Synthesis and reactivity of (η1-Alkynyl)diorganoplatinum(IV) species, including structural studies of PtIMe(p-Tol)(C≡CSiMe 3)(dmpe) [dmpe = 1,2-bis(dimethylphosphino)ethane] and the platinum(II) reagent PtPh2(dmpe)

Article abstract of DOI:10.1021/om800122k

Synthetic routes to diaryl(alkynyl)platinum(IV) and methyl(aryl)(alkynyl) platinum(IV) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from platinum(IV) centers, and convenient synthetic routes

Full text of DOI:10.1021/om800122k

Organometallics 2008, 27, 3203–3209
3203
Synthesis and Reactivity of (η1-Alkynyl)diorganoplatinum(IV)
Species, Including Structural Studies of
PtIMe(p-Tol)(Ct CSiMe3)(dmpe) [dmpe )
1,2-bis(dimethylphosphino)ethane] and the Platinum(II) Reagent
PtPh2(dmpe)
Allan J. Canty,* Russell P. Watson, Samuel S. Karpiniec, Thomas Rodemann,
Michael G. Gardiner, and Roderick C. Jones
School of Chemistry, UniVersity of Tasmania, Hobart, Tasmania 7001, Australia
ReceiVed February 11, 2008
Synthetic routes to diaryl(alkynyl)platinum(IV) and methyl(aryl)(alkynyl)platinum(IV) motifs are
presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from
platinum(IV) centers, and convenient synthetic routes to the platinum(II) reagents PtR2(dmpe) [R ) Me
(1), p-Tol (2), Ph (3), dmpe ) 1,2-bis(dimethylphosphino)ethane], PtMe(p-Tol)(dmpe) (4), and PtMe(p-
Tol)(COD) (COD ) 1,5-cyclooctadiene). The hypervalent iodine(III) reagent IPh(Ct CSiMe3)(OTf) (OTf-
) CF3SO3-) oxidizes the Pt(II) complexes PtR1R2(dmpe) [1: R1 ) R2 ) Me; 2: R1 ) R2 ) p-Tol; 3:
R1 ) R2 ) Ph; 4: R1 ) Me, R2 ) p-Tol; dmpe ) 1,2-bis(dimethylphosphino)ethane] to Pt(IV) complexes
that are stable at low temperatures. Those complexes resulting from oxidation of 1 and 4 adopt
configurations in which the triflate and η1-alkynyl ligands are cis to each other, Pt(OTf)-
R1R2(Ct CSiMe3)(dmpe) (1a, 4a), with the alkynyl group trans to phosphorus, and form equilibria with
triflate-free complexes (1c, 4c), assumed to be solvento cations. The mixtures of dimethylplatinum(IV)
species (1a and 1c) and of methyl(p-tolyl)platinum(IV) species (4a and 4c) react with sodium iodide,
acetonitrile, and pyridine to form the cis-configured isomers of the complexes PtIR1R2(Ct CSiMe3)(dmpe)
(1b, 4b) and [PtR1R2(Ct CSiMe3)(dmpe)(L)](OTf) (L ) NCMe: 1d, 4d; L ) py: 1e, 4e). The
diarylplatinum(II) complexes 2 and 3 are oxidized primarily to species with the triflate and alkynyl groups
trans to each other, Pt(OTf)Ar2(Ct CSiMe3)(dmpe) (2a, 3a). The trans-isomers of diaryl(triflato)plati-
num(IV) complexes do not take part in ligand substitution reactions with sodium iodide, acetonitrile, or
pyridine, but minor Pt(IV) complexes in equilibrium with 2a and 3a do react with iodide to form
PtIAr2(Ct CSiMe3)(dmpe) (2b, 3b). Structural studies of PtPh2(dmpe) (3) and PtIMe(p-Tol)-
(Ct CSiMe3)(dmpe) (4b) reveal square-planar and octahedral geometries, respectively. On warming above
-10 °C in acetone, the Pt(IV) triflate stages of all of the systems decompose by reductive elimination
via methyl-methyl, methyl-aryl, or aryl-aryl coupling. Similarly, decomposition of PtIMe2-
(Ct CSiMe3)(dmpe) (1b) under mild conditions in acetone results in Me-Me coupling. Decomposition
of the isolated iodo complexes (2b, 3b, 4b) at temperatures above 50 °C reveals involvement of the
alkynyl group in reductive elimination processes, giving minor quantities of Me3SiCt CI and ∼1:1 ratios
for the dominant products Me3SiCt C-Ar and Ar-Ar (2b, 3b), and Me3SiCt C-(p-Tol) and Me-(p-Tol)
for 4b.
alkynylpalladium(IV) species are widely proposed as potential
intermediates in stoichiometric and catalytic transformations,5,6
but to date, the single η1-alkynylpalladium(IV) complex reported
decomposes at -50 °C,4e and thus the synthesis of Pt(IV)
species more suitable for reactivity studies is desirable.
One route to η1-alkynyl complexes of transition metals
involves formal transfer of [Ct CR]+ from the hypervalent
iodine(III) reagents IPh(Ct CR)(OTf), where R is an organic
group and OTf- ) CF3SO3-, to a metal center that results in
overall oxidative addition at the metal and reduction of the
iodonium reagent to iodobenzene. The utility of these iodonium
reagents in organometallic chemistry and organic synthesis,
including proposed mechanisms, has recently been reviewed.7
Introduction
η1-Alkynylplatinum(IV) species have been proposed as
intermediates in catalytic reactions,1 and addition of the oxidant
iodine promotes the stoichiometric synthesis of macrocycles via
carbon-carbon bond formation at the platinum(II) center of η1-
alkynyl complexes.2 The relatively small number of reported
syntheses of η1-alkynylplatinum(IV) compounds3,4 has prompted
us to investigate methods of preparing new classes of these
tetravalent complexes and their decomposition, in particular the
potential for carbon-carbon bond formation. In addition, η1-
* To whom correspondence should be addressed. E-mail: Allan.Canty@
utas.edu.au. Fax: (61-3) 6226-2858.
(1) Jagadeesh, M. N.; Thiel, W.; Ko¨hler, J.; Fehn, A. Organometallics
2002, 21, 2076.
We previously reported reactions of the iodine(III) reagents
IPh(Ct CR)(OTf) (R ) SiMe3, Ph) with diorganoplatinum(II)
complexes of ligand systems that included the pincer ligands
(2) Fuhrmann, G.; Debaerdemaeker, T.; Ba¨uerle, P. Chem. Commun.
2003, 948.
10.1021/om800122k CCC: $40.75
2008 American Chemical Society
Publication on Web 06/05/2008

3204 Organometallics, Vol. 27, No. 13, 2008
Canty et al.
Scheme 1
Mercury Plus 300 MHz spectrometer. 1H NMR spectra were
secondary-referenced to residual solvent signals. 31P NMR spectra
were externally referenced to 85% H3PO4. Microanalyses and
LSIMS analyses were performed by the Central Science Laboratory,
University of Tasmania. GC-MS analyses were performed using
an HP 5890 gas chromatograph equipped with an HP5790 MSD
and a 25 × 0.32 mm HP1 column (0.52 µm film thickness, He at
8 psi).
PtMe2(dmpe) (1). Methyllithium (1.6 M in Et2O, 3.2 mL, 5.12
mmol) was added dropwise to a stirred suspension of PtCl2(SEt2)2
(1.01 g, 2.26 mmol) in Et2O (40 mL) at -20 °C. After addition
was complete, the reaction mixture was allowed to warm to 0 °C
and was stirred at this temperature for 2 h. The solution was then
quenched by the dropwise addition of saturated NH4Cl, and the
aqueous phase was extracted with Et2O (3 × 20 mL). The combined
extracts were dried over MgSO4 and filtered under argon into a
dried flask. 1,2-Bis(dimethylphosphino)ethane (0.38 mL, 2.37
mmol) was added and the solution stirred for 1 h. Removal of the
solvent in Vacuo gave a white solid, which was washed with pentane
to afford 1 (0.64 g, 76%). The characterization of this product
matched that given in the literature.11
[2,6-(dimethylaminomethyl)phenyl-N,C,N]-, 2,2′-bipyridine, and
1,2-bis(dimethylphosphino)ethane (dmpe).4e In these reactions,
the platinum(II) starting materials were oxidized to give the first
examples of aryl(η1-alkynyl)platinum(IV) and dimethyl(alky-
nyl)platinum(IV) complexes, where in situ ligand exchange of
iodide for triflate resulted in characterizable, and in some
instances isolable, complexes.
Alkynylplatinum(IV) complexes containing nitrogen donor
ligands from the above reactions were found to be thermally
stable at room temperature, but for the dmpe complexes
reductive elimination occurs under mild conditions in solution
to give ethane and the isolable platinum(II) compounds
PtI(Ct CR)(dmpe), as shown in Scheme 1. We report herein a
study of the iodonium oxidation chemistry of the family of
complexes PtR1R2(dmpe), where R1 and R2 are alkyl or aryl
groups, in order to probe the behavior of a range of
PtIVR1R2(alkynyl) motifs.
Experimental Section
Air-sensitive materials were handled under an argon atmosphere
using standard Schlenk techniques. All solvents were dried and
distilled by conventional methods prior to use. The compounds
PtCl2(SEt2)2,8 Pt(p-Tol)2(COD) (COD ) 1,5-cyclooctadiene),9
PtClMe(COD),10 and IPh(Ct CSiMe3)(OTf)11 were prepared as
previously reported. NMR spectra were recorded on a Varian
Pt(p-Tol)2(dmpe) (2). 1,2-Bis(dimethylphosphino)ethane (15 µL,
0.091 mmol) was added to a stirred solution of Pt(p-Tol)2(COD)
(0.044 g, 0.091 mmol) in Et2O (5 mL). A white precipitate formed
during the addition. The suspension was stirred for 10 min and the
precipitate isolated by filtration to yield 2 (0.026 g, 54%). Anal.
1
Calcd (Found): C, 45.54 (45.26); H, 5.73 (5.49). H NMR (300
MHz, acetone-d6): δ 7.21 (m, 4 H, JPtH ) 57 Hz, o-Tol), 6.69 (m,
4 H, m-Tol), 2.07 (overlapping with solvent, 6 H, C6H4CH3), 1.83
(m, 4 H, PCH2), 1.29 (m, 12 H, PCH3). 31P NMR (121 MHz,
acetone-d6): δ 21.1 (JPtP ) 1674 Hz).
(3) (a) Janzen, M. C.; Jenkins, H. A.; Jennings, M. C.; Rendina, L. M.;
Puddephatt, R. J. J. Chem. Soc., Dalton Trans. 1999, 1713. (b) Janzen,
M. C.; Jenkins, H. A.; Jennings, M. C.; Rendina, L. M.; Puddephatt, R. J.
Organometallics 2002, 21, 1257. (c) Belluco, U.; Bertani, R.; Michelin,
R. A.; Mozzon, M. J. Organomet. Chem. 2000, 600, 37. (d) Long, N. J.;
Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586.
PtPh2(dmpe) (3). PtPh2(dmpe) was prepared by the same
procedure as for PtMe2(dmpe) (1) using the following reagents:
phenyllithium (1.8 M in Bu2O, 1.4 mL, 2.52 mmol) and PtCl2(SEt2)2
(0.50 g, 1.12 mmol) in Et2O (20 mL); dmpe (0.20 mL, 1.25 mmol).
The yield of 3 was 0.42 g (76%). The characterization of this
product matched that given in the literature.12a X-ray quality crystals
were grown by layering a CH2Cl2 solution of 3 with pentane.
PtMe(p-Tol)(COD). A solution of p-iodotoluene (1.85 g, 8.49
mmol) in Et2O (15 mL) was added dropwise to magnesium metal
(0.21 g, 8.6 mmol) to which a crystal of iodine had been added to
initiate the reaction. After the addition was complete, the green-
gold Grignard system was heated at reflux for 30 min, cooled to
room temperature, and added by syringe over 10 min to a precooled
(0 °C) solution of PtClMe(COD) (1.5 g, 4.24 mmol) in CH2Cl2
(75 mL). During the addition of the Grignard reagent, the solution
became cloudy but eventually cleared to a golden-brown color. After
addition was complete, the solution was stirred at 0 °C for 30 min
and then cooled to -78 °C. Degassed isopropyl alcohol (5 mL)
was added at once, the cold bath was removed, and the solution
was allowed to warm to 0 °C. Degassed water (100 mL) was then
added, and the system was stirred at 0 °C for 1 h. The layers were
separated, and the aqueous phase was extracted with CH2Cl2 (2 ×
25 mL). The addition of small amounts of THF aided in this
extraction. The combined organic phases were washed with water
(100 mL), dried over MgSO4, and treated with decolorizing
charcoal. Removal of the solvent by rotary evaporation gave a
(4) (a) Geisenberger, J.; Nagel, U.; Sebald, A.; Beck, W. Chem. Ber.
1983, 116, 911. (b) James, S. L.; Younus, M.; Raithby, P. R.; Lewis, J. J.
Organomet. Chem. 1997, 543, 233. (c) Canty, A. J.; Rodemann, T. Inorg.
Chem. Commun. 2003, 6, 1382. (d) Canty, A. J.; Rodemann, T.; Skelton,
B. W.; White, A. H. Inorg. Chem. Commun. 2005, 8, 55. (e) Canty, A. J.;
Rodemann, T.; Skelton, B. W.; White, A. H. Organometallics 2006, 25,
3996.
(5) Gevorgyan, V. In Handbook of Organopalladium Chemistry for
Organic Synthesis; Negishi, E.-I., Ed.; Wiley: New York, 2002; Vol. 1,
Chapter IV.5, p 1463.
(6) (a) Trost, B. M.; Chan, C.; Ruhter, G. J. Am. Chem. Soc. 1987, 109,
3486. (b) Alper, H.; Saldana-Maldonado, M. Organometallics 1989, 8, 1124.
(c) Catellani, M.; Marmiroli, B.; Fagnola, M. C.; Acquotti, D. J. Organomet.
˝
Chem. 1996, 507, 157. (d) Herrmann, W. A.; Reisinger, C.-P.; Ofele, K.;
Brossmer, C.; Beller, M.; Fischer, H. J. Mol. Catal. A 1996, 108, 51. (e)
Naka, A.; Okada, T.; Ishikawa, M. J. Organomet. Chem. 1996, 521, 163.
(f) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ru¨hter, G. J. Am.
Chem. Soc. 1997, 119, 698.
(7) (a) Deprez, N. R.; Sanford, M. S. Inorg. Chem. 2007, 46, 1924. (b)
Canty, A. J.; Rodemann, T.; Ryan, J. H. AdV. Organomet. Chem. 2008, 55,
279.
(8) Kauffman, G. B.; Cowan, D. O. Inorg. Synth. 1960, 6, 211.
(9) Shekhar, S.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 13016.
(10) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.
(11) Bachi, M. D.; Bar-Ner, N.; Crittell, C. M.; Stang, P. J.; Williamson,
B. L. J. Org. Chem. 1991, 56, 3912.
(12) (a) Peters, R. G.; White, S.; Roddick, D. M. Organometallics 1998,
17, 4493. (b) Booth, G.; Chatt, J. J. Chem. Soc. A 1966, 634. (c) Goikhman,
R.; Aizenberg, M.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 1996,
118, 10894. (d) Smith, D. C.; Haar, C. M.; Stevens, E. D.; Nolan, S. P.;
Marshall, W. J.; Moloy, K. G. Organometallics 2000, 19, 1427.

Synthesis of (η1-Alkynyl)diorganoplatinum(IV) Species
Organometallics, Vol. 27, No. 13, 2008 3205
brown solid, which was recrystallized from a minimum of boiling
hexanes to give PtMe(p-Tol)(COD) (0.88 g, 51%) as brown
crystalline flakes. Anal. Calcd (Found): C, 46.94 (46.72); H, 5.42
(5.16). The characterization of this product matched that given in
the literature.13
PtMe(p-Tol)(dmpe) (4). 1,2-Bis(dimethylphosphino)ethane (0.20
mL, 1.2 mmol) was added by syringe to a degassed benzene solution
(50 mL) of PtMe(p-Tol)(COD) (0.50 g, 1.2 mmol). The resulting
solution was stirred at room temperature under argon for 1.5 h.
The solvent was removed in Vacuo, affording 4 (0.42 g, 76%),
which could be used without further purification. The product could
be recrystallized, if necessary, from hot hexanes. Anal. Calcd
1
(Found): C, 37.25 (37.46); H, 5.81 (5.92). H NMR (300 MHz,
acetone-d6): δ 7.17 (t, J ) 6.9 Hz, JPtH ) 56 Hz, 2 H, o-Tol), 6.74
(d, J ) 6.6 Hz, 2 H, m-Tol), 2.09 (s, 3 H, C6H4CH3), 1.80-1.68
(m, 4 H, PCH2), 1.47-1.37 (m, 6 H, PCH3), 1.28-1.17 (m, 6 H,
PCH3), 0.31 (t, J ) 7.8 Hz, JPtH ) 69 Hz, 3 H, PtCH3). 31P NMR
(121 MHz, acetone-d6): δ 31.6 (JPtP ) 1752), 28.8 (JPtP ) 1680).
MS ESI(+): m/z (rel % abund) [assgn]: 474 (10) [M + Na]+, 436
(15) [M - CH3]+, 360 (100) [M - tolyl]+.
Oxidation Studies. The following procedure was used for the
formation and NMR studies of the Pt(IV) complexes
PtIR1R2(Ct CSiMe3)(dmpe) [R1 ) R2 ) Me (1b); R1 ) R2 ) p-Tol
(2b); R1 ) R2 ) Ph (3b); R1 ) Me, R2 ) p-Tol (4b)]: A solution
of IPh(Ct CSiMe3)(OTf) (0.010 g, 0.022 mmol) in acetone-d6 (1
mL) at -50 °C was added to a solution or suspension of
PtR1R2(dmpe) (0.022 mmol) in acetone-d6 (1 mL) at -50 °C, and
the mixture was stirred at -50 °C for 30 min (1 h for 2 and 3)
under argon. NMR spectra of an aliquot of this resulting triflate
intermediate solution were recorded. To the remaining original
solution was added NaI (0.006 g, 0.04 mmol), and the system was
stirred at -50 °C for a further 1 h. An aliquot of the resulting
solution was then removed and its NMR spectra were recorded.
Reactions involving NaOTf, MeCN, and pyridine were performed
as follows: PtR1R2(dmpe) was treated with IPh(Ct CSiMe3)(OTf)
and stirred at -50 °C as described above. An excess of NaOTf
(20 mg), MeCN (5 µL), or pyridine (5 µL) was added, and the
solution stirred at -50 °C for a further 1 h. The NMR spectra of
the resulting solution were then recorded.
Figure 1. ORTEP representations of the structures of (a)
PtPh2(dmpe) (3) and (b) PtIMe(p-Tol)(Ct CSiMe3)(dmpe) (4b).
Displacement ellipsoids are drawn at the 50% probability level,
and hydrogen atoms are omitted for clarity. (a) PtPh2(dmpe) (3):
atom C(1) is disordered over two positions at half-occupancy.
Selected bond lengths (Å) and angles (deg): Pt(1)-C(3, 7) 2.076(7),
2.066(6); Pt(1)-P(1, 2) 2.284(2), 2.279(3); C(3)-Pt(1)-C(7)
92.0(3), C(3)-Pt(1)-P(1, 2) 176.1(2), 91.1(2); P(1)-Pt(1)-P(2)
84.96(9), C(7)-Pt(1)-P(1, 2) 91.87(18). 176.83(16). (b) PtIMe(p-
Tol)(Ct CSiMe3)(dmpe) (4b): Pt(1)-C(1, 6, 7) 2.04(2), 2.079(19),
2.155(18); Pt(1)-P(1, 2) 2.330(6), 2.380(5); Pt(1)-I(1) 2.757(3),
C(1)-C(2) 1.14(3), C(2)-Si(1) 1.89(2), C(1)-Pt(1)-C(6,7) 88.1(8),
86.3(9); C(6)-Pt(1)-C(7) 90.0(8), C(1)-Pt(1)-P(1, 2) 173.9(5),
92.5(6); C(6)-Pt(1)-P(1, 2) 87.1(7), 88.9(6); C(7)-Pt(1)-P(1, 2)
97.5(7), 178.4(5); I(1)-Pt(1)-C(1, 6, 7) 91.0(5), 177.9(6), 91.8(5);
P(1)-Pt(1)-P(2)83.6(2),Pt(1)-C(1)-C(2)167.6(19),C(1)-C(2)-Si(1)
169(2).
PtIMe(p-Tol)(Ct CSiMe3)(dmpe) (4b).
A
solution of
IPh(Ct CSiMe3)(OTf) (0.051 g, 0.11 mmol) in acetone (25 mL) at
-50 °C was added to a solution of PtMe(p-Tol)(dmpe) (4) (0.051
g, 0.11 mmol) in acetone (25 mL) at -50 °C, and the resulting
colorless solution was stirred at -50 °C for 30 min under argon.
To this solution was added NaI (0.025 g, 0.17 mmol), and the
system was stirred at -50 °C for 1 h, after which time the solution
was allowed to warm to room temperature and stirred for a further
16 h. The solvent was removed in Vacuo, and CH2Cl2 (3 mL) was
added. The resulting suspension was filtered through Celite/cotton.
Pentane (5 mL) was added to the filtrate, giving a fine precipitate,
and the system was left at -20 °C for 30 min. The recrystallized
product was isolated by suction filtration, washed with pentane,
and dried in air, affording 4b (0.018 g, 24%) as a colorless solid.
Anal. Calcd (Found): C, 33.78 (33.96); H, 5.22 (5.47). IR (KBr):
νCt C ) 2100 cm-1. 1H NMR (300 MHz, acetone-d6): δ 7.71 (t, J
) 7.8 Hz, JPtH ) 40 Hz, 2 H, o-Tol), 6.73 (d, J ) 6.0 Hz, 2 H,
m-Tol), 2.48-1.93 (m, PCH2, PCH3; overlapping singlet at δ 2.18,
PhCH3; total integration: 16 H), 1.66-1.46 (m, PCH3), 1.38 (t, J
) 6.6 Hz, JPtH ) 34 Hz, PtCH3; overlapping with PCH3, total
integration: 6 H), 0.06 (s, 9 H, SiMe3). 31P NMR (121.4 MHz,
acetone-d6): δ 3.91 (JPtP ) 1088 Hz), -0.20 (JPtP ) 1757 Hz).
Crystals for a structural analysis were obtained from pentane with
the minimum quantity of dichloromethane required to ensure
solubility.
Structural Determinations. Data were collected at 193 K with
an Enraf Nonius TurboCAD4 with Mo KR radiation (0.71073 Å)
on prismatic crystals of PtPh2(dmpe) (3) and PtIMe(p-Tol)-
(Ct CSiMe3)(dmpe) (4b), belonging to the space groups P21/m (No.
11) and P21/c (No. 14), respectively. A summary of crystallographic
data, data collection parameters and refinement parameters, and
views of molecules of the complexes (Figure 1) are given below.
The structures were solved by heavy atom methods with SHELXS-
97, refined using full-matrix least-squares routines against F2 with
SHELXL-97,14 and visualized using X-SEED.15 All non-hydrogen
atoms were subsequently refined anisotropically, except for PtIMe(p-
Tol)(Ct CSiMe3)(dmpe), for which isotropic refinement was neces-
(14) Sheldrick, G. M. SHELX97, Programs for Crystal Structure
Analysis; Universita¨t Go¨ttingen: Germany, 1998.
(15) Barbour, L. J. J. J. Supramol. Chem. 2001, 1, 189.
(13) Jawad, J. K.; Puddephatt, R. J.; Stalteri, M. A. Inorg. Chem. 1982,
21, 332.

3206 Organometallics, Vol. 27, No. 13, 2008
Canty et al.
PtCl2(SEt2)(i) excess RLiPtR2(dmpe) R ) Me (1), Ph (3) (1)
sary for a number of carbon centers. Hydrogens were included in
calculated positions using a riding model, with C-H distances in
the range 0.95-0.99 Å and with Uiso(H) ) 1.2Ueq(C), except for
methyl H atoms, where Uiso(H) ) 1.5Ueq(C).
(ii) dmpe
The new complex Pt(p-Tol)2(dmpe) (2) was also conveniently
prepared from Pt(p-Tol)2(COD) by ligand exchange with dmpe.
The new methyl/aryl complex PtMe(p-Tol)(dmpe) (4) was
prepared in two steps from PtClMe(COD) using p-tolylmag-
nesium iodide to give the isolable complex PtMe(p-Tol)(COD).
Subsequent ligand exchange of COD for dmpe yielded 4. The
intermediate PtMe(p-Tol)(COD) has been previously prepared
using organotin reagents.13
The primitive monoclinic unit cell of PtPh2(dmpe) (3) contains
two molecules, with the asymmetric unit containing one-half of a
molecule of 3. Molecules of 3 lie upon crystallographic mirror
planes (x, 3/4, z). A disorder in the torsion of the chelating dmpe
ligand was apparent in Fourier maps and was modeled as a two-
site occupancy disorder across the crystallographic mirror plane
for a single methylene carbon center lying off the mirror plane (C1,
site occupancy fixed at 0.5). No other resolvable atomic positions
as a consequence of this disorder were apparent in the remaining
portions of the diphosphine ligand or the phenyl ligands, and they
are thus refined with large anisotropic thermal parameters in some
cases. Structure refinement in various space groups yielded the same
disorder, with no improvements in the disorder model and/or
residuals. Thus, refinement in the highest symmetry space group
matching the observed systematic data absences is presented. The
overall noncrystallographic molecular symmetry of PtPh2(dmpe)
is likely to be C2, but approximates to C2V with the exception of
the conformation of the diphosphine ligand chelate ring. Crystals
of PtIMe(p-Tol)(Ct CSiMe3)(dmpe) (4b) decomposed substantially
during data collection, which resulted in a relatively poor refinement
model despite data corrections being applied for the decay of the
regularly measured intensity standards. Data were collected on
several crystals, with similar outcomes.
PtClMe(COD)(i) p-TolMglPtMe(p - Tol)(dmpe) (4)
(2)
(ii) dmpe
Syntheses of Pt(IV) Complexes: Triflate Stage. To better
understand the formation of 1b and its decomposition (Scheme
1), we examined the immediate product resulting from the
combination of solutions of PtMe2(dmpe) and IPh(Ct CSiMe3)-
(OTf) at -50 °C, yielding the “triflate stage” of the overall
reaction in Scheme 1, before addition of NaI. The 31P NMR
spectrum of the triflate stage of 1 at -50 °C displays two
dominant signals of equal intensity at 29.4 and 24.7 ppm (JPtP
) 1210 and 1826 Hz, respectively; Table 1).A weaker pair of
resonances at 25.3 (JPtP ) 1181 Hz) and 20.7 (JPtP ) 1795 Hz)
is also present. In both the major and minor sets, the signal at
lower field has the smaller JPtP, ca. 1200 Hz, whereas the upfield
signal has a JPtP of ca. 1800 Hz. The distinct values of the
respective coupling constants indicate the two phosphorus nuclei
of dmpe in each complex are coupled to groups with disparate
trans influences, and the spectra are consistent with the presence
of two cis-configured species (Scheme 2). When a 5-fold excess
of NaOTf is added at -50 °C, intensification of the minor set
of 31P signals (1a) indicates that the other species (1c) may be
the solvento cation [PtMe2(dmpe)(Ct CSiMe3)(OCMe2)]+. Al-
though the addition of an excess of triflate increases the
abundance of 1a at -50 °C, at -20 °C the species 1c again
predominates. The thermal instability of the triflate stage species
prohibits investigations at higher temperatures.
Crystal Data. Complex 3: C18H26P2Pt, M ) 499.42, monoclinic,
space group P21/m, a ) 8.624(9) Å, b ) 10.9514(18) Å, c )
10.323(3) Å, ꢀ ) 106.99(3)o, V ) 932.4(10) Å3, Z ) 2, Dc )
1.779 g cm-3, µ ) 7.688 mm-1, specimen 0.20 × 0.18 × 0.22
mm, 1812 measured reflections, 1716 unique reflections, Rint
)
0.047, R1 ) 0.028 for observed data and wR2 ) 0.071 for all data.
Complex 4b: C19H35IP2PtSi, M ) 675.49, monoclinic, space group
P21/c, a ) 16.982(10) Å, b ) 10.492(5) Å, c ) 15.289(12) Å, ꢀ
) 113.21(8)o, V ) 2504(3) Å3, Z ) 4, Dc ) 1.792 g cm-3, µ )
7.013 mm-1, specimen 0.43 × 0.20 × 0.18 mm, 4024 measured
reflections, 3870 unique reflections, Rint ) 0.141, R1 ) 0.071 for
observed data and wR2 ) 0.211 for all data.
Results
Syntheses of Pt(II) Starting Materials. The complex
PtMe2(dmpe) (1) has been previously prepared by treating
PtCl2(dmpe)withmethyllithiumormethylmagnesiumbromide,12a,b
or by ligand exchange between PtMe2(COD) and dmpe.12c,d The
latter route has also been employed for the synthesis of
PtPh2(dmpe) (3).12a Complexes 1 and 3 were prepared in high
yield by the alternative route given in eq 1. The reactions of
PtCl2(SEt2)2 with RLi (R ) Me, Ph) afforded the thioether-
bridged dimers [PtR2(µ-SEt2)]2,16 which were converted without
isolation to the dmpe complexes PtR2(dmpe) by ligand ex-
change.
1
In the corresponding H NMR spectrum of the triflate stage
in the dimethylplatinum system (1a, 4a), resonances from the
product iodobenzene are observed at low field, while the upfield
region displays the complicated overlapping splitting patterns
expected from the methyl and methylene groups of the dmpe
ligand. The most diagnostic features of the spectrum are the
overlapping Pt-CH3 signals at 1.0-0.8 ppm, accompanied by
195Pt satellites, which are deshielded relative to the Pt(II) starting
material. A dominant trimethylsilyl signal near 0 ppm and
Table 1. Observed 31P NMR Resonancesa and JPtP Coupling Constantsb for Compounds 1-4
PtIVR1R2(Ct CSiMe3)(dmpe)
PtIIR1R2(dmpe)
triflate stagec
PtIVIR1R2(Ct CSiMe3)(dmpe)
R1 ) R2 ) Me
32.4 (1783)
29.4 (1210), 24.7 (1826);
25.3 (1181), 20.7 (1795)
(1a and 1c)
25.5 (1121)
(2a)
25.8 (1119)
(3a)
27.5 (1171), 26.0 (1838);
23.7 (1139), 21.4 (1750)
(4a and 4c)
6.3 (1158),2.1(1744)
(1)
(1b)
R1 ) R2 ) p-Tol
R1 ) R2 ) Ph
29.0 (1684)
(2)
29.1 (1684)
(3)
6.8 (1116),4.0(1800)
(2b)
7.0 (1115),4.3(1797)
(3b)
R1 ) Me, R2 ) p-Tol
32.0 (1771), 29.6 (1690)
5.8 (1099),2.5(1718)
(4)
(4b)
a δ units, -50 °C, acetone-d6. b In parentheses, Hz. c Pt(OTf)R1R2(dmpe)(Ct CSiMe3) or [PtR1R2(dmpe)(Ct CSiMe3)(OCMe2)]OTf.

Synthesis of (η1-Alkynyl)diorganoplatinum(IV) Species
Organometallics, Vol. 27, No. 13, 2008 3207
Scheme 2a
a
Configurations at Pt for 4a and 4c are unknown.
Scheme 3
MeCN is used, resonances from triflate stage species persist
until the temperature is raised to -20 °C, whereas the formation
of 1d is nearly instantaneous at -50 °C. The corresponding
pyridine adducts [PtMe2(dmpe)(Ct CSiMe3)(py)](OTf) (1e; py
) pyridine) and [PtMe(p-Tol)(dmpe)(Ct CSiMe3)(py)](OTf)
(4e) (Scheme 4) are formed in similar fashion to their MeCN
counterparts, giving single sets of 31P signals at 18.4 and 15.1
ppm (JPtP ) 1135 and 1747 Hz) for 1e and 17.7 and 17.3 ppm
(JPtP ) 1119 and 1765 Hz) for 4e. Quantitative formation of 1e
and 4e is slower than for the MeCN analogues, occurring over
1 day at -20 °C. In contrast to the triflate stages, (1a with 1c)
and (4a with 4c), the diarylplatinum complexes Pt(OTf)(p-Tol)2-
weaker overlapping trimethylsilyl signals again suggest a
mixture of products.
(dmpe)(Ct CSiMe3)
(2a)
and
Pt(OTf)Ph2(dmpe)-
(Ct CSiMe3) (3a) do not react with MeCN or pyridine.
Reaction of the triflate stage equilibrium mixture, 1a with
1c (Scheme 2), with NaI results in complete conversion to the
iodo complex PtIMe2(Ct CSiMe3)(dmpe) (1b, Scheme 1), which
decomposes slowly at room temperature to give ethane and the
isolable Pt(II) complex PtI(Ct CSiMe3)(dmpe).4e
The mixed methyl/tolyl triflate stage (4a with 4c) most closely
resembles the dimethylplatinum system in its reaction with NaI.
Within 30 min, the pairs of resonances in the 31P NMR spectrum
corresponding to the triflate stage species (4a with 4c) are
replaced by signals at 5.8 and 2.5 ppm, with JPtP values similar
to PtIMe2(Ct CSiMe3)(dmpe) (Table 1). Residual signals from
the triflate stage can still be observed at -50 °C, but at higher
temperatures are no longer detected. Thus, the reaction appears
to be somewhat slower than in the PtIVMe2 system. Unlike any
of the other Pt(IV) compounds in this study, 4b can be isolated
as a pure solid that is stable for at least two months at -20 °C
but shows signs of decomposition after several weeks at room
temperature.
After treatment of the diarylplatinum(IV) triflate species 2a
and 3a with an excess of NaI, the 31P NMR spectra exhibit two
new signals near 7 and 4 ppm (Table 1), corresponding to the
iodo complexes PtI(p-Tol)2(Ct CSiMe3)(dmpe) (2b) and
PtIPh2(Ct CSiMe3)(dmpe) (3b). Although the trans-isomers
dominate the triflate stages of the diaryl systems, the pairs of
31P NMR signals and the presence of nonequivalent tolyl groups
for 2b indicate the formation of the respective cis-iodo
complexes. Residual resonances of unreacted triflate species
gradually disappear as the temperature is raised from -50 °C,
and by 10 °C new signals downfield corresponding to Pt(II)
decomposition products replace the single resonances for 2a
and 3a. When an excess of NaOTf is used to eliminate minor
Pt(IV) species and form 2a and 3a quantitatively as described
above, no reaction with NaI is observed, indicating that reaction
with iodide occurs via the minor Pt(IV) species rather than 2a
and 3a.
Reactions of Pt(p-Tol)2(dmpe) (2) and PtPh2(dmpe) (3) with
IPh(Ct CSiMe3)(OTf) give colorless solutions, whose 31P NMR
spectra show that the single resonance observed at 29 ppm in
the Pt(II) starting material is replaced by one dominant signal
near 26 ppm (Table 1) and several much weaker signals.
Addition of an excess of NaOTf at -50 °C results in the
intensification of this dominant signal and the diminution of
the weaker ones. At -20 °C, only the dominant signal and its
195Pt satellites are observed. These NMR data are consistent
with the preferred formation of the trans-isomers Pt(OTf)(p-
Tol)2(dmpe)(Ct CSiMe3) (2a) and Pt(OTf)Ph2(dmpe)-
(Ct CSiMe3) (3a), shown in Scheme 3.
The complex PtMe(p-Tol)(dmpe) (4) behaves similarly to the
dimethylplatinum complex 1 (Scheme 2). Thus, its oxidized
triflate stage 31P NMR spectrum reveals two sets of resonances
(Table 1), with the lower field signals dominating, whose
chemical shifts and coupling constants are very similar to 1a
and 1c. The triflate stage of this system is therefore assigned as
comprising Pt(OTf)Me(p-Tol)(dmpe)(Ct CSiMe3) (4a) and the
solvento complex [PtMe(p-Tol)(dmpe)(Ct CSiMe3)(OCMe2)]-
(OTf) (4c).
Syntheses of Pt(IV) Complexes: Ligand Substitutions.
When stoichiometric amounts of acetonitrile are added to the
triflate stages of the PtIVMe2 and PtIVMe(p-Tol) systems, (1a
with 1c) and (4a with 4c), the adducts [PtMe2(dmpe)-
(Ct CSiMe3)(NCMe)](OTf)
(1d)
and
[PtMe(p-Tol)-
(dmpe)(Ct CSiMe3)(NCMe)](OTf) (4d) are formed (Scheme 4),
as evidenced by the appearance of two new 31P signals at 18.2
and 15.4 ppm (JPtP ) 1164 and 1753 Hz, respectively) for 1d
and 17.5 and 16.2 ppm (JPtP ) 1121 and 1763 Hz) for 4d.
Formation of 1d and 4d is not quantitative, however, unless a
large excess of MeCN is present. At -50 °C, signals from the
two platinum-bound methyl groups of 1d are nearly coincident,
but raising the temperature to -10 °C allows the identification
of the two nonequivalent groups. The formation of 4d is
markedly slower than that of 1d. Even when a large excess of
Structural Studies of PtPh2(dmpe) (3) and PtIMe-
(p-Tol)(Ct CSiMe3)(dmpe) (4b). The complexes exhibit the
expected square-planar (3) and octahedral (4b) coordination
geometries appropriate for Pt(II) and Pt(IV) (Figure 1). The
(16) (a) Kuyper, J.; van der Laan, R.; Jeanneaus, F.; Vrieze, K. Trans.
Met. Chem. 1976, 1, 199. (b) Steele, B. R.; Vrieze, K. Trans. Met. Chem.
1977, 2, 140.

3208 Organometallics, Vol. 27, No. 13, 2008
Canty et al.
Scheme 4a
1
2
1
2
a
1a-e: R ) R ) Me; 4a-e: R ) Me, R ) p-Tol, relative configurations of Me and p-Tol at Pt are unknown.
Scheme 5 Scheme 6
Pt(IV) complex has the fac-PtC3 configuration with cis-oriented
iodo and alkynyl groups, while the alkynyl group is trans to a
phosphorus. In both structures the aryl groups form large
interplanar angles to the PtC2P2 mean plane [90° for 3, 49.0(7)o
for 4b], minimizing Ph · · · Ph interactions in 3 and aryl · · · PMe2
interactions in 3 and 4b; the smaller interplanar angle in 4b
also allows minimization of p-Tol · · · Me and p-Tol · · · I interac-
tions. For related Pt-C(aryl) and Pt-P bonds, longer distances
are found in the higher oxidation state, as expected, by ∼0.09
Å for Pt-C and ∼0.07 Å for Pt-P. For the bidentate phosphine
ligand this is reflected in a smaller PtP2 chelate bite angle in
the Pt(IV) complex [84.97(9)o for 3, 83.6(2)o for 4b]. The η1-
alkynylplatinum(IV) complex has Pt-C 2.04(3) Å and Ct C
1.14(3) Å, and the Pt(1)-C(1)-C(2) angle is 167.6(19)o; a
similar bending [172.7(3)o] occurs in the pincer complex
Pt(O2CArF)I(Ct CSiMe3)(NCN) (ArF ) p-CF3C6H4, NCN )
[2,6-(dimethylaminomethyl)phenyl-N,C,N]-).4e
Decomposition of Pt(IV) Complexes. On warming above
-10 °C in acetone, the colorless triflate stage mixtures of all
the systems in this study turn dark and opaque. 1H NMR spectra
and GC-MS analyses reveal that decomposition occurs through
reductive elimination to give ethane from PtIVMe2(Ct CSiMe3)
species (1a/1c), 4,4′-dimethylbiphenyl from PtIV(p-Tol)2-
(Ct CSiMe3) species (2a), biphenyl from PtIVPh2(Ct CSiMe3)
species (3a), and p-xylene from PtIVMe(p-Tol)(Ct CSiMe3)
species (4a with 4c) (eq 3). The complex expected from the
reductive eliminations, Pt(OTf)(Ct CSiMe3)(dmpe), could not
be isolated from the dark suspensions. The MeCN and pyridine
complexes of systems 1 and 4 decompose in the same manner
as their respective triflate stages, thus giving ethane from the
mixture of 1d and 1e and p-xylene from the mixture of 4d and
4e, along with unidentified Pt-containing products. The pyridine
adducts 1e and 4e, however, are thermally more stable than their
respective triflate and acetonitrile complexes and persist at room
temperature for several days.
during GC-MS experiments to give Me3SiCt CAr and (Ar)2 in
∼1:1 ratio together with Me3SiCt CI (trace for 2b, ∼0.07 for
3b) (Scheme 6). Similarly, the methyl/aryl complex PtIMe(p-
Tol)(Ct CSiMe3)(dmpe) (4b), which is obtained in pure form,
decomposes with heating to form Me3SiCt C-(p-Tol) and (p-
Tol)2 with, in this case, an appreciable quantity of Me3SiCt CI
(∼0.15 but not reliably quantified due to solid state decomposi-
tion in GC-MS) (Scheme 7). The less stable species
PtIMe2(Ct CSiMe3)(dmpe) (1b), which cannot be isolated and
studied under identical conditions, decomposes in acetone to
give ethane and PtI(Ct CSiMe3)(dmpe).
Discussion
The results presented above illustrate a simple route to new
diaryl(alkynyl)- and methyl(aryl)(alkynyl)platinum(IV) systems
as well as differences in preferred configurations and reactivities
of diaryl(alkynyl)platinum(IV) complexes compared to the
dimethyl- and methyl(aryl)platinum(IV) complexes, which
behave similarly. Thus, although for PtXR1R2(Ct CSiMe3)-
(dmpe) the triflate stages of the PtIVMe2 and PtIVMeAr systems
(X ) OTf: 1a, 4a) as well as all iodo species detected (X ) I:
1b, 2b, 3b, 4b) have the alkynyl group cis to X, the triflate
stages of the PtIVAr2 systems (X ) OTf: 2a, 3a) have the aryl
ligands in the square plane containing the dmpe ligand such
that the alkynyl and triflate ligands are trans to each other.
Furthermore, the MeCN and pyridine adducts of the PtIVMe2
and PtIVMeAr systems (1d and 1e, 4d and 4e) form readily,
also adopting a cis-configuration, whereas the formation of these
neutral ligand adducts of the PtIVAr2 systems is not observed.
Scheme 7
Pt(OTf)R1R2(C t CSiMe3)(dmpe) warming8
and other species
R1-R2 + Unidentified Products (3)
The more stable iodoplatinum(IV) complexes 2b and 3b,
PtIMeAr2(Ct CSiMe3)(dmpe), which are isolated accompanied
by Pt(II) decomposition products, decompose upon heating

Synthesis of (η1-Alkynyl)diorganoplatinum(IV) Species
Organometallics, Vol. 27, No. 13, 2008 3209
All solutions formed on addition of IPh(Ct CSiMe3)(OTf)
to platinum(II) reagents PtR1R2(dmpe) contain species in
addition to the major product Pt(OTf)R1R2(Ct CSiMe3)(dmpe)
that are most likely solvento cations, and only in the case of
the PtIVAr2 systems can the equilibria be shifted entirely to the
triflate species by addition of NaOTf. Only when the equilibrium
is shifted in this way to the OTf species does addition of NaI
not result in formation of PtIAr2(Ct CSiMe3)(dmpe), implying
that substitution by I- occurs from the solvento species.
The syntheses reported here have provided an opportunity
to examine selectivity in reductive elimination at Pt(IV) centers
containing combinations of unidentate, unrestrained methyl, aryl,
and alkynyl groups (methyl/alkynyl, aryl/alkynyl, methyl/aryl/
alkynyl) together with variation in ancillary ligands (triflate/
solvent/iodide).
The preferred decomposition pathways under mild conditions
in solution for the triflate stage complexes, as well as the MeCN
and pyridine adducts, regardless of configuration (cis in Scheme
2; trans in Scheme 3), indicate that methyl-aryl and aryl-aryl
coupling are more favorable than coupling involving the alkynyl
ligands (eq 3). In coupling involving p-tolylplatinum(IV) species
there is no indication of isomerization of aromatic products, as
only 4,4′-ditolyl and p-xylene are observed. No alkynyl coupling
products are observed from the triflate systems, and an identical
preference is observed for the unstable iodo complex
PtIMe2(Ct CSiMe3)(dmpe) (1b), which decomposes under
similar conditions to form ethane. In the thermally stable iodo
complexes, PtIAr2(Ct CSiMe3)(dmpe) (2b, 3b) and PtIMe(p-
Tol)(Ct CSiMe3)(dmpe) (4b), heating above 50 °C (solid phase
decomposition) results in competitive aryl-alkynyl and aryl-aryl
coupling together with minor quantities of Me3SiCt CI.
Methyl-alkynyl coupling has not been detected in any of the
systems examined, indicating that the potential for development
of organic synthesis via C-C bond formation at Pt(V) centers
involving alkynyl groups may be favored for groups other than
alkyl.
Acknowledgment. We thank the Australian Research
Council for financial support.
Supporting Information Available: X-ray crystallographic files
in CIF format for 3 and 4b. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM800122K