(2a), [Pt(dppp)(CHPhCH2Ph)](OTf) (2b) and [Pt(dppp)-
(CHPhCH(OMe)Ph)](OTf) (3), and a series of linked 2H labelling
For the GC-MS measurements where the effect of hydrogen
was studied, a methanol solution (2 ml) of the platinum complex
(ca. 6 mg) and diphenylacetylene (ca. 80 fold excess: 48 mg)
was prepared and separated into two 1 ml volumes which were
degassed. One was then placed under an H2 atmosphere (2 atm)
and the second placed under vacuum. The mixtures were then
heated to 36 ◦C and left to react at this temperature for 1 h while
being shaken every 15 min. The reactions in these mixtures were
quenched by degassing and the samples and placing them in a dry
ice and acetone bath (ca. -85 ◦C) prior to GC-MS analysis.
studies. The later species, 3, is proposed to form by the addition
-
≡
of MeO to [Pt(dppp)(CPh CPh)](OTf)2, followed by hydrogen
addition. Magnetisation transfer from the alkyl protons of 2a
and 3 establishes that these species are involved in the formation
of trans-stilbene. The observation of the successful transfer
hydrogenation of diphenylacetylene by methanol which competes
with the H2 reduction pathway further establishes the complexity
of the reaction chemistry shown by these systems.
Synthesis of [Pt(PhCN)2(Cl)2]21
Experimental
40 ml of benzonitrile was heated to 100 ◦C and 1.5 g of PtCl2 added
in small portions with vigorous stirring after which the solution
was left at 100 ◦C for 30 min. The solution was then filtered hot,
and 300 ml of petroleum ether added in order to precipitate the
complex as a pale yellow solid. After filtration, the solid was dried
in vacuo. Yield: 2.6 g of product. (93%).
General Conditions
All manipulations were carried out under inert atmospheric
conditions, using standard Schlenk techniques (with vacuum of
up to 10-2 mbar, with N2 or Ar as an inert atmosphere) or high
vacuum techniques (10-4 mbar). Dry N2 and Ar for the Schlenk
lines were purchased from BOC Gases. Storage and manipulation
of samples was carried out using standard glove box techniques
under an atmosphere of N2, using an Alvic Scientific Gas Shield
glove box, equipped with a freezer (-32 ◦C), vacuum pump and
N2 purge facilities. Solvents were obtained as Analytical Grade
from Fisher. Diethyl ether was dried by refluxing under nitrogen
over sodium wire, dichloromethane and methanol by refluxing
over calcium hydride or magnesium. The deuterated solvents,
methanol-d4, methylenedichloride-d2 and benzene-d6 were pur-
chased from Aldrich, degassed and used without further purifica-
tion. Pt(PhCN)2Cl2 was prepared as described in the literature21
PtCl2 was purchased from Johnson Matthey, and PhCN from
Lancaster. Bis-Diphenyl phosphino propane (dppp) and AgOTf
were obtained from Strem and Aldrich respectively and used
Synthesis of [Pt(dppp)(Cl)2]23
0.73g (1.58 mmol) of [Pt(PhCN)2(Cl)2] was dissolved in 40 ml
of dichloromethane in a Schlenk tube. To this solution, 0.64 g
of Bis-diphenylphosphinopropane (dppp), dissolved in 15 ml of
dichloromethane, was added dropwise over 20 min. The solution
was stirred at room temperature for 2 h, during which time a white
precipitate formed. The volume of the solution was then reduced
to 15 ml and the resulting white solid isolated by filtration (in air)
as 0.88 g of [Pt(dppp)(Cl)2]. Yield 83%. NMR data of the product
agreed with the literature (31P d–5.48; s, JPPt = 1705 Hz).
as received. The ligand bucope (C6H4(CH2P(But)2P(C8H14)) was
t
Synthesis of [Pt(dppp)(OTf)2] (1b)
provided by SHELL where it was synthesized as reported in the
literature.8,22
400 mg (0.65 mmol) of [Pt(dppp)Cl2] was dissolved in 60 ml of
degassed dichloromethane in a Schlenk tube. To this solution,
1.34 g (5.2 mmol) of AgOTf was added and the reaction mixture
protected from light. After 48 h of stirring at room temperature
the resulting suspension was filtered and reduced in volume to ca.
15 ml. Dry diethylether was then added to the filtrate to precipitate
a solid which was dried in vacuo for 1 h to yield the title compound
as a white solid. Yield: 300 mg, 67%. NMR CD2Cl2: 31P d–10.2, s.
This data agrees with that in the literature.23
NMR spectra were obtained on Bruker Avance III 400 and
Bruker Avance II 700 spectrometers.
GC-MS data were collected on a Varian SATURN GC-MS
2000 gas chromatograph coupled to a mass spectrometer detector.
A Factor-FormTM VF-6M capillary column (30 m ¥ 0.25 mm ID
and 0.25 mm film thickness) was used for the GC separation. The
initial oven temperature was 373.15 K. The temperature was then
programmed to increase from 373.15 K to 418.15 K at 2.5 K min-1
from which time a temperature increase of 30 K min-1 was used
to reach the maximum temperature of 523.15 K where it was
held for 50 min. Helium was used as carrier gas at a flow rate of
1.0 mL min-1. Mass spectra were recorded in the EI mode, at 70
eV, scanning the 30-650 m/z range.
Synthesis of [Pt(tbucope)(Cl)2]
0.54 g (1.4 mmol) of [Pt(COD)(Cl)2] was dissolved in 30 ml
of dichloromethane. To this solution, 0.56 g (1.6 mmol) of
tbucope (C6H4(CH2P(But)2P(C8H14)), dissolved in 20 ml of
dichloromethane, was added slowly over 10 min. The solution
was stirred for 2 h. The volume of the resulting colourless solution
was reduced to 15 ml and 50 ml of pentane added to precipitate
the product. The solution was filtered (in air) to give the complex
In the GC-MS measurements, a dichloromethane, a methanol
or a methanol-d4 solution (1 ml) of the platinum complex (ca. 3 mg)
and diphenylacetylene (ca. 40 fold excess, 24 mg) were degassed
and placed under an H2 atmosphere (2 atm). The mixture was then
◦
heated at 36 C for 1 h while being shaken every 15 min. In the
control experiment identical preparation and reaction conditions
were used. With respect to the additionally stated alkene based
control experiments, a 0.5 ml methanol solution was prepared and
either an excess of trans-stilbene (ca 20 fold excess: 10 mg) or
cis-stilbene (ca. 20 fold excess: 10 ml) employed respectively.
1
as a white solid. Yield: d 31P{ H} (500 MHz, CD2Cl2): d 57.8 (d,
Jpp = 19.6 Hz, JPPt = 1882 Hz, PtBu2), -7.76 (d, Jpp = 19.6 Hz,
JPPt = 1673 Hz (PC8H14) Anal. Calcd for C23H38Cl2P2Pt: C, 43.90;
H, 6.15. Found: C, 42.457; H, 5.817. MS (EI): m/z 606 (M+ - Cl).
3498 | Dalton Trans., 2010, 39, 3495–3500
This journal is
The Royal Society of Chemistry 2010
©
Boutain, Marie
