Bis(2,6-dinitroaryl)platinum(II) complexes. Cis/trans isomerization

Article abstract of DOI:10.1021/om060398t

The complexes cis-[Pt(κ²-Aryl)(κ¹-Aryl)L] (κ²-Aryl = κ²-(C,O)-C₆(NO ₂)₂-2,6-(OMe)₃, κ¹-Aryl = κ¹-(C)-C₆(NO₂)₂-2,6-(OMe) ₃, L = S-dmso (2cis), XyNC (4cis; Xy = 2,6-Me₂C ₆H₄), CO (5cis), PPh₃ (7cis)) have been obtained by reacting at room temperature cis-[Pt(κ²-Aryl) (κ¹-Aryl)(OH₂)] (1cis) with dimethyl sulfoxide (dmso; 1:1 or excess), XyNC (1:1), or CO (excess) or cis-(Me₄N) [Pt(κ²-Aryl)(κ¹-Aryl)Cl] with PPh₃ (1:1), respectively. The room-temperature reaction of 1cis with XyNC (1:2), of 5cis with PPh₃ (1:1), or of cis-(Me₄N) [Pt(κ²-Aryl)(κ¹-Aryl)Cl] with PPh₃ (1:2) gives cis-[Pt(κ¹-Aryl)₂LL′] (L = L′ = XyNC (3cis), PPh₃ (8cis); L = CO, L′ = PPh ₃ (6cis)). Complexes 3cis, 4cis, and 5cis isomerize on heating in solution or in the solid state to give 3trans, 4trans, and 5trans, respectively, while 6cis and 8cis decompose to give 7cis instead of their trans isomers; these, however, can be prepared by reacting 5trans or 6trans with PPh ₃ in molar ratios of 1:1 or 1:2, respectively. When they are heated, 6trans and 8trans also descompose to 7cis, while 2cis and cis- [Pt(κ²-Aryl)(κ¹-Aryl)L] (L = H₂O (1cis), PhCN, tht) decompose to a mixture of unidentified products (1cis) or are recovered unchanged. These results, and others reported in the literature, on the stability of cis- and trans-diaryl complexes of platinum or palladium can be explained as the result of two competing factors, transphobia and the steric requirements of the ligands. The X-ray crystal structures of 2cis, 3cis, 3trans, 4trans·CHCl₃, 5cis·CH₂Cl₂, 5cis·0.Shexane, 6cis, 6trans·CHCl₃, 7cis-Me ₂CO, and 8trans·0.5CHCl₃ have been determined.

Full text of DOI:10.1021/om060398t

Organometallics 2006, 25, 4247-4259
4247
Articles
Bis(2,6-dinitroaryl)platinum(II) Complexes. Cis/Trans Isomerization†
Jose´ Vicente,* Aurelia Arcas,‡ and Mar´ıa-Dolores Ga´lvez-Lo´pez
Grupo de Qu´ımica Organometa´lica, Departamento de Qu´ımica Inorga´nica,
Facultad de Qu´ımica, UniVersidad de Murcia, Aptdo. 4021, E-30071 Murcia, Spain
Peter G. Jones*
Institut fu¨r Anorganische und Analytische Chemie, Technische UniVersita¨t Braunschweig, Postfach 3329,
38023 Braunschweig, Germany
ReceiVed May 9, 2006
The complexes cis-[Pt(κ2-Aryl)(κ1-Aryl)L] (κ2-Aryl ) κ2-(C,O)-C6(NO2)2-2,6-(OMe)3, κ1-Aryl ) κ1-
(C)-C6(NO2)2-2,6-(OMe)3, L ) S-dmso (2cis), XyNC (4cis; Xy ) 2,6-Me2C6H4), CO (5cis), PPh3 (7cis))
have been obtained by reacting at room temperature cis-[Pt(κ2-Aryl)(κ1-Aryl)(OH2)] (1cis) with dimethyl
sulfoxide (dmso; 1:1 or excess), XyNC (1:1), or CO (excess) or cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] with
PPh3 (1:1), respectively. The room-temperature reaction of 1cis with XyNC (1:2), of 5cis with PPh3
(1:1), or of cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] with PPh3 (1:2) gives cis-[Pt(κ1-Aryl)2LL′] (L ) L′ )
XyNC (3cis), PPh3 (8cis); L ) CO, L′ ) PPh3 (6cis)). Complexes 3cis, 4cis, and 5cis isomerize on
heating in solution or in the solid state to give 3trans, 4trans, and 5trans, respectively, while 6cis and
8cis decompose to give 7cis instead of their trans isomers; these, however, can be prepared by reacting
5trans or 6trans with PPh3 in molar ratios of 1:1 or 1:2, respectively. When they are heated, 6trans and
8trans also descompose to 7cis, while 2cis and cis-[Pt(κ2-Aryl)(κ1-Aryl)L] (L ) H2O (1cis), PhCN, tht)
decompose to a mixture of unidentified products (1cis) or are recovered unchanged. These results, and
others reported in the literature, on the stability of cis- and trans-diaryl complexes of platinum or palladium
can be explained as the result of two competing factors, transphobia and the steric requirements of the
ligands. The X-ray crystal structures of 2cis, 3cis, 3trans, 4trans‚CHCl3, 5cis‚CH2Cl2, 5cis‚0.5hexane,
6cis, 6trans‚CHCl3, 7cis‚Me2CO, and 8trans‚0.5CHCl3 have been determined.
sponding [Sn(aryl)Me3] compound at 90-100 °C, have a trans
geometry when aryl ) 2,3,4,5,6-pentamethylphenyl, 2,4,6-
trimethylphenyl, 2,6-dimethylphenyl and a cis geometry for
those complexes with phenyl and 2-tolyl ligands. DFT calcula-
tion results agreed well with the experimental data.3 These
complexes react in refluxing toluene with PEt3 to give [Pt(aryl)2-
(PEt3)2] with the same geometry as the dmso precursors.4
The above controversy gives a good picture of how we have
failed to understand the relative stability of geometric isomers
in Pt(II) complexes and, in particular, of the diaryl derivatives.
The reasons for this situation are the limited studies devoted to
isomerization reactions and the inertness of Pt(II) complexes.
The latter means that the isolated complex in many reactions
at moderate temperatures and reaction times is usually the kinetic
product, often with retention of the geometry around the
platinum center, but not the thermodynamic product.5 Thus, cis-
or trans-[Pt(o-tolyl)2(PEt3)2] could be prepared by reacting cis-
or trans-[PtCl2(PEt3)2], respectively, with 2-tolyllithium at room
temperature.6 In addition, the complex cis-[Pt(C6F5)2(CO)(tht)],
obtained from cis-[Pt(C6F5)2(tht)2] and cis-[Pt(C6F5)2(CO)2],7 has
Introduction
The cis/trans isomerization of square-planar platinum(II)
complexes is still a subject of great interest. Thus, in agreement
with the claim that cis-diorganoplatinum complexes are ther-
modynamically more stable than the corresponding trans
isomers,1,2 van Koten et al.2 reported last year that the presence
of ortho substituents in [Pt(C∧N)2] complexes, where C∧N is
a (dimethylamino)methylaryl ligand, favors the formation of the
cis isomers, even when starting from trans-[PtCl2(SMe2)2], and
that the trans isomers isomerize irreversibly to the thermody-
namically favored cis isomers upon heating. Almost simulta-
neously, Klein et al.3 reached apparently opposite conclusions:
the complexes [Pt(aryl)2(S-dmso)2] (dmso ) dimethyl sulfox-
ide), obtained by reacting cis-[PtCl2(dmso)2)] with the corre-
* To whom correspondence should be addressed. E-mail: jvs@um.es
(J.V.); p.jones@tu-bs.de (P.G.J.).Web: http://www.scc.um.es/gi/gqo/ (J.V.).
† Dedicated to Dr. Jose-Antonio Abad, with best wishes, on the occasion
of his retirement.
‡ E-mail: aurelia@um.es.
(1) Brune, H. A.; Schmidtberg, G.; Wiege, M. Z. Naturforsch., B 1984,
39, 517. Hoogervorst, W. J.; Koster, A. L.; Lutz, M.; Spek, A. L.; Elsevier,
C. J. Organometallics 2004, 23, 1161. Jawad, J. K.; Puddephatt, R. J.;
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Koten, G. Organometallics 2005, 24, 2944.
(3) Klein, A.; Schurr, T.; Kno¨dler, A.; Gudat, D.; Klinkhammer, K. W.;
Jain, V. K.; Zalis, S.; Kaim, W. Organometallics 2005, 24, 4125.
(5) Falvello, L. R.; Fornies, J.; Gomez, J.; Lalinde, E.; Martin, A.;
Mart´ınez, F.; Moreno, M. T. Dalton Trans. 2001, 2132. Ara, I.; Falvello,
L. R.; Fornies, J.; Lalinde, E.; Martin, A.; Mart´ınez, F.; Moreno, M. T.
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10.1021/om060398t CCC: $33.50 © 2006 American Chemical Society
Publication on Web 07/29/2006

4248 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
Chart 1
We are involved in the study of the reactivity of organomer-
cury complexes as transmetalating agents.23 In this context, we
have recently reported the synthesis of the diaryl complex cis-
(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] by high-temperature transmeta-
lation from [Hg(κ1-Ar)2] and [PtCl4]2- and of some of their
derivatives, cis-(Me4N)[Pt(κ2-Aryl)(κ1-Ar)(O,O-acac)] and [Pt-
(κ2-Aryl)(κ1-Ar)L] (L ) H2O (1cis), PhCN, tetrahydrothiophene),
as well as a family of complexes containing Pt-Hg bonds. All
of these bis(2,6-dinitroaryl)platinum complexes had a cis
geometry.22,24 Here we report the syntheses of new cis-bis(2,6-
dinitroaryl)platinum complexes and a study of their thermal
stability that has allowed us to prepare some of their trans
isomers. The latter have been used to prepare, by ligand
substitution, other trans-diaryl complexes not accessible by
thermal isomerization. The study of the thermal stability of these
complexes has allowed us to observe decomposition reactions,
not involving the C-Pt bonds, that lead to a cis-diaryl complex.
This has given us more data to formulate the factors that promote
the stability of cis- or trans-diaryl complexes of group 10 metals
and, consequently, to predict which of them would be easily
isomerized. However, it is important to realize that the thermal
isomerizations have been observed because the presence of the
two nitro groups in the ortho positions of the aryl ligands confers
on them a remarkably high thermal stability.
been used to prepare other cis-[Pt(C6F5)2LL′] complexes.7-9
However, recently trans-[Pt(C6F5)2(CO)(tht)] has been obtained
by heating the cis isomer in benzene or cyclohexane.10
In agreement with the above data, the much greater number
of reported crystal structures of cis-diarylplatinum(II) complexes
(173) as compared to the number of those for trans-diarylplati-
num(II) (23) complexes11 cannot be used as evidence for the
greater stability of the cis isomers. To establish the character-
istics that stabilize cis- or trans-diarylplatinum(II), we have
selected (i) those characterized by X-ray diffraction studies,12
(ii) those whose geometry is not imposed by the other ligands,
and (iii) those that were obtained by prolonged heating of the
reactants. The 11 trans-diarylplatinum(II) complexes obtained
under these conditions are [Pt(R)(R′)(PR′′3)2] (R ) R′ ) C6H4-
CF3-4,13 2,6-Me2C6H3, 2,4,6-Me3C6H2 (R′′ ) Et), 2,4,6-
4
Experimental Section
(MeO)3C6H2,14 3,5-(CF3)2C6H3,15 Ph16 (R′′ ) Ph); R ) Ph,
R-biphenylenyl, R′ ) R-biphenyl (R′′ ) Et), [Pt(2,2′-tetraphe-
nyl)(PEt3)2]),17 and [PtR2(S-dmso)2] (R ) C6H3Me2-2,6, C6H2-
Me3-2,4,6).3 The 9 cis-diarylplatinum(II) complexes are 3 of
the type [PtR2L2] (L ) S-dmso, R ) Ph,18 2-tolyl;3 L ) PEt3,
R ) Ph),4 the 6 orthoplatinated complexes [Pt(C∧X)(C′∧X′)]
(C∧X ) C′∧X′ ) 2-X-R: X ) NHPPh2, R ) C6H4;19 X )
CH2NMe2, R ) 1-naphthyl, C6H2Br-4-CH2NMe2-5;2 X )
CH2P(CH2Ph)2, R ) C6H4;20 C∧X: X ) PPh2, R ) C6H4;
C′∧X′: X′ ) PPh2(HgCl)C6H4PPh2-2, R ) C6H4),21 and
[Pt(C∧X)(R)Cl]- (C∧X ) κ2-Aryl, R ) κ1-Aryl; see Chart 1).22
In this paper we present new data and the factors that influence
the stability of diarylplatinum(II) complexes.
Unless otherwise stated, the reactions were carried out without
precautions to exclude light or atmospheric oxygen or moisture.
The IR (Nujol/polyethylene), C, H, and N analyses, and melting
point determinations were carried out as described elsewhere.25
NMR spectra were recorded on Varian Unity 300, Bruker AC 200,
Avance 300 and 400, and Bruker 600 spectrometers at room
temperature unless otherwise stated. Chemical shifts were referenced
to TMS (1H, 13C{1H}) or H3PO4 (31P{1H}). The NMR probe
temperature was calibrated using ethylene glycol 1H NMR standard
methods. The complex cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] and CH2-
Cl2 and Et2O solutions of cis-[Pt(κ2-Aryl)(κ1-Aryl)(OH2)] (1cis)
were prepared as reported previously.22 The aryl group C6(NO2)2-
2,6-(OMe)3 and the ligands κ1-(C)-C6(NO2)2-2,6-(OMe)3 and κ2-
(C,O)-C6(NO2)2-2,6-(OMe)3 are represented by Aryl, κ1-Aryl, and
κ2-Aryl (see Chart 1).
(6) Chatt, J.; Shaw, B. L. J. Chem. Soc. 1959, 808. Rieger, A. L.;
Carpenter, G. B.; Rieger, P. H. Organometallics 1993, 12, 842.
(7) Uson, R.; Fornies, J.; Espinet, P.; Fortuno, C.; Tomas, M.; Welch,
A. J. J. Chem. Soc., Dalton Trans. 1988, 3005.
(8) Ara, I.; Berenguer, J. R.; Fornie´s, J.; Lalinde, E.; Toma´s, M.
Organometallics 1996, 15, 1014.
(9) Berenguer, J. R.; Fornie´s, J.; Lalinde, E.; Mart´ınez, F. Organometallics
1995, 14, 2532.
(10) Berenguer, J. R.; Fornies, J.; Martin, L. F.; Martin, A.; Menjon, B.
Inorg. Chem. 2005, 44, 7265.
Synthesis of cis-[Pt(κ2-Aryl)(κ1-Aryl)(dmso)] (2cis). To a stirred
solution of 1cis (0.12 mmol) in CH2Cl2 (5 mL) was added dmso
(9.15 mg, 0.12 mmol). The resulting solution was concentrated to
dryness, and Et2O (20 mL) was added to give a suspension, which
was filtered to give an orange solid that was washed with Et2O
and identified as 2cis (48 mg). The filtrate was concentrated (2
mL), n-hexane (2 mL) was added, and the suspension was filtered
to give a solid that was washed with n-hexane to give a second
(11) CSD version 5.26 (May 2005).
(12) We only consider complexes characterized by X-ray diffraction
studies because some studied only by NMR were later corrected.3
(13) Mintcheva, N.; Nishihara, Y.; Tanabe, M.; Hirabayashi, E.; Mori,
A.; Osakada, K. Organometallics 2001, 20, 1243.
(14) Brune, H. A.; Wiege, M.; Debaerdemaeker, T. Z. Naturforsch., B
1984, 39, 907.
1
crop of 2cis (41 mg). Yield: 89 mg, 96%. Mp: 188-192 °C. H
NMR (400 MHz, CDCl3): δ 4.07 (s, 6 H, OMe), 4.04 (s, 3 H,
OMe), 4.02 (s, 3 H, OMe), 3.91 (s, 3 H, OMe), 3.84 (s, 3 H, OMe),
3
3.24 (s + d, 6 H, Me, JPtH ) 13,5 Hz). 13C{1H} NMR (100.81
MHz, CDCl3, 25 °C): δ 154.83 (m-C κ2-Aryl), 154.00 (m-C κ2-
(15) Konze, W. V.; Scott, B. L.; Kubas, G. J. Chem. Commun. 1999,
1807.
(16) Ertl, J.; Debaerdemaeker, T.; Brune, H. A. Chem. Ber. 1982, 115,
3860.
(17) Edelbach, B. L.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc.
1998, 120, 2843.
(18) Bardi, R.; Del Pra, A.; Piazzesi, A. M.; Trozzi, M. Cryst. Struct.
Commun. 1981, 10, 301.
(19) Gaw, K. G.; Slawin, A. M. Z.; Smith, M. B. Organometallics 1999,
18, 3255.
(23) Vicente, J.; Chicote, M. T.; Arcas, A.; Artigao, M. Inorg. Chim.
Acta 1982, 65, L251. Vicente, J.; Arcas, A.; Ferna´ndez-Herna´ndez, J. M.;
Sironi, A.; Masciocchi, N. Chem. Commun. 2005, 1267. Vicente, J.; Arcas,
A.; Ferna´ndez-Herna´ndez, J. M.; Bautista, D. Organometallics 2001, 20,
2767. Vicente, J.; Chicote, M. T.; Ram´ırez-de-Arellano, M. C.; Pelizzi, G.;
Vitali, F. J. Chem. Soc., Dalton Trans. 1990, 279. Vicente, J.; Martin, J.;
Solans, X.; Font-Altaba, M. Organometallics 1989, 8, 357. Vicente, J.; Abad,
J. A.; Rink, B.; Herna´ndez, F.-S.; Ram´ırez de Arellano, M. C. Organome-
tallics 1997, 16, 5269.
(20) Porzio, W. Inorg. Chim. Acta 1980, 40, 257.
(21) Bennett, M. A.; Contel, M.; Hockless, D. C. R.; Welling, L. L.;
Willis, A. C. Inorg. Chem. 2002, 41, 844.
(24) Vicente, J.; Arcas, A.; Ga´lvez-Lo´pez, M. D.; Jones, P. G. Orga-
nometallics 2004, 23, 3528.
(22) Vicente, J.; Arcas, A.; Ga´lvez-Lo´pez, M. D.; Jones, P. G. Orga-
nometallics 2004, 23, 3521.
(25) Vicente, J.; Chicote, M. T.; Huertas, S.; Bautista, D.; Jones, P. G.;
Fischer, A. K. Inorg. Chem. 2001, 40, 2051.

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4249
3
Aryl), 148.33 (m-C κ1-Aryl, 3JPtC ) 68 Hz), 147.32 (o-C κ1-Aryl),
147.02 (o-C κ2-Aryl), 144.84 (p-C κ2-Aryl), 143.84 (p-C Aryl),
136.82 (o-C κ2-Aryl), 128.40 (i-C Aryl), 110.86 (i-C Aryl), 62.35
(m-OMe), 62.19 (m-OMe), 61.64 (p-OMe), 61.29 (p-OMe), 42.92
31 Hz), 147.29 (m-C κ1-Aryl, JPtC ) 74 Hz), 144.07 (p-C Aryl),
144.00 (p-C Aryl), 137.32 (o-C Aryl), 136.10 (o-C Xy), 135.84
(br, CtN), 130.05 (p-C Xy), 128.11 (i-C Aryl), 128.05 (m-C Xy),
1
125.61 (br, i-C Xy), 105.13 (i-C Aryl, JPtC ) 1145 Hz), 62.29
2
(Me, JPtC ) 32 Hz). Anal. Calcd for C20H24N4O15PtS: C, 30.50;
(m-OMe κ1-Aryl), 62.23 (m-OMe), 62.07 (m-OMe), 61.54 (p-OMe),
61.28 (p-OMe), 18.33 (Me). Anal. Calcd for C27H27N5O14Pt:
C, 38.58; H, 3.24; N, 8.33. Found: C, 38.43; H, 3.18; N,
8.39.
H, 3.07; N, 7.11; S, 4.07. Found: C, 30.18; H, 3.06; N, 7.16; S,
3.67. Single crystals of 2cis were obtained by slow diffusion of
n-hexane into an acetone solution of 2cis.
Synthesis of cis-[Pt(κ1-Aryl)2(CNXy)2] (3cis). To a solution of
1cis (0.25 mmol) in CH2Cl2 (4 mL) was added XyNC (Xy ) 2,6-
dimethylphenyl; 65 mg, 0.50 mmol), and the resulting solution was
concentrated (2 mL). Addition of Et2O (10 mL) gave a suspension,
which was filtered off; the solid was washed with Et2O and air-
dried in vacuo to give 3cis as a pale yellow solid. Yield: 225 mg,
Synthesis of trans-[Pt(κ2-Aryl)(κ1-Aryl)(CNXy)] (4trans). To
a stirred solution of 5trans (96 mg, 0.13 mmol) in CH2Cl2 (2 mL)
was slowly added (for 1 h) a solution of XyNC (17 mg, 0.13 mmol)
in CH2Cl2 (20 mL). The resulting solution was concentrated
to dryness, and the residue was stirred with Et2O (10 mL) in
a cold bath (ice/water). The resulting suspension was filtered,
the filtrate was concentrated to dryness, and Et2O (1 mL) and
n-pentane (3 mL) were added. The suspension was filtered off, and
the solid was washed with pentane and air-dried to give 4trans as
an orange solid. Yield: 55 mg, 50%. Mp: 214-216 °C. IR (cm-1):
1
94%. Dec pt: 240 °C. IR (cm-1): ν(CtN) 2199, 2179. H NMR
(300 MHz, CDCl3): δ 7.27-7.22 (m, 2 H, p-H Xy), 7.09-7.07
(m, 4 H, m-H Xy), 3.94 (s, 12 H, OMe), 3.90 (s, 6 H, OMe), 2.29
(s, 12 H, Me). 13C{1H} NMR (100.81 MHz, CDCl3): δ 148.43
(o-C Aryl, 2JPtC ) 15 Hz), 147.39 (m-C Aryl, 3JPtC ) 53 Hz), 143.89
(p-C Aryl), 135.86 (o-C Xy), 135.59 (br, CtN), 130.08 (p-CH Xy),
1
ν(CtN) 2194. H NMR (300 MHz, CDCl3): δ 7.22-7.17 (m, 1
H, p-H Xy), 7.12-7.09 (m, 2 H, m-H Xy), 4.03 (s, 12 H, OMe),
128.12 (m-CH Xy), 125.74 (br, i-C Xy), 122.64 (i-C Aryl, 1JPtC
)
3.88 (s, 6 H, OMe), 2.46 (s, 6 H, Me). H NMR (400.91 MHz,
1
880 Hz), 62.27 (m-OMe), 61.13 (p-OMe), 18.29 (Me). Anal. Calcd
for C36H36N6O14Pt: C, 44.49; H, 3.73; N, 8.65. Found: C, 44.38;
H, 3.70; N, 8.74. Crystals of 3cis‚CHCl3 suitable for X-ray
diffraction studies were obtained by slow diffusion of n-hexane
into a solution of 3cis in CDCl3.
CD2Cl2, -60 °C): δ 7.23-7.19 (m, 1 H, p-H Xy), 7.13-7.11 (m,
2 H, m-H Xy), 4.12 (s, 3 H, OMe), 4.02 (s, 3 H, OMe), 3.90 (s, 6
H, OMe), 3.81 (s, 3 H, OMe), 3.77 (s, 3 H, OMe), 2.37 (s, 6 H,
Me). 13C{1H} NMR (75.45 MHz, CDCl3): δ 151.11 (br, C Aryl),
144.54 (br, C Aryl), 143.72 (C Aryl), 135.75 (o-C Xy), 129.42
(p-C Xy), 127.79 (m-C Xy), 126.90 (br, i-C Xy), 113.40 (br, i-C
Aryl), 62.22 (m-OMe), 61.37 (p-OMe), 18.25 (Me). Anal. Calcd
for C27H27N5O14Pt: C, 38.58; H, 3.24; N, 8.33. Found: C, 38.22;
H, 3.11; N, 8.39. Single crystals of 4trans were obtained by slow
diffusion of n-pentane into a solution of 4trans in CDCl3.
Synthesis of trans-[Pt(κ1-Aryl)2(CNXy)2] (3trans). A solution
of 1cis (0.15 mmol) in CH2Cl2 (2 mL) was concentrated to dryness,
and XyNC (40 mg, 0.30 mmol) in toluene (5 mL) was then added.
The resulting pale yellow suspension was stirred at 150 °C for 75
min in a Carius tube and then concentrated to dryness. CH2Cl2
(2 mL) and Et2O (10 mL) were added, and the precipitate was
filtered off, washed with Et2O, and air-dried, to give 3trans as a
pale yellow solid. Yield: 83 mg, 56%. Dec pt: 326 °C. IR (cm-1):
ν(CtN) 2196. 1H NMR (300 MHz, CDCl3): δ 7.23-7.18
(m, 2 H, p-H Xy), 7.07-7.04 (m, 4 H, m-H Xy), 3.95 (s, 12 H,
OMe), 3.90 (s, 6 H, OMe), 2.33 (s, 12 H, Me). 13C{1H} NMR
(75.45 MHz, CDCl3): δ 148.84 (o-C Aryl), 146.83 (m-C Aryl, 3JPtC
) 38 Hz), 143.34 (p-C Aryl), 136.31 (o-C Xy), 134.70 (br, CtN),
130.01 (p-C Xy), 127.92 (m-C Xy), 125.50 (i-C Xy), 124.50 (i-C
Aryl, 1JPtC ) 640 Hz), 62.16 (m-OMe), 61.13 (p-OMe), 18.14 (Me).
Anal. Calcd for C36H36N6O14Pt: C, 44.49; H, 3.73; N, 8.65.
Found: C, 44.64; H, 4.12; N, 8.60. Single crystals of 3trans were
obtained by slow diffusion of Et2O into a solution of 3trans in
CHCl3.
Synthesis of cis-[Pt(κ2-Aryl)(κ1-Aryl)(CO)] (5cis). A stream of
CO was bubbled at atmospheric pressure into a solution of 1cis
(0.32 mmol) in CH2Cl2 (5 mL) until the red color of the solution
changed to yellow. The mixture was filtered though Celite and
MgSO4, the filtrate was concentrated (2 mL), and n-hexane (10
mL) was added. The suspension was filtered, and the solid was
washed with n-hexane and air-dried to give 5cis as a yellow solid.
Yield: 215 mg, 92%. Mp: 160-162 °C. IR (cm-1): ν(CtO) 2128.
1H NMR (300 MHz, CDCl3): δ 4.08 (s, 6 H, OMe), 4.05 (s, 3 H,
OMe), 4.04 (s, 3 H, OMe), 3.96 (s, 3 H, OMe), 3.86 (s, 3 H, OMe).
13C{1H} NMR (100.81 MHz, CDCl3, 25 °C): δ 170.28 (CO, 1JPtC
3
) 1251 Hz), 154.73 (m-C κ2-Aryl, JPtC ) 44 Hz), 153.98 (m-C
3
3
κ2-Aryl, JPtC ) 70 Hz), 148.32 (m-C κ1-Aryl, JPtC ) 71 Hz),
147.43 (o-C κ1-Aryl, 2JPtC ) 23 Hz), 146.71 (o-C κ2-Aryl, 2JPtC
)
47 Hz), 145.44 (p-C Aryl), 144.95 (p-C Aryl), 136.82 (o-C κ2-
Aryl, 2JPtC ) 51 Hz), 133.98 (i-C κ2-Aryl, 1JPtC ) 977 Hz), 101.02
(i-C κ1-Aryl, 2JPtC ) 1115 Hz), 62.40 (m-OMe κ2-Aryl), 62.34 (m-
OMe κ1-Aryl), 62.25 (m-OMe κ2-Aryl), 61.71 (p-OMe), 61.25 (p-
OMe). Anal. Calcd for C19H18N4O15Pt: C, 30.95; H, 2.46; N, 7.60.
Found: C, 30.71; H, 2.36; N, 7.50. Crystals suitable for X-ray
diffraction studies were obtained by slow diffusion of n-hexane
into a solution of 5cis in CH2Cl2. When the ratio hexane/CH2Cl2
was 5/1, crystals of 5cis‚0.5(hexane) were isolated, but a smaller
ratio led to the crystallization of 5cis‚CH2Cl2.
Synthesis of trans-[Pt(κ2-Aryl)(κ1-Aryl)(CO)] (5trans). Method
a. The solid complex 5cis (105 mg, 0.14 mmol) was placed in a
flask and heated in a bath at 150 °C with stirring. This temperature
was maintained until the resulting liquid solidified to a red solid
that was cooled to room temperature. CH2Cl2 (4 mL) was added,
and the suspension was filtered through Celite. The filtrate was
concentrated (1 mL), n-pentane (15 mL) was added, and the
resulting suspension was filtered off. The solid was washed with
n-pentane and air-dried to give 5trans as a red solid. Yield: 96
mg, 93%.
Synthesis of cis-[Pt(κ2-Aryl)(κ1-Aryl)(CNXy)] (4cis). Method
a. To a stirred solution of 1cis (0.09 mmol) in CH2Cl2 (2 mL) was
slowly added a solution of XyNC (11 mg, 0.08 mmol) in CH2Cl2
(15 mL) over 1 h. The solution was concentrated to dryness, the
residue was stirred with Et2O (5 mL), and the resulting suspension
was filtered. The solid was washed with Et2O and air-dried to give
4cis as an orange solid. The filtrate was concentrated (2 mL), and
n-pentane (10 mL) was added to give a second crop of 4cis. Yield:
54 mg, 76%.
Method b. A solution of XyNC (10 mg, 0.08 mmol) in CH2Cl2
(20 mL) was slowly added (for 1 h) to a stirred solution of 5cis
(50 mg, 0.07 mmol) in CH2Cl2 (2 mL). The resulting solution was
concentrated to dryness, the residue was stirred with Et2O (2 mL),
and the resulting suspension was concentrated (1 mL). n-Pentane
was added, the suspension was filtered, and the solid was washed
with n-pentane and air-dried to give 4cis as an orange solid. Yield:
26 mg, 52%. Mp: 181-182 °C. IR (cm-1): ν(CtN) 2188.
1H NMR (300 MHz, CDCl3): δ 7.27-7.21 (m, 1 H, p-H Xy),
7.10-7.08 (m, 2 H, m-H Xy), 4.05 (s, 6 H, OMe), 4.04 (s, 3 H,
OMe), 4.02 (s, 3 H, OMe), 3.94 (s, 3 H, OMe), 3.86 (s, 3 H, OMe),
2.34 (s, 6 H, Me). 13C{1H} NMR (75.45 MHz, CDCl3): δ 154.35
Method b. A solution of 5cis (76 mg, 0.10 mmol) in toluene
(15 mL) was refluxed for 1 h. After 12 h at room temperature the
2
(m-C κ2-Aryl), 153.80 (m-C κ2-Aryl), 148.01 (o-C Aryl, JPtC
)

4250 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
solution was evaporated to dryness, the solid was extracted with
CH2Cl2 (2 mL), and the mixture was filtered through Celite and
MgSO4. n-Hexane (8 mL) was added to the filtrate, and the
suspension was filtered and the solid washed with n-hexane and
air-dried to give 5trans as a red solid. Yield: 45 mg. 61%. Mp:
172-174 °C. IR (cm-1): ν(CtO) 2106. 1H NMR (300 MHz,
CDCl3): δ 4.10 (s, 12 H, OMe), 3.91 (s, 6 H, OMe). 13C{1H} NMR
146.29 (d, o-C Aryl, 3JPC ) 2.6 Hz), 143.84 (p-C k1-Aryl), 143.32
5
1
(d, p-C κ2-Aryl, JPC ) 2 Hz), 141.30 (d, i-C κ2-Aryl, JPC ) 109
Hz), 137.31 (d, o-C κ2-Aryl, JPC ) 5 Hz), 134.25 (d, o-C PPh3,
2JPC ) 10 Hz), 130.80 (p-C PPh3), 129.00 (d, i-C PPh3, 1JPC ) 52
3
Hz), 128.26 (d, m-C PPh3, JPC ) 11 Hz), 114.68 (d, i-C κ1-Aryl,
2JPC ) 12 Hz), 62.25 (OMe), 62.01 (2 OMe), 61.95 (OMe), 61.38
(2 OMe). Anal. Calcd for C36H33N4O14PPt: C, 44.50; H, 3.42; N,
5.77. Found: C, 44.44; H, 3.35; N, 5.68. Single crystals of 7cis‚
Me2CO were obtained by slow diffusion of Et2O or n-hexane into
a solution of 4cis in acetone.
1
(100.81 MHz, CDCl3, 25 °C): δ 154.06 (CO, JPtC ) 2120 Hz),
152.53 (C Aryl, JPtC ) 34 Hz), 144.58 (C Aryl), 143.55 (C Aryl),
134.85 (i-C Aryl, 1JPtC ) 680 Hz), 62.45 (m-OMe), 61.56 (p-OMe).
Anal. Calcd for C19H18N4O15Pt: C, 30.95; H, 2.46; N, 7.60.
Found: C, 30.75; H, 2.16; N, 7.64.
Synthesis of cis-[Pt(κ1-Aryl)2(PPh3)2] (8cis). To a solution of
cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] (116 mg, 0.14 mmol) in CH2-
Cl2 (5 mL) was added PPh3 (149 mg, 0.57 mmol). The resulting
suspension was filtered, the filtrate was concentrated (1 mL), and
Et2O (15 mL) was added. The suspension was filtered off and the
solid was washed with Et2O and air-dried to give 8cis as a yellow
solid. Yield: 152 mg, 87%. Mp: 130-132 °C. 1H NMR (300 MHz,
CDCl3): δ 7.71-6.96 (m, 30 H, PPh3), 4.028 (s, 3 H, OMe), 3.996
(s, 3 H, OMe), 3.849 (s, 3 H, OMe), 3.846 (s, 6 H, OMe), 3.805
(s, 3 H, OMe), 3.754 (s, 6 H, OMe), 3.750 (s, 12 H, OMe).
Synthesis of cis-[Pt(κ1-Aryl)2(CO)(PPh3)] (6cis). To a stirred
solution of 5cis (56 mg, 0.08 mmol) in CH2Cl2 (3 mL) was added
PPh3 (20 mg, 0.08 mmol). The resulting yellow solution was
concentrated to dryness, Et2O (2 mL) was added, and the suspension
was filtered off. The solid was washed with Et2O and air-dried to
give 6cis as a pale yellow solid. Yield: 63 mg, 83%. Mp: 262-
1
264 °C. IR (cm-1): ν(CtO) 2100. H NMR (300 MHz, CDCl3):
δ 7.60-7.27 (m, 15 H, PPh3), 3.94 (s, 6 H, OMe), 3.90 (s, 3 H,
1
31P{1H} NMR (121 MHz, CDCl3): δ 16.53 (s, JPtP ) 2579 Hz),
OMe), 3.77 (s, 6 H, OMe), 3.74 (s, 3 H, OMe). 31P{1H} NMR
1
1
6.50 (s, JPtP ) 2369 Hz), -4.61 (s, PPh3). Anal. Calcd for
(121.50 MHz, CDCl3): δ 14.05 (s, PPh3, JPtP ) 2262 Hz). 13C-
C54H48N4O14P2Pt: C, 52.56; H, 3.92; N, 4.5. Found: C, 52.34; H,
4.19; N, 4.46.
{1H} NMR (75.45 MHz, CDCl3, 25 °C): δ 170.86 (d, CO, 2JPC
9 Hz, JPtC ) 1192 Hz), 150.06 (d, m-C Aryl trans CO, JPC ) 2
)
1
4
Synthesis of trans-[Pt(κ1-Aryl)2(PPh3)2] (8trans). A solution
of 6trans (65 mg, 0.09 mmol) in CH2Cl2 (5 mL) was stirred for 7
h with PPh3 (47 mg, 0.18 mmol) under N2. The resulting solution
was filtered through Celite, the filtrate was concentrated (2 mL),
and Et2O (15 mL) was added. The suspension was filtered off and
the solid washed with Et2O and air-dried to give 8trans as a yellow
solid. The filtrate was concentrated to dryness, the residue was
extracted with Et2O (15 mL), and the suspension was filtered off
to give a second crop of 8trans. Yield: 90 mg, 83%. Mp: 163-
3
4
Hz, JPtC ) 56 Hz), 148.016 (d, m-C Aryl trans PPh3, JPC ) 6.6
Hz, 3JPtC ) 51 Hz), 148.023 (d, C Aryl, JPC ) 2.2 Hz), 144.79 (d,
C Aryl, JPC ) 2.2 Hz), 144.61 (C Aryl, JPtC ) 10 Hz), 144.39 (d,
C Aryl, JPC ) 1.7 Hz, JPtC ) 11 Hz), 134.43 (br, o-C PPh3), 133.36
2
(d, i-C Aryl trans CO, JPC ) 11 Hz), 131.41 (p-C PPh3), 129.05
(C), 128.49 (d, m-C PPh3, 3JPC ) 9.4 Hz), 121.86 (d, i-C Aryl trans
PPh3, 2JPC ) 104 Hz), 62.34 (m-OMe), 62.05 (m-OMe), 61.11 (p-
OMe), 61.03 (p-OMe). Anal. Calcd for C37H33N4O15PPt: C, 44.45;
H, 3.33; N, 5.60. Found: C, 44.40; H, 3.42; N, 5.53. Single crystals
of 6cis were obtained by slow diffusion of Et2O into a CDCl3
solution of 6cis.
1
164 °C. H NMR (300 MHz, CDCl3): δ 7.57-7.51 (m, 12 H,
PPh3), 7.25-7.17 (m, 18 H, PPh3), 3.61 (s, 6 H, OMe), 3.52 (s, 12
1
H, OMe). 31P{1H} NMR (121.5 MHz, CDCl3): δ 8.33 (s, JPtP
)
Synthesis of trans-[Pt(κ1-Aryl)2(CO)(PPh3)] (6trans). To a
stirred solution of 5trans (40 mg, 0.05 mmol) in CH2Cl2 (2 mL)
was added PPh3 (14 mg, 0.05 mmol). The solution was concentrated
(1 mL), and Et2O (15 mL) was added to give a suspension, which
was filtered off. The resulting solid was washed with Et2O and
air-dried to give 6trans as a pale yellow solid. Yield: 30 mg, 55%.
Mp: 248-250 °C. IR (cm-1): ν(CtO) 2122, 2114. 1H NMR (300
MHz, CDCl3): δ 7.40-7.25 (m, 15 H, PPh3), 3.80 (s, 6 H, OMe),
3.78 (s, 12 H, OMe). 31P{1H} NMR (121 MHz, CDCl3): δ 5.75
2890 Hz). 13C{1H} NMR (75.45 MHz, CDCl3): δ 148.15 (t, m-C
4
3
3
Aryl, JPC ) 1 Hz, JPtC ) 41 Hz), 146.68 (t, o-C Aryl, JPC ) 2
Hz, 3JPtC ) 19 Hz), 142.73 (p-C Aryl, JPtC ) 1 Hz), 137.36 (t, i-C
Aryl, 2JPC ) 11 Hz), 134.70 (vt, o-C PPh3, | JPC + 4JPC| ) 6 Hz),
2
1
3
131.07 (vt, i-C PPh3, | JPC + JPC| ) 28 Hz), 129.64 (p-C PPh3),
127.05 (vt, m-C PPh3, | JPC + 5JPC| ) 5 Hz), 61.65 (m-OMe), 60.94
3
(p-OMe). Anal. Calcd for C54H48N4O14P2Pt: C, 52.56; H, 3.92; N,
4.50. Found: C, 52.62; H, 3.93; N, 4.52. Single crystals of 8trans‚
0.5CHCl3 were obtained by slow diffusion of n-hexane into a
solution of 8trans in CHCl3.
1
(s, PPh3, JPtP ) 3263 Hz). 13C{1H} NMR (100.81 MHz, CDCl3,
25 °C): δ 168.29 (d, CO, 2JPC ) 150 Hz), 148.62 (m-C Aryl, 3JPtC
X-ray Structure Determinations. Numerical details are pre-
sented in Table 1. Data were recorded at low temperature on a
Bruker SMART 1000 CCD diffractometer using Mo KR radiation.
Absorption corrections were based on indexed faces (2cis, 3trans,
7cis) or multiple scans (all other structures; program SADABS).
Structures were refined anisotropically on F2 using the program
SHELXL-97 (Prof. G. M. Sheldrick, University of Go¨ttingen).
Restraints to light atom displacement factors and local ring
symmetry were employed to improve the stability of refinement.
Hydrogen atoms were refined using a riding model or rigid methyl
groups. Special features of the refinements are as follows. 3cis:
the chloroform molecule is disordered over two positions, as is the
methyl group C17. 4trans: the extremely large cell led to a weak
diffraction pattern. An extensive system of restraints was used. Only
two molecules per block could be refined simultaneously. Four areas
of poorly defined electron density were tentatively identified as
disordered solvent (chloroform), but no suitable refinement model
was found. The program SQUEEZE26 was therefore used to
mathematically remove the effects of the solvent. Methyl H atoms
2
) 39 Hz), 147.53 (o-C Aryl, JPtC ) 15 Hz), 144.19 (p-C Aryl),
2
3
133.92 (d, o-C PPh3, JPC ) 10 Hz, JPtC ) 18 Hz), 130.89 (p-C
PPh3, 4JPC ) 2.2 Hz), 128.16 (d, m-C PPh3, 3JPC ) 11 Hz), 127.55
2
1
(d, i-C Aryl, JPC ) 10 Hz), 127.16 (d, i-C PPh3, JPC ) 61 Hz),
61.97 (m-OMe), 61.07 (p-OMe). Anal. Calcd for C37H33N4O15PPt:
C, 44.18; H, 3.55; N, 5.46. Found: C, 44.45; H, 3.33; N, 5.60.
Single crystals of 6trans‚CHCl3 were obtained by slow diffusion
of n-hexane into a CDCl3 solution of 6trans.
Synthesis of cis-[Pt(κ2-Aryl)(κ1-Aryl)(PPh3)] (7cis). To a solu-
tion of cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] (220 mg, 0.27 mmol)
in CH2Cl2 (4 mL) was added PPh3 (70 mg, 0.27 mmol). The orange
solution was concentrated (1 mL), and Et2O (15 mL) was added.
The resulting suspension was filtered off, and the solid was washed
with Et2O and air-dried to give 7cis as an orange solid. Yield: 250
mg, 96%. Mp: 305-309 °C. 1H NMR (300 MHz, CDCl3): δ 7.43-
7.32 (m, 15 H, PPh3), 4.03 (s, 3 H, OMe), 4.00 (s, 3 H, OMe),
3.852 (s, 3 H, OMe), 3.848 (s, 6 H, OMe), 3.81 (s, 3 H, OMe).
1
31P{1H} NMR (121.50 MHz, CDCl3): δ 16.53 (s, JPtP ) 2579
Hz). 13C{1H} NMR (75.45 MHz, CDCl3): δ 154.25 (d, m-C κ2-
Aryl, 4JPC ) 8 Hz), 154.17 (d, m-C κ2-Aryl, 4JPC ) 12 Hz), 148.36
(26) Spek, A. L. SQUEEZE; University of Utrecht, Utrecht, The
Netherlands.
4
3
(d, m-C κ1-Aryl, JPC ) 2 Hz, JPtC ) 76 Hz), 146.98 (o-C Aryl),

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4251
Table 1. Crystallographic Data for the Complexes 2cis, 3cis‚CHCl3, 3trans, 4trans‚CHCl3, 5cis‚CH2Cl2, 5cis‚0.5(hexane), 6cis,
6trans‚CHCl3, 7cis‚Me2CO, and 8trans‚0.5CHCl3
2cis
3cis‚CHCl3
3trans
4trans‚CHCl3
5cis‚CH2Cl2
formula
Mr
C20H24N4O15PtS
787.58
C37H37Cl3N6O14Pt
1091.17
C36H36N6O14Pt
971.80
C28H28Cl3N5O14Pt
959.99
C20H20Cl2N4O15Pt
822.39
cryst habit
cryst size (mm)
cryst syst
space group
cell constants
a, Å
orange tablet
0.22 × 0.19 × 0.09
monoclinic
P21/c
pale yellow tablet
0.38 × 0.28 × 0.16
triclinic
pale yellow lath
0.38 × 0.10 × 0.03
monoclinic
orange prism
0.30 × 0.12 × 0.08
monoclinic
P2/n
orange lath
0.41 × 0.11 × 0.05
monoclinic
P21/n
P1h
P21/c
9.3407(8)
34.741(3)
8.6000(6)
90
103.794(4)
90
9.9644(15)
13.156(2)
17.352(3)
84.802(3)
74.979(3)
85.990(3)
2185.4
2
21.1834(16)
11.2289(8)
16.2941(12)
90
93.091(2)
90
32.917(3)
8.5440(8)
51.357(5)
90
104.698(8)
90
10.5115(8)
9.5613(6)
26.9995(18)
90
92.123(3)
90
b, Å
c, Å
R, deg
â, deg
γ, deg
V (Å3)
2710.3
4
3870.2
4
13971
16
2711.7
4
Z
λ (Å)
0.710 73
1.930
5.33
1544
143
0.710 73
1.658
3.46
1084
143
0.710 73
1.668
3.70
1936
143
0.710 73
1.826
4.32
7552
133
0.710 73
2.014
5.45
1600
143
F(calcd) (Mg m-3
)
µ (mm-1
F(000)
T (K)
)
2θmax (deg)
61
59 825
8272
0.28-0.60
0.045
86/378
0.0523
0.0263
1.23
60
60
52.6
60
42 013
7934
0.52-0.93
0.047
36/380
0.0680
0.0285
1.09
no. of rflns measd
no. of indep rflns
transmissions
Rint
36 041
12 710
0.51-0.75
0.045
627/606
0.0635
0.0274
1.03
82 134
11 308
0.30-0.87
0.073
148/524
0.0554
0.0255
1.00
164 110
28 569
0.40-0.75
0.136
3554/1701
0.184
0.073
0.99
3.2
no. of restraints/params
Rw(F2, all rflns)
R(F, >4σ(F))
S
max ∆F (e Å-3
)
1.3
1.5
1.9
2.7
5cis‚0.5(hexane)
6cis
6trans‚CHCl3
7cis‚Me2CO
8trans‚0.5CHCl3
formula
Mr
C22H25N4O15Pt
780.55
C37H33N4O15Pt
999.73
C38H34Cl3N4O15Pt
1119.10
C39H39N4O15Pt
1029.80
C54.5H48.5Cl1.5N4O14P2Pt
1293.68
cryst habit
cryst size (mm)
cryst syst
space group
cell constants
a, Å
red prism
0.29 × 0.14 × 0.12
triclinic
pale yellow tablet
0.38 × 0.30 × 0.15
orthorhombic
Pbca
amber tablet
0.36 × 0.15 × 0.06
monoclinic
red tablet
yellow prism
0.22 × 0.17 × 0.13
triclinic
0.28 × 0.20 × 0.08
monoclinic
P21/n
P1h
P21/n
P1h
9.0734(6)
10.5091(8)
15.3912(11)
72.588(3)
88.431(3)
83.900(3)
1392.4
2
18.1068(11)
20.7282(13)
20.7627(13)
90
90
90
9.9072(8)
40.753(3)
10.6809(8)
90
103.874(3)
90
20.9579(14)
9.4999(6)
22.4791(16)
90
115.389(3)
90
12.2189(8)
13.1105(10)
18.8240(14)
88.649(4)
76.049(4)
63.967(4)
2617.9
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V (Å3)
7792.7
8
4186.8
4
4043.3
4
Z
λ (Å)
0.710 73
1.862
5.12
766
133
0.710 73
1.704
3.72
3968
133
0.710 73
1.775
3.66
2216
133
0.710 73
1.692
3.59
2056
143
0.710 73
1.641
2.89
1298
133
F(calcd) (Mg m-3)
µ (mm-1
F(000)
T (K)
)
2θmax (deg)
60
32 640
8134
0.47-0.70
0.027
39/385
0.0430
0.0172
1.00
60
60
60
61
no. of rflns measd
no. of indep rflns
transmissions
Rint
127 547
11 404
0.52-0.75
0.028
84/529
0.0495
0.0191
1.03
76 053
10 391
0.58-0.83
0.050
72/565
0.0897
0.0436
1.23
84 387
11 837
0.41-0.76
0.060
99/549
0.0529
0.0228
0.99
53 092
15 887
0.59-0.71
0.038
no. of restraints/params
Rw(F2, all rflns)
R(F, > 4σ(F))
S
6/713
0.0298
0.0686
1.06
max ∆F (e Å-3
)
1.6
1.4
1.9
1.1
1.6
of the isonitrile ligands were indistinct. Esd’s of molecular
dimensions are appreciably larger than for all other structures
reported here. 7cis: solvent H atoms are indistinct. 8trans: the
chloroform molecule is disordered over an inversion center. CCDC-
600162 (2cis), CCDC-600163 (3cis‚CHCl3), CCDC-600164 (3trans),
CCDC-600165 (4trans‚CHCl3), CCDC-600166 (5cis‚CH2Cl2),
CCDC-600167 (5cis‚0.5hexane), CCDC-600168 (6cis), CCDC-
600169 (6trans‚CHCl3), CCDC-600170 (7cis‚Me2CO), and CCDC-
600171 (8trans‚0.5CHCl3) contain supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.ca-
m.ac.uk/data_request/cif.
Results and Discussion
Reactivity of cis-[Pt(κ2-Aryl)(κ1-Aryl)(OH2)] (1cis) toward
dmso and XyNC. Synthesis of cis- and trans-[Pt(κ1-Aryl)2-
(CNXy)2] and cis- and trans-[Pt(κ2-Aryl)(κ1-Aryl)(CNXy)].
The addition of dmso to a CH2Cl2 or Et2O solution of complex
1cis (1:1 or 1:2 molar ratio) gave cis-[Pt(κ2-Aryl)(κ1-Aryl)(S-

4252 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
Scheme 1. Synthesis of Complexes 3 and 4
CH2Cl2 or acetone solution of complex 1cis for 5 min at room
temperature, the yellow complex cis-[Pt(κ2-Aryl)(κ1-Aryl)(CO)]
(5cis) was obtained (Scheme 2). The reaction between the red
cis-[Pt(κ2-(C,O)-C6H4NO2)2] and excess CO was also reported
to give a yellow solution, but attempts to isolate the expected
carbonyl complex, probably formed in solution, gave the starting
material.29
The complex 5cis is stable in CH2Cl2, acetone, toluene, and
CHCl3 solutions and also in the solid state at room temperature;
it decomposes on melting (160 °C) to give trans-[Pt(κ2-Aryl)-
(κ1-Aryl)(CO)] (5trans). The complex 5trans could also be
obtained by heating a solution of 5cis (1 h refluxing in toluene
or at 150 °C in a Carius tube), but the yields (61 or 51%,
respectively) were smaller than that of the fusion method (93%).
In this case, the mechanism must be the one proposed above
for the isomerization of 3cis or 4cis involving the formation of
a five-coordinate intermediate through a κ1-Aryl f κ2-Aryl
transformation, because the other, involving the dissociation of
the neutral ligand, would in this case lead to decomposition
instead of isomerization.
In an attempt to prepare a complex containing Pt-Hg bonds,
similar to those that we reported previously,24 we reacted 5cis
at room temperature with Hg(OAc)2 in a 2:1 molar ratio but,
surprisingly, we isolated complex 5trans and observed the
formation of mercury. It is likely that the isomerization process
occurs through an unstable Pt-Hg intermediate that decomposes
to give Hg, some coupling product, and 5trans.
Reactivity of cis- and trans-[Pt(κ2-Aryl)(κ1-Aryl)(CO)] (5).
Complexes 5 have been shown to be suitable precursors for
the synthesis of cis- and trans-[Pt(κ2-Aryl)(κ1-Aryl)L] complexes
(Scheme 3). With this purpose, we chose the neutral ligands
XyNC and PPh3. The room-temperature reactions of complexes
5 with XyNC (1:2) led to the corresponding complexes 3
(Scheme 2). When equimolecular amounts of XyNC and 5 were
reacted, mixtures of the corresponding complexes 3-5 were
identified in solution. However, pure complexes 4 could be
isolated from these solutions in moderate yields (approximately
50%) by crystallization.
PPh3 reacts differently from XyNC with equimolecular
amounts of complexes 5. Thus, instead of replacing CO, PPh3
coordinates trans to the κ1-Aryl ligand, replacing the oxygen
atom of κ2-Aryl and giving cis-[Pt(κ1-Aryl)2(CO)(PPh3)] (6cis)
or trans-[Pt(κ1-Aryl)2(CO)(PPh3)] (6trans) (Scheme 2). All
attempts to isomerize complexes 6 by heating were unfruitful,
because the complex cis-[Pt(κ2-Aryl)(κ1-Aryl)(PPh3)] (7cis) was
obtained instead (Scheme 3). This complex results by replace-
ment of the carbonyl ligand by the oxygen atom of a nitro group
and, in the case of 6trans, after an additional isomerization.
Correspondingly, 1H and 31P NMR spectra show that 6cis
decomposes in solution at room temperature more quickly than
6trans. In addition, the intermediate product of the isomerization
process of the latter (probably the product of CO substitution,
7trans) was not observed. If 7trans is an intermediate, it is
probably highly unstable, and its isomerization very fast, because
of the steric hindrance between PPh3 and the uncoordinated nitro
group of the κ2-Aryl ligand. The analogous 4trans complex is
stable because of the smaller spatial demand of the XyNC
around the metal center.
dmso)] (2cis; Scheme 1). The reaction (1:1 or 1:2 molar ratio)
was followed in d6-acetone by 1H NMR spectroscopy, and the
only platinum complex observed in solution was 2cis.
The room-temperature reaction of 1cis with XyNC (1:2; Xy
) 2,6-Me2C6H4) in CH2Cl2 gives almost instantly cis-[Pt(κ1-
Aryl)2(CNXy)2] (3cis; Scheme 1). When the same mixture of
reagents was refluxed in toluene for 5 h, a mixture of 3cis and
3trans (approximately 1:1.2) was isolated. The pure complex
trans-[Pt(κ1-Aryl)2(CNXy)2] (3trans) can be obtained by heating
a mixture of 1cis and XyNC (1:2) at 150 °C in a Carius tube or
3cis in toluene for 75 min. An excess of XyNC catalyzes this
isomerization process. Thus, heating a toluene solution of 3cis
(45 mg in 10 mL) at 150 °C in a Carius tube gave after 1 h
only a 25:1 mixture of 3cis and 3trans, while the same
experiment in the presence of 10 equiv of XyNC gave a 1:1
mixture. The isomerization is favored in the presence of added
XyNC because it assists the formation of the required five-
coordinate transition state.27 The mechanism for the thermal
isomerization without addition of XyNC (and also for that of
the others reported below) can imply the formation of a high-
energy five-coordinate intermediate involving a κ2-Aryl ligand
or the dissociation of XyNC.28
When the reaction between 1cis and XyNC was attempted
at room temperature in a 1:1 molar ratio, equimolecular amounts
of 1cis and 3cis were obtained, instead of the expected complex
cis-[Pt(κ2-Aryl)(κ1-Aryl)(CNXy)] (4cis). For the synthesis of
4cis, it is necessary to slowly add a CH2Cl2 solution of XyNC
to a CH2Cl2 solution of 1cis, in a 1:1 molar ratio. Therefore,
complex 4cis is an intermediate in the process of formation of
3cis from 1cis, the second step being faster than the first. Melting
of the complex 4cis (181-182 °C) led to its isomer 4trans
(Scheme 1).
The complex 7cis can be obtained more directly in better
yield (96%) by reacting PPh3 with cis-(Me4N)[Pt(κ2-Aryl)(κ1-
Aryl)Cl], the starting material for all members of this family of
bis(2,6-dinitroaryl)platinum complexes, in a 1:1 molar ratio
Reactions of 1cis with CO. Synthesis of cis- and trans-
[Pt(κ2-Aryl)(κ1-Aryl)(CO)]. By bubbling CO through a red
(27) Favez, R.; Roulet, R.; Pinkerton, A. A.; Schwarzenbach, D. Inorg.
Chem. 1980, 19, 1356.
(28) Price, J. H.; Birk, J. P.; Wayland, B. B. Inorg. Chem. 1978, 17,
(29) Vicente, J.; Chicote, M. T.; Martin, J.; Jones, P. G.; Fittschen, C.;
2245.
Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1986, 2215.

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4253
Scheme 2. Synthesis of Complexes 3-6
(Scheme 3). A 1:2 reaction gives a mixture of 7cis and cis-[Pt-
(κ1-Aryl)2(PPh3)2] (8cis). As the complex 8cis is in solution in
equilibrium with 7cis + PPh3 (see Spectroscopic Properties),
the isolation of pure 8cis requires an excess of PPh3 (1:4);
otherwise, mixtures of 7cis and 8cis are isolated. The complex
8trans can be prepared by the room-temperature reaction of
6trans with PPh3. It is air stable at room temperature, in the
solid state, and, in contrast to the case for 8cis, in solution (see
below).
In contrast to 3cis-5cis, PPh3 complexes 6-8 do not
isomerize when they are heated for 1 h at 150 °C in a Carius
tube. Instead, complexes 6cis and 6trans give 7cis, even in
solution at room temperature, 7cis remains unaltered, and 8cis
and 8trans give 7cis and OPPh3 when they melt. This thermal
decomposition of 8trans can occur after isomerization to 8cis
and decomposition to 7cis or, as we have suggested above for
the decomposition of 6trans, through the intermediacy of 7trans.
We also believe that this second reaction pathway is more
reasonable because all thermally stable [Pt(aryl)2(PPh3)2] com-
plexes are trans.14-16
Attempts to isomerize cis-[Pt(κ2-Aryl)(κ1-Aryl)L] (L ) H2O
(1cis), PhCN, tht,22 S-dmso (2cis)) by heating a toluene solution
for 1 h at 150 °C in a Carius tube or heating at the melting
point were unsuccessful. The complex 1cis gave a mixture of
unidentified products, and the others were recovered unchanged.
Conclusions on the Cis/Trans Isomerization Reactions.
The cis to trans thermal isomerization occurs for cis-[Pt(κ2-
Aryl)(κ1-Aryl)L] when L is the carbon donor ligand CO or
XyNC but not when L is an N, S, or O donor or for cis-[Pt-
(κ2-Aryl)(κ1-Aryl)Cl]-. A reasonable explanation for this be-
havior is that because the carbon donor ligands display a similar
transphobia (see refs 30 and 31), i.e. T[Aryl/Aryl] ≈ T[Aryl/
CNR] ≈ T[Aryl/CO], the trans isomers are preferred on steric
grounds. There have been no other [M(κ2-aryl)(κ1-aryl)L] (M
) Pd, Pt; L ) CO, RNC) complexes characterized by X-ray
diffraction studies,11 but it would be interesting to study the
stability of related complexes as a function of the nature of L
and the steric requirements of the ligands. The fact that some
cis complexes resist high temperatures without isomerization
means that repulsions between the diaryl ligands are not
important enough to compensate for transphobia effects because
T[Aryl/Aryl] . T[Aryl/L(N,S,O,Cl)] (L(N,S,O) ) ligand with
N, S, or O donor atoms, e.g. PhCN, tht, S-dmso, O-bonded nitro
group, Cl-). All the known group 10 metal complexes [M(aryl)2-
(30) Vicente, J.; Arcas, A.; Bautista, D.; Jones, P. G. Organometallics
1997, 16, 2127. Vicente, J.; Abad, J. A.; Frankland, A. D.; Ram´ırez de
Arellano, M. C. Chem. Eur. J. 1999, 5, 3066. Vicente, J.; Arcas, A.; Bautista,
D.; Ram´ırez de Arellano, M. C. J. Organomet. Chem. 2002, 663, 164.
Vicente, J.; Abad, J. A.; Mart´ınez-Viviente, E.; Jones, P. G. Organometallics
2002, 21, 4454.
(31) Albert, J.; Cadena, J. M.; Delgado, S.; Granell, J. J. Organomet.
Chem. 2000, 603, 235. Albert, J.; Cadena, J. M.; Granell, J. R.; Solans, X.;
Font Bardia, M. Tetrahedron: Asymmetry 2000, 11, 1943. Albert, J.;
Bosque, R.; Cadena, J. M.; Granell, J. R.; Muller, G.; Ordinas, J. I.
Tetrahedron: Asymmetry 2000, 11, 3335. Albert, J.; Bosque, R.; Cadena,
J. M.; Delgado, S.; Granell, J. J. Organomet. Chem. 2001, 634, 83. Amatore,
C.; Bahsoun, A. A.; Jutand, A.; Meyer, G.; Ntepe, A. N.; Ricard, L. J. Am.
Chem. Soc. 2003, 125, 4212. Bartolome, C.; Espinet, P.; Vicente, L.;
Villafan˜e, F.; Charmant, J. P. H.; Orpen, A. G. Organometallics 2002, 21,
3536. Carbayo, A.; Cuevas, J. Y.; Garcia Herbosa, G.; Garcia Granda, S.;
Miguel, D. Eur. J. Inorg. Chem. 2001, 2361. Carbayo, A.; Cuevas, J. V.;
Garcia Herbosa, G. J. Organomet. Chem. 2002, 658, 15. Crespo, M.;
Granell, J.; Solans, X.; Font-Bard´ıa, M. J. Organomet. Chem. 2003, 681,
143. Fernandez, S.; Navarro, R.; Urriolabeitia, E. P. J. Organomet. Chem.
2000, 602, 151. Fernandez, A.; Vazquez Garcia, D.; Fernandez, J. J.; Lo´pez
Torres, M.; Suarez, A.; Castro Juiz, S.; Vila, J. M. Eur. J. Inorg. Chem.
2002, 2389. Fernandez-Rivas, C.; Cardenas, D. J.; Martin-Matute, B.;
Monge, A.; Gutierrez-Puebla, E.; Echavarren, A. M. Organometallics 2001,
20, 2998. Jalil, M. A.; Fujinami, S.; Nishikawa, H. Dalton Trans. 2001,
1091. Larraz, C.; Navarro, R.; Urriolabeitia, E. P. New J. Chem. 2000, 24,
623. Lohner, P.; Pfeffer, M.; Fischer, J. J. Organomet. Chem. 2000, 607,
12. Lo´pez, C.; Caubet, A.; Pe´rez, S.; Solans, X.; Font-Bard´ıa, M. J.
Organomet. Chem. 2003, 681, 82. Marshall, W. J.; Grushin, V. V.
Organometallics 2003, 22, 555.

4254 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
Scheme 3. Synthesis of Complexes 7 and 8
aryl ) C6F5, R ) C6H4-1,2, but it was obtained at room
temperature from trans-[Pt(C6F5)2(AsPh3)2].35 The only reported
[M(κ1-aryl)2(CNR)2] complexes characterized by X-ray diffrac-
tion (M ) group 10 elements) are those with M ) Ni, aryl )
t
C6F5, R ) Bu33 and M ) Pd, aryl ) C6H2(CF3)3-2,4,6, R )
C6H5Me-4,36 and these are also trans. Supporting the greater
thermodynamic stabilility of these trans isomers is the fact that
the Ni complex is obtained from cis-[Ni(κ1-aryl)2L2] (L ) CO,
thf) at room temperature. Although in solution a mixture of the
cis and trans isomers is formed, the isolated and stable species
in the solid state is the trans isomer. The more stable members
of the family of diaryl complexes [Pd(R)2(L)(L′)] (R ) C6H2-
(CF3)3-2,4,6) and L ) MeCN, L′ ) Me2S, tht; L ) L′ )
4-picoline) and [Pd(κ1-aryl)2X(L)]- (L ) Me2S, tht, X ) I)36
are also of trans geometry, despite the expected electronic
preferences (T[Aryl/Aryl] > T[Aryl/L(N,S,I)]), which means
that the crowding associated with these two cis ligands is much
more important than in our complexes. The same can be
assumed about the great stability of complexes trans-[Pt(R)-
(R′)L2] (R ) R′ ) 2,3,4,5,6-pentamethylphenyl, 2,4,6-trimeth-
ylphenyl, 2,6-dimethylphenyl and L ) S-dmso, PEt33,4 or R )
R′ ) C6H4CF3-4,13 2,6-Me2C6H3, 2,4,6-Me3C6H2,4 (L ) PEt3),
2,4,6-(MeO)3C6H2,14 3,5-(CF3)2C6H3,15 Ph16 (L ) PPh3); R )
Ph, R-biphenylenyl, R′ ) R-biphenyl (R ) PEt3)) and [Pt(2,2′-
tetraphenyl)(PEt3)2]).17 The large T[Aryl/PR3] values of those
complexes with L ) PR3, and the steric demand of the
phosphine in those with L ) PPh3, are also in favor of the trans
geometry.
The thermal decomposition of the PPh3 complexes 6 and 8
to give 7cis prevents us from establishing whether the cis
isomers are more stable than the trans isomers or not. The
formation of 7cis from the cis complexes is favored by the
facility of CO and PPh3 replacement by the oxygen atom of
the nitro group, even at room temperature, and by the chelate
effect. The nonisomerization of 7cis is probably attributable to
the steric hindrance between PPh3 and the uncoordinated nitro
group of the κ2-Aryl ligand in its isomer 7trans and also to
T[Aryl/Aryl] being slightly greater than T[Aryl/PR3]. The
instability of 7trans is probably the reason for the formation of
7cis from 6trans and 8trans because, as mentioned above,
7trans could be the first product of the decomposition of these
complexes. These trans to cis isomerizations and those recently
reported by van Koten ([Pt(C∧N)2], where C∧N ) ortho-
substituted (dimethylamino)methylaryl),2 can be explained as
the consequence of T[Aryl/Aryl] > T[Aryl/L] and of the similar
(probably in van Koten’s case) or greater (our case) interligand
repulsions in the trans isomers. The same applies to the other
stable cis-diarylplatinum(II) complexes,3,4,18 although those
having a P-donor ligand19-21 are, in agreement with our
proposal, on the borderline between the stable cis and trans
isomers because T[Aryl/Aryl] is only slightly greater than
T[Aryl/PR3]. In fact, a 5:1 mixture of cis- and trans-[Pt{κ(C,P)-
C6H3(NHPPh2)-2-C(O)Me-3}2] is obtained in the thermal cy-
cloplatination of [PtMe2{P(Ph)2NHC6H4C(O)Me-2}].19
(CO)L] (aryl ) C6F5,8,9,32,33 Ph;34 M ) Ni,33 Pt8,9,32,34) charac-
terized by X-ray diffraction studies are of cis geometry, unless
the nature of some ligand forces a trans geometry. However,
they were all prepared from cis complexes and isolated at room
or lower temperatures. In agreement with our results, the thermal
treatment of some of these C6F5 or related 2,6-disubstituted aryl
complexes could give their trans isomers. Indeed, it has recently
been reported that heating a benzene or cyclohexane solution
of cis-[Pt(C6F5)2(CO)(tht)] at 50-60 °C for 1 h results in the
formation of the corresponding trans isomer.9
The thermal isomerization of 3cis to 3trans also agrees with
the greater stability of the trans isomers on steric grounds. There
has only been one platinum complex of the type trans-[Pt3(aryl)6-
{(CN)2R}3] characterized by X-ray diffraction studies, where
We believe that, in view of our results and those of others,
the complexes cis-[Pt(aryl)2L2] are more stable than the trans
isomers if L ligands are N, O, or S donor ligands because
T[Aryl/Aryl] . T[Aryl/L(N,O,S)] unless the aryl or L ligands
are highly voluminous. However, because T[Aryl/Aryl] is similar
to T[Aryl/L(C,P)], the complexes trans-[Pt(aryl)2{L(C,P)}2] can
be more stable than the cis isomers if interligand repulsions
(32) Berenguer, J. R.; Fornies, J.; Lalinde, E.; Martin, A.; Moreno, M.
T. J. Chem. Soc., Dalton Trans. 1994, 3343. Casas, J. M.; Fornies, J.;
Martinez, F.; Rueda, A. J.; Tomas, M.; Welch, A. J. Inorg. Chem. 1999,
38, 1529. Falvello, L. R.; Fornies, J.; Fortuno, C.; Martin, A.; Martinez-
Sarinena, A. P. Organometallics 1997, 16, 5849. Uso´n, R.; Fornie´s, J.; Uso´n,
M. A.; Yague, J. F.; Jones, P. G.; Meyer-Ba¨se, K. J. Chem. Soc., Dalton
Trans. 1986, 947.
(33) Fornies, J.; Martin, A.; Martin, L. F.; Menjon, B.; Kalamarides, H.
A.; Rhodes, L. F.; Day, C. S.; Day, V. W. Chem. Eur. J. 2002, 8, 4925.
(34) Romeo, R.; Arena, G.; Scolaro, L. M.; Plutino, M. R.; Bruno, G.;
Nicolo, F. Inorg. Chem. 1994, 33, 4029.
(35) Espinet, P.; Soulantica, K.; Charmant, J. P. H.; Orpen, A. G. Chem.
Commun. 2000, 915.
(36) Bartolome, C.; Espinet, P.; Martin Alvarez, J. M.; Villafan˜e, F. Eur.
J. Inorg. Chem. 2004, 2326.

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4255
Scheme 4. Proposed Pseudorotation Processes To Explain
the K2-Aryl / K1-Aryl Exchange in trans- and
cis-Diarylplatinum(II) Complexes
However, while in C both C-Pt-O angles are expected to be
around 90° (they are approximately 80° in the crystal structures
of 2cis, 5cis, and 7cis), in C′ the C2-Pt-O2 angle is expected
to be around 120°. Therefore, this route does not allow κ2-Aryl
/ κ1-Aryl exchange in the cis isomers because C′ would be
unstable, giving B′ after the cleavage of the Pt-O2 bond. For
the trans complexes, the intermediate C would give D and finally
E. However, for the cis isomers there is a dissociative route III
involving the equilibria A′ / B′ / C′′ / D′′ / E′′ / F′′ that
would allow the fluxionality, the only condition being that the
ligand L dissociates easily from the square-pyramidal intermedi-
ate D′′. Our results establish that this condition is not met by L
) XyNC (4cis) or CO (5cis). However, the previously reported
complexes cis-[Pt(κ2-Aryl)(κ1-Aryl)(OH2)] and cis-Me4N[Pt(κ2-
Aryl)(κ1-Aryl)(O2CCF3)]22 are fluxional because of the weak
-
coordination of the ligands H2O and CF3CO2
.
The 31P{1H} NMR spectrum of 8cis in CDCl3 shows three
singlet resonances at 6.50 ppm (1JPtP ) 2369 Hz), assigned to
8cis, 16.53 ppm (1JPtP ) 2579 Hz), due to 7cis, and -4.61 ppm
assigned to PPh3, in accordance with the equilibrium 8cis /
7cis + PPh3. Correspondingly, its 1H NMR spectrum in CDCl3
shows five 2:1:1:1:1 MeO singlets due to 8cis and two 2:1
singlets corresponding to 7cis. However, complex 8trans is
stable in solution, showing the expected 1H, 13C{1H}, and 31P-
{1H} NMR spectra.
The following order of trans influence can be deduced using
1
the JPtC(Aryl) values:38 Aryl (640-680 Hz) > XyNC (880 Hz)
> CO (977 Hz) > ON(O) (1115-1145 Hz), although slight
differences with respect to this order were found using structural
1
data (see below). The same is observed for the JPtCO value in
complexes 5: it is lower for the cis isomer (CO trans to Aryl;
1251 Hz) than for the trans (CO trans to ON(O); 2120 Hz).
The order of π-acceptor character, κ2-Aryl ≈ PPh3 > ON-
(O) ≈ κ1-Aryl, can be deduced from the wavenumbers of the
ν(CO) mode in 5cis (2128 cm-1), 6trans (2122 cm-1), 5trans
(2106 cm-1), and 6cis (2100 cm-1). As in other nitroaryl
derivatives,39 all complexes show νasym(NO2) (vs) and νsym(NO2)
are important. Therefore, the complexes cis-[Pt(aryl)2L2] con-
taining C (CO, isocyanides, etc.) or P donor ligands could
isomerize to their trans isomers by heating if the temperature
required for such isomerization is below their decomposition
temperatures and the ligands are sufficiently bulky.
(m) at 1368-1346 and 1310-1278 cm-1 respectively. How-
,
ever, the band due to νsym(NO2) of the coordinated nitro group
Spectroscopic Properties. At room temperature, the 1H and
13C NMR spectra of complexes show the expected three (1:1:
1) or two (2:1) MeO singlets per κ2-Aryl or κ1-Aryl groups,
respectively, except in those of 8cis, which shows the equilib-
rium 8cis a 7cis + PPh3 (see below) and 4trans and 5trans,
which show only two MeO resonances (2:1), instead of five,
because both aryl ligands are rapidly exchanging their roles:
κ2-Aryl a κ1-Aryl. This process can be slowed enough at -60
°C in 4trans to see the expected five resonances in its 1H NMR
spectrum, but in 5trans even at -90 °C only two broad signals
were observed. To explain why this exchange occurs in 4trans
and 5trans and not in the corresponding 4cis and 5cis, we
propose the pseudorotation processes shown in Scheme 4. The
first step in these fluxional processes should transform the
starting complex A (route I for the trans complexes) or A′ (route
II for the cis complexes) into the square-pyramidal structure B
or B′, respectively, after coordination of O2. One way to achieve
the structure resulting after the κ2-Aryl / κ1-Aryl exchange (E
in route I or F′′ in route III) is to transform B or B′ into a
structure in which O1 occupies the axial position of a square-
pyramidal structure, as in D (route I). This requires O1 to be a
piVot atom,37 i.e., it has to be placed first in the equatorial plane
of a trigonal bipyramid such as in C (route I) or C′ (route II).
in κ2-Aryl groups, expected around 1250-1270 cm-1 29
, could
not be assigned because in this region other bands appear when
there is not a κ2-Aryl group.
Crystal Structures. The crystal structures of complexes 2cis
(Figure 1), 3cis‚CHCl3 (Figure 2), 3trans (Figure 3), 4trans‚
CHCl3 (Figure 4), 5cis‚CH2Cl2 and 5cis‚0.5hexane (Figure 5),
6cis (Figure 6), 6trans‚CHCl3 (Figure 7), 7cis‚Me2CO (Figure
8), and 8trans‚CHCl3 (Figure 9) have been solved. All of them
show an approximately square planar geometry, although a
tendency for ligands to lie alternately slightly above and below
the plane (by as much as (0.16 Å for 8trans) is noted for 3cis,
6cis, 6trans, 7cis, and 8trans. In complexes containing only
κ1-Aryl ligands, the angles at platinum are close to the ideal
square-planar values and the aryl rings are tilted from the
coordination plane by 69-87°. The bite angle of the chelate
κ2-Aryl ligands is significantly smaller than 90° (79.18(7)-
79.94(9)°) and, correspondingly, the C(κ2-Aryl)-Pt-C(κ1-Aryl)
angles are larger than 90° (98.83(8)-101.61(10)°). The aryl and
chelate rings of the κ2-Aryl ligands are almost parallel (inter-
planar angles 4-11°) and the κ1-Aryl rings essentially perpen-
dicular (82-90°) to the coordination plane. The last structural
(38) Pregosin, P. S. Coord. Chem. ReV. 1982, 44, 247.
(39) Vicente, J.; Arcas, A.; Chicote, M. T. J. Organomet. Chem. 1983,
252, 257.
(37) Purcell, K. F.; Kotz, J. C. Inorganic Chemistry; W. B. Saunders:
London, 1977; p 404.

4256 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
Figure 1. Ellipsoid representation of 2cis (50% probability).
Selected bond lengths (Å) and angles (deg): Pt-C(21) ) 1.999-
(2), Pt-C(11) ) 2.032(3), Pt-O(11) ) 2.0770(18), Pt-S ) 2.2930-
(6), S-O(1) ) 1.474(2), C(12)-N(11) ) 1.433(3), C(16)-N(12)
) 1.478(3), N(11)-O(12) ) 1.209(3), N(11)-O(11) ) 1.291(3),
N(12)-O(16) ) 1.220(3), N(12)-O(17) ) 1.224(3), C(22)-N(21)
) 1.474(3), C(26)-N(22) ) 1.465(3); C(21)-Pt-C(11) ) 101.61-
(10), C(11)-Pt-O(11) ) 79.74(9), C(21)-Pt-S ) 87.96(7),
O(11)-Pt-S ) 90.70(5).
Figure 3. Ellipsoid representation of 3trans (30% probability).
Selected bond lengths (Å) and angles (deg): Pt-C(40) ) 1.951-
(2), Pt-C(30) ) 1.954(3), Pt-C(11) ) 2.079(2), Pt-C(21) )
2.081(2), C(12)-N(11) ) 1.475(3), C(16)-N(12) ) 1.480(3),
C(22)-N(21) ) 1.473(3), C(26)-N(22) ) 1.479(3), C(30)-N(30)
) 1.143(3), C(31)-N(30) ) 1.410(3), C(40)-N(40) ) 1.149(3),
C(41)-N(40) ) 1.403(3), N(11)-O(12) ) 1.200(3), N(11)-O(11)
) 1.218(3), N(12)-O(16) ) 1.206(3), N(12)-O(17) ) 1.221(3),
N(21)-O(22) ) 1.210(3), N(21)-O(21) ) 1.218(3), N(22)-O(26)
) 1.208(3), N(22)-O(27) ) 1.222(3); C(40)-Pt-C(11) ) 89.38-
(9), C(30)-Pt-C(11) ) 90.27(9), C(40)-Pt-C(21) ) 91.02(9),
C(30)-Pt-C(21) ) 89.29(9).
Figure 2. Ellipsoid representation of 3cis‚CHCl3 (30% probability).
The molecule of CHCl3 is omitted for clarity. Selected bond lengths
(Å) and angles (deg): Pt-C(30) ) 1.961(2), Pt-C(40) ) 1.969-
(2), Pt-C(21) ) 2.062(2), Pt-C(11) ) 2.071(2), C(12)-N(11) )
1.478(3), C(16)-N(12) ) 1.477(3), C(22)-N(21) ) 1.477(3),
C(26)-N(22) ) 1.473(3), C(30)-N(30) ) 1.159(3), C(31)-N(30)
) 1.398(3), C(40)-N(40) ) 1.158(3), C(41)-N(40) ) 1.403(3),
N(11)-O(12) ) 1.209(3), N(11)-O(11) ) 1.228(3), N(12)-O(16)
) 1.217(3), N(12)-O(17) ) 1.230(3), N(21)-O(21) ) 1.225(3),
N(21)-O(22) ) 1.226(3), N(22)-O(26) ) 1.213(3), N(22)-O(27)
) 1.234(3), N(21)-O(22) ) 1.216(3), N(21)-O(21) ) 1.224(3),
N(22)-O(27) ) 1.229(3), N(22)-O(26) ) 1.233(3); C(30)-Pt-
C(40) ) 93.27(9), C(40)-Pt-C(21) ) 89.76(8), C(30)-Pt-C(11)
) 86.01(8), C(21)-Pt-C(11) ) 91.82(8).
Figure 4. Ellipsoid representation of one of four independent
molecules of 4trans‚CHCl3 (30% probability). The molecule of
CHCl3 is omitted for clarity. Selected bond lengths (Å) and angles
(deg) (average of four values): Pt(1)-C(11) ) 2.035, Pt(1)-C(21)
) 2.084, Pt(1)-C(30) ) 1.868, Pt(1)-O(11) ) 2.047, C(12)-
N(11) ) 1.429, C(16)-N(12) ) 1.494, C(22)-N(21) ) 1.466,
C(26)-N(22) ) 1.486, C(30)-N(30) ) 1.160, C(31)-N(30) )
1.413, N(11)-O(11) ) 1.286, N(11)-O(12) ) 1.220, N(12)-O(16)
) 1.213, N(12)-O(17) ) 1.219, N(21)-O(21) ) 1.238, N(21)-
O(22) ) 1.205, N(22)-O(26) ) 1.182, N(22)-O(27) ) 1.235;
C(30)-Pt(1)-C(11) ) 101.4, O(11)-Pt(1)-C(11) ) 86.9, C(30)-
Pt(1)-C(21) ) 89.9, O(11)-Pt(1)-C(21) ) 86.9, C(30)-N(30)-
C(31) ) 169.2, N(30)-C(30)-Pt(1) ) 175.3.
features agree with the aforementioned π-acceptor character of
κ2-Aryl being greater than that of κ1-Aryl on the basis of IR
data.
The Pt-C(κ1-Aryl) bond lengths do not vary greatly, whether
trans to each other (3trans, 2.079(2), 2.081(2) Å; 6trans‚CHCl3,
2.087(4), 2.088(4) Å; 8trans‚0.5CHCl3, 2.089(2), 2.094(2) Å),
to CO (3trans, 2.079(2), 2.081(2) Å; 6cis, 2.0867(19) Å), or to
PPh3 (6cis, 2.0964(17) Å). However, they are slightly or
significantly shorter when they are trans to an isonitrile (3cis‚
CHCl3, 2.062(2), 2.071(2) Å) or to the O-nitro group in 2cis,
5cis, and 7cis (1.997(2)-2.009(3) Å), respectively, due to the
order of trans influence κ1-Aryl ≈ CO ≈ PPh3 > XyNC .
ON(O). Similarly, the Pt-C(κ2-Aryl) bond distances are not
significantly different, despite being trans to S-dmso (2cis,
2.032(3) Å), CO (5cis‚CH2Cl2, 2.033(3) Å; 5cis‚0.5(hexane),
2.0397(18) Å), or PPh3 (7cis, 2.045(2) Å). In view of the larger
esd’s of 4trans (see Experimental Section), it would be

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4257
Figure 6. Ellipsoid representation of 6cis (30% probability).
Selected bond lengths (Å) and angles (deg): Pt-C(1) ) 1.909(2),
Pt-C(11) ) 2.0867(19), Pt-C(21) ) 2.0964(17), Pt-P ) 2.3303-
(4), O(1)-C(1) ) 1.123(2), O(11)-N(11) ) 1.231(2), O(12)-
N(11) ) 1.226(2), O(16)-N(12) ) 1.225(2), O(17)-N(12) )
1.2227(19), O(21)-N(21) ) 1.222(2), O(22)-N(21) ) 1.2304-
(19), O(26)-N(22) ) 1.219(3), O(27)-N(22) ) 1.214(3), N(11)-
C(12) ) 1.472(2), N(12)-C(16) ) 1.477(2), N(21)-C(22) )
1.470(2), N(22)-C(26) ) 1.470(2); C(1)-Pt-C(21) ) 86.90(7),
C(11)-Pt-C(21) ) 92.47(7), C(1)-Pt-P ) 90.58(6), C(11)-Pt-P
) 90.47(5), O(1)-C(1)-Pt ) 176.14(18).
Figure 5. Ellipsoid representations of 5cis: (top) dichloromethane
solvate, 30% probability; (bottom) hexane hemisolvate, 50%
probability. The two forms are not isostructural. The solvent
molecules are omitted for clarity. Selected bond lengths (Å) and
angles (deg) for 5cis‚CH2Cl2: Pt-C(1) ) 1.937(3), Pt-C(21) )
2.009(3), Pt-C(11) ) 2.033(3), Pt-O(11) ) 2.079(2), C(1)-O(1)
) 1.118(4), C(12)-N(11) ) 1.431(4), C(16)-N(12) ) 1.476(4),
C(22)-N(21) ) 1.481(4), C(26)-N(22) ) 1.469(4), O(11)-N(11)
) 1.295(3), O(12)-N(11) ) 1.206(3), O(16)-N(12) ) 1.220(4),
O(17)-N(12) ) 1.225(3), O(21)-N(21) ) 1.221(4), O(22)-N(21)
) 1.218(4), O(26)-N(22) ) 1.225(4), O(27)-N(22) ) 1.228(4);
C(1)-Pt-C(21) ) 85.66(13), C(21)-Pt-C(11) ) 100.32(12),
C(1)-Pt-O(11) ) 94.43(11), C(11)-Pt-O(11) ) 79.74(10),
O(1)-C(1)-Pt ) 178.0(3). The bond lengths and angles for 5cis‚
0.5hexane are not significantly different from those for 5cis‚CH2-
Cl2; a least-squares fit of both molecules (omitting hydrogens,
terminal O of uncoordinated nitro groups, and terminal C of
methoxy groups) gave an rms deviation of 0.12 Å.
Figure 7. Ellipsoid representation of 6trans‚CHCl3 (30% prob-
ability). Selected bond lengths (Å) and angles (deg): Pt-C(1) )
1.935(5), Pt-C(21) ) 2.087(4), Pt-C(11) ) 2.088(4), Pt-P )
2.3312(12), O(1)-C(1) ) 1.087(6), O(11)-N(11) ) 1.199(6),
O(12)-N(11) ) 1.185(6), O(16)-N(12) ) 1.223(6), O(17)-N(12)
) 1.224(6), O(21)-N(21) ) 1.214(6), O(22)-N(21) ) 1.203(6),
O(26)-N(22) ) 1.213(6), O(27)-N(22) ) 1.216(6), N(11)-C(12)
) 1.478(6), N(12)-C(16) ) 1.467(6), N(21)-C(22) ) 1.482(6),
N(22)-C(26) ) 1.472(6); C(1)-Pt-C(21) ) 89.40(19), C(1)-
Pt-C(11) ) 89.55(19), C(21)-Pt-P ) 91.39(13), C(11)-Pt-P
) 90.55(12), O(1)-C(1)-Pt ) 174.9(5).
inadvisable to overinterpret small differences, but it seems clear
that the Pt-C(κ2-Aryl) (average 2.035 Å) and Pt-C(κ1-Aryl)
(average 2.084 Å) distances are in the ranges found for the other
complexes containing these ligands trans to aryl, CO, PPh3, or
S-dmso (2.032(3)-2.045(2) and 2.079(2)-2.0964(17) Å, re-
spectively). For all these complexes, the Pt-C(κ2-Aryl) bond
lengths are shorter than the Pt-C(κ1-Aryl) bond lengths due to
the aforementioned greater π-acceptor character of the κ2-Aryl
ligand. However, the Pt-(κ1-Aryl) lengths in 2cis, 5cis‚CH2-
Cl2, 5cis‚0.5(hexane), and 7cis (1.999(2), 2.009(3), 2.0069(18),
and 1.997(2) Å, respectively) are shorter than the corresponding
Pt-C(κ2-Aryl) distances (2.032(3), 2.033(3), 2.0397(18), and
2.045(2) Å, respectively), as a consequence of the weaker trans
influence of the O-nitro ligand compared to that of CO, XyNC,
PPh3, or S-dmso ligands. The greater π-acceptor character of
the κ2-Aryl as compared to that of κ1-Aryl is also shown by the
Pt-CO bond length in 5cis (1.937(3), 1.939(2) Å) being
significantly longer than in 6cis (1.909(2) Å). However, although
this should produce in 6cis an increase in the C-O bond distance
with respect to 5cis, the increase is not significant: 1.123(2) vs
1.118(4) Å. Similarly, the greater π-acceptor character of PPh3
as compared to that of κ1-Aryl can explain the observation that
the Pt-CO and PtC-O bond lengths in the complex 6cis (1.909-
(2) and 1.123(2) Å) are significantly shorter and longer,
respectively, than the corresponding distances in 6trans (1.935-
(5) and 1.087(6) Å). Both Pt-CO bond lengths should be similar
if only the trans influences of κ1-Aryl and PPh3 are considered.
The Pt-CCNXy (trans to κ1-Aryl, 3cis 1.961(2), 1.969(2) Å;
trans to XyNC, 3trans 1.951(2), 1.954(3) Å; trans to ON(O),
4trans average of four molecules 1.868 Å), the Pt-O (trans to

4258 Organometallics, Vol. 25, No. 18, 2006
Vicente et al.
Figure 8. Ellipsoid representation of 7cis‚Me2CO (50% probability;
solvent omitted). Selected bond lengths (Å) and angles (deg): Pt-
C(21) ) 1.997(2), Pt-C(11) ) 2.045(2), Pt-O(11) ) 2.0789(14),
Pt-P ) 2.3074(6), O(11)-N(11) ) 1.300(2), O(12)-N(11) )
1.219(2), O(16)-N(12) ) 1.225(3), O(17)-N(12) ) 1.213(3),
O(21)-N(21) ) 1.209(3), O(22)-N(21) ) 1.206(3), O(26)-N(22)
) 1.226(2), O(27)-N(22) ) 1.223(2), C(12)-N(11) ) 1.424(3),
C(16)-N(12) ) 1.482(3), C(22)-N(21) ) 1.482(3), C(26)-N(22)
) 1.463(3); C(21)-Pt-C(11) ) 98.83(8), C(11)-Pt-O(11) )
79.18(7), C(21)-Pt-P ) 92.20(6), O(11)-Pt-P ) 90.12(4).
Figure 10. Association of molecules of 3trans via π‚‚‚π stacking
of XyNC rings and C-H‚‚‚π interactions to give a chain. All NO2
groups, hydrogen atoms (except those involved in the C-H‚‚‚π
interactions), and κ2-Aryl atoms (except the C and O atoms bonded
to Pt) have been omitted for clarity.
Figure 9. Ellipsoid representation of 8trans‚0.5CHCl3 (50%
probability; solvent omitted). Selected bond lengths (Å) and angles
(deg): Pt-C(11) ) 2.089(2), Pt-C(21) ) 2.094(2), Pt-P(2) )
2.3267(7), Pt-P(1) ) 2.3397(7), C(12)-N(11) ) 1.475(3), C(16)-
N(12) ) 1.475(3), C(22)-N(21) ) 1.474(3), C(26)-N(22) )
1.481(3), O(11)-N(11) ) 1.228(3), O(12)-N(11) ) 1.228(3),
O(16)-N(12) ) 1.225(3), O(17)-N(12) ) 1.227(3), O(21)-N(21)
) 1.221(3), O(22)-N(21) ) 1.230(3), O(26)-N(22) ) 1.230(3),
O(27)-N(22) ) 1.224(3); C(11)-Pt-P(2) ) 89.92(7), C(21)-
Pt-P(2) ) 90.81(7), C(11)-Pt-P(1) ) 89.42(7), C(21)-Pt-P(1)
) 90.83(7).
Figure 11. Association of two molecules of 4trans‚CHCl3 via
π‚‚‚π stacking of XyNC rings and C-H‚‚‚π interactions. All NO2
groups, hydrogen atoms (except those involved in the C-H‚‚‚π
interactions), and κ2-Aryl atoms (except the C and O atoms bonded
to Pt) have been omitted for clarity.
κ1-Aryl, 2cis 2.0770(18) Å, 5cis 2.079(2) Å, 7cis 2.0789(14)
Å; trans to XyNC, 4trans average of four molecules 2.047 Å),
and the Pt-P bond distances (trans to κ1-Aryl, 6cis 2.3303(4)
Å; trans to CO, 6trans 2.3312(12) Å; trans to PPh3, 8trans
2.3267(7), 2.3397(7) Å) reveal the same aforementioned order
of trans influence: κ1-Aryl ≈ CO ≈ PPh3 > XyNC . ON(O).
The π-acceptor character of the κ2-Aryl ligand should cause a
lengthening of the trans Pt-P bond in 7cis with respect to 6cis.
However, since the bond is shorter in 7cis (2.3074(6) Å), we
can only explain it by assuming that trans influence κ1-Aryl >
κ2-Aryl.
In the complex 2cis, the geometry of the dimethyl sulfoxide
moiety is virtually unaffected by S coordination and the S-O
bond length (1.474(2) Å) is similar to that in solid dimethyl
sulfoxide, determined at -60 °C (1.471(8) Å).40 The Pt-S bond
(40) Viswamitra, M. A.; Kannan, K. K. Nature 1966, 209, 1016.

Bis(2,6-dinitroaryl)platinum(II) Complexes
Organometallics, Vol. 25, No. 18, 2006 4259
distance (2.2930(6) Å) lies in the range reported in other aryl
Pt(II) complexes containing an S-dmso ligand bonded trans to
an aryl group (2.2693(5)-2.324(2) Å),18,41,42 but is longer than
those in aryl Pt(II) complexes with an S-dmso ligand bonded
trans to N42,43 or O,44 as a consequence of the trans influence
of an aryl group being stronger than that of a N or O donor
ligand.
As has been observed previously in other nitroaryl com-
plexes,22,24,29,45 the N-O(Pt) bond distance is longer (average
1.293 Å) than the others (average 1.216 Å).
All of the complexes display a variety of contacts in
their packing (e.g. C-H‚‚‚O interactions, solvent Cl‚‚‚O, axial
Pt‚‚‚O), but a full description would be extremely long. Instead,
we present one motif associated with the XyNC ligand; the
molecules associate in dimers with a π‚‚‚π stacking of the XyNC
rings46 and a short contact from the para hydrogen of the XyNC
ring to the centroid of κ1-Aryl. In 3cis the rings are parallel by
symmetry, have an intercentroid distance of 3.62 Å, a per-
pendicular distance of 3.44 Å, and an offset of 1.1 Å, and the
H‚‚‚Cent distance (C21-C26) is 2.66 Å. For 3trans (see Figure
10) both XyNC rings are involved in such interactions, leading
to a chain of molecules parallel to the y axis. For rings C31-
C36 and C41-C46, the corresponding values are 3° and 3.58,
3.42, and 1.1 Å and H‚‚‚Cent ) 2.48 (C11-C16), 2.50 Å (C21-
C26). Molecules 1 and 2 of the four present in the asymmetric
unit cell of 4trans‚CHCl3 form a “dimer” through such π‚‚‚π
stacking/CH‚‚‚π contacts (Figure 11). The centroid-centroid
distance is 3.82 Å, the perpendicular distance 3.50 Å,
the interplanar angle 2°, and the centroid offset 1.5 Å. The
H‚‚‚Cent distance is 2.68 Å for both molecules.
Color of the Complexes. In agreement with previous
observations,22,24 complexes with a κ2-Aryl ligand have intense
colors (yellow (5cis), red (5trans), and orange (2cis, 4cis, 4trans,
and 7cis)), while in those having only κ1-Aryl ligands, these
colors fade to pale yellow (3cis, 3trans, 6cis, 6trans, 8cis, and
8trans).
(41) Minghetti, G.; Doppiu, A.; Stoccoro, S.; Zucca, A.; Cinellu, M. A.;
Manassero, M.; Sansoni, M. Eur. J. Inorg. Chem. 2002, 431. Owen, J. S.;
Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004, 126, 8247.
(42) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Stoccoro, S.; Minghetti, G.;
Manassero, M. Organometallics 2002, 21, 783.
(43) Cave, G. W. V.; Alcock, N. W.; Rourke, J. P. Organometallics 1999,
18, 1801. Ryabov, A. D.; Otto, S.; Samuleev, P. V.; Polyakov, V. A.;
Alexandrova, L.; Kazankov, G. M.; Shova, S.; Revenco, M.; Lipkowski,
J.; Johansson, M. H. Inorg. Chem. 2002, 41, 4286.
Acknowledgment. We thank the Direccio´n General de
Investigacio´n, Ministerio de Educacio´n y Ciencia, and FEDER
for financial support (Grant CTQ2004-05396). M.D.G.-L. thanks
the Fundacio´n Se´neca (Comunidad Auto´noma de la Regio´n de
Murcia, Spain) for a Grant. We thank Dr. I. Dix and Dr. R.
Herbst-Irmer (University of Go¨ttingen) for checking the data
set of 4trans for possible twinning effects.
(44) Izakovich, E. N.; Kachapina, L. M.; Shibaeva, R. P.; Khidekel, M.
L. IzV. Akad. Nauk SSSR, Ser. Khim. 1983, 1389.
(45) Vicente, J.; Arcas, A.; Borrachero, M. V.; de Goicoechea, M. L.;
Lanfranchi, M.; Tiripicchio, A. Inorg. Chim. Acta 1990, 177, 247. Vicente,
J.; Arcas, A.; Borrachero, M. V.; Tiripicchio, A.; Tiripicchio-Camellini,
M. Organometallics 1991, 10, 3873.
(46) Gupta, B. D.; Yamuna, R.; Mandal, D. Organometallics 2006, 25,
706. Janiak, C. Dalton Trans. 2000, 3885. Okawa, H. Coord. Chem. ReV.
1998, 92, 1.
Supporting Information Available: CIF files for 2cis, 3cis‚
CHCl3, 3trans, 4trans‚CHCl3, 5cis‚CH2Cl2, 5cis‚0.5(hexane), 6cis,
6trans‚CHCl3, 7cis‚Me2CO, and 8trans‚0.5CHCl3. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM060398T