20 Tetracarbonylalkylcobalts from Tetracarbonylhydridocobalt and Dimethyl Fumarate or Aldehydes F e r e n c U n g v á r y , Attila Sisak, and László M a r k ó Institute of Organic Chemistry, University of V e s z p r é m , V e s z p r é m , Hungary 8201
Tetracarbonylalkylcobalts, supposed intermediates in olefin hydroformylation and aldehyde reduction, were prepared. When tetracarbonylhydridocobalt reacted with dimethyl fumarate at 10 °C, tetracarbonyl[l,2-bis(methoxycarbonyl)ethyl] cobalt was formed and isolated in 65% yield. The rate of the accompanying carbon monoxide uptake was found to be 0.5 order with respect to CO (CO) . Tetracarbonyl-α-hydroxyalkylcobalts were prepared by the reactions of tetracarbonylhydridocobalt with formaldehyde, pivalaldehyde, glyoxal, ethyl glyoxylate, and crotonaldehyde between -40 and -79 °C and characterized partly in the form of their silylated derivatives by IR and NMR spectroscopy. An ionic path that accounts for the observed regiochemistry is suggested for the reaction with aldehydes. 2
8
C A R B O N Y L A L K Y L C O B A L T S A N D C A R B O N Y L A C Y L C O B A L T S are intermediates
in olefin hydroformylation (J, 2). The studies of Heck and Breslow (3) leave little doubt of this fact. However, only tetracarbonylacylcobalts have been detected under catalytic reaction conditions by high-temperature, high-pressure infrared spectroscopy (4). The failure to detect carbonylalkylcobalts can be explained by the assumption that at high pressure the alkyl-acyl equilibrium is far on the side of the acyl complex. Under ambient conditions we can detect and in some cases isolate tetracarbonylalkylcobalts in reaction mixtures of C o H ( C O )
4
and olefins bearing electron-withdrawing substit-
uents. 0065-2393/92/0230-0297$06.00/0 © 1992 American Chemical Society
298
H O M O G E N E O U S TRANSITION M E T A L C A T A L Y Z E D REACTIONS
Intermediate complex formation between aldehydes and C o H ( C O ) was repeatedly postulated in mechanistic suggestions for aldehyde reductions under catalytic (5, 6) and stoichiometric (7) conditions, C O reductions (8), and alcohol homologations (9). We found that complex formation between formaldehyde and C o H ( C O ) takes place at -40 °C (10). Further experiments showed that tetracarbonyl-a-hydroxyalkylcobalts are formed with other al dehydes as well; they can be isolated in form of their silylated and P P h substituted derivatives. 4
4
3
Experimental Details All manipulations involving air-sensitive compounds were carried out by the usual Schlenk technique (II) using deoxygenated dry solvents and gases and thermostated reaction vessels with magnetic stirring. Kinetic runs were per formed in a gasometric apparatus fitted with a mercury-filled gas burette. In frared spectra were recorded by using a 0.06-mm C a F cuvette on a spectrometer (Specord IR 75; Carl Zeiss, Jena, Germany), which was calibrated with benzene (1959.6 cm" ) and polystyrene (1601.4 cm" ). *H N M R spectra were obtained on an 80-MHz spectrometer (BS-487; Tesla, Brno, Czechoslovakia), using hexamethyldisiloxane as an internal reference. A C N M R spectrum was obtained on a 20-MHz spectrometer (CFT 20, Varian, Palo Alto, California). Solutions of CoH(CO) in n-pentane or η-octane, which were prepared from Co (CO) , dimethylformamide (DMF), and concentrated H C l (12), contained 1-3 mol % of C o ( C O ) according to IR and Co analyses. Other starting materials were com mercial products purified by crystallization or distillation. 2
1
1
1 3
4
2
2
8
8
Preparation of Tetracarbonyl[l,2-bis(methoxycarbonyl)ethyl]cobalt. A 1.0 M solution of CoH(CO) in n-pentane (16 mL, -60 °C) was added through a cannula to a stirred solution of 13.83 g (96 mmol) of dimethyl fumarate in 400 mL of a 2.5:1 (v:v) mixture of dichloromethane and n-pentane under C O at mosphere at 10 °C. The C O pressure was then raised to 150 mm Hg (—20 x 10 Pa) over atmospheric pressure. After 3 h of continuous stirring, the resulting light brown solution was concentrated in vacuum at -20 °C and placed on dry ice overnight. Cold filtration at dry ice temperature on a P-2 glass frit gave 10.8 g of crystals and a light reddish-yellow filtrate. After the crystals were washed with 5 X 10 m L of n-pentane at -10 °C, 10.2 g of dimethyl fumarate remained on the frit and 0.5 g of C o ( C O ) could be crystallized from the dark brown npentane solution at -79 °C. The light reddish-yellow filtrate was further con centrated in vacuum at -20 °C to 70 m L and crystallized on dry ice overnight. After separation of a light yellow crystalline solid (1.0 g), the filtrate was concentrated to 20 m L in vacuum at -20 °C and stored on dry ice overnight. After separation of ca. 0.2 g of solid and a repetition of the foregoing procedure, the final concentrate (ca. 7 mL) was diluted with 14 m L of n-pentane and crystallized at -79 °C. Cold filtration, washing with 3 x 4 m L of cold n-pentane, and drying in vacuum at -20 °C gave 3.27 g (65% yield) of the title compound as ivory-colored crystals. For the IR spectrum, see Table I and Figure 1. C N M R spectroscopy (CDC1 , -15 °C, tetramethylsilane) revealed chemical shifts downfield (δ) at 194.10 (CO) , 177.60 ( C H C 0 M e ) , 169.91 ( C H C 0 M e ) , 50.0Φ-19.77 ( C H 0 C ) , 39.59 (CH ), 19.95 (CH) ppm. 4
3
2
8
1 3
3
4
3
2
2
2
2
2
20.
299
UNGVÂRY ET AL. Tetracarbonylalkylcobalts
Table I . Infrared Spectroscopic Data of R R CHCo(CO)4-Type Complexes in the C = Q Stretching Region !
R
R
!
2
2
2
2
z
2
2
N O T E : In
1
H H Me0 CCH Et0 CCH Me Et Ph Me
z
Réf.
ν (CO) (cm- )
2
H EtO C Me0 C Et0 C EtO C Et0 C Me0 C CN
2
2
2
2104, 2111, 2111, 2110, 2107, 2106, 2106, 2109,
2035, 2046, 2046, 2044, 2041, 2040, 2040, 2044,
2018 2036, 2036, 2036, 2031, 2030, 2031, 2029,
2027, 2026, 2024, 2021, 2020, 2025, 2020
15 16 this work this work 17, 18 18 17 19
1720 1744, 1720 1740, 1714 1726 1718 1717
n-hexane solution. 2100
2000
j
1
1900
1
1800
1700
,
,
cm"
1
Figure 1. The infrared spectrum of the reaction mixture of dimethyl fumarate and CoH(CO) just after CO uptake has stopped and Co^COjs and dimethyl fumarate have been removed at -79 °C. 4
Preparation of Tetracarbonyl( 1-hydroxy, l-formyl)methylcobalt, l c . To 58 mg (1 mmol) of monomeric glyoxal (13) dissolved in 3.8 m L of dichloromethane, 1 mmol of CoH(CO) in 1.2 m L of n-pentane was added under Ar at -79 °C. Overnight storage on dry ice resulted in a bright yellow precipitate, which was filtered off and dried in an Ar stream. This compound is extraordinarily sensitive to air and heat; it decomposes above -50 °C. Its IR spectrum was recorded at this temperature in dichloromethane solution (Table II). 4
Preparation of Tetracarbonyl( 1-hydroxy, l-ethoxycarbonyl)methylcobalt, Id. This compound was prepared analogously in toluene-n-pentane from ethyl glyoxylate. Preparation of Tetracarbonyl(2-trimethylsflyloxy)-frane-3-pentenoylcobalt, 4e. To 201 μ ί α (2.43 mmol) of crotonaldehyde in 4 m L of n-hexane, 0.81 mmol of CoH(CO) in 1.0 m L of n-pentane was added under C O at -55 °C. After 1 min, 213 of bis(trimethylsilyl)trifluoroacetamide (BSTFA) was injected into the reaction mixture. Within 5 min the solution turned lemon yellow. In addition to some C o ( C O ) , tetracarbonylacylcobalt 4e resulted (Table II). 4
2
8
2100, 2109, 2105, 2109, 2100, 2101, 2107, 2102, 2051, 2041,
2050, 2048, 2045, 2051, 2032, 2035, 2044, 2042, 1986, 1973,
2021 2032, 2027, 2028, 2019, 2022, 2028, 2023, 1964, 1958,
fc
d
f
b
c
e
J
6
2024 2018, 2013, 2008 2005 2010, 2003, 1688, 1647 c
£/
d
1701 1695' 1672
1729, 1712 1695*
1
a
0.03 (s, 9H), 4.45 (s, 2H), 6.6-7.4 (m, 15H) 0.03 (s, 9H), 0.93 (s, 9H), 3.54 (s, 1H), 6.5-6.8 (m, 15H)
3.30 (s, 1H), 3.93 (s, 2H) 0.07 (s, 9H), 4.97 (s, 2H)
Ή NMR :h (ppm)
Table IL Spectral Data of Complexes 1-5
IR: ν (CO) (cm- )
"In toluene-*/*In dichloromethane. In toluene. \n n-heptane. 'In n-hexane-n-pentane mixture.
la lc Id 2a 3a 3b 4a 4e 5a 5b
Compound
20.
UNGVARY ET AL. Tetracarbonylalkylcobalts
301
Preparation of Tetracarbonyl( l-trimethylsilyloxy-2,2-dimethyl)propyl cobalt, 3b, and Tricarbonyltriphenylphosphine(2-trimethylsilyloxy-3,3-dimethyl)butanoylcobalt, 5b. To a solution of 172 μ ΐ , (162 mmol) of pivalaldehyde in 3 m L of n-hexane, 1.62 mmol of CoH(CO) in 2.0 m L of n-pentane was added under Ar at -55 °C. After 1 min, 472 μL· (1.62 mmol) of BSTFA was injected. The IR spectrum recorded after 45 min reaction time showed the complete conversion of CoH(CO) and the presence of 3b together with traces of Co (CO) . Addition of P P h in 10 mol % excess and stirring at 0 °C for 3 h gave a yellow precipitate, which was filtered and washed with 2 X 1 m L of n-pentane and dried in vacuum to produce 480 mg of 5b (50% yield). For spectral data, see Table II. 4
4
2
8
3
Results and Discussion Reaction of Dialkyl Fumarate with CoH(CO) .
Diethyl fumarate
4
(DEF) reacts readily with C o H ( C O ) at 10 °C under atmospheric pressure of C O . This reaction forms diethyl succinate (DES) as the hydrogenated product (14) and diethyl 2-formylsuccinate as hydroformylated product (eqs 1 and 2). 4
DEF DEF
+ 2 C o H ( C O ) -> D E S + C o ( C O ) 4
+ 2CoH(CO)
4
2
(1)
8
+ C O -> E t 0 C C H C H C 0 E t + C o ( C O ) 2
2
2
2
(2)
8
CHO Both reactions were found to be autocatalytic with respect to C o ( C O ) . Thus, when these reactions were started at different C o ( C O ) concentra 2
2
8
8
tions, the induction period decreased with increasing initial C o ( C O ) con centration (Figure 2), and the initial rates showed a 0.5-order dependence in [ C o ( C O ) ] (Table III). 2
2
8
8
0
In experiments with excess diethyl fumarate, a large part (60-70%) of the converted C o H ( C O ) could not be accounted for by the products of reactions 1 and 2. Instead, the formation of tetracarbonyl[l,2bis(ethoxycarbonyl)ethyl]cobalt could be observed (eq 3). 4
DEF
+ CoH(CO) - » E t 0 C C H C H C 0 E t 4
2
2
(3)
2
I Co(CO)
4
Just after C O uptake stopped, and after C o ( C O ) was removed by crystallization at -79 °C, the infrared spectrum of the reaction mixture showed carbonyl stretching bands characteristic of a tetracarbonylalkylcobalt (Table I; cf. refs. 15-19), as well as bands for two different ester carbonyls. With the dimethyl ester of fumaric acid, not only C o ( C O ) but the surplus dimethyl fumarate as well could be removed by low-temperature 2
8
2
8
302
H O M O G E N E O U S TRANSITION M E T A L C A T A L Y Z E D REACTIONS
Figure 2. The effect of initial Co^CO)^ concentration on the reaction of diethyl fumarate (DEF) with CoH(CO) under CO atmosphere at 10 °C in n-octane. [DEF]o = 0.152 M , [CoH(CO) ] = 0.030 M , [CO] = 0.00946 M. 4
4
0
Table III. Effect of Initial Co (CO) Concentration on the Amount of Absorbed C O and on the Initial Rate of C O Absorption in the Reaction of D E F with CoH(CO) _______ 2
8
4
[C (CO) ]o (M) 03
[mol CO/mol CoH(CO) ]
10 Γ,η (Ms- )
0.159 0.167 0.176 0.16
1.58 6.22 11.5 16.1
CO,mx
H
0.001 0.015 0.049 0.10
iœrJ[Co.2(CO)s]o (M s- )
6
4
05
05
1
1
5.0 5.1 5.2 5.1
NOTE: C O is adsorbed C O ; r is the initial rate of C O absorption; [CO] is 0.00946 M ; [ D E F ] is 0.152 M ; [CoH(CO) ] is 0.030 M ; 10 °C; η-octane solution. n i a x
in
4
0
fractional crystallization (Figure
1).
From this solution pure tetracar-
bonyl[l,2-bis(methoxycarbonyl)ethyl]cobalt
could be crystallized at -79 °C
in 65% yield. O n the basis of the kinetic behavior of reactions 1 and 2, similar to that already observed for 1-heptene, 1-octene (20), and ethyl acrylate (18) under the same conditions, we assume that the role of C o ( C O ) is to catalyze the 2
8
formation of a tricarbonyl(hydridoolefincobalt) intermediate according to Scheme I. This intermediate converts to a tricarbonylalkylcobalt, which then reacts in competing fast reactions to form the products of reactions 1, 2, and
0
20.
UNGVÂRY E T A L .
303
Tetracarbonylalkylcobalts
Co (CO) 2
•coico)
-
*)C'c{
A
^.CofCOU
8
Co(C0) CC=C( ) » CoHICOU 3
- coicoiaiX-c;) s l o w
CoH(C0) ( X=C' ) -
-
V
3
-
ComC0) r,C°C< ) • Co (COU 3
)CH-Ç-Co(C0)
)CH-CH • Co (C0) " " " " ^ 2
• CO
3
)CH-C-Co(C0)
