Reactivity of trans-[PtX2(ketoxime)2] Complexes toward m-Chloroperoxybenzoic Acid: An Efficient Route to Coordinated Nitrosoalkanes and Solvent Dependence of the Reaction

Article abstract of DOI:10.1021/ic9600691

The platinum(II) compounds trans-[PtX₂(RR'C=NOH)₂] [X = Cl, R = R' = Me, RR' = (CH₂)₄, (CH₂)₅; X = Br, R = R' = Me] react with m-chloroperoxybenzoic acid (MCPBA) in dimethylformamide to give the platinum(II) complexes [PtX₂{N(=O)CRR'ONCRR'}] containing coordinated nitrosoalkane ligands. The complexes [PtX₂-{N(=O)CRR'ONCRR'}] were characterized by elemental analysis, EI-MS, IR, electronic absorption, and ¹H NMR spectroscopy; X-ray structure analysis was performed for [PtCl₂{N(=O)CC₅H₁₀ONCC₅H ₁₀}]. The latter compound crystallizes in the triclinic P1? space group with a = 9.214(2) ?, b = 9.577(2) ?, c = 10.367(2) ?, a = 109.14(2)°, β= 91.87(2)°, γ = 115.62(2)°, V = 762.8(3) ?³, Z = 2, and ρ_calcd = 2.135 g cm^-3. The reaction between trans-[PtX₂(RR'C=NOH)₂] and MCPBA displays a solvent dependence: interaction of these reagents in ketones, R₁R₂C=O, yields the platinum(IV) chelates [PtX₂(OCR₁R₂ON=CRR')₂], while the oxidation state of the oxime N atom remains unchanged. Heating [PtCl₂(OCR₁R₂ON=CRR')₂] in DMF or in DMF-d₇ at 100 °C leads to the extrusion of R₁R₂C=O and the formation of [PtCl₂{N(=O)CRR'ONCRR'}].

Full text of DOI:10.1021/ic9600691

4926
Inorg. Chem. 1996, 35, 4926-4931
Reactivity of trans-[PtX2(ketoxime)2] Complexes toward m-Chloroperoxybenzoic Acid: An
Efficient Route to Coordinated Nitrosoalkanes and Solvent Dependence of the Reaction
Vadim Yu. Kukushkin,*,1a,b David Tudela,*,1a Youlia A. Izotova,1a,c Vitaly K. Belsky,1d and
Adam I. Stash1d
Departamento de Qu´ımica Inorga´nica, Universidad Auto´noma de Madrid, 28049 Madrid, Spain, and
L. Ya. Karpov Physico-Chemical Institute, Obukha Str. 10, 103064 Moscow, Russian Federation
ReceiVed January 19, 1996X
The platinum(II) compounds trans-[PtX2(RR′CdNOH)2] [X ) Cl, R ) R′ ) Me, RR′ ) (CH2)4, (CH2)5; X )
Br, R ) R′ ) Me] react with m-chloroperoxybenzoic acid (MCPBA) in dimethylformamide to give the platinum(II)
complexes [PtX2{N(dO)CRR′ONCRR′}] containing coordinated nitrosoalkane ligands. The complexes [PtX2-
1
{N(dO)CRR′ONCRR′}] were characterized by elemental analysis, EI-MS, IR, electronic absorption, and H
NMR spectroscopy; X-ray structure analysis was performed for [PtCl2{N(dO)CC5H10ONCC5H10}]. The latter
compound crystallizes in the triclinic P1h space group with a ) 9.214(2) Å, b ) 9.577(2) Å, c ) 10.367(2) Å, R
) 109.14(2)°, â ) 91.87(2)°, γ ) 115.62(2)°, V ) 762.8(3) Å3, Z ) 2, and Fcalcd ) 2.135 g cm-3. The reaction
between trans-[PtX2(RR′CdNOH)2] and MCPBA displays a solvent dependence: interaction of these reagents
in ketones, R1R2CdO, yields the platinum(IV) chelates [PtX2(OCR1R2ONdCRR′)2], while the oxidation state of
the oxime N atom remains unchanged. Heating [PtCl2(OCR1R2ONdCRR′)2] in DMF or in DMF-d7 at 100 °C
leads to the extrusion of R1R2CdO and the formation of [PtCl2{N(dO)CRR′ONCRR′}].
Introduction
As far as the redox chemistry of oxime ligands is concerned,
the oxime nitrogen has the formal oxidation state 1- and, like
the parent hydroxylamine, can be either reduced or oxidized.
In contrast to reduction of oximes,5-8 metal-ion assisted
oxidation of RR′CdNOH is an essentially unexplored area, and
only oxidative deoximation involving high oxidation state metal
ions has been reported for a variety of free oximes.9,10
Moreover, apart from data presented recently by two of us,11
no other reports have been published on the oxidation of
coordinated oxime ligands. In the latter work,11 it was
demonstrated that the oxidation of cis-[PtCl2(Me2CdNOH)2]
by molecular chlorine yields cis-[PtCl4(Me2CdNOH)2] (reaction
(i) in Scheme 1). The ketoxime ligands survive the reaction
conditions, although it is known that free ketoximes can be easily
converted into the nitroso compounds, RR′ClC-NO, by chlo-
rination with Cl2.12 The platinum(IV) complex cis-[PtCl4-
The syntheses, structures, and solution chemistry of metal
oxime and oximato complexes have been extensively studied
and described in a large number of reviews.2,3 However, metal-
ion assisted reactions of oximes and reactivity of oxime-
containing metal complexes have received much less attention.
Despite this, data gradually accumulated in the literature show
that the reactivity of coordinated RR′CdNOH ligands and their
complexes is impressively rich.4
X Abstract published in AdVance ACS Abstracts, August 1, 1996.
(1) (a) Universidad Auto´noma de Madrid. Fax: +34-1-397 4833. E-
mail: DATUDELA@ccuam3.sdi.uam.es. (b) On sabbatical leave from
St. Petersburg State University. Fax: +7-812-316 6441. E-mail:
prof@inorg.spb.su. (c) On leave from St. Petersburg State Techno-
logical Institute. (d) L. Ya. Karpov Physico-Chemical Institute.
E-mail: belsky@cc.nifhi.ac.ru.
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Schrauzer, G. N. Angew. Chem., Int. Ed. Engl. 1976, 15, 417; Angew.
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Khim. 1981, 7, 1123; Chem. Abstr. 1981, 95, 161127y. (l) Voiculescu,
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(6) For reduction with formation of azavinylidene complexes see: (a)
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1987, 26, 248; Angew. Chem. 1987, 99, 277. (b) Daniel, T.; Mu¨ller,
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S0020-1669(96)00069-9 CCC: $12.00 © 1996 American Chemical Society

trans-[PtX2(ketoxime)2] Complexes
Inorganic Chemistry, Vol. 35, No. 17, 1996 4927
Scheme 1. Studied Conversions of the Oxime Complexesa
In continuation of the work on the oxidation of ketoxime
ligands in Pt complexes, we have studied the reactions of trans-
[PtCl2(RR′CdNOH)2] with another oxidantsm-chloroperoxy-
benzoic acid (MCPBA)sin dimethylformamide (DMF) solution.
We report herein the reaction between the trans-ketoxime
platinum(II) complexes and MCPBA in DMF, which results in
oxidation of the ligands to afford the chelates [PtX2{N(dO)-
CRR′ONCRR′}] while the Pt(II) oxidation state remains the
same (reaction (V) in Scheme 1).13 This reaction is of synthetic
utility and can be used for the preparation of very little studied
Pt(II) complexes with nitrosoalkane species.
Previously, we have observed that the same platinum(II)
complexes trans-[PtCl2(RR′CdNOH)2], where R ) R′ ) Me
and RR′ ) (CH2)4 and (CH2)5, react with MCPBA in Me2CO
to give the platinum(IV) compounds [PtCl2(OCMe2ONdCRR′)2]
without change in the oxidation state of the oxime N atom.14
We have now observed that the reaction proceeds in the same
way in the ketones R1R2CO (R1 ) Me, R2 ) Et; R1 ) R2 )
Et). This remarkable solvent dependence and the unusual
conversion of [PtCl2(OCR1R2ONdCRR′)2] into [PtCl2{N(dO)-
CRR′ONCRR′}] will also be the subject of this article.
a Key: (i) Cl2, R ) R′ ) Me; X ) Cl. (ii) Spontaneous reaction in
a water-acetone mixture; R ) R′ ) Me; X ) Cl. (iii) , solid state;
R ) R′ ) Me; RR′ ) (CH2)4, (CH2)5; X ) Cl; R ) R′ ) Me, X ) Br.
(iV) MCPBA in Me2CO; R ) R′ ) Me; R ) Me, R′ ) Et, RR′ )
(CH2)4, (CH2)5; X ) Cl; R ) R′ ) Me, X ) Br. (V) MCPBA in DMF;
R ) R′ ) Me; X ) Cl, Br; RR′ ) (CH2)4, (CH2)5; X ) Cl. (Vi) MCPBA
in the ketones R1R2CO; R ) R′ ) Me; RR′ ) (CH2)4, (CH2)5; X ) Cl,
R ) R′ ) Me, X ) Br, ketone ) Me2CO; R ) R′ ) Me, RR′ )
(CH2)5; X ) Cl, ketone ) MeEtCO; R ) R′ ) Me; X ) Cl, ketone )
Et2CO. (Vii) , DMF; R1 ) R2 ) R ) R′ ) Me; R1 ) Me, R2 ) Et,
R ) R′ ) Me; R1 ) R2 ) Et, R ) R′ ) Me; R1 ) Me, R2 ) Et, RR′
) C5H10; X ) Cl.
Experimental Section
Materials and Instrumentation. The oxime ligands were purchased
from Aldrich and used as received. K2[PtCl4] was obtained from
Reakhim and recrystallized from water. MCPBA was purchased from
Aldrich (57-86%; contains 7-10% 3-chlorobenzoic acid, the remainder
being water) and was not titrated. trans-[PtX2(RR′CdNOH)2] com-
plexes (X ) Cl, R ) R′ ) Me, RR′ ) (CH2)4, (CH2)5; X ) Br, R )
R′ ) Me) were prepared by heating the appropriate cis-isomers in the
solid phase at 140, 135, 140, and 140 °C, respectively (reaction (iii) in
Scheme 1).15 All other chemicals and solvents were obtained from
commercial sources and were used as received. C, H, and N elemental
analyses were carried out by the Microanalytical Service, Universidad
Auto´noma de Madrid. Electron impact mass spectra (EI-MS) were
obtained with a VG Autospec instrument. Decomposition points were
determined in capillary. For TLC, Riedel-deHae¨n 60 F 254 SiO2 plates
with layer thickness 0.2 mm have been used. Infrared spectra (4000-
220 cm-1) were recorded on a Perkin-Elmer 1650 FT-IR instrument,
using Nujol mulls between CsI windows. 1H NMR and electronic
absorption spectra were recorded on a Bruker AMX-300 and Pye
Unicam SP8-100 instruments, respectively.
(Me2CdNOH)2], on standing in water-acetone solution, un-
dergoes a spontaneous Pt(IV)-mediated redox coupling leading
to the platinum(II) chelate [PtCl2{N(dO)CMe2ONCMe2}]
(reaction (ii) in Scheme 1).
(8) For reduction of oximes involving low- or medium-oxidation-state
metal ions see: (a) McMurry, J. E. Acc. Chem. Res. 1974, 7, 281. (b)
Timms, G. H.; Wildsmith, E. Tetrahedron Lett. 1971, 195. (c)
Christofis, O.; Habeeb, J. J.; Steevensz, R.; Tuck, D. G. Can. J. Chem.
1978, 56, 2269. (d) Barton, D. H. R.; Bowles, T.; Husinec, S.; Forbes,
J. E.; Llobera, A.; Porter, A. E. A.; Zard, S. Z. Tetrahedron Lett. 1988,
29, 3343. (e) Leeds, J. P.; Kirst, H. A. Synth. Commun. 1988, 18,
777. (f) Kamochi, Y.; Kudo, T. Nippon Kagaki Kaishi 1993, 500. (g)
Kamochi, Y.; Kudo, T. Tetrahedron Lett. 1991, 32, 3511. (h) Kudo,
T.; Kamochi, Y. Kidorui 1991, 18, 150. (i) Souppe, J.; Danon, L.;
Namy, J. L.; Kagan, H. B. J. Organomet. Chem. 1983, 250, 227. (j)
Corey, E. J.; Richmann, J. E. J. Am. Chem. Soc. 1970, 92, 5276. (k)
Olah, G. A.; Arvanaghi, M.; Prakash, G. K. S. Synthesis 1980, 220.
(l) Balasubramanian, P. N.; Gould, E. S. Inorg. Chem. 1984, 23, 824.
(m) Balicki, R.; Kaczmarek, L.; Malinowski, M. Liebigs Ann. Chem.
1989, 1139. (n) Vakatkar, V. V.; Tatake, J. G.; Sunthankar, S. V.
Chem. Ind. (London) 1977, 742.
(9) (a) McKillop, A.; Hunt, J. D.; Naylor, R. D.; Taylor, E. C. J. Am.
Chem. Soc. 1971, 93, 4918. (b) Firouzabadi, H.; Mohammadpoor-
Baltork, I. Synth. Commun. 1994, 24, 489. (c) Prasada Rao, L. V. S.;
Brahmaji Rao, S. J. Indian Chem. Soc. 1988, 65, 404. (d) Aizpurua,
J. M.; Palomo, C. Tetrahedron Lett. 1983, 24, 4367. (e) Aizpurua, J.
M.; Juaristi, M.; Lecea, B.; Palomo, C. Tetrahedron 1985, 41, 2903.
(f) Firouzabadi, H.; Sardarian, A. R.; Moosavipour, H.; Afshari, G.
M. Synthesis 1986, 285. (g) Firouzabadi, H.; Iranpoor, N.; Kiaeezadeh,
F.; Toofan, J.Tetrahedron 1986, 42, 719. (h) Ramakrishnan, K.;
Sankaran, K. R.; Srinivasan, V. S. Indian J. Chem. 1990, 29A, 843.
(i) Rao, V. V.; Sethuram, B.; Rao, T. N. Indian J. Chem. 1980, 19A,
1127. (j) Firouzabadi, H.; Mottghinejad, E.; Seddighi, M. Synthesis
1989, 378. (k) Firouzabadi, H.; Sardarian, A. Synth. Commun. 1983,
13, 863. (l) Firouzabadi, H.; Sardarian, A. R.; Naderi, M.; Vessal, B.
Tetrahedron 1984, 40, 5001.
Synthetic Work and Characterization. Reaction of trans-[PtX2-
(RR′CdNOH)2] (R ) R′ ) Me, RR′ ) (CH2)4, (CH2)5, X ) Cl; R
) R′ ) Me, X ) Br) with MCPBA in DMF (General Method),
Reaction (W) in Scheme 1. A 0.6-0.7 mmol amount of trans-[PtX2-
(RR′CdNOH)2] was dissolved at 40 °C in the minimum amount of
DMF, and to this solution an excess of solid MCPBA (0.27-0.30 g,
0.9-1.5 mmol according to purity range) was added. Immediately after
addition, the color of the solution turned from yellow to dark-red. The
nitrosoalkane complexes [PtX2{N(dO)CRR′ONCRR′}] were isolated
by vapor diffusion of Et2O (R ) R′ ) Me; X ) Cl, Br) or by addition
of water (RR′ ) (CH2)4, (CH2)5; X ) Cl). Yields were 50-60%.
[PtCl2{N(dO)CMe2ONCMe2}]: Dark-red needlelike crystals formed
from a water-acetone solution, mp ) 125 °C (dec). EI-MS, m/z: 409
[M - H]+. Anal. Calcd for C6H12Cl2N2O2Pt: C, 17.6; H, 3.0; N, 6.8.
Found: C, 17.8; H, 3.1; N, 6.7. IR data (Nujol), cm-1: 1625 m
ν(CdN), 1543 vs ν(NdO), 354 ms and 336 ms ν(Pt-Cl). 1H NMR
(11) Kukushkin, V. Yu.; Belsky, V. K.; Aleksandrova, E. A.; Konovalov,
V. E.; Kirakosyan, G. A. Inorg. Chem. 1992, 31, 3836.
(12) Barnes, M. W.; Patterson, J. M. J. Org. Chem. 1976, 41, 733 and
references therein.
(10) (a) Vankar, P.; Rathore, R.; Chandrasekaran, S. J. Org. Chem. 1986,
51, 3063. (b) Kumar, H.; Kaur, B.; Kumar, B. Indian J. Chem. 1991,
30B, 869. (c) Olah, G. A.; Welch, J.; Henninger, M. Synthesis 1977,
308. (d) Olah, G. A.; Welch, J. J. Am. Chem. Soc. 1978, 100, 5396.
(e) Ho, T.-L. Synthesis 1973, 347. (f) Shilov, V. P.; Krot, N. N.;
Stepanova, E. S. Radiokhimia 1976, 18, 355. (g) Tananaev, I. G.;
Shilov, V. P.; Krot, N. N. Radiokhimia 1986, 28, 92.
(13) A preliminary communication concerning part of this work has been
published: Kukushkin, V. Yu.; Izotova, Yu. A.; Tudela, D. Zh. Obsch.
Khim. 1995, 65, 1918.
(14) Kukushkin, V. Yu.; Belsky, V. K.; Tudela, D. Inorg. Chem. 1996,
35, 510.
(15) Kukushkin, V. Yu.; Tudela, D.; Izotova, Yu. A.; Belsky, V. K.; Stash,
A. I. Unpublished results (1996).

4928 Inorganic Chemistry, Vol. 35, No. 17, 1996
Kukushkin et al.
in acetone-d6, δ, ppm: 1.55 (OC(CH3)2), 2.63 (4JPtH 5.5 Hz) and 2.71
(4JPtH 9.5 Hz) (NdC(CH3)2).
[PtCl2(OCMe2ONdCMe2)2] to [PtCl2{N(dO)CMe2ONCMe2}], 1.55
(6H, OCMe2), 2.62 (3H, NCMe2) and 2.71 ppm (3H, NCMe2); Me2CO,
2.08 ppm; trans-[PtCl2(Me2CdNOH)2], 2.15 (3H), 2.67 (3H) and 11.86
ppm (broad, OH); from [PtCl2(OCMeEtONdCMe2)2] to [PtCl2-
{N(dO)CMe2ONCMe2}], 1.55 (6H, OCMe2), 2.62 (3H, NCMe2) and
2.71 ppm (3H, NCMe2); MeEtCO, triplet 0.93 (J1-2 7.3 Hz, CH2CH3,
3H), quartet 2.46 (J1-3 7.3 Hz, CH2CH3, 2H) and 2.084 ppm (CH3,
3H); Me2CO, 2.083 ppm; trans-[PtCl2(Me2CdNOH)2], 2.15 (3H), 2.67
(3H) and 11.86 ppm (broad, OH); from [PtCl2(OCEt2ONdCMe2)2] to
[PtCl2{N(dO)CMe2ONCMe2}], 1.55 (6H, OCMe2), 2.62 (3H, NCMe2)
and 2.71 ppm (3H, NCMe2); Et2CO, triplet 0.94 (J1-2 7.3 Hz, CH2CH3,
6H) and quartet 2.44 (J1-3 7.3 Hz, CH2CH3, 4H); Me2CO, 2.083 ppm;
trans-[PtCl2(Me2CdNOH)2], 2.15 (3H), 2.67 (3H) and 11.86 ppm
(broad, OH).
In all reactions the TLC (Me2CO:CHCl3 ) 1:1) displays an orange-
red spot with Rf ) 0.62 due to [PtCl2{N(dO)CMe2ONCMe2}] and a
spot of small intensity in UV254 with Rf ) 0.70 due to trans-[PtCl2-
(Me2CdNOH)2]. Electronic spectrum, λmax, nm: 414 for [PtCl2-
{N(dO)CMe2ONCMe2}].
The thermal conversion of [PtCl2(OCMeEtONdCC5H10)2] resulted
in the formation of [PtCl2{N(dO)C(C5H10)ONC(C5H10)}] [TLC, Me2CO:
CHCl3 ) 1:5, Rf ) 0.65] and MeEtCO [1H NMR spectrum in DMF-
d7, δ, ppm: triplet 0.93 (J1-2 7.3 Hz, CH2CH3, 3H), quartet 2.46 (J1-3
7.3 Hz, CH2CH3, 2H) and 2.084 ppm (CH3, 3H)]. Cyclohexanone was
not detected by means of 1H NMR spectroscopy due to the complexity
of signals and overlapping with peaks from [PtCl2{N(dO)C(C5H10)-
ONC(C5H10)}], but it was unambiguously identified by means of EI
mass spectrometry.
X-ray Structure Determination of [PtCl2{N(dO)CC5H10-
ONCC5H10}]. Crystals suitable for X-ray analysis were grown by slow
evaporation of an acetone-toluene solution. Diffraction data were
collected on an Enraf-Nonius CAD 4 diffractometer. Cell parameters
were obtained from 12 centered reflections with θ between 10 and
12.5°; 1914 independent reflections with 1836 with I g 3σ(I) were
measured up to 50° by the θ/2θ scan technique. Range of hkl: h ) 0
to +8, k ) -11 to +10, l ) -12 to +12. Diffractometer data were
processed by the program PROFIT16 with profile analysis of reflections.
The structure was solved by means of Fourier synthesis based upon
the Pt atom coordinates obtained from the Patterson synthesis using
the SHELXTL package.17 After that, all reflections with I < 3σ(I)
were excluded from calculations. Refinement was done by full-matrix
least squares based on F2 using the SHELX-93 package.18 All non-H
atoms were treated anisotropically. Hydrogen coordinates were found
from difference synthesis and were included in refinement with fixed
coordinates and thermal parameters. An extinction correction has been
applied. Lorentz, polarization, and absorption corrections were made.19
Crystal size: 0.28 × 0.10 × 0.06 mm. The crystal was packed in
Cyacrine glue to prevent decomposition. In spite of the safety coating,
the crystal decayed by 30% and that affects the R-factor value and
standard deviations in bond lengths and angles. Tmin and Tmax are 0.349
and 0.607, respectively. Scattering factors were obtained from ref 20.
Crystal data are given in Table 1, and bond lengths and angles, in Table
2.
[PtCl2{N(dO)C(C4H8)ONC(C4H8)}]: Dark-red rhombic crystals
formed from a MeNO2/2-PrOH mixture, mp ) 134 °C (dec). EI-MS,
m/z: 462 [M]+. Anal. Calcd for C10H16Cl2N2O2Pt: C, 26.0; H, 3.5;
N, 6.1. Found: C, 25.7; H, 3.3; N, 5.9. IR data (Nujol), cm-1: 1651
m ν(CdN), 1540 vs ν(NdO), 345 ms and 337 ms ν(Pt-Cl). 1H NMR
in CD2Cl2, δ, ppm: complex multiplet at 1.75-2.10, triplet 2.95 (JHH
7.4 Hz) and triplet 3.07 (JHH 7.0 Hz) (R-CH2 within the oxime moiety).
[PtCl2{N(dO)C(C5H10)ONC(C5H10)}]: Dark-red rodlike crystals
formed from acetone, mp ) 136 °C (dec). EI-MS, m/z: 489 [M -
H]+. Anal. Calcd for C12H20Cl2N2O2Pt: C, 29.4; H, 4.1; N, 5.7.
Found: C, 29.4; H, 3.8; N, 5.5. IR data (Nujol), cm-1: 1618 m
ν(CdN), 1538 vs ν(NdO), 349 ms and 342 ms ν(Pt-Cl). 1H NMR
in nitromethane-d3, δ, ppm: complex multiplet at 1.2-2.1, triplet 3.11
(JHH 6.2 Hz) and triplet 3.19 (JHH 6.3 Hz) (R-CH2 within the oxime
moiety).
[PtBr2{N(dO)CMe2ONCMe2}]: Dark-red needle- and plateslike
crystals from a water-acetone mixture, mp ) 122-124 °C. EI-MS,
m/z: 469 [M - NO]+. Anal. Calcd for C6H12Br2N2O2Pt: C, 14.5; H,
2.4; N, 5.6. Found: C, 14.4; H, 2.6; N, 5.8. IR data (Nujol), cm-1
:
1630 m ν(CdN), 1550 vs ν(NdO), 227 m and 224 mw ν(Pt-Br). 1H
NMR in nitromethane-d3, δ, ppm: 1.51 (OC(CH3)2), 2.58 (4JPtH 7.3
Hz) and 2.71 (4JPtH 10.5 Hz) (NdC(CH3)2).
Reaction of trans-[PtX2(RR′CdNOH)2] (R ) R′ ) Me, RR′ )
(CH2)4, (CH2)5, X ) Cl; R ) R′ ) Me, X ) Br) with MCPBA in
the Ketones Me2CO, MeEtCO, and Et2CO (General Method),
Reaction (Wi) in Scheme 1. The procedure is similar to that described
for the preparation of [PtCl2(OCMe2ONdCC4H8)2].14 Yields were 30-
60% based on Pt. All compounds are very poorly soluble in most
common solvents. The latter property does not allow the measurement
of NMR spectra of the complexes even with high accumulation. The
complexes [PtCl2(OCMe2ONdCRR′)2] (R ) R′ ) Me, RR′ ) (CH2)4
and (CH2)5) were previously characterized.14
[PtBr2(OCMe2ONdCMe2)2] was prepared from trans-
[PtBr2(Me2CdNOH)2] and MCPBA in Me2CO. The complex forms
small rhombic dark-orange crystals from the reaction mixture. The
compound has no characteristic melting point. On heating it decom-
poses from ca. 140 °C. Anal. Calcd for C12H24Br2N2O4Pt: C, 23.4;
H, 3.9; N, 4.6. Found: C, 23.8; H, 3.8; N, 4.6. EI-MS, m/z: 601 ([M
- CH3]+). IR (selected bands), cm-1: 1645 m ν(CdN), 253 s ν(Pt-
Br).
[PtCl2(OCMeEtONdCMe2)2] was prepared from trans-[PtCl2-
(Me2CdNOH)2] and MCPBA in MeEtCO. The complex forms small
orange crystals from the reaction mixture, mp ) 190-192 °C. Anal.
Calcd for C14H28Cl2N2O4Pt: C, 30.3; H, 5.1; N, 5.1. Found: C, 30.2;
H, 4.8; N, 4.8. EI-MS, m/z: 525 (100%) [M - C2H5]+, 467 (15%)
[M - C2H5 - CH2]+ and 453 (85%) [M - 2CH3 - CCH3C2H5]+. IR
(selected bands), cm-1: 1645 ms ν(CdN), 337 s ν(Pt-Cl).
[PtCl2(OCEt2ONdCMe2)2] was prepared from trans-
[PtCl2(Me2CdNOH)2] and MCPBA in Et2CO. The complex forms
square-planar bright orange crystals from the reaction mixture, mp )
186-188 °C. Anal. Calcd for C16H32Cl2N2O4Pt: C, 33.0; H, 5.5; N,
4.8. Found: C, 32.7; H, 5.3; N, 4.5. EI-MS, m/z: 553 (65%) [M -
C2H5]+, 467 (15%) [M - C2H5 - C2H4]+. IR (selected bands), cm-1
1644 ms ν(CdN), 337 s ν(Pt-Cl).
:
Discussion
[PtCl2(OCMeEtONdCC5H10)2] was prepared from trans-[PtCl2-
(C5H10CdNOH)2] and MCPBA in MeEtCO. The complex forms
platelike bright orange crystals from the reaction mixture, mp ) 115-
117 °C (dec). Anal. Calcd for C20H36Cl2N2O4Pt: C, 37.9; H, 5.7; N,
4.4. Found: C, 38.1; H, 5.8; N, 4.2. EI-MS, m/z: 605 ([M - C2H5]+).
IR (selected bands), cm-1: 1636 m ν(CdN), 337 s ν(Pt-Cl).
Reaction between trans-[PtX2(RR′CdNOH)2] and MCP-
BA in DMF. Primary and secondary nitrosoalkanes are usually
irreversibly rearranged to give the corresponding oximes.21 This
reactivity mode is preserved when nitrosoalkane species are
(16) Strel’tsov, V. A.; Zavodnik, V. E. Kristallografia 1989, 34, 1369.
(17) Sheldrick, G. M. SHELXTL User Manual, Revision 3; Nicolet XRD
Corp.: Cupertino, CA, 1981.
(18) Sheldrick, G. M. SHELX-93; University of Go¨ttingen: Go¨ttingen,
Germany, 1993.
(19) Axelrud, L. G.; Grin, Yu. N.; Zavalii, P. Yu.; Pecharsky, V. K.;
Fundamensky, V. S. CSD-universal program package for single crystal
and/or powder structure data treatment. Collected Abstracts, XIIth
European Crystallographic Meeting, Moscow, Aug 1989; USSR
Academy of Sciences: Moscow, 1989; p 155.
(20) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV.
Thermal Conversion of the [PtX2(OCR1R2ONdCMe2)2] Com-
plexes in DMF-d7, Reaction (Wii) in Scheme 1. In a typical experiment
ca. 0.01 g of the complex was placed in a NMR tube and 0.5 mL of
DMF-d7 was added, whereafter the tube was closed and heated at 100
°C for 15 min with periodical shaking. During this time the solid
gradually disappeared and a dark-red solution was formed. The solution
1
was cooled down until room temperature, and the H NMR spectrum
was measured. The same sample was used for TLC monitoring and,
after dilution with DMF, for measuring the electronic absorption
spectrum. The following products were identified from NMR: From

trans-[PtX2(ketoxime)2] Complexes
Inorganic Chemistry, Vol. 35, No. 17, 1996 4929
rise to Mo(η2-O,N-ONdCMe2)(CO)2Cp complex containing a
η2-2-propanone oximato ligand.23
Table 1. Crystal Data and Structure Refinement for
[PtCl2{N(dO)CC5H10ONCC5H10}]
empirical formula
fw
cryst system
space group
a, Å
b, Å
c, Å
C12H20Cl2N2O2Pt
490.29
The formally or schematically reverse reaction, i.e. the
conversion of coordinated oximes into nitrosoalkane species,
was observed for the first time on studying the redox coupling
of the neighboring ketoxime ligands in cis-[PtCl4-
(Me2CdNOH)2].11 To the best of our knowledge, no other
works on oxidation of coordinated oximes and their transforma-
tion into nitrosoalkanes have been published to date.24 Fur-
thermore, complexes of platinum(II) with tert-nitrosoalkane
ligandsswhich cannot tautomerize to the appropriate oximessare
very scarce and restricted only to a few derivatives of tBuNdO
which were prepared earlier by direct addition of the C-nitroso
compound to a complex.24,25
We have now found that the reaction of trans-[PtX2-
(RR′CdNOH)2] (X ) Cl, Br) and MCPBA in dimethylform-
amide results in oxidation of the ketoxime ligands to afford
complexes [PtX2{N(dO)CRR′ONCRR′}] containing coordi-
nated nitrosoalkane species (reaction (V) in Scheme 1) and this
reaction is of synthetic importance.
triclinic
P1h (No. 2)
9.214(2)
9.577(2)
10.367(2)
109.14(2)
91.87(2)
115.62(2)
762.8(3)
2
2.135
293(2)
Mo KR, 0.71073
9.547
R, deg
â, deg
γ, deg
V, Å3
Z
F(calcd), mg m-3
T, K
radiation, λ (Å)
µ, mm-1
θ range, deg
no. of collcd reflcns
no. of reflcns for calc
R1a
2.12-24.96
2743
1836
0.0609
0.1636
wR2b
R1 ) ∑(|Fo| - |Fc|)/∑|Fo|. wR2 ) [∑w(Fo - Fc2)2/∑wFo ]1/2
.
a
b
2
4
It has been observed that the starting trans-ketoxime com-
plexes undergo a complete transformation in DMF almost
immediately after addition of MCPBA to the reaction mixtures.
The color of the solutions changes from pale yellow to dark
red; trans-[PtX2(RR′CdNOH)2] complexes were not found by
TLC a few minutes after mixing the reagents, but orange-red
spots which correspond to the final products (see below) were
detected. Further addition of diethyl ether or water to the
reaction mixtures results in the formation of solids which, on
Table 2. Bond Lengths (Å) and Angles (deg) for
[PtCl2{N(dO)CC5H10ONCC5H10}]
Bond Lengths
Pt-N(1)
1.907(13)
2.063(10)
2.279(5)
2.277(4)
1.21(2)
1.51(2)
1.25(2)
1.44(2)
1.45(2)
1.52(2)
1.52(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(7)-C(8)
C(7)-C(12)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
C(11)-C(12)
1.52(3)
1.50(3)
1.50(3)
1.56(2)
1.45(3)
1.51(2)
1.55(3)
1.52(3)
1.53(3)
1.55(3)
Pt-N(2)
Pt-Cl(1)
Pt-Cl(2)
N(1)-O(2)
N(1)-C(1)
N(2)-C(7)
N(2)-O(1)
O(1)-C(1)
C(1)-C(6)
C(1)-C(2)
1
the basis of elemental analyses and EI-MS, IR, and H NMR
spectra, were formulated as [PtX2{N(dO)CRR′ONCRR′}]. It
is noteworthy that all the complexes are red in color, which is
unusual for [PtIIX2L2] compounds but seems to be characteristic
of platinum(II) nitrosoalkane complexes.11,25 The complex
[PtCl2{N(dO)CMe2ONCMe2}] is identical to that prepared
earlier on redox coupling of the ketoxime ligands in cis-[PtCl4-
(Me2CdNOH)2].11 Compound [PtCl2{N(dO)C(C5H10)ONC-
(C5H10)}] has been structurally characterized. A plot of the
molecular structure is shown in Figure 1, and bond distances
and angles are collected in Table 2. The coordination poly-
hedron of the Pt atom is a slightly distorted square plane. The
chelate ligand is coordinated to platinum Via the N atom of the
nitrosoalkane group and the N atom of the O-alkylated oxime.
The resulting Pt containing five-membered ring is in an
envelope-like conformation. The Pt-N(oxime) bond is sig-
nificantly longer than the Pt-N(nitroso) bond. This was also
observed in the structure of [PtCl2{N(dO)CMe2ONCMe2}], but
the difference was not significant.11 While the fairly large
standard deviations in the structure of [PtCl2{N(dO)CMe2-
ONCMe2}] precluded any meaningful comparison of the Pt-
Cl bond lengths,11 both distances are essentially identical in the
present compound, thus pointing to similar trans-influences of
the nitrosoalkane and alkyloxime ligands. Most distances and
angles in the structure of [PtCl2{N(dO)C(C5H10)ONC(C5H10)}]
Bond Angles
N(1)-Pt-N(2)
N(1)-Pt-Cl(2)
N(2)-Pt-Cl(2)
N(1)-Pt-Cl(1)
N(2)-Pt-Cl(1)
Cl(2)-Pt-Cl(1)
80.8(5)
177.0(4)
97.1(4)
92.9(4)
170.4(3)
88.9(2)
O(1)-C(1)-C(2)
N(1)-C(1)-C(6)
C(6)-C(1)-C(2)
C(3)-C(2)-C(1)
C(4)-C(3)-C(2)
C(5)-C(4)-C(3)
103.7(14)
112.5(14)
111.2(13)
115(2)
110(2)
112(2)
O(2)-N(1)-C(1) 115.6(13) C(4)-C(5)-C(6)
110(2)
O(2)-N(1)-Pt
C(1)-N(1)-Pt
129.9(11) C(1)-C(6)-C(5)
114.3(10) N(2)-C(7)-C(8)
112(2)
121(2)
121(2)
118(2)
115(2)
111(2)
111(2)
C(7)-N(2)-O(1) 116.4(13) N(2)-C(7)-C(12)
C(7)-N(2)-Pt
O(1)-N(2)-Pt
137.7(11) C(8)-C(7)-C(12)
104.1(8) C(7)-C(8)-C(9)
N(2)-O(1)-C(1) 106.2(11) C(10)-C(9)-C(8)
O(1)-C(1)-N(1) 107.0(12) C(9)-C(10)-C(11)
O(1)-C(1)-C(6) 113.3(14) C(10)-C(11)-C(12) 115(2)
N(1)-C(1)-C(6) 109.0(14) C(7)-C(12)-C(11)
109(2)
coordinated to a metal center. It has been shown that N-
coordinated ligands R1R2HCsNdO (R1 ) R2 ) alkyl; R1 )
alkyl, R2 ) H) undergo a spontaneous tautomerization into the
oxime ligands, R1R2CdNOH.22 Tertiary nitrosoalkanes are
commonly stable toward conversion into oximes. However,
some of these nitrosoalkanes still can be used as precursors for
the generation of oximato complexes, e.g. the treatment of
NaMo(CO)3Cp with excess of 2-bromo-2-nitrosopropane gives
(22) (a) Waters, W. A. J. Chem. Soc., Perkin Trans. 2 1976, 732. (b)
Schoonover, M. W.; Baker, E. C.; Eisenberg, R. J. Am. Chem. Soc.
1979, 101, 1880. (c) Legzdins, P.; Wassink, B.; Einstein, F. W. B.;
Willis, A. C. J. Am. Chem. Soc. 1986, 108, 317. (d) Legzdins, P.;
Richter-Addo, G. B.; Wassink, B.; Einstein, F. W. B.; Jones, R. H.;
Willis, A. C. J. Am. Chem. Soc. 1989, 111, 2097. (e) Chang, J.; Seidler,
M. D.; Bergman, R. G. J. Am. Chem. Soc. 1989, 111, 3258.
(23) Khare, G. P.; Doedens, R. J. Inorg. Chem. 1977, 16, 907.
(24) (a) Cameron, M.; Gowenlock, B. G.; Vasapollo, G. Chem. Soc. ReV.
1990, 19, 355. (b) Vasapollo, G. Private communication (1995).
(25) (a) Mansuy, D.; Dreˆme, M.; Chottard, J. C.; Guilhem, J. J. Organomet.
Chem. 1978, 161, 207. (b) Boyd A. S. F.; Browne, G.; Gowenlock,
B. G.; McKenna P. J. Organomet. Chem. 1988, 345, 217.
(21) (a) Coombes, R. G. In ComprehensiVe Organic Chemistry; Barton,
D., Ollis, W. D., Eds.; Pergamon Press: New York, 1979; Vol. 2
(Sutherland, I. O., Ed.), p 305. (b) Boyer, J. H. In The Chemistry of
the Nitro and Nitroso Groups; Feuer, H., Ed.; Interscience Publish-
ers: New York, 1969; p 215. (c) Senechal-Tocquer, M.-C.; Senechal,
D.; Le Bihan, J.-Y.; Gentric, D.; Caro, B.; Gruselle, M.; Jaouen, G. J.
Organomet. Chem. 1992, 433, 261.

4930 Inorganic Chemistry, Vol. 35, No. 17, 1996
Kukushkin et al.
of both the solvents and reagents in the reactions studied and
that the reactions are solvent dependent because they follow a
different path in DMF and ketones. The reactions carried out
are among the first oxidations of Pt(II) complexes involving
the use of a peroxybenzoic acid.27
Generation of [PtCl2{N(dO)CRR′ONCRR′}] by Thermal
Conversion of [PtCl2(OCR1R2ONdCRR′)2]. Complexes
[PtCl2(OCR1R2ONdCRR′)2] are very poorly soluble in most
common solvents (i.e. H2O, MeOH, EtOH, Me2CO, MeNO2,
CH2Cl2, CHCl3, and C6H6) even on boiling of their suspensions.
In search of an appropriate solvent for [PtCl2(OCR1R2-
ONdCRR′)2], we have established that keeping the solid
compounds in DMF or DMF-d7 at 100 °C for ca. 15 min leads
to chemical reactions rather than just dissolution. In all cases,
the bright orange solids [PtCl2(OCR1R2ONdCMe2)2] gradually
disappeared on heating with the formation of red solutions. TLC
and spectrophotometric monitoring provide evidence for the
generation of the nitrosoalkane chelates [PtCl2{N(dO)-
CRR′ONCRR′}] described above. The products of the thermal
conversion of [PtCl2(OCR1R2ONdCMe2)2] (R1 ) R2 ) Me,
1
Et; R1 ) Me, R2 ) Et) in DMF-d7 were subject to H NMR
Figure 1. View of [PtCl2{N(dO)CC5H10ONCC5H10}] with atomic
analysis. Apart from the complex [PtCl2{N(dO)CMe2ONCMe2}]
and small (<5%) amounts of trans-[PtCl2(Me2CdNOH)2], the
ketones R1R2CO and Me2CO were unambiguously identified.
In the case of the thermal conversion of [PtCl2-
(OCMeEtONdCC5H10)2], the complex [PtCl2{N(dO)C(C5H10)-
ONC(C5H10)}] and MeEtCO were found. Cyclohexanone was
numbering.
and [PtCl2{N(dO)CMe2ONCMe2}]11 are close to each other;
the most noticeable differences being in the Pt-N(oxime)
distance [2.063(10) Vs 1.97(2) Å] and Pt-N(oxime)-O angle
[104.1(8) Vs 110(1)°].
1
not detected by means of H NMR spectroscopy, due to the
Thus, it has been established that oxidation of the trans-
oximes of platinum(II) by MCPBA in dimethylformamide
results in oxidation of the oxime ligands with formation of
nitrosoalkane chelates [PtX2{N(dO)CRR′ONCRR′}], while the
Pt(II) oxidation state remains the same. The overall reaction
includes 2e- oxidation of one of the oxime ligand, change in
the relative positions of N-donor species around the Pt atom,
and the ring-closure. The formation of [PtX2{N(dO)-
CRR′ONCRR′}] can also be achived starting from the isomeric
cis-[PtX2(RR′CdNOH)2] and MCPBA in acetone (reaction (iV)
in Scheme 1).26 Oxidations of both trans- and cis-[PtX2-
(ketoxime)2] complexes by MCPBA provide a good synthetic
method for the preparation of unusual and little investigated
nitrosoalkane complexes of platinum.
complexity of signals and overlapping with peaks from the
nitrosoalkane complex, but it was identified by means of EI
mass spectrometry.
In the reactions studied, the ketones R1R2CO are probably
formed by thermal extrusion from the chelate ligand in
[PtCl2(OCR1R2ONdCMe2)2], while acetone, as a byproduct, can
be generated by either uncontrolled hydrolysis of the CdN bond
or oxidative deoximation9,10 by the Pt(IV) ion. The hydrolysis
could proceed due to an extremely strong electrophilic activation
of the ligands by the quadruply-charged Pt ionsa so-called
Lewis superacid.28 Examples of Pt(II)- and Pt(IV)-mediated
hydrolysis of ligands containing the CdN and CtN bonds are
well-documented.29 Oxidative deoximation of RR′CdNOH by
platinum(IV) has not been studied so far. However, Bleaupre´
and Holland have investigated the extraction of H2[PtCl6] from
aqueous solutions at low pH by methyl ethyl ketone oxime and
4-heptanone oxime.30 It was reported that, in very acidic
solutions, Pt(IV) species are reduced to give Pt(II) species.
Apparently, this observation supports the possibility of oxidative
deoximation mediated by Pt(IV).
Hence, heating of [PtCl2(OCR1R2ONdCRR′)2] in DMF or
in DMF-d7 results at least in two reactions. The first process
formally involves extrusion of the ketone from the chelate, 2e-
oxidation of one of the N-donor species formed, 2e- reduction
of platinum(IV), and ring-closure. The second transforma-
tion is the hydrolysis of the CdN bond and/or oxidative
deoximation.
Solvent Dependence of the Reaction between trans-[PtX2-
(RR′CdNOH)2] and MCPBA. Our experiments demonstrate
that the reaction between trans-[PtX2(RR′CdNOH)2] and
MCPBA displays an intriguing solvent-dependent path. Indeed,
recently we have reported that the platinum(II) complexes trans-
[PtCl2(RR′CdNOH)2] [R ) R′ ) Me; RR′ ) (CH2)4, (CH2)5]
react with MCPBA in Me2CO to give the platinum(IV)
complexes [PtCl2(OCMe2ONdCRR′)2] (reaction (Vi) in Scheme
1).14 As an extension of this work, we have now performed
this reaction with trans-[PtBr2(Me2CdNOH)2] and isolated the
appropriate platinum(IV) bromide complex [PtBr2(OCMe2-
ONdCMe2)2]. Furthermore, we have found that the MCPBA
oxidation of trans-[PtCl2(RR′CdNOH)2] proceeds also in some
other ketones; e.g. interaction of trans-[PtCl2(Me2CdNOH)2]
and MCPBA in either methyl ethyl ketone or diethyl ketone
gives rise to [PtCl2(OCR1R2ONdCMe2)2] (R1 ) Me, R2 ) Et;
(27) (a) Browning, C. S.; Farrar, D. H. Organometallics 1989, 8, 813. (b)
Harvie, I. J.; McQuillin, F. J. J. Chem. Soc., Chem. Commun. 1977,
241. (c) Tomohiro, T.; Laitalainen, T.; Shimura, T. Stud. Org. Chem.
(Amsterdam) 1988, 33; Chem. Abstr. 1988, 108, 230949u.
R1
) R2 ) Et), while treatment of trans-[PtCl2-
{(C5H10)CdNOH}2] with MCPBA in methyl ethyl ketone leads
to [PtCl2{OCMeEtONdCC5H10}2]. All these observations
indicate that the reaction (Vi) has a general character for different
trans-ketoxime complexes of platinum(II). These experiments
also additionally prove that the R1R2CO ketones play the role
(28) Paul, P.; Nag, K. Inorg. Chem. 1987, 26, 1586.
(29) (a) Kukushkin, V. Yu.; Zenkevich, I. G.; Belsky, V. K.; Konovalov,
V. E.; Moiseev, A. I.; Sidorov, E. O. Inorg. Chim. Acta 1989, 166,
79. (b) Rochon, F. D.; Kong, P. C.; Melanson, R. C. Inorg. Chem.
1990, 29, 1352. (c) Erxleben, A.; Mutikainen, I.; Lippert, B. J. Chem.
Soc., Dalton Trans. 1994, 3667. (d) Cross, R. J.; Davidson, M. F.;
Rocamora, M. J. Chem. Soc., Dalton Trans. 1988, 1147.
(26) Kukushkin, V. Yu.; Oskarsson Å., Elding, L.-I. Unpublished results
(1993).
(30) Bleaupre´, P. W.; Holland, W. J. Mikrochim. Acta 1983, 3, 341.

trans-[PtX2(ketoxime)2] Complexes
Inorganic Chemistry, Vol. 35, No. 17, 1996 4931
In conclusion, it is worthwhile to mention that the MCPBA
oxidation of bis(ketoxime) complexes of platinum(II) both in
DMF and in the ketones provides a route for the preparation of
new types of unusual chelates (all reactions and products studied
are depicted in Scheme 1). However, the mechanisms of these
processes are not yet clear. In fact, it is not established whether
oxidation of the oxime ligands by MCPBA proceeds directly
or Via intermediate oxidation of Pt(II). Undoubtedly, this
information would be important not only for the correct choice
of starting materials and reaction conditions but also for
predicting the occurrence of some other metal-ion-assisted
reactions of oximes.
Acknowledgment. The authors are grateful to the Spanish
Direccio´n General de Investigacio´n Cient´ıfica y Te´cnica for
financial support (Project PB93-0277) and the award of a
sabbatical fellowship to V.Yu.K. (Grant SAB 94-0317). V.K.B.
is grateful to the Russian Fund of Basic Research for Grant
95-03-09030a.
Supporting Information Available: Tables of atomic coordinates
and equivalent isotropic displacement parameters, anisotropic displace-
ment parameters, and hydrogen coordinates and isotropic displacement
parameters (3 pages). Ordering information is given on any current
masthead page.
IC9600691