Palladium(II)- and platinum(II)-catalyzed addition of stabilized carbon nucleophiles to ethylene and propylene

Article abstract of DOI:10.1039/b316734h

PdCl₂(CH₃CN)₂ and [PtCl₂(H ₂C=CH₂)]₂ catalyze the addition of β-dicarbonyl compounds to ethylene and propylene.

Full text of DOI:10.1039/b316734h

Palladium(II)- and platinum(II)-catalyzed addition of stabilized carbon
nucleophiles to ethylene and propylene†
Xiang Wang and Ross A. Widenhoefer*
P. M. Gross Chemical Laboratory, Duke University, Durham, NC 27708-0346, USA.
E-mail: rwidenho@chem.duke.edu
Received (in Corvallis, OR, USA) 22nd December 2003, Accepted 21st January 2004
First published as an Advance Article on the web 10th February 2004
PdCl
2
(CH
3
CN)
2
and [PtCl
2
(H
2
CNCH
2
)]
2
catalyze the addition
(Table 2, entry 3). Formation of the a-vinyl b-diketone rather than
the a-ethylidene b-diketone is presumably due to unfavorable steric
interaction between the ethylidene methyl group and the proximal
tert-butyl group in the latter isomer. Consistent with this hypoth-
esis, palladium-catalyzed reaction of 5,5-dimethyl-2,4-hexane-
dione with ethylene formed (E)-3-ethylidene-5,5-dimethyl-
2,4-hexanedione as the exclusive isomer in 86% isolated yield
(Table 1, entry 4). In a similar manner, palladium-catalyzed
reaction of ethylene with ethyl 4,4-dimethyl-3-oxopentanoate
formed (Z)-ethyl 2-(2,2-dimethylpropionyl)-2-butenoate in 59%
isolated yield as a single isomer (Table 1, entry 5).
of b-dicarbonyl compounds to ethylene and propylene.
The development of efficient, atom-economical processes for the
utilization of readily abundant carbon sources in the production of
fine chemicals remains an important challenge in organic synthesis
and homogeneous catalysis. Although ethylene and a-olefins
represent one of the most important carbon feedstocks employed in
the large-scale production of polymers, the direct utilization of
ethylene and a-olefins in fine chemical synthesis remains problem-
atic due to the paucity of mild and efficient C–C bond forming
1
2
3
transformations applicable to simple olefins. Notable examples
Palladium-catalyzed olefin alkylation was also applicable to
include Co- or Rh-catalyzed hydroformylation and hydrocarbox-
propylene, provided that the b-diketone was activated with EuCl
3
ylation,4 Pd-catalyzed arylation, Ni-catalyzed hydrocyanation,
5
6
(Table 2, entries 6 and 7). For example, reaction of 2,6-dimethyl-
3,5-heptanedione with propylene (50 psi) in the presence of a
7
1,8
and Ni-catalyzed dimerization and heterodimerization.
An
alternative approach to C–C bond formation that has not been
realized is via the transition metal-catalyzed addition of a stabilized
carbon nucleophile to a simple olefin. Rather, alkylation of
unactivated olefins requires employment of either a highly basic,
catalytic amount of 1 and a stoichiometric mixture of EuCl
3
and
CuCl at 100 °C for 24 h led to the isolation of 3-isopropylidene-
2
2,6-dimethyl-3,5-heptanedione in 51% yield and 3-isobutyryl-
2-isopropyl-5-methylfuran in 24% yield (Table 2, entry 6). The
furan is presumably formed via palladium-catalyzed cyclization of
9
unstabilized carbon nucleophile or a stoichiometric amount of a
1
0
15
transition metal complex. Here we report the first examples of the
transition metal-catalyzed addition of stabilized carbon nucleo-
philes to ethylene and propylene.
the initially formed 4-allyl-2,6-dimethyl-3,5-heptanedione.
Because selective intermolecular olefin hydroalkylation was not
realized employing palladium catalyst 1, we sought to identify an
alternative catalyst for this transformation. Maresca has reported
that stabilized carbon nucleophiles react readily with Pt(II)–olefin
complexes, and that the resulting platinum alkyl complexes are
reactive toward protonolysis but not toward b-hydride elimina-
tion.16 Because these steps constitute a potential catalytic cycle for
We have recently reported the intramolecular hydroalkyl-
1
1,12
13
ation
and oxidative alkylation of alkenyl b-diketones and
related substrates14 catalyzed by PdCl
(CH CN) (1), which
2
3
2
represent the first examples of the transition metal-catalyzed
addition of a stabilized carbon nucleophile to an unactivated olefin.
Given the mild reaction conditions and high regioselectivity of
palladium-catalyzed intramolecular olefin alkylation, this system
represented a viable starting point for the development of an
effective protocol for intermolecular olefin alkylation. In an initial
experiment, reaction of 2,4-nonanedione (2) with ethylene (1 atm)
in the presence of a catalytic amount of 1 (20 mol%) and a
12
olefin hydroalkylation, we targeted simple platinum(II) com-
plexes as catalysts for ethylene hydroalkylation. To this end,
reaction of 2 with ethylene (50 psi) and a catalytic mixture of
2 2 2 2
[PtCl (H CNCH )] (5) (2.5 mol%) and HCl (0.2 equiv.) in dioxane
at 90 °C for 5 h led to the isolation of 4 in 68% yield without
formation of detectable amounts of 3 (Scheme 1).¶ In addition to 2,
stoichiometric amount of CuCl
conversion with formation of a 36 : 64 mixture of 3-ethylidene-
,4-nonanedione (3) and 3-ethyl-2,4-nonanedione (4) (Table 1,
entry 1). Both the efficiency and the selectivity of the conversion of
to 3 increased with increasing ethylene pressure (Table 1), and
2
at 90 °C for 12 h led to 67%
Table 1 Effect of ethylene pressure on product distribution for the reaction
of ethylene with 2 catalyzed by 1
2
2
palladium-catalyzed reaction of 2 with ethylene (200 psi) led to the
exclusive formation of 3 (Table 1, entry 4), which was isolated in
7
1
7% yield as a separable mixture of E and Z isomers (Table 2, entry
).‡ § The enhanced selectivity for 3 relative to 4 at higher ethylene
,
pressure is likely due to the increased rate of associative olefin
displacement relative to protonolysis from an equilibrating mixture
of palladium olefin hydride and alkyl complexes, respectively.12
In addition to 2, a number of b-dicarbonyl compounds reacted
with ethylene in the presence of a catalytic amount of 1 and a
stoichiometric amount of CuCl to form the corresponding a-
2
ethylidene or a-vinyl b-dicarbonyl compound in good yield (Table
2
2
, entries 2–5). For example, the sterically hindered b-diketone
Ethylene
pressure
Catalyst
loading
,2,6,6-tetramethyl-3,5-heptanedione underwent palladium-cata-
Entry
3 : 4
a
Conversion
a
lyzed addition to ethylene to form 2,2,6,6-tetramethyl-4-vinyl-
3,5-heptanedione as the exclusive product in 72% isolated yield
1
2
3
4
15 psi
45 psi
80 psi
20%
10%
10%
10%
36 : 64
68 : 32
89 : 11
98 : 2
67%
76%
90%
†
Electronic supplementary information (ESI) available: experimental
200 psi
> 95%
procedures, analytical and spectroscopic data for new compounds. See
http://www.rsc.org/suppdata/cc/b3/b316734h/
a
Determined by GC analysis versus an internal standard.
6
60
C h e m . C o m m u n . , 2 0 0 4 , 6 6 0 – 6 6 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Table 2 Oxidative alkylation of ethylene (200 psi) or propylene (50 psi)
philes to ethylene and propylene. We are currently working to
further expand the scope of these transformations.
We thank the NSF (CHE-03-04994) for support of this research.
R.W. thanks the Camille and Henry Dreyfus Foundation and
GlaxoSmithKline for unrestricted financial assistance.
with b-dicarbonyl compounds catalyzed by 1 (10 mol%) and CuCl
2
(3
equiv.) at 90 °C for 10–24 h
Entry
1
b-Diketone
Olefin
Product(s)
ethylene
Notes and references
‡
Turnover numbers for the conversion of 2 to 3 catalyzed by 1 were limited
by the use of CuCl as the terminal oxidant and not by catalyst
decomposition or deactivation. For example, when a suspension of 2 (5
mmol), 1 (0.05 mmol), and CuCl (2.0 mmol) was heated under ethylene
200 psi) for 2 h, ~ 20% of 2 was consumed. When the tube was sparged
2
2
2
(
3
2
with O , repressurized with ethylene, and heated overnight, an additional
~
20% of 2 was consumed. We did not employ catalytic amounts of CuCl
2
in these transformations due to safety issues associated with heating
pressurized mixtures of ethylene and oxygen.
4
2
§ Employment of < 2 equiv. of CuCl in the reaction of 2 with ethylene
catalyzed by 1 led to incomplete conversion without affecting the 3 : 4
ratio.
¶
2
Treatment of 2 with ethyl chloride in the presence of PtCl (5 mol%) or
with HCl (0.2 equiv.) in the absence of platinum led to no detectable
consumption of 2 after 5 h at 90 °C.
5
1
2
3
T. V. Rajanbabu, N. Nomura, J. Jin, B. Radetich, H. Park and M. Nandi,
Chem. Eur. J., 1999, 5, 1963.
6a
propylene
P. A. Arjunan, J. E. McGrath, T. L. Hanlon, Eds., Olefin Polymeriza-
tion: Emerging Frontiers, Oxford University Press, New York, 2000.
G. W. Parshall and S. D. Ittel, Homogeneous Catalysis: The Applica-
tions and Chemistry of Catalysis by Soluble Transition Metal Com-
plexes, John Wiley and Sons, New York, 1992.
7a
4
H. M. Colquhoun, D. J. Thompson and M. V. Twigg, Carbonylation,
Plenum Press, New York, 1991.
5
6
R. F. Heck, Org. React., 1982, 27, 345.
C. A. Tolman, R. J. McKinney, W. C. Seidel, J. D. Druliner and W. R.
Stevens, Adv. Catal., 1985, 33, 1.
7
8
Y. Chauvin and H. Olivier, in Applied Homogeneous Catalysis with
Organometallic Compounds Vol. 1, B. Cornils, W. A. Herrmann, Eds.,
VCH, New York, 1996.
a
Reaction run in the presence of EuCl
3
(1 equiv.) at 100 °C.
Transition metal-catalyzed functionalization of simple olefins via C–H
bond activation has also been reported: (a) F. Kakiuchi and S. Murai,
Acc. Chem. Res., 2002, 35, 826; (b) M. Lail, B. N. Arrowood and T. B.
Gunnoe, J. Am. Chem. Soc., 2003, 125, 7506; (c) K. L. Tan, R. G.
Bergman and J. A. Ellman, J. Am. Chem. Soc., 2002, 124, 13964.
(a) H. Pines, Acc. Chem. Res., 1974, 7, 155; (b) U. M. Dzhemilev and
O. S. Vostrikova, J. Organomet. Chem., 1985, 285, 43; (c) A. H.
Hoveyda and Z. Xu, J. Am. Chem. Soc., 1991, 113, 5079.
both phenyl- and 2-furyl-substituted b-diketones underwent plati-
num-catalyzed hydroalkylation with ethylene to form the corre-
sponding a-ethyl b-diketones in good yield (Scheme 1).
In summary, we have presented the first examples of the
transition metal-catalyzed addition of stabilized carbon nucleo-
9
10 T. Hayashi and L. S. Hegedus, J. Am. Chem. Soc., 1977, 99, 7093.
11 T. Pei and R. A. Widenhoefer, J. Am. Chem. Soc., 2001, 123, 11290.
12 H. Qian and R. A. Widenhoefer, J. Am. Chem. Soc., 2003, 125, 2056.
13 T. Pei, X. Wang and R. A. Widenhoefer, J. Am. Chem. Soc., 2003, 125,
6
48.
1
4 (a) T. Pei and R. A. Widenhoefer, Chem. Commun., 2002, 650; (b) X.
Wang, T. Pei, X. Han and R. A. Widenhoefer, Org. Lett., 2003, 5,
2
699.
1
1
5 X. Han and R. A. Widenhoefer, J. Org. Chem., in press.
6 F. P. Fanizzi, F. P. Intini, L. Maresca and G. Natile, J. Chem. Soc.,
Dalton Trans., 1992, 309.
Scheme 1
C h e m . C o m m u n . , 2 0 0 4 , 6 6 0 – 6 6 1
661