Mendeleev
Communications
Mendeleev Commun., 2008, 18, 209–210
Fullerene complexes with palladium and rhodium
as catalysts for acetylenic bond hydrogenation
a
b
b
Eugenia V. Starodubtseva,* Viatcheslav I. Sokolov,* Vasily V. Bashilov,
b
b
a
a
Yurii N. Novikov, Ekaterina V. Martynova, Maxim G. Vinogradov and Olga V. Turova
a
b
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow,
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
DOI: 10.1016/j.mencom.2008.07.014
The catalytic activity of the fullerene complexes (C )Pd(PPh ) , (C )Pd(PPh ) , (C )Pd[(+)-DIOP] and (C )RhH(CO)(PPh )
3 2
6
0
3 2
70
3 2
60
60
in the hydrogenation of acetylenic bond has been studied using diphenylacetylene as a model substrate.
Fullerenes are of interest because of their properties, such as
hydrophobicity, electron-accepting ability, photoactivity and
potential catalytic action (for metal complexes ). For example,
Table 1 Hydrogenation of diphenylacetylene 1 catalysed by fullerene
a
complexes I–IV.
1
Reaction
Reaction
a polymeric complex (C ) Pd , which is not an individual
60 x
y
products
(mol%)
c
conditions
Conversion TON /
compound, is used as a catalyst in hydrogenation reactions and
its catalytic properties can be explained by the presence of a
Entry Catalyst
–
1
(mol%)
h
Solventb
C H
T/°C
2
3
2
metal palladium admixture.
Previously3 it was found that the pure palladium complex
-C )Pd(PPh ) catalyses the hydrogenation of acetylenic
,4
1
2
3
4
5
6
7
8
9
0
I
I
50
Traces
35
—
9
21
36
38
63
73
—
5.5
—
1.4
3.3
5.6
5.9
9.8
6
6
( 2
C6H6/MeOH 60
C H 50
C H /Pr OH 100
60
—
80
83
67
76
58
21
58
40
—
20
17
33
24
42
79
42
60
3 2
II
II
II
II
III
IV
IV
IV
6
6
alcohols in solution. Here, we report that the complexes of
fullerenes C60 and C70 with palladium and rhodium are cataly-
tically active in the hydrogenation of the CºC bond without
i
6
6
C H /PriOH
80
C6H6/MeOH 60
6
6
i
†
C H /Pr OH
80
80
functional groups. The hydrogenation of diphenylacetylene 1 as
6
6
i
C H /Pr OH
6
6
a model substrate affords a mixture of cis-stilbene 2 and
C H /MeOH 80
11.4
11.7
6
6
diphenylethane 3 (Scheme 1, Table 1).‡
1
C H /MeOH 60
75
6
6
As can be seen in Table 1, no Pd-catalysed tolan hydro-
genation was observed in an aprotic solvent (benzene, entries 1, 3).
The reaction proceeds only in a protic medium (C H /MeOH
a[Substrate]/[catalyst] = 120–130, [1] = 0.23 mol dm , P = 20 atm (H ),
–3
2
b
c
8
h. C H /alcohol = 1:1 (v/v). Turnover number.
6 6
6
6
i
or C H /Pr OH, entries 2, 4–6). This effect is typical of homo-
6
6
5
geneous metal complex catalysis. It is explained by the fact that
H2 / catalyst
the protic solvent facilitates H heterolysis to give catalytically
2
Ph
Ph
Ph
Ph
+
PhCH2CH
2
Ph
6
active metal hydride intermediates. The addition of benzene to
i
1
2
3
MeOH or Pr OH increases the solubility of fullerene complexes
in these polar solvents. Tolane hydrogenation catalysed by com-
Catalysts:
I
(C60)Pd(PPh
II (C70)Pd(PPh
III (C60)Pd[(+)-DIOP]
IV (C60)RhH(CO)(PPh )
3 2
3
)
)
2
plexes I and II under the same conditions (C H /MeOH, 60 °C)
6
6
3
2
gave similar results with both catalysts (cf. entries 2 and 6).
These conditions are likely to be optimal as an increase in the
reaction temperature up to 100 °C causes catalyst deactivation
Scheme 1
(entry 4). Rhodium complex IV showed the highest catalytic
†
Fullerene metal complexes were obtained according to published
procedures7 and recrystallised from toluene. They were characterised
activity: 75% conversion at 60 °C (entry 10).
–9
In contrast to the reduction of an acetylenic bond in the
presence of palladium complexes, they did not catalyse the
hydrogenation of the carbonyl group (acetophenone was used
as a starting reagent). In the case of rhodium complex IV
1
31
by elemental analysis data and H and P NMR spectra. The complexes
were kept and handled under an argon atmosphere. Argon was purified
by passing through columns containing a nickel–chromium catalyst,
copper supported on Kieselguhr (80 °C) and molecular sieves. Hydrogen
was purified by passing through columns with a nickel–chromium catalyst
and molecular sieves. Hydrogenation products were analysed by H NMR
spectroscopy on a Bruker AM-300 instrument.
A catalyst (3.6 mol) and tolan (0.45 mmol) were placed in a glass
tube for hydrogenation, the tube was three times evacuated and filled
with argon. A degassed solvent (2 ml) was added to the tube, and the
latter was placed in a stainless steel autoclave (50 ml) filled with argon.
The autoclave was purged with hydrogen, and the H pressure was adjusted
to 20 atm. The reaction mixture was magnetically stirred (700 rpm) in
the course of hydrogenation.
as a catalyst, 8% acetophenone conversion could be achieved
i
1
(C H /Pr OH = 1:1, 40 atm H , 80 °C, 9 h).
6
6
2
0
I
Thus, the Pd and Rh fullerene complexes show catalytic
activity in the hydrogenation of the CºC bond, but they are
inactive or weakly active in the hydrogenation of the C=O bond.
‡
This work was supported by the Russian Academy of
Sciences (programme DCSM-1) and by Rosnauka (project
nos. 02.513.11.3066 and 02.513.11.3209, 2007).
2
©
2008 Mendeleev Communications. All rights reserved.
– 209 –
Starodubtseva, Eugenia V.
