Platinum-Assisted Addition of Carbonyl-Stabilized Phosphorus Ylides to Pentafluorobenzonitrile and Acetonitrile to Give Platinum(II) Complexes Containing Iminophosphorane and/or N-Bonded β-Imino Phosphorus Ylide Ligands. Crystal and Molecular Structures o

Article abstract of DOI:10.1021/ic951666a

PtCl₂ reacts with C₆F₅CN to give trans-[PtCl₂(NCC₆F₅)₂] (1) which, in turn, reacts with carbonyl-stabilized phosphorus ylides Ph₃P=CHR [R = C(O)Me, CO₂Et] t

Full text of DOI:10.1021/ic951666a

6592
Inorg. Chem. 1996, 35, 6592-6598
Platinum-Assisted Addition of Carbonyl-Stabilized Phosphorus Ylides to
Pentafluorobenzonitrile and Acetonitrile To Give Platinum(II) Complexes Containing
Iminophosphorane and/or N-Bonded â-Imino Phosphorus Ylide Ligands. Crystal and
Molecular Structures of trans-[PtCl2{E-NHdC(C6F5)C(dPPh3)C(O)Me}2] and
trans-[PtCl2{E-N(dPPh3)C(C6F5)dCHCO2Et}{E-NHdC(C6F5)C(dPPh3)CO2Et}]†
Jose´ Vicente,*,‡ Mar´ıa Teresa Chicote,* and Michael A. Beswick
Grupo de Qu´ımica Organometa´lica,§ Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica,
Universidad de Murcia, Apartado 4021, Murcia, 30071 Spain
M. Carmen Ramirez de Arellano
University Chemical Laboratory, Lensfield Road, CB2 1EW Cambridge, U.K.
ReceiVed December 28, 1995X
PtCl2 reacts with C6F5CN to give trans-[PtCl2(NCC6F5)2] (1) which, in turn, reacts with carbonyl-stabilized
phosphorus ylides Ph3PdCHR [R ) C(O)Me, CO2Et] to give trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}-
{NCC6F5}] (2a), trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}2] (3a), trans-[PtCl2{E-NHdC(C6F5)C(dPPh3)C-
(O)Me}2] (3b) or trans-[PtCl2{E-N(dPPh3)C(C6F5)dCHCO2Et}{E-NHdC(C6F5)C(dPPh3)CO2Et}] (4), depending
on the reaction conditions. Similarly, Ph3PdCHCO2Me reacts with trans-[PtCl2(NCMe)2] to give trans-
[PtCl2{NHdCMeC(dPPh3)CO2Me}(NCMe)] (2b). Complex 3b‚CH2Cl2 crystallizes in the triclinic system, space
group P1h, with a ) 7.596(2) Å, b ) 12.694(3) Å, c ) 16.962(3) Å, R ) 104.28(3)°, â ) 102.73(3)°, γ )
104.43(3)°, V ) 1464.2(6) Å3, and Z ) 1. The structure was refined to values of R1 ) 0.0411 and wR2 )
0.1172 [I >2σ(I)] and shows two chloro and two N-bonded â-imino phosphorus ylide ligands in a trans geometry.
Complex 4 crystallizes in the monoclinic system, space group P21/c, with a ) 16.400(8) Å, b ) 14.354(7) Å, c
) 23.221(12) Å, R ) 90(3)°, â ) 92.42(2)°, γ ) 90°, V ) 5462(5) Å3, and Z ) 4. The structure was refined
to values of R1 ) 0.0246 and wR2 ) 0.0557 [I >2σ(I)]. This complex has also a trans-geometry and shows that
while the attack of the ylide on one of the nitrile ligands produces a â-imino-phosphorus ylide ligand the addition
on the second nitrile leads to an iminophosphorane ligand.
Introduction
temperature). We started these studies by reacting [PtCl2-
(NCPh)2] with Ph3PdCHCO2R (R ) Me, Et) and, to our
surprise, we obtained the first iminophosphorano complexes of
platinum which involves CsP bond cleavage and CdC bond
formation (see B in Scheme 2).8 Recently, we have reacted
[PtCl2(NCR)2] (R ) Me, Ph) and To3PdCH(py-2) (To )
4-MeC6H4; py-2 ) 2-pyridyl) in an attempt to force the
coordination of the ylide assisted by the pyridine substituent
(see A in Scheme 2). However, from the mixture obtained, we
isolated the first complexes containing a N-bonded â-imino-
phosphorus ylide ligand of platinum after a CsH addition of
the ylide to the CtN bond of the nitrile.9
In this paper we report reactions of carbonyl stabilized
phosphorus ylides Ph3PdCHC(O)R (R ) Me, OEt) with trans-
[PtCl2(NCR)2] (R ) C6F5, Me) that again do not lead to [PtCl2-
(ylide)2] but to complexes containing N-bonded â-iminophos-
phorus ylide (we will call these ylideimino complexes; see a in
[PtCl2(NCMe)2] was reported to react with carbonyl-
stabilized phosphorus ylides at the refluxing temperature of
MeCN to give complexes [PtCl2{CH(PPh3)C(O)R}2] (R ) alkyl,
aryl, alkoxy, aryloxy; see Scheme 1).1 However, the same
authors proved later that some of these products were really
mixtures of phosphonium salts and orthometalated complexes
[Pt{CH{P(C6H4-2)Ph2}{C(O)R}(µ-Cl)]2 (see Scheme 1).2 We
became interested in these reactions first because we were
preparing a series of carbonyl-stabilized phosphorus ylido
complexes of gold(I),3,4 -(II),4 and -(III),3b Pd(II),5 Ag(I),6 and
heteronuclear AuAg, AuCu7 and second because nobody had
reexamined such reactions to see if the complexes [PtCl2(ylide)2]
can be prepared from [PtCl2(NCR)2] using different nitriles and
the same or other experimental conditions (e.g., at room
† Dedicated to Professor Rafael Uso´n on the occasion of his 70th birthday.
‡ E-mail: jvs@fcu.um.es
§ http://www.scc.um.es/gi/gqo
(5) (a) Vicente, J.; Chicote, M. T.; Lagunas, M. C.; Jones, P. G.;
Bembenek, E. Organometallics 1994, 13, 1243. (b) Vicente, J.;
Chicote, M. T.; Saura-Llamas, I.; Lo´pez-Mun˜oz, M. J.; Jones, P. G.
J. Chem. Soc., Dalton Trans. 1990, 3683. (c) Vicente, J.; Chicote, M.
T.; Fernandez-Baeza, J. J. Organomet. Chem. 1989, 364, 407.
(6) Vicente, J.; Chicote, M. T.; Saura-Llamas, I. J. Chem. Educ. 1993,
70, 163 and references therein.
X Abstract published in AdVance ACS Abstracts, October 1, 1996.
(1) Weleski, E. T., Jr.; Silver, J. L.; Jansson, M. D.; Burmeister, J. L. J.
Organomet. Chem. 1975, 102, 365.
(2) Illingsworth, M. L.; Teagle, J. A.; Burmeister, J. L.; Fultz, W. C.;
Rheingold, A. L. Organometallics 1983, 2, 1364. Teagle J. A.;
Burmeister, J. L. Inorg. Chim. Acta 1986, 118, 65.
(3) (a) Vicente, J.; Chicote, M. T.; Saura-Llamas, I.; Lagunas, M. C. J.
Chem. Soc., Chem. Commun. 1992, 915. (b) Vicente, J.; Chicote, M.
T.; Lagunas, M. C.; Jones, P. G. J. Chem. Soc., Dalton Trans. 1991,
2579 and references therein.
(4) Vicente, J.; Chicote, M. T.; Saura-Llamas, I. J. Chem. Soc., Dalton
Trans. 1990, 1941 and references therein.
(7) Vicente, J.; Chicote, M. T.; Lagunas, M. C. Inorg. Chem. 1993, 32,
3748 and references therein.
(8) Vicente, J.; Chicote, M. T.; Ferna´ndez-Baeza, J.; Lahoz, F. Inorg.
Chem. 1991, 30, 3617
(9) Vicente, J.; Chicote, M. T.; Lagunas, M. C.; Jones, P. G. Inorg. Chem.
1995, 34, 5441.
S0020-1669(95)01666-1 CCC: $12.00 © 1996 American Chemical Society

Platinum-Assisted Addition of Ylides
Inorganic Chemistry, Vol. 35, No. 22, 1996 6593
Scheme 1
Chart 1
methylidenetriarylphosphoranes, to form imino ether, amidino,11
and ylideimino complexes.12 Some examples of the reverse
reaction, namely the attack of C6F5CN to cationic complexes
of Pt containing methanol as a ligand, [{M}-MeOH]+ have
been reported to yield the corresponding imino ether derivatives
[{M}-NHdC(OMe)C6F5]+.10 It has also been reported that
the formation of some hydrido Re(III) complexes occurs through
methyleneamido intermediates resulting from the protonation
of a nitrile ligand.13 The only reported platinum complexes
containing ylideimine or iminophosphorane ligands are four
ylideimino complexes prepared by us8,9 and a family of
iminophosphorano complexes recently reported.14
Scheme 2. Synthesis of Complexes 2-4 and Previous
Results
Experimental Section
All the reactions were carried out in normal laboratory conditions.
Technical grade solvents were purified by standard procedures. The
IR, elemental analyses, melting point determinations, and NMR spectra
recording were carried out as described elsewhere.5a Chemical shifts
are referred to TMS (1H) or H3PO4 [31P{1H}] or CFCl3 (19F).
trans-[PtCl2(NCC6F5)2] (1). PtCl2 (720 mg, 2.70 mmol) was
refluxed in C6F5CN (15 mL) for 4 h. The solution was filtered while
hot through MgSO4, allowed to cool to room temperature, and left
overnight at which point a yellow precipitate formed from the brown
solution. The brown liquid was decanted off and the precipitate
recrystallized from dichloromethane and diethyl ether, giving the yellow
compound 1. Yield: 1306 mg, 74%. Anal. Calcd for C14Cl2F10N2Pt:
C, 25.78; N, 4.30. Found: C, 25.96; N, 4.30. Mp: >320 °C. 19F{1H}-
NMR (CDCl3, δ): -155.22 (m), -134.66 (m), -126.46 (m) ppm. IR
(Nujol): νCtN 2314, νPtCl 362, 329, 299 cm-1
trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}(NCC6F5)] (2a).
.
1
(200 mg, 0.30 mmol) and Ph3PdCHCO2Et (107 mg, 0.30 mmol) were
stirred for 24 h in acetone (20 mL). The resulting yellow solution
was concentrated to near dryness, and on the addition of diethyl ether
(20 mL) the yellow compound 2a precipitated. It was recrystallized
from dichloromethane/diethyl ether. Yield: 230 mg, 75%. Anal. Calcd
for C36H21Cl2F10N2O2PPt: C, 43.22; H, 2.12; N, 2.80. Found C, 43.33;
H, 2.07; N, 2.70. Mp: 180 °C. 1H NMR (CDCl3, δ): 0.46 (t, 3H,
Me), 3.68 (q, 2H, CH2), 7.48-7.62 (m, 15H, PPh3), 10.69 (s, 1H, NH)
ppm. 31P{1H} NMR (CDCl3, δ): 18.19 (s) ppm. 19F NMR (CDCl3
δ): -162.19 (m, 2F, C6F5), -156.64 (m, 2F, C6F5), -153.24 (t, 1F,
C6F5), -138.01 (m, 1F, C6F5), -134.09 (m, 2F, C6F5), -127.57 (m,
2F, C6F5), ppm. IR (Nujol): νNH 3195, νCtN 2350, νPtCl 329 cm-1
.
(10) (a) Clark, H. C.; Manzer, L. E. Inorg. Chem. 1971, 10, 2699. (b) Clark,
H. C.; Manzer, L. E. Inorg. Chem. 1972, 11, 2749. (c) Manzer, L. E.
J. Chem. Soc., Dalton Trans. 1974, 1535. (d) Clark, H. C.; Manzer,
L. E. J. Organomet. Chem. 1973, 47, C17.
(11) (a) Cini, R.; Caputo, P. A.; Intini, F. P.; Natile, G. Inorg. Chem. 1995,
34, 1130 and references therein. (b) Bertani, R.; Gotti, M.; Michelin,
R. A.; Mozzon, M.; Bandoli, G.; Angelici, R. J. Organometallics, 1996,
15, 1236 and references therein.
(12) Knoll, L. J. Organomet. Chem. 1978, 155, C63. Knoll, L.; Wolff, H.
Chem. Ber. 1979, 112, 2709. Knoll, L. J. Organomet. Chem. 1980,
186, C42
(13) Frau´sto da Silva, J. R.; Guedes da Silva, M. F. C.; Henderson, R. A.;
Pombeiro, A. J. L.; Richards,R. L. J. Organomet. Chem. 1993, 461,
141.
(14) Avis, M. W.; Vrieze, K.; Kooijman, H.; Veldman, N.; Speck, A. L.;
Elsevier, C. J. Inorg. Chem. 1995, 34, 4092. Avis, M. W.; Vrieze, K.;
Ernsting, J. M.; Elsevier, C. J.; Veldman, N.; Speck, A. L.; Katti, K.
V.; Barnes, C. L. Organometallics 1996, 15, 2376. Avis, M. W.;
Elsevier, C. J.; Veldman, N.; Kooijman, H.; Speck, A. L. Inorg. Chem.
1996, 35, 1518.
Chart 1) or this and iminophosphorane (see b in Chart 1) ligands
depending on the nature of the ylide and of R and on the reaction
conditions. These reactions involving nucleophilic attack
towards coordinated nitriles have attracted interest since the
pionering works of Clark and Manzer10 to the present.11 The
polarizing action of the metal renders the ligands more
susceptible to the attack of alcohols, amines, carbanions, or

6594 Inorganic Chemistry, Vol. 35, No. 22, 1996
Vicente et al.
trans-[PtCl2{NHdC(Me)C(dPPh3)CO2Me}(NCMe)] (2b). trans-
[PtCl2(NCMe)2] (237 mg, 0.68 mmol) and Ph3PdCHCO2Me (455 mg,
1.36 mmol) were stirred in acetone (10 mL) for 48 h. The resulting
suspension was filtered off and the yellow solid washed twice with
acetone (2 mL) and air dried to give 2b, which was recrystallized from
dichloromethane/diethyl ether. Yield: 280 mg, 60%. Anal. Calcd
for C25H25Cl2N2O2PPt: C, 44.00; H, 3.69; N, 4.10. Found: C, 43.90;
H, 3.46; N, 3.96. Mp: 199 °C. 1H NMR (CD2Cl2, δ): 1.87 (s, 3 H,
Me), 2.41 (s, 3 H, MeCN), 2.99 (s, 3H, CO2Me), 7.56-7.83 (m, 15 H,
PPh3), 9.50 (s, br, 1H, NH) ppm. 31P{1H} NMR (CD2Cl2, δ): 17.87
Table 1. Crystallographic Data for 3b and 4
3b
4
formula
M
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V(Å3)
Z
C57H40Cl4F10N2O2P2Pt
1373.74
P1h
C58H42Cl2F10N2O4P2Pt
1348.87
P21/c
16.400(8)
14.354(7)
7.596(2)
12.694(3)
16.962(3)
104.28(3)
102.73(3)
104.43(3)
1464(2)
1
23.221(12)
92.42(2)
(s) ppm. IR (Nujol): νNH 3259, νCtN 2329, νPtCl 345, 327 cm-1
.
trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}2] (3a). 1 (150 mg,
0.23 mmol) and Ph3PdCHCO2Et (176 mg, 0.51 mmol) were stirred in
acetone (20 mL) in an ice bath for 30 min. The resulting orange
solution was concentrated to near dryness and on the addition of diethyl
ether (20 mL) an orange precipitate formed (220 mg) containing (by
NMR) a mixture of 4 and 3a (in approximately a 3:2 ratio). When the
crude product was dissolved in the minimum of dichloromethane and
layered with methanol, a first set of orange crystals formed, which
proved to be compound 4 (30 mg); the crystals were removed and the
solution allowed to slowly evaporate over 24 h, yielding yellow crystals
which proved to be compound 3a. Yield: 38%. Anal. Calcd for
C58H42Cl2F10N2O4P2Pt: C, 51.64; H, 3.14; N, 2.08. Found: C, 51.49;
H, 3.15; N, 1.86. Mp: 184 °C. 1H NMR (CDCl3, δ): 0.49 (t, 3 H,
Me), 3.60 (q, 2H, CH2), 7.4-7.57 (m, 15 H, PPh3), 10.53 (s, 1H, NH)
ppm. 31P{1H} NMR (CDCl3, δ): 17.68 (s) ppm. 19F NMR (CDCl3,
δ): -164.93 (s, 2F, CF), -156.52 (t, 2F, CF), -136.57 (m, 1F, CF)
5462(1)
4
153
0.710 73
1.640
2672
T (K)
λ (Å)
293
0.710 73
1.558
678
2.7
F
calcd (g cm-3
)
F(000)
µ (mm-1
)
2.8
7330/714
no. of reflns/
Params
3888/386
R(F)a
0.041
0.117
0.025
0.056
Rw(F2)b
a R(F) ) Σ||Fo| - |Fc||/Σ|Fo| for reflections with F > 4σ(F). b Rw(F2)
2
2
) {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo )2]}0.5 for all reflections; w-1 ) σ2(Fo ) +
(aP)2 + bP, where P ) [Fo2 + 2Fc2]/3 and a and b are constants set by
the program.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3a
ppm. IR (Nujol): νNH 3190, νPtCl 336 cm-1
.
trans-[PtCl2{NHdC(C6F5)C(dPPh3)C(O)Me}2] (3b). 1 (94 mg,
0.14 mmol) and Ph3PdCHCOMe (100 mg, 0.31 mmol) were refluxed
in acetone (20 mL) for 1 h, the resulting yellow solution was
concentrated to near dryness, and on addition of diethyl ether (30 mL)
the yellow compound 3b precipitated. Yield: 152 mg, 82%. Anal.
Calcd for C56H38Cl2F10N2O2P2Pt: C, 52.19; H, 2.97; N, 2.17. Found:
C, 51.81; H, 3.06; N, 2.07. Mp: 243 °C. 1H NMR (CD2Cl2, δ): 2.02
(s, 3 H, Me), 7.4-7.6 (m, 15 H, PPh3), 8.05 (s, br, 1H, NH) ppm.
31P{1H} NMR (CD2Cl2, δ): 14.52 (s) ppm. 19F{1H} NMR (CD2Cl2,
δ): -162.13 (s, 2F), -152.07 (s, 1F), -133.22 (s, 2F) ppm. IR
Pt-N
1.997(6)
1.294(9)
1.434(10)
Pt-Cl
2.302(2)
1.443(10)
1.767(7)
N-C(1)
C(2)-C(3)
C(1)-C(2)
C(2)-P
N-Pt-Cl
C(1)-N-Pt
N-C(1)-C(41)
C(3)-C(2)-C(1)
C(1)-C(2)-P
94.8(2)
136.2(5)
117.0(6)
127.6(7)
122.6(5)
N-Pt-Cla
N-C(1)-C(2)
C(2)-C(1)-C(41)
C(3)-C(2)-P
85.2(2)
125.1(6)
117.9(6)
109.7(5)
a Symmetry operator: -x, -y, -z.
(Nujol): νNH 3293, νPtCl 331, 321 cm-1
.
A yellow prism 0.45 × 0.35 × 0.28 mm of 3b‚CH2Cl2, obtained by
vapor diffusion of diethyl ether into a solution of 3b in dichloromethane,
was used to collect 3888 reflections on a Siemens R3mV diffractometer
(2θmax 45°, 3715 unique, Rint 0.023). Data were collected using Mo
KR radiation. The orientation matrix was refined from setting angles
of 32 reflections in the 2θ range 20-25°. An absorption correction
based on ψ-scans was applied, with transmission factors 0.334-0.484.
The structure was solved by direct methods and refined anisotropically
on all F2 data using SHELXL-93 (G. M. Sheldrick, University of
Go¨ttingen). Hydrogen atoms were included using a riding model. The
final wR2 for 386 parameters was 0.117 [R1 ) 0.041 for I > 2σ(I)].
The dichloromethane molecule is disordered over two sites. Tables 1
and 2 give crystallographic data and selected bond lengths and angles,
respectively.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 4
Pt-N(1)
2.005(3)
2.3022(13)
1.303(5)
1.454(6)
1.349(5)
1.770(4)
Pt-N(2)
2.086(3)
2.3066(12)
1.435(5)
1.399(5)
1.463(6)
1.643(3)
Pt-Cl(2)
Pt-Cl(1)
N(1)-C(1)
C(2)-C(3)
C(6)-C(7)
C(2)-P(1)
C(1)-C(2)
N(2)-C(6)
C(7)-C(8)
N(2)-P(2)
N(1)-Pt-Cl(2)
N(1)-Pt-Cl(1)
C(1)-N(1)-Pt
84.99(10) N(2)-Pt-Cl(2)
95.91(10) N(2)-Pt-Cl(1)
88.80(9)
90.19(9)
123.7(4)
139.2(3)
N(1)-C(1)-C(2)
N(1)-C(1)-C(11) 116.5(3)
C(2)-C(1)-C(11) 119.8(3)
C(1)-C(2)-C(3)
C(3)-C(2)-P(1)
C(6)-N(2)-Pt
118.8(3)
112.9(3)
120.8(2)
126.5(3)
C(1)-C(2)-P(1)
C(6)-N(2)-P(2)
P(2)-N(2)-Pt
128.3(3)
121.2(3)
116.9(2)
trans-[PtCl2{N(dPPh3)C(C6F5)dCHCO2Et}{E-NHdC(C6F5)
C(dPPh3)CO2Et}] (4). 1 (150 mg, 0.23 mmol) and Ph3PdCHCO2Et
(176 mg, 0.51 mmol) were refluxed in acetone (20 mL) for 2 h, the
resulting orange solution was concentrated to near dryness, and on the
addition of diethyl ether (20 mL) the orange compound 4 precipitated.
Yield: 225 mg, 73%. Anal. Calcd for C58H42Cl2F10N2O4P2Pt: C,
51.64; H, 3.14; N, 2.08. Found: C, 51.74; H, 3.28; N, 2.12. Mp:
178 °C. 1H NMR (CDCl3, δ): 0.43 (t, 3 H, Me), 0.89 (t, 3 H, Me),
3.58 (q, 2H, CH2), 3.69 (q, 2H, Me), 5.04 (s, 1H, CH), 7.38-7.70 (m,
24 H, PPh3), 8.07 (m, 6 H, PPh3), 10.18 (s, 1H, NH) ppm. 31P{1H}
NMR (CDCl3, δ): 18.07 (s, PdC), 36.85 (s, PdN) ppm. 19F NMR
(CDCl3, δ): -164.89 (t, 2F), -162.82 (t, 2F), -156.53 (t, 1F), -154.59
(t, 1F), -135.94(m, 4F) ppm. IR (Nujol): νNH 3195, νPdN 1274, νPtCl
C(7)-C(6)-N(2)
C(7)-C(6)-C(51) 120.8(3)
N(2)-C(6)-C(51) 112.7(3)
angles of 42 reflections in the 2θ range 20-25°. An absorption
correction based on ψ-scans was applied, with transmission factors
0.953-0.732. The structure was solved by direct methods and refined
anisotropically on all F2 data using SHELXL-93 (G. M. Sheldrick,
University of Go¨ttingen). Hydrogen atoms for the methyl group were
refined using a rigid model and the others riding. The final wR2 for
714 parameters was 0.056 [R1 ) 0.025 for I > 2σ(I)]. Tables 1 and
3 give crystallographic data and selected bond lengths and angles,
respectively.
331 cm-1
.
An orange block 0.41 × 0.38 × 0.35 mm, obtained by slow diffusion
of methanol into a solution of 4 in dichloromethane, was used to collect
7330 reflections at 153 K on a Stoe STADI-4 diffractometer (2θmax
45°, 7118 unique, Rint 0.015). Data were collected at low temperature
using Mo KR radiation. The orientation matrix was refined from setting
Results
When PtCl2 is refluxed in C6F5CN a solution is obtained from
which trans-[PtCl2(NCC6F5)2] (1) is obtained on cooling. The
reaction of 1 with Ph3PdCHCO2Et gives three different products

Platinum-Assisted Addition of Ylides
Inorganic Chemistry, Vol. 35, No. 22, 1996 6595
depending on the reaction conditions. Thus, when an equi-
molecular mixture of 1 and the ylide is stirred in acetone for
24 h at room temperature, the complex containing one N-bonded
â-iminophosphorus ylide ligand (we will call it ylideimine
ligand), trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}{NCC6F5}]
(2a), is obtained in high yield (see Scheme 2). A related
complex, trans-[PtCl2{NHdCMeC(dPPh3)CO2Me}{NCMe}]
(2b), is obtained by reacting [PtCl2(NCMe)2] with Ph3PdCHCO2-
Me (1:2, acetone, 48 h).
Scheme 3. Proposed Reaction Pathway for the Formation of
Complexes 2-4
When a mixture of 1 and Ph3PdCHCO2Et (1:2.2 molar ratio)
is stirred in acetone in an ice bath for 30 min, a mixture
containing trans-[PtCl2{NHdC(C6F5)C(dPPh3)CO2Et}2] (3a)
and trans-[PtCl2{E-N(dPPh3)C(C6F5)dCHCO2Et}{E-NHdC-
(C6F5)C(dPPh3)CO2Et}] (4) in a 2:3 molar ratio (according to
NMR data) is obtained (see Scheme 2). When the same reaction
mixture is stirred at room temperature for 24 h, a mixture of 3a
and 4 is also obtained but in this case the molar ratio is 1:3. If
the same reaction mixture is refluxed in acetone for 2 h, an
orange solution is obtained from which 4 is isolated. The yield
(73%) does not increase if the reflux is maintained for 2 days.
Complex 1 reacts with Ph3PdCHC(O)Me (1:2) in acetone
at room temperature for 1 h to give a solution from which, upon
concentration and addition of diethyl ether, trans-[PtCl2{E-
NHdC(C6F5)C(dPPh3)C(O)Me}2] (3b) is obtained in high
yield. 3b is also obtained in similar yield when the reaction
time is 24 h or when the reaction mixture is refluxed for 1 h.
This complex is recovered unchanged after refluxing it in ethanol
for 2 h.
moiety. Although the trans nucleophilic addition of alcohols
on nitrile-Pt complexes leading to the Z-isomers has been
reported to be favored, isomerization to the more stable
E-isomers takes place readily unless the substituent in the nitrile
is very bulky.11 Similarly, the rehybridization of the C(sp3) to
C(sp2) from c to d seems to occur to minimize repulsions
between PPh3 and the substituents attached to such carbon atom
because a final cis positions of the H atom and the NdPPh3
moiety is obtained, as observed in the X-ray crystal structure
of 4 (see below). This geometry was also that of the complex
obtained by reacting [PtCl2(NCPh)2] and Ph3PdCHCO2Et.8
The complex [PtCl2(PhCN)2] is the only one giving an
iminophosphorane ligand in the first attack of the ylide
Ph3PdCHCO2R to the nitrile (see B in Scheme 2) while the
analogous MeCN and C6F5CN complexes give an ylideimine
ligand (2a,b). However, due to the complex nature of the
mixture obtained in the reactions with [PtCl2(PhCN)2], it is
difficult to explain this different behavior.8 The isolation of
the ylideimino complex 2a in the 1:1 reaction and the presence
of the same ligand in the 2:1 reaction products 3a and 4 suggests
that a cis C-H addition of the ylide to the nitrile (intermediate
b) is the first step in all reactions between Ph3PdCHCO2Et and
1. The trans C-H addition observed in the reaction between
[PtCl2(NCR)2] (R ) Me, Ph) and To3PdCH(py-2) (To )
4-MeC6H4; py-2 ) 2-pyridyl, see A in Scheme 2)9 is imposed
by the coordination of the pyridinic nitrogen.
The different behavior of [PtCl2(C6F5CN)2] and [PtCl2-
(MeCN)2] against ylides Ph3PdCHCO2R (R ) Me or Et) can
be interpreted having in mind that, after formation of the
monoadducts 2a and 2b, respectively, the better donor ability
of the resulting ylideimine ligand when R ) Me than C6F5
should induce a decrease of the electrophilic character of the
nitrile carbon atom of the remaining nitrile ligand. This decrease
would be enough as to impede, or severely reduce, formation
of a diadduct such as 3 or 4 when [PtCl2(MeCN)2] reacts with
Ph3PdCHCO2Me in 1:2 molar ratio. Although formation of
some amount of a diadduct can not be discarded, the mother
liquor resulting after removing the first crop of 2b contains a
complex mixture in which the main component is 2b.
When 1 is reacted with Ph3PdCHC(O)R (R ) OMe, Ph)
(1:2) in acetone at room temperature for 24 h, the solutions
concentrated and diethyl ether added, solid compounds are
obtained which elemental analyses correspond to 2:1 adducts.
However their 1H, 19F, and 31P{1H} NMR spectra show complex
mixtures which we could not resolve.
Discussion
From the above and previous results,8,9 it can be inferred that
the attack of the ylides to the platinum-coordinated nitrile ligands
is dependent on the nature of the nitrile and of the ylide and on
reaction conditions. Remarkable differences are found between
different nitriles. Thus, Ph3PdCHCO2Me reacts (2:1) with
trans-[PtCl2(NCMe)2] to give the product of the addition of the
ylide to only one nitrile ligand (see 2b in Scheme 2), whereas
the analogous Ph3PdCHCO2Et reacts with 1 giving products
of addition of the ylide to both nitrile ligands (see 3a and 4 in
Scheme 2). Moreover, ylides Ph3PdCHCO2R (R ) Me, Et)
react (1:1) with trans-[PtCl2(NCPh)2] to give iminophosphorane
complexes (B in Scheme 2)8 whereas with 1 Ph3PdCHCO2Et
gives an ylideimino complex (2a).
The nature of the ylide and the reaction conditions also have
influence on the result. Thus, 1 reacts with Ph3PdCHC(O)Me
(ca. 1:2) to give only the bis(ylideimino) complex 3b whereas
with Ph3PdCHCO2Et (ca. 1:2) it gives 4 or mixtures of 4 and
3a depending on reaction conditions (Scheme 2).
Scheme 3 is our proposal to rationalize the above results.
We assume, as is usual,11 that the nitrile carbon atom suffers a
nucleophilic attack by the ylide to give an intermediate that we
represent in Scheme 3 in two different conformations, a and
a′. Formation of the ylideimine ligand in b or the iminophos-
phorane ligand in d only requires migration of the ylidic
hydrogen atom or, respectively, the PPh3 group to the nitrile
nitrogen. In the first case, the final trans positions of the R
group and the H atom (E-isomer), as observed in the X-ray
crystal structure of 3b (see below), suggest that the attack of
the ylide is trans to the more congested group, i.e., the platinum
The results obtained in the 1:2 reactions between 1 and
Ph3PdCHCO2Et show that attack of the ylide to the remaining

6596 Inorganic Chemistry, Vol. 35, No. 22, 1996
Vicente et al.
Scheme 4
Figure 1. Structure of compound 3b. H atoms and CH2Cl2 of
crystallization are omitted for clarity.
or CF3CN (see eq 2 in Scheme 4).15b C6F5CN is an exception
because it reacts with stabilized and nonstabilized ylides
R3PdCHR′ (R ) p-tolyl, R′ ) 2-pyridyl; R ) Ph, R′ ) CO2Me,
CO2Et, C(O)NMe2) giving rise to the substitution of the p-F
atom (see eq 3 in Scheme 4).16 Therefore, coordination of
C6F5CN to platinum not only changes the atom to which the
ylide attacks but also allows an iminophosphorane to form in
spite of the electron-withdrawing nature of the C6F5 group.
Scheme 2 resumes all the different products that can be
obtained by reacting trans-[PtCl2(NCR)2] with ylides: Z-
(complexes A)9 and E-ylideimino (2a, 2b), E-iminophosphorano
(complexes B),8 bis(E-ylideimino) (3a, 3b), and mixed E-
ylideimino, E-iminophosphorano (4) complexes.
coordinated nitrile occurs in two different ways to give
complexes 3a and 4. The isolation of this mixture and the fact
that the amount of 4 increases when the reaction temperature
raises could be interpreted assuming that complex 3a is first
formed and then one ylideimine ligand isomerizes to an
iminophosphorane ligand to give 4 (see b f d in Scheme 3).
Fortunately, it is quite ease to verify this assumption simply by
refluxing an acetone solution of 3a. The recovering of 3a from
this experiment, after 2h refluxing, proves that syntheses of both
complexes follow two independent ways as shown in Scheme
3. The a′ f c f d reaction way leading to an iminophos-
phorane ligand has a noticeable temperature dependence likely
due to the steric hindrance of the PPh3 group. Thus, when the
temperature is lowered, the reactions rates leading to b and c
are comparable and at 0° a 2:3 mixture of 3a and 4 is obtained.
However, the process a′ f c f d is clearly favored when the
temperature is raised because at acetone refluxing only 4 is
obtained.
Structure of Complexes. The crystal structure of complex
3b‚CH2Cl2 has been solved (see Figure 1); Tables 1 and 2 give
crystal data and selected bond lengths and angles. It displays
a crystallographic symmetry center. The coordination around
platinum is planar with NPtN and ClPtCl angles of 180° and
ClPtN angles of 94.8 and 85.2°. The Pt-Cl [2.302(2) Å] and
Pt-N [1.997(5) Å] distances are normal for a Pt(II) complex
and very similar to those found in cis-[PtCl2{E-HNdC(OMe)-
Me}2] [Pt-Cl 2.298(2) and 2.301(2) Å and Pt-N 1.989(7) and
2.009(8) Å]11 indicating that Cl and both imino ligands have
similar trans influence. The atoms O(1), C(3), C(2), P, and
C(1) are in a plane (mean deviation 0.0094 Å) while the N atom
is out of this plane (N-C(1)-C(2)-P 39°). In favor of a
delocalization of electron density over the O(1), C(3), C(2), P,
and C(1) atoms is the P-C(2) distance [1.767(7) Å] which is
2
intermediate between that corresponding to a P(4)-Csp single
bond (mean value 1.793 Å)17 and that found in the related ylide
Ph3PdC(C6F4CN-4)CO2Et [1.722(3) Å].16b The C(1)-N
[1.294(9) Å] bond length is similar to those found in cis-[PtCl2-
{E-HNdC(OMe)Me}2] [1.307(11) and 1.294(12) Å].11 Only
marginal deviations of the bond distances C(2)-C(3) [1.434(10)
Å Vs the mean value of 1.471 Å for the single bond in a
CdCsC(O)sC arrangement], and C(3)dO [1.240(9) Å Vs the
mean value of 1.210 Å for the CsC(dO)sC arrangement] are
observed. The C(1)-C(2) bond length is normal for a single
The different behavior of ylides Ph3PdCHCO2Et and
Ph3PdCHCOMe against complex 1 can be explained using our
proposed reaction pathway. The greater electron-withdrawing
character of the C(O)Me group with respect to that of CO2Et
confers a greater acidic character of the CH proton, increasing
the rate of the reaction a f b. This and the high activation
energy due to the steric hindrance of the PPh3 group can be the
reasons for obtaining the bis(ylideimino) complex 3b and not a
mixture of 3b and a complex similar to 4 when R′ ) Me.
Non-resonance-stabilized ylides react with aliphatic and
aromatic nitriles to give iminophosphoranes. In these processes
formation of intermediates similar to a′ and c have also been
postulated (see eq 1 in Scheme 4).15a However, resonance-
stabilized ylides, like those here studied, only react with nitriles
carrying strong electron-withdrawing groups, such as NCCN
(15) (a) Johnson, A. W. Ylides and Imines of Phosphorous; J. Wiley &
Sons: New York, 1993; p 201. (b) Ciganek, E. J. Org. Chem. 1970,
11, 3631.
(16) (a) Vicente, J.; Chicote, M. T.; Ferna´ndez-Baeza, J.; Ferna´ndez-Baeza,
A.; Jones, P. G. J. Am. Chem. Soc. 1993, 115, 794. (b) Vicente, J.;
Chicote, M. T.; Fernandez-Baeza, J.; Fernandez-Baeza, A. New J.
Chem. 1994, 18, 263.
(17) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2, 1987, S1.

Platinum-Assisted Addition of Ylides
Inorganic Chemistry, Vol. 35, No. 22, 1996 6597
The IR spectra of 1, 2a, and 2b show the ν(CN) stretching
mode as a weak band in the 2310-2350 cm-1 range while in
the spectra of complexes 2a-4 the ν(NH) stretching mode
appears as a weak broad band (sharp in 3b) in the 3190-3300
cm-1 range. Although trans-[PtCl2L2] complexes have only one
IR-active ν(PtCl) mode, two or even three bands are observed
to appear in the 300-370 cm-1 region in complexes with L )
nitrile and imidoester.18b Because the cis isomer should give
two bands, the number of bands in this region does not have
diagnostic utility. In our complexes one (2a, 3a, 4), two (2b,
3b), or three (1) bands are observed in this region. In the
Experimental Section, we have indicated these bands as ν(PtCl)
although some of them could not be due to such modes. The
cis or trans geometry of products of addition of different
nucleophiles to [PtCl2(NCR)2] have been shown to be the same
as the starting complexes11a unless the nucleophile induces a
change of geometry as occurs in the synthesis of complex A
(see Scheme 2).9 Therefore the trans geometry of complexes
3b and 4 points to a trans geometry for 1, and consequently,
the other complexes (2 and 3a) should have the same geometry.
The X-ray crystal structure of complex B (see Scheme 2) also
agrees with this rule.8 In addition, the method of synthesis and
isolation of 1 are those established for the synthesis of trans-
[PtCl2(NCR)2] complexes.18b
The IR spectrum of 4 shows the ν(PdN) at 1274 cm-1, very
close to those observed in other iminophosphorano-Pt(II)
complexes reported by us (at 1270 cm-1).8 Given that ν(CdO),
ν(CdN) and ν(CdC) bands should appear in the same region,
unequivocal assignment is precluded in some cases. These
bands are observed in the 1705-1570 cm-1 region. However,
of the two bands at 1646 and 1575 cm-1 in complex 3b, the
first can be assigned to ν(CdN).10a,c Therefore, ν(CO) (at 1571
cm-1) is shifted 31 cm-1 to a higher wavenumber with respect
to the same band in the parent ylide Ph3PdCHC(O)Me, which
means that the ylene form [Ph3PdC(R)C(O)Me] [R )
C(C6F5)dNH{Pt}] is in 3b more important than that in the
parent ylide (R ) H). Hence, the nitrogen ligand in 3b must
be viewed as a â-imino-stabilized phosphorus ylide, according
to the name we have given to it and to its representation in
Scheme 2.
Figure 2. Structure of compound 4. H atoms are omitted for clarity.
bond [1.443(10) Å Vs the mean value of 1.460 Å in a CdCsC-
(O)R arrangement].
The crystal structure of 4 shows the platinum atom in a
distorted square planar environment and the same trans geom-
etry of the starting complex (see Figure 2). Tables 1 and 3
give crystal data and selected bond lengths and angles. In the
ylideimine ligand the significant bond distances and angles as
well as the Pt-N(1) bond length are almost identical with those
found in complex 3b while those in the iminophosphorane ligand
and the Pt-N(2) bond length are almost the same as those found
in the iminophosphorano complex trans-[PtCl2{E-
N(dPPh3)C(Ph)dCHCO2Et}(NCPh)] (see B in Scheme 2, R′
) OEt) reported by us.8 The E geometry of the iminophos-
phorane ligand is also a common feature of both complexes.
When both crystal structures are compared, the most striking
feature is the difference in the relative positions of the two C6F5
groups they contain. While in 3b both C6F5 groups lie on
opposite sides with respect to the N-Pt-N axis, in 4 they lie
on the same side which can be interpreted as a consequence of
the larger steric hindrance caused by the PPh3 when it is bonded
to the nitrogen atom.
The 19F NMR of complex 1 shows three intense resonances
corresponding to one the two possible isomers for a [PtCl2-
(NCC6F5)2] stoichiometry while only a trace amount of the other
isomer is present. We assume complex 1 to be the trans isomer
based on its preparation procedure because it has been reported
that although the cis-[PtCl2(NCR)2] complexes are kinetically
favored they isomerize to the trans species on heating or on
prolonged stirring at room temperature.18 If the 19F NMR
spectra of complexes 1-4 are compared, the resonances due to
the ligand C6F5CN appear in the ranges -155.22 to -156.64,
-134.66 to -138.01, and -126.46 to -127.57 ppm, those
corresponding to the ylideimine ligand in the ranges -162.13
to -163.4, -152.07 to -155.08, and -133.22 to -134.94 ppm,
and those due to the iminophosphorane ligand at -164.89,
-156.53, and -135.94 ppm. Similarly, from the 31P NMR
spectra of 2a, 2b, 3a, 3b, and 4 the two resonances correspond-
ing to PPh3 appearing in 4 at 18.07 and 36.85 ppm can be
assigned to the ylideimine and the iminophosphorane ligands,
respectively. The 31P resonance corresponding to the imino-
phosphorane ligand is in the same region as those observed in
the previously reported iminophosphorano complexes trans-
[PtCl2{E-N(dPPh3)C(Ph)dCHCO2R}(NCPh)] (R ) Me (36.19
ppm), Et (36.02 ppm)).8 The δ(NH) in the 1H NMR of
complexes 2a, 2b, 3a, 3b, and 4 is observed as a broad singlet
in the 8.05-10.69 ppm range.
Conclusions. The reactivity of [PtCl2(NCR)2] with carbonyl
stabilized phosphorus ylides Ph3PdCHC(O)R′ is even more
complex than previously assumed. We have shown that
ylideimine and iminophosphorane ligands can be generated as
a result of the nucleophilic attack of an ylide to a coordinated
nitrile. The results depend on the nature of R and R′. When R
) Me, only one nitrile is attacked, giving an monoylideimino
complex. When R ) C6F5, the result depends on the basic
character of the ylide. The ylide with R′ ) Me gives a bis-
(ylideimino) complex while the more basic ylide with R′ ) OEt
gives preferentially a mixed ylideimino-iminophosphorano
complex although a bis(ylideimino) complex can also be isolated
if the reaction is carried out at low temperature.
In this paper we have shown several facts for the first time:
(i) ylides can attack two nitrile ligands of a complex; (ii) this
double attack can give two different types of complexes, bis-
(ylideimino) (3a,b) or mixed ylideimino-iminophosphorano (4)
complexes; (iii) these two types of complexes are obtained
because the second nucleophilic attack can occur through two
independent reaction ways depending on reaction conditions;
(iv) complexes containing two ylideimine ligands can be
synthesized (3a,b); (v) one complex containing ylideimine and
iminophosphorane ligands was synthesized (4); (vi) the cis
addition of an ylide to a nitrile ligand in a platinum complex
(18) (a) Fanizzi, F. P.; Intini, F. P.; Maresca, L.; Natile, G. J. Chem. Soc.,
Dalton Trans. 1990, 199. (b) Fraccarollo, D.; Bertani, R.; Mozzon,
M.; Belluco, U.; Michelin, R. A. Inorg. Chim. Acta 1992, 201, 15.

6598 Inorganic Chemistry, Vol. 35, No. 22, 1996
Vicente et al.
took place (vii) X-ray crystal structures of complexes containing
a cis-ylideimine ligand were obtained (3b, 4).
acknowledges The Royal Society for a European Science
Exchange fellowship.
Acknowledgment. We thank Direccio´n General de Inves-
tigacio´n Cient´ıfica y Te´cnica (Grant PB92-0982-C) for financial
support and the University of Cambridge for data collection
facilities. M.C.R.A. thanks the Commission of the European
Communities for a research training fellowship from the Human
Capital and Mobility Research Program. M.A.B gratefully
Supporting Information Available: Tables giving crystal data and
details of the structure determination, atom coordinates, bond lengths
and angles, and anisotropic displacement coefficients for 3b and 4 (11
pages). Ordering information is given on any current masthead page.
IC951666A