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21 Oxides as Heterogeneous Promoters for Liquid-Phase Hydrocarbonylation Reactions with Iodocarbonylruthenium Catalysts Giuseppe Braca , Anna Maria Raspolli Galletti , Glauco Sbrana , and Elizeu Trabuco 1
1
1
2
Department of Chemistry, University of Pisa, 56126 Pisa, Italy Instituto de Biocencias, Letras e Ciencias Exatas, Universidade Estadual Paulista, San Jose do Rio Preto, Brazil
1 2
Basic or acid oxides, used as heterogeneous promoters of carbonylruthenium catalysts in liquid-phase hydrocarbonylation reactions on oxygenated substrates, strongly affect the activity and selectivity of the catalytic system. Concurrent or successive reactions of simple carbonylation, homologation, hydrogenationto hydrocarbons, and etherification take place to varying extents. Carbonylation and etherification are favored by acid oxides and homologation and hydrogenation by basic oxides. This behavior is related to the formation and stabilization by the oxides of H and H hydridocarbonylruthenium catalytic species, whose relative concentrations in solution depend on the nature of the oxide. Heterogeneous oxides are easily separated and recycled from the reaction mixture. Their use simplifies the catalytic system and allows one to direct the catalytic process toward the target product. +
IN
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H O M O G E N E O U S A N D H E T E R O G E N E O U S CATALYSIS, promoters or cocat-
alysts generally operate in the same phase of the catalytically active species. This feature is practically an unvarying rule in heterogeneous gas-solid catalysis, whereas it is not essential in homogeneous liquid-phase systems. Liquid-phase promoters and cocatalysts can interact directly and easily with 0065-2393/92/0230-0309$06.00/0 © 1992 American Chemical Society
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310
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
the soluble active species. However, chemical interactions at the liquid-solid interface are also important when the two components are in different phases. In our research on carbonylation and hydrocarbonylation reactions of oxygenated substrates with carbonylruthenium iodide systems, we demonstrated the important role various promoters play in the activity and selectivity of the reaction: iodide derivatives (I), complexing agents, Lewis acids, and protonic acids (2). Moreover, promoters with different acid-base properties can modify the nature or the relative concentration of the different earbonylmetal species present in solution and thus change the total activity and selectivity of the system (3, 4). Analogous effects related to acid-base interactions are also extensively reported in the literature for carbon monoxide hydrogénation with rhodium and ruthenium heterogeneous catalysts (5-8). With the aim of establishing a bridge between homogeneous and heterogeneous catalytic phenomena related to the role of promoters, we studied the effect of some heterogeneous oxides, y - A l 0 , M g O , L a 0 , T i 0 , and N b O . These oxides have different Lewis or Bronsted acidity or basicity on hydrocarbonylation reactions of oxygenated substrates catalyzed by homogeneous carbonyl- and iodocarbonylruthenium systems. 2
2
3
2
3
2
s
Carbonylation-Homologation
of Ethanol and 1-Butanol
The test reaction chosen was the carbonylation-homologation of ethanol and 1-butanol with synthesis gas. It was carried out under typical conditions used for the hydrocarbonylation of oxygenated substrates with iodocarbonylruthenium systems (9): ruthenium precursor, Ru(acac) (acac is acetyl acetonate, C H 0 ) or R u ( C O ) I ; iodide promoter, C H I or H I ; Γ, 200 ° C ; C O / H , 1; P, 14 M P a (Tables I and II). Under these conditions a number of concurrent and successive reactions (Scheme I), catalyzed either by the protonic cocatalyst or by the ruthenium species, take place. The relative selectivities are greatly affected by the reaction conditions and by the intervention of the added promoters. Under specific conditions, products coming from the direct activation of C O are also produced. Water produced in various reactions also plays an important role by interacting with the surfaces of the oxides and affecting their acid-base properties (JO, IJ). 3
5
7
2
4
2
3
2
To better distinguish and compare the action of the cocatalysts and of the ruthenium species, the tables indicate both the total conversion and the conversion due only to metal-catalyzed reactions.
Soluble and Insoluble Aluminum Promoters.
The role of soluble
aluminum halides acting as effective Lewis acids in the activation of C O groups bound to organometallic derivatives has been extensively reviewed
3
CH I AhV CH3I CH3I AII3 CH3I
2
2
Al 0
3
(2.0) 11.7
16.8
36.0 46.7
40.0
85.3 18.4
26.6
44.4
20.2
53.6
12.2 49.7
3.7
8.9
5.6
92.3
60.1
64.1
Estenflcation
41.6
47.2
53.2
25.8
14.0
6.2
33.0
20.1
42.7
27.1
31.0
Homolo gation
43.6
29.2
47.8
45.0
38.2
52.5 36.1
14.5
39.9 57.7
40.0
29.3
Hydrogen ation
Reactions (% selectivity) Carbonyl ation
Metal-Catalyzed
30.3
MetalCatalyzed
Types of Reactions (% selectivity) Etheriflcation
28.7
(3.6) (3.6) (1.2) (3.6)
(2.0)
24.0
3
21.6
71.2
Al 0
b
B
77.4
A"
(2.1)
(3.6)
ω
Oxide
Conversion (%)
c
b
3
2
NOTES: Reaction conditions: Ru(acac) , 0 . 3 6 mmol; E t O H , 480 mmol; temperature, 200 °C; time, 8 h; pressure, 14 MPa; C O / H , 1; I/Ru, 10. In runs 4 - 6 the solvent was 14 mL of toluene. Total conversion. Con version to metal-catalyzed reaction products. I/Ru, 17.
6
5
4
3
2
1
Run
Iodide Supplier (mmol)
Promoter System
Table L Hydrocarbonylation of Ethanol with Soluble or Insoluble Aluminum Promoters
Homogeneous Transition Metal Catalyzed Reactions Downloaded from pubs.acs.org by CORNELL UNIV on 05/18/17. For personal use only.
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312
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
ΙΟ
00 00
t
Ο
O
CD
ΙΩ
00
CD
Tf
O
(75 f-- O 00 rf
