Synthesis of the first family of platinum(IV) complexes with phosphorus ylide ligands

Article abstract of DOI:10.1021/om020113m

The synthesis of the first family of platinum(IV) complexes with phosphorous ylide ligands was discussed. The reduction was the starting point to study and describe a general, selective, and high yield method for the synthesis of difficult-to-obtain imine Pt(II) complexes by reducing the corresponding readily available Pt(IV)-based imines with carbonyl-stabilized ylides. The platinum(II) compounds were obtained by replacing Me₂S, chloride, nitriles, or ethylene or by bridge-splitting of dimeric chloro-platinum(II) complexes with the corresponding ylides.

Full text of DOI:10.1021/om020113m

3744
Organometallics 2002, 21, 3744-3748
Syn th esis of th e F ir st F a m ily of P la tin u m (IV) Com p lexes
w ith P h osp h or u s Ylid e Liga n d s
Nadezhda A. Bokach,†,‡ Stanislav I. Selivanov,‡ Vadim Yu. Kukushkin,*,‡
J ose Vicente,*,§ Matti Haukka, and Armando J . L. Pombeiro*,†
Centro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais,
1049-001 Lisbon, Portugal, Department of Chemistry, St. Petersburg State University,
198904 Stary Petergof, Russian Federation, Department of Chemistry, Grupo de Qu´ımica
Organometa´lica, Departamento de Quı´mica Inorga´nica, Facultad de Quı´mica, Universidad de
Murcia, Apartado 4021, 30071-Murcia, Spain, and Department of Chemistry, University of
J oensuu, P.O. Box 111, FIN-80101, J oensuu, Finland
Received February 12, 2002
The reactions of (PPN)[PtCl5(NH2R′)] [PPN ) Ph2PdNdPPh2; R′ ) H (1), Me (2)], prepared
by treatment of [PtCl4(NH2R′)(Me2SO)] with [PPN]Cl, with 1 equiv of the carbonyl-stabilized
phosphorus ylides Ph3PdCHC(O)R (R ) OMe, OEt, Me) lead to the substitution of one
chloride to afford the first Pt(IV) complexes containing phosphorus ylides, cis-[PtCl4(NH2R′)-
{CH(PPh3)C(O)R}] [R ) OMe, R′ ) H (4), Me (5); R ) OEt, R′ ) H (6), Me (7); R ) Me, R′
) H (8), Me (9)]. Their electrochemical behavior was investigated by cyclic voltammetry
and controlled potential electrolysis, and the crystal structure of complex 4 was determined
by X-ray diffraction studies.
In tr od u ction
scribed,5 and many of them were synthesized by reacting
chloromethylene complexes, [Pt]-CH2Cl, with phos-
phines. The abundance of (ylide)Pt(II) complexes dra-
matically contrasts with the few reported fruitless
attempts to synthesize complexes of platinum(IV). In-
deed, to the best of our knowledge, there is one report6
describing the insufficiently characterized platinum(IV)
compound “{(Me2N)3PCH2}4PtI4” (only C and H elemen-
tal analyses were given and no other data presented6)
and an account on several unsuccessful attempts to
Complexes of phosphorus ylides have attracted much
attention in synthetic and theoretical chemistry1 and
also have some useful practical implications, e.g., as
polymerization catalysts.2 Phosphorus ylides form com-
plexes with virtually every metal of the periodic table.1
In particular, many platinum(II) complexes with phos-
phorus ylides have been prepared, for instance, contain-
ing the carbonyl-stabilized ylides, Ph3PdCHC(O)R [R
) Me, Ph, OMe, OEt].3,4 These platinum(II) compounds
were obtained by replacing Me2S, chloride, nitriles, or
ethylene or by bridge-splitting of dimeric chloro-plati-
num(II) complexes with the corresponding ylides. Com-
plexes with nonstabilized ylides have also been de-
prepare Pt(IV) complexes with the phosphorus diylide
-
Ph3PdCdPPh3 by reacting it with [PtMe3X] (X ) PF6
,
CF3SO3-, I-). From these reactions only one Pt(II)
species was isolated and characterized.7
(4) (a) Weleski, E. T.; Silver, J . L.; J ansson, M. D.; Burmeister, J .
L. J . Organomet. Chem. 1975, 102, 365. (b) Oosawa, Y.; Urabe, H.;
Saito, T.; Sasaski, Y. J . Organomet. Chem. 1976, 122, 113. (c) Kato,
M.; Urabe, H.; Oosawa, Y.; Saito, T.; Sasaki, Y. J . Organomet. Chem.
1976, 121, 81. (d) Koezuka, H.; Matsubayashi, G.-E.; Tanaka, T. Inorg.
Chem. 1976, 15, 417. (e) Teagle, J . A.; Burmeister, J . L. Inorg. Chim.
Acta 1986, 118, 65. (f) Bertani, R.; Casarin, M.; Ganis, P.; Maccato,
C.; Pandolfo, L.; Venzo, A.; Vittadini, A.; Zanotto, L. Organometallics
2000, 19, 1373. (g) Larraz, C.; Navarro, R.; Urriolabeitia, E. P. New J .
Chem. 2000, 24, 623. (h) Falvello, L. R.; Fernandez, S.; Larraz, C.;
Llusar, R.; Navarro, R.; Urriolabeitia, E. P. Organometallics 2001, 20,
1424.
(5) (a) Schmidbaur, H.; Gasser, O.; Krueger, C.; Sekutowski, J . C.
Chem. Ber. 1977, 110, 3517. (b) Blaschke, G.; Schmidbaur, H.; Kaska,
W. C. J . Organomet. Chem. 1979, 182, 251. (c) Basset, J . M.; Mandl,
J . R.; Schmidbaur, H. Chem. Ber. 1980, 113, 1145. (d) Ghaffar, T.;
Kieszkiewicz, A.; Nyburg, S. C.; Parkins, A. W. J . Organomet. Chem.
1996, 517, 227. (e) Scherer, O. J .; J ungmannn, H. Z. Naturforsch., B
1981, 36, 1663. (f) Scherer, O. J .; J ungmannn, H. J . Organomet. Chem.
1982, 228, C61. (g) Engelter, C.; Moss, J . R.; Niven, M. L.; Nassimbeni,
L. R.; Reid, G. J . Organomet. Chem. 1982, 232, C78. (h) Holy, N.;
Deschler, U.; Schmidbaur, H. Chem. Ber. 1982, 115, 1379. (i) Engelter,
C.; Moss, J . R.; Nassimbeni, L. R.; Niven, M. L.; Reid, G.; Spiers, J . C.
J . Organomet. Chem. 1986, 315, 255. (j) Herring, A. M.; Markham, D.
P.; Shaw, B. L.; Thornton-Pett, N. J . Chem. Soc., Chem. Commun.
1987, 643. (k) Hoover, J . F.; Stryker, J . M. J . Am. Chem. Soc. 1988, 7,
2082. (l) Hoover, J . F.; Stryker, J . M. J . Am. Chem. Soc. 1990, 112,
464.
* Corresponding authors. (V.Yu.K.) E-mail:
kukushkin@
VK2100.spb.edu; (J .V.) E-mail: jvs@um.es; (A.J .L.P.) E-mail:
pombeiro@ist.utl.pt.
† Instituto Superior Te´cnico.
‡ St. Petersburg State University.
§ Universidad de Murcia.
University of J oensuu.
(1) (a) Schmidbaur, H. Pure Appl. Chem. 1980, 52, 1057. (b) Belluco,
U.; Michelin, R. A.; Mozzon, M.; Bertani, R.; Facchin, G.; Zanotto, L.;
Pandolfo, L. J . Organomet. Chem. 1998, 557, 37. (c) Navarro, R.;
Urriolabeitia, E. P. J . Chem. Soc., Dalton Trans. 1999, 4111. (d)
J ohnson, A. V.; Kaska, W. C.; Starzewski, K. A. O.; Dixon, D. A. Ylides
and Imines of Phosphorus; J . Wiley & Sons: New York, 1993. (e)
Kolodiazhnyi, O. I. Phosphorus Ylides: Chemistry and Applications
in Organic Synthesis; Wiley-VCH: Weinheim, 1999. (f) Kaska, W. C.
Coord. Chem. Rev. 1983, 48, 1. (g) Schmidbaur, H. Angew. Chem., Int.
Ed. Engl. 1983, 22, 907.
(2) Ostoja Starzewski, K. A.; Born, L. Organometallics 1992, 11,
2701, and references therein.
(3) (a) Arnup, P. A.; Baird, M. C. Inorg. Nucl. Chem. Lett. 1969, 5,
65. (b) Illingsworth, M. L.; Teagle, J . A.; Burmeister, J . L.; Fultz, W.
C.; Rheingold, A. L. Organometallics 1983, 2, 1364. (c) Facchin, G.;
Zanotto, L.; Bertani, R.; Nardin, G. Inorg. Chim. Acta 1996, 245, 157.
(d) Belluco, U.; Michelin, R. A.; Bertani, R.; Facchin, G.; Pace, G.;
Zanotto, L.; Mozzon, M.; Furlan, M.; Zangrando, E. Inorg. Chim. Acta
1996, 252, 355. (e) Ferna´ndez, S.; Garc´ıa, M. M.; Navarro, R.;
Urriolabeitia, E. P. J . Organomet. Chem. 1998, 561, 67. (f) Benetollo,
F.; Bertani, R.; Ganis, P.; Pandolfo, L.; Zanotto, L. J . Organomet. Chem.
2001, 629, 201.
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10.1021/om020113m CCC: $22.00 © 2002 American Chemical Society
Publication on Web 08/06/2002

Pt(IV) Complexes with Phosphorus Ylide Ligands
Organometallics, Vol. 21, No. 18, 2002 3745
Sch em e 1
In recent years, our group has been involved in
investigations of the reactivity of metal-activated ni-
triles,8,9 a topic that we recently reviewed.10 In particu-
lar, one of us has been investigating the nucleophilic
attack of phosphorus ylides11 to nitriles coordinated to
platinum(II) and observed that trans-[PtCl2(NCR)2] (R
) Me, Ph, C6F5) react with the carbonyl-stabilized ylides
to give complexes containing ylideimino or/and imino-
phosphorano ligands. To ascertain the influence of the
oxidation state of the metal in these reactions, we
planned to study the reactivity of [PtCl4(NCR)2] with
the carbonyl-stabilized ylides. We also realized the
interest of the reaction products if simple substitution
reactions would occur to give the first Pt(IV) complexes
with phosphorus ylides.
Resu lts a n d Discu ssion
Syn th etic P a r t. All anionic complexes [PPN][PtCl5-
(amine)] [PPN ) Ph2PdNdPPh2; amine ) NH3 (1),
NH2Me (2), NHEt2 (3)] were prepared by substitution
of dimethyl sulfoxide in the platinum(IV) complex
[PtCl4(amine)(Me2SO)], in accord with the method
published for a similar compound, i.e., [Ph3PCH2Ph]-
[PtCl5(NH3)].9c The choice of the PPN+ counterion is
determined by its high lipophilicity, which provides good
solubility in the most common organic solvents.
Treatment of [PPN][PtCl5(NH2R′)] (R′ ) H, Me) with
1 equiv of the carbonyl-stabilized phosphorus ylide
Ph3PdCHC(O)R (R ) OMe, OEt) in chloroform leads
to substitution of one chloride to afford the neutral
complexes cis-[PtCl4(NH2R′){CH(PPh3)C(O)R}] [R )
OMe, R′ ) H (4), Me (5); R ) OEt, R′ ) H (6), Me (7)]
and [PPN]Cl (Scheme 1).
Complexes 4 and 5 were released as yellow crystalline
products directly from the reaction mixture and isolated
in 50-65% yields, while 6 and 7, which exhibit much
higher solubilities, were isolated by removal of the
solvent followed by their purification by column chro-
matography on silica gel. These four complexes have
been characterized by elemental analyses, FAB-mass
spectrometry, 1H, 13C{1H}, 31P{1H}, and 195Pt{1H} NMR
(including the inverse detection HMQC method), and
IR spectroscopies and 4 by X-ray crystallography also.
The reactions of ylides Ph3PdCHC(O)R with [PPN]-
[PtCl5(NHEt2)] gave a broad mixture of compounds,
among which the substitution products were not de-
tected by NMR spectroscopy.
The reactions of [PPN][PtCl5(NH2R′)] (R′ ) H, Me)
with Ph3PdCHC(O)Me lead to the unstable substitution
products [PtCl4(NH2R′){CH(PPh3)C(O)Me}] [R′ ) H (8),
Me (9)]. All our attempts to isolate 8 or 9 as pure
compounds were unsuccessful since they rapidly decom-
posed either on SiO2 or upon washing with Et2O after
removal of the solvent in a vacuum. However, they were
characterized by FAB-MS from their CDCl3 solutions
and the reactions monitored by NMR spectroscopy. The
greater relative stability of complexes 4-7 could be due
to the more basic character of the ylides with R ) OMe,
OEt than that with R ) Me. However, when the Pt(IV)
complexes 4-7 were heated in solution and also in the
solid phase, an overall degradation with no dominant
compound was observed.
Disappointingly, the reaction of [PtCl4(NCMe)2] with
Ph3PdCHCO2Me led to a mixture of the platinum(II)
complexes (Ph3PCH2CO2Me)[PtCl3(NCMe)] and [PtCl2-
(NCMe)2].12 However, this reduction was the starting
point to study and describe a general, selective, and high
yield method for the synthesis of difficult-to-obtain
imine Pt(II) complexes by reducing the corresponding
readily available Pt(IV)-based imines with carbonyl-
stabilized ylides.12 Moreover, from the latter results, we
concluded that to prepare Pt(IV) complexes with phos-
phorus ylides via the substitution route, the Pt(IV)
precursor must be a weaker oxidant than the previously
studied12 complexes containing nitriles, imines, sulfox-
ides, or thioethers. We hypothesized that anionic com-
plexes with efficient electron-donor ligands, such as
[PtCl5(amine)]-, would be promising candidates, and in
accord with our expectations, it was observed that the
ylides Ph3PdCHC(O)R (R ) OMe, OEt, Me) react with
[PPN][PtCl5(NH2R′)] (PPN ) Ph2PdNdPPh2, R′ ) H,
Me) displacing the chloride, in a nonredox process, to
give the first family of Pt(IV) complexes with phospho-
rus ylides. These results are reported herein.
(8) (a) Bokach, N. A.; Kuznetsov, M. L.; Garnovskii, D. A.; Natile,
G.; Kukushkin, V. Yu.; Pombeiro, A. J . L. Inorg. Chem. 2002, 41, 2041.
(b) Ferreira, C. M. P.; Guedes da Silva, M. F. C.; Frau´sto da Silva, J .
J . R.; Pombeiro, A. J . L.; Kukushkin, V. Yu.; Michelin, R. A. Inorg.
Chem. 2001, 40, 1134. (c) Wagner, G.; Haukka, M.; Frau´sto da Silva,
J . J . R.; Pombeiro, A. J . L.; Kukushkin, V. Yu. Inorg. Chem. 2001, 40,
264. (d) Kukushkin, V. Yu.; Pakhomova, T. B.; Bokach, N. A.; Wagner,
G.; Kuznetsov, M. L.; Galanski, M.; Pombeiro, A. J . L. Inorg. Chem.
2000, 39, 216. (e) Wagner, G.; Pombeiro, A. J . L.; Kukushkin, V. Yu.
J . Am. Chem. Soc. 2000, 122, 3106. (f) Kukushkin, V. Yu.; Pakhomova,
T. B.; Kukushkin, Yu. N.; Herrmann, R.; Wagner, G.; Pombeiro, A. J .
L. Inorg. Chem. 1998, 37, 6511.
(9) (a) Kopylovich, M. N.; Kukushkin, V. Yu.; Guedes da Silva, M.
F. C.; Haukka, M.; Frau´sto da Silva, J . J . R.; Pombeiro, A. J . L. J .
Chem. Soc., Perkin Trans. 1 2001, 1569. (b) Garnovskii, D. A.;
Kukushkin, V. Yu.; Haukka, M.; Wagner, G.; Pombeiro, A. J . L. J .
Chem. Soc., Dalton Trans. 2001, 560. (c) Kuznetsov, M. L.; Bokach,
N. A.; Kukushkin, V. Yu.; Pakkanen, T.; Wagner, G.; Pombeiro, A. J .
L. J . Chem. Soc., Dalton Trans. 2000, 4683. (d) Kukushkin, V. Yu.;
Ilichev, I. V.; Zhdanova, M. A.; Wagner, G.; Pombeiro, A. J . L. J . Chem.
Soc., Dalton Trans. 2000, 1567. (e) Kukushkin, V. Yu.; Ilichev, I. V.;
Wagner, G.; Frau´sto da Silva, J . J . R.; Pombeiro, A. J . L. J . Chem.
Soc., Dalton Trans. 1999, 3047. (f) Wagner, G.; Pombeiro, A. J . L.;
Bokach, N. A.; Kukushkin, V. Yu. J . Chem. Soc., Dalton Trans. 1999,
4083.
(10) Kukushkin, V. Yu.; Pombeiro, A. J . L. Chem. Rev. 2002, 102,
1771.
(11) Vicente, J .; Chicote, M. T.; Beswick, M. A.; Ram´ırez de Arellano,
M. C. Inorg. Chem. 1996, 35, 6592. Vicente, J .; Chicote, M. T.; Lagunas,
M. C.; J ones, P. G. Inorg. Chem. 1995, 34, 5441. Vicente, J .; Chicote,
M. T.; Ferna´ndez-Baeza, J .; Lahoz, F. J .; Lo´pez, J . A. Inorg. Chem.
1991, 30, 3617.
(12) Wagner, G.; Pakhomova, T. B.; Bokach, N. A.; Frau´sto da Silva,
J . J . R.; Vicente, J .; Pombeiro, A. J . L.; Kukushkin, V. Y. Inorg. Chem.
2001, 40, 1683.
For the most sterically hindered compounds of the
series, i.e., [PtCl4(NH2Me){CH(PPh3)CO2Et}] (7) and
[PtCl4(NH2Me){CH(PPh3)C(O)Me}] (9), cis-to-trans
isomerization in solution was detected, thus indicating
that the substitution in [PtCl5(NH2R′)]- occurs at the

3746 Organometallics, Vol. 21, No. 18, 2002
Bokach et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for
cis-[P tCl4(NH3){CH(P P h 3)CO2Me}]‚(DMF )
cis position to the amine, in accord with higher trans-
effect of Cl- ligand versus amine,13 and that the isomer-
ization occurs due to steric reasons.
empirical formula
C24H29Cl4N2O3PPt
fw
761.35
NMR a n d IR Ch a r a cter iza tion of th e (Ylid e)P t-
(IV) Com p lexes. NMR spectra for the stable complexes
4-7 were measured in dmso-d6 due to their low solubil-
ity in the most common deuterated organic solvents. For
the two unstable species 8 and 9, NMR data were
obtained by 1H NMR monitoring of the reaction in
CDCl3. All complexes exhibit a doublet with satellites
due to the CH proton coupled with 31P and 195Pt. This
resonance appears in the range 6.21-6.34 (in dmso-d6)
and 6.34-6.55 (in CDCl3) ppm, which is, as expected,
low field shifted with respect to the corresponding
resonance in similar Pt(II) complexes (3.82-5.60 ppm).3
temp, K
λ, Å
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
120(2)
0.71073
P1h (No. 2)
10.0137(1)
10.7147(1)
27.8702(4)
79.3810(6)
80.5840(5)
73.0038(5)
2791.50(6)
4
F
calcd, g/cm3
1.812
5.496
0.0351
0.0739
µ(Mo KR), mm-1
a
R1 (I g 2σ)
wR2 (I g 2σ)
2
b
The values of 2J P-H (6.5-9.8 Hz) and J Pt-H (89.0-97.5
Hz) are not significantly different from those previously
reported for Pt(II) complexes.3 The corresponding CH
carbon gives a doublet in the 13C{1H} NMR at 15.17-
15.37 ppm (1J P-C 44.5-48.2 Hz) with 195Pt satellites
(1J Pt-C 569.0-573.6 Hz). 31P{1H} NMR spectra display
a singlet in the range 31.36-33.28 ppm (for cis-isomers
R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for cis-[P tCl4(NH3){CH(P P h 3)CO2Me}]‚(DMF )
(4)
A
B
2
in dmso-d6) flanked by 195Pt satellites with J PPt ca. 60
Pt(1)-Cl(1)
2.3673(16)
2.3259(15)
2.3157(15)
2.3323(16)
2.043(5)
2.3799(15)
2.3309(16)
2.3062(15)
2.3221(16)
2.057(5)
2.131(6)
1.833(6)
1.504(8)
1.339(7)
1.217(7)
1.459(8)
119.7(3)
179.04(17)
177.28(15)
176.75(6)
125.0(5)
110.8(5)
115.7(5)
Hz. The chemical shift of the 195Pt resonance is mainly
dependent on the nature of the ylide, although the
difference in solvents also should be taken into account.
Thus, complexes with R ) OMe, OEt, 4-7, show such
resonance at lower field (-579 to -657 ppm) than the
others with R ) Me (8, -749.7 ppm; 9, -729, -813
ppm). One of the two resonances observed in 9, that at
lower frequency, could be assigned to the trans-isomer
in good agreement with the data reported in the
literature for cis- and trans-isomers of platinum(IV)
complexes [PtCl4L2].8a,d,9b,14 This assignment allows the
trans geometry to be attributed to the only isomer of 7
detected in solution after data acquisition of the 195Pt-
{1H} NMR spectrum. The chemical shift of this reso-
nance (-657 ppm) is abnormally lower than the corre-
sponding one in their cis homologous 4-6 appearing in
the range from -579 to -584 ppm.
Pt(1)-Cl(2)
Pt(1)-Cl(3)
Pt(1)-Cl(4)
Pt(1)-N(1)
Pt(1)-C(1)
2.121(6)
1.827(6)
1.526(8)
1.335(7)
1.202(7)
1.456(8)
120.0(3)
C(1)-P(1)
C(1)-C(2)
C(2)-O(3)
C(2)-O(4)
O(3)-C(3)
Pt(1)-C(1)-P(1)
Cl(1)-Pt(1)-C(1)
Cl(4)-Pt(1)-N(1)
Cl(2)-Pt(1)-Cl(3)
C(1)-C(2)-O(4)
C(1)-C(2)-O(3)
C(2)-O(3)-C(3)
178.22(15)
177.17(15)
176.70(6)
124.9(5)
110.1(5)
115.2(5)
Ta ble 3. Cyclic Volta m m etr ic Da ta a for th e
Com p lexes cis-[P tCl4(a m in e)(ylid e)]
red
red
complex
Ep
Ep/2
The frequency of the band assigned to the ν(CdO)
stretching mode in free carbonyl-stabilized ylides is
unusually low for a carbonyl group [R ) Me (1540 cm-1),
OEt (1610 cm-1), OMe (1620 cm-1)] because of the
contribution of the resonance form [Ph3P(+)CHdC(R)-
O(-)]. When such ylides are C-protonated,14 to give
phosphonium salts, or are C-coordinated to a metal, the
bond order of the CO group increases because the only
possible resonance form is M(-)-CH(P(+)Ph3){C(R)dO}.
Correspondingly, upon C-coordination, the band as-
signed to the ν(CdO) stretching mode for a given M,
νΜ(CdO), must appear at higher frequencies than in the
4
5
6
7
-0.60
-0.67
-0.62
-0.62
-0.49
-0.55
-0.45
-0.48
Values in V( 0.02 vs SCE, measured by CV at 200 mV s-1
a
scan rate, at a platinum-disk electrode, in 0.2 mol dm-3 [NBu4][BF4]/
CH2Cl2 in the presence of ferrocene as the internal standard.
(CdO) ) 35-40 cm-1 15
In the isolated complexes 4-6,
.
the values of ν(CdO) are in the range 1686-1691 cm-1
and ∆νPtCl (amine)(CdO) are in the range 27-34 cm-1
.
4
These values of ∆ν are similar to those of the groups
[Au(PPh3)]+ (30),15 [PtCl(dppe)]+ (dppe ) 1,2-bis-dipheyl-
phosphinoethane, ∆ν ) 32),3d [PtCl(cyclometalated phos-
phine)] (32),3e or [Pt(Me)(dppe)]+ (20).3f
free ylide. We have shown that for a given R the higher
+
frequency corresponds to the phosphonium salt νH
-
(CdO) and that in a series of gold(I) and gold(III)
complexes the value of ∆ν[Au](CdO) ) νH+(CdO) - ν[Au]
-
Electr och em ica l Ch a r a cter iza tion . The electro-
chemical behavior of the complexes was investigated by
cyclic voltammetry (CV) and controlled potential elec-
trolysis (CPE) in 0.2 mol dm-3 [NBu4][BF4]/CH2Cl2.
They exhibit an irreversible reduction wave at a poten-
tial (Table 3) that is somewhat sensitive to a change of
the amine or ylide ligand (Epred in the range from -0.60
(CdO) decreases when the electron-withdrawing char-
acter of the group [Au] is increased. For example, when
R ) OMe, OEt, ∆νAuCl (CdO) ) 0-5 cm-1 and ∆νAu(ylide)
-
+
3
(13) Davies, J . A.; Hockensmith, C. M.; Kukushkin, V. Yu.; Kuku-
shkin, Yu. N. Synthetic Coordination Chemistry: Principles and
Practice; World Scientific: Singapore-New J ersey, 1996; pp 492.
(14) The O-protonation of Ph3PdCH(O)Me has recently been ob-
served in solution. Berry, D. E.; Patenaude, G. W. J . Chem. Educ. 2002,
79, 498.
(15) Vicente, J .; Chicote, M. T.; Saura-Llamas, I.; Turp´ın, J .;
Ferna´ndez-Baeza, J . J . Organomet. Chem. 1987, 333, 129.

Pt(IV) Complexes with Phosphorus Ylide Ligands
Organometallics, Vol. 21, No. 18, 2002 3747
Exp er im en ta l Section
The yields, elemental analyses, and FAB, IR, and NMR data
for the complexes are in the Supporting Information (see
below).
Ma ter ia ls a n d In str u m en ta tion . Solvents were obtained
from commercial sources and used as received. Ph3PdCHCO2-
Me and [(Ph3P)2N]Cl were purchased from Lancaster and
Aldrich, respectively, while other ylides16 and the plati-
num(IV) complexes [PtCl4(amine)(Me2SO)]17 were prepared in
accord with the published methods. C, H, and N elemental
analyses were carried out by the Microanalytical Service of
the Instituto Superior Te´cnico. 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. Negative-ion FAB
mass spectra were obtained on a Fisons VG-Austospec spec-
trometer by bombarding NBA matrixes of the samples. Infra-
red spectra (4000-400 cm-1) were recorded on a BIO-RAD FTS
3000MX instrument in KBr pellets.
NMR Stu d ies. All NMR spectra were recorded at ambient
temperature on a Varian UNITY 300 [299.95, 121.42, 75.42,
and 64.48 MHz for H, 31P, 13C, and 195Pt, respectively] and/or
1
Bruker DPX 300 [300.13, 121.49, and 75.47 MHz for 1H, 31P,
and 13C, respectively]. 1H and 13C chemical shifts are given
relative to dmso (δ ) 2.50 and 39.5, respectively). 31P chemical
shifts were measured relative to 80% H3PO4 as standard (δ )
0 ppm). 195Pt chemical shifts are given relative to Na2[PtCl6]
(by using K2[PtCl4], δ ) -1630 ppm, as a standard), and the
half-height line width is given in parentheses. The inverse
detection HMQC method with the BIRD sequence during the
preparation period18 was used to determine the heteronuclear
F igu r e 1. ORTEP view of cis-[PtCl4(NH3){CH(PPh3)CO2-
Me}] (4) with atomic numbering scheme. The thermal
ellipsoids are drawn at the 50% probability level.
to -0.67 V vs SCE). By exhaustive cathodic CPE at the
potential of this wave, two electrons per molecule are
transferred and a new irreversible anodic wave is then
ox
detected by CV at Ep of 1.30 (4), 1.32 (5), 1.27 (6), or
1.32 (7) V vs SCE, conceivably due to the oxidation of
the cathodically generated Pt(II) product. In accord with
the proposed reduction of the starting Pt(IV) complexes
at the metal center, no reduction wave was detected for
any of the free ligands.
195
13
spin-spin coupling constants J
C. HMQC spectra resulted
Pt-
from 128 × 1024 data matrix size with 256 scans per t1 value
(the delay for creation of antiphase magnetization was 3.5 ms
and the relaxation delay was 1.0 s), and broadband 13C
decoupling with GARP-119 was applied during the acquisition
(13C 90° pulse of 60 ms). The data were zero-filled in t1
dimension and a sine-bell filter was applied in both dimensions
before the Fourier transformation. The coupling constants
X-r a y Cr ysta l Str u ctu r e of Com p lex 4. The coor-
dination geometry at platinum is essentially octahedral
(Figure 1). The bond distances between Pt and Cl trans
to the ylide ligand [Pt-Cl(1): 2.3673(16), 2.3799(15) Å]
are much longer than the other three [2.3062(15)-
2.3323(16) Å] because of the greater trans influence of
carbon donors than chloro or amine ligands. Surpris-
ingly, the bond distances between Pt and mutually trans
Cl ligands are significantly different in molecule B, the
distances Pt-Cl(2) [2.3309(16) Å] being longer than Pt-
Cl(3) [2.3062(15) Å]. Probably, this difference is due to
packing effects because the enviroment of Cl(2) is more
crowded than that of Cl(3) in molecule B. The Pt-C
bond distances [2.121(6), 2.131(6) Å] are shorter than
that reported for the Pt(II) complex cis-[Pt(Me){CH-
(PPh3)CO2Et}(dppe)] [2.162(7) Å].3f The CdO bond
distance in this complex [1.203(9) Å] is similar to those
found in complex 4 [1.202(7), 1.217(7) Å].
1
13
J
were defined from the INEPT spectrum.
H-
C
X-r a y Str u ctu r e Deter m in a tion of cis-[P tCl4(NH3){CH-
(P P h 3)CO2Me}] (4). The yellow crystal plates for the X-ray
analysis were obtained by slow diffusion of Et2O in a DFM
solution of the complex. X-ray diffraction data were collected
with a Nonius KappaCCD diffractometer using Mo KR radia-
tion (λ ) 0.71073 Å). Denzo and Scalepack20 programs were
used for cell refinements and data reduction. The structure
was solved by direct methods using the SHELXS-9721 program
with the WinGX22 graphical user interface. The structure
refinement was carried out with SHELXL-97.23 A multiscan
absorption correction, based on equivalent reflections (XPERP
in SHELXTL v5.1),24 was applied to the data (Tmax/Tmin
0.29588/0.22433). All hydrogen atoms were placed on idealized
(16) Vicente, J .; Chicote, M. T.; Saura-Llamas, I. J . Chem. Educ.
1993, 70, 163.
(17) Kukushkin, V. Yu.; Moiseev, A. I.; Sidorov, E. O. Zh. Obsch.
Khim. 1989, 59, 1958; J . Gen. Chem. (Engl. Transl.) 1989, 59, 1750.
(18) Bax, A.; Sabramanian, S. J . Magn. Reson. 1986, 67, 565.
(19) Shaka, A. J .; Barker, P. B.; Freeman, R. J . Magn. Reson. 1985,
64, 547.
(20) Otwinowski, Z.; Minor, W. DENZO-SCALEPACK, Processing
of X-ray Diffraction Data Collected in Oscillation Mode. In Methods
in Enzymology, Volume 276, Macromolecular Crystallography, part A;
Carter, C. W., J r., Sweet, R. M., Eds.; Academic Press: New York,
1997; pp 307-326.
(21) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1997.
(22) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(23) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1997.
(24) Sheldrick, G. M. SHELXTL Version 5.1; Bruker Analytical
X-ray Systems, Bruker AXS, Inc.: Madison, WI, 1998.
Con clu d in g Rem a r k s
An easy method has been found for the synthesis of
the first family of Pt(IV) complexes with phosphorus
ylide ligands, showing the possibility of generating this
type of high-valent metal complexes despite the known
reducing power of the ylides on Pt(IV) centers. Hence,
this study opens up the possibility of extending to
Pt(IV) a promising ylide-based organometallic chemis-
try. Once it has been proved that such complexes can
exist, other synthetic ways can be attempted, for
example, oxidation of platinum(II) ylide complexes

3748 Organometallics, Vol. 21, No. 18, 2002
Bokach et al.
positions and constrained to ride on their parent atom. The
asymmetric unit consists of two independent cis-[PtCl4-
(NH3){CH(PPh3)CO2Me}] molecules and two DMF solvent
molecules. Crystallographic data are summarized in Table 1
and selected bond lengths and angles in Table 2.
Syn th esis of (Ylid e)P t(IV) Com p lexes. The ylide (0.030
mmol) was added to a solution of [PPN][PtCl5(NH2R)] (R )
H, Me) (25 mg, 0.027 mmol) in CHCl3 (0.7 mL). The reaction
mixture was left to stand at room temperature for 12 h, and
the resulting pale yellow crystals released (4, 5) were filtered
off, washed with CHCl3 (two 1 mL portions), and dried in air
at room temperature. When complexes were not released from
the reaction mixture (6, 7), they were isolated by removal of
the solvent in a vacuum followed by column chromatography
on silica gel upon elution with CH2Cl2/Et2O. The isolation of
complexes 8 and 9 was unsuccessfully attempted because they
rapidly decomposed either on SiO2 or upon washing with Et2O
after removal of the solvent in a vacuum. However, they were
characterized by FAB-MS and NMR spectroscopy from their
CDCl3 solutions.
Electr och em ica l Stu d y. The electrochemical experiments
were performed on an EG&G PARC 273A potentiostat/gal-
vanostat connected to a PC computer through a GPIB interface
(National Instruments PC-2A). Cyclic voltammetry (CV) ex-
periments were undertaken in a two-compartment three-
electrode cell, at a platinum-disk working electrode probed by
a Luggin capillary connected to a silver-wire pseudo-reference
electrode; a platinum auxiliary electrode was employed. Con-
trolled potential electrolyses (CPE) were carried out in a two-
compartment three-electrode cell with platinum-gauze working
and counter electrodes in compartments separated by a glass
frit; a Luggin capillary, probing the working electrode, was
connected to a silver-wire pseudo-reference electrode. The
electrochemical experiments were performed in a N2 atmo-
sphere at room temperature. The potentials were measured
by CV at 200 mV s-1 scan rate, in 0.2 mol dm-3 [NBu4][BF4]/
CH2Cl2 in the presence of ferrocene as the internal standard,
and the values are quoted relative to the saturated calomel
electrode (SCE) by using the [Fe(η5-C5H5)2]0/+ redox couple (E°
) 0.53 vs SCE, in CH2Cl2). The use, as reference electrode, of
the SCE or other electrode in aqueous medium was avoided
due to the sensitivity of the systems to water. The CPE
experiments were monitored regularly by CV to ensure that
no significant potential drift occurred along the electrolyses.
P r ep a r a tion of th e Sta r tin g Ma ter ia ls. A suspension of
[PtCl4(amine)(Me2SO)] (0.25 mmol) and [PPN]Cl (0.25 mmol)
in CH2Cl2 (3 mL) was heated at 45 °C until homogenization
of the reaction mixture occurred (ca. 12 h). The resulting
orange solution was evaporated in a vacuum at 20-25 °C to
give an orange oily residue that was stirred with Et2O to give
an orange solid that was collected on a filter and dried in air
at room temperature.
Ack n ow led gm en t. V.Yu.K. and J .V. are indebted
to INTAS for the grant 97-0166. N.A.B. expresses
gratitude to the International Science Foundation (Soros
Foundation) and also to Centro de Qu´ımica Estrutural,
Complexo I, Instituto Superior Te´cnico, Portugal, for the
fellowships. V.Yu.K. thanks the International Science
Foundation for Soros Professorship. V.Yu.K. and A.J.L.P.
are very much obliged to the FCT (Foundation for
Science and Technology) and the PRAXIS XXI and
POCTI programs for financial support. J .V. and V.Yu.K.
thank Ministerio de Ciencia y Tecnologia and FEDER
(BQU2001-0133) for financial support.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic files for the complex cis-[PtCl4(NH3){CH(PPh3)CO2-
Me}]‚(DMF). The yields, elemental analyses, and FAB, IR, and
NMR data for complexes. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM020113M