Iminoacylation Part 6: Coupling of chloro- and amidoximes Ar(R)C=NOH (R = Cl, NH2) with acetonitrile ligands coordinated to platinum(IV)

Article abstract of DOI:10.1016/S0020-1693(99)00556-3

Addition of chloro- and amidoximes RR¹C=NOH (R/R¹ = Cl/Ph, Cl/C₆H₄-p-Me, Cl/C₆H₄-p-NO₂, NH₂/Ph) to the acetonitrile ligands in trans-[PtCl₄(MeCN)₂] proceeds much slower as compared to ketoximes with donor substituents R/R¹ [V.Yu. Kukushkin, T.B. Pakhomova, Yu.N. Kukushkin, R. Herrmann, G. Wagner, A.J.L. Pombeiro, Inorg. Chem. 37 (1998) 6511] and leads to the complexes with iminoacylated species [ligating (alkylideneaminooxy)imines] trans-[PtCl₄{NH=C(Me)ON=CRR¹}₂]. X-ray crystal structure determination of two iminoacylated compounds (R/R¹ = Cl/C₆H₄-p-Me, Cl/C₆H₄-p-NO₂) disclosed their overall trans geometry with monodentate organic ligands in E-conformation and indicated =NH···N hydrogen bonding between the imino H atom and the oxime nitrogen. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00556-3

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Inorganica Chimica Acta 300–302 (2000) 499–504
Iminoacylation
Part 6: Coupling of chloro- and amidoximes Ar(R)CꢀNOH
(R=Cl, NH2) with acetonitrile ligands coordinated to
platinum(IV)ꢀ
Dmitrii A. Garnovskii a,b, M. Fa´tima C. Guedes da Silva b,c,
Tatyana B. Pakhomova d, Gabriele Wagner b, M. Teresa Duarte b,
Joa˜o J.R. Frau´sto da Silva b, Armando J.L. Pombeiro b,*1, Vadim Yu. Kukushkin e,*2
a Institute of Physical and Organic Chemistry, Rosto6 State Uni6ersity, 344090, Rosto6-on-Don, Russia
b Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, A6. Ro6isco Pais, 1049–001 Lisbon, Portugal
c Uni6ersidade Luso´fona de Humanidades e Tecnologias, A6. Campo Grande 376, 1749–024 Lisbon, Portugal
d Inorganic Chemistry, St. Petersburg State Technological Institute, Zagorodny Pr. 49, 198013 St.Petersburg, Russia
e Department of Chemistry, St. Petersburg State Uni6ersity, 198904 Stary Petergof, Russia
Received 11 October 1999; accepted 25 November 1999
Abstract
Addition of chloro- and amidoximes RR1CꢀNOH (R/R1=Cl/Ph, Cl/C6H4-p-Me, Cl/C6H4-p-NO2, NH2/Ph) to the acetonitrile
ligands in trans-[PtCl4(MeCN)2] proceeds much slower as compared to ketoximes with donor substituents R/R1 [V.Yu.
Kukushkin, T.B. Pakhomova, Yu.N. Kukushkin, R. Herrmann, G. Wagner, A.J.L. Pombeiro, Inorg. Chem. 37 (1998) 6511] and
leads to the complexes with iminoacylated species [ligating (alkylideneaminooxy)imines] trans-[PtCl4{NHꢀC(Me)ONꢀCRR1}2].
X-ray crystal structure determination of two iminoacylated compounds (R/R1=Cl/C6H4-p-Me, Cl/C6H4-p-NO2) disclosed their
overall trans geometry with monodentate organic ligands in E-conformation and indicated ꢀNH···N hydrogen bonding between
the imino H atom and the oxime nitrogen. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Nitrile complexes; Platinum(IV) complexes; Nucleophilic addition; Iminoacylation; Oximes; Imine ligands
sisted reaction between the platinum(IV) complexes
1. Introduction
[PtCl4(RCN)2] (R=Me, CH2Ph, Ph) and ketoximes
and aldoximes, R1R2CꢀNOH (R1=R2=Me; R1R2=
In so-called pure organic chemistry, organonitriles
are useful and versatile reagents for the formation of
CꢁC, CꢁN and CꢁO moieties [1]. Metal-mediated reac-
tions enrich significantly the chemistry of nitriles, i.e.
C4H8, R1R2=C5H10, R1/R2=H/Ph, R1/R2=H/C6H4-
o-OH), which led to isolation of unusual and un-
expectedly stable iminoacylated compounds [PtCl4{NHꢀ
C(R)ONꢀCR1R2}2] [3]. Since then our efforts in ex-
metal-ion control of the reactivity in many instances
ploitation of this synthetic pathway for generation of
allows one to promote or inhibit certain reactions or
imino species, NHꢀCRR%, have been focused on (i)
even to perform new synthetic routes, which are not
application for the iminoacylation of other organoni-
feasible without the involvement of metal-ions [2]. Re-
trile metal complexes with the central atom in high
cently we observed a facile and high-yield metal-as-
oxidation state, i.e. Rh(III) [4] (iminoacylation of ke-
toximes followed by chelation of newly formed ligands
ꢀ For part 5, see Ref. [5]
to the rhodium center was observed) and Re(IV) [5]
compounds (giving monodentate iminoacylated spe-
cies); (ii) use of other ligands containing the NꢁOH
1*Corresponding author. Tel.: +351-1-841 9237; fax: +351-1-846
4455/4457; e-mail: pombeiro@alfa.ist.utl.pt
2*Corresponding author. E-mail: kukushkin@vk2100.spb.edu
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00556-3

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functionality, i.e. alkylated hydroxylamines to observe
unprecedented O-addition of R2NOH to acetonitrile
in [PtCl4(MeCN)2] [6]; (iii) use of 6ic-dioxime ligands
forming, after the one-end iminoacylation by organo-
nitriles, a novel type of metallaligands [7]. We now
report on a further extension of the iminoacylation
reaction that involves chloroximes RR1CꢀNOH (R/
R1=Cl/Ph, Cl/C6H4-p-Me, Cl/C6H4-p-NO2), which
— in contrast to the previously investigated oximes
— contain a strong acceptor substituent, i.e. Cl,
bound to the CꢀNOH group. In fact, we wondered
whether the iminoacylation was inhibited by acceptor
groups making the oximes less nucleophilic or, on the
contrary, promoted by easier deprotonation of the
OH group thus favoring the formation of the more
nucleophilic oximates. For comparative reasons we
also studied the iminoacylation of [PtCl4(MeCN)2] by
amidoxime (R/R1=NH2/Ph) and these results, along
with two X-ray crystal structures of the iminoacylated
products, are discussed below.
5-ml portions of Et2O and dried in vacuo at room
temperature.
2.3. [PtCl4{NHꢀC(Me)ONꢀC(Cl)Ph}2] (I)
Reaction time is 38 h. Yield is 79%. Anal. Calc. for
C18H18N4Cl6O2Pt: C, 29.61; H, 2.49; N, 7.67. Found:
C, 29.56; H, 2.47; N, 7.51%. M.p. 216°C (dec.). IR
spectrum (selected bands), cm−1: 3285 m-w w(NꢁH),
1664 s w(CꢀN), 1180 w(CꢁO). The compound is insol-
uble in all common NMR solvents.
2.4. [PtCl4{NHꢀC(Me)ONꢀC(Cl)(C6H4-p-Me)}2] (II)
Reaction time is 32 h. Yield is 82%. Anal. Calc. for
C20H22N4Cl6O2Pt: C, 31.65; H, 2.93; N, 7.39. Found:
C, 31.76; H, 2.71; N, 7.26%. M.p. 221°C (dec.). IR
spectrum (selected bands), cm−1: 3286 m-w w(N–H),
1672 s w(CꢀN), 1188 m w(C–O). The compound is
insoluble in all common NMR solvents.
2. Experimental
2.5. [PtCl4{NHꢀC(Me)ONꢀC(Cl)(C6H4-p-NO2)}2] (III)
2.1. Materials and instrumentation
Reaction time is 240 h. Yield is 86%. Anal. Calc.
for C18H16N6Cl6O6Pt: C, 26.36; H, 1.97; N, 10.25.
Found: C, 26.83; H, 2.04; N, 9.86%. M.p. 209°C
(dec.). IR spectrum (selected bands), cm−1: 3296 m-w
w(NꢁH), 1672 s w(CꢀN), 1182 m w(CꢁO). The com-
pound is insoluble in all common NMR solvents.
Solvents were obtained from commercial sources
and used as received. The complex [PtCl4(MeCN)2]
was prepared as previously described [8]. Benzohy-
droximoylchlorides were prepared by chlorination of
corresponding oximes [9]. C, H and N elemental
analyses were carried out by the Microanalytical Ser-
vice of the Instituto Superior Te´cnico. Melting points
were determined on a Kofler table. Infrared spectra
(4000–400 cm−1) were recorded on a Bio-Rad FTS
2.6. [PtCl4{NHꢀC(Me)ONꢀC(NH2)Ph}2] (IV)
Reaction time is 27 h. Yield is 84%. Anal. Calc. for
C18H22N6Cl4O2Pt: C, 31.27; H, 3.21; N, 12.16. Found:
C, 31.62; H, 3.71; N, 12.37%. M.p. 203°C (dec.). IR
spectrum (selected bands), cm−1: 3503 m-w w(NH2),
3000MX instrument in KBr pellets. H, 13C{1H}, and
1
195Pt NMR spectra were measured on Varian UNITY
300 spectrometer at ambient temperature. 195Pt chemi-
cal shifts are given relative to aqueous K2[PtCl4]=
−1630 ppm and half-height line widths are shown in
parenthesis.
3364 m-w w(NH2), 3227 m-w w(N–H), 1629
s
w(CꢀN), 1195 m w(CꢁO). 1H NMR spectrum in
4
DMSO-d6, l: 2.67 (s+d, JPtH 3.8 Hz, 3H
(ꢀC(Me)O), 7.55 (m, 3H) and 7.70 (d, 7.5 Hz,
4
2H)(Ph), 7.56 (s, br, 2H, NH2), 8.53 (s+d, JPtH 33.3
2.2. Preparation of [PtCl4{NHꢀC(Me)ONꢀCRR1}2]
(R/R1=Cl/Ph, Cl/C6H4-p-Me, Cl/C6H4-p-NO2,
NH2/Ph)
Hz, 1H, NH). 13C{1H} NMR spectrum in DMSO-d6,
l: 17.8 (3JPtC 7.5 Hz, ꢀC(Me)O), 127, 128.8, 130.1,
and 131.5 (Ph), 158.6 (NꢀC(NH2)), 173.9 (2JPtC 44
Hz, CꢀNH). 195Pt NMR spectrum in DMSO-d6, l:
−38 (355 Hz).
A solution of an oxime (0.096 mmol) in CH2Cl2 (2
ml) is added to a suspension of [PtCl4(MeCN)2] (20
mg, 0.048 mmol) in CH2Cl2 (5 ml) and refluxed for
1–10 days depending on the oxime employed (reac-
tion time is indicated below). The progress of the
reaction is monitored by IR spectroscopy, i.e. by dis-
appearance of w(CꢂN) (2290 cm−1) and increase of
intensity of w(CꢀN) (1672–1629 cm−1) stretching vi-
brations. Precipitates formed are filtered off, washed
with two 5-ml portions of warm (35°C) CH2Cl2, two
2.7. X-ray structure determination of trans-[PtCl4-
{N(H)ꢀC(Me)ONꢀC(Cl)(C6H4-p-Me)}2] (II)
[and trans-[PtCl4{N(H)ꢀC(Me)ONꢀC(Cl)
(C6H4-p-NO2)}2] (III)]
X-ray measurements were made using an Enraf–
Nonius Mach-3 (and CAD4) diffractometers with

D.A. Garno6skii et al. / Inorganica Chimica Acta 300–302 (2000) 499–504
501
Table 1
Crystal data and structure refinement for trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl) (C6H4-p-Me)}2] (II) and trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl)(C6H4-p-
NO2)}2] (III)
II
III
Empirical formula
Formula weight
Temperature (K)
C20H21.5N4Cl6O2Pt
757.70
293(2)
C18H16N6Cl6O6Pt
820.16
293(2)
,
Wavelength (A)
0.71069
monoclinic
P21/n (no. 14)
0.56083
monoclinic
P21/c (no. 14)
Crystal system
Space group
,
a (A)
13.939(3)
14.413(2)
14.056(3)
110.162(10)
2650.7(9)
4
1.899
8.227(3)
11.808(2)
14.111(2)
106.10(3)
1317.0(6)
2
2.068
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
zcalc (Mg m−3
)
Collection method
q/2q
q/2q
Radiation monochromator
Absorption coefficient (mm−1
F(000)
graphite
5.924
1462
i-filter
3.230
788
)
Crystal size
Limiting indices
0.28×0.23×0.18
05h516, 05k517, −165l515
4840/4639, [Rint=0.0351]
full-matrix-block least-squares on F2
4305/0/326
0.45×0.36×0.12
−105h50, 05k515, −165l517
1875/1761, [Rint=0.0223]
full-matrix-block least-squares on F2
1761/0/201
Reflections collected/unique
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I \2|(I)]
R indices (all data)
1.055
1.080
R1=0.036, wR2=0.08056
R1=0.0565, wR2=0.1031
1.99 and −1.20
R1=0.0180, wR2=0.0460
R1=0.0180, wR2=0.0460
1.20 and −0.482
−3
,
Largest difference peak and hole (e A
)
graphite (and b-filter) monochromatised Mo Ka (and
Ag Ka) radiation. Cell dimensions were obtained from
centred reflections with q between 2 and 25° (3 and
22°). The data were entered into the SHELXS-86 [10]
system for structure determination and into SHELXL-93
[11] (and SHELXL-97 [12]) for refinement. The Pt atoms
were located from a Patterson map; in III half of the
molecule was found in the asymmetric unit with the Pt
atom in a special position. All the other non-hydrogen
atoms were found from subsequent difference Fourier
syntheses. While in III H atoms were located and
refined isotropically, in II all hydrogen atoms were
included in idealized positions, except for the N(1) and
N(2) protons [H(1) and H(2), respectively] which were
located and refined at a fixed distance of the parent
nitrogen atom [N(1) and N(2)]; these atoms, H(1) and
H(2), are within the plane defined by N(11)ꢁO(11)ꢁ
C(1)ꢁN(1) and N(21)ꢁO(21)ꢁC(2)ꢁN(1), respectively.
Least-squares refinements with anisotropic thermal
motion parameters for all the non-hydrogen atoms
and isotropic for the remaining atoms, gave good
agreement factors. The maximum and minimum peaks
tions were made. Lorentz, polarization, and absorption
corrections were applied. Crystal data are given in
Table 1, and selected bond distances and angles, in
Table 2.
Table 2
,
Selected bond lengths (A) and angles (°) for trans-
[PtCl4{Na(H)ꢀC(Me)ONbꢀC(Cl)(C6H4-p-Me)}2] (II) and trans-
PtCl4Na(H)ꢀC(Me)ONbꢀC(Cl)(C6H4-p-NO2)2 (III)
II
III
PtꢁNa
PtꢁCl
2.007(5), 2.014(6)
2.304(2), 2.313(2),
2.316(2), 2.321(2)
1.265(9), 1.270(9)
1.271(8), 1.272(8)
1.355(8), 1.367(8)
0.73(5), 0.80(8)
2.019(4)
2.3066(14),
2.3124(14)
1.271(5)
1.272(5)
1.348(5)
0.75(5)
NaꢁC
NbꢁC
CꢁO
NaꢁH
NaꢁPtꢁNa%
CꢁNaꢁPt
NaꢁCꢁO
NbꢁOꢁC
178.1(2)
136.0(5)
120.2(6), 121.6(6)
111.1(5), 111.9(5)
180.0
134.2(3)
122.5(4)
113.7(3)
Hydrogen bonding
H···Nb
Na···Nb
2.21(9), 2.21(6)
2.521(8), 2.558(8)
104(7), 110(5)
2.22(6)
2.615(5)
113(5)
in the final difference electron density map for II are
−3
,
of +1.993 and −1.196 e A
located in the immedi-
NaꢁH···Nb
ate vicinity of the platinum atom. Extinction correc-

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D.A. Garno6skii et al. / Inorganica Chimica Acta 300–302 (2000) 499–504
3. Results and discussion
In contrast to the reaction of trans-[PtCl4(MeCN)2]
with ketoximes containing donor substituents R/R1
(that proceeds within 10 min at 56°C), the addition of
chloro- and amidoximes occurs much slower (1–10
days at 56°C) and leads to the complexes trans-
[PtCl4{NHꢀC(Me)ONꢀCRR1}2] with two ligating imi-
noacylated species that can be regarded as (alkyl-
ideneaminooxy)imine ligands, Scheme 1 for the cases of
unsubstituted phenyl rings:
All compounds gave satisfactory elemental analyses
and expected peaks in FAB+ MS spectra. Complexes
were characterized by IR spectroscopy [the absence of
CꢂN stretching vibrations and presence of characteristic
w(CꢀN) and w(C–O) peaks] and in the case of
[PtCl4{NHꢀC(Me)ONꢀC(NH2)Ph}2] by 1H, 13C{1H},
and 195Pt NMR spectroscopy; all other complexes were
insufficiently soluble in all common deuterated solvents
to measure even 1H NMR spectra at high accumulation
Scheme 1. Iminoacylation of benzohydroximoylchloride by coordi-
nated acetonitrile.
Fig. 1. ORTEP view of trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl)(C6H4-p-Me)}2] (II) with atomic numbering scheme.

D.A. Garno6skii et al. / Inorganica Chimica Acta 300–302 (2000) 499–504
503
Fig. 2. ORTEP view of trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl)(C6H4O-p-NO2)}2] (III) with atomic numbering scheme.
time. Complexes trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl)-
(C6H4-p-Me)}2] and trans-[PtCl4{NHꢀC(Me)ONꢀC(Cl)-
(C6H4-p-NO2)}2] were characterized by X-ray single-
crystal diffractometry. In both compounds the coordi-
nation polyhedron is a slightly distorted octahedron
formed by four chlorine and two nitrogen atoms (Figs.
1 and 2).
effects rather than that of the resonance ones, thus
showing the predominance of the former over the lat-
ter. Hence, no significant conjugation between the sub-
stituent and the oxime-NO group is disclosed, as also
substantiated by the X-ray data.
In III, the Pt atom is situated in a center of symmetry
while in II it is in a pseudo twofold axis giving a pseudo
4. Supplementary material
,
symmetry to the molecule. The PtꢁCl [2.31ꢁ2.32 A] and
Crystal data have been deposited at the Cambridge
Crystallographic Data Centre (CCDC) with deposition
numbers CCDC 135419 and CCDC 135420. Copies of
this information may be obtained free of charge from:
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
,
PtꢁN [2.01–2.02 A] bond lengths and also all bond
angles around the Pt centers agree well with reported
values for other platinum(IV) complexes [13]. All bonds
and angles in the arene fragments are of normal values
[14]. The imine ligands are mutually trans and both are
in the E-conformation, which is held by a rather weak
N–H···N hydrogen bond between the imine ꢀNH atom
and the oxime nitrogen with the following observed
distances and angles for II and III: N(1)···N(2),
N(1)ꢁH, N(1)H···N(2) are 2.539(8) [2.615(5)], 0.76(7)
Acknowledgements
,
[0.75(6)] and 2.21(8) [2.22(6)] A; N(1)–H···N(2) angle is
D.G. and G.W. are grateful to the PRAXIS XXI
program for fellowships (BPD16368/98 and BPD11779/
97). A.J.L.P. thanks the FCT (Foundation for Science
and Technology) and the PRAXIS XXI program for
financial support. V.Yu.K. is very much obliged to the
Russian Fund for Basic Research (grant 97-03-33626a)
and the PRAXIS XXI program (grant BCC16428/98)
for financial support of this study.
107(6)° [113(5)°]. These values are similar to those
previously found for platinum(IV) complexes with both
iminoacylated ketoximes and iminoacylated diethyl-
hydroxyl amine [3,6]. No evidence for [PtCl4{NHꢀ
C(Me)ONꢀC(NH2)Ph}2] Z-conformation in solution
was obtained by NMR spectroscopy.
In summary, the results obtained indicate that the
activation of ligating acetonitriles by the Pt(IV) center
towards nucleophilic attack is such that they still be-
have as iminoacylating agents of oximes with strong
electron-acceptor substituents that make them weaker
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