First Coordinatively Saturated Carbene Complexes of Platinum(II): Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1021/om990240r

Coordinatively saturated carbene complexes of platinum(II) have been obtained by oxidative addition of [ClCH=NMe₂]Cl to Pt(0) precursors. The cationic products of general formula [PtCl(CHNMe₂)(N,N-chelate)(olefin)]Cl have been characterized through NMR spectroscopy and for [PtCl(CHNMe₂)(2,9-Me₂-1,10-phen)(Z-MeO ₂CCH=CHCO₂Me)]Cl by X-ray diffractometry. The latter species reacts with nucleophiles affording dimethylformamide and the corresponding Pt(0) precursor [Pt(2,9-Me₂-1,10-phen)(Z-MeO₂CCH=CHCO₂Me)]. Attempts to obtain related complexes containing carbene groups Pt=CHY without a heteroatom in α-position (Y = CO₂Et, CO₂NMe₂, CN) have led to the isolation of complexes of formula [PtR(dmphen){η¹,η²-CH(Y)O₂CCH=CHCO ₂Me}] (R = Me, Ph), formally derived from an intramolecular nucleophilic addition to a carbene intermediate. The X-ray structure of a representative product, [PtMe(dmphen){η¹,η²-CH(CO₂Et)O ₂CCH=CHCO₂Me}], is reported.

Full text of DOI:10.1021/om990240r

3482
Organometallics 1999, 18, 3482-3489
F ir st Coor d in a tively Sa tu r a ted Ca r ben e Com p lexes of
P la tin u m (II): Syn th esis, Str u ctu r e, a n d Rea ctivity
Maria E. Cucciolito,* Achille Panunzi, and Francesco Ruffo
Dipartimento di Chimica, via Mezzocannone 4, 80134 Napoli, Italy
Vincenzo G. Albano* and Magda Monari
Dipartimento di Chimica “G. Ciamician”, via Selmi 2, 40126 Bologna, Italy
Received April 6, 1999
Coordinatively saturated carbene complexes of platinum(II) have been obtained by
oxidative addition of [ClCHdNMe2]Cl to Pt(0) precursors. The cationic products of general
formula [PtCl(CHNMe2)(N,N-chelate)(olefin)]Cl have been characterized through NMR
spectroscopy and for [PtCl(CHNMe2)(2,9-Me2-1,10-phen)(Z-MeO2CCHdCHCO2Me)]Cl by
X-ray diffractometry. The latter species reacts with nucleophiles affording dimethylformamide
and the corresponding Pt(0) precursor [Pt(2,9-Me2-1,10-phen)(Z-MeO2CCHdCHCO2Me)].
Attempts to obtain related complexes containing carbene groups PtdCHY without a
heteroatom in R-position (Y ) CO2Et, CO2NMe2, CN) have led to the isolation of complexes
of formula [PtR(dmphen){η1,η2-CH(Y)O2CCHdCHCO2Me}] (R ) Me, Ph), formally derived
from an intramolecular nucleophilic addition to a carbene intermediate. The X-ray structure
of a representative product, [PtMe(dmphen){η1,η2-CH(CO2Et)O2CCHdCHCO2Me}], is re-
ported.
In tr od u ction
carbene complexes of platinum(II), of general formula
[PtCl(CHNMe2)(N,N)(olefin)]Cl (1), where N,N is a N,N-
chelate. The structure of one of the complexes, i.e.,
[PtCl(CHNMe2)(dmphen)(Z-MeO2CCHdCHCO2Me)]-
Cl (dmphen ) 2,9-Me2-1,10-phenanthroline), has been
determined by X-ray diffraction and compared with that
of [PtCl(H2O)(dmphen)(Z-MeO2CCHdCHCO2Me)]Cl,
which differs only in the presence of a pure σ-donor in
place of the carbene. Nucleophilic additions on the
carbene group have been accomplished on complexes 1.
Moreover, the synthesis of carbene derivatives related
to 1 by reaction of a five-coordinate water complex with
N2CHY (Y ) CO2Et, CONMe2, CN) has been attempted.
The structure of the final products is of the type
resulting from a nucleophilic addition to a carbene
intermediate, as demonstrated by the X-ray structure
of [PtMe(dmphen){η1,η2-CH(CO2Et)O2CCHdCHCO2-
Me}].
Involvement of carbene groups bound to transition
ions in several useful reactions, e.g., insertion pro-
cesses,1 attracts continuous interest in carbene com-
plexes.2 In fact, these species are claimed to be inter-
mediates in important catalytic processes such as olefin
metathesis,3a metathetical polymerizations,3b and Fis-
cher-Tropsch production of hydrocarbons3c and are
useful precursors in stoichiometric syntheses.4 Plati-
num(II) has afforded so far the most well-characterized
carbene derivatives among the d8 ions of the 10th
column.5 To the best of our knowledge, all the known
Pt(II) complexes are coordinatively unsaturated com-
pounds displaying the typical square-planar geometry.
This work, which is related to previous studies on five-
coordinate d8 species,6 describes the synthesis and the
characterization of the first trigonal bipyramidal 18e-
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; pp 379-382.
(2) Vyboshikov S. F.; Frenking, G. Chem. Eur. J . 1998, 4, 1428.
(3) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; pp 475-485. (b)
Moore, J . S. In Comprehensive Organometallic Chemistry II; Abel, E.
W, Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995;
Chapter 12.2, pp 1209. (c) Sneeden, R. P. A. In Comprehensive
Organometallic Chemistry; Abel, E. W, Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon: Oxford, 1982; Chapter 50.2, p 48.
(4) See, for example: Doyle, M. P. In Comprehensive Organometallic
Chemistry II; Abel, E. W, Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Chapter 5.1, p 389.
(5) Anderson, G. K. In Chemistry of Platinum Metals; Hartley, F.
R., Ed.; Elsevier: Amsterdam, 1991; Chapter 12, p 343.
(6) Albano, V. G.; Natile, G.; Panunzi, A. Coord. Chem. Rev. 1994,
133, 67.
Exp er im en ta l Section
1H NMR spectra were recorded on a 250 MHz Bruker model
AC-250 spectrometer. CDCl3, C2D2Cl4, CD3NO2, and (CD3)2-
SO were used as solvents, and CHCl3 (δ ) 7.26), C2HDCl4 (δ
) 5.98), CHD2NO2 (δ ) 4.33), 13CDCl3 (δ ) 77), 13CHD2NO2 (δ
) 62.9), and (13CHD2)2SO (δ ) 39.5) as internal standards.
The following abbreviations were used for describing NMR
multiplicities: no attribute, singlet; d, doublet; t, triplet; m,
multiplet; app, apparent. IR spectra were recorded in Nujol
mulls on a Perkin-Elmer 457 spectrophotometer using CsI
windows. Solvents were dried before use. All reactions were
carried out under a nitrogen atmosphere by using Schlenk
techniques. The ligands 1,10-phenanthroline (phen) and 2,9-
Me2-1,10-phenanthroline (dmphen) were commercially avail-
able (Aldrich). 6,6′-Me2-2,2′-bipyridine (dmbipy) was obtained
according to literature methods.7 The syntheses of [Pt(N,N)-
(7) Rode, T.; Breitmaier, E. Synthesis 1987, 574.
(8) De Renzi, A.; Panunzi, A.; Ruffo, F. Inorg. Synth. 1998, 32, 158.
10.1021/om990240r CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/30/1999

Carbene Complexes of Platinum(II)
Organometallics, Vol. 18, No. 17, 1999 3483
(olefin)],8 [PtMe(phen)(E-MeO2CCHdCHCO2Me)]BF4,9 [PtCl-
(Ph)(SMe2)2],10 N2CPh2,11 N2CONMe2,12 N2CHCN,13 and [PtMe-
(dmphen)(H2O)(olefin)]BF414 are reported elsewhere. The other
isomer of the latter compound, i.e., with maleate substituents
pointing toward Me, was obtained by reacting the appropriate
[PtMe(I)(dmphen)(Z-MeO2CCHdCHCO2Me)]14 precursor with
AgBF4 in dichloromethane/acetone.
N, 6.18. Calcd for C21H21Cl2N5Pt (1d ): C, 41.39; H, 3.47; N,
11.49. Found: C, 41.60; H, 3.33; N, 11.62.
Syn th esis of [P tCl(CHNMe2)(p h en )]Cl (4). To a mag-
netically stirred solution of chloromethylenedimethylammo-
nium chloride (0.026 g, 0.20 mmol) in nitromethane (2 mL)
was added solid [Pt(phen)(Z-MeO2CCHdCHCO2Me)] (0.11 g,
0.20 mmoL) at room temperature. The crude precipitate was
washed with methylene chloride and dried, giving a yellow
solid (0.083 g, 80% yield). Selected 1H NMR resonances (δ, CD3-
Syn th esis of [P tCl(CHNMe2)(d m p h en )(Z-MeO2CCHd
CHCO2Me)]Cl (1a ). To a magnetically stirred solution of
chloromethylenedimethylammonium chloride (0.026 g, 0.20
mmol) in nitromethane (2 mL) was added solid [Pt(dmphen)-
(Z-MeO2CCHdCHCO2Me)] (0.11 g, 0.20 mmol) at room tem-
perature. The reaction mixture was worked up immediately
in case both isomers of the product had to be obtained.
Otherwise, the solution was kept 1 h at room temperature, so
as to contain only the more stable isomer (1a ′). Careful
addition of diethyl ether afforded the crystalline pale yellow
2
NO2): 10.90 (1H, J Pt-H ) 10 Hz, Pt-CH); 9.45 (d, 1H, H2 or
H9); 9.00 (d, 1H, H9 or H2); 4.07 (3H, NMeMe); 3.97 (3H,
NMeMe). Anal. Calcd for C15H15Cl2N3Pt: C, 35.80; H, 3.00;
N, 8.35. Found: C, 35.95; H, 3.08; N, 8.24.
Syn th esis of [P tCl(P h )(d m p h en )(Z-MeO2CCHdCHCO2-
Me)]. To a solution of [PtCl(Ph)(SMe2)2] (0.086 g, 0.20 mmol)
in chloroform (5 mL) was added dmphen (0.042 g, 0.20 mmol)
and dimethylmaleate (0.14 g, 1.0 mmol). The solution was
refluxed for 18 h. Diethyl ether was added to complete the
precipitation of the product, which was collected, washed with
ether, and dried in vacuo (70%). Selected 1H NMR data (δ,
1
product(s) in high yield (96%). Selected H NMR data (δ, CD3-
NO2): 1a ′, 9.90 (1H, 2J Pt-H ) 30 Hz, Pt-CH), 4.60 (2H, 2J Pt-H
)
80 Hz, dCHCO2Me), 3.82 (6H, OMe), 3.52 (6H, Me2-phen), 3.17
2
3
(3H, NMeMe), 2.96 (3H, NMeMe); 1a ′′, 9.80 (1H, J Pt-H ) 10
C2D2Cl4): 6.61 (d, 2H, J Pt-H ) 35 Hz, H2, H6-Ph), 4.54 (2H,
Hz, Pt-CH), 4.55 (2H, 2J Pt-H ) 70 Hz, dCHCO2Me), 3.72 (6H,
OMe), 3.42 (6H, Me2-phen), 2.90 (3H, NMeMe). Selected 13C
NMR resonances (δ, CD3NO2): 1a ′, 181 (1J Pt-C ) 1006 Hz, Pt-
CH), 171.3 (CO2Me), 53.8 (NMeMe), 53.6 (CO2Me), 46.2
(NMeMe), 42.7 (1J Pt-C ) 353 Hz, dCHCO2Me), 28.6 (Me2-
phen). Anal. Calcd for C23H27Cl2N3O4Pt: C, 40.90; H, 4.03; N,
6.22. Found: C, 40.78; H, 3.96; N, 6.21.
2J Pt-H ) 85 Hz, dCHCO2Me), 3.65 (6H, OMe), 3.42 (6H, Me2-
phen). Anal. Calcd for C26H25ClN2O4Pt: C, 47.31; H, 3.82; N,
4.24. Found: C, 47.50; H, 3.90; N, 4.31.
Syn th esis of [P tP h (H2O)(d m p h en )(Z-MeO2CCHdCH-
CO2Me)]BF 4. To a suspension of [PtCl(Ph)(dmphen)(Z-MeO2-
CCHdCHCO2Me)] (0.066 g, 0.10 mmol) in nitromethane (5
mL) was added a solution of AgBF4 (0.020 g, 0.10 mmol) in
acetone (1.5 mL). After 2 h of stirring, AgCl was removed by
filtration. The product was obtained in almost quantitative
yield as a white powder by removing the solvents in vacuo.
Syn th esis of [P tCl(CHNMe2)(d m bip y)(Z-MeO2CCHd
CHCO2Me)]Cl (1b). To a magnetically stirred solution of
chloromethylenedimethylammonium chloride (0.026 g, 0.20
mmol) in nitromethane (2 mL) was added solid [Pt(dmbipy)-
(Z-MeO2CCHdCHCO2Me)] (0.105 g, 0.20 mmol) at room
temperature. Addition of diethyl ether afforded the crystalline
pale yellow product(s) (isomers 1b′/1b′′ in the ratio 3:1) (60%
yield). Selected 1H NMR data (δ, CD3NO2): 1b′, 9.85 (1H,
1
3
Selected H NMR data (δ, CD3NO2): 6.60 (d, 2H, J Pt-H ) 35
2
Hz, H2, H6-Ph), 3.88 (6H, OMe), 3.70 (2H, J Pt-H ) 63 Hz,
dCHCO2Me), 3.55 (6H, Me2-phen). Anal. Calcd for C26H27
-
BF4N2O5Pt: C, 42.81; H, 3.73; N, 3.84. Found: C, 42.75; H,
3.83; N, 3.95.
2
2J Pt-H ) 25 Hz, Pt-CH); 4.46 (2H, J Pt-H ) 80 Hz, dCHCO2-
Syn th esis of [P tMe(d m p h en ){η1,η2-CH(Y)O2CCHdCH-
CO2Me}] (Y ) CO2Et, 2a ; Y ) CONMe2, 2b; Y ) CN, 2c).
To a solution of [PtMe(H2O)(dmphen)(Z-MeO2CCHdCHCO2-
Me)]BF4 (0.066 g, 0.10 mmol) in methanol (0.6 mL) was added
N2CHY (0.12 mmoL) at room temperature. In the case of 2a
and 2c the crystalline product (yield > 95%) was collected after
ca. 2 h by filtration. In the case of 2b no precipitate was formed
and solvent was removed in vacuo to recover the product. The
residue was washed with ether to give crude 2b together with
Me); 3.80 (6H, OMe); 3.32 (3H, NMeMe); 3.30 (6H, Me2bipy);
2
2.92 (3H, NMeMe); 1b′′, 10.0 (1H, J Pt-H ) 20 Hz, Pt-CH);
2
3.82 (2H, J Pt-H ) 76 Hz, dCHCO2Me); 3.80 (6H, OMe); 3.33
(6H, Me2bipy). Selected 13C NMR resonances (δ, CD3NO2): 1b′,
176.5 (1J Pt-C ) 1022 Hz, Pt-CH); 166 (CO2Me); 48.5 (NMeMe);
48.0 (CO2Me); 40.5 (NMeMe); 37.5 (2J Pt-H ) 354 Hz, dCHCO2-
Me); 22.8 (Me2-bipy); 1b′′, 190 (Pt-CH). Anal. Calcd for C21H27
-
Cl2N3O4Pt: C, 38.72; H, 4.18; N, 6.45. Found: C, 38.88; H,
4.23; N, 6.61.
1
the precursor (ca. 35%). Selected H NMR resonances (δ, CD3-
2
Syn th esis of [P tCl(CHNMe2)(d m p h en )(E-RCHdCHR)]-
Cl (R ) CO2Me, 1c; R ) CN, 1d ). To a magnetically stirred
solution of chloromethylenedimethylammonium chloride (0.026
g, 0.20 mmol) in nitromethane (2 mL) was added an equal
amount of solid [Pt(dmphen)(E-RCHdCHR)] at room temper-
ature. After 1 h addition of diethyl ether afforded the crystal-
line pale yellow product in high yield (1c 82%; 1d 96%).
NO2): 2a , 4.59 (1H, J Pt-H ) 55 Hz, CHCO2Et), 3.77 (3H,
2
OMe), 3.76 (d, 1H, J Pt-H ) 80 Hz, dCH), 3.20 (3Η, Me-Me-
2
phen), 3.06 (3H, Me-Me-phen), 2.90 (d, 1H, J Pt-H ) 60 Hz,
dCH), 2.70 (m, 1H, CO2CHHMe), 1.85 (m, 1H, CO2CHHMe),
2
0.16 (app t, 3H, CO2CH2Me), -0.37 (3H, J Pt-H ) 50 Hz, Pt-
2
Me); 2b, 4.59 (1H, J Pt-H ) 48 Hz, CHCONMe2), 3.80 (3H,
OMe), 2.95 (3Η, Me-Me-phen), 2.85 (3H, Me-Me-phen), 1.60
1
Selected H NMR data (δ, CD3NO2): 1c, 9.30 (1H, 2J Pt-H ) 26
(1H, CONMeMe), 1.45 (1H, CONMeMe), 0.06 (3H, 2J Pt-H ) 50
2
Hz, Pt-CH); 4.77 (d, 1H, dCHCO2Me), 4.53 (d, 1H, dCHCO2-
Me), 3.84 (3H, OMe), 3.80 (3H, OMe), 3.56 (3H, Me-Me-phen),
3.46 (3H, Me-Me-phen), 3.34 (br, 6H, NMe2); 1d , 9.60 (1H,
2J Pt-H ) 20 Hz, Pt-CH), 4.50 (m, 2Η, 2J Pt-H ) 70 Hz, dCHCN),
3.60 (3Η, Me-Me-phen), 3.53 (3Η, Me-Me-phen), 3.43 (3H,
NMeMe), 3.30 (3H, NMeMe). Anal. Calcd for C23H27Cl2N3O4-
Pt (1c): C, 40.90; H, 4.03; N, 6.22. Found: C, 40.65; H, 4.10;
Hz, Pt-Me); 2c, 4.51 (1H, J Pt-H ) 50 Hz, dCHCN), 3.80 (d,
2
1H, J Pt-H ) 65 Hz, dCH), 3.79 (3H, OMe), 3.16 (3Η, Me-Me-
2
phen), 3.11 (3H, Me-Me-phen), 3.00 (d, 1H, J Pt-H ) 50 Hz,
2
dCH), -0.22 (3H, J Pt-H ) 50 Hz, Pt-Me). Selected 13C NMR
resonances (δ, CD3NO2): 2a , 70.4 (1J Pt-C ) 397 Hz, Pt-CH),
43.5 (1J Pt-C ) 397 Hz, dCH), 31.2 (1J Pt-C ) 397 Hz, dCH),
30.0 (Me-Me-phen), 29.0 (Me-Me-phen), -8.0 (1J Pt-C ) 437 Hz,
Pt-Me); 2c (in (CD3)2SO), 52.4 (1J Pt-C ) 400 Hz, Pt-CH), 51.5
(CO2Me), 41.7 (1J Pt-C ) 400 Hz, dCH), 29.6 (1J Pt-C ) 400 Hz,
dCH), 28.2 (Me-Me-phen), 27.6 (Me-Me-phen), -10.0 (Pt-Me).
Anal. Calcd for C24H26N2O6Pt (2a ): C, 45.50; H, 4.14; N, 4.42.
Found: C, 45.68; H, 4.20; N, 4.41. Calcd for C22H21N3O4Pt
(2c): C, 45.05; H, 3.61; N, 7.16. Found: C, 44.92; H, 3.76; N,
7.27.
(9) Fusto, M.; Giordano, F.; Orabona, I.; Ruffo, F.; Panunzi, A.
Organometallics 1997, 16, 5981.
(10) Cucciolito, M. E.; De Felice, V.; Panunzi, A.; Vitagliano, A.
Organometallics 1989, 8, 1180, and references therein.
(11) Staudinger, H.; Anthes, E.; Pfenninger F. Ber. Dtsch. Chem.
Ges. 1916, 49, 1928.
(12) Bartlett, P. A.; Carruthers, N. I.; Winter, B. M.; Long, K. P. J .
Org. Chem. 1982, 47, 1284.
(13) Dewar, M. J . S.; Pettit R. J . Chem. Soc. 1956, 2026.
(14) De Felice, V.; Ferrara, M. L.; Orabona, I.; Ruffo, F. J . Orga-
nomet. Chem. 1996, 519, 75.
Syn th esis of [P tP h (d m p h en )] {η1,η2-CH(Y)O2CCHdCH-
CO2Me}] (Y ) CO2Et, 2d ; Y ) CN, 2e). Compounds 2d and
2e were prepared by a procedure similar to that reported for

3484 Organometallics, Vol. 18, No. 17, 1999
Cucciolito et al.
2a by starting from [PtPh(H2O)(dmphen)(Z-MeO2CCHdCHCO2-
Me)]BF4 and isolated as crystalline precipitates from the
reaction mixture in high yield (>95%). Selected 1H NMR
resonances (δ, CD3NO2): 2d , 4.87 (1H, 2J Pt-H ) 53 Hz, CHCO2-
of the solution, dimethylformamide was detected in all cases,
accompanied by methanol in case of methoxide addition and
by dimethyl malonate in the case of malonate addition.
Cr ysta llogr a p h y. Crystal data and details of the data
collection for [PtCl(CHNMe2)(2,9-Me2-1,10-phen)(Z-MeO2CCHd
CHCO2Me)]Cl‚H2O, 1a ‚H2O, [PtMe(dmphen){η1,η2-CH(CO2-
Et)O2CCHdCHCO2Me}], 2a, and [PtCl(H2O)(dmphen)(Z-MeO2-
CCHdCHCO2Me)]Cl‚H2O are given in Table 1. The diffraction
experiments were carried out at low temperature for all
compounds on a fully automated Enraf-Nonius CAD-4 diffrac-
tometer using graphite-monochromated Mo KR radiation. The
unit cell parameters were determined by a least-squares fitting
procedure using 25 reflections. Data were corrected for Lorentz
and polarization effects, and for two species, namely, 1a ‚H2O
and 2a a decay correction (25% and 8%, respectively) was
applied. An empirical absorption correction was applied to all
compounds by using the azimuthal scan method.15 The posi-
tions of the metal atoms were found by direct methods using
the SHELXS 86 program16 and all the non-hydrogen atoms
located from difference Fourier maps. Most hydrogen atoms
were experimentally located in the final stages of refinement
but were placed in calculated positions and refined riding the
pertinent carbon atoms. The carbene hydrogen H(15) in 1a
was freely refined. Isotropic thermal parameters for the H
atoms were assigned 1.2 and 1.5 times Ueq of the carrier atoms
for sp2 and sp3 carbons, respectively. The final refinement on
F2 proceeded by full-matrix least-squares calculations (SHELXL
93)17 using anisotropic thermal parameters for all the non-
hydrogen atoms.
2
Et), 3.85 (d, 1H, J Pt-H ) 80 Hz, dCH), 3.80 (3H, OMe), 3.40
(3Η, Me-Me-phen), 3.38 (3H, Me-Me-phen), 3.12 (d, 1H, 2J Pt-H
) 60 Hz, dCH), 2.80 (m, 1H, CO2CHHMe); 1.90 (m, 1H, CO2-
2
CHHMe), 0.07 (app t, 3H, CO2CH2Me); 2e, 4.80 (1H, J Pt-H
)
2
45 Hz, CHCN), 3.88 (d, 1H, J Pt-H ) 80 Hz, dCH), 3.80 (3H,
OMe), 3.39 (3Η, Me-Me-phen), 3.32 (3Η, Me-Me-phen), 3.22
(d, 1H, J Pt-H ) 61 Hz, dCH). Anal. Calcd for C29H28N2O6Pt
2
(2d ): C, 50.07; H, 4.06; N, 4.03. Found: C, 50.21; H, 3.99; N,
4.09. Calcd for C27H23N3O4Pt (2e): C, 50.00; H, 3.57; N, 6.48.
Found: C, 50.15; H, 3.60; N, 6.42.
Isola tion of Solid [P tMe{CH(OH2)CO2Et}(d m p h en )(Z-
MeO2CCHdCHCO2Me)][BF 4], 3a . To a solution of [PtMe-
(H2O)(dmphen)(Z-MeO2CCHdCHCO2Me)]BF4 (0.133 g, 0.22
mmol) in nitromethane (1 mL) was added 0.023 mL (0.22
mmol) of N2CHCO2Et at room temperature. An effervescence
was observed, and immediately 0.5 mL of diethyl ether was
added. A whitish solid precipitated, which was separated by
filtration, washed with diethyl ether, and dried. The crude
product (0.092 g) was impure due to the presence of significant
1
amounts (ca. 20%) of 2a . Selected H NMR data (δ, CD3NO2):
2
5.60 (1H, J Pt-H ) 35 Hz, CHCO2Et), 4.56 (3H, OMe), 4.40 (d,
2
1H, dCH), 3.88 (3H, OMe), 3.26 (d, 1H, J Pt-H ) 50 Hz, d
CH), 3.24 (3Η, Me-Me-phen), 2.99 (3Η, Me-Me-phen), 2.90 (m,
1H, CO2CHHMe), 2.15 (m, 1H, CO2CHHMe), 0.21 (app t, 3H,
2
CO2CH2Me), 0.01 (3H, J Pt-H ) 50 Hz, Pt-Me). Selected 13C
NMR resonances (δ, CD3NO2) 89.2 (1J Pt-C ) 428 Hz, Pt-CH);
34.4 (1J Pt-C ) 409 Hz, dCH); 33.8 (1J Pt-C ) 377 Hz, dCH);
30.6 (Me-Me-phen); 29.4 (Me-Me-phen); -6.9 (1J Pt-C ) 396 Hz,
Pt-Me). IR (Nujol): ν ) 1000 cm-1 (BF4-).
Resu lts a n d Discu ssion
Syn th eses. The procedure that so far has proved to
be effective18 in the preparation of type 1 compounds
involves the oxidative addition of chloromethylenedim-
ethylammonium chloride20 to a suitable nucleophilic
Pt(0) species of the type [Pt(N,N)(olefin)] (Scheme 1):
NMR Tu be Rea ction s of [P tR(H2O)(d m p h en )(Z-MeO2-
CCHdCHCO2Me)]BF 4 w ith N2CHY (Y ) CONMe2 a n d R
) Me, 3b; Y ) CO2Et a n d R ) P h , 3d ). To an NMR tube
containing a solution of [PtR(H2O)(dmphen)(Z-MeO2CCHd
CHCO2Me)]BF4 (0.03 mmol) in deuterionitromethane (0.5 mL)
was added N2CHY (0.036 mmol) at room temperature. The
spectrum monitored after 5 min showed that all the precursor
Sch em e 1
1
had reacted to give the type 3 intermediates. Selected H NMR
2
resonances (δ): 3b, 6.00 (1H, J Pt-H ) 30 Hz, CHCONMe2),
4.50 (3H, OMe), 4.40 (d, 2J Pt-H ) 70 Hz, dCH), 3.88 (3H, OMe),
3.30 (3Η, Me-Me-phen), 3.21 (d, dCH), 3.01 (3H, Me-Me-phen),
1.39 (3H, CONMeMe), 1.30 (3H, CONMeMe); 3d , 5.93 (1H,
2
2J Pt-H ) 38 Hz, CHCO2Et), 4.69 (3H, OMe), 4.51 (d, J Pt-H
)
75 Hz, dCH), 3.98 (3H, OMe), 3.50 (3Η, Me-Me-phen), 3.48
(d, J Pt-H ) 50 Hz, dCH), 3.33 (3H, Me-Me-phen), 3.06 (m,
2
1H, CO2CHHMe), 2.23 (m, 1H, CO2CHHMe), 0.13 (app t, 3H,
CO2CH2Me). When the above-reported procedures were at-
tempted by reacting the [PtMe(dmphen) (H2O)(Z-MeO2CCHd
CHCO2Me)]BF4 isomer in which maleate substituents face Me,
mixtures of several unidentified compounds were obtained.
NMR Tu be Rea ction s of [P tMe(p h en )(E-MeO2CCHd
CHCO2Me)]BF 4 w ith N2CXY (X ) H, Y ) CO2Et; X ) Y )
P h ). To an NMR tube containing a solution of [PtMe(phen)-
(E-MeO2CCHdCHCO2Me)]BF4 (0.03 mmol) in deuterioni-
tromethane (0.5 mL) was added N2CXY (0.036 mmol) at room
temperature. The 1H NMR spectrum monitored after 5 min
showed that all the precursor had reacted to give CH2dCPh2
(X ) Y ) Ph) or CH2dCHCO2Et (X ) H, Y ) CHCO2Et) and
a mixture of platinum compounds, whose analysis was not
attempted.
Nu cleop h ilic Ad d ition to 1a . In a typical experiment, 1a
(0.03 g, 0.05 mmol) was suspended in deuteriomethanol (0.75
mL) in a nitrogen atmosphere. To this stirred suspension was
added the appropriate nucleophile (MeONa, NaBH4, LiOH, or
KCH(CO2Me)2, 0.15 mmol), dissolved in a minimum amount
of the same solvent. After 16 h a yellow precipitate was
removed by filtration. This was identified as [Pt(dmphen)(Z-
MeO2CCHdCHCO2Me)]. By monitoring the 1H NMR spectrum
The syntheses have been carried out in carefully dried
nitromethane, since the iminium salt is poorly soluble
(15) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect A 1968, 24, 351.
(16) Sheldrick, G. M. SHELXS 86, Program for crystal structure
solution; University of Gottingen, 1986.
(17) Sheldrick, G. M. SHELXL 93, Program for crystal structure
refinement; University of Gottingen, 1993.
(18) During this work one other method was attempted, i.e., addition
of electrophiles to five-coordinate complexes of the type [PtCl(COR)-
(N,N)(olefin)].19 In our hands a few preliminary attempts gave uni-
dentified mixtures of products.
(19) De Felice, V.; Giovannitti, B.; Panunzi, A.; Ruffo, F.; Tesauro,
D. Gazz. Chim. Ital. 1993, 123, 65.
(20) See for instance: Hartshorn, A. J .; Lappert, M. F.; Turner, K.
J . Chem. Soc., Dalton Trans. 1978, 348.

Carbene Complexes of Platinum(II)
Organometallics, Vol. 18, No. 17, 1999 3485
Ta ble 1. Cr ysta l Da ta a n d Exp er im en ta l Deta ils for
[P tCl(CHNMe2)(d m p h en )(Z-MeO2CCHdCHCO2Me)]Cl‚H2O, 1a ‚H2O,
[P tMe(d m p h en ){η1,η2-CH(CO2Et)O2CCHdCHCO2Me}], 2a , a n d
[P tCl(H2O)(d m p h en )(Z-MeO2CCHdCHCO2Me)]Cl‚H2O
1a ‚H2O
2a
formula
M
C
23H27Cl2N3O4Pt‚H2O
C24H26N2O6Pt
633.56
C20H22Cl2N2O5Pt‚H2O
654.40
693.48
temperature, K
wavelength, Å
crystal symmetry
space group
a, Å
200(2)
200(2)
0.71069
orthorhombic
Pbn21 (No. 33)
11.492(7)
13.779(8)
14.253(9)
90
90
90
2257(2)
4
1.865
6.261
1240
220(2)
0.71069
monoclinic
P21/c (No. 14)
16.257(9)
9.766(4)
17.632(7)
90
114.41(5)
90
2549(2)
4
0.71069
triclinic
P 1 bar (No. 2)
8.157(6)
9.987(3)
14.049(8)
98.93(3)
101.47(6)
93.65(4)
1103(1)
b, Å
c, Å
R, deg
â, deg
γ, deg
cell volume, Å3
Z
2
Dc, Mg m-3
1.807
5.753
1360
1.971
6.644
636
µ(Mo KR), mm-1
F(000)
crystal size, mm
θ limits, deg
scan mode
reflns collected
no. of unique observed
reflns [Fo > 4σ(Fo)]
goodness of fit on F2
R1 (F)a, wR2 (F2)b
weighting scheme a, b
largest diff peak and hole, e‚Å-3
0.15 × 0.17 × 0.20
0.12 × 0.20 × 0.38
0.05 × 0.075 × 0.15
2-28
2-30
2-27
ω
ω
ω
6101((h, +k, +l)
6094
7737((h, +k, + l)
4790((h, (k, +l)
4782
3218
1.040
1.068
1.003
0.0370, 0.0899
0.0515, 6.9685
1.54 and -1.49
0.0312, 0.0643
0.0341, 2.9443
1.20 and -0.74
0.0379, 0.0903
0.0618, 2.5249b
2.35 and -2.33
R1 ) ∑||Fo| - |Fc|/∑|Fo|. wR2 ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2, where w ) 1/[σ2(Fo2) + (aP)2 + bP], where P ) (Fo + 2Fc2)/3.
a
b
2
2
in other common solvents and is quite sensitive to
carbomethoxy groups face the carbene ligand (see later).
By comparing the 1H NMR spectrum of 1a ′ and 1a ′′,
and also from previous results21 on compounds similar
to 1, a lower field shift and a higher 195Pt coupling
constant can be reasonably assigned to olefin protons
facing the halide ligand. Thus, it is reasonable that also
in the thermodynamically preferred isomer 1b′ the
carbomethoxy groups are on the carbene side.
hydrolysis. On the other hand, the isolated carbenes are
air stable. They are slightly soluble in methanol and
chloroform, but fairly soluble in nitromethane. The type
of the coordinated olefins was suggested by previous
findings6 on the favorable influence of electron-with-
drawing substituents on the stability of complexes
similar to 1. The selection of the N,N ligands was
dictated by sterical requirements,.as it is known6 that
the stabilization of the five-coordinate geometry in
complexes related to 1 requires in-plane steric hindrance
of the N,N-chelate. In fact, if phen is substituted for
dmphen in the precursor of 1a , upon reaction with the
iminium salt, the olefin is lost and the carbene complex
formed is a typical square-planar 16e- species (eq 1):
Other noteworthy features of the NMR spectra of the
carbene complexes are as follows: (a) The low-field shifts
and the J Pt-H constants (20-30 Hz) of the signals
pertaining to the carbene hydrogens are within the
typical range for related octahedral Pt(IV) carbene
derivatives.22 (b) The two halves of the N,N-chelate
appear chemically equivalent. This could result either
from a “free” rotation about the Pt-carbene bond or
from a frozen conformation of the carbene group main-
taining Cs symmetry. The first hypothesis seems more
reasonable also considering the unsymmetrical carbene
conformation found in the solid state (see later). Low-
temperature NMR spectra (213 K) do not disclose
further splitting of the signals. (c) Separate signals for
the two NMe groups give evidence of hindered rotation
around the Ccarbene-N bond. No coalescence of the two
signals is observed in high-temperature spectra (350-
390 K in deuterionitrobenzene). Distinct 13C signals are
also observed for the two NMe carbons. These spectro-
scopic features are explained by the double-bond char-
acter of the C-N interaction discussed further on.
[Pt(phen)(Z-MeO2CCHdCHCO2Me)] +
[(CHCldNMe2)]Cl )
[PtCl(CHNMe2)(phen)]Cl (4) +
Z-MeO2CCHdCHCO2Me (1)
The reactions affording complexes 1 have been moni-
1
tored by H NMR in CD3NO2 and are complete in the
time required for the acquisition of the spectrum.
Dimethylmaleate can afford two geometrical isomers
generated by the orientation of the CO2Me groups
relative to the axial ligands. Actually both of them have
been observed shortly after the addition, in 2:1 (1a ′:1a ′′)
and 3:1 (1b′:1b′′) ratio, respectively. In the former case
aging of the solution affords only one isomer (1a ′), while
in the case of 1b, containing a less rigid chelate, the
equilibrium mixture attained by isomerization still
contains a large amount of the less favored compound
1b′′ (ca. 30%). As for the configuration assignment to
the isomers, the X-ray structure of 1a shows that the
Taking into account the good stability of type 1
compounds, the synthesis of non heteroatom-stabilized
(21) Bartolucci, S.; Carpinelli, P.; De Felice, V.; Giovannitti, B.; De
Renzi, A. Inorg. Chim. Acta 1992, 197, 51.
(22) Rendina, L. M.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1995, 14, 1030.

3486 Organometallics, Vol. 18, No. 17, 1999
Cucciolito et al.
Sch em e 2
carbenes23 has also been attempted. To achieve this
purpose, some diazoaceto derivatives N2CHY (Y ) CO2-
Et, CONMe2, or CN) have been reacted with the five-
coordinate complexes [PtR(H2O)(dmphen)(Z-MeO2CCHd
CHCO2Me)]BF4, bearing the labile H2O ligand in axial
position. A clean reaction occurs only with the isomer
in which carbomethoxy groups face water. The final
products are not carbene derivatives, and type 2 species
are obtained instead (Scheme 2).
On the grounds of all the above data, 3a could be
considered a carbene complex only in the case where
asymmetry of the N,N and olefin 1H NMR patterns
could be ascribed to a high rotation barrier around the
Pt-C bond, and a strong shielding could be responsible
for the quite peculiar low-field shift (δ 5.60) of the
putative carbene proton. More reasonably, it can be
conceived that a water molecule has attacked this
unrevealed carbene, and 3a is in fact a protonated form
of this addition product, i.e. an oxo-cation stabilized by
intramolecular interactions, as indicated in Figure 1.
The presence in apical position of a ligand stronger
than water (methyl cyanide or pyridine) prevents the
formation of any reaction product. Type 2 products have
Further support for this assignment stems from the 13
C
1
been characterized by H NMR spectroscopy, and the
NMR spectra. The shifts for the Pt-bound carbon atom
in deuteronitromethane solution are 70.4 and 89.2 ppm
for 2a and 3a , respectively. It should be noted that in
the same solvent the carbon shifts pertaining to Me2O
X-ray structure of 2a has been determined (see later).
A type 2 compound could derive from the intramo-
lecular attack of one carbomethoxy oxygen on an axially
bound CHY carbene group with involvement of a water
molecule. To gain further information on the mode of
formation of 2, the reaction yielding 2a has been
monitored in an NMR tube. The addition of diazoacetate
affords immediate release of nitrogen, and the spectrum
of the fresh solution shows that another five-coordinate
compound (3a ) is initially formed, which then decom-
poses to 2a and methanol. Attempts to isolate pure 3a
have been unsuccessful, and only solid mixtures of 3a
and at least 20% of 2a could be recovered upon careful
workup of the reaction mixture.
-
and Me3O+BF4 are 67.1 and 86.7 ppm, respectively.
Substantially similar results have been obtained by
reacting the phenyl complex with diazoacetate or the
methyl precursor with dimethyldiazoacetamide. No type
3 intermediate is detected by NMR spectroscopy on
reaction of both aqua complexes with diazoacetonitrile,
before the formation of 2c and 2e, respectively.
It is to be noted that when the synthesis of the
carbene complex is attempted by reacting N2CHCO2Et
with [PtMe(phen)(E-MeO2CCHdCHCO2Me)]BF4 (i.e.,
avoiding stabilization of tbp geometry by the chelate
ligand), ethyl acrylate is obtained. A similar reaction
affording Ph2CdCH2 is observed when the carbene
precursor is N2CPh2. Also on the grounds of previous
findings25 it seems reasonable that a reactive 16e-
intermediate undergoes carbene insertion in the Pt-
Me bond, finally affording the unsaturated product by
â-elimination.
Solu tion Beh a vior a n d Rea ctivity of Ca r ben es.
None of the type 1 carbene complexes described here
show any tendency to intramolecular insertion of the
carbene group in the Pt-Cl bond, in contrast to square-
planar derivatives.25 This is in keeping with the trans
arrangement of the methyl and carbene ligands in the
The more significant features of the signals pertaining
1
to 3a in the H NMR spectrum are the following: (a) a
one-proton signal appears at δ 5.60 coupled to 195Pt
(J Pt-H ) 35 Hz); (b) the two halves of the chelate are
magnetically nonequivalent; (c) two different signals (δ
4.40, 3.26; J Pt-H ) 35 Hz) pertain to the olefin protons;
(d) two different signals are observed for the methoxy
protons; (e) a signal at δ 0.01 is typical of axially bound
methyl. Further information on 3a includes the follow-
ing: (i) The mixture of solid 3a and 2a , dissolved in
nitromethane, is conducting. Considering that 2a is non-
ionic, the data are consistent with 3a being a 1:1
electrolyte (85.3 S mol-1 cm2). (ii) The IR spectrum of
the mixture shows a broad band around 1000 cm-1
,
typical of BF4-. (iii) The elemental analyses of the
mixture disclose a fluorine content consistent with the
-
presence of BF4 in 3a (in 1:1 ratio).
(23) Very few examples of similar carbenes are known, as in the
case of coordinatively saturated Ru(II).24 In the platinum group this
type of carbene has been invoked as an intermediate25 in insertion
processes, but as far as we know, it has never been isolated.
(24) Collman, J . P.; Brothers, P. J .; McElwee-White, L.; Rose, E.;
Wright, L. J . J . Am. Chem. Soc. 1985, 107, 4570.
(25) Bergamini, P.; Costa, E.; Orpen, A. G.; Pringle, P. G.; Smith,
H. B. Organometallics 1995, 14, 3178.
F igu r e 1. Proposed structure of 3a .

Carbene Complexes of Platinum(II)
Organometallics, Vol. 18, No. 17, 1999 3487
Sch em e 3
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [P tCl(CHNMe2)(2,9-Me2-1,10-p h en )-
(Z-MeO2CCHdCHCO2Me)]Cl‚H2O, 1a ‚H2O
trigonal bipyramidal, with the dmphen and the double
bond of the maleate ester defining the equatorial plane
and the chloride and CHNMe2 aminocarbene ligands
occupying the axial sites. The ion adopts an asymmetric
conformation because neither the CO2Me groups in the
maleate ester nor the aminocarbene ligand conforms to
a potential Cs symmetry. The interest of this structure
lies primarily in the CHNMe2 ligand, found for the first
time in a five-coordinate complex. The bond parameters
concerning the carbene ligand are as follows: Pt-C
2.006(6) Å, CdN 1.273(8) Å, Pt-C-N 129.6(4)°, Pt-Cl-
(trans) 2.389(2) Å. The same ligand has been reported
in four- and six-coordinate species trans to a chloride.
Strictly comparable values have been found in the
electron precise octahedral platinum(IV) cation22 [PtCl2-
Me(CHNMe2)(6,6′-di-t-Bu-2,2′-bipyridine)]+: Pt-Ccarbene
1.99(2) Å, CdN 1.31(2) Å, Pt-C-N 131(2)°, Pt-Cl-
(trans) 2.378(5) Å. Slightly shorter values have been
reported for the unsaturated four-coordinate molecule
[PtCl2(PPh3)(CHNMe2)]: Pt-C 1.96(1) Å, CdN 1.25(1)
Å, Pt-C-N 130.5(4)°, Pt-Cl(trans) 2.347(3) Å.26 It is
evident that the ligand geometry is little affected by the
chemical environment, and relevant features of the
three species are a substantially localized CdN double
bond and predominantly single-bond character of the
Pt-C interaction. The above considerations are rein-
forced by the observation that the carbon-nitrogen
distance in the coordinated ligand is in the range of
values reported for uncoordinated iminium cations
[1.26-1.30 Å].27,28 In addition the difference between
Pt-Ccarbene and Pt-Calkyl average distances in saturated
species6 [2.00 and 2.05 Å, respectively] is slightly larger
than the difference between the carbon radii in sp2 and
sp3 hybridization (0.03 Å). On the other hand evidence
that pure σ-donation is not the most appropriate bond-
ing model for the carbene ligand can be drawn from an
analysis of its trans influence. The average Pt-Cl
distance in five-coordinate species6 is 2.30 and 2.47 Å,
when the trans ligand is another chloride or an alkyl
group, respectively. The distance in the present cation
[2.389(2) Å] falls between the just cited values, indicat-
ing that the carbene ligand acts differently from an alkyl
group; that is, a π-bond contribution is to be invoked.
The bonding parameters of the dmphen and maleate
ligands are normal:6 Pt-Nav 2.19, Pt-Cav 2.07, CdC
1.428(9) Å. It should be noted that the carbonyl oxygens
of the CO2Me appendages in the maleate ester face the
aminocarbene ligand and establish short interligand
Pt-C(15)
Pt-C(18)
Pt-C(19)
Pt-N(2)
2.006(6)
2.073(6)
2.066(6)
2.161(5)
2.210(4)
2.389(2)
1.273(8)
1.465(8)
1.459(7)
0.86(4)
C(18)-C(19)
C(18)-C(20)
C(19)-C(21)
C(20)-O(20)
C(21)-O(21)
C(21)-O(23)
C(20)-O(22)
O(22)-C(22)
C(23)-O(23)
1.428(9)
1.502(9)
1.501(9)
1.206(8)
1.185(8)
1.334(7)
1.328(7)
1.457(8)
1.438(9)
Pt-N(3)
Pt-Cl(1)
C(15)-N(1)
N(1)-C(16)
N(1)-C(17)
C(15)-H(1)
N(2)-Pt-N(3)
C(15)-N(1)-C(17)
Pt-C(15)-N(1)
76.1(2)
125.8(5)
130.5(4)
C(15)-N(1)-C(16)
C(16)-N(1)-C(17)
120.6(5)
113.6(5)
F igu r e 2. ORTEP drawing (30% probability level) of the
cation [PtCl(CHNMe2)(2,9-Me2-1,10-phen)(Z-MeO2CCHd
CHCO2Me)]+, 1a .
coordinatively saturated environment. In fact, the com-
pounds are stable in nitromethane solution for several
days.
No reaction has been observed with water or other
neutral oxygen nucleophiles. The complexes react with
strong nucleophiles, such as malonate, methoxide,
LiOH, and NaBH4. In all cases the metal is reduced and
[Pt(dmphen)(Z-MeO2CCHdCHCO2Me)] is formed, while
dimethylformamide is obtained from the carbene moi-
ety. Thus, it appears that an iminium derivative (un-
dergoing successive hydrolysis to the amide) is formed
by nucleophilic attack on the metal-bonded carbon.
The reactions effected on 1a are reported in Scheme
3.
Molecu la r St r u ct u r e of t h e [P t Cl(CH NMe2)-
(d m p h en )(Z-MeO2CCHdCHCO2Me)]+ Ca tion (1a )
a s Its Ch lor id e Sa lt Mon oh yd r a te. The stereogeom-
etry of the cation 1a is represented in Figure 2, and
relevant bond parameters are listed in Table 2. The
coordination geometry around the platinum atom is
(26) Barefield, E. K.; Carrier, A. M.; Sepelah, D. J .; Van Derveer,
D. G. Organometallics 1982, 1, 103.
(27) Knop, O.; Cameron, T. S.; Bakshi, P. K.; Kwiatkowski, W.; Choi,
S. C.; Adhikesavalu, D. Can. J . Chem. 1993, 90, 3139.
(28) Clark, G. R.; Shaw, G. L.; Surman, P. W. J .; Tailor, M. J .; Steele,
D. J . Chem. Soc., Faraday Trans. 1994, 90, 3139.

3488 Organometallics, Vol. 18, No. 17, 1999
Cucciolito et al.
F igu r e 4. ORTEP drawing (30% probability level) of [PtCl-
(H2O)(dmphen)(Z-MeO2CCHdCHCO2Me)]Cl.
F igu r e 3. ORTEP drawing (30% probability level) of the
molecule [PtMe(dmphen){η1,η2-CH(CO2Et)O2CCHdCHCO2-
Me}], 2a .
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [P tCl(H2O)(d m p h en )-
(Z-MeO2CCHdCHCO2Me)]Cl‚H2O
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [P tMe(d m p h en )-
Pt-O
2.049(5)
2.082(7)
2.088(8)
2.184(6)
2.190(6)
2.269(2)
1.45(1)
2.93
C(3)-C(6)
C(5)-O(2)
C(4)-O(1)
C(6)-O(4)
C(4)-O(2)
C(6)-O(3)
C(7)-O(3)
O(1)‚‚‚H(19)
1.47(1)
1.45(1)
1.229(9)
1.20(1)
1.312(9)
1.326(9)
1.45(1)
1.65
Pt-C(2)
Pt-C(3)
Pt-N(1)
Pt-N(2)
Pt-Cl(1)
C(2)-C(3)
Cl(2)‚‚‚O
{η1,η2-CH(CO2Et)O2CCHdCHCO2Me}], 2a
Pt-C(8)
2.10(1)
1.99(1)
2.118(7)
2.140(7)
2.14(1)
2.17(1)
1.49(2)
1.16(1)
1.38(1)
1.43(1)
C(8)-C(7)
C(6)-O(4)
C(6)-O(3)
O(3)-C(2)
C(2)-C(3)
C(3)-O(2)
C(3)-O(1)
O(1)-C(4)
C(4)-C(5)
C(7)-C(6)
1.45(1)
1.18(1)
1.34(1)
1.48(2)
1.47(1)
1.20(1)
1.343(9)
1.49(1)
1.59(3)
1.52(2)
Pt-C(7)
Pt-C(1)
Pt-C(2)
Pt-N(2)
Pt-N(1)
C(8)-C(9)
C(9)-O(5)
C(9)-O(6)
C(10)-O(6)
N(1)-Pt-N(2)
Cl(2)‚‚‚H(18)-O
76.3(2)
163
Cl(1)-Pt-O
O-H(19)‚‚‚O(1)
177.7(2)
152
CH-CHdNCy)] [2.14 Å, av]29 and [Pt2Me8(bpym)] [2.13
Å, av].30 The bond distances for the equatorial ligands
Pt-Nav 2.15, Pt-C(olefin)av 2.05, and CdC 1.45(1) Å are
normal and in accord with the values just discussed for
1a .
N(1)-Pt-N(2)
C(7)-C(6)-O(3)
Pt-C(2)-O(3)
C(6)-O(3)-C(2)
76.3(2)
115.8(9)
108.4(8)
117.5(7)
O(3)-C(2)-C(3)
C(1)-Pt-C(2)
Pt-C(2)-C(3)
106(1)
175.9(4)
110.5(6)
Molecu la r Str u ctu r e of th e [P tCl(H2O)(d m p h en )-
(Z-MeO2CCHdCHCO2Me)]+ Ca tion a s Its Ch lor id e
Sa lt Mon oh yd r a te.31 The molecular structure of the
title cation is represented in Figure 4, and relevant bond
parameters are reported in Table 4. The overall stereo-
geometry is that usual for this family of compounds6
and analogous to that just described for 1a and 2a . Were
it not for the asymmetric conformation of the CO2Me
groups in the maleate ligand and the orientation of the
hydrogens of the coordinated water, the ion would
conform to a Cs symmetry. This cation is chemically
related to the cation 1a , [PtCl(CHNMe2)(dmphen)(Z-
MeO2CCHdCHCO2Me)]+, from which it derives by
substitution of the water molecule for the aminocarbene
ligand. The bond distances in the equatorial plane are
normal: [Pt-Nav 2.19, Pt-Cav 2.08, CdC 1.45(1) Å] and
in good agreement with the corresponding values in 1a
and 2a . Expectedly different are the interactions of the
axial ligands. The Pt-Cl distance 2.269(2) Å is the
shortest found in five-coordinate species (average value
2.30 Å),6 probably because of the poor donor ability of
the trans water oxygen. The Pt-OH2 distance (2.049-
(5) Å) is normal. Among the numerous determinations
contacts: O(21)‚‚‚C(15) 2.90, O(20)‚‚‚C(15) 3.10,
O(20)‚‚‚N(15) 3.03 Å. Therefore the molecular conforma-
tion favors a possible intramolecular attack on the
carbene carbon (vide infra).
Molecu la r Str u ctu r e of [P tMe(d m p h en ){η1,η2-
CH (CO2E t )O2CCH dCH CO2Me}] (2a ). The stereo-
geometry of the title compound is shown in Figure 3,
and relevant bond parameters are listed in Table 3. The
trigonal bipyramidal coordination is adopted with
dmphen and maleate double bond in the equatorial
plane and two alkyl groups in axial positions, Me and
CH(CO2Et)OR. A major stereochemical feature is the
coordination of two strong trans influencing sp3 carbons
in opposite sites. We assume that the actual ligand
arrangement is stabilized by the formation of a chelate
ring connecting equatorial and axial sites. The molecule
contains three chiral centers: the olefin carbons C(7)
and C(8) and the axial carbon C(2). The crystal consists
of the racemic mixture, and the diastereoisomer is
defined by the configurations R,S,R of the carbons C(8),
C(7), and C(2), respectively, with reference to Figure 3.
The two Pt-C(sp3) distances [2.118, 2.140(7) Å] are
slightly different, the shorter value being that of the
better donor methyl group. The average Pt-C(sp3)
distance [2.13 Å] is significantly longer than that
observed when the opposite ligand is the chloride ion
(mean value 2.05 Å).6 The actual value is in accord with
what was recently found for mutually trans methyl
groups in the platinum(IV) compounds [PtMe4(CyNd
(29) Hasenzahl, S.; Hausen, H. D.; Kaim, W. Chem. Eur. J . 1995,
1, 95.
(30) Klein, A.; Kaim, W.; Hornung, F. M.; Fiedler, J .; Zalis, S. Inorg.
Chim. Acta 1997, 264, 269.
(31) Very small amounts of this compound accompanied the syn-
thesis of 1a in two runs. It was nearly undetectable through NMR
spectroscopy, and hence, its spectrum was not attributable with
confidence. Attempts of crystallizing crude 1a afforded by chance very
few single crystals of this aquo complex. Analogous species containing
a neutral ligand and a halogen have been described.32

Carbene Complexes of Platinum(II)
Organometallics, Vol. 18, No. 17, 1999 3489
of the platinum-water interaction the most appropriate
comparison is with that reported for [PtCl2(DMSO)-
(H2O)] [2.08(2) Å]33 because water and chloride are
mutually trans in this molecule. The water ligand is
stabilized by two hydrogen bonds, one with a maleate
oxygen O(1)‚‚‚H(19) [1.65(4) Å] and a second with the
chloride counterion Cl(2)‚‚‚H(18) [1.95(3) Å].
philic addition of water. Further rearrangement involv-
ing a carbonyl group of the olefin appendages leads to
formation of a stable five-coordinate complex containing
a η1,η2-C,CdC-chelating moiety.
Addition of nucleophiles to [PtCl(CHNMe2)(dmphen)(Z-
MeO2CCHdCHCO2Me)]Cl affords dimethylformamide
and the corresponding Pt(0) precursor [Pt(dmphen)(Z-
MeO2CCHdCHCO2Me)].
Con clu sion
Ack n ow led gm en t. The authors thank the Consiglio
Nazionale delle Ricerche, the MURST (Programmi di
Ricerca Scientifica di Rilevante Interesse Nazionale,
Cofinanziamento, 1998-1999) for financial support and
the Centro Interdipartimentale di Metodologie Chimico-
Fisiche, Universita` di Napoli “Federico II”, for NMR
facilities. Thanks are also given to Prof. A. Vitagliano
for helpful discussion. V.G.A. and M.M. wish to thank
the University of Bologna for financial support (“Funds
for Selected Research Topics”).
This work has demonstrated the synthesis of tbp
platinum(II) complexes [PtX(CHY)(N,N-chelate)(ole-
fin)]+ (X ) Cl, Me, or Ph) containing carbene ligands
:CHY in apical position. As thoroughly demonstrated
elsewhere6 for complexes with similar coordination
environments, the presence of a sterically crowded
nitrogen chelate is a requisite necessary for their
stability. When Y is NMe2, i.e., a donor substituent, the
complexes can be isolated. On the other hand, their
stability seems to be reduced in the presence of electron-
withdrawing Y substituents (Y ) CO2Et, CONMe2, CN),
as the Ccarbene atom appears to undergo a fast nucleo-
Su p p or t in g In for m a t ion Ava ila b le: Listing of atomic
coordinates, bond lengths and angles, anisotropic thermal
parameters, and hydrogen atom coordinates for compounds 1a ‚
H2O, 2a , and [PtCl(H2O)(dmphen)(Z-MeO2CCHdCHCO2Me)]-
Cl. This material is available free of charge via the Internet
at http://pubs.acs.org.
(32) Albano, V. G.; Castellari, C.; De Felice, V.; Panunzi, A.; Ruffo,
F. Organometallics 1992, 11, 3665.
(33) Rochon, F. D.; Kong, P. C.; Melanson, R. Inorg. Chem. 1990,
29, 2708.
OM990240R