The hydrovinylation reaction: A new highly selective protocol amenable to asymmetric catalysis

Full text of DOI:10.1021/ja973548n

J. Am. Chem. Soc. 1998, 120, 459-460
Scheme 1. Mechanism of Hydrovinylation
459
The Hydrovinylation Reaction: A New Highly
Selective Protocol Amenable to Asymmetric Catalysis
Nobuyoshi Nomura, Jian Jin, Haengsoon Park, and
T. V. RajanBabu*
Department of Chemistry, The Ohio State UniVersity
100 West 18th AVenue, Columbus, Ohio 43210
ReceiVed October 10, 1997
Carbon-carbon bond forming reaction is arguably the most
important type of bond construction in organic chemistry; yet,
paucity of methods for the stereoselective incorporation of
2
abundantly available carbon feedstocks such as CO, CO , HCN,
or simple olefins to prochiral substrates is one of the major
limitations in this area.1 One potentially important class of such
+
reactions is the cationic [Ni-H] -catalyzed olefin dimerization
reaction.2 There had been only limited success in finding an
enantioselective variation of this reaction partly because of the
competing oligomerization of starting olefins and isomerization
of the primary products (eq 1). In this paper we report our initial
,3
EtAlCl
2
and an esoteric azaphospholene ligand (1).2 Subsequent
7
work directed at simplifying the ligand structure has shown that
the original system is narrow in scope and is possibly of limited
value for the development of a broadly applicable hydrovinylation
reaction. More recent procedures are complicated by the need
for higher pressures (15-25 bar) of ethylene or incompatibility
with substrates which have Lewis basic centers. Selectivities
8
9
findings on a new and versatile protocol for the heterodimerization
of vinyl arenes and ethylene. We further demonstrate that high
enantioselectivity for this reaction can be achieved by using a
chiral phosphine with an appropriately placed hemilabile coor-
dinating group. To the best of our knowledge, such a control
element has not been exploited in asymmetric catalysis.
4
5
6
of rhodium, ruthenium and palladium catalyzed codimerization
of styrene and ethylene are also poor.
In search of hydrovinylation conditions amenable to asymmetric
catalysis, we decided to concentrate our efforts on improving the
synthesis of the cationic nickel hydride complex and the associated
counterion (Scheme 1, 3), which could act as the catalyst in the
reaction. This species is formed by the Lewis acid-assisted
dissociation of the Ni-X bond from the 16-electron phosphine
complex 2, coordination of ethylene, coupling of the allyl and
vinyl moieties, and subsequent â-hydride elimination. Insertion
of the vinyl arene to the Ni-H gives a benzylic complex (4) which
can be stabilized as an η-3 intermediate (4′). The coordinatively
unsaturated 4 can react with ethylene (and possibly not another
Vinyl arene, if the phosphine is sufficiently bulky) to give 5, which
can undergo an insertion followed by â-hydride elimination,
completing the catalytic cycle. The problems encountered in the
previous attempts could be traced to two factors: (a) the poor
reactivity of the substrates carrying a heteroatom could result from
The hydrovinylation reaction has a long history2-9 and, as early
as 1988, Wilke cited unpublished results of an asymmetric
hydrovinylation of styrene in the presence of allyl nickel halide,
(1) For a topical, highly readable article dealing with the new challenges
facing synthetic organic chemistry, see: Trost, B. M. Angew. Chem., Int. Ed.
Engl. 1995, 34, 259. For lead references to highly catalytic asymmetric C-C
bond-forming reactions using feedstock carbon sources, see: (hydroformy-
lation) Agbossou, F.; Carpentier, J.; Mortreux, A. Chem. ReV. 1995, 95, 2485.
Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.; Mano, S.; Horiuchi, T.;
Takaya, H. J. Am. Chem. Soc. 1997, 119, 4413. (hydrocyanation) Casalnuovo,
A. L.; RajanBabu, T. V.; Ayers, T. A.; Warren, T. H. J. Am. Chem. Soc.
1
994, 116, 9869. (use of olefins) Mortreux, A. In Metal Promoted SelectiVity
in Organic Synthesis; Noels, A. F., Graziani, M., Hubert, A. J., Eds.; Catalysis
by Metal Complexes, Vol. 12; Kluwer Academic: Dordrecht, The Netherlands,
1
991; p 47.
(2) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185. Wilke, G.;
Monkiewicz, J.; Kuhn, H. U.S. Patent No. 4,912,274, 1990. Jolly, P. W.; Wilke,
G. In Applied Homogeneous Catalysis with Organometallic Compounds;
Cornils, B., Herrmann, W. A., Eds.; VCH: New York, 1996; Vol. 2, p 1024.
the reaction of the Lewis acid (for example, Et
Lewis basic centers; (b) the isomerization of the initially formed
-aryl-1-butene (6) to 2-aryl-2-butene (7) is presumably mediated
2
AlCl) with these
3
(
3) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235.
(
4) For the first report of codimerization of ethylene (1000 atm) and styrene
by the nickel hydride. We reasoned that the scope and selectivity
of hydrovinylation could be significantly increased by eliminating
the troublesome Lewis acid through the use of weakly coordinat-
using Rh(III), see: Alderson, T.; Jenner, E. L.; Lindsey, R. V. J. Am. Chem.
Soc. 1965, 87, 5638.
(5) Umezaki, H.; Fujiwara, Y.; Sawara, K.; Teranishi, S. Bull. Chem. Soc.
Jpn. 1973, 46, 2230.
6) (a) Britovsek, G. J. P.; Keim, W.; Mecking, S.; Sainz, D.; Wagner, T.
(
(8) Ceder, R.; Muller, G.; Ordinas, J. I. J. Mol. Catal. 1994, 92, 127. For
an earlier version of this reaction, see: Kawata, N.; Maruya, K.; Mizoroki,
T.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 3217.
(9) Monteiro, A. L.; Seferin, M.; Dupont, J.; Souza, R. F. Tetrahedron
Lett. 1996, 37, 1157.
J. Chem. Soc., Chem. Commun. 1993, 1632. (b) Drent, E. U.S. Patent No.
5
,227,561, 1993. (c) Unpublished results from this laboratory.
7) Angermund, K.; Eckerle, A.; Lutz, F. Z. Naturforsch., B: Chem. Sci.
995, 50b, 488.
(
1
S0002-7863(97)03548-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/03/1998

460 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Communications to the Editor
Table 1. Hydrovinylation of Vinylarenes
variety of useful intermediates via organometallic cross-coupling
reactions. As expected,8 the use of a number of chelating
phosphines, aminophosphines, and 1,2-bis-diarylphosphinites gave
no product under otherwise identical conditions.6
c,12
Preliminary
experiments indicate that olefins with strongly electron-withdraw-
ing substituents on the aromatic nucleus (for example, 3,5-bis-
(trifluoromethyl)styrene, 2-vinylpyidine) are poor substrates for
this reaction. Methyl substitution at the R- or â-carbons of styrene
also leads to poor yields (21 and 49%, respectively).
The new reaction protocol is easily adapted for an asymmetric
reaction. Considering the intermediacy of several cationic nickel
species in this reaction, we decided that a monophosphine that
also carrries a hemilabile group6 might have an advantage, since
such a ligand can stabilize these intermediates by internal
coordination. Our choice for this purpose was Hayashi’s 2-(diphen-
a,13
1
4
ylphosphino)-2′-methoxy-1,1′-binaphthyl (MOP) ligand (8a),
which carries, in addition to the phosphine, a methoxy group that
could now serve as the ancillary ligand. Most gratifyingly, in
the initial attempts using the (R)-MOP as the ligand, 2-methoxy-
6-vinylnaphthalene (MVN) and 4-isobutylstyrene gave nearly
quantitative yields of the products (S-isomers) in 62 and 40%
enantiomeric excess (ee),11 respectively (eq 3). In addition, we
a
In brackets are the yields estimated by gas chromatography. b See
the text: (i) [(allyl)NiBr]
h; (ii) [(allyl)NiBr] , (0.70 mol %)/(R)-MOP (8a)/Ar′
56 °C/2 h; (iii) [(allyl)NiBr] , (0.70 mol %)/(R)-MOP-OBn (8b)/
/-56 °C/2 h.
2 3 2 2
, (0.35 mol %)/Ph P/AgOTf/CH Cl /-55 °C/2
-
+
2
4 2 2
B Na /CH Cl /
-
Ar′
2
-
+
4
B Na /CH
2
Cl
2
-
10
also discovered that with the MOP ligands, tetrakis[3,5-bis-
4
ing counteranions such as triflate or tetraaryl borate (Ar B ).
15
(trifluoromethyl)phenyl]borate anion (TFPB) gave a substantially
Furthermore, it should be possible to prevent the isomerization
of the initially formed terminal olefin (e.g., 6 f 7) by manipula-
tion of the phosphine ligand, P and/or the metal.
improved catalyst vis- a´ -vis the corresponding triflate (entries 7
and 8). A minor modification in the ligand structure (use of
-
OCH
2
Ph, 8b, instead of -OMe) improves the ee for MVN to
After an extensive scouting program, we have found that most
of the our expectations have been borne out. The hydrovinylation
of various vinylarenes proceeds with unprecedented chemical
yield and selectivity when a combination of allylnickel bromide
8
0% when the reaction is carried out at -70 °C. These weakly
coordinating O-alkyl groups of the ligand appear to be crucial
for the success of the reaction since yield and enantioselectiVity
for the ligand with an ethyl group (9) in place of the methoxy
group are only 13 and 3% ee, respectiVely.
-
dimer, a weakly coordinating counterion such as triflate (OTf )
-
or Ar
4
B
and a monophosphine is employed as the precatalyst
Further work in this area will involve optimization of the initial
results by electronic and steric tuning of the MOP ligands and
identification of other chiral ligand systems with hemilabile
groups. Such studies and extensions to other heterodimerizations
involving dienes and other monolefins are in progress.
(eq 2 and Table 1). Typically the reaction is carried out at -56
Acknowledgment. This work was supported by grants from the U.S.
National Science Foundation (CHE-9706766). Further support by Petro-
leum Research Fund of the American Chemical Society, The Dupont
Company, and Hoechst Marion Roussel are also acknowledged. Dedi-
cated to Professor G. Wilke in recognition of his numerous contributions
to organometallic chemistry.
°
C in methylene chloride as solvent under 1 atm of ethylene
11
pressure using 0.007 equiv of the catalyst.
conditions, no oligomerization of either the vinyl arene or ethylene
is detected. In sharp contrast to the previously reported Lewis
acid-mediated reactions, vinylarenes with Lewis basic centers
such as oxygen, chlorine, and bromine undergo the reaction with
remarkable ease (entries 3-5 and 8). 4-Isobutylstyrene, 3-fluoro-
4
Under these
9
Supporting Information Available: Details of experimental proce-
dures and spectroscopic, GC, and HPLC data of products (8 pages). See
any current masthead page for ordering and Internet access instructions.
-phenylstyrene, and 2-methoxy-6-vinylnaphthalene (entries 7, 8,
), all potential precursors for important antiinflammatory agents,
JA973548N
9
(
12) These include 1,3-bis(diphenylphosphino)propane (DPPP), 2,2′-bis-
diphenylphosphino)-1,1′-binaphthyl (BINAP), (2,2-dimethyl-1,3-dioxolane-
,5-diylbismethylene)bisdiphenylphosphine (DIOP), N-(tert-butoxycarbonyl)-
4-(diphenylphosphino)-2-[(diphenylphosphino)methyl]pyrrolidine (BPPM).
13) (a) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658. (b)
gave excellent yields of the expected hydrovinylation products.
Hydrovinylation product of 4-bromostyrene (entry 5) is another
potentially important precursor that could be transformed into a
(
4
(
(
10) For the use of Ar
P. S.; Brookhart, M. J. Am. Chem. Soc. 1996, 118, 6225.
11) See the Supporting Information for detailed experimental procedures
and identification of the configuration of the products.
4
B- in related reactions, see: DiRenzo, G. M.; White,
Bader, A.; Lindner, E. Coord. Chem. ReV. 1991, 108, 27.
(14) Uozumi, Y.; Tanahashi, A.; Lee, S.-Y.; Hayashi, T. J. Org. Chem.
1993, 58, 1945.
(
(15) Brookhart, M.; Grant, B.; Volpe, A. Organometallics 1992, 11, 3920.