One-pot synthesis of trans mono- or diarylalkynyl substituted platinum(II) compounds with tertiary phosphine or phosphite ligands

Article abstract of DOI:10.1021/om060616i

An efficient one-pot synthesis has been developed for preparation of trans-mono- or diarylalkynyl bisphosphine or bisphosphite Pt(II) compounds. In the procedure, the alkyne and the tertiary phosphorus ligands are mixed with PtCl₂ in tetrahydro

Full text of DOI:10.1021/om060616i

5500
Organometallics 2006, 25, 5500-5502
One-Pot Synthesis of trans Mono- or Diarylalkynyl Substituted
Platinum(II) Compounds with Tertiary Phosphine or Phosphite
Ligands
Marcus Carlsson* and Bertil Eliasson
Department of Chemistry, Organic Chemistry, Umeå UniVersity, SE-901 87 Umeå, Sweden
ReceiVed July 10, 2006
Summary: An efficient one-pot synthesis has been deVeloped for
preparation of trans-mono- or diarylalkynyl bisphosphine or
bisphosphite Pt(II) compounds. In the procedure, the alkyne and
the tertiary phosphorus ligands are mixed with PtCl2 in
tetrahydrofuran and triethylamine solution. CuI is added for
synthesis of disubstituted complexes, but the catalyst is not used
for preparation of monosubstituted complexes. MicrowaVe
irradiation is preferably employed to giVe the trans-mono- or
diarylalkynyl Pt(II) compound in short time and high yield.
reflux of the solution for a few hours the major product was
the monochloroacetylide.7 The same strategy was reported by
Schanze et al., who synthesized trans-chloro-phenylethynyl-bis-
(tri-n-butylphoshine)platinum(II) in 88% yield from cis-PtCl2-
(PBu3)2 in DEA.13
In this paper we report on the development of a one-pot
reaction to synthesize mono- or disubstituted arylalkynyl Pt(II)
complexes using microwave irradiation (Scheme 1). The scope
of the present work includes a simplification of the synthesis,
where prior preparation of the PtCl2(PR3)2 complex is not needed
for the coupling of the acetylide. Instead, the mono-arylalkynyl
Pt(II) compound is prepared by reaction of the acetylide, tertiary
phosphorus ligand, and PtCl2, while CuI is employed for bis-
substitution. The PtCl2(PR3)2 intermediate is formed in situ
during the reaction, and the mono- or diarylalkynyl Pt(II)
compound is typically obtained in good yield at significantly
shorter time in comparison with the more common procedure.
Introduction
In the last decade there has been an increased interest in
arylalkynyl Pt(II) compounds for construction of stable and rigid
systems with nonlinear optical properties that may find use in,
for instance, the field of photonics.1-7 A typical synthesis of a
mono- or diarylalkynyl Pt(II) compound is performed via initial
preparation and purification of the trans- or cis-PtCl2(PR3)2
precursor.8-10 The dehydrohalogenation reaction between a
PtCl2(PR3)2 complex and an acetylenic compound is often
performed with a cuprous halide in the presence of an amine
as catalyst.11 Treatment of the platinum complex with g2 equiv
of the acetylenic compound in the presence of CuI and amine
often gives the disubstituted compound in good yield.12 In the
synthesis of the monoarylalkynyl Pt(II) compounds, we previ-
ously experienced that both the mono- and diarylalkynyl
substituded Pt(II) compounds appear in the product mixture
when the PtCl2(PR3)2 complex is treated with 1 equiv of alkynyl
compound in the presence of CuI and amine. To obtain
monochloro Pt(II) acetylides, D’Amato et al. coupled the
acetylide with the cis-salt of PtCl2(PPh3)2 in CHCl3 containing
a small amount of diethylamine but no cuprous halide.7 After
Results and Discussion
The one-pot monoarylalkynyl Pt(II) reaction was optimized
for compound 1 (Scheme 2). Initially, 1-ethynyl-4-methoxy-
benzene (1 equiv), PtCl2 (1 equiv), and PBu3 (2 equiv) were
allowed to react in a CHCl3/TEA (48:1 ratio) solution using
microwave irradiation at 130 °C for 15 min, resulting in a 25%
yield. Changing the solvent to THF/TEA (1:1 ratio) using the
same reaction conditions gave the same result. In an attempt to
increase the rate of the reaction, it was performed at 160 °C for
1 h, with two different solvent mixtures. When CHCl3/TEA was
used as solvent, compound 1 was collected in 42% yield after
full consumption of the acetylenic compound, as determined
1
from H NMR analysis of the crude product. A change of
solvent to THF/TEA gave 45% yield of 1 with only half of the
amount of alkyne being reacted and with trans-PtCl2(PBu3)2
formed as the main byproduct. From these reactions we
suspected that CHCl3 was not a suitable solvent for this high-
temperature reaction and that the generation of trans-PtCl2-
(PBu3)2 inhibits the coupling reaction. Kaufmann discovered
that the cis isomer of PtCl2(PBu3)2 is converted to the
thermodynamically more stable trans isomer by heating.10 Grim
et al. added PPhPr2 to a dichloromethane solution of the trans
compound to convert trans-PtCl2(PPhPr2)2 to the kinetically
favored cis isomer.14 Hence, to achive a maximum yield of cis-
PtCl2(PBu3)2 in situ, the concentration of PBu3 was doubled.
This resulted in an increase in yield to 73% after purification.
Using the latter reaction conditions we also synthesized
compounds 2a and 2b (Scheme 3).
* Corresponding author. E-mail: Marcus.Carlsson@chem.umu.se.
Phone: +46 90 7866286. Fax: +46 90 138885.
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J., Ed.; McGraw Hill: New York, 1963; Vol. 7, p 245.
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S.; Hagihara, N. J. Organomet. Chem. 1978, 145, 101.
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10.1021/om060616i CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/29/2006

Notes
Organometallics, Vol. 25, No. 22, 2006 5501
Scheme 1
Scheme 2. One-Pot Synthesis of trans-Chloro-[4-methoxyphenylethynyl]bis(tri-n-butylphosphine)platinum(II)a
a Reaction conditions: TEA and THF (1:1), 160 °C for 1 h using microwave irradiation; 73% yield after purification.
Scheme 3. One-Pot Synthesis of trans-Chloro-arylalkynyl Platinum(II) Compounds with Tertiary Phosphine Ligandsa
a Reaction conditions: TEA and THF (1:1), 160 °C for 1 h using microwave irradiation. The yield (%) is after purification.
Scheme 4. One-Pot Synthesis of trans-Diarylalkynyl Platinum(II) Compounds with Tertiary Phosphine or Phosphate Ligandsa
b
a Reaction conditions: TEA and THF (1:1), 60 °C for 6 min. The yield (%) is after purification. CHCl3/TEA (3:1) was used instead of THF/
TEA (1:1).
Bruker DRX 400 MHz or Bruker DRX 360 MHz at 298 K. For
solution in CDCl3, 1H and 13C chemical shifts are reported relative
to CHCl3 (δH 7.26 ppm) or CDCl3 (δC 77.0 ppm) as internal
reference, while 31P chemical shifts are given relative to external
0.1 M P(C6H5)3 in CDCl3 with δ ) -4.89, which corresponds to
δ ) 0 for 85% H3PO4. Elemental analyses were performed at
Mikrokemi AB, Uppsala, Sweden.
The one-pot reaction of the diarylalkynyl-Pt(II) complexes
was performed at 60 °C using alkyne (2.1 equiv), PtCl2 (1equiv),
CuI (2 equiv), and PR3 (2 equiv) in THF and TEA solution
(Scheme 4). Two equivalents of PR3 was used in order to form
more of the trans-PtCl2(PBu3)2 in situ. In the synthesis of
compound 3b, CHCl3 and TEA were used as solvent in order
to increase the solubility of PPh3.
General Procedure for Synthesis of Mono-arylalkynyl Pt(II)
Phosphines Exemplified by Compound 1. PtCl2 (50 mg, 0.19
mmol) and 1-ethynyl-4-methoxybenzene (26 mg, 0.19 mmol) were
mixed with THF (2.5 mL) and TEA (2.5 mL). PBu3 (0.19 mL,
0.75 mmol) was added under stirring, and the solution was heated
with microwaves in a monomode instrument at 160 °C for 1 h.
The resulting mixture was diluted with CHCl3 and washed two times
with 1 M HCl(aq). The organic extract was dried with anhydrous
MgSO4(s), filtered, and concentrated. Flash chromatography over
silica [40:1 heptane/EtOAc] gave 1 as a yellow solid in 73%
yield: 1H NMR (400 MHz, CDCl3) δ 7.16 (d, J ) 8.78 Hz, 2 H),
6.75 (d, J ) 8.78 Hz, 2 H), 3.77 (s, 3 H), 2.08-1.92 (m, 12 H),
1.63-1.50 (m, 12 H), 1.50-1.37 (12 H), 0.92 (t, J ) 7.32 Hz, 18
H); 13C NMR (100 MHz, CDCl3) δ 157.3, 131.8, 121.4, 113.5,
100.2, 80.0 (apparent triplet 14 Hz), 55.2, 26.0, 24.3 (apparent triplet
7 Hz), 21.9 (apparent triplet 17 Hz), 13.8; 31P NMR (146 MHz,
CDCl3) δ 7.4 (JP-Pt ) 2381 Hz).
Experimental Section
General Considerations. Compounds 2a,15 3a,c,16 3b,7 and 3d17
have been synthesized earlier via initial preparation and purification
of the trans- or cis-PtCl2(PR3)2 precursor. Solvents and chemicals
used for synthesis were of reagent grade and used without
purification. Microwave synthesis was performed on a monomode
reactor: Smith synthesizer (Personal Chemistry AB). Reaction
vials: Smith process vials, 2.0-5.0 mL filling volume, sealed with
Teflon septa and an aluminum crimp top. TLC was performed on
silica gel 60 F254 (Merck) with detection by UV light. Flash column
chromatography (eluent given in brackets) was performed on silica
gel (matrix, 60 Å, 35-70 µm, Grace Amicon). Organic extracts
were dried over anhydrous magnesium sulfate prior to solvent
concentration. H, 13C, and 31P NMR spectra were recorded on a
1
(15) Cooper, T. M.; Krein, D. M.; Burke, A. R.; McLean, D. G.; Rogers,
J. E.; Slagle, J. E.; Fleitz, P. A. J. Phys. Chem. A 2006, 110, 4369.
(16) Sebald, A.; Wrackmeyer, B.; Beck, W. Z. Naturforsch., B: Anorg.
Chem., Org. Chem. 1983, 38B, 45.
(17) McKay, T. J.; Bolger, J. A.; Staromlynska, J.; Davy, J. R. J. Chem.
Phys. 1998, 108, 5537.
Compound 2a. Flash chromatography over silica [20:1 heptane/
EtOAc] followed by recrystallization from EtOH gave 2a as
colorless crystals in 47% yield: 1H NMR (400 MHz, CDCl3) δ
7.55-7.47 (m, 2 H), 7.41-7.29 (m, 5 H), 7.19 (d, J ) 8.04 Hz, 2
H), 2.10-1.92 (m, 12 H), 1.66-1.51 (m, 12 H), 1.51-1.37 (m, 12

5502 Organometallics, Vol. 25, No. 22, 2006
Notes
H), 0.93 (t, J ) 7.32 Hz); 13C NMR (100 MHz, CDCl3) δ 131.5,
131.2, 130.6, 129.0, 128.3, 128.0, 123.5, 119.5, 101.3, 89.9, 89.9,
87.0 (apparent triplet 14 Hz), 26.1, 24.3 (apparent triplet 6.7 Hz),
22.0 (apparent triplet 17 Hz), 13.8; 31P NMR (146 MHz, CDCl3) δ
7.5 (JP-Pt ) 2365 Hz).
Compound 3c. Flash chromatography over silica [15:1 heptane/
EtOAc] followed by recrystallization from EtOH (99.5%) gave 3c
as yellow needles in 60% yield: 1H NMR (360 MHz, CDCl3) δ
8.09 (d, J ) 8.93 Hz, 4 H), 7.31 (d, J ) 8.93 Hz, 4 H), 2.19-1.99
(m, 12 H), 1.67-1.51 (m, 12 H), 1.51-1.36 (m, 12 H), 0.92 (t, J
) 7.31 Hz, 18 H); 13C NMR (90 MHz, CDCl3) δ 144.5, 135.9,
130.9, 123.6, 119.1 (apparent triplet 15 Hz), 109.6, 26.3 (apparent
triplet 11 Hz), 24.4 (apparent triplet 7 Hz), 24.0 (apparent triplet
17 Hz), 13.7; 31P NMR (146 MHz, CDCl3) δ 4.3 (JP-Pt ) 2312
Hz).
Compound 2b. Flash chromatography over silica [200:35
CHCl3/heptane] followed by recrystallization from EtOH (99.5%)
gave 2b as yellow crystals in 69% yield: 1H NMR (400 MHz,
CDCl3) δ 7.85-7.72 (m, 12 H), 7.50-7.35 (m, 20 H), 7.35-7.28
(m, 3 H), 7.04 (d, J ) 8.23 Hz, 2 H), 6.09 (d, J ) 8.23 Hz, 2 H);
13C NMR (100 MHz, CDCl3) δ 135.1 (apparent triplet 6 Hz), 131.4,
130.8, 130.5, 130.3, 130.3, 130.0, 129.7, 128.3, 127.9 (apparent
triplet 5 Hz), 123.5, 119.1, 106.2, 90.0, 89.7, 89.6 (apparent triplet
15 Hz); 31P NMR (146 MHz, CDCl3) δ 22.3 (JP-Pt ) 2645 Hz).
General Procedure for Synthesis of Bis-arylalkynyl Pt(II)
Phosphines Exemplified by Compound 3a. PtCl2 (75 mg, 0.28
mmol) and 1-ethynyl-4-methoxybenzene (78 mg, 0.59 mmol) were
mixed with THF (2.5 mL) and TEA (2.5 mL). PBu3 (0.15 mL,
0.56 mmol) was added under stirring, after which a clearer solution
appeared, and CuI (107 mg, 0.56 mmol) was added. The solution
was heated with microwaves in a monomode instrument at 60 °C
for 6 min. The resulting mixture was diluted with CHCl3 and
washed two times with 1 M HCl(aq). The organic extract was dried
with anhydrous MgSO4(s), filtered, and concentrated. Flash chro-
matography over silica [40:1 heptane/EtOAc] and recrystallization
from EtOH (99.5%) gave 3a as colorless crystals in 63% yield: 1H
NMR (360 MHz, CDCl3) δ 7.20 (d, J ) 7.27 Hz, 4 H), 6.75 (d, J
) 7.27 Hz, 4 H), 3.78 (s, 6 H), 2.23-2.04 (m, 12 H), 1.67-1.52
Compound 3d. Flash chromatography over silica [40:1 heptane/
EtOAc] and recrystallization from EtOH/CHCl3 gave 3d as yellow
1
crystals in 76% yield; H NMR (360 MHz, CDCl3) δ 7.55-7.49
(m, 4 H), 7.41-7.27 (m, 10 H), 7.27-7.19 (m, 4 H), 2.19-2.07
(m, 12 H), 1.68-1.55 (m, 12 H), 1.51-1.39 (m, 12 H), 0.93 (t, J
) 7.33 Hz, 18 H); 13C NMR (90 MHz, CDCl3) δ 131.5, 131.2,
130.6, 129.0, 128.3, 128.0, 123.5, 119.2, 111.7 (apparent triplet 15
Hz), 109.3, 90.0, 89.8, 26.3, 24.4 (apparent triplet 7 Hz), 23.9
(apparent triplet 17 Hz), 13.8; 31P NMR (146 MHz, CDCl3) δ 3.7
(JP-Pt ) 2344 Hz).
Compound 3e. Flash chromatography over silica [10:1 heptane/
EtOAc]. Compound 3e crystallizes under concentration of solvents.
After filtration compound 3e was recrystallized from EtOH (99.5%)
as colorless needles in 63% yield: 1H NMR (360 MHz, CDCl3) δ
7.53-7.48 (m, 4 H), 7.39-7.29 (m, 10 H), 7.26-7.21 (m, 4 H),
4.29-4.19 (m, 12 H), 1.75-1.64 (m, 12 H), 1.48-1.35 (m, 12 H),
0.88 (t, J ) 7.27 Hz, 18 H); 13C NMR (90 MHz, CDCl3) δ 131.5,
131.1, 128.4, 128.3, 128.0, 123.5, 119.6, 110.6 (apparent triplet 3
Hz), 102.8 (apparent triplet 19 Hz), 89.9, 89.8, 66.3, 32.5 (apparent
triplet 3 Hz), 18.9, 13.7; 31P NMR (146 MHz, CDCl3) δ 99.1 (JP-Pt
) 4082 Hz). Anal. Calcd for C56H72O6P2Pt: C, 61.25; H, 6.61.
Found: C, 61.0; H, 7.0.
(m, 12 H), 1.52-1.37 (m, 12 H), 0.92 (t, J ) 6.59 Hz, 18 H); 13
C
NMR (90 MHz, CDCl3) δ 157.0, 131.8, 121.7, 113.4, 108.0, 105.3
(apparent triplet 14.8 Hz), 55.2, 26.3, 23.6 (apparent triplet 7 Hz),
21.9 (apparent triplet 17 Hz), 13.8; 31P NMR (146 MHz, CDCl3) δ
3.5 (JP-Pt ) 2368 Hz).
Compound 3b. CHCl3 was used instead of THF. Recrystalli-
zation from CHCl3/EtOH gave compound 3b as yellow crystals in
59% yield: 1H NMR (400 MHz, CDCl3) δ 7.82-7.72 (m, 16 H),
7.48-7.34 (m, 18 H), 6.31 (d, J ) 8.73 Hz, 4 H); 13C NMR (100
MHz, CDCl3) δ 144.3, 135.4, 134.9 (apparent triplet 6 Hz), 131.0,
130.8, 130.6, 130.5, 128.8 (apparent triplet 5.3 Hz), 122.7, 121.5
(apparent triplet 15 Hz), 113.2 (t, 2.3 Hz); 31P NMR (146 MHz,
CDCl3) δ 19.2 (JP-Pt ) 2599 Hz). Anal. Calcd for C52H38N2O4P2-
Pt: C, 61.72; H, 3.79; N, 2.77. Found: C, 61.6; H, 3.9; N, 2.7.
Acknowledgment. This work has been supported by the
Swedish Defence Nano Technology Programme managed by
the Swedish Defence Research Agency (FOI).
Supporting Information Available: 31P NMR spectra for all
compounds and 13C NMR spectra for compounds 1, 2b, and 3e.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM060616I