Co(I)-catalyzed inter- and intramolecular hydroacylation of olefins with aromatic aldehydes

Full text of DOI:10.1021/ja9639776

J. Am. Chem. Soc. 1997, 119, 3165-3166
3165
Table 1. Hydroacylation of Vinyltrimethylsilane by Substituted
Aromatic Aldehydes (X-ArC(O)H)
Co(I)-Catalyzed Inter- and Intramolecular
Hydroacylation of Olefins with Aromatic Aldehydes
ratio of aldehyde to olefin to catalyst
20:20:1
TOF,a convn,b convn,b
Christian P. Lenges and Maurice Brookhart*
30:50:1 100:100:1
aromatic
aldehyde (X)
convn,c
%
Department of Chemistry, UniVersity of North Carolina at
entry
[TO/h]
%
%
Chapel Hill, Chapel Hill, North Carolina 27599-3290
1 (a) 4-Me2N-
2 (b) 4-Me-O-
3 (c) 4-Me-
6.7
6.2
6.1
4.0
3.2
4.4
2.9
100
100
100
77
30
35
100
100
100
85
45
42
100, (65)d
100, (82)d
90, (75)d
70, (33)d
45, (85)d
52, (83)d
38, (85)d
ReceiVed NoVember 18, 1996
4 (d) 3,4-(MeO)2-
5 (e) 3,4,5-(MeO)3-
Intramolecular hydroacylation of olefins using Rh(I) catalyst
precursors has been extensively studied by Bosnich1-6 and
others;7-16 however, intermolecular versions have received little
attention.9,10,17-20 The most notable example of intermolecular
catalysis is Marder’s and Milstein’s report20 of addition of
benzaldehyde to ethylene catalyzed by η5-C8H7Rh(C2H4)2 (4
TO/h, 100 °C, 70 atm C2H4). Recently we reported that Co(I)
complex 1 containing bulky, highly labile vinyltrimethylsilane
ligands exhibits H/D exchange in C6D6 presumably via inter-
mediate 2 involving oxidative addition of benzene to a Co(I)
species21 (eq 1). The formation of olefin-coupled aromatic
products was not observed.
6 (f)
7 (g)
3-Me-
H
19
25
1
a Initial TOF determined by H NMR; 0.7 mL of benzene-d6 at 35
°C, 0.005 g of 1 (1.27 × 10-5 mol). b Catalysis competes with aldehyde
decarbonylation generating 6 and 7 except for entries 1-3. c Conversion
based on 1H NMR analysis of a scaled up reaction in 3.5 mL of toluene,
0.01 g of 1 (2.54 × 10-5 mol). d Isolated yield based on conversion
after chromatography on silica with hexane/ethyl acetate.
Scheme 1
We report here the use of complex 1 as a precatalyst for both
intra- and intermolecular hydroacylation of certain substrates
together with a mechanistic study of these reactions.
Initial studies involved hydroacylation of vinyltrimethylsilane
using a series of aromatic aldehydes in benzene or acetone as
shown in eq 2.22 Results are summarized in Table 1.
Using p-dimethylaminobenzaldehyde, 4a, a large number of
turnovers (>250) can be achieved without significant catalyst
decomposition, thus mechanistic studies were carried out using
this electron-rich benzaldehyde derivative. Monitoring initial
turnover frequencies (benzene-d6, 35 °C) as a function of olefin
and aldehyde concentrations established that the TO rate is first-
order in aldehyde and inverse order in olefin, turnover frequency
(TOF) ) k[aldehyde]/[olefin]. For example, the initial TOF
(35 °C, C6D6) at ratios of olefin:aldehyde:catalyst of 20:20:1,
50:20:1, and 20:50:1 are 6.7/h, 2.2/h, and 14.8/h, respectively.
More extensive data and kinetic plots appear in the Supporting
Information. At a 1:1 molar ratio of aldehyde:olefin the TO
frequency is invariant with percent conversion and linear plots
of turnover number vs reaction time are observed up to 100%
conversion. The sole cobalt species detected by in situ NMR
spectroscopy during catalysis, the catalyst resting state, was
complex 1. Based on these results the mechanism of hydro-
acylation must involve a rapid pre-equilibrium between 1 and
an olefin/aldehyde adduct prior to the turnover-limiting step. A
possible catalytic cycle is shown in Scheme 1.
(1) Bosnich, B.; Fairlie, D. P. Organometallics 1988, 7, 936-945.
(2) Bosnich, B.; Fairlie, D. P. Organometallics 1988, 7, 946-954.
(3) Bosnich, B.; Whelan, J.; Bergens, S. H.; Noheda, P.; Wang, X.;
Barnhart, R. W. Tetrahedron 1994, 50, 4335-4346.
(4) Bosnich, B.; Wang, X. Organometallics 1994, 13, 4131-4133.
(5) Bosnich, B.; Whelan, J.; Bergens, S. H.; Noheda, P.; Wang, X.;
Barnhart, R. W. J. Am. Chem. Soc. 1994, 116, 1821-1830.
(6) Bosnich, B.; Barnhart, R. W. Organometallics 1995, 14, 4343-4348.
(7) Sakai, K.; Ide, J.; Oda, O.; Nakamura, N. Tetrahedron Lett. 1972,
1287-1290.
(8) Miller, R. G.; Campbell, R. E.; Lochow, C. F.; Vora, K. P. J. Am.
Chem. Soc. 1980, 102, 5824-5830.
(9) Miller, R. G.; Lochow, C. F. J. Am. Chem. Soc. 1976, 98, 1281-
1283.
(10) Miller, R. G.; Lochow, C. F.; Vora, K. P. J. Organomet. Chem.
1980, 192, 257-264.
(11) Larock, R. C.; Potter, G. F.; Oertle, K. J. Am. Chem. Soc. 1979,
102, 190-197.
(12) James, B. R.; Young, C. G. J. Chem. Soc., Chem. Commun. 1983,
1215-1216.
(13) Sakai, K.; Kawahara, T.; Suemune, H. Chem. Pharm. Bull. 1986,
34, 550-557.
(14) Gable, K. P.; Benz, G. A. Tetrahedron Lett. 1991, 32, 3473-3476.
(15) Vinogradov, M. G.; Tuzikov, A. B.; Nikishin, G. I.; Shelimov, B.
N.; Kazansky, V. B. J. Organomet. Chem. 1988, 348, 123-134.
(16) Certain products from Co(I)-catalyzed cyclizations of diyne alde-
hydes may involve metal-mediated hydroacylation of an alkyne unit:
Vollhart, K. P. C.; Gotteland, V. Private communication. See, also: Harvey,
D. F.; Johnson, B. M.; Ung, C. S.; Vollhart, K. P. C. Synlett 1989, 15-18.
(17) Sneeden, R. P. A.; Denise, B.; Isnard, P. J. Organomet. Chem. 1982,
240, 285-288.
Use of deuterated aldehyde, p-NMe2C6H4C(O)D, results in
formation of p-Me3SiCHDCH2C(O)C6H4NMe2; no evidence for
H/D scrambling in the product is seen.20 Following the reaction
by 1H NMR spectroscopy revealed no formation of protio
aldehyde, p-NMe2C6H4C(O)H, during the reaction which sug-
gests that a species such as 8 in which the methylene hydrogens
are equivalent does not form prior to the transition state.
(However, note that formulation of 8 as an η2-acyl complex
results in the methylene hydrogens being diastereotopic and thus
(18) Watanabe, Y.; Tsuji, Y.; Kondo, T.; Tetrahedron Lett. 1987, 28,
6229-6230.
(19) Watanabe, Y.; Tsuji, Y.; Kondo, T.; Akazome, M. W. Y. J. Org.
Chem. 1990, 55, 1286-1291.
(20) Marder, T. B.; Roe, C. D.; Milstein, D. Organometallics 1988, 7,
1451-1453.
(21) Brookhart, M.; Lenges, C. P.; Grant, B. E. J. Organomet. Chem.
1997, in press.
S0002-7863(96)03977-7 CCC: $14.00 © 1997 American Chemical Society

3166 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Communications to the Editor
remaining inequivalent.) An alternative mechanism for ketone
formation, the migration of the acyl moiety to olefin, as opposed
to the migration of the hydride to olefin seems unlikely based
on the observed exclusive regiochemistry of aldehyde addition
and the site selectivity for H/D exchange in this system.21
Using excess olefin, complex 1 is the only organometallic
species present after complete catalytic conversion of 4a to 5a.
With excess aldehyde, complete conversion of olefin to ketone
is observed; however, the cobalt species present reacts with
excess aldehyde to produce decarbonylation products (N,N-
dimethylaniline) and the cobalt carbonyl complexes 622 and
722,23-25 (eq 3). Increasing the aldehyde:olefin ratio increases
the 7:6 ratio. Reaction of 1 with 15 equiv of 4a produces only
5a, N,N-dimethylaniline, and 7. Complexes 6 and 7 are not
active in hydroacylation catalysis. Thermolysis of 6 does not
yield 7 (benzene-d6, 12 h, 35 °C), and treatment of 7 with
vinyltrimethylsilane under the reaction conditions does not give
6. These results suggest decarbonylation reactions and forma-
tion of inactive cobalt carbonyl complexes are major routes for
catalyst deactivation.
Intramolecular hydroacylation reactions of aromatic aldehydes
were also examined. Treatment of 1 with o-formylstyrene
(benzene, 25 °C) results in formation of 9 which has been
isolated and characterized.22 Diagnostic for this cobalt(I)
complex are the NMR features of the coordinated aldehyde (1H,
9.35 ppm, 13C, 178.8 ppm).28 Thermolysis of 9 with excess
o-formylstyrene at 60 °C results in slow formation of cyclic
ketone 10, but only ca. 5 turnovers can be achieved before
catalyst decomposition and formation of unidentified organo-
metallic products. To extend the chelate ring size, compound
11 was prepared from salicylaldehyde.22 Exposure of 11
(benzene-d6, 35 °C) to 1 (1%) results in quantitative catalytic
conversion to the intramolecular hydroacylation product, cyclic
ketone 13.22 A turnover frequency of 2.3/h is observed and is
independent of substrate concentration (a turnover vs time plot
is presented in the Supporting Information). Consistent with
these kinetics, analysis of the catalytic reaction by NMR
spectroscopy shows that 1 is rapidly converted to 12, the catalyst
resting state, which persists throughout the reaction. Complex
12 could be characterized by 1H and 13C NMR spectroscopy at
-10 °C where hydroacylation is slow.22 Notable features are
1
the H and 13C shifts of the coordinated aldehyde (5.05 and
91.1 ppm) which suggest a π-coordination of the aldehyde
moiety.29
Using aromatic aldehydes with less electron-donating sub-
stituents, catalyst lifetimes are substantially decreased due to
decarbonylation and catalyst deactivation, but initial turnover
frequencies are not significantly affected (see Table 1). For
example, with p-CH3C6H4C(O)H complete conversion is ob-
tained with 5% catalyst loading, but conversion drops to ca.
90% with 1% catalyst (compare entry 3, columns 1 vs 3). With
unsubstituted benzaldehyde, only 19% conversion is achieved
with 5% catalyst loading; however, increasing the olefin:
aldehyde ratio to retard decarbonylation (see above) increases
conversion to 25% with only 3.3% catalyst (see entry 7, column
2). Similar trends are evident for other aldehydes reported in
Table 1.
Other vinylsilanes are effective substrates. Using 1 as the
precatalyst, p-NMe2C6H4C(O)H adds to vinyltriphenylsilane
with higher initial TO frequencies (102 TO/h, 35 °C); complete
conversion at 0.5% catalyst load is observed.26 Reaction of
vinyltrimethoxysilane is significantly slower (initial TOF: 0.5
TO/h, 35 °C), yet complete conversion at 1% catalyst load is
observed.27 Variation in these rates probably reflects the relative
binding affinities of the olefins to the Co(I) center as controlled
by sterics.
Transition metal-catalyzed intermolecular hydroacylation
reactions are potentially useful general methods for carbon-
carbon bond formation. Results presented here establish key
mechanistic features of the hydroacylation of olefins catalyzed
by Co(I) complex 1 and show that for certain substrate
combinations useful catalytic lifetimes and turnover frequencies
can be achieved under mild conditions. Future studies are aimed
at broadening the scope of this reaction and providing additional
mechanistic details.
Acknowledgment is made to the National Institute of Health (Grant
GM 28938) for financial support. M.B. thanks the Miller Institute (UC-
Berkeley) for support. C.P.L. thanks the German National Scholarship
Foundation for a travel grant.
(22) All organic products and organometallic complexes have been
characterized by NMR and IR spectroscopy, elemental analysis or mass
spectroscopy; these data are summarized in the Supporting Information.
(23) Brintzinger, H. H.; Lee, W.-S. J. Organomet. Chem. 1981, 209,
401-406.
(24) Dahl, L. F.; Ginsburg, R. E.; Cirjak, L. M. J. Chem. Soc., Chem.
Commun. 1979, 468-472.
(25) Dahl, L. F.; Ginsburg, R. E.; Cirjak, L. M. Inorg. Chem. 1982, 21,
940-957.
(26) In a solution of vinyltriphenylsilane and 1 in acetone-d6 the mixed
olefin complex, C5Me5Co(C2H3SiMe3)(C2H3SiPh3), is generated in equi-
librium with 1. During rapid conversion of vinyltriphenylsilane to ketone
in the presence of aldehyde the resting state changes and the concentration
of the mixed olefin complex decreases in favor of 1.
(27) Upon addition of vinyltrimethoxysilane, 1 is converted to a new
olefin complex, C5Me5Co(C2H3Si(OMe)3)2. This species is the only Co-
complex present during hydroacylation catalysis.
Supporting Information Available: Details of synthesis and
characterization of organic products and organometallic complexes and
descriptions and complete results of kinetic experiments (12 pages).
See any current masthead page for ordering and Internet access
instructions.
JA9639776
(28) The assignment of complex 9 as the σ-carbonyl coordinated isomer
is tentative; substrate coordination involving the aromatic system cannot
be ruled out.
(29) Gladysz, J. A.; Arif, A. M.; Seyler, J. W.; Mendez, N. Q. J. Am.
Chem. Soc. 1993, 115, 2323-2334.