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.
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