, T. B.; Bokach, N. A.; Wagner, G.;
Kuznetsov, M. L.; Galanski, M.; Pombeiro, A. J. L. Inorg. Chem.
2000, 39, 216. (b) Kukushkin, V. Yu.; Pakhomova, T. B.; Kukushkin,
Yu. N.; Herrmann, R.; Wagner, G.; Pombeiro, A. J. L. Inorg. Chem.
1998, 37, 6511.
(30) Kuznetsov, M. L.; Bokach, N. A.; Kukushkin, V. Yu.; Pakkanen, T.;
Wagner, G.; Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 2000,
4683.
(31) Wagner, G.; Pombeiro, A. J. L.; Kukushkin, Yu. N.; Pakhomova, T.
B.; Ryabov, A. D.; Kukushkin, V. Yu. Inorg. Chim. Acta 1999, 292,
272.
(32) Ferreira, C. M. P.; Guedes da Silva, M. F. C.; Frau´sto da Silva, J. J.
R.; Pombeiro, A. J. L.; Kukushkin, V. Yu.; Michelin, R. A. Inorg.
Chem. 2001, 40, 1134.
(33) Kukushkin, V. Yu.; Ilichev, I. V.; Zhdanova, M. A.; Wagner, G.;
Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 2000, 1567. (b)
Kukushkin, V. Yu.; Ilichev, I. V.; Wagner, G.; Frau´sto da Silva, J. J.
R.; Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 1999, 3047.
(34) Wagner, G.; Pombeiro, A. J. L.; Bokach, N. A.; Kukushkin, V. Yu.
J. Chem. Soc., Dalton Trans. 1999, 4083.
(35) Podlaha, J.; Cisarova, I.; Soukupova, L.; Schraml, J. Collect. Czech.
Chem. Commun. 2000, 65, 1273.
(36) Luzyanin, K. V.; Haukka, M.; Bokach, N. A.; Kuznetsov, M. L.;
Kukushkin, V. Yu.; Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans.
2002, 1882.
(27) Keck, G. E.; Wager, T. T.; McHardy, S. F. Tetrahedron 1999, 55,
11755.
2982 Inorganic Chemistry, Vol. 41, No. 11, 2002

NoWel ReactiWity Mode of Hydroxamic Acids
Table 1. Crystal Data for
trans-[PtCl4{E-NHdC(Et)ONdC(OH)Ph}2]‚2(Me2SO)
empirical formula
fw
C24H36Cl4N4O6PtS2
877.58
temp, K
λ, Å
cryst syst
space group
a, Å
150(2)
0.71073
triclinic
P1h (No. 2)
7.9885(2)
8.6198(2)
12.4855(3)
87.562(1)
75.856(1)
86.901(1)
832.08(3)
1
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Figure 1. ORTEP drawing of trans-[PtCl4{NHdC(Et)ONdC(OH)Ph}2]‚
2(Me2SO) with the atomic numbering scheme (two Me2SO molecules are
omitted for clarity). The thermal ellipsoids are drawn at the 50% probability
level. Selected bond lengths (Å) and angles (deg): Pt(1)-Cl(1) 2.3147(8),
Pt(1)-Cl(2) 2.3193(8), Pt(1)-N(1) 2.028(3), N(1)-C(1) 1.277(4), C(1)-
C(2) 1.494(4), C(1)-O(1) 1.345(4), O(1)-N(2) 1.443(4), N(2)-C(4) 1.291-
(4), C(4)-O(2) 1.316(4), C(4)-C(5) 1.481(5), Cl(1)-Pt(1)-Cl(2) 91.11(3),
Cl(1)-Pt(1)-N(1) 84.62(8), Cl(2)-Pt(1)-N(1) 88.38(9), Pt(1)-N(1)-C(1)
134.8(2), N(1)-C(1)-O(1) 120.7(3), O(1)-N(2)-C(4) 108.1(3), N(2)-
C(4)-O(2) 127.3(3).
Z
θ-range, deg
3.75-27.46
F
calcd, g/cm3
1.751
µ(Mo KR), mm-1
reflns collected/unique
Rint
4.705
7928/3756
0.0464
0.0270
0.0648
R1a (I g 2σ)
wR2b (I g 2σ)
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
MP244 level on the basis of the equilibrium Hartree-Fock
geometries also have been performed in order to take into account
the electron correlation effects. A quasirelativistic Stuttgart pseudo-
potential described 60 core electrons, and the appropriate contracted
basis set (8s7p6d)/[6s5p3d] for the platinum atom45 was used. The
standard basis set of Gauss functions 6-31G46,47 was selected for
all other atoms, and d-type polarization functions with exponent
0.7547,48 were added for the Cl atoms. The Hessian matrix was
calculated numerically for all structures in order to prove the
location of correct minima (all structures have no imaginary
frequencies), and the zero-point vibrational energies have been
estimated. The starting conformation of trans-[PtCl4(NtCMe)-
{N(H)dC(Me)ONC(OH)Me}] (HI) corresponded to the experi-
mental structure from this work. For trans-[PtCl4(NtCMe){N(H)d
C(Me)ON(H)C(dO)Me}] (HA), the experimental structural data
are unavailable, and in order to check all possible conformations
of this form, the calculations have been carried out on the basis of
the structures with the different conformation of the N(H)dC(Me)-
ON(H)C(dO)Me fragment.
were performed in a CEM focused microwave synthesis system
(model Discover).
X-ray Structure Determination of trans-[PtCl4{NHdC(Et)-
ONdC(OH)Ph}2]‚2(Me2SO). The X-ray diffraction data were
collected on a Nonius Kappa CCD diffractometer using Mo KR
radiation (λ ) 0.71073 Å) and the Collect37 data collection program.
The Denzo-Scalepack38 program package was used for cell refine-
ments and data reduction. The structure was solved by direct
methods using the SIR97 program.39 An empirical absorption
correction based on equivalent reflections40 was applied to data
(Tmax/Tmin) 0.38569 and 0.21172). The structure was refined with
the SHELXL9741 program and the WinGX graphical user inter-
face.42 Pt was placed on a center of symmetry, and the asymmetric
unit contained half of the trans-[PtCl4{NHdC(Et)ONdC(OH)Ph}2]
molecule. The sulfur atom in the Me2SO solvent molecule was
disordered in two positions with occupation parameters of ∼0.9
and 0.1. Hydrogens H(1) and H(2), bonded to nitrogen and oxygen,
respectively, were located from the difference Fourier map and
refined isotropically. All other hydrogens were placed in idealized
positions and were fixed or constrained to ride on their parent atom.
Crystallographic data are summarized in Table 1, and selected bond
lengths and angles, in the Figure 1 legend.
Addition of RC6H4C(dO)NHOH (R ) p-MeO, p-Me, H, p-Cl,
o-HO) to trans-[PtCl4(EtCN)2]. In a typical experiment, trans-
[PtCl4(EtCN)2] (0.050 g, 0.11 mmol) is dissolved in dichlo-
romethane (5 mL) at 20-25 °C, the hydroxamic acid (0.22 mmol)
is added, and the reaction mixture is heated in a sealed tube at
45-47 °C for 2-3 h until the hydroxamic acid is dissolved. The
Computational Details. The full geometry optimization of all
structures has been carried out at the restricted Hartree-Fock level
of theory with help of the GAMESS43 program package. Symmetry
operations were not applied. The single-point calculations at the
1
orange solution is evaporated to ∼ /2 of its initial volume, and
diethyl ether (2 mL) is added. An excess of the hydroxamic acid
precipitates and is removed by filtration. In the case of p-
methoxybenzohydroxamic acid, the filtrate is evaporated to dryness,
and diethyl ether (5 mL) is added to the residue formed giving a
yellow solution, which is left to stand overnight in a closed flask.
The bright yellow crystals formed are filtered off and dried in air
at room temperature. In the case of other acids, the filtrate is
(37) Collect, data collection software; Nonius B.V.: Delft, The Netherlands,
1997-2000.
(38) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Macromolecular Crystallography,
Part A; Carter, C. W., Jr., Sweet, R. M., Eds.; Methods in Enzymology
Volume 276; Academic Press: New York, 1997; pp 307-326.
(39) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(44) Møller, C.; Plesset, M. S. Phys. ReV. 1934, 46, 618. (b) Binkley, J.
S.; Pople, J. A. Int. J. Quantum. Chem. 1975, 9, 229.
(45) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123.
(46) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257.
(47) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M.
S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
(48) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(40) Sheldrick, G. M. SHELXTL, Version 5.1; Bruker Analytical X-ray
Systems, Bruker AXS, Inc.: Madison, WI, 1998.
(41) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(42) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(43) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon,
M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su,
S. J.; Windus, T. L.; Dupuis, M.; Montgomery, J. A. J. Comput. Chem.
1993, 14, 1347.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2983

Luzyanin et al.
Scheme 1
evaporated to dryness and the solid washed with pentane. Yields
are 70-80%, based on Pt. The reaction is accelerated by focused
300 W microwave irradiation and completed for ∼15 min at 50
°C giving the same isolated yields.
[PtCl4{NHdC(Et)ONdC(OH)(C6H4OMe-p)}2]. Anal. Calcd
for C22H28N4Cl4O6Pt: C, 33.81; H, 3.61; N, 7.17%. Found: C,
33.49; H, 3.71; N, 7.00%. FAB+-MS, m/z: 783 [M + H], 710 [M
- 2Cl], 674 [M - 3Cl + H]. TLC on SiO2: Rf ) 0.38 (eluent
Me2CO/CHCl3 ) 3:1). IR spectrum (selected bands), cm-1: 3265
mw ν(NsH), 1709 (variable intensity, see text) ν(CdO), 1669 m
and 1608 s ν(CdN), 1256 s ν(CsOMe), 1024 s ν(OsMe), 839 s
1
δ(CsH) (aryl). H NMR spectrum in DMSO-d6, δ: 1.29 (t, J 7.5
Hz, 3H, CH2Me), 3.12 (quart, J 7.5 Hz, 2H, CH2Me), 3.82 (s, 3H,
OMe), 7.10 (d, J 8.8 Hz, 2H, meta) and 7.79 (d, J 8.8 Hz, 2H,
ortho) (aryl), 8.56 (s, br, 1H, CdNH). 13C{1H} NMR in DMSO-
d6, δ: 10.8 (CH3) and 26.0 (CH2) (Et), 55.2 (OCH3), 114.0, 114.3,
114.9 and 119.8 (C6H4OMe), 164.8 and 176.6 (CdO and HNdC).
[PtCl4{NHdC(Et)ONdC(OH)(C6H4Me-p)}2]‚1/2Et2O. Anal.
Calcd for C22H28N4Cl4O4Pt‚1/2Et2O: C, 36.65; H, 4.23; N, 7.12%.
Found: C, 36.52; H, 4.25; N, 7.22%. FAB+-MS, m/z: 749 [M +
H], 713 [M - Cl], 642 [M - 3Cl - H], 606 [M - 4Cl - H]. TLC
on SiO2: Rf ) 0.61 (eluent Me2CO/CHCl3 ) 3:1). IR spectrum
(selected bands), cm-1: 3273 mw ν(NsH), 1705 (variable intensity,
see text) ν(CdO), 1648 and 1611 s ν(CdN), 827 m δ(CsH) (aryl).
1H NMR spectrum in DMSO-d6, δ: 1.31 (t, J 7.2 Hz, 3H, CH2Me),
3.14 (quart, J 7.2 Hz, 2H, CH2Me), 2.39 (s, 3H, CMe), 7.38 (d, J
7.8 Hz, 2H, meta) and 7.74 (d, J 7.8 Hz, 2H, ortho) (aryl), 8.58 (s,
br, 1H, CdNH), 11.12 (s, br, 1H, OH). 13C{1H} NMR in DMSO-
d6, δ: 10.9 (CH3) and 21.0 (CH2) (Et), 20.4 (C6H4CH3), 118.0,
118.3, 126.9, 128.7, 129.1 and 129.9 (C6H4Me), 164.3 and 179.7
(CdO and HNdC). The solvated Et2O has been detected in the
NMR spectra.
However, our attempts to isolate [PtCl4{NHdC(Et)ONdC(OH)-
(C6H4OH-o)}2] in the pure form by recrystallization or by column
chromatography failed because of either thermal instability of the
compound or decomposition on SiO2, respectively. FAB+-MS,
m/z: 717 [M - Cl], 681 [M - 2Cl], 645 [M - 3Cl]. IR spectrum
(selected bands), cm-1: 3559 m ν(OsH), 3260 mw ν(NsH), 1728
(variable intensity, see text) ν(CdO), 1697 s and 1611 m ν(Cd
N), 1082 m ν(ArylsCl), 829 s δ(CsH) (aryl). 1H NMR spectrum
in DMSO-d6, δ: 0.97 (t, J 7.5 Hz, 3H, CH2Me), 2.04 (quart, J 7.5
Hz, 2H, CH2Me), 6.91-7.26 (m, 4H) (aryl), 8.30 (s, br, 1H, Cd
NH), 11.62 (s, 1H, OH). 13C{1H} NMR in DMSO-d6, δ: 11.0 (CH3)
and 23.5 (CH2) (Et), 126.5, 127.5, 128.1, 128.7, 129.1 and 129.4
(C6H4OH-o), 166.5 and 176.8 (CdO and HNdC).
Results and Discussion
The reaction between the nitrile complex trans-[PtCl4-
(EtCN)2] (addressed for this study because of its rather good
solubility in CH2Cl2) and benzohydroxamic acids RC6H4C-
(dO)NHOH (R ) p-MeO, p-Me, H, p-Cl, o-HO) proceeds
smoothly in CH2Cl2 at ∼45 °C for 2-3 h (sealed tube), and
subsequent workup allowed the isolation of new complexes
in good yields. The reaction is accelerated by focused 300
W microwave irradiation and completed for ∼15 min at 50
°C giving the compounds in 70%-80%. The satisfactory
elemental analyses and coherent FAB-MS and NMR data
favor the addition of the hydroxamic acids to the nitrile
carbon atom giving the iminoacylated products, which, in
principle, can be obtained in two tautomeric forms, I and II
(Scheme 1).
The products of the reaction show no bands of ν(CtN)
stretching vibrations but display two intense bands in the
range 1697-1611 cm-1 due to ν(CdN),29 and one more band
at ∼1710 cm-1, whose intensity varies randomly from sample
to sample within the same compound and also depends on
the R radical of the reagent. If the later band can be attributed
to ν(CdO), and this assumption is supported by the
conducted quantum chemical calculations, in the hydroxamic
form I (Scheme 1), the results obtained give collateral
evidence in favor of concurrent formation of the two
tautomers in a ratio which depends on both experimental
conditions and type of hydroxamic acid employed.
[PtCl4{NHdC(Et)ONdC(OH)Ph}2]‚1/2CH2Cl2. Anal. Calcd
for C20H24N4Cl4O4Pt‚1/2CH2Cl2: C, 32.24; H, 3.30; N, 7.34%.
Found: C, 32.26; H, 3.53; N, 7.00%. FAB+-MS, m/z: 650 [M -
2Cl], 614 [M - 3Cl - H], 579 [M - 4Cl]. TLC on SiO2: Rf )
0.50 (eluent Me2CO/CHCl3 ) 3:1). IR spectrum (selected bands),
cm-1
: 3216 mw ν(NsH), 1710 (variable intensity, see text)
ν(CdO), 1663 and 1609 s ν(CdN), 832 s δ(CsH) (aryl). 1H NMR
spectrum in CDCl3, δ: 1.35 (t, JHH 7.5 Hz, 3H, CH2Me), 3.18 (quart,
JHH 7.5 Hz, 2H, CH2Me), 7.40-7.51 (m, 3H, meta + para) and
7.74 (m, 2H, ortho) (Ph), 8.70 (br, 1H, CdNH), 11.31 (s, br, 1H,
OH). 13C{1H} NMR in DMSO-d6, δ: 11.0 (CH3) and 24.3 (CH2)
(Et), 127.2, 128.9, 129.7 and 132.6 (Ph), 162.8 and 178.5 (CdO
and HNdC). The solvated CH2Cl2 has been detected in the NMR
spectra.
[PtCl4{NHdC(Et)ONdC(OH)(C6H4Cl-p)}2]. Anal. Calcd for
C20H22N4Cl6O4Pt: C, 30.40; H, 2.81; N, 7.09%. Found: C, 30.18;
H, 2.95; N, 7.00%. FAB+-MS, m/z: 755 [M - Cl], 717 [M - 2Cl
+ H], 683 [M - 3Cl], 647 [M - 4Cl]. TLC on SiO2: Rf ) 0.38
(eluent Me2CO/CHCl3 ) 3:1). IR spectrum (selected bands), cm-1
:
3270 mw ν(NsH), 1711 (variable intensity, see text) ν(CdO), 1665
and 1619 s ν(CdN), 1092 s ν(ArylsCl), 839 s δ(CsH) (aryl). 1H
NMR spectrum in DMSO-d6, δ: 1.29 (t, J 7.5 Hz, 3H, CH2Me),
3.12 (quart, J 7.5 Hz, 2H, CH2Me), 3.82 (s, 3H, OMe), 7.51 (d, J
8.6 Hz, 2H, meta) and 7.83 (d, J 8.6 Hz, 2H, ortho) (aryl), 8.57 (s,
br, 1H, CdNH), 11.25 (s, br, 1H, OH). 13C{1H} NMR in DMSO-
d6, δ: 11.0 (CH3) and 21.5 (CH2) (Et), 128.5, 128.7, 129.1 and
129.4 (C6H4OCl-p), 176.5 and 166.7 (CdO and HNdC).
[PtCl4{NHdC(Et)ONdC(OH)(C6H4OH-o)}2]. In the case of
salycylhydroxamic acid, the addition is not selective, and the
reaction gives a mixture of products. The target addition product
was detected in the mixture and characterized as indicated later.
All the complexes exhibit rather poor solubility in the most
common solvents, and NMR spectra were obtained only in
dmso-d6 where the compounds gradually decompose (∼50%
2984 Inorganic Chemistry, Vol. 41, No. 11, 2002

NoWel ReactiWity Mode of Hydroxamic Acids
Table 2. Calculated Total Energies Etot (Hartree), Zero-Point Energies,
ZPE (kcal/mol) and Relative Energies, Erel (kcal/mol) with the Most
Stable Isomer as a Reference
degradation is observed for ∼3-4 h) to give some yet
unidentified reddish-brown Pt-containing species and EtC-
(dO)NH2. However, measuring the spectra soon after
dissolution allowed the observation of only one set of signals
from one tautomeric form, and these peaks were attributed
to the HNdC(Et) part of the hydroxamic/hydroximic func-
tionality.
HF//HF
ZPE
MP2//HF
Etot Erel
a
Etot
Erel
HI
-2502.800085 124.83 0.72 (0.48) 2504.640755 2.02
2504.643972 0.0
HA1 -2502.801239 125.07 0.0 (0.0)
HA2 -2502.799745 124.82 0.93 (0.71) 2504.641026 1.85
HA3 -2502.795449 124.94 3.63 (3.50) 2504.636135 4.92
HA4 -2502.794768 125.04 4.06 (4.06) 2504.634886 5.70
In one case, a crystalline material, that is, [PtCl4{NHdC(Et)-
ONdC(OH)Ph}2], appeared soon after dissolution of the
complex in dmso-d6, and these crystals were subject to X-ray
study. The coordination polyhedron of the bis-solvated
complex is a slightly distorted octahedron, Figure 1.
The PtsCl and PtsN bond lengths and also all bond
angles around the Pt center are normal, and they are of typical
values for other platinum(IV) complexes.29,49 The imine
ligands are mutually trans. The two CdN bonds are equal
within 3σ [1.277(4) and 1.291(4) Å], and they agree well
with typical values for the CdN double bonds;50 concur-
rently, the CsO bond [1.316(4) Å] is a typical single bond.
Inspection of these values clearly indicates that the imino-
acylated ligand is stabilized in the hydroximic tautomeric
form (II) in the E-configuration with NsH‚‚‚H hydrogen
bond between the imine CdNH atom and the hydroximic
nitrogen with the following observed distances and angles:
N(1)sH(1) 0.85(5), N(1)‚‚‚N(2) 2.559(3), N(1)sH(1)‚‚‚N(2)
2.11(5), and the angle N(1)sH(1)‚‚‚N(2) is 113(4)°. Unfor-
tunately, comparison of the IR spectra of [PtCl4{NHdC(Et)-
ONdC(OH)Ph}2] before the dissolution in dmso-d6 and after
the isolation of the bis-solvate was not constructive because
in the latter case the two dimethyl sulfoxide molecules in
the lattice strongly affect the fingerprint area.
a Values in parentheses include zero-point corrections.
form, and to get additional arguments favoring this assump-
tion, a theoretical study on the relative stabilities of the two
tautomeric forms has been conducted.
The full geometry optimization of the two model com-
pounds bearing the iminoacyl ligands in the hydroximic and
the hydroxamic forms, that is, trans-[PtCl4(NtCMe)-
{N(H)dC(Me)ONC(OH)Me}] (HI) and trans-[PtCl4(Nt
CMe){N(H)dC(Me)ON(H)C(dO)Me}] (HA), has been per-
formed. The conformation of the equilibrium structure of
HI and the H-bonding pattern correspond to the experimental
ones, and the main calculated bond lengths are in very good
agreement with the experimental X-ray data (the maximum
deviation of 0.043 Å for the Pt-Cl bonds and not higher
than 0.021 Å for the other bonds). For HA, four minima,
associated with four structures (HA1-4, Table 2) having
different conformations of the hydroxamic moiety, were
located on the potential energy surface; the bond lengths for
all the HA structures are very close to each other. The
calculations at the Hartree-Fock level show that the differ-
ence of the total energies of HI and the most energetically
favorable HA structures (HA1 and HA2; the schematic
representation of HA1 is given in Scheme 1 as I) is small
and does not exceed 1 kcal/mol; the zero-point correction
additionally decreases this difference. The electron correla-
tion correction at MP2//HF level increases the relative
stability of HA1 and HA2 although the energy difference
between HI and HA1 is still rather small, that is, 2.02 kcal/
mol. Hence, the theoretical study gives further support to
our assumptions stating that in the coordinated ligands both
forms have comparable stability. We also anticipate that the
addition of the hydroxamic acids gives a mixture of HA and
HI tautomers which then (R ) Ph) crystallizes from dimethyl
sulfoxide preferably in the HI form.
The isolation of the complex in the pure hydroximic form
is unusual insofar as it is well-documented by both theoreti-
cal5,51 and experimental studies that the hydroxamic form is
the dominant one in free hydroxamic acids,52 metal hydrox-
amates,53 and O-acylated or O-silylated hydroxamic acids.54
We assumed, albeit based on so far scarce experimental data,
that the coordination led to a higher stabilization of the II
(49) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1. (b) Bokach, N.
A.; Haukka, M.; Pombeiro, A. J. L.; Morozkina, S. N.; Kukushkin,
V. Yu. Inorg. Chim. Acta, accepted for publication. (c) Ryabov, A.
D.; Kazankov, G. M.; Panyashkina, I. M.; Grozovsky, O. V.;
Dyachenko, O. G.; Polyakov, V. A.; Kuzmina, L. G. J. Chem. Soc.,
Dalton Trans. 1997, 4385.
(50) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
In conclusion, it is worthwhile to mention that: (i) The
addition of hydroxamic acids across the CtN bond is
platinum(IV)-mediated because 1H NMR experiments show
that noncoordinated EtCN does not react with the hydroxamic
acids under the reaction or even harsher (45 °C, 5 d)
conditions. Moreover, it has been reported that namely
nitriles are formed upon pyrolysis of hydroxamic acids55 or
their deoxygenation, for example, by PBr3.56 The imino-
(51) Remko, M.; Sefcikova, J. THEOCHEM 2000, 528, 287. (b) El Yazal,
J.; Pang, Y.-P. J. Phys. Chem. A 1999, 103, 8346. (c) Remko, M.;
Mach, P.; Schleyer, P.; Exner, O. THEOCHEM 1993, 98, 139. (d)
Turi, L.; Dannenberg, J. J.; Rama, J.; Ventura, O. N. J. Phys. Chem.
1992, 96, 3709. (e) Fitzpatrick, N. J.; Mageswaran, R. Polyhedron
1989, 8, 2255.
(52) Salmon, L.; Prost, E.; Merienne, C.; Hardre, R.; Morgant, G.
Carbohydr. Res. 2001, 335, 195. (b) Hoshino, Y.; Murase, N.; Oishi,
M.; Yamamoto, H. Bull. Chem. Soc. Jpn. 2000, 73, 1653. (c)
Henriksen, A.; Schuller, D. J.; Meno, K.; Welinder, K. G.; Smith, A.
T.; Gajhede, M. Biochemistry 1998, 37, 8054.
(53) Santana, M. D.; Garcia, G.; Perez, J.; Molins, E.; Lopez, G. Inorg.
Chem. 2001, 40, 570. (b) Swiatek-Kozlowska, J.; Fritsky, I. O.;
Dobosz, A.; Karaczyn, A.; Dudarenko, N. M.; Sliva, T. Yu; Gumienna-
Kontecka, E.; Jerzykiewicz, L. J. Chem. Soc., Dalton Trans. 2000,
4064. (c) Chen, W.; Gao, S.; Liu, S.-X. Acta Crystallogr., Sect. C
1999, C55, 531. (d) Gaynor, D.; Starikova, Z. A.; Haase, W.; Nolan,
K. B. J. Chem. Soc., Dalton Trans. 2001, 1578.
(54) Artemenko, A. I.; Anufriev, E. K.; Tikunova, I. V.; Exner, O. Zh.
Prikl. Spektrosk. 1980, 33, 131; Chem. Abstr. 1981, 94, 46316. (b)
Schraml, J.; Kvicalova, M.; Blechta, V.; Soukupova, L.; Exner, O.;
Boldhaus, H.-M.; Erdt, F.; Bliefert, C. Magn. Reson. Chem. 2000,
38, 795.
(55) Shahnaz, F. GoV. Rep. Announce. Index (U. S.) 1993, 93 (4), Abstract
No. 308,980; Chem. Abstr. 1994, 120, 216694.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2985

Luzyanin et al.
acylated products of our study are presumably formed by
nucleophilic attack of the OH group of the hydroxamic acids
on the activated carbon atom of the platinum(IV)-bound
organonitrile, a process similar to that for the addition of
oximes.28-34 (ii) Although the metal-mediated hydroxamic
acid-nitrile coupling is entirely unusual, it is still reasonable
to expect the addition with platinum nitrile complexes
because the soft metal center has less pronounced ability to
bind such hard bases as hydroxamates. Indeed, to the best
of our knowledge, platinum hydroxamates are unknown, and
moreover, there are only scarce reports of hydroxamates of
some other platinum group metal ions.57 (iii) The study
establishes a novel type of metalla-Pinner reaction with
potential application in organic synthesis of imine compounds
with the hydroxamic/hydroximic function. Moreover, it is
anticipated the extension of this investigation to bifunctional
hydroxamic acids to obtain compounds with remote unligated
sC(dO)(H)NOH groups which may be useful for further
complexation, for example, with hard metal centers, and
construction of heterometallic systems58,59 with potential
application in the material science and this project is
underway in our group.
Acknowledgment. K.V.L. and V.Yu.K. express gratitude
to the International Science Foundation (Soros Foundation)
for the fellowships, while K.V.L. additionally thanks the
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior
Te´cnico, Portugal, for a grant. M.L.K., D.A.G., and V.Yu.K.
are very much obliged to the PRAXIS XXI and POCTI
programs (Portugal) for the grants BPD16369/98//BPD/5558/
2001, BPD16368/98, and BCC16428/98, correspondingly.
A.J.L.P. and V.Yu.K. are grateful to the FCT (Foundation
for Science and Technology) and the PRAXIS XXI and
POCTI programs for financial support of these studies.
(56) Liguori, A.; Sindona, G.; Romeo, G.; Uccella, N. Synthesis 1987, 168.
(57) Mishra, R. S. J. Indian Chem. Soc. 1969, 46, 1074.
(58) For review see: Garnovskii, A. D.; Sadimenko, A. P.; Uraev, A. I.;
Vasilchenko, I. S.; Garnovskii, D. A. Russ. J. Coord. Chem. 2000,
26, 311.
(59) For recent works see: Darensbourg, D. J.; Adams, M. J.; Yarbrough,
J. C. Inorg. Chem. 2001, 40, 6543. Scoles, L.; Yamamota, J. H.;
Brissieux, L.; Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Inorg.
Chem. 2001, 40, 6731. Darensbourg, D. J.; Lee, W. Z.; Yarbrough, J.
C. Inorg. Chem. 2001, 40, 6533. Tanase, T.; Inukai, H.; Onaka, T.;
Kato, M.; Yano, Sh.; Lippard, S. J. Inorg. Chem. 2001, 40, 3943.
Han, J.; Coucouvanis, D. J. Am. Chem. Soc. 2001, 123, 11304.
Supporting Information Available: Tables S1-S6 listing
crystallographic data, atomic coordinates, bond lengths and bond
angles, anisotropic displacement parameters, hydrogen coordinates
and isotropic displacement parameters, and torsion angles. X-ray
crystallographic files in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC025554C
2986 Inorganic Chemistry, Vol. 41, No. 11, 2002