[2 + 3] Cycloaddition of nitrones to platinum-bound organonitriles: Effect of metal oxidation state and of nitrile substituent

Article abstract of DOI:10.1021/ic000477b

The ligated benzonitriles in the platinum(II) complex [PtCl₂(PhCN)₂] undergo metal-mediated [2 + 3] cycloaddition with nitrones ^-ON⁺(R³)=C(R¹)(R²) [R¹/R²/R³ = H/Ph/Me, H/p-MeC₆H₄/Me, H/Ph/CH₂Ph] to give Δ⁴-1,2,4-oxadiazoline complexes, [PtCl₂{N=C(Ph)O-N(R³)-C(R¹)(R²)} ₂] (2a, 4a, 6a), as a 1:1 mixture of two diastereoisomers, in 60-75% yields, while [PtCl₂(MeCN)₂] is inactive toward the addition. However, a strong activation of acetonitrile was reached by application of the platinum(IV) complex [PtCl₄(MeCN)₂] and both [PtCl₄-(RCN)₂] (R = Me, Ph) react smoothly with various nitrones to give [PtCl₄{N=C(R)O-N(R³)-C(R¹)(R²)} ₂] (1b-6b). The latter were reduced to the corresponding platinum(II) complexes [PtCl₂{N=C(R)O-N(R³)-C-(R¹)(R²)} ₂] (1a-6a) by treatment with PhCH₂NHOH, while the reverse reaction, i.e. conversion of 1a-6a to 1b-6b, was achieved by chlorination with Cl₂. The diastereoisomers of [PtCl₂{N=C(R)O-N(R³)-C(R¹)(R²)} ₂] (1a-6a) exhibit different kinetic labilities, and liberation of the Δ⁴-1,2,4-oxadiazolines by substitution with 1,2-bis(diphenylphosphino)ethane (dppe) in CDCl₃ proceeds at different reaction rates to give free N=C(R)O-N(R³)-C(R¹)(R²) and [PtCl₂(dppe)] in almost quantitative NMR yield. All prepared compounds were characterized by elemental analyses, FAB mass spectrometry, and IR and ¹H, ¹³C{¹H}, and ¹⁹⁵Pt (metal complexes) NMR spectroscopies; X-ray structure determination of the first (Δ⁴-1,2,4-oxadiazoline)Pt(II) complexes was performed for (S,S)/(R,R)-rac-[PtCl₂{N=C(Me)O-N(Me)-C(H)Ph}₂] (1a) (a = 9.3562(4), b = 9.8046(3), c = 13.1146(5) A; α = 76.155(2), β = 83.421(2), γ = 73.285(2)°; V = 1117.39(7) A³; triclinic, P1, Z = 2), (R,S)-meso-[PtCl₂-(N=(Ph)O-N(Me)-C(H)Ph)₂] (2a) (a = 8.9689(9), b = 9.1365(5), c = 10.1846(10) A; α = 64.328(6), β = 72.532(4), γ = 67.744(6)°; V = 686.82(11) A³; triclinic, P1, Z = 1), (S,S)/(R,R)-rac-[PtCl₂(N=C(Me)O-N(Me)-C(H)(p-C₆H ₄Me))₂] (3a) (a = 11.6378(2), b = 19.0767(7), c = 11.5782(4) A; β = 111.062(2)°; V = 2398.76(13) A³; monoclinic, P2₁/c, Z = 4), and (S,S)/(R,R)-rac-[PtCl₂(N=C(Me)O-N(CH₂Ph)-C(H)Ph ₂] (5a) (a = 10.664(2), b = 10.879(2), c = 14.388(3) A; α = 73.11(3), β = 78.30(3), γ = 88.88(3)°; V = 1562.6(6) A³; triclinic, P1, Z = 2).

Full text of DOI:10.1021/ic000477b

264
Inorg. Chem. 2001, 40, 264-271
[2 + 3] Cycloaddition of Nitrones to Platinum-Bound Organonitriles: Effect of Metal
Oxidation State and of Nitrile Substituent
Gabriele Wagner,† Matti Haukka,‡ Joa˜o J. R. Frau´sto da Silva,†
Armando J. L. Pombeiro,*,† and Vadim Yu. Kukushkin*,§
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais,
1049-001 Lisbon, Portugal, Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101,
Joensuu, Finland, and St. Petersburg State University, 198904 Stary Petergof, Russian Federation
ReceiVed May 2, 2000
The ligated benzonitriles in the platinum(II) complex [PtCl2(PhCN)2] undergo metal-mediated [2 + 3] cycloaddition
with nitrones -ON+(R3)dC(R1)(R2) [R1/R2/R3 ) H/Ph/Me, H/p-MeC6H4/Me, H/Ph/CH2Ph] to give ∆4-1,2,4-
oxadiazoline complexes, [PtCl2{NdC(Ph)O-N(R3)-C(R1)(R2)}2] (2a, 4a, 6a), as a 1:1 mixture of two
diastereoisomers, in 60-75% yields, while [PtCl2(MeCN)2] is inactive toward the addition. However, a strong
activation of acetonitrile was reached by application of the platinum(IV) complex [PtCl4(MeCN)2] and both [PtCl4-
(RCN)2] (R ) Me, Ph) react smoothly with various nitrones to give [PtCl4{NdC(R)O-N(R3)-C(R1)(R2)}2]
(1b-6b). The latter were reduced to the corresponding platinum(II) complexes [PtCl2{NdC(R)O-N(R3)-C-
(R1)(R2)}2] (1a-6a) by treatment with PhCH2NHOH, while the reverse reaction, i.e. conversion of 1a-6a to
1b-6b, was achieved by chlorination with Cl2. The diastereoisomers of [PtCl2{NdC(R)O-N(R3)-C(R1)(R2)}2]
(1a-6a) exhibit different kinetic labilities, and liberation of the ∆4-1,2,4-oxadiazolines by substitution with
1,2-bis(diphenylphosphino)ethane (dppe) in CDCl3 proceeds at different reaction rates to give free NdC(R)O-
N(R3)-C(R1)(R2) and [PtCl2(dppe)] in almost quantitative NMR yield. All prepared compounds were characterized
1
by elemental analyses, FAB mass spectrometry, and IR and H, 13C{1H}, and 195Pt (metal complexes) NMR
spectroscopies; X-ray structure determination of the first (∆4-1,2,4-oxadiazoline)Pt(II) complexes was performed
for (S,S)/(R,R)-rac-[PtCl2{NdC(Me)O-N(Me)-C(H)Ph}2] (1a) (a ) 9.3562(4), b ) 9.8046(3), c ) 13.1146(5)
Å; R ) 76.155(2), â ) 83.421(2), γ ) 73.285(2)°; V ) 1117.39(7) Å3; triclinic, P1h, Z ) 2), (R,S)-meso-[PtCl2-
(NdC(Ph)O-N(Me)-C(H)Ph)2] (2a) (a ) 8.9689(9), b ) 9.1365(5), c ) 10.1846(10) Å; R ) 64.328(6),
â ) 72.532(4), γ ) 67.744(6)°; V ) 686.82(11) Å3; triclinic, P1h, Z ) 1), (S,S)/(R,R)-rac-[PtCl2(NdC(Me)O-
N(Me)-C(H)(p-C6H4Me))2] (3a) (a ) 11.6378(2), b ) 19.0767(7), c ) 11.5782(4) Å; â ) 111.062(2)°; V )
2398.76(13) Å3; monoclinic, P21/c, Z ) 4), and (S,S)/(R,R)-rac-[PtCl2(NdC(Me)O-N(CH2Ph)-C(H)Ph2] (5a)
(a ) 10.664(2), b ) 10.879(2), c ) 14.388(3) Å; R ) 73.11(3), â ) 78.30(3), γ ) 88.88(3)°; V ) 1562.6(6) Å3;
triclinic, P1h, Z ) 2).
Introduction
the nucleophiles used, much attention has been drawn to
additions of water to RCN to give carboxylic acids or amides,2,3
alcohols to produce iminoethers or esters,4-7 amines to give
amidines,8 and also compounds exhibiting significant C-H
acidity to form the new C-C bond due to the addition.9-11 One
of the main problems encountered in reactions of nucleophilic
In organic chemistry, transformations of organonitriles play
an important role in both laboratory and industry due to their
chemical versatility. In particular, the addition of electrophiles1
or nucleophiles2-11 to the CtN triple bond offers an attractive
route for creation of novel C-C, C-N, and C-O bonds. Among
(4) Neilson, D. G. The Chemistry of Amidines and Imidates; Patai, S.,
Ed.; John Wiley & Sons: London, 1975.
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(7) Andres, C.; Maestro, A.; Pedrosa, R.; Perez-Encabo, A.; Vicente, M.
Synlett 1992, 45.
* Authors to whom correspondence should be addressed. Fax: +351-
21-846 4455 or +7-8124286939. E-mail: pombeiro@ist.utl.pt or
kukushkin@vk2100.spb.edu.
† Instituto Superior Te´cnico.
‡ University of Joensuu.
§ St. Petersburg State University.
(1) Gridnev, I. D.; Gridneva, N. A. Usp. Khim. (Russ. Chem. ReV.) 1995,
(8) Boyd, G. V. The Chemistry of Amidines and Imidates; Patai, S.,
Rappoport, Z., Eds.; Wiley: Chichester, U.K., 1991; Vol. 2, p 339.
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Interscience: New York, 1970; p 73.
10.1021/ic000477b CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/12/2000

Addition of Nitrones to Pt-Bound Organonitriles
Inorganic Chemistry, Vol. 40, No. 2, 2001 265
addition is insufficient electrophilic activation even by very
strong electron-accepting groups R at RCN, e.g. Cl3CCN, to
perform the addition, and numerous examples of limitations of
so-called pure organic chemistry in this field are illustrative.12-16
These difficulties, however, can be overcome with the use of
metal ions9ssometimes even in low-oxidation-states24sas
extremely strong activators toward nucleophilic attack. This
activation can result in enhancement of the rate of the addition
commonly in the range of 106-108 17 (and occasionally to
1018 25). Moreover, metal-mediated processes in many instances
allow the performance of certain reactions which are not feasible
without the involvement of metal ions.
Scheme 1. [2 + 3] Cycloaddition of Nitrones to Pt(IV)-
Bound Acetonitrile Ligands
complexes [PtCl4{NdC(Me)O-N(R3)-C(R1)(R2)}2], as a 1:1
mixture of two diastereoisomers, in good to almost quantitative
yields.32
Our recent results in the field of RCN ligands reactivity are
relevant to (i) the observation of the fast and high-yield reaction
between the platinum(IV) complexes [PtCl4(RCN)2] and oximes,
R1R2CdNOH,26 and Vic-dioximes, HON){spacer})NOH (spacer
) C(Me)C(Me), C{C4H8}C, C{C5H10}C, C{C6H12}C),27 which
led to the isolation of unusual iminoacylated [or (alkylidene-
aminooxy)imine] compounds [PtCl4(NHdC(R)ONdCR1R2)2]
or novel types of metallaligands [PtCl4(NHdC(R)ON)
{spacer})NOH)2], respectively, (ii) the extension of the imi-
noacylation reaction involving Pt(IV) compounds to Re(IV)28
and Rh(III)29,30 organonitrile complexes, and (iii) the establish-
ment of an unprecedented Ag+- or Cu2+-catalyzed coupling of
dialkylcyanamides with oximes at a platinum(II) center.31 Our
interest in further exploring the metal-mediated reactions of
organonitriles was recently sparked by the observation of a facile
[2 + 3] cycloaddition between acetonitrile ligands in the highly
reactive platinum(IV) complex [PtCl4(MeCN)2] and various
nitrones of the type -ON+(R3)dC(R1)(R2) that gives-due to
Pt(IV)-assisted cycloaddition (Scheme 1)-∆4-1,2,4-oxadiazoline
Moreover, the liberation of the newly formed ligands by
reaction of [PtCl4{NdC(Me)O-N(R3)-C(R1)(R2)}2] with py-
ridine was performed, and that opened up a route to ∆4-1,2,4-
oxadiazoline heterocyclic species whose synthesis and chemistry
are very little developed. We anticipated the mild reaction
conditions of the [2 + 3] cycloaddition to be a viable synthetic
pathway for the preparation of that type of metal-bound
heterocycles. However, the precise role of the metal oxidation
state on the control of the reactivity and/or the effect of
substituents R at the [Pt]-NCR center were not completely
understood and we felt that further reactivity studies on the [2
+ 3] cycloaddition of nitrones to metal-bound nitriles deserved
additional efforts.
In the framework of our research program on the reactivity
of organonitrile complexes33-42 and as an extension of our
previous work32 on the [2 + 3] cycloaddition, it was decided
to examine whether the cycloaddition is peculiar for platinum-
(IV) compounds or it represents a more general type of reaction
of nitrones and nitrile metal complexes and also to verify factors
affecting the addition. For achieving that goal, we addressed
for the current work (organonitrile)PtII complexes and compared
their reactivity toward the cycloaddition with that of the
corresponding platinum(IV) compounds. It has been found that,
for the highly reactive platinum(IV) complexes [PtCl4(RCN)2],
the cycloaddition can be performed under mild conditions
starting even from a very unreactive organonitrile bearing an
electron-donor substituent, e.g. R ) Me, while for the much
less reactive organonitriles in platinum(II) complexes [PtCl2-
(RCN)2] the cycloaddition occurs only in the case of the
organonitrile with an electron-acceptor substituent, i.e. R ) Ph.
Furthermore, it was observed that Pt(II)-bound ∆4-1,2,4-
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Frau´sto da Silva, J. J. R.; Pombeiro, A. J. L.; Michelin, R. A.; Belluco,
U.; Bertani, R.; Mozzon, M.; Bombieri, G.; Benetollo, F.; Kukushkin,
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266 Inorganic Chemistry, Vol. 40, No. 2, 2001
Wagner et al.
Table 1. Crystallographic Data for rac-1a, meso-2a, rac-3a, and rac-5a
rac-1a
meso-2a
rac-3a
rac-5a
chem formula
fw
temp, K
λ, Å
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C20H24N4Cl2O2Pt
618.41
120
C30H28N4Cl2O2Pt
742.54
120
C22H28N4Cl2O2Pt
646.46
120
0.710 73
P21/c (No. 14)
11.6378(2)
19.0767(7)
11.5782(4)
90
111.062(2)
90
2398.76(13)
4
1.790
6.098
C32H32N4Cl2O2Pt
770.60
293
0.710 73
P1h (No. 2)
9.3562(4)
9.8046(3)
13.1146(5)
76.155(2)
83.421(2)
73.285(2)
1117.39(7)
2
1.838
6.541
0.0232
0.0520
0.710 73
P1h (No. 2)
8.9689(9)
9.1365(5)
10.1846(10)
64.328(6)
72.532(4)
67.744(6)
686.82(11)
1
1.795
5.338
0.0294
0.0639
0.710 73
P1h (No. 2)
10.664(2)
10.879(2)
14.388(3)
73.11(3)
78.30(3)
88.88(3)
1562.6(6)
2
1.638
4.696
0.0511
0.1208
Z
F
calcd, g/cm3
µ(Mo KR), mm-1
a
R1
wR2
0.0316
0.0664
b
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
Table 2. Bond Lengths (Å) and Angles (deg) for rac-1a
oxadiazolines can be liberated by a novel route, based on
substitution with 1,2-bis(diphenylphosphino)ethane (dppe) or
with PPh3, and all these results are reported herein.
Pt(1)-Cl(1)
Pt(1)-Cl(1A)
Pt(1)-N(1)
Pt(1)-N(1A)
O(1)-N(2)
2.3019(10)
2.3019(10)
1.999(3)
2.015(3)
1.501(5)
1.350(5)
1.489(5)
1.342(5)
1.492(5)
1.273(5)
N(1A)-C(1A)
N(1A)-C(2A)
N(2)-C(1)
1.477(5)
1.280(5)
1.482(5)
1.476(6)
1.490(5)
1.467(6)
1.515(6)
1.505(5)
1.473(6)
1.462(7)
N(2)-C(3)
Experimental Section
N(2A)-C(1A)
N(2A)-C(3A)
C(1)-C(4)
C(1A)-C(4A)
C(2)-C(10)
C(2A)-C(10A)
O(1)-C(2)
Materials and Instrumentation. Aldehydes and N-alkylhydroxy-
lamines were purchased from Aldrich. Solvents were obtained from
commercial sources and used as received. Nitrones were synthesized
by condensation of the corresponding aldehyde, and N-alkylhydroxy-
lamine, according to the published methods.43 The complexes 1b, 3b,
5b,32 [PtCl4(RCN)2] (R ) Me, Ph),26 and cis-/trans-[PtCl2(PhCN)2]44
were prepared as previously described. C, H, and N elemental analyses
were carried out by the Microanalytical Service of the Instituto Superior
Te´cnico. Melting points were determined on a Kofler table. 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 (ca.
1.28 × 1015 J) Xe atoms. Mass calibration for data system acquisition
was achieved using CsI. Infrared spectra (4000-400 cm-1) were
O(1A)-N(2A)
O(1A)-C(2A)
N(1)-C(1)
N(1)-C(2)
Cl(1)-Pt(1)-Cl(1A)
Cl(1)-Pt(1)-N(1)
Cl(1)-Pt(1)-N(1A)
Cl(1A)-Pt(1)-N(1)
Cl(1A)-Pt(1)-N(1A)
N(1)-Pt(1)-N(1A)
N(2)-O(1)-C(2)
178.15(3) C(1)-N(2)-C(3)
110.8(3)
86.95(8) O(1A)-N(2A)-C(1A) 103.6(3)
91.44(8) O(1A)-N(2A)-C(3A) 103.1(3)
91.31(8) C(1A)-N(2A)-C(3A) 112.4(4)
90.34(8) N(1)-C(1)-N(2)
175.60(11) N(1)-C(1)-C(4)
103.7(3)
110.8(3)
112.9(3)
106.2(3)
N(2)-C(1)-C(4)
N(2A)-O(1A)-C(2A) 106.6(3)
N(1A)-C(1A)-N(2A) 104.1(3)
N(1A)-C(1A)-C(4A) 112.0(3)
N(2A)-C(1A)-C(4A) 112.1(3)
O(1)-C(2)-N(1)
O(1)-C(2)-C(10)
N(1)-C(2)-C(10)
Pt(1)-N(1)-C(1)
Pt(1)-N(1)-C(2)
C(1)-N(1)-C(2)
Pt(1)-N(1A)-C(1A)
Pt(1)-N(1A)-C(2A)
C(1A)-N(1A)-C(2A) 108.8(3)
O(1)-N(2)-C(1)
O(1)-N(2)-C(3)
119.3(2)
132.3(2)
108.4(3)
120.8(2)
129.6(3)
115.1(3)
116.5(3)
128.3(4)
1
recorded on a Bio-Rad FTS 3000MX instrument in KBr pellets. H,
13C{1H}, 31P{1H}, and 195Pt NMR spectra were measured on a Varian
Unity 300 spectrometer at ambient temperature. 31P chemical shifts are
quoted relative to 80% H3PO4 ) 0 ppm. 195Pt chemical shifts are given
relative to aqueous K2[PtCl4] ) -1630 ppm, with half-height line width
in parentheses.
O(1A)-C(2A)-N(1A) 115.5(4)
O(1A)-C(2A)-C(10A) 116.1(4)
N(1A)-C(2A)-C(10A) 128.4(4)
102.5(3)
103.7(3)
located in a difference Fourier map and refined isotropically. An
extinction correction was not applied. Lorentz, polarization, and
absorption corrections were made.48 Scattering factors were from ref
49 Crystal data are given in Table 1, and bond distances and angles in
Table 5.
X-ray Structure Determinations of rac-1a, meso-2a, and rac-3a.
Pale yellow blocks of rac-1a and pale yellow needles of meso-2a and
of rac-3a were grown by diffusion of diethyl ether into CH2Cl2 solutions
of the corresponding complexes. X-ray diffraction data for rac-1a, meso-
2a, and rac-3a were collected with a Nonius KappaCCD diffractometer
using Mo KR radiation (λ ) 0.710 73 Å) and the φ-/ω-scan or φ-scan
data collection mode with a Collect50 collection program. Denzo and
Scalepack51 programs were used for cell refinements and data reduction.
A multiscan absorption correction, based on equivalent reflections
X-ray Structure Determination of rac-5a. Yellow prisms of rac-
5a were obtained by slow evaporation of a dichloromethane/acetone
mixture. Diffraction data were collected on an Enraf-Nonius CAD 4
diffractometer. Cell parameters were obtained from 24 centered
reflections with θ between 11 and 138˚. Range of hkl: h ) -13 to 13;
k ) 0 to 12; l ) -16 to 17. Standard reflections were measured every
60 min and showed practically no change with time ((1%). Diffrac-
tometer data were processed by the program PROFIT45 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 SHELXTL package.46 After that, all reflections
with I < 2σ(I) were excluded from calculations. The refinement was
done by full-matrix least squares based on F2 using the SHELX-97
package.47 All non H-atoms were treated anisotropically. H atoms were
(48) 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, August 1989; USSR
Academy of Sciences: Moscow, 1989; p 155.
(49) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV.
(50) Collect data collection software; Nonius: Delft, The Netherlands, 1999.
(51) Otwinowski, Z.; Minor, W. In Methods in Enzymology, Volume 276,
Macromolecular Crystallography; Carter, C. W., Jr., Sweet, R. M.,
Eds.; Academic Press: New York, 1997; Part A, pp 307-326.
(43) Houben-Weyl, Methoden der Organischen Chemie (Methods of
Organic Chemistry), 4th ed.; Thieme Verlag: Stuttgart, Germany,
1990; Vol. E14b, part 2, p 1372.
(44) Hartley, F. R. The Chemistry of Platinum and Palladium; Applied
Science Publishers: London, 1973.
(45) Strel’tsov, V. A.; Zavodnik, V. E. Kristallografia 1989, 34, 1369.
(46) Sheldrick, G. M. SHELXTL User Manual, rev. 3; Nicolet XRD
Corp.: Madison WI, 1981.
(47) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Addition of Nitrones to Pt-Bound Organonitriles
Inorganic Chemistry, Vol. 40, No. 2, 2001 267
Table 5. Bond Lengths (Å) and Angles (deg) for rac-5a
Table 3. Bond Lengths (Å) and Angles (deg) for meso-2aa
Pt-Cl(1)
2.3085(14)
2.000(4)
1.469(7)
1.356(7)
1.506(7)
N(1)-C(2)
N(2)-C(1)
N(2)-C(3)
C(1)-C(4)
C(2)-C(10)
1.281(8)
1.477(8)
1.469(9)
1.524(8)
1.469(8)
Pt-Cl(1)
2.283(4)
2.295(3)
1.997(8)
1.992(9)
1.298(14)
1.326(13)
1.506(12)
1.473(15)
1.453(14)
1.468(16)
N(2)-C(4)
1.457(17)
1.487(14)
1.265(11)
1.345(11)
1.473(14)
1.474(12)
1.480(11)
1.484(10)
1.482(14)
1.498(10)
Pt-N(1)
Pt-Cl(2)
C(1)-C(11)
N(3)-C(18)
C(18)-O(2)
O(2)-N(4)
N(4)-C(17)
C(17)-N(3)
C(18)-C(19)
N(4)-C(20)
C(17)-C(27)
O(1)-N(2)
O(1)-C(2)
N(1)-C(1)
Pt-N(1)
Pt-N(3)
N(1)-C(2)
C(2)-O(1)
O(1)-N(2)
N(2)-C(1)
C(1)-N(1)
C(2)-C(3)
Cl(1)-Pt-N(1)
92.19(14) O(1)-N(2)-C(1)
180.00
87.81(14) C(1)-N(2)-C(3)
87.81(14) N(1)-C(1)-N(2)
180.00
101.9(4)
103.2(5)
112.8(5)
103.9(5)
109.4(5)
112.5(4)
114.7(5)
Cl(1)-Pt-Cl(1)#1
Cl(1)-Pt-N(1)#1
Cl(1)#1-Pt-N(1)
N(1)-Pt-N(1)#1
Cl(1)#1-Pt-N(1)#1
N(2)-O(1)-C(2)
Pt-N(1)-C(1)
O(1)-N(2)-C(3)
N(1)-C(1)-C(4)
92.19(14) N(2)-C(1)-C(4)
Cl(1)-Pt-Cl(2)
N(1)-Pt-Cl(1)
N(1)-Pt-Cl(2)
N(3)-Pt-Cl(1)
N(3)-Pt-Cl(2)
N(1)-Pt-N(3)
Pt-N(1)-C(2)
Pt-N(1)-C(1)
N(1)-C(2)-O(1) 114.8(9)
C(2)-O(1)-N(2) 106.3(8)
O(1)-N(2)-C(1) 101.9(7)
N(2)-C(1)-N(1) 104.6(9)
C(1)-N(1)-C(2) 108.1(9)
N(1)-C(2)-C(3) 126.4(10)
O(1)-C(2)-C(3) 118.8(10)
O(1)-N(2)-C(4) 104.8(8)
178.89(12) C(1)-N(2)-C(4)
113.3(10)
113.4(9)
112.8(9)
128.9(6)
122.9(6)
115.7(7)
105.9(7)
103.0(8)
103.7(6)
107.1(4)
119.0(3)
134.1(4)
106.5(4)
O(1)-C(2)-N(1)
90.7(3)
88.4(3)
91.6(3)
89.3(3)
177.6(4)
127.9(7)
123.9(7)
N(2)-C(1)-C(11)
C(11)-C(1)-N(1)
Pt-N(3)-C(18)
O(1)-C(2)-C(10) 115.6(5)
Pt-N(1)-C(2)
C(1)-N(1)-C(2)
a Symmetry transformations used to generate equivalent atoms: #1,
-x, -y, -z.
N(1)-C(2)-C(10) 129.7(5)
Pt-N(3)-C(17)
N(3)-C(18)-O(2)
C(18)-O(2)-N(4)
O(2)-N(4)-C(17)
N(4)-C(17)-N(3)
Table 4. Bond Lengths (Å) and Angles (deg) for rac-3a
C(17)-N(3)-C(18) 107.6(7)
N(3)-C(18)-C(19) 128.8(6)
O(2)-C(18)-C(19) 115.5(6)
Pt(1)-Cl(1)
Pt(1)-Cl(1A)
Pt(1)-N(1)
Pt(1)-N(1A)
O(1)-N(2)
2.3065(16)
2.3120(16)
2.015(5)
2.007(6)
1.491(7)
1.354(7)
1.496(7)
1.352(7)
1.484(7)
1.286(8)
N(1A)-C(1A)
N(1A)-C(2A)
N(2)-C(1)
1.474(8)
1.275(8)
1.498(8)
1.477(9)
1.509(8)
1.457(9)
1.508(9)
1.523(9)
1.471(8)
1.489(8)
O(2)-N(4)-C(20)
104.4(8)
N(2)-C(3)
C(17)-N(4)-C(20) 111.5(8)
N(4)-C(17)-C(27) 111.6(6)
C(27)-C(17)-N(3) 113.0(7)
N(2A)-C(1A)
N(2A)-C(3A)
C(1)-C(4)
O(1)-C(2)
O(1A)-N(2A)
O(1A)-C(2A)
N(1)-C(1)
C(1A)-C(4A)
C(2)-C(10)
C(2A)-C(10A)
(ii) Via Reduction. Water (one drop, ca. 0.03 mL) is added to a
slurry of the platinum(IV) complex (1b-6b) (0.10 mmol), PhCH2-
NHOH•HCl (32 mg, 0.20 mmol), and NaHCO3 (21 mg, 0.25 mmol)
in CH2Cl2 (2 mL), and the reaction mixture is stirred at 20-25 °C for
12 h, whereafter the solvent is removed in vacuo to give an oily residue.
The platinum(II) complexes 1a-6a are purified by column chroma-
tography (SiO2/CH2Cl2).
N(1)-C(2)
Cl(1) -Pt(1)-Cl(1A)
Cl(1)-Pt(1)-N(1)
Cl(1)-Pt(1)-N(1A)
Cl(1A)-Pt(1)-N(1)
Cl(1A)-Pt(1)-N(1A)
N(1)-Pt(1)-N(1A)
N(2)-O(1)-C(2)
177.24(5) C(1)-N(2)-C(3)
109.7(5)
87.62(15) O(1A)-N(2A)-C(1A) 101.7(4)
92.13(17) O(1A)-N(2A)-C(3A) 104.1(5)
92.86(15) C(1A)-N(2A)-C(3A) 111.4(5)
87.61(17) N(1)-C(1)-N(2)
175.16(19) N(1)-C(1)-C(4)
106.2(4)
103.8(4)
114.3(5)
112.6(6)
[PtCl2{NdC(Me)O-N(Me)-C(H)Ph}2] (1a) (Two Diastereoiso-
mers, ca. 1:1). The yield is 56% (method ii). Anal. Calcd for C20H24N4-
Cl2O2Pt: C, 38.84; H, 3.91; N, 9.06. Found: C, 39.09; H, 4.07; N,
9.18. FAB+-MS, m/z: 641 [M + Na]+, 618 [M]+, 581 [M - HCl]+,
546 [M - 2HCl]+, 410 [M - 2HCl - PhCHdN(Me)O]+, 369 [M -
2HCl - PhCHdN(Me)O - MeCN]+. Mp: 168 °C. TLC on SiO2: Rf
N(2)-C(1)-C(4)
N(2A)-O(1A)-C(2A) 105.8(5)
N(1A)-C(1A)-N(2A) 103.9(5)
N(1A)-C(1A)-C(4A) 113.7(5)
N(2A)-C(1A)-C(4A) 112.0(5)
Pt(1)-N(1)-C(1)
Pt(1)-N(1)-C(2)
C(1)-N(1)-C(2)
Pt(1)-N(1A)-C(1A)
Pt(1)-N(1A)-C(2A)
125.8(4)
125.4(4)
107.9(5)
125.0(4)
126.3(5)
O(1)-C(2)-N(1)
O(1)-C(2)-C(10)
N(1)-C(2)-C(10)
O(1A)-C(2A)-N(1A) 115.7(5)
O(1A)-C(2A)-C(10A) 115.3(5)
N(1A)-C(2A)-C(10A) 128.9(6)
115.1(5)
117.0(5)
127.9(6)
) 0.28 and 0.32 (eluent CH2Cl2). IR spectrum (selected bands), cm-1
:
1
1656 and 1660 s ν(CdN). H NMR spectrum in CDCl3, δ: 2.47 and
2.49 (two s, 3H of each isomer, C-N(Me)-O), 2.89 (s, br, 3H of each
isomer, dC(Me)O), 5.68 and 5.74 (two s, br, 1H of each isomer,
N-CH-N), 7.40 (m, 4H) and 7.59 (m, 6H) (Ph). 13C{1H} NMR
spectrum in CDCl3, δ: 13.25 and 13.30 (NdC(Me)O), 46.4 (C-
N(Me)-O), 91.9 and 92.0 (br, N-CH-N), 128.1 and 128.2 (o-Ph),
128.4 and 128.5 (m-Ph), 129.3 (p-Ph), 135.7 and 136.2 (ipso-Ph), 167.0
and 167.3 (CdN). 195Pt NMR spectrum in CDCl3, δ: -2210 (400 Hz)
and -2203 (400 Hz).
C(1A)-N(1A)-C(2A) 108.2(5)
O(1)-N(2)-C(1)
O(1)-N(2)-C(3)
102.0(4)
103.8(5)
(MULABS52 or XPREP in SHELXTL v. 5.153), was applied to all data
(Tmax/Tmin was 0.3032/0.2464, 0.7762/0.6174, and 0.4098/0.3516 for
rac-1a, meso-2a, and rac-3a, respectively). Structures were solved by
the Patterson method using the DIRDIF-99 program.54 Structure
refinements were carried out with the SHELXL-97 program.47 All non-
hydrogen atoms were refined anisotropically, and hydrogens were
placed on idealized positions (-CH, Uiso ) 1.2Ueq(CCH); C-H, 1.00
Å; -CH3, Uiso ) 1.5Ueq(CCH3); C-H, 0.98 Å; CHarom., Uiso ) 1.2Ueq-
(Carom.); C-Harom, 0.95 Å). Crystallographic data are summarized in
Table 1, and bond lengths and angles are listed in Tables 2-4.
Preparation of the Platinum(II) Oxadiazoline Complexes. (i) Via
Cycloaddition. A solution of cis/trans-[PtCl2(PhCN)2] (47 mg, 0.10
mmol) and the corresponding nitrone (0.20 mmol) in CH2Cl2 (2 mL)
are stirred for 1 d at room temperature, and the progress of the reaction
is monitored by TLC. After chromatography on SiO2/CH2Cl2 and
evaporation of the solvent, the product (2a, 4a, or 6a) is obtained as a
pale yellow powder.
[PtCl2(NdC(Ph)O-N(Me)-C(H)Ph)2] (2a) (Two Diastereoisomers,
ca. 1:1). The total yield is 75% (method i). Anal. Calcd for C30H28N4-
Cl2O2Pt: C, 48.53; H, 3.80; N, 7.55. Found: C, 48.63; H, 3.81; N,
7.48. FAB+-MS, m/z: 765 [M + Na]+, 742 [M]+, 706 [M - HCl]+,
670 [M - 2HCl]+, 535 [M - 2HCl - PhCHdN(Me)O]+, 431 [M -
2HCl - PhCHdN(Me)O - PhCN]+. Recrystallization from CHCl3/
diethyl ether gave a mixture of colorless and yellow crystals which
were separated mechanically. Data follow for the colorless isomer.
Mp: 191 °C. TLC on SiO2: Rf ) 0.65 (eluent CH2Cl2). IR spectrum
(selected bands), cm-1: 1645 vs ν(CdN) + ν(CdC). 1H NMR spectrum
in CDCl3, δ: 2.96 (s, 3H, C-N(Me)-O), 5.94 (s, br, 1H, N-CH-N),
7.40 (t, 7.8 Hz, 2H), 7.50 (m, 3H), 7.65 (m, 3H), and 8.68 (d, 7.5 Hz,
2H) (two Ph). 13C{1H} NMR spectrum in CDCl3, δ: 46.0 (br,
C-N(Me)-O), 94.7 (br, N-CH-N), 122.3, 128.2, 128.6, 128.8, 129.7,
130.4, 133.4 and 136.0 (two Ph), 164.1 (CdN). 195Pt NMR spectrum
in CDCl3, δ: -2109 (380 Hz). Data follow for the yellow isomer. Mp:
184 °C. TLC on SiO2: Rf ) 0.60 (eluent CH2Cl2). IR spectrum (selected
bands), cm-1 1623 vs ν(CdN) + ν(CdC). 1H NMR spectrum in CDCl3,
δ: 2.99 (s, 3H, C-N(Me)-O), 5.89 (s, br, 1H, N-CH-N), 7.37 (t,
7.6 Hz, 2H), 7.50 (m, 3H), 7.59 (m, 3H), and 8.84 (d, 7.6 Hz, 2H)
(52) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(53) Sheldrick, G. M., SHELXTL, version 5.1; Bruker Analytical X-ray
Systems, Bruker AXS, Inc.: Madison, WI, 1998.
(54) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garcia-Granda, S.;
Gould, R. O.; Israel, R.; Smits, J. M. M. The DIRDIF-99 program
system; Crystallography Laboratory, University of Nijmegen: Nijmegen,
The Netherlands, 1999.

268 Inorganic Chemistry, Vol. 40, No. 2, 2001
Wagner et al.
(two Ph). 13C{1H} NMR spectrum in CDCl3, δ: 46.3 (br, C-N(Me)-
O), 94.8 (br, N-CH-N), 122.5, 128.3, 128.6, 128.7, 129.6, 130.6, 133.6
and 136.1 (two Ph), 163.5 (CdN). 195Pt NMR spectrum in CDCl3, δ:
- 2121 (480 Hz).
[PtCl2{NdC(Ph)O-N(CH2Ph)-C(H)Ph}2] (6a) (Two Diastereo-
isomers 1:1). The yield is 60% (method i). Anal. Calcd for C42H36N4-
Cl2O2Pt: C, 56.38; H, 4.06; N, 6.26. Found: C, 56.52; H, 4.14; N,
6.19. FAB+-MS, m/z: 917 [M + Na]+, 895 [M]+, 859 [M - Cl]+,
822 [M - 2HCl]+, 611 [M - 2HCl - PhCHdN(CH2Ph)O]+, 507 [M
- 2HCl - PhCHdN(CH2Ph)O - PhCN]+. Mp: 164 °C. TLC on
SiO2: Rf ) 0.60 and 0.73 (eluent CH2Cl2). IR spectrum (selected bands),
[PtCl2(NdC(Me)O-N(Me)-C(H)(p-C6H4Me)2] (3a) (Two Di-
astereoisomers, ca. 1:1). The yield is 54% (method ii). Anal. Calcd for
C22H28N4Cl2O2Pt: C, 40.87; H, 4.37; N, 8.67. Found: C, 41.00; H,
4.38; N, 8.63. FAB+-MS, m/z: 669 [M + Na]+, 646 [M]+, 610 [M -
HCl]+, 574 [M - 2Cl]+, 425 [M - 2HCl - (MeC6H4)CHdN(Me)O]+,
384 [M - 2HCl - (MeC6H4)CHdN(Me)O - MeCN]+. Recrystalli-
zation from CH2Cl2/diethyl ether/pentane gave a mixture of pale yellow
needles and yellow plates which were separated mechanically. Data
follow for the pale yellow needles. Mp: 131 °C. TLC on SiO2: Rf )
0.31 (eluent CH2Cl2). IR spectrum (selected bands), cm-1: 1660 and
1
cm-1: 1622 s ν(CdN) + ν(CdC). H NMR spectrum in CDCl3, δ:
4.17, 4.19, 4.39, and 4.40 (four d, 12.7 Hz each, 4H, CH2Ph), 6.18 and
6.21 (two s, 1H each, N-CH-N), 7.30-7.74 (m, 26H), 8.73 (d, 7.2
Hz, 2H), and 8.82 (d, 7.4 Hz, 2H)(Ph, CH2Ph and NdC(Ph). 13C{1H}
NMR spectrum in CDCl3, δ: 62.4 and 62.6 (CH2Ph), 92.0 (N-CH-
N), 122.1 and 122.4, 128.3, 128.4, 128.5, 128.6, 129.3, 129.8, 129.9,
130.7, 132.0 and 132.1, 133.5 and 133.6, 136.0 (NdCPh, Ph and
CH2Ph), 163.9 (CdN). 195Pt NMR spectrum in CDCl3, δ: -2115 (380
Hz) and -2129 (520 Hz).
1
1651 s ν(CdN), 322 m ν(Pt-Cl). H NMR spectrum in CDCl3, δ:
2.40 (s, 3H, C6H4Me), 2.47 (s, 3H, C-N(Me)-O), 2.87 (s, br, 3H,
dC(Me)O), 5.63 (s, br, 1H, N-CH-N), 7.22 (d, 7.2 Hz, 2H) and 7.48
(d, 7.8 Hz, 2H) (C6H4Me). 13C{1H} NMR spectrum in CDCl3, δ: 13.25
(NdC(Me)O), 21.4 (C6H4Me), 46.3 (C-N(Me)-O), 91.9 (br, N-CH-
N), 128.1 (CH), 129.2 (CH), 135.5 (Cq), 139.0 (Cq) (C6H4Me), 166.8
(CdN). 195Pt NMR spectrum in CDCl3, δ: -2205 (350 Hz). Data follow
for the yellow plates. Mp: 157 °C. TLC on SiO2: Rf ) 0.38 (eluent
CH2Cl2). IR spectrum (selected bands), cm-1: 1647 s ν(CdN), 335 m
ν(Pt-Cl). 1H NMR spectrum in CDCl3, δ: 2.40 (s, 3H, C6H4Me), 2.49
(s, 3H, C-N(Me)-O), 2.87 (s, br, 3H, dC(Me)O), 5.69 (s, br, 1H,
N-CH-N), 7.20 (d, 7.2 Hz, 2H) and 7.48 (d, 7.8 Hz, 2H) (C6H4Me).
13C{1H} NMR spectrum in CDCl3, δ: 13.30 (NdC(Me)O), 21.4
(C6H4Me), 46.3 (C-N(Me)-O), 91.8 (br, N-CH-N), 128.0 (CH),
129.1 (CH), 135.5 (Cq), 139.1 (Cq), 166.8 (CdN). 195Pt NMR spectrum
in CDCl3, δ: -2200 (350 Hz).
Preparation of the Platinum(IV) Oxadiazoline Complexes. (i) Via
Cycloaddition. A mixture of [PtCl4(PhCN)2] (42 mg, 0.10 mmol) with
the corresponding nitrone (0.20 mmol) in CH2Cl2 (2 mL) is stirred for
1.5 h at room temperature, whereupon the initial suspension became a
homogeneous yellow solution. After chromatography on SiO2/CH2Cl2
and evaporation of the solvent, the product is obtained as a pale yellow
powder. Yields given below are relevant to this method.
(ii) Via Chlorination of Pt(II) Complexes. Chlorination of 1a-6a
is performed by passing an excess of Cl2 through a CDCl3 solution of
0.03 mmol of the corresponding complex at room temperature for 10-
1
15 s, and after 5 min the reaction mixture is monitored by H NMR
spectroscopy. The formation of 1b-6b is almost quantitative.
[PtCl4{NdC(Ph)O-N(Me)-C(H)Ph}2] (2b) (Two Diastereoisomers
1:1). The yield is 82%. Anal. Calcd for C30H28N4Cl4O2Pt: C, 44.30;
H, 3.47; N, 6.89. Found: C, 44.20; H, 3.31; N, 6.89. FAB+-MS, m/z:
671 [M - 4Cl - 2H]+. Mp: 173 °C. TLC on SiO2: Rf ) 0.56 (eluent
pentane/CH2Cl2, 1:2). IR spectrum (selected bands), cm-1: 1607 and
1573 s ν(CdN) + ν(CdC). 1H NMR spectrum in CDCl3, δ: 3.09 and
[PtCl2{NdC(Ph)O-N(Me)-C(H)(p-C6H4Me)}2] (4a) (Two Di-
astereoisomers, ca. 1:1). The yields are 71% (method i) and 45%
(method ii). Anal. Calcd for C32H32N4Cl2O2Pt: C, 49.87; H, 4.19; N,
7.27. Found: C, 49.64; H, 4.11; N, 7.16. FAB+-MS, m/z: 793 [M +
Na]+, 770 [M]+, 735 [M - Cl]+, 698 [M - 2HCl]+, 549 [M - 2HCl
- (MeC6H4)CHdN(Me)O]+, 446 [M - 2HCl - (MeC6H4)CHd
N(Me)O - PhCN]+. Mp: 178 °C (dec). TLC on SiO2: Rf ) 0.54 and
0.62 (eluent CH2Cl2). IR spectrum (selected bands), cm-1: 1641 and
1627 s ν(CdN) + ν(CdC). 1H NMR spectrum in CDCl3, δ: 2.43 and
2.46 (two s, 3H each, C6H4Me), 2.95 and 2.98 (two s, 3H each,
C-N(Me)-O), 5.87 and 5.91 (two s, broad, 1H each, N-CH-N), 7.29
(m, 2H of each isomer) 7.48 and 7.56 (two d, 7.6 Hz, 2H of each
isomer) (C6H4Me), 7.40 (m, 2H of each isomer), 7.63 (m, 1H of each
isomer), 8.70 and 8.83 (two d, 7.5 Hz, 1H of each isomer) (Ph). 13C-
{1H} NMR spectrum in CDCl3, δ: 21.5 (C6H4Me), 45.9 and 46.1 (C-
N(Me)-O), 94.7 (N-CH-N), 122.4 and 122.6 (NdCPh), 128.2
(C6H4Me), 128.6 and 128.7 (NdCPh), 129.2 and 129.3 (C6H4Me),
130.5 and 130.7 (NdCPh), 133.1 and 133.2 (C6H4Me), 133.4 and 133.5
(NdCPh), 139.3 and 139.5 (C6H4Me), 163.4 and 163.9 (CdN). 195Pt
NMR spectrum in CDCl3, δ: -2104 (650 Hz) and -2113 (420 Hz).
3
3.10 (two s, 3H each, C-N(Me)-O), 6.65 and 6.66 (two s + d, JPtH
13.2 Hz each, 2H, N-CH-N), 7.35-7.51 (m, 14H), 7.66 (m, 2H),
and 8.18 (m, 4H) (Ph and NdC(Ph). 13C{1H} NMR spectrum in CDCl3,
δ: 46.5 (C-N(Me)-O), 92.56 and 92.73 (2JPtC 20.3 Hz, N-CH-N),
123.61 and 123.68 (NdCPh), 126.03 (o-Ph), 127.70 (NdCPh), 128.34
and 128.37 (m-Ph), 128.77 and 128.81 (p-Ph), 131.90 and 131.96 (Nd
CPh), 133.97 and 134.04 (NdCPh), 138.30 and 138.45 (ipso-Ph),
172.56 and 172.40 (CdN). 195Pt NMR spectrum in CDCl3, δ: -126
(390 Hz).
[PtCl4{NdC(Ph)O-N(Me)-C(H)(p-C6H4Me)}2] (4b) (Two Di-
astereoisomers 1:1). The yield is 71%. Anal. Calcd for C32H32N4Cl4O2-
Pt: C, 45.67; H, 3.83; N, 6.66. Found: C, 45.53; H, 3.82; N, 6.60.
FAB+-MS, m/z: 863 [M + Na]+, 841 [M + H]+, 805 [M - Cl]+, 792
[M - 2Cl + Na]+, 770 [M - 2Cl]+, 735 [M - 3Cl]+, 698 [M - 4Cl
- 2H]+. Mp: 169 °C (dec). TLC on SiO2: Rf ) 0.59 (eluent pentane/
CH2Cl2, 1:2). IR spectrum (selected bands), cm-1: 1608 and 1577 s
1
ν(CdN) + ν(CdC). H NMR spectrum in CDCl3, δ: 2.33 and 2.34
[PtCl2(NdC(Me)O-N(CH2Ph)-C(H)Ph)2] (5a) (Two Diastereo-
isomers, ca. 2:1). The yield is 70% (method ii). Anal. Calcd for
C32H32N4Cl2O2Pt: C, 49.88; H, 4.19; N, 7.27. Found: C, 50.32; H,
4.20; N, 7.43. FAB+-MS, m/z: 792 [M + Na]+, 770 [M + H]+, 734
[M - HCl]+. Mp: 180 °C. TLC on SiO2: Rf ) 0.71 (eluent CH2Cl2).
(two s, 3H each, C6H4Me), 3.07 and 3.08 (two s, 3H each, C-N(Me)-
3
O), 6.60 and 6.61 (two s + d, JPtH 12.6 Hz each, 2H, N-CH-N),
7.17 (m, 2H of each isomer) and 7.31 (m, 2H of each isomer) (C6H4-
Me), 7.45 (m, 2H of each isomer), 7.65 (m, 1H of each isomer), 8.17
(m, 2H of each isomer) (Ph). 13C{1H} NMR spectrum in CDCl3, δ:
21.2 (C6H4Me), 46.4 (C-N(Me)-O), 92.6 and 92.7 (N-CH-N), 123.7
(NdCPh), 125.9 (C6H4Me), 127.7 (NdCPh), 129.09, and 129.13 (C6H4-
Me), 131.88 and 131.92 (NdCPh), 133.89 and 133.97 (NdCPh), 134.0
(C6H4Me), 138.6 (C6H4Me), 172.2 (CdN). 195Pt NMR spectrum in
CDCl3, δ: -123 (420 Hz).
:
IR spectrum (selected bands), cm-1 1653 s ν(CdN). 1H NMR
spectrum in CDCl3, δ: 2.53 (minor) and 2.56 (major) (two s, 3H of
each isomer, dC(Me)O), 4.08 (d, 12.3 Hz, 1H of each isomer), 4.30
(d, 12.3 Hz, 1H of each isomer) (CH2Ph), 6.00 and 6.04 (two s, br, 1H
of each isomer, N-CH-N), 7.32-7.50 (m, 10H of each isomer, Ph
and CH2Ph). 13C{1H} NMR spectrum in CDCl3, δ: 13.3 (minor) and
13.4 (major) (NdC(Me)O), 62.5 (major) and 62.7 (minor) (CH2Ph),
88.9 (major) and 89.1 (minor) (br, N-CH-N), 127.8 (major) and 127.9
(minor) (o-Ph), 128.3 (m-Ph), 128.4 and 128.7 (p-Ph and p-PhCH2),
129.0 (PhCH2), 129.67 (minor) and 129.73 (major) (PhCH2), 133.73
(major) and 133.75 (minor) (ipso-PhCH2), 136.3 (major) and 136.4
(minor) (ipso-Ph), 167.6 (major) and 167.8 (minor) (CdN). 195Pt NMR
spectrum CDCl3, δ: -2204 (640 Hz).
[PtCl4{NdC(Ph)O-N(CH2Ph)-C(H)Ph}2] (6b) (Two Diastereo-
isomers 1:1). The yield is 84%. Anal. Calcd for C42H36N4Cl4O2Pt: C,
52.24; H, 3.76; N, 5.80. Found: C, 51.95; H, 3.79; N, 5.68. FAB+-
MS, m/z: 966 [M + H]+, 917 [M - 2HCl + Na]+, 894 [M - 2Cl -
H]+, 857 [M - 3Cl - 2H]+, 822 [M - 4Cl - 2H]+, 610 [M - 4Cl -
2H - PhCHdN(CH2Ph)O]+, 507 [M - 4Cl - 2H - PhCHdN(CH2-
Ph)O - PhCN]+. Mp: 136 °C. TLC on SiO2: Rf ) 0.42 (eluent

Addition of Nitrones to Pt-Bound Organonitriles
Inorganic Chemistry, Vol. 40, No. 2, 2001 269
Scheme 2. Observed Transformationsa
and other nitrones by its ligation to the platinum(II) center and
the formation of (∆4-1,2,4-oxadiazoline)PtII complexes 2a, 4a,
and 6a (Scheme 1) was achieved faster than in the case of free
PhCN and under much milder conditions. In particular, the
process takes only 1 d at 20-25 °C to furnish 2a. Furthermore,
an additional strong activation of benzonitrile was reached by
application of the platinum(IV) complex [PtCl4(PhCN)2] in the
reaction with -ON+(Me)dC(H)(Ph), and the end point in the
formation of the oxadiazoline compound 2b, under conditions
similar to the preparative ones, was detected by 1H NMR
spectroscopy already after 1 h at room temperature. The final
products from the cycloaddition to both platinum(II) and
platinum(IV) nitrile complexes were purified by chromatography
on SiO2 and obtained in the solid state as meso-(R,S) and rac-
(S,S)/(R,R) diastereoisomers.
It is remarkable that the alteration of the substituent R at RCN
(from acceptor Ph to donor Me)-like the change in the oxidation
state of the metal ion-plays a dramatic role on the reactivity.
Thus, the acetonitrile complex [PtCl4(MeCN)2] and -ON+(Me)d
C(H)(Ph) give the appropriate oxadiazoline complex after 6 h
at room temperature,32 while the corresponding platinum(II)
compound [PtCl2(MeCN)2] does not react with the nitrone for
2 weeks at room temperature, whereas on heating at 56 °C for
2 d a variety of unidentified products, with no oxadiazoline
compound, were observed by 1H and 13C{1H} NMR monitoring.
In connection to these experiments attention should be drawn
to the work by Hermkens et al.,64 who established that free
acetonitrile does not react with nitrones even under harsh
conditions (high pressure, reflux, 3 d).
a R/R1/R2/R3 ) Me/H/Ph/Me (1), Ph/H/Ph/Me (2), Me/H/p-MeC6H4/
Me (3), Ph/H/p-MeC6H4/Me (4), Me/H/Ph/CH2Ph (5), and Ph/H/Ph/
CH2Ph (6). For syntheses of 1b, 3b, and 5b, see ref 32.
pentane/CH2Cl2, 1:1). IR spectrum (selected bands), cm-1: 1607 and
1
1574 s ν(CdN) + ν(CdC). H NMR spectrum in CDCl3, δ: 4.44,
4.46, 4.51 and 4.52 (four d, 12.5 Hz each, 4H, CH2Ph), 6.78 and 6.79
(two s + d, 3JPtH 13.0 Hz each, 1H, N-CH-N), 7.28-7.50 (m, 20H),
7.59 (m, 4H), 7.66 (m, 2H) and 8.20 (m, 4H)(Ph, CH2Ph and NdC(Ph).
13C{1H} NMR spectrum in CDCl3, δ: 61.5 and 61.6 (CH2Ph), 90.5
and 90.6 (N-CH-N), 123.66 and 123.70 (NdCPh), 126.08 (Ph),
127.72 (NdCPh), 128.30 and 128.38 (Ph), 128.65, 128.68, and 128.81
(Ph and CH2Ph), 129.81 and 129.86 (CH2Ph), 131.98 and 132.05 (Nd
CPh), 133.61 and 133.67 (CH2Ph), 134.00 and 134.10 (NdCPh),
138.34 and 138.60 (Ph), 172.7 (CdN). 195Pt NMR spectrum in CDCl3,
δ: -112 (420 Hz).
Mutual Redox Interconversions of Pt(II) and Pt(IV)
Oxadiazoline Complexes. In the current work, two types of
synthetic strategy to obtain platinum(II) ∆4-1,2,4-oxadiazoline
complexes, i.e. [2 + 3] cycloaddition of nitrones to (organo-
nitrile)PtII species (described above) and reduction of [PtCl4-
Results and Discussion
Cycloaddition Reaction. For this study we choose the
platinum(II) complexes cis/trans-[PtCl2(RCN)2], containing
donor (R ) Me) and acceptor (R ) Ph) radicals attached to the
nitrile group, and the nitrones -ON+(R3)dC(R1)(R2) [R1/R2/
R3 ) H/Ph/Me, H/p-MeC6H4/Me or H/Ph/CH2Ph ] (see Scheme
2). For comparative purposes, we have also investigated if the
[2 + 3] cycloaddition occurs in the case of the corresponding
platinum(IV) complexes [PtCl4(PhCN)2].
Couplings of nitrones and free organonitriles RCN bearing
electron-withdrawing groups R are known from organic
chemistry.55-63 In particular, it has been reported that the
reaction of -ON+(Me)dC(H)(Ph) and neat benzonitrile requires
rather harsh reaction conditions (10 d, 110 °C) to give the
corresponding 2-methyl-3,5-diphenyl-∆4-1,2,4-oxadiazoline in
moderate yield (57%).64 Our experiments indicate that benzoni-
trile is activated toward the [2 + 3] cycloaddition with the same
{NdC(R)O-N(R3)-C(R1)(R2)}2] to give the appropriate Pt(II)
derivatives, were tested. Whereas (oxadiazoline)PtII complexes
derived from acetonitrile are not accessible by direct cycload-
dition of a nitrone to [PtCl2(MeCN)2], we succeded (Scheme
2) in their synthesis by a selective reduction of the corresponding
Pt(IV) complexes with PhCH2NHOH as the reducing agent
(other reducing agents, e.g. cyclopentadiene, triphenylphosphine,
trimethyl phosphite, or cysteine, gave the (oxadiazoline)PtII
compounds contaminated with a large amount of unidentified
byproducts). The reverse reaction-conversion of [PtCl2{Nd
C(R)O-N(R3)-C(R1)(R2)}2] to afford the platinum(IV) com-
plexes 1b-6b (Scheme 2)-was carried out by addition of Cl2
to solutions of 1a-6a in CDCl3, and products were identified
1
by H NMR spectroscopy.
(55) Yu, Y.; Ohno, M.; Eguchi, S. J. Chem. Soc., Chem. Commun. 1994,
331.
(56) Yu, Y.; Watanabe, N.; Ohno, M.; Eguchi, S. J. Chem. Soc., Perkin
Trans. 1 1995, 11, 1417.
(57) Yu, Y.; Fujita, H.; Ohno, M.; Eguchi, S. Synthesis 1995, 498.
(58) van den Broek, L. A. G. M. Tetrahedron 1996, 52, 4467.
(59) Sang, H.; Janzen, E. G.; Poyer, L. J. Chem. Soc., Perkin Trans. 2
1996, 1183.
(60) Plate, R.; Hermkens, P. H. H.; Smits, J. M. M.; Nivard, R. J. F.;
Ottenheijm, H. C. J. J. Org. Chem. 1987, 52, 1047.
(61) Smits, J. M. M.; Beurskens, P. T.; Smits, J. R. M.; Plate, R.;
Ottenheijm, H. J. Crystallogr. Spectrosc. Res. 1988, 18, 15.
(62) Eberson, L.; Hartshorn, C. M.; Hartshorn, M. P.; McCullough, J. J.
Synth. Commun. 1997, 27, 3779.
All isolated complexes derived from both the direct addition
of nitrones (see previous section) and from the reduction
experiments were characterized by elemental analyses, FAB
1
mass spectrometry, and IR and H, 13C{1H}, and 195Pt NMR
spectroscopies (see Experimental Section); X-ray structure
determinations were performed for four oxadiazoline Pt(II)
complexes (meso-2a was obtained from the addition, while rac-
1a, rac-3a, and rac-5a were from the reduction experiments).
In all these compounds, the coordination polyhedron of platinum
is slightly distorted square-planar with the oxadiazoline ligands
in trans positions to each other. In the meso-(R,S)-2a complex
(Figure 1) and in rac-(S,S)+(R,R)-5a (Figure 4), the oxadiazoline
rings, similar to the Pt(IV) complex of our previous study,32
adopt half-chair conformations that are slightly twisted around
(63) Eberson, L.; McCullough, J. J.; Hartshorn, C. M.; Hartshorn, M. P. J.
Chem. Soc., Perkin Trans. 2 1998, 1, 41.
(64) Hermkens, P. H. H.; van Maarseveen, J. H.; Kruse, C. G.; Scheeren,
H. W. Tetrahedron 1988, 44, 6491.

270 Inorganic Chemistry, Vol. 40, No. 2, 2001
Wagner et al.
Figure 3. PLATON view of rac-[PtCl2(NdC(Me)O-N(Me)-C(H)-
(p-C6H4Me)2] (3a) with atomic numbering scheme. The (S,S)-enanti-
omer is shown.
Figure 1. PLATON view of (R,S)-meso-[PtCl2(NdC(Ph)O-N-
(Me)-C(H)Ph)2] (2a) with atomic numbering scheme.
Figure 4. PLATON view of rac-[PtCl2(NdC(Me)O-N(CH2Ph)-C-
(H)Ph)2] (5a) with atomic numbering scheme. The (S,S)-enantiomer is
shown.
Figure 2. PLATON view of rac-[PtCl2{NdC(Me)O-N(Me)-C(H)-
Ph}2] (1a) with atomic numbering scheme. The (S,S)-enantiomer is
shown.
Liberation of ∆4-1,2,4-Oxadiazolines from the Platinum-
(II) Complexes. Although liberation of the ∆4-1,2,4-oxadiazo-
line is facile when the platinum(IV) complexes [PtCl4-
the N(2)-C(1) (for 2a) or the N(2)-C(1) or N(4)-C(17) (for
5a) bonds. The rac-(S,S)+(R,R)-1a complex (Figure 2) occupies
an intermediate position with only one ring twisted on N(2)-
C(1), whereas the other ring is in the envelope conformation
on N(2A). In the rac-(S,S)+(R,R)-3a complex (Figure 3), even
both oxadiazoline rings, similar to the few structurally charac-
terized purely organic oxadiazoline compounds,61-63 were found
in an envelope conformation with the N(2) or N(2A) atom at
the “flap”. This shows that there is no general preference for
one conformation in the Pt(II)-oxadiazoline complexes, and
interconversion between the conformers can occur easily.
The geometrical parameters of the oxadiazoline rings in the
four Pt(II) complexes are the same within 3σ as those in the
previously described Pt(IV) complex32 and also in a few known
examples of structurally characterized uncoordinated ∆4-1,2,4-
oxadiazolines.61-63 All other bonds and angles (Tables 2-5)
are also of normal values.65,66
{NdC(Me)O-N(R3)-C(R1)(R2)}2] are treated with pyridine,32
it does not proceed easily in the case of corresponding platinum-
(II) derivatives, thus indicating a stronger Pt-N(imine) bond
in the latter group of compounds. Indeed, we were unable to
substitute the heterocyclic ligands from the [PtCl2(∆4-1,2,4-
oxadiazoline)2] with pyridine, thiourea, and also with such strong
chelating agents as 2,2′-bipyridine and cycloheptanedione
dioxime under heating conditions. The release was successful,
however, with dppe or PPh3 though slow even on heating in
the presence of a large excess of the ligand.
For example, in the case of 2a two diastereoisomers were
1
mechanically separated and in CDCl3 gave distinct H NMR
spectra. It was observed that the isomers do not interconvert to
each other on heating in this solvent for 2 d at 56 °C. Addition
of 1 equiv of dppe to a mixture of the two isomers (1 equiv
each), followed by heating to ca. 56 °C of the solution formed,
(65) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(66) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
1
resulted (as revealed by H and 31P{1H} NMR monitoring of
the progress of the reaction) in a slow substitution to generate
the previously characterized64 oxadiazoline (1H NMR spectrum,

Addition of Nitrones to Pt-Bound Organonitriles
Inorganic Chemistry, Vol. 40, No. 2, 2001 271
δ: 5.77 N-CH-N, 8.04 Ph; remaining Ph’s signals overlapping
with peaks due to dppe) along with the well-known [PtCl2-
(dppe)]67,68 complex. Interestingly, the reactivity of the isomers
toward the substitution is different and one (1H NMR spectrum,
δ: 5.94 N-CH-N, 8.68 Ph) reacts more readily than the other
one (1H NMR spectrum, δ: 5.89 N-CH-N, 8.84 Ph; the trans-
(R,S)-structure of this complex was determined). To speed up
the reaction, a further 10 equiv of dppe was added, and the
completion of the substitution is observed after 8 d at 56 °C.
Concluding Remarks. By extension to a platinum(II) center
the previously observed activation, by a platinum(IV) site, of
organonitriles toward nucleophilic addition of a nitrone, this
work demonstrates a considerable generality for this reaction
showing that it can occur for a much weaker activating (and
more easily available) metal center than the initially applied
rather strong Lewis acid Pt(IV) system. The expected weaker
activation of the organonitrile by the platinum(II) center is
corroborated by the lower ν(NtC) shift experienced on
coordination (e.g. for platinum(II) complexes ∆ ) ν(NtC)coord
- ν(NtC)free ) ca. 50 cm-1, while for the appropriate platinum-
(IV) complexes ∆ ) ca. 100 cm-1), which, nevertheless, is
sufficient for such a type of activation, suggesting that the
cycloaddition reaction can occur at a much wider variety of
binding transition-metal centers. The reduced activation by the
platinum(II) site is also indicated by the lower reaction rate and
by the emergence of a selectivity toward the type of organonitrile
substituent R group, which becomes a controlling factor of the
reaction that is then prevented by an electron-donor R moiety
such as an alkyl.
The reaction can be applied to the convenient synthesis, under
mild conditions and using easily prepared platinum(II) com-
pounds, of the still rare and previously inaccessible (or difficult
to obtain) ∆4-1,2,4-oxadiazoline compounds whose chemistry
can then be further developed. However, for optically pure
products, the enantioselectivity has to be promoted, and for this
purpose the studies now reported on the basic factors controlling
the reaction constitute an important basis and starting stage to
be further developed. The different kinetic lability, now
recognized, of the ligated oxadiazoline toward displacement at
the diastereoisomers of its complexes should be further explored
with the aim of getting pure diastereoisomers.
Acknowledgment. G.W. is grateful to the PRAXIS XXI
program for a fellowship (BPD11779/97). A.J.L.P. thanks the
FCT (Foundation for Science and Technology) and the PRAXIS
XXI program for financial support. M.H. and V.Yu.K. are
grateful to the Nordic Council of Ministers for a grant. V.Yu.K.
is very much obliged to the PRAXIS XXI program (grant
BCC16428/98). We also thank Mr. I. Marques (Centro de
Qu´ımica Estrutural) for the FAB-MS measurements and Prof.
V. K. Belsky (L. Ya. Karpov Physicochemical Institute,
Moscow) for the X-ray diffraction analysis of rac-5a.
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes [PtCl2{NdC(Me)O-N(Me)-C(H)Ph}2]
(rac-1a), [PtCl2(NdC(Ph)O-N(Me)-C(H)Ph)2] (meso-2a), [PtCl2-
(NdC(Me)O-N(Me)-C(H)(p-C6H4Me))2] (rac-3a), and [PtCl2-
(NdC(Me)O-N(CH2Ph)-C(H)Ph)2] (rac-5a). This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
(67) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. Chem. Soc., Dalton
Trans. 1976, 439.
(68) Lindner, E.; Fawzi, R.; Mayer, H. A.; Eichele, K.; Hiller, W.
Organometallics 1992, 11, 1033.
IC000477B