Syngas reactions

Journal of Molecular Catalysis, 43 (1987)

65 - 77

SYNGAS REACTIONS PART XI. THE RUTHENIUM ‘MELT’ CATALYZED INTERNAL OLEFINS

65

OXONATION OF

JOHN F. KNIFTON Texaco Chemical Co., P. 0. Box 15730, Austin, TX 78761 (U.S.A.) (Received November 6, 1986; accepted January 14, 1987)

Summary The hydroformylation of internal olefin substrates to give predominantly linear ‘0x0’ alcohols is catalyzed by ruthenium carbonyl ‘melt’ catalysts, wherein the ruthenium carbonyls are dispersed in low m-p. quaternary phosphonium salts. The anionic ruthenium cluster, [HRu~(CO)~~]-, is the predominant metal carbonyl species in the reactant solutions. Improved alcohol linearity can be achieved through addition of certain chelating N- and P-donor ligands, such as 2,2’-bipyridyl, as well as by the choice of quaternary phosphonium salt matrix. Mixed metal catalysis, particularly Ru-Co, allows the corresponding aldehyde to be the preclominant product fraction. These reactant solutions show the presence of both ruthenium carbonyl and ]Co(CO)J anionic species.

While industrial hydroformylation processes currently employ homogeneous cobalt and rhodium catalysis [l], in recent years there has been a shifting interest towards analogous ruthenium chemistry [2,3]. Published work has so far focused, however, primarily upon the oxonation of terminal (ac-)olefins [ 37. In an extension of our earlier work on the selective synthesis of low MW oxygenates from syngas [4], we report here our more recent studies dealing with ruthenium ‘melt’ oxonation catalysis, where ruthenium and Ru-Co carbonyls are dispersed in low melting (m.p. <150 “C) quaternary phosphonium salts as reaction media. The principal thrust of this work has been the prep~ation of 0x0 alcohols/aldehydes, p~ti~ul~ly linear primary alcohols from internal olefin substrates ]5 - 71. The incentive for developing this technology has been to upgrade the readily available, economically attractive, internal olefin feedstocks presently generated through paraffin dehydrogenation and olefin metathesis. 0304-5102/87/$3.50

@ Elsevier ~quoia/Printed

in The Netherlands

66

Results Typical hydrofo~ylation activity is illustrated in Table 1 for a model internal, linear-backbone, olefin mixture (2-, 3- and 4-octenes), using as catalyst precursor a dispersion of ruthenium(IV) oxide hydrate in tetrabutylphosphonium bromide (ex. 1). Optionally, a cobalt carbonyl-tertiary phosphine cocatalyst may be added (ex. 10). Hydroformylation is facile under moderate syngas pressures (turnover frequency > 90 mol (g-atom Ru)-’ h-l), and the major products are linear alkanols (1-nonanol, eqn. 1). Nonanals may also predominate under certain conditions (e.g. see ex. 10). Other Cl1 and C,&,4 internal olefin fractions may likewise be converted to the corresponding 0x0 alcohols (e.g. ex. 12) [5 3. A typical preparative procedure is outlined in the Experimental Section. RCH=CHR’ + CO/H, \

R”CH2CH,CH20H + R”CHCH,OH

R~CH*CH~C~O + R”CHCH0

(1)

f

I

where R+R’ = R” With regard to the importance of catalyst structure, we find in ruthenium ‘melt’ catalysis that precursors other than rutheni~(IV) oxide hydrate can be employed (ex. 2,3) without significantly affecting either the rate of oxonation or the n/is0 distribution. Chloride ion is the notable exception (ex. 4). Using Rus(CO)i?, Ru(acac), and RuOz as ruthenium sources, the reactant solutions each show the ]HRus(CO),,]polynuclear anion to be the major metal species present (ch~acteristic Y(CO) bands in the IR region at 1957, 1990 and 2016 cm-‘, see Fig. 1A [8]) together with smaller quantities of [Ru(CO),Br,][9] and Ru(CO)s [lo] (2036 and 2112 cm-‘). Weaker bands, such as at 1968 cm-‘, may be symptomatic of more highly nucleated ruthenium cluster anions [ 11 J . These same solutions are also very effective for cu-olefin oxonation [ 51, while similar ruthenium car-bony1 clusters have been reported by Bianchi et al. to catalyze double bond isomerization [3]. The ruthenium ‘melt’ catalysts do not, however, lead to a preponderance of a-olefin when starting with typical internal olefin fractions (see Table 2, ex. 14), although measurable quantities of ar-olefin can be detected after syngas treatment. An important practical consideration with this new class of ruthenium hydroformylation catalyst is that, in contrast to analogous homogeneous systems [ 121, the ruthenium carbonyl species are stable in the quaternary phosphonium salt matrix, even under low pre~ure/h~h temperature conditions. Consequently, both the desired alcohol and aldehyde product fractions can be readily isolated from the crude product mix by fractional distillation, and the residual ‘melt’ catalyst recycled without loss of activity [ 51. With regard to the effect of added @donor, 7r-acceptor ligands, in the case of ~thenium oxide dispersed in Bu,PBr salt, the addition of small quantities of tri-n-butylphosphine induces little or no effect upon either the

6’7

0

cv &

0

d

1

1

I

t-

0

5 N

, 2400

A 0

I

I

2200

Fig. 1. Oxonation of internal octenes. Spectra precursor RuOdBu$Br (ex. 1); B. catalyst Experimental conditions as defined in Table 1.

oxonation rate or the n/is0 other hand, can have a large, IR spectra of these reacting show high concentrations (PBu& (v(C0) 1883 cm-’ ruthenium carbonyl anion

1

I

2000 WAVENUMBERS

I800 of typical precursor

7

1600 product solutions. RuOTBIPY/Bu$Br

A. Catalyst (ex. 7).

ratio (ex. 5). Excess trialkylphosphine, on the adverse influence upon 0x0 activity (ex. 6). The solutions (four-fold excess of PBu,) typically of the ruthenium neutral complex, Ru(CO), [13]), but no remaining quantities of either [HRu,( CO) 1J or [ Ru(CO),Brs]. Similar

RuO,DIPHOSk

9

2octene internal oiefinsf internal olefinsf internal olefinsf internal oiefinsf internal olefinsf internal olefinsf internal olefinsf internal olefinsf internal olefins’ internal olefinsf internal undecenes

Olefin charge

70

3

53

291

361

52

4

>99

7

>99

>99

98

Octene conv. (%)

54”

nd.

9.1

15j

21j

35

nd.

73

n.d.s

65

65

66

37

46

55

63

69

47

40

42

49


46

55

63

68

77

nd.

64

59

62

79

nd.

73

nd.

66

66

50 50

72

46

Linearityd (%)

Total Ca alcohol + aldehyda yield (mol%)

180 “C, 83 bar CO/Hz (1:2) initial charge;

0.2

25

2.oj

0.53

5.4

0.1

0.2

n.d.

1.0

0.8

5.1

Productivity’ (mol %)

ProductivityC (mol %)

Linearityd (mol %)

Cs Aldehyde

composition

Cs Alcohol

Product

aRun charge: Ru, 6.0 mmol; Bu#Br, 20.0 g; internal octene mix, 200 mmol; run conditions: 4h. bProduct analysis by GLC, product identification by GLC-FTIR; isolation, NMR. ‘Productivity cafe. basis octene charged.

12

11

RuOzCo2 (CO)s-Bu#”

RuOa-TDPEP’

8

10

RuO,BIPYh

RuO&&P

RuOT2Bu$’

RuC13

Ru(acac)a

Catalyst? composition

7

1 2

EX.

TABLE 1

dLinearity calculated basis linear alcohol or aldehyde/total alcohol or aldehyde. eYield calculated basis olefin converted. ‘Internal octenes comprising: 1-octene, 2.5%; trans-2-octene, 25%; cis-2-octene, 12%; cis-3-octene, 9%; trans-3-octene, 6%; trans-4-octane, 17%. gn.d. = none determined by GLC, cont.
cis-4-octene,

70

TABLE 2 Ex.

Substrate

13

frans-2-octene

14

mixed internal octenes n-nonanal

15

Catalyst precursor

Rua(CO)rr Bu&Bra RUBLEB@Brb Ru0.r-3u4PBrC

Substrate conv. (X)

94d 95

Product composition Ce Aldehyde

Cs Alcohol Productivity (mol%)

Linearity (%)

Productivity (mol%)

42

51

7.9

91

-

-

95

-

aRun charge: Ru, 6.0 mmol; Bu$Br, 20.0 g; trans-2-octene, 200 mmol; run conditions: 180 “C; 83 bar CO/H2 (1:2) initial charge; 1 h. bPretreated with 28 bar CO/Hz (1:2), 180 “C, 2 h prior to internal octenes addition in in situ; run at 180 “C, 2 h under CO, 28 bar; internal order to generate [HRu3(CO),r]octenes composition as in Table 1. ‘Run charge: Ru, 6.0 mmol; Bu,@r, 20,O g; nonanal, 200 mmol; run conditions; 180 “C, 83 bar CO/HI (1:2) initial charge; 4 h. dEstimated turnover frequency: 31 mol (g atom Ru)-” h-r. eOctene composition as in starting material, see Table 1, no significant increase in loctene concentration.

trends were noted with added triphenylphosphine. Suppression of rutheniumcatalyzed 0x0 activity by the addition of arylphosphine has been previously reported by Wilkinson for analogous Ru(C0)3(PPh,), systems-run homogeneously or in molten phosphine [ 141. In contrast to the observed effect of PBu, (Table l), the addition of controlled quantities of certain chelating N- and P-donor ligands can significantly alter both the oxonation rate and the regioselectivity to linear alcohol product. Of the numerous bidentate and multidentate tertiary phosph~e [ 61, N-heterocyclics, tertiary amines [7] and Group IVB donor ligands evaluated in this work, we find that the addition of one molar equivalent of 2,2’-bipyridyl (BIPY) induces a significant improvement in both nonanal and nonanol linearities-to 68 and 69%, respectively (see ex. 7). Predominantly linear 0x0 alcohols are also synthetized where the ruthenium precursor is coupled with certain polydentate P-ligands; tris(2-phenylphosphinoethyl)phosphine and 1,2-bis(diphenylphosphino)ethane are especially effective in this regard (ex. 8 and 9). The spectra of the RuO,--BIPY/Bu$Br catalystproduct solutions (ex. 7, Fig. 1B) in the metal carbonyl region continue to be dominated by bands typical of ]HRu,(CO),,](1959, 1990 and 2017 cm-‘), but peaks at 1990,203O and 2073 cm-’ may be indicative also of the presence of known [15] ruthenium carbonyl bipyridyl clusters. Ruthenium carbonyl mononuclear complexes of 2,2’-bipyridyl [16] appear less likely to be present in measurable quantities. The mixed Ru-Co melt catalysts are particularly efficient for the selective linear aldehyde synthesis from internal olefins (ex. 10). Here the

71

spectra of the reaction mix show the presence of [Co(CO)J (v(C0) 1886 cm-‘) plus a series of bands at 1943, 1974, 2004,2038 and 2052 cm-’ (see Fig. 2A). Again we may be seeing more highly nucleated ruthenium carbonyl cluster anions [ 111. However, both the relative intensity and position of the individual bands in this set do vary as a function of initial catalyst concentration, olefin conversion, etc., suggesting that two or more metal carbonyl

9, 0

I

I

2400

1

2200

1

I

I

2000 WAVENUMBERS

I

I

I600

1600

b A 0 d

2400

2 200

t t 2000 WAVENUMBERS

L

I600

I

I

I600

Fig. 2. Oxonation of internal octenes. Spectra of typical product solutions. .A. Catalyst precursor RuO~~o~(CO)~PBu~Bu~~; B. catalyst precursor RuO~fBu$OAc (ex. 21). Experimental conditions as defined in Table 1.

72

species may be in dynamic equilibrium under the 0x0 conditions. There appears to be no definitive evidence in these spectra for the presence of known mixed Ru-Co carbonyl clusters 1171. It is noteworthy that the initial Ru-Co concentration has a significant impact upon both the overall rate of oxonation and the aldehyde/alcohol product distribution (see Fig. 3). Subsequent aldehyde hydrogenation to

ALKANOL / ALDEHYDE YIELD (mmole)

O0

0.5

1.5

Ru CONTENT 1 mmola) Fig. 3. Oxonation of internal octene mix to nonanals and nonanols. Total nonanals, X ; total nonanols, 0. Catalyst precursor RuOa-CoZ(CO)s-PBu3/Bu,+PBr (Ru:Co:P = 1:l: 1.5); internal octenes charge, 200 mmol. Run conditions: 180 “C, 83 bar CO/Hz (1:2) initial charge, 6 h. Estimated turnover frequency: 94 mol (g atom Ru)-’ h-l, for initial Ru content of 0.19 mmol.

73

alcohol can be conducted in a separate step by [HRu,(CO),,]-/Bu,PBr (see Table 2, ex. 15). A small but measurable quantity of non-linear product is generated in this case. Cobalt carbonyl ‘melt’ alone, in the absence of ruthenium, exhibits very poor hydroformylation activity (ex. 11). This, of course, is in contrast to the established data for cobalt carbonyl catalysts in solvent-solubilized systems [ 11. Rate enhancement by mixed homogeneous cobalt-ruthenium bimetallic catalysis has recently been disclosed by Hidai [ 181. While the quaternary phosphonium salts provide the unique reaction media for these 0x0 syntheses, their structure can also have a significant impact upon catalytic activity and selectivity (Table 3). Starting with internal Cs-olefins, the highest nonanal/nonanol linearity is achieved with the ruthenium(IV) oxide-tetrabutylphosphonium acetate couple. In this case the linearity of the nonanol fraction is 68% (ex. 21). The spectra of the solutions are again dominated by the v(C0) at 1954, 1989 and 2015 cm-‘, characteristic of the ruthenium carbonyl cluster anion, [HRu,(CO),,]-. The presence of a pair of additional bands at 1710 and 1743 cm-’ in the bridging carbonyl region (Fig. 2B) may indicate, however, the importance of both solvent-separated and contact ion-paired species [ 191 in this media. 31P NMR spectra of the used ‘melt’ catalysts, after recovery of the 0x0 alcohol/aldehyde product, show no detectable degradation of the quaternary phosphonium salts under the conditions of Tables 1 - 3.

Discussion The ruthenium hydrocarbonyl anion, [HRu,(CO),,]-, appears from this work to have a number of distinct roles to play in the syntheses of eqn. 1, particularly in catalyzing double bond migration, olefin hydroformylation as well as aldehyde reduction to alcohol. The overall reaction profile of internal olefins going to aliphatic linear alcohols may be frozen at any of these stages, either by control of conditions, or by addition of suitable reagents. The [HRu,(CO),,]has earlier been demonstrated by us to be effective in numerous CO hydrogenation sequences [4], where it appears to be stable over a broad range of syngas conditions. Suss-Fink and Herrman have recently provided evidence that the ruthenium-catalyzed hydroformylation of ethylene proceeds via catalysis by intact clusters [2], specifically [HRu3 (CO),,]-. Such a mechanism (modified in Scheme 1) is consistent, but not proven, by our data. Regioselectivity to straight-chain aldehyde and alcohol products from internal olefin substrates (eqn. 1) is enhanced with the ruthenium ‘melts,’ either by increasing the steric bulk around the ruthenium with certain N- and P-coordinating ligands (Table 1, ex. 7 - 9), or by changing the nature of the quaternary salt matrix (Table 3). The changes in regioselectivity with addition of chelating N- and P-ligands are paralleled many times by sharp changes in the IR solution spectra, particularly for the ruthenium-carbonyl-phosphine

RUO* RuOz RuOs RuOa Ru02 Ru02

Catalyst

Compositiona

CW-WWBr &PI EtPhQI Bu&z!l Bu$OAc

C7H1d’Wfh

Media

56

>99 >99 >99 90 >99

Octene conv. (%)

‘Reaction charge and run conditions as per Table 1. bProductivity and linearity designations as per Table 1.

16 17 18 19 20 21

Ex.

TABLE 3

Linearity (%I 40 50 nd. nd. 50 68

Ca Aldehyde Productivity (mol%) 0.5 6.6 1.3 12 0.5 4.3

Linearity (%I 45 44 44 50 44 69

Ca Alcohol Productivity (mol%) 73 80 82 50 75 25

Product compositionb

74 81 83 68 76 52

Total Co alcohol + aldehyde yield (mol%)

;:

75 RCH =CHR’

R”CH,CH,CH,OH

f

I

,,_

J

[RU,(CO),,(CH~CH~R”

)] -

f

cH2cH2R”ll

-

PC0

HZ Scheme (CO),,]-

1. Oxonation of internal as the catalyst-proposed

olefins to linear aldehydes mechanism; R+R’ = R”.

and alcohols

with

[HRua

complexes. But in the case of Ru-BIPY (where the highest alcohol/ aldehyde linearity is achieved), the ruthenium carbonyl-bipyridyl complexes formed in situ appear in low concentrations, and in equilibrium with larger quantities of [HRu,(CO),,]-. Their individual contributions to the oxonation activity, and their quantitative effects upon the n/iso ratios, have yet to be defined. The influence of quaternary salt structure may be minimal for the phosphonium halides (Table 3), in contrast to results for methanol/glycol generation using similar catalysis [4,20], but for tetrabutylphosphonium acetate the improvement in product alcohol regioselectivity likely has its roots in the ion pair interactions with the [HRu,(CO),,]cluster anion (Fig. 2B). The modest loss in alcohol linearity during nonanal hydrogenation (ex. 15) is consistent with the earlier proposal [2] that each of the elementary steps of Scheme 1 is reversible under these 0x0 conditions. Consistent with the results in Tables 1 and 2, olefin double bond isomerization must be fast, relative to the rate of subsequent hydroformylation, with the Ru melt catalyst systems, while the CO insertion step in Scheme 1 favors the formation of linear, rather than branched, n-acylruthenium intermediates,Ru3 (CO)i,(CCH,CH,R), irrespective of the structure of the initial formed Rua

76

alkyl precursor. The sensitivity of the alcohol/aldehyde product linearities to CO partial pressures [21] indicates that generally this CO insertion step has greater influence over the n/iso ratios than either the mode of initial olefin insertion into the Ru-H bond, or the reductive elimination step. More detailed parameter studies for the ruthenium ‘melt’ 0x0 catalysts using cr-olefin substrates will be reported subsequently. Experimental All syntheses were conducted batchwise in pressurized reactors under carefully controlled temperature/pressure conditions. The ruthenium compounds, tertiary phosphines, N-heterocyclics and quaternary phosphonium salts were purchased from outside suppliers. Synthesis gas was purchased in various CO/H, proportions from Big Three Industries. Mixed internal olefins were freshly distilled prior to use. All product solutions were analyzed through a combination of GLC, GLC-IR and GLC-NMR techniques. 0x0 alcohol and aldehyde fractions were isolated by fractional distillation in vucuo, and indentified by the same analytical techniques. FTIR spectral measurements were made using a Digilab FTS 15C instrument. Typical oxonation synthesis Ruthenium(IV) oxide hydrate (1.15 g, 6.0 mmol) is dispersed in tetrabutylphosphonium bromide (20.0 g, 58.9 mmol) and diluted with 2-octene (22.4 g, 200 mmol), then transferred in a glass liner, under nitrogen purge, to an 850 ml capacity pressure reactor equipped with heating and means of agitation. The reactor is sealed, flushed with CO/H, and pressured to 83 bar with CO/H, (1:2), The mixture is heated to 180 “C with agitation, held at this temperature for 4 h, and then allowed to cool. Upon reaching ambient temperature, the reactor pressure (54 bar) is noted, a typical gas sample taken, and the excess gas vented. The deep-red liquid product (48.3 g) is analyzed by GLC and Karl Fischer titration. Analysis of typical liquid sample shows the presence of the following: 33.9 wt.% l-nonanol, 29.7 wt.% 2-methyloctanol, 6.1 wt.% 2ethylheptano1, 3.8 wt.% 1-nonanol, 1.6 wt.% branched Cg aldehydes, 9.1 wt.% n-octane, 1.9 wt.% octenes, 0.6 wt.% water. Analyses of typical gas samples show the presence of: 53 wt.% hydrogen, 26 wt.% carbon monoxide, 20 wt.% carbon dioxide. Estimated conversion of octene charge = 98%, estimated total yield of C, alcohols plus aldehydes = 72 mol%. Acknowledgement The author thanks Texaco Inc. for permission to publish this paper, Messrs. D. W. White, R. Gonzales and M. R. Swenson for experimental assistance and Mr. J. M. Schuster for the FTIR data.

77

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5 6 7 8

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Organometallics, 5 (1986) 724. 17 E. Roland and H. Vahrenkamp,

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