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Syngas reactions
Journal of Molecular
Catalysis,
47 (1988)
99 - 116
SYNGAS REACTIONS PART XIII. THE RUTHENIUM ‘MELT’-CATALYZED TERMINAL OLEFINS
99
OXONATION
OF
JOHN F. KNIFTON Texaco Chemical
Co., P.O. Box 15730, Austin,
(Received October 7,1987;
TX 78761 (U.S.A.)
accepted December 7, 1987)
Terminal olefins may be regioselectively hydroformylated to give 0x0 alcohols and aklehydes which are >99% linear (l/b ratio >lOO) through the use of N- and P-ligand-modified ruthenium ‘melt’ catalysis. Preferred catalyst precursors include ruthenium( IV) oxide hydrate and triruthenium dodecacarbonyl in combination with N- and P-ligands such as 2,2’-bipyridine, 2,2’-bipyrimidine, 1,2-bis(diphenylphosphino)ethane and bis(2-diphenylphosphinoethyl)phenylphosphine, dispersed in a low-melting quaternary phosphonium salt such as tetrabutylphosphonium bromide. ar-olefin hydroformylation to aldehyde, as well as subsequent hydrogenation to 0x0 alcohol, has been examined with reference to syngas composition, temperature, and olefin concentration as well as ruthenium catalyst composition and concentration. A mechanism involving association of the aolefin substrate with the N- and P-ligated ruthenium carbonyl, or hydrogen transfer to form an alkyl-Ru intermediate, has been proposed as ratedetermining steps under normal oxonation conditions. The critical importance of the Rus(CO),&L-L) cluster complexes (L-L, DIPHOS) has been confirmed through IR and 13CNMR.
Introduction 0x0 chemistry and processing continues to be a major topic of interest in the published literature [ 1 - 201. In a previous paper in this series, we described the hydroformylation of internal olefin substrates to give predominantly linear ‘0x0’ alcohols catalyzed by ruthenium ‘melt’ catalysts, where ruthenium carbonyl derivatives are dispersed in low-m.p. quaternary phosphonium salts [21]. The principal thrust of the new work described in this paper has been to demonstrate that highly linear 0x0 alcohols and aldehydes with linear-to-branched (l/b) ratios of >lOO may be readily prepared from terminal olefin feedstocks (eqn. 1) also using the concept of ruthenium ‘melt’ catalysis. 0 Elsevier Sequoia/Printed
in The Netherlands
100
RCH&!H&!HO +
RCH=CH* + CO/H2 -
RCHCHO AH3
HZ +
RCHZCH2CH20H +
(1)
RCHCH*OH A H3
Other objectives have been to: (a) optimize regioselectively to linear aldehyde/alcohols (b) maximize the yield of derived 0x0 products (c) understand the mode of ruthenium ‘melt’-catalyzed oxonation through reaction parameter studies, etc. Homogeneous ruthenium-catalyzed hydroformylation of olefins was patented more than 20 years ago [22 - 241. Wilkinson and coworkers [25, 261 described the use of several tertiary phosphine-ruthenium complexes in the catalytic hydroformylation of alkenes to aldehydes; a mechanism involving Ru(H),(CO), (PPh,) as the principal active catalytic species was suggested. Ruthenium-catalyzed hydroformylation exhibiting one of the highest selectivities for straightchain aldehydes (97 + 1%) has been reported by Laine [27]. Siiss-Fink finds the cluster anion [HRu,(CO),,]catalyzes a-olefin hydroformylation under mild conditions to give high yields of unbranched aldehyde [28, 291; isotope labelling studies provide indirect evidence for catalysis at intact clusters [30]. Other recent developments in ruthenium-catalyzed oxonation include the use of photochemical [ 311 and polymer-supported [32] catalysis. Our studies with internal olefin substrates [21, 331 showed the anionic ruthenium cluster, [HRu,(CO),,]-, to be the dominant metal carbonyl species in the reactant solutions. Mixed metal catalysis, particularly Ru-Co, allows the corresponding aldehydes to be the major product fraction; these reactant solutions showed the presence of both ruthenium carbonyl and [Co(CO),]- anionic species. Results The experimental data detailed infru are subdivided into ruthenium catalyst studies using different N- and P-ligand structures, and an examination of the effect of various reaction parameters. N-ligand effects
Table 1 deals with the production of predominantly linear alcohols and aldehydes (1-nonanol and l-nonanal) from a typical a-olefin stock, 1-octene, catalyzed by N-heterocyclic and tertiary amine-promoted ruthenium catalysts [33]. In Example 1, 1-nonanol is synthesized using 1:2 (CO/H,) syngas with the ruthenium(IV) oxide-2,2’-bipyridine (BIPY) couple dispersed in tetrabutylphosphonium bromide. Cgalcohol concentration in the crude liquid product is 79.6%, the linearity of this fraction is 86% and the estimated nonanol yield is 72 mol%.
RuOz-2,2 ‘-bipyridine RuOz-2,2’-bipyridine RuO? RuOz RuOz-l,lO-phenanthroline RuOz-2,3’-bipyridine RuOz-2,4’-bipyridine RuOz-2,2’-dipyridylamine RuOz-2,2’,2”tripyridine RuOx-2,2’-bipyrimidine Rua(CO)r2-2,2’-bipyrimidine Rua(C0)i~ *2,2’-bipyridine Ru(acac)s-2,2’-bipyridine Rus(CO)r2-2,2’-bipyridine Rua(CO)r-2,2’-bipyridine RuOz-pyridine RuOz-3,5-lutidine RuOz-2,6-lutidine RuOz-2,2’-biquinoline RuOz-2,4,6-tri(2-pyridyl)-s-triazine RuO~-N,N,N’,N’-tetramethylethylenediamine
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu,PBr Bu4PBr BudPI Bu,POAc Bu$Br Bu$Br Bu,PBr Bu$Br Bu$Br Bu$Br
Bu4PBr -
Reaction media
34.5 1.8 0.6 4.2
9.0
Octenes
9.1 11.7 33.5 12.3 11.4 16.4 22.4 8.4 12.0 5.8 5.1 11.3 12.0 5.2 5.2 0.1 0.1 17.4 13.5 7.5 13.0
Octane
0.1 0.2 0.4 0.9 6.8
0.3 0.3 0.1 10.6 10.3 0.6 0.1 4.2 0.1 30.9 4.3
0.2 0.1 0.3
4.5 0.2 5.3 0.2 0.2 0.2 0.3 0.3 2.0 3.6
0.2 0.1 1.7 1.5 0.1 8.7 6.4 0.3
0.2 68.7 37.4 38.2 50.7 55.7 47.9 38.5 42.5 40.2 52.2 57.2 44.9 43.5 23.5 44.8 40.8 47.3 40.3 42.4 43.1 48.2
Linear
Linear
Branchede
Nonanol
( %)c*d
Nonanal
Liquid product composition
aRun charge: Ru, 6.0 mmol; Ru/N, 1:2; BuJPBr, 10.0 g; 1-octene, 200 mmol. bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2), 4 h. CLiquid products analyzed by GLC and Karl Fisher titration. dProducts identified by GLC-MS, GLC-FTIR. e2-Methyloctanal, 2-ethylheptanal, 2-propylhexanal. f2-Methyloctanol, 2-ethylheptanol. sRun at 160 “C.
Catalyst precursor
effect of N-ligandsaqb
Ex.
1-Octene hydroformylation:
TABLE 1
10.9 8.6 22.1 29.1 18.9 22.1 28.6 7.9 14.0 9.4 3.6 7.5 16.9 2.4 9.0 24.7 25.0 26.3 29.3 14.3 13.6
Branchedf 2.0 4.0 1.3 0.5 0.6 0.6 0.3 2.2 2.1 0.4 0.1 1.3 0.9 3.5 0.6 0.3 0.4 0.2 0.7 2.2 1.6
Water
86 81 63 64 75 68 57 84 74 85 94s 86 72 91s 83g 62 65 61 59 75 78
Nonanol linearity (%)
102
In fact, predominantly linear nonyl alcohol syntheses are illustrated in Table 1, ex. 5-21, for various combinations of: (a) ruthenium precursors: e.g. RuOz, Rus(CO)iZ, Ru(acac)s (b) different tertiary amine promoters: e.g. 2,2’-bipyridine, l,lO-phenanthroline, 2,2’,2”tripyridine, 2,2’-bipyrimidine, N,N,N’,N’-tetramethylethylenediamine, 2,2’dipyridylamine, 2,3’-bipyridine, 2,4,6-tri( 2-pyridyl)-s-triazine (c) dispersed in various quaternary phosphonium salts: e.g. Bu,PBr, Bu,PI, Bu,POAc. Selectivity to linear l-nonanol of >80% and total nonanol yields of 72 mol%, are routinely achieved under the conditions of Table 1 with both the RuOz-2,2’-BIPY/Bu4PBr and Rus(C0)i2-2,2’-BIPY/Bu4PBr catalyst precursors. Other experiments in this series (see Table 1) serve to confirm the critical importance of all three catalyst components, i.e., the ruthenium source, the N-promoter and the quaternary phosphonium salt, in achieving the desired linearity and yield of 0x0 products [34]. Of particular note: (a) high alcohol product linearity (>80%) is achieved only in the presence of certain N-promoters (cf. ex. 1 and 4); (b) the absence of quaternary phosphonium salt invariably leads to lower levels of olefin conversion, lower total alcohol concentrations and yields, and proportionally more paraffinic byproduct (cfi ex. 1 and 2); (c) the absence of both tertiary amine and quaternary phosphonium salt also provides lower concentrations and yields of desired alcohol, lower selectivities to desired linear alcohol and higher concentrations of byproduct hydrocarbon (cf. ex. 1 and 3). Generally, to ensure high alcohol linearity in ruthenium-catalyzed cw-olefin oxonation, the N-promoter (L-L) should be a bidentate N-heterocyclic compound capable of forming chelate complexes with ruthenium [ 331. This class of amine is best illustrated by 2,2’-bipyridine (I, ex. 1 and 12) 2,2’dipyridylamine (II, ex. 8) and 2,2’-bipyrimidine (III, ex. 10 and 11). The importance of N-ligand chelation is exemplified by comparing ex. 1, 6 and 7; here the influence of bipyridine structure upon alcohol linearity shows that only the 2;2’-bipyridine (I) provides the desired >80% linearity. ex. 1 2,2’-bipyridine (I) nonanol linearity 86% ex. 1 2,3’-bipyridine (IV) nonanol linearity 68% ex. 7 2,4’-bipyridine (V) nonanol linearity 57%. The spectra of the RuOz-BIPY/Bu,PBr catalyst solutions (e.g. ex. 1) in the metal carbonyl region continue to be dominated by bands typical of [HRu~(CO)~J-~ (1959, 1990 and 2017 cm-‘) [35], but peaks at 1990, 2030 and 2073 cm-’ may be indicative also of the presence of known ruthenium carbonyl bipyridyl clusters [36, 371. Ruthenium carbonyl mononuclear complexes of 2,2’-bipyridine [ 38 - 421 appear less likely to be present in measurable quantities.
103
(2)
TABLE 2 1 -0ctene hydroformylation phosphino)alkane ligands
catalyzed
Ex. Ru :BIPY ratio a, b Total nonanol + nonanal (mmol) Nonanol linearity (W)
22 1:0.25 108.5
23 1:0.5 109.0
24 1:l 121.4
25 1:1.5 125.9
26 1:2 120.1
27 1:3 114.1
75.8
77.4
81.1
84.3
82.0
82.1
28 1 72.5
29
2 108.9
30 3 92.3
31 4 59.7
32 5 62.6
86.7
84.5
84.1
66.3
63.8
Ex. Ph2P(CH2),PPh2C*d, n = Total nonanol + nonanal (mmol) Nonanol linearity (%) aRun charge: Ru, 3.0 mmol, bOperating conditions: 1200 CRun charge: Ru, 6.0 mmol; dOperating conditions: 1200
by ruthenium-2,2’-bipyridine
and -bis(diphenyl-
BIPY, 0.75 - 9.0 mmol; Bu4PBr, 5.0 g; Cs-, 200 mmol. psi (CO/Hz, 1:2); 180 “C; 4 h. PhzP(CH2),PPh2, 6.0 mmol; BuJPBr, 10.0 g; Cs-, 200 mmol. psi (CO/Hz, 1:2); 180 ‘C; 4 h.
With regard to the preferred Ru-N stoichiometry, for a series of runs at different initial Ru-BIPY molar ratios (Table 2, ex. 22 - 27), the highest nonanal + nonanol yield, and the highest linearity of the nonanol product, are achieved with ratios of cu. 1:l - 1:1.5. Less 2,2’-bipyridine leads to lower yields of 0x0 product and lower linearity of the 0x0 alcohol fraction. Ruthenium:2,2’-bipyridine ratios of 1:2, or greater, appear to slightly suppress activity with no attendant improvement in l/b ratio. Since the more selective species are generated at Ru-BIPY ratios of 1 - 1.5, it is possible that two (or three) nitrogen donor atoms are bound to each ruthenium atom in the most effective catalyst precursor. In view of the spectral data described above, however, this preferred stoichiometry may in fact reflect only the equilibria of eqns. 3 and 4 - between the known ruthenium carbonyl clusters, [HRu,(CO),,]-, Rus(CO)i,,(BIPY) [36, 371 and their derivatives. Additional 2,2’-bipyridine would serve then only to
104
displace the remaining carbonyls leading possibly to the formation of species of different activity, e.g. (L-L)ZRuJ(CO)s-type complexes (eqn. (5)) [43]. The water-gas shift activity of the Rus(C0)i2--2,2’-bipyridine couple has recently been disclosed [44] by the same group in Finland. [HRu,(CO),,]Rus(CO),,
+ BIPY &
+ BIPY +
[HRu,(CO),(BIPY)]-
+ 2C0
Ru~(CO)~~(BIPY) + 2C0
Ru~(CO)~,,(BIPY) + BIPY +
Ru~(CO),(BIPY)~
(3) (4)
+ 2C0
(5)
P-ligand effects
A series of other novel ruthenium-Group 15 donor ligand chelate combinations have been found to provide ‘0x0’ alcohols with >80% linearity from typical cx-olefin stocks [ 451. The data in Table 3 illustrate the preparation of predominantly linear nonyl alcohols from CO/H2 plue l-octene catalyzed by different combinations of ruthenium precursor (e.g. RuOz, Ru(acac)g), phosphorus promoter and quaternary phosphonium Ru3(COh, salts (e.g. Bu,PBr, C16H33Bu3PBr). Selectivity to linear 1-nonanol of >80% is again achieved only with certain chelating bidentate or multidentate ligands (ex. 33 - 42), particularly: Phz PCHzPPhz Ph2P(CH2)2PPhZ Ph,P(CH,),PPh2 Ph,P(CH,),PPh2 CH3*C(CH,PPh2)s P(CH&H2PPhZ)3 PhP(CHZCH2PPhZ),
(ex. (ex. (ex. (ex. (ex. (ex. (ex.
33) 34) 35) 36) 40) 41) 42)
87% linearity 8 5% linearity 84% linearity 8 1% linearity 84% linearity 81% linearity 94% linearity
The ruthenium oxide-bis(2diphenylphosphinoethyl)phenylphosphine (TRIPHOS) couple provides the highest selectivity to linear aliphatic alkanol (94% l/b >lO) under these screening conditions (Table 3, ex. 42). This tridentate ligand combination has the disadvantages, however, of giving twophase liquid products and lower levels of olefin conversion than certain of its bidentate analogues. The importance of ligand chelation is reinforced in a third series of experiments, where RuOz is in combination with a series of arylphosphines of the general structure: Ph2P(CH2),PPh2. Run data are summarized in the lower half of Table 2, ex. 28 - 32. Productivity again is clearly maximized for the DIPHOS (1,2-bis(diphenylphosphino)ethane) ligand, known to form five-membered ring complexes with ruthenium carbonyls [25, 26, 46, 471. Similarly, nonanol linearity is acceptable for all Ru-PhzP(CH2),PPh2 combinations where n = 1, 2 or 3. Again it is these P-ligands that are most likely to form chelated intermediates. The Ru-DIPHOS reactant solutions are dominated by the Ru3(CO),,(DIPHOS) cluster complex (IR carbonyl stretches at 1970, 1983, 2004(s), 2035, 2066 cm-‘*, i3C NMR sharp triplet at 209.9 ppm at r.t.), in line with *Some Ru-DIPHOS
solutions also show VW hands at 1914 and 1936 cm-‘.
36.9 30.1 28.2 19.0 13.9 18.4 5.3 61.7 36.2 91.0 43.3 87.3 26.8 1.9 4.3
Octenes
Liquid
dTwo-phase
liquid
product.
200 mmol.
16.6 10.8 17.4 10.5 9.8 38.9 46.1 6.7 10.9 2.8 17 9.6 6.1 16.2 14.9 0.3
2.4 0.7 0.4 2.8 2.3 0.6
4.5 1.7 0.6 4.1 4.3 0.7 0.7 0.9 0.4 1.0 4.7 0.9 5.5 1.0 0.4 0.3 0.7 0.5 3.1 0.1 0.4
Linear
Branched
Linear 29.9 40.9 42.4 38.0 38.1 30.4 28.6 22.0 38.2 1.9 37.5 0.2 29.4 45.2 42.1
Nonanol
(%)
Nonanal
composition
Octane
product
aRun charge: Ru, 6.0 mmol; Ru/P, 1:2; BuaPBr, 10.0 g; l-octene, bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2); 4 h. CRu/P = 1:3.
Bu4PBr Bu4PBr Bu4PBr Bu4PBr
43 44 45 46
Ru02-[(CH3)2NPh],P RuOa-[PhaPCsH4]2Fe Ru02-PPh3 Ru02-PBu3
Bu4PBr
Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Cr6HssBusPBr Bu4PBr Bu4PBr
Reaction media
of P-ligandsa+b
42
RuOa-PhzPCHzPPhz RuO*-PhzP(CHa)aPPh2 Ru02-PhzP(CH2)sPPh2 Ru02-Ph2P( CH2)4PPh2 RuOa-Ph2P(CH2)sPPh2 Ru~(CO~~-P~~P(CH~)~PP~~ Ru(acac)3-Ph2P(CH2)4PPh2 Ru02-CH3C(CH2PPh2)a Ru02-P(CH2CH2PPh2)3
effect
33 34 35 36 31 38 39 40 41
precursor
hydroformylation:
Catalyst
3
Ex.
l-Octene
TABLE
4.6 7.5 8.0 19.3 21.6 8.4 6.9 4.2 8.7 0.4 2.2 1.0 8.0 30.4 27.5
Branched 1.4 1.3 1.2 1.1 1.3 0.2 1.0 1.3 1.2 0.1 2.7 0.1 2.1 0.4 0.5
Water
79 60 60
94
87 85 84 66 64 78 81 84 81
d
1
Nonanol linearity (%)
106
analogous data reported by Cotton and Hanson [48] for decacarbonyl[bis(diphenylphosphino)methane]triruthenium. Spectral data indicate that the equilibrium of eqn. (6) is reached rapidly. Ruthenium-DIPHOS solutions containing excess chelate (e.g. Ru: DIPHOS 1:5) are catalytically inactive, and oxonation invariably leads to the precipitation of most of the ruthenium as mononuclear Ru(CO),(DIPHOS)type [25] complexes (eqn. (7)). The importance of amine or phosphine basicity [49 - 521 appears minimal (e.g. compare ex. 45 and 46) with regard to its effect on either the rate or regioselectivity. Ru,(C0)i2
+ DIPHOS +
Rus(CO),,-,(DIPHOS) + 2C0
Ru~(CO)~,,(DIPHOS) + BDIPHOS ti
3Ru(CO)s(DIPHOS)
(6) + CO
(7)
Propylene oxonation The highest level of a-olefin regioselectivity has been achieved in this program using the triruthenium dodecacarbonyl-2,2’-bipyrimidine (III) couple dispersed in tetrabutylphosphonium bromide. Under standard screening conditions [33, 341, propylene is oxonated to n-butanol in 89% selectivity with the butanol linearity being >99% by GLC (l/b ratio >lOO, see Table 4, ex. 47). Total butanol plus butanal selectivity is estimated to be 96%. Butanol linearities of >99% have also been obtained when employing the same catalyst couple in continuous processing [ 531. The ruthenium dodecacarbonyl-2,2’-bipyridine couple, solubilized in phosphonium quat. plus ldodecanol, generates butanol at a rate of 23 mol (g atom Ru)-’ h-i (ex. 49). In each of these runs, ex. 47 - 49, the principal byproducts are 2ethylhexanal and 2ethylhexanol. Effect of operating parameters For one of the more effective ruthenium ‘melt’ catalysts, the ruthenium(IV)oxide-2,2’-bipyridine (BIPY)/tetrabutylphosphonium bromide, performance - particularly the yields of alcohol/aldehyde 0x0 products and the linearity of the 0x0 alcohol/aldehyde generated from typical a-olefin stocks has been examined as a function of certain critical operating parameters, particularly: (1) the initial Ru:BIPY ratio (2) ruthenium concentration (3) operating temperature (4) syngas pressure (5) hydrogen and carbon monoxide partial pressures. For one standard synthesis, l-octene to nonanol/nonanal, the linearity of these 0x0 products generated by this procedure has again been raised to 99% (l/b N loo), from the data in Tables 1 - 3, through careful modification of the hydroformylation conditions.
R~a(C0)~2-2,2’-hipyrimidine Rua(CO)i2-2,2’-bipyridine Rua(CO)ia-2,2’-bipyridine
47 48 49
Bu4PBrb*e Bu4PBrC*e Bu4PBr/C12HzsOHd*f
Reaction media
Wonfirmed by GLC-MS; GLC-FTIR. bRun charge: Ru, 6.0 mmol; 2,2’-BIPY, 6.0 mmol; Bu4PBr, 10.0 CRun charge: Ru, 6.0 mmol; 2,2’-BIPY, 6.0 mmol; Bu.+PBr, 10.0 dRun charge: Ru, 3.0 mmol; 2,2’-BIPY, 3.0 mmol; BudPBr, 10.0 eTypical operating conditions: 1200 psi (CO/Hz, 1:2), 160 “C, 4 ‘Operating conditions: 1800 psi (CO/Hz, 1:2) constant pressure.
Catalyst precursor
Ex.
Propylene hydroformylation
TABLE 4
1.2 4.3
89.5 53.4 5.3 5.6 0.9
Branched 0.2 2.6 6.2
Water
g; propylene, 400 mmol. g; propylene, 400 mmol. g; 1-dodecanol, 15.7 g; propylene, 400 mmol. h.
6.4 11.4 36.7
Linear
Linear
Branched
ButanoV’
(%)
Butanala
Liquid product composition
90 91
Butanal linearity (%)
>99 91 85
Butanol linearity (%)
108
NONANOL/
NON ANAL I
NONANOLI NONANAL/ OCTANE ‘RODUCTNITY (mmols
LINEARITY (% )
1
/ /8’ XI
,
9, 100
‘0/ /
I20
\ 140 OPERATING
160 TEMP
(‘C
0 \
n
160
200
)
Fig. 1. Effect of operating temperature upon 0x0 activity, 0, total nonanol; ‘J, total nonanal; A, nonanol linearity; V, nonanal linearity; X, total octane. Reaction charge: Ru, 6.0 mmol; Ru:BIPY, l:l; BusPBr, 10.0 g; CS-, 200 mmol; operating conditions: 1200 psi (CO/HI = 1:2); 4 h.
Varying the reaction temperature has probably the most dramatic influence upon Ru-melt catalyst performance (see Fig. 1). At 200 “C, the C9-0x0 product is almost exclusively nonanol, and octene conversion exceeds 98%. By contrast, at 140 “C or less, nonanals are the predominant products. The linearity of both the alcohol and aldehyde product fractions increases significantly with a lowering of the operating temperature from 200 to 100 “C. Below 140 “C, both the nonanol and nonanal products show linearities of >97% (l/b 230). In one run, at 100 “C, the nonanal linearity is 99% (l/b -100, see Fig. 1). To some degree, the loss of linearity at higher temperatures can be compensated for by the addition of excess N-ligand. At 200 “C, for example, the use of a lo-fold excess of BIPY raises the nonanol linearity percentage, from 65% (see Fig. 1) to 76%, and interestingly enough, in contrast to Rh oxonation [ll], this improvement is achieved without a marked loss in hydroformylation rate.
109
Wilkinson and coworkers report the optimum temperature for ruthenium homogeneous hydroformylation to be cc. 120 “C [25]. By contrast, ruthenium ‘melt’ 0x0 catalysts routinely show a steady rise in alcohol productivity in the 100 - 200 “C temperature range (see @ data points, Fig. 1). Only above 200 “C, with 2:l Hz/CO syngas, do we see evidence of catalyst breakdown, and the formation of black insoluble residues. Aldehyde production, on the other hand, appears to be maximized at temperatures of ca. 130 “C for the ruthenium(IV) oxide-2,2’-bipyridinel Bu4PBr precursor. Below this temperature, the rates of hydroformylation are slow. Above 140 “C, subsequent aldehyde reduction to alkanol becomes increasingly important. Increases in CO partial pressure, at constant initial hydrogen pressure, lead to a substantial decrease in nonanol productivity (see Fig. 2) and a significant (El-fold) improvement in nonanal yield. However, the size, and even direction, of this aldehyde productivity change is particularly sensitive to the choice of operating temperature - selected here in Fig. 2 to be 180 “C. For temperatures below 140 “C, e.g. 120 “C, where aldehydes generally comprise the majority (>90%) of the total 0x0 product, the effect of increasing CO 150
IO0 NONANOLI NONANALI OCTANE ;;~LR$TIVITY
400
1200
600 CO
PARTIAL
lb00 PRESSURE
2000
2400
(psi)
Fig. 2. Effect of CO partial pressure upon 0x0 activity. Symbols as per Fig. 1, 0, total
nonanol + nonanal; operating conditions: 800 psi Hz; 180 “C; 4 h.
110
partial pressure is a moderate drop in total nonanal productivity (90 mmol (see Fig. 1) to 58 mmol, same CO partial pressure range as Fig. 2). 0x0 alcohol/aldehyde linearity figures and the formation of hydrocarbon byproduct exhibit only a modest sensitivity to CO partial pressure (e.g. Fig. 2), particularly where the operating temperature is <140 “C. Changes in hydrogen partial pressure bring about an interesting maxima in alcohol productivity (see Fig. 3). At high Hz partial pressure, where in this experimental series the CO/H2 molar ratio is in the region of l/5, the alcohol productivity drops off quite dramatically, as the level of competing olefin hydrogenation rises. Alcohol linearity also drops - on the average of cc. 10% - over the [H,] range studied, at this temperature. The significance of these findings is rationalized in the following Discussion Section. At 120 “c, aldehyde productivity is relatively insensitive to changes in H2 partial pressure (91- 83 mmol CsH,,CHO, Hz pressure range as in Fig. 3). Raising the total syngas pressure from 600 to 3000 psi (see Fig. 4) unexpectedly also leads to a dramatic decrease in nonanol yields - from 53 to 24% - and this is accompanied by a substantial increase in nonanal formation (3 - 34%) under these selected conditions (i.e. operating tempera150
3-
100 NONANOL LINEARITY PI. I
NONANOLI NONANAL/ OCTANE PRODUCTIVITY lmmolr) Sl,-
800 H2 PARTIAL
I200 PRESSURE
1600
2000
(psi)
Fig. 3. Effect of H2 partial pressure upon 0x0 activity. Symbols and reaction charge as per Fig. 1; operating conditions: 400 psi CO; 180 “C; 4 h.
111
NONINOL LINEARITY w.
I
1000
2000 TOTAL
PRESSURE
(psi
3000 I
Fig. 4. Effect of total pressure upon 0x0 activity. Symbols and reaction charge as per Fig. 1; operating conditions: CO/Hz, 1:2; 160 “C; 4 h.
ture 160 “C, syngas composition l/2). Similar trends in aldehyde/alcohol yields are replicated at higher temperatures. At 120 “C, however, where Cg aldehydes are the almost exclusive 0x0 product, the productivity of nonanals is relatively insensitive to total syngas pressure (82 - 90 mmol, same pressure range as Fig. 4). There is an approximately linear first-order dependence of aldehyde productivity upon the quantity of l-octene charged, under the conditions of Table 5. Similarly, both the alcohol and total Cg aldehyde + alcohol productivities increase with the rise in olefin charge (ex. 50 - 54). Under the same conditions, even a modest change in [Ru] leads to a corresponding substantial increase in alkanol productivity. Total nonanol f nonanal remains unchanged, consequently the aldehyde/alcohol molar ratio drops precipitously, from cu. 1:l to 1:37, as the ruthenium charge increases from 1.5 to 9.0 mmol (see Table 5, ex. 51,55 - 57). Once again the choice of experimental conditions, particularly the selected operating temperature, pressure and syngas composition, will affect the data trends in Table 5. At 120 “C, for example, where the rate of alcohol formation is hardly measur-
112 TABLE 5 1-Octene hydroformylation:
effect of [ Ru] and [Cs-]a.b
Ex. Ru (mmol) 1-Octene (mmol) Total nonanol (mmol) Total nonanal (mmol) Nonanol + nonanal (mmol) Nonanol linearity (W)
50 1.5 100 30.2 30.8 61.0 83.7
51 1.5 200 59.4 61.9 121.3 83.0
52 1.5 300 67.1 87.2 154.3 84.0
53 1.5 400 70.6 134.2 204.9 81.5
54 1.5 600 84.9 202.1 287.0 77.9
55 3.0 200 74.8 46.6 121.4 77.3
56 6.0 200 101.5 24.1 125.6 75.5
57 9.0 200 122.3 3.3 125.6 77.7
aRun charge: Ru/BIPY, l:l, Bu4PBr, 5.0 g. bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2), 4 h.
able, nononal productivity is fractional order in ruthenium over the same Ru concentration range. Discussion The ruthenium-ligand-stabilized ‘melt’ catalysts illustrated in Tables 1 - 4 and Fig. 1 can clearly catalyze both basic oxonation reactions - hydroformylation of cx-olefin substrates to predominantly linear 0x0 aldehydes, and subsequent reduction of these aldehydes to the corresponding alcohol. Our data [21] are consistent with a stepwise, two-step mode to alcohol formation (Scheme l), rather than invoking a common intermediate partitioning RCH=CH2 f
I
-c
CRU~(CO)~(L-L)(OCH~CH*CH~R]-
Y
0
Scheme 1. Proposed mechanism for 0x0 alcohol and aldehyde formation via ligandmodified ruthenium ‘melt’ catalysis. L-L = bidentate N- or P-ligand such as 2,2’-bipyridine or 1,2-bis(diphenylphosphino)ethane.
113
between alcohol and aldehyde products, The choice of dominant product be it alcohol or aldehyde (eqn. (1)) - is controlled primarily by the operating temperature (Fig. 1). In this regard, the Ru ‘melt’ catalysis parallels cobalt hydroformylation processes [ 171. The apparent higher activation energy for the ruthenium ‘melt’-catalyzed aldehyde reduction, ensures that at operating temperatures of <140 “C, the primary product is the 0x0 aldehyde, while at temperatures of >180 “c, 0x0 alcohols are generally favored. Initial [Ru] and olefin concentration factors can also affect the aldehyde/alcohol balance (see Table 5), however, as can the syngas composition (Figs. 2 - 4) and, to a lesser degree, the nature of the coordinated ligands (Tables 1 and 3). The second commercially critical parameter by which this 0x0 processing must be judged - the linearity of the final aldehyde/alcohol products has been raised in this study to >99% (l/b >lOO) by careful control of operating conditions (Table 4 and Fig. 1). The primary influencing factors here are the nature of the N- and P-chelating ligand structures (Tables 1 and 3) and the ability of these ligands to form stable complexes with ruthenium under 0x0 conditions (e.g. eqns. (3) - (7)). Temperature (Fig. 1) and initial ruthenium-ligand mole ratio (Table 2) also play a role. Generally, the l/b ratio of the 0x0 alcohol products are comparable to that of the intermediate aldehyde (see Fig. l), and small differences likely reflect GLC analytical errors. Total alcohol yield is determined mainly by syngas composition and pressure (Figs. 2 - 4). While aldehyde hydrogenation ability of the Ru catalyst decreases with increasing CO partial pressure at 180 “C (Fig. 2), increases in H, partial pressure, by contrast, increase competing olefin reduction (Fig. 3). Because the aldehyde reduction rate (steps 4 and 5, Scheme 1) is the more sensitive to CO/H2 partial pressure changes (see Figs. 2 and 3, data trends 0, B versus X), increases in total CO/H2 gas pressure at this temperature have the net effect of raising aldehyde yield at the expense of alcohol (Fig. 4). Oxonation to aldehyde is also influenced by CO partial pressure (see Results Section) at 120 “C. In fact, the trends evident in Figs. 2 - 4 suggest that (a) a number of the critical steps in this oxonation (Scheme 1) have similar rates, and (b) there are complex equilibria in these catalyst solutions involving addition/displacement of CO and Group 15 ligands bonded to ruthenium (e.g. eqns. (3) through (7)). Because Hz and CO partial pressures only modestly influence the total oxonation activity (nonanal + nonanol, e.g. 0 data points, Fig. 2) at 180 “C, neither oxidative addition of Hz nor addition of CO are likely to be rate determining under these particular conditions. The ratedetermining step for aldehyde formation is most probably association of ligated Ru complex with the 1-octene reactant, or hydride transfer to coordinated alkene to form an alkyl-ruthenium cluster [ 541 (step 1, Scheme 1). This is also consistent with aldehyde productivity at 120 “C being relatively insensitive to Hz and syngas pressures (see Results). On the other hand, the marked drop in alcohol/aldehyde ratio at higher CO partial pressures and 180 “C (Fig. 2) we believe due to the formation of
114
coordinatively saturated, carbonyl-rich ruthenium intermediates that do not allow facile oxidative addition of Hz and therefore result in a lowering of the ability to form/protonate the alkoxy-ruthenium intermediates (steps 4 and 5) to alcohol. The spectral identification of these species remains under study. Increases in alcohol yield with increasing Hz partial pressure (Fig. 3) accompanied by a decline in alcohol yield at higher Hz partial pressures may be rationalized in terms of competing rates of intermediate aldehyde hydrogenation to alcohol, uersus the rate of olefin reduction to hydrocarbon (steps 4 and 5 versus 1A in Scheme 1). Aldehyde reduction to alcohol (step 5) becomes increasingly important as the Hz partial pressure rises to cu. 1200 psi. Beyond 1200 psi, however, the rate of competing &olefin reduction (1A) starts to dominate, significantly lowering the available quantities of a-olefin for oxonation. A shift in the linear alkyl-ruthenium uersus branched alkyl-ruthenium equilibria would account for the drop in 1:b ratio in Fig. 3. The rate at which this equilibria is established is known to be fast, relative to oxonation, from our earlier work with internal olefin substrates
WI.
Step 1 (Scheme 1) being rate determining over the 120 - 180 “C temperature range is also in line with the apparent first-order dependence upon olefin charge (see Table 5). The insensitivity of total nonanal + nonanol productivity to [Ru] at 180 “C is, however, less easy to rationalize; a fractional (l/3) order might be expected here, and indeed a fractional order at 120 “C is evident. Likely there is a change in rate-limiting steps over this temperature range, but further work will be needed to clarify this point. On the other hand, conversion of aldehyde to alcohol is very sensitive to [Ru] and it is this sensitivity that so dramatically changes the aldehyde-toalcohol ratio in Table 5, ex. 51,55 - 57. In conclusion, we have demonstrated that highly linear alkanols and alkanals can be readily generated through regioselective a-olefin oxonation with l&and-modified ruthenium ‘melt’ catalysis. While all the interrelationships linking catalyst structure and the various operating parameters are not yet fully understood (particularly in a quantitative sense), the data presented in this paper do allow the design of high yield syntheses of either the desired 0x0 aldehyde or alkanol using essentially the same classes of ruthenium ‘melt’ catalysts. Experimental All syntheses were conducted batchwise in pressurized reactors under carefully controlled temperature/pressure conditions. The ruthenium compounds, N-heterocyclics, tertiary phosphines and quatemary phosphonium salts were purchased from outside suppliers. Synthesis gas was purchased in various CO/H? proportions from Big Three Industries. Terminal olefin stocks 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
115
were isolated by fractional distillation in vacua, and identified by the same analytical techniques. GLC analyses were conducted using an 8 ft 10% Carbowax 20M column on Chromasorb-W high performance support, programmed from 75 to 250 “C at 8 “C min-' . FTIR spectral measurements were made using a Digilab FTS 15C instrument.
Typical oxona tion syntheses Ruthenium(IV) oxide, hydrate (1.146 g, 6.0 mmol) and 2,2’-bipyridine (0.937 g, 6.0 mmol) are dispersed in tetrabutylphosphonium bromide (10.0 g, 29.5 mmol) and diluted with l-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/H2 and pressured to 1200 psig with CO/H, (1:2). The mixture is heated to 120 “C with agitation, held at temperature for 4 h, and then allowed to cool. Upon reaching ambient temperature, the reactor pressure (1075 psi) is noted, a typical gas sample taken, and the excess gas vented. The deep-red liquid product (38.0 g) is analyzed by GLC and Karl Fisher titration. Analysis of the typical liquid sample shows the presence of the following: 49.1 wt.% nonanal, 1.2 wt.% 2-methyloctanal, 2.8 wt.% nonanol, 4.5 wt.% octane, 37.3 wt.% octenes, 5.1 wt.% water. Analyses of typical gas samples show the presence of: 69.3% hydrogen, 30.5% carbon monoxide, 0.3% carbon dioxide and98%. 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. References
6 7 8 9 10 11
See for example: 0x0 AZcohoZs, S.R.I. International Report No. 21C, April 1986. PERP Topical Reports, Chem Systems, Vol. 2,1986, p. 1. 0x0 Alcohols, Chem Systems Report #77-4, May 1978. B. Cornils, R. Payer and K. C. Traenckner, Hydrocarbon Process., June (1975) 83. B. A. Murrer and M. J. H. Russel, Royal Sot. Chem., Specialist Periodic Report Catalysis, 6 (1983) 169. U.S. Pat. 3 917 661 (1975) to R. L. Pruett and J. A. Smith. 0. R. Hughes and J. D. Unruh, J. Mol. Catal., 12 (1981) 71. M. Matsumato and M. Tamura, J. Mol. Catal., 19 (1983) 365. U.S. Pat. 3 239 569 (1966) to L. H. Slaugh and R. D. Mullineaux. F. E. Paulik, Catal. Rev., 6 (1972) 49. A. A. Oswald, D. E. Hendriksen, R. V. Kastrup and J. S. Merola, Am. Chem. Sot. Meeting, March 28,1982, ACS Petroleum Division Reprints, Vol. 27, p. 292.
116 12 13 14 15 16 17 18 19 20
A. M. Trzeciak and J. J. Ziolkowski, J. Mol. Catal., 34 (1986) 213. A. Fusi, E. Cesarotti and R. Ugo, J. Mol. Catal., 10 (1981) 213. R. A. Dubois and P. E. Garrou, Organometallics, 5 (1986) 466. C. Botteghi, R. Ganzerla, M. Lenarda and G. Moretti, J. Mol. Catal., 40 (1987) 129. A. Scrivanti, A. Berton, L. Toniolo and C. Botteghi, J. Organometall. Chem., 314 (1986) 369. M. Orchin,Acc. Chem. Res., 14 (1981) 259. P. Parrinello, R. Deschenaux and J. K. Stille, J. Org. Chem., 51 (1986) 4189. P. Escaffre, A. Thorez and P. Kalck, J. Chem. Sot., Chem. Commun., (1987) 146. W. R. Jackson, P. Perlmutter and G. H. Suh, J. Chem. Sot., Chem. Commun., (1987)
724. 21 22 23 24 25 26
J. F. Knifton,
J. Mol. Catal., 43 (1987) 65. U.S. Pat. 3 239 566 (1966) to L. H. Slaugh and R. D. Mullineaux. U.K. Pat. 999 461 (1965) to G. F. Cox and G. H. Whitfield. U.K. Pat. 966 482 (1964) to P. Smith and H. H. Jager. R. A. Sanchez-Delgado, J. S. Bradley and G. Wilkinson, J. Chem. SOC., Dalton
Trans.,
(1976) 399. K. Kurter, D. Ribola,
27 28 29 20 31 32 33 34 35
R. A. Jones, D. J. Cole-Hamilton, and G. Wilkinson, J. Chem. Trans., (1980) 55. R. M. Laine, J. Am. Chem. Sot., 100 (1978) 6451. G. Siiss-Fink, J. Organometall. Chem., 193 (1980) C20. G. S&s-Fink and J. Reiner, J. Mol. CafaZ., 16 (1982) 231. G. Siiss-Fink and G. Herman, J. Chem. Sot., Chem. Commun., (1985) 735. E. M. Gordon and R. Eisenberg, J. Organometall. Chem., 306 (1986) C53. C. U. Pittman and G. M. Wilemon, J. Org. Chem., 46 (1981) 1901. U.S. Pat. 4 451 679 (1984) to J. F. Knifton, J. J. Lin, R. A. Grigsby and W. H. Brader. U.S. Pat. 4 469 895 (1984) to J. F. Knifton and R. A. Grigsby. B. J. G. Johnson, J. Lewis, P. R. Raithby and 0. Siiss, J. Chem. Sot., Dalton Trans.
36
(1979) 1356. See: M. I. Bruce,
Sot.,
Dalton
J. Organometall. 37 38
T. Venalainen, (1985) 1348. See for example:
M. G. Humphrey, M. R. Snow, E. R. T. Tiekink 314 (1986) 311. J. Pursiainen and T. P. Pakkanen, J. Chem. Sot.,
and R. C. Wallas,
Chem.,
Chem. Commun.,
D. Choudhury, R. F. Jones, G. Smith and D. J. Cole-Hamilton, Trans., (1982) 1143 and references therein. J. M. Kelly and J. G. Vos,Angew. Chem. Znt. Ed. Engl., 21 (1982) 628. K. Tanaka, M. Morimoto and T. Tanaka, Chem. Lett. (1983) 901. D. S. C. Black, G. D. Deacon and N. C. Thomas, Aust. J. Chem., 35 (1982) 2445. H. Ishida, K. Tanaka, M. Morimoto and T. Tanaka, Organometallics, 5 (1986) 724. W. R. Cullen and D. A. Harbourne, Znorg. Chem., 9 (1970) 839. T. Venalainen, T. A. Pakkanen, T. T. Pakkanen and E. Iiskola, J. Organometall. Chem.,
J. Chem. Sot. Dalton 39 40 41 42 43 44 45 46
314 (1986) C49. U.S. Pat. 4 45Z 680 (1984) M. R. Churchill,
to J. F. Knifton. R. A. Lashewyez, J. S. Shapley
and S. I. Richter,
Znorg. Chem.,
19
(1980) 1277. 47 C. W. Jung and P. E. Garrou, 48 49 50 51 52 53 54
Organometallics, 1 (1982) 658. F. A. Cotton and B. E. Hanson, Znorg. Chem., 16 (1977) 3369. T. AIlman and R. G. Goel, Can. J. Chem., 60 (1982) 716. J. Halpern and P. F. Phelan, J. Am. Chem. Sot., 94 (1972) 1881. R. Angelici and M. D. Malone, Znorg. Chem., 6 (1967) 1731. R. P. Stewart and P. M. Treichel, Znorg. Chem., 7 (1968) 1942. J. F. Knifton, R. A. Grigsby and R. G. Duranleau, unpublished data. D. Mani, H. T. Schacht, A. Powell and H. Vahrenkamp, Organometallics, 1360.
6 (1987)
Catalysis,
47 (1988)
99 - 116
SYNGAS REACTIONS PART XIII. THE RUTHENIUM ‘MELT’-CATALYZED TERMINAL OLEFINS
99
OXONATION
OF
JOHN F. KNIFTON Texaco Chemical
Co., P.O. Box 15730, Austin,
(Received October 7,1987;
TX 78761 (U.S.A.)
accepted December 7, 1987)
Terminal olefins may be regioselectively hydroformylated to give 0x0 alcohols and aklehydes which are >99% linear (l/b ratio >lOO) through the use of N- and P-ligand-modified ruthenium ‘melt’ catalysis. Preferred catalyst precursors include ruthenium( IV) oxide hydrate and triruthenium dodecacarbonyl in combination with N- and P-ligands such as 2,2’-bipyridine, 2,2’-bipyrimidine, 1,2-bis(diphenylphosphino)ethane and bis(2-diphenylphosphinoethyl)phenylphosphine, dispersed in a low-melting quaternary phosphonium salt such as tetrabutylphosphonium bromide. ar-olefin hydroformylation to aldehyde, as well as subsequent hydrogenation to 0x0 alcohol, has been examined with reference to syngas composition, temperature, and olefin concentration as well as ruthenium catalyst composition and concentration. A mechanism involving association of the aolefin substrate with the N- and P-ligated ruthenium carbonyl, or hydrogen transfer to form an alkyl-Ru intermediate, has been proposed as ratedetermining steps under normal oxonation conditions. The critical importance of the Rus(CO),&L-L) cluster complexes (L-L, DIPHOS) has been confirmed through IR and 13CNMR.
Introduction 0x0 chemistry and processing continues to be a major topic of interest in the published literature [ 1 - 201. In a previous paper in this series, we described the hydroformylation of internal olefin substrates to give predominantly linear ‘0x0’ alcohols catalyzed by ruthenium ‘melt’ catalysts, where ruthenium carbonyl derivatives are dispersed in low-m.p. quaternary phosphonium salts [21]. The principal thrust of the new work described in this paper has been to demonstrate that highly linear 0x0 alcohols and aldehydes with linear-to-branched (l/b) ratios of >lOO may be readily prepared from terminal olefin feedstocks (eqn. 1) also using the concept of ruthenium ‘melt’ catalysis. 0 Elsevier Sequoia/Printed
in The Netherlands
100
RCH&!H&!HO +
RCH=CH* + CO/H2 -
RCHCHO AH3
HZ +
RCHZCH2CH20H +
(1)
RCHCH*OH A H3
Other objectives have been to: (a) optimize regioselectively to linear aldehyde/alcohols (b) maximize the yield of derived 0x0 products (c) understand the mode of ruthenium ‘melt’-catalyzed oxonation through reaction parameter studies, etc. Homogeneous ruthenium-catalyzed hydroformylation of olefins was patented more than 20 years ago [22 - 241. Wilkinson and coworkers [25, 261 described the use of several tertiary phosphine-ruthenium complexes in the catalytic hydroformylation of alkenes to aldehydes; a mechanism involving Ru(H),(CO), (PPh,) as the principal active catalytic species was suggested. Ruthenium-catalyzed hydroformylation exhibiting one of the highest selectivities for straightchain aldehydes (97 + 1%) has been reported by Laine [27]. Siiss-Fink finds the cluster anion [HRu,(CO),,]catalyzes a-olefin hydroformylation under mild conditions to give high yields of unbranched aldehyde [28, 291; isotope labelling studies provide indirect evidence for catalysis at intact clusters [30]. Other recent developments in ruthenium-catalyzed oxonation include the use of photochemical [ 311 and polymer-supported [32] catalysis. Our studies with internal olefin substrates [21, 331 showed the anionic ruthenium cluster, [HRu,(CO),,]-, to be the dominant metal carbonyl species in the reactant solutions. Mixed metal catalysis, particularly Ru-Co, allows the corresponding aldehydes to be the major product fraction; these reactant solutions showed the presence of both ruthenium carbonyl and [Co(CO),]- anionic species. Results The experimental data detailed infru are subdivided into ruthenium catalyst studies using different N- and P-ligand structures, and an examination of the effect of various reaction parameters. N-ligand effects
Table 1 deals with the production of predominantly linear alcohols and aldehydes (1-nonanol and l-nonanal) from a typical a-olefin stock, 1-octene, catalyzed by N-heterocyclic and tertiary amine-promoted ruthenium catalysts [33]. In Example 1, 1-nonanol is synthesized using 1:2 (CO/H,) syngas with the ruthenium(IV) oxide-2,2’-bipyridine (BIPY) couple dispersed in tetrabutylphosphonium bromide. Cgalcohol concentration in the crude liquid product is 79.6%, the linearity of this fraction is 86% and the estimated nonanol yield is 72 mol%.
RuOz-2,2 ‘-bipyridine RuOz-2,2’-bipyridine RuO? RuOz RuOz-l,lO-phenanthroline RuOz-2,3’-bipyridine RuOz-2,4’-bipyridine RuOz-2,2’-dipyridylamine RuOz-2,2’,2”tripyridine RuOx-2,2’-bipyrimidine Rua(CO)r2-2,2’-bipyrimidine Rua(C0)i~ *2,2’-bipyridine Ru(acac)s-2,2’-bipyridine Rus(CO)r2-2,2’-bipyridine Rua(CO)r-2,2’-bipyridine RuOz-pyridine RuOz-3,5-lutidine RuOz-2,6-lutidine RuOz-2,2’-biquinoline RuOz-2,4,6-tri(2-pyridyl)-s-triazine RuO~-N,N,N’,N’-tetramethylethylenediamine
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu,PBr Bu4PBr BudPI Bu,POAc Bu$Br Bu$Br Bu,PBr Bu$Br Bu$Br Bu$Br
Bu4PBr -
Reaction media
34.5 1.8 0.6 4.2
9.0
Octenes
9.1 11.7 33.5 12.3 11.4 16.4 22.4 8.4 12.0 5.8 5.1 11.3 12.0 5.2 5.2 0.1 0.1 17.4 13.5 7.5 13.0
Octane
0.1 0.2 0.4 0.9 6.8
0.3 0.3 0.1 10.6 10.3 0.6 0.1 4.2 0.1 30.9 4.3
0.2 0.1 0.3
4.5 0.2 5.3 0.2 0.2 0.2 0.3 0.3 2.0 3.6
0.2 0.1 1.7 1.5 0.1 8.7 6.4 0.3
0.2 68.7 37.4 38.2 50.7 55.7 47.9 38.5 42.5 40.2 52.2 57.2 44.9 43.5 23.5 44.8 40.8 47.3 40.3 42.4 43.1 48.2
Linear
Linear
Branchede
Nonanol
( %)c*d
Nonanal
Liquid product composition
aRun charge: Ru, 6.0 mmol; Ru/N, 1:2; BuJPBr, 10.0 g; 1-octene, 200 mmol. bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2), 4 h. CLiquid products analyzed by GLC and Karl Fisher titration. dProducts identified by GLC-MS, GLC-FTIR. e2-Methyloctanal, 2-ethylheptanal, 2-propylhexanal. f2-Methyloctanol, 2-ethylheptanol. sRun at 160 “C.
Catalyst precursor
effect of N-ligandsaqb
Ex.
1-Octene hydroformylation:
TABLE 1
10.9 8.6 22.1 29.1 18.9 22.1 28.6 7.9 14.0 9.4 3.6 7.5 16.9 2.4 9.0 24.7 25.0 26.3 29.3 14.3 13.6
Branchedf 2.0 4.0 1.3 0.5 0.6 0.6 0.3 2.2 2.1 0.4 0.1 1.3 0.9 3.5 0.6 0.3 0.4 0.2 0.7 2.2 1.6
Water
86 81 63 64 75 68 57 84 74 85 94s 86 72 91s 83g 62 65 61 59 75 78
Nonanol linearity (%)
102
In fact, predominantly linear nonyl alcohol syntheses are illustrated in Table 1, ex. 5-21, for various combinations of: (a) ruthenium precursors: e.g. RuOz, Rus(CO)iZ, Ru(acac)s (b) different tertiary amine promoters: e.g. 2,2’-bipyridine, l,lO-phenanthroline, 2,2’,2”tripyridine, 2,2’-bipyrimidine, N,N,N’,N’-tetramethylethylenediamine, 2,2’dipyridylamine, 2,3’-bipyridine, 2,4,6-tri( 2-pyridyl)-s-triazine (c) dispersed in various quaternary phosphonium salts: e.g. Bu,PBr, Bu,PI, Bu,POAc. Selectivity to linear l-nonanol of >80% and total nonanol yields of 72 mol%, are routinely achieved under the conditions of Table 1 with both the RuOz-2,2’-BIPY/Bu4PBr and Rus(C0)i2-2,2’-BIPY/Bu4PBr catalyst precursors. Other experiments in this series (see Table 1) serve to confirm the critical importance of all three catalyst components, i.e., the ruthenium source, the N-promoter and the quaternary phosphonium salt, in achieving the desired linearity and yield of 0x0 products [34]. Of particular note: (a) high alcohol product linearity (>80%) is achieved only in the presence of certain N-promoters (cf. ex. 1 and 4); (b) the absence of quaternary phosphonium salt invariably leads to lower levels of olefin conversion, lower total alcohol concentrations and yields, and proportionally more paraffinic byproduct (cfi ex. 1 and 2); (c) the absence of both tertiary amine and quaternary phosphonium salt also provides lower concentrations and yields of desired alcohol, lower selectivities to desired linear alcohol and higher concentrations of byproduct hydrocarbon (cf. ex. 1 and 3). Generally, to ensure high alcohol linearity in ruthenium-catalyzed cw-olefin oxonation, the N-promoter (L-L) should be a bidentate N-heterocyclic compound capable of forming chelate complexes with ruthenium [ 331. This class of amine is best illustrated by 2,2’-bipyridine (I, ex. 1 and 12) 2,2’dipyridylamine (II, ex. 8) and 2,2’-bipyrimidine (III, ex. 10 and 11). The importance of N-ligand chelation is exemplified by comparing ex. 1, 6 and 7; here the influence of bipyridine structure upon alcohol linearity shows that only the 2;2’-bipyridine (I) provides the desired >80% linearity. ex. 1 2,2’-bipyridine (I) nonanol linearity 86% ex. 1 2,3’-bipyridine (IV) nonanol linearity 68% ex. 7 2,4’-bipyridine (V) nonanol linearity 57%. The spectra of the RuOz-BIPY/Bu,PBr catalyst solutions (e.g. ex. 1) in the metal carbonyl region continue to be dominated by bands typical of [HRu~(CO)~J-~ (1959, 1990 and 2017 cm-‘) [35], but peaks at 1990, 2030 and 2073 cm-’ may be indicative also of the presence of known ruthenium carbonyl bipyridyl clusters [36, 371. Ruthenium carbonyl mononuclear complexes of 2,2’-bipyridine [ 38 - 421 appear less likely to be present in measurable quantities.
103
(2)
TABLE 2 1 -0ctene hydroformylation phosphino)alkane ligands
catalyzed
Ex. Ru :BIPY ratio a, b Total nonanol + nonanal (mmol) Nonanol linearity (W)
22 1:0.25 108.5
23 1:0.5 109.0
24 1:l 121.4
25 1:1.5 125.9
26 1:2 120.1
27 1:3 114.1
75.8
77.4
81.1
84.3
82.0
82.1
28 1 72.5
29
2 108.9
30 3 92.3
31 4 59.7
32 5 62.6
86.7
84.5
84.1
66.3
63.8
Ex. Ph2P(CH2),PPh2C*d, n = Total nonanol + nonanal (mmol) Nonanol linearity (%) aRun charge: Ru, 3.0 mmol, bOperating conditions: 1200 CRun charge: Ru, 6.0 mmol; dOperating conditions: 1200
by ruthenium-2,2’-bipyridine
and -bis(diphenyl-
BIPY, 0.75 - 9.0 mmol; Bu4PBr, 5.0 g; Cs-, 200 mmol. psi (CO/Hz, 1:2); 180 “C; 4 h. PhzP(CH2),PPh2, 6.0 mmol; BuJPBr, 10.0 g; Cs-, 200 mmol. psi (CO/Hz, 1:2); 180 ‘C; 4 h.
With regard to the preferred Ru-N stoichiometry, for a series of runs at different initial Ru-BIPY molar ratios (Table 2, ex. 22 - 27), the highest nonanal + nonanol yield, and the highest linearity of the nonanol product, are achieved with ratios of cu. 1:l - 1:1.5. Less 2,2’-bipyridine leads to lower yields of 0x0 product and lower linearity of the 0x0 alcohol fraction. Ruthenium:2,2’-bipyridine ratios of 1:2, or greater, appear to slightly suppress activity with no attendant improvement in l/b ratio. Since the more selective species are generated at Ru-BIPY ratios of 1 - 1.5, it is possible that two (or three) nitrogen donor atoms are bound to each ruthenium atom in the most effective catalyst precursor. In view of the spectral data described above, however, this preferred stoichiometry may in fact reflect only the equilibria of eqns. 3 and 4 - between the known ruthenium carbonyl clusters, [HRu,(CO),,]-, Rus(CO)i,,(BIPY) [36, 371 and their derivatives. Additional 2,2’-bipyridine would serve then only to
104
displace the remaining carbonyls leading possibly to the formation of species of different activity, e.g. (L-L)ZRuJ(CO)s-type complexes (eqn. (5)) [43]. The water-gas shift activity of the Rus(C0)i2--2,2’-bipyridine couple has recently been disclosed [44] by the same group in Finland. [HRu,(CO),,]Rus(CO),,
+ BIPY &
+ BIPY +
[HRu,(CO),(BIPY)]-
+ 2C0
Ru~(CO)~~(BIPY) + 2C0
Ru~(CO)~,,(BIPY) + BIPY +
Ru~(CO),(BIPY)~
(3) (4)
+ 2C0
(5)
P-ligand effects
A series of other novel ruthenium-Group 15 donor ligand chelate combinations have been found to provide ‘0x0’ alcohols with >80% linearity from typical cx-olefin stocks [ 451. The data in Table 3 illustrate the preparation of predominantly linear nonyl alcohols from CO/H2 plue l-octene catalyzed by different combinations of ruthenium precursor (e.g. RuOz, Ru(acac)g), phosphorus promoter and quaternary phosphonium Ru3(COh, salts (e.g. Bu,PBr, C16H33Bu3PBr). Selectivity to linear 1-nonanol of >80% is again achieved only with certain chelating bidentate or multidentate ligands (ex. 33 - 42), particularly: Phz PCHzPPhz Ph2P(CH2)2PPhZ Ph,P(CH,),PPh2 Ph,P(CH,),PPh2 CH3*C(CH,PPh2)s P(CH&H2PPhZ)3 PhP(CHZCH2PPhZ),
(ex. (ex. (ex. (ex. (ex. (ex. (ex.
33) 34) 35) 36) 40) 41) 42)
87% linearity 8 5% linearity 84% linearity 8 1% linearity 84% linearity 81% linearity 94% linearity
The ruthenium oxide-bis(2diphenylphosphinoethyl)phenylphosphine (TRIPHOS) couple provides the highest selectivity to linear aliphatic alkanol (94% l/b >lO) under these screening conditions (Table 3, ex. 42). This tridentate ligand combination has the disadvantages, however, of giving twophase liquid products and lower levels of olefin conversion than certain of its bidentate analogues. The importance of ligand chelation is reinforced in a third series of experiments, where RuOz is in combination with a series of arylphosphines of the general structure: Ph2P(CH2),PPh2. Run data are summarized in the lower half of Table 2, ex. 28 - 32. Productivity again is clearly maximized for the DIPHOS (1,2-bis(diphenylphosphino)ethane) ligand, known to form five-membered ring complexes with ruthenium carbonyls [25, 26, 46, 471. Similarly, nonanol linearity is acceptable for all Ru-PhzP(CH2),PPh2 combinations where n = 1, 2 or 3. Again it is these P-ligands that are most likely to form chelated intermediates. The Ru-DIPHOS reactant solutions are dominated by the Ru3(CO),,(DIPHOS) cluster complex (IR carbonyl stretches at 1970, 1983, 2004(s), 2035, 2066 cm-‘*, i3C NMR sharp triplet at 209.9 ppm at r.t.), in line with *Some Ru-DIPHOS
solutions also show VW hands at 1914 and 1936 cm-‘.
36.9 30.1 28.2 19.0 13.9 18.4 5.3 61.7 36.2 91.0 43.3 87.3 26.8 1.9 4.3
Octenes
Liquid
dTwo-phase
liquid
product.
200 mmol.
16.6 10.8 17.4 10.5 9.8 38.9 46.1 6.7 10.9 2.8 17 9.6 6.1 16.2 14.9 0.3
2.4 0.7 0.4 2.8 2.3 0.6
4.5 1.7 0.6 4.1 4.3 0.7 0.7 0.9 0.4 1.0 4.7 0.9 5.5 1.0 0.4 0.3 0.7 0.5 3.1 0.1 0.4
Linear
Branched
Linear 29.9 40.9 42.4 38.0 38.1 30.4 28.6 22.0 38.2 1.9 37.5 0.2 29.4 45.2 42.1
Nonanol
(%)
Nonanal
composition
Octane
product
aRun charge: Ru, 6.0 mmol; Ru/P, 1:2; BuaPBr, 10.0 g; l-octene, bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2); 4 h. CRu/P = 1:3.
Bu4PBr Bu4PBr Bu4PBr Bu4PBr
43 44 45 46
Ru02-[(CH3)2NPh],P RuOa-[PhaPCsH4]2Fe Ru02-PPh3 Ru02-PBu3
Bu4PBr
Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Bu4PBr Cr6HssBusPBr Bu4PBr Bu4PBr
Reaction media
of P-ligandsa+b
42
RuOa-PhzPCHzPPhz RuO*-PhzP(CHa)aPPh2 Ru02-PhzP(CH2)sPPh2 Ru02-Ph2P( CH2)4PPh2 RuOa-Ph2P(CH2)sPPh2 Ru~(CO~~-P~~P(CH~)~PP~~ Ru(acac)3-Ph2P(CH2)4PPh2 Ru02-CH3C(CH2PPh2)a Ru02-P(CH2CH2PPh2)3
effect
33 34 35 36 31 38 39 40 41
precursor
hydroformylation:
Catalyst
3
Ex.
l-Octene
TABLE
4.6 7.5 8.0 19.3 21.6 8.4 6.9 4.2 8.7 0.4 2.2 1.0 8.0 30.4 27.5
Branched 1.4 1.3 1.2 1.1 1.3 0.2 1.0 1.3 1.2 0.1 2.7 0.1 2.1 0.4 0.5
Water
79 60 60
94
87 85 84 66 64 78 81 84 81
d
1
Nonanol linearity (%)
106
analogous data reported by Cotton and Hanson [48] for decacarbonyl[bis(diphenylphosphino)methane]triruthenium. Spectral data indicate that the equilibrium of eqn. (6) is reached rapidly. Ruthenium-DIPHOS solutions containing excess chelate (e.g. Ru: DIPHOS 1:5) are catalytically inactive, and oxonation invariably leads to the precipitation of most of the ruthenium as mononuclear Ru(CO),(DIPHOS)type [25] complexes (eqn. (7)). The importance of amine or phosphine basicity [49 - 521 appears minimal (e.g. compare ex. 45 and 46) with regard to its effect on either the rate or regioselectivity. Ru,(C0)i2
+ DIPHOS +
Rus(CO),,-,(DIPHOS) + 2C0
Ru~(CO)~,,(DIPHOS) + BDIPHOS ti
3Ru(CO)s(DIPHOS)
(6) + CO
(7)
Propylene oxonation The highest level of a-olefin regioselectivity has been achieved in this program using the triruthenium dodecacarbonyl-2,2’-bipyrimidine (III) couple dispersed in tetrabutylphosphonium bromide. Under standard screening conditions [33, 341, propylene is oxonated to n-butanol in 89% selectivity with the butanol linearity being >99% by GLC (l/b ratio >lOO, see Table 4, ex. 47). Total butanol plus butanal selectivity is estimated to be 96%. Butanol linearities of >99% have also been obtained when employing the same catalyst couple in continuous processing [ 531. The ruthenium dodecacarbonyl-2,2’-bipyridine couple, solubilized in phosphonium quat. plus ldodecanol, generates butanol at a rate of 23 mol (g atom Ru)-’ h-i (ex. 49). In each of these runs, ex. 47 - 49, the principal byproducts are 2ethylhexanal and 2ethylhexanol. Effect of operating parameters For one of the more effective ruthenium ‘melt’ catalysts, the ruthenium(IV)oxide-2,2’-bipyridine (BIPY)/tetrabutylphosphonium bromide, performance - particularly the yields of alcohol/aldehyde 0x0 products and the linearity of the 0x0 alcohol/aldehyde generated from typical a-olefin stocks has been examined as a function of certain critical operating parameters, particularly: (1) the initial Ru:BIPY ratio (2) ruthenium concentration (3) operating temperature (4) syngas pressure (5) hydrogen and carbon monoxide partial pressures. For one standard synthesis, l-octene to nonanol/nonanal, the linearity of these 0x0 products generated by this procedure has again been raised to 99% (l/b N loo), from the data in Tables 1 - 3, through careful modification of the hydroformylation conditions.
R~a(C0)~2-2,2’-hipyrimidine Rua(CO)i2-2,2’-bipyridine Rua(CO)ia-2,2’-bipyridine
47 48 49
Bu4PBrb*e Bu4PBrC*e Bu4PBr/C12HzsOHd*f
Reaction media
Wonfirmed by GLC-MS; GLC-FTIR. bRun charge: Ru, 6.0 mmol; 2,2’-BIPY, 6.0 mmol; Bu4PBr, 10.0 CRun charge: Ru, 6.0 mmol; 2,2’-BIPY, 6.0 mmol; Bu.+PBr, 10.0 dRun charge: Ru, 3.0 mmol; 2,2’-BIPY, 3.0 mmol; BudPBr, 10.0 eTypical operating conditions: 1200 psi (CO/Hz, 1:2), 160 “C, 4 ‘Operating conditions: 1800 psi (CO/Hz, 1:2) constant pressure.
Catalyst precursor
Ex.
Propylene hydroformylation
TABLE 4
1.2 4.3
89.5 53.4 5.3 5.6 0.9
Branched 0.2 2.6 6.2
Water
g; propylene, 400 mmol. g; propylene, 400 mmol. g; 1-dodecanol, 15.7 g; propylene, 400 mmol. h.
6.4 11.4 36.7
Linear
Linear
Branched
ButanoV’
(%)
Butanala
Liquid product composition
90 91
Butanal linearity (%)
>99 91 85
Butanol linearity (%)
108
NONANOL/
NON ANAL I
NONANOLI NONANAL/ OCTANE ‘RODUCTNITY (mmols
LINEARITY (% )
1
/ /8’ XI
,
9, 100
‘0/ /
I20
\ 140 OPERATING
160 TEMP
(‘C
0 \
n
160
200
)
Fig. 1. Effect of operating temperature upon 0x0 activity, 0, total nonanol; ‘J, total nonanal; A, nonanol linearity; V, nonanal linearity; X, total octane. Reaction charge: Ru, 6.0 mmol; Ru:BIPY, l:l; BusPBr, 10.0 g; CS-, 200 mmol; operating conditions: 1200 psi (CO/HI = 1:2); 4 h.
Varying the reaction temperature has probably the most dramatic influence upon Ru-melt catalyst performance (see Fig. 1). At 200 “C, the C9-0x0 product is almost exclusively nonanol, and octene conversion exceeds 98%. By contrast, at 140 “C or less, nonanals are the predominant products. The linearity of both the alcohol and aldehyde product fractions increases significantly with a lowering of the operating temperature from 200 to 100 “C. Below 140 “C, both the nonanol and nonanal products show linearities of >97% (l/b 230). In one run, at 100 “C, the nonanal linearity is 99% (l/b -100, see Fig. 1). To some degree, the loss of linearity at higher temperatures can be compensated for by the addition of excess N-ligand. At 200 “C, for example, the use of a lo-fold excess of BIPY raises the nonanol linearity percentage, from 65% (see Fig. 1) to 76%, and interestingly enough, in contrast to Rh oxonation [ll], this improvement is achieved without a marked loss in hydroformylation rate.
109
Wilkinson and coworkers report the optimum temperature for ruthenium homogeneous hydroformylation to be cc. 120 “C [25]. By contrast, ruthenium ‘melt’ 0x0 catalysts routinely show a steady rise in alcohol productivity in the 100 - 200 “C temperature range (see @ data points, Fig. 1). Only above 200 “C, with 2:l Hz/CO syngas, do we see evidence of catalyst breakdown, and the formation of black insoluble residues. Aldehyde production, on the other hand, appears to be maximized at temperatures of ca. 130 “C for the ruthenium(IV) oxide-2,2’-bipyridinel Bu4PBr precursor. Below this temperature, the rates of hydroformylation are slow. Above 140 “C, subsequent aldehyde reduction to alkanol becomes increasingly important. Increases in CO partial pressure, at constant initial hydrogen pressure, lead to a substantial decrease in nonanol productivity (see Fig. 2) and a significant (El-fold) improvement in nonanal yield. However, the size, and even direction, of this aldehyde productivity change is particularly sensitive to the choice of operating temperature - selected here in Fig. 2 to be 180 “C. For temperatures below 140 “C, e.g. 120 “C, where aldehydes generally comprise the majority (>90%) of the total 0x0 product, the effect of increasing CO 150
IO0 NONANOLI NONANALI OCTANE ;;~LR$TIVITY
400
1200
600 CO
PARTIAL
lb00 PRESSURE
2000
2400
(psi)
Fig. 2. Effect of CO partial pressure upon 0x0 activity. Symbols as per Fig. 1, 0, total
nonanol + nonanal; operating conditions: 800 psi Hz; 180 “C; 4 h.
110
partial pressure is a moderate drop in total nonanal productivity (90 mmol (see Fig. 1) to 58 mmol, same CO partial pressure range as Fig. 2). 0x0 alcohol/aldehyde linearity figures and the formation of hydrocarbon byproduct exhibit only a modest sensitivity to CO partial pressure (e.g. Fig. 2), particularly where the operating temperature is <140 “C. Changes in hydrogen partial pressure bring about an interesting maxima in alcohol productivity (see Fig. 3). At high Hz partial pressure, where in this experimental series the CO/H2 molar ratio is in the region of l/5, the alcohol productivity drops off quite dramatically, as the level of competing olefin hydrogenation rises. Alcohol linearity also drops - on the average of cc. 10% - over the [H,] range studied, at this temperature. The significance of these findings is rationalized in the following Discussion Section. At 120 “c, aldehyde productivity is relatively insensitive to changes in H2 partial pressure (91- 83 mmol CsH,,CHO, Hz pressure range as in Fig. 3). Raising the total syngas pressure from 600 to 3000 psi (see Fig. 4) unexpectedly also leads to a dramatic decrease in nonanol yields - from 53 to 24% - and this is accompanied by a substantial increase in nonanal formation (3 - 34%) under these selected conditions (i.e. operating tempera150
3-
100 NONANOL LINEARITY PI. I
NONANOLI NONANAL/ OCTANE PRODUCTIVITY lmmolr) Sl,-
800 H2 PARTIAL
I200 PRESSURE
1600
2000
(psi)
Fig. 3. Effect of H2 partial pressure upon 0x0 activity. Symbols and reaction charge as per Fig. 1; operating conditions: 400 psi CO; 180 “C; 4 h.
111
NONINOL LINEARITY w.
I
1000
2000 TOTAL
PRESSURE
(psi
3000 I
Fig. 4. Effect of total pressure upon 0x0 activity. Symbols and reaction charge as per Fig. 1; operating conditions: CO/Hz, 1:2; 160 “C; 4 h.
ture 160 “C, syngas composition l/2). Similar trends in aldehyde/alcohol yields are replicated at higher temperatures. At 120 “C, however, where Cg aldehydes are the almost exclusive 0x0 product, the productivity of nonanals is relatively insensitive to total syngas pressure (82 - 90 mmol, same pressure range as Fig. 4). There is an approximately linear first-order dependence of aldehyde productivity upon the quantity of l-octene charged, under the conditions of Table 5. Similarly, both the alcohol and total Cg aldehyde + alcohol productivities increase with the rise in olefin charge (ex. 50 - 54). Under the same conditions, even a modest change in [Ru] leads to a corresponding substantial increase in alkanol productivity. Total nonanol f nonanal remains unchanged, consequently the aldehyde/alcohol molar ratio drops precipitously, from cu. 1:l to 1:37, as the ruthenium charge increases from 1.5 to 9.0 mmol (see Table 5, ex. 51,55 - 57). Once again the choice of experimental conditions, particularly the selected operating temperature, pressure and syngas composition, will affect the data trends in Table 5. At 120 “C, for example, where the rate of alcohol formation is hardly measur-
112 TABLE 5 1-Octene hydroformylation:
effect of [ Ru] and [Cs-]a.b
Ex. Ru (mmol) 1-Octene (mmol) Total nonanol (mmol) Total nonanal (mmol) Nonanol + nonanal (mmol) Nonanol linearity (W)
50 1.5 100 30.2 30.8 61.0 83.7
51 1.5 200 59.4 61.9 121.3 83.0
52 1.5 300 67.1 87.2 154.3 84.0
53 1.5 400 70.6 134.2 204.9 81.5
54 1.5 600 84.9 202.1 287.0 77.9
55 3.0 200 74.8 46.6 121.4 77.3
56 6.0 200 101.5 24.1 125.6 75.5
57 9.0 200 122.3 3.3 125.6 77.7
aRun charge: Ru/BIPY, l:l, Bu4PBr, 5.0 g. bRun conditions: 180 “C; 1200 psi (CO/Hz, 1:2), 4 h.
able, nononal productivity is fractional order in ruthenium over the same Ru concentration range. Discussion The ruthenium-ligand-stabilized ‘melt’ catalysts illustrated in Tables 1 - 4 and Fig. 1 can clearly catalyze both basic oxonation reactions - hydroformylation of cx-olefin substrates to predominantly linear 0x0 aldehydes, and subsequent reduction of these aldehydes to the corresponding alcohol. Our data [21] are consistent with a stepwise, two-step mode to alcohol formation (Scheme l), rather than invoking a common intermediate partitioning RCH=CH2 f
I
-c
CRU~(CO)~(L-L)(OCH~CH*CH~R]-
Y
0
Scheme 1. Proposed mechanism for 0x0 alcohol and aldehyde formation via ligandmodified ruthenium ‘melt’ catalysis. L-L = bidentate N- or P-ligand such as 2,2’-bipyridine or 1,2-bis(diphenylphosphino)ethane.
113
between alcohol and aldehyde products, The choice of dominant product be it alcohol or aldehyde (eqn. (1)) - is controlled primarily by the operating temperature (Fig. 1). In this regard, the Ru ‘melt’ catalysis parallels cobalt hydroformylation processes [ 171. The apparent higher activation energy for the ruthenium ‘melt’-catalyzed aldehyde reduction, ensures that at operating temperatures of <140 “C, the primary product is the 0x0 aldehyde, while at temperatures of >180 “c, 0x0 alcohols are generally favored. Initial [Ru] and olefin concentration factors can also affect the aldehyde/alcohol balance (see Table 5), however, as can the syngas composition (Figs. 2 - 4) and, to a lesser degree, the nature of the coordinated ligands (Tables 1 and 3). The second commercially critical parameter by which this 0x0 processing must be judged - the linearity of the final aldehyde/alcohol products has been raised in this study to >99% (l/b >lOO) by careful control of operating conditions (Table 4 and Fig. 1). The primary influencing factors here are the nature of the N- and P-chelating ligand structures (Tables 1 and 3) and the ability of these ligands to form stable complexes with ruthenium under 0x0 conditions (e.g. eqns. (3) - (7)). Temperature (Fig. 1) and initial ruthenium-ligand mole ratio (Table 2) also play a role. Generally, the l/b ratio of the 0x0 alcohol products are comparable to that of the intermediate aldehyde (see Fig. l), and small differences likely reflect GLC analytical errors. Total alcohol yield is determined mainly by syngas composition and pressure (Figs. 2 - 4). While aldehyde hydrogenation ability of the Ru catalyst decreases with increasing CO partial pressure at 180 “C (Fig. 2), increases in H, partial pressure, by contrast, increase competing olefin reduction (Fig. 3). Because the aldehyde reduction rate (steps 4 and 5, Scheme 1) is the more sensitive to CO/H2 partial pressure changes (see Figs. 2 and 3, data trends 0, B versus X), increases in total CO/H2 gas pressure at this temperature have the net effect of raising aldehyde yield at the expense of alcohol (Fig. 4). Oxonation to aldehyde is also influenced by CO partial pressure (see Results Section) at 120 “C. In fact, the trends evident in Figs. 2 - 4 suggest that (a) a number of the critical steps in this oxonation (Scheme 1) have similar rates, and (b) there are complex equilibria in these catalyst solutions involving addition/displacement of CO and Group 15 ligands bonded to ruthenium (e.g. eqns. (3) through (7)). Because Hz and CO partial pressures only modestly influence the total oxonation activity (nonanal + nonanol, e.g. 0 data points, Fig. 2) at 180 “C, neither oxidative addition of Hz nor addition of CO are likely to be rate determining under these particular conditions. The ratedetermining step for aldehyde formation is most probably association of ligated Ru complex with the 1-octene reactant, or hydride transfer to coordinated alkene to form an alkyl-ruthenium cluster [ 541 (step 1, Scheme 1). This is also consistent with aldehyde productivity at 120 “C being relatively insensitive to Hz and syngas pressures (see Results). On the other hand, the marked drop in alcohol/aldehyde ratio at higher CO partial pressures and 180 “C (Fig. 2) we believe due to the formation of
114
coordinatively saturated, carbonyl-rich ruthenium intermediates that do not allow facile oxidative addition of Hz and therefore result in a lowering of the ability to form/protonate the alkoxy-ruthenium intermediates (steps 4 and 5) to alcohol. The spectral identification of these species remains under study. Increases in alcohol yield with increasing Hz partial pressure (Fig. 3) accompanied by a decline in alcohol yield at higher Hz partial pressures may be rationalized in terms of competing rates of intermediate aldehyde hydrogenation to alcohol, uersus the rate of olefin reduction to hydrocarbon (steps 4 and 5 versus 1A in Scheme 1). Aldehyde reduction to alcohol (step 5) becomes increasingly important as the Hz partial pressure rises to cu. 1200 psi. Beyond 1200 psi, however, the rate of competing &olefin reduction (1A) starts to dominate, significantly lowering the available quantities of a-olefin for oxonation. A shift in the linear alkyl-ruthenium uersus branched alkyl-ruthenium equilibria would account for the drop in 1:b ratio in Fig. 3. The rate at which this equilibria is established is known to be fast, relative to oxonation, from our earlier work with internal olefin substrates
WI.
Step 1 (Scheme 1) being rate determining over the 120 - 180 “C temperature range is also in line with the apparent first-order dependence upon olefin charge (see Table 5). The insensitivity of total nonanal + nonanol productivity to [Ru] at 180 “C is, however, less easy to rationalize; a fractional (l/3) order might be expected here, and indeed a fractional order at 120 “C is evident. Likely there is a change in rate-limiting steps over this temperature range, but further work will be needed to clarify this point. On the other hand, conversion of aldehyde to alcohol is very sensitive to [Ru] and it is this sensitivity that so dramatically changes the aldehyde-toalcohol ratio in Table 5, ex. 51,55 - 57. In conclusion, we have demonstrated that highly linear alkanols and alkanals can be readily generated through regioselective a-olefin oxonation with l&and-modified ruthenium ‘melt’ catalysis. While all the interrelationships linking catalyst structure and the various operating parameters are not yet fully understood (particularly in a quantitative sense), the data presented in this paper do allow the design of high yield syntheses of either the desired 0x0 aldehyde or alkanol using essentially the same classes of ruthenium ‘melt’ catalysts. Experimental All syntheses were conducted batchwise in pressurized reactors under carefully controlled temperature/pressure conditions. The ruthenium compounds, N-heterocyclics, tertiary phosphines and quatemary phosphonium salts were purchased from outside suppliers. Synthesis gas was purchased in various CO/H? proportions from Big Three Industries. Terminal olefin stocks 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
115
were isolated by fractional distillation in vacua, and identified by the same analytical techniques. GLC analyses were conducted using an 8 ft 10% Carbowax 20M column on Chromasorb-W high performance support, programmed from 75 to 250 “C at 8 “C min-' . FTIR spectral measurements were made using a Digilab FTS 15C instrument.
Typical oxona tion syntheses Ruthenium(IV) oxide, hydrate (1.146 g, 6.0 mmol) and 2,2’-bipyridine (0.937 g, 6.0 mmol) are dispersed in tetrabutylphosphonium bromide (10.0 g, 29.5 mmol) and diluted with l-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/H2 and pressured to 1200 psig with CO/H, (1:2). The mixture is heated to 120 “C with agitation, held at temperature for 4 h, and then allowed to cool. Upon reaching ambient temperature, the reactor pressure (1075 psi) is noted, a typical gas sample taken, and the excess gas vented. The deep-red liquid product (38.0 g) is analyzed by GLC and Karl Fisher titration. Analysis of the typical liquid sample shows the presence of the following: 49.1 wt.% nonanal, 1.2 wt.% 2-methyloctanal, 2.8 wt.% nonanol, 4.5 wt.% octane, 37.3 wt.% octenes, 5.1 wt.% water. Analyses of typical gas samples show the presence of: 69.3% hydrogen, 30.5% carbon monoxide, 0.3% carbon dioxide and
6 7 8 9 10 11
See for example: 0x0 AZcohoZs, S.R.I. International Report No. 21C, April 1986. PERP Topical Reports, Chem Systems, Vol. 2,1986, p. 1. 0x0 Alcohols, Chem Systems Report #77-4, May 1978. B. Cornils, R. Payer and K. C. Traenckner, Hydrocarbon Process., June (1975) 83. B. A. Murrer and M. J. H. Russel, Royal Sot. Chem., Specialist Periodic Report Catalysis, 6 (1983) 169. U.S. Pat. 3 917 661 (1975) to R. L. Pruett and J. A. Smith. 0. R. Hughes and J. D. Unruh, J. Mol. Catal., 12 (1981) 71. M. Matsumato and M. Tamura, J. Mol. Catal., 19 (1983) 365. U.S. Pat. 3 239 569 (1966) to L. H. Slaugh and R. D. Mullineaux. F. E. Paulik, Catal. Rev., 6 (1972) 49. A. A. Oswald, D. E. Hendriksen, R. V. Kastrup and J. S. Merola, Am. Chem. Sot. Meeting, March 28,1982, ACS Petroleum Division Reprints, Vol. 27, p. 292.
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A. M. Trzeciak and J. J. Ziolkowski, J. Mol. Catal., 34 (1986) 213. A. Fusi, E. Cesarotti and R. Ugo, J. Mol. Catal., 10 (1981) 213. R. A. Dubois and P. E. Garrou, Organometallics, 5 (1986) 466. C. Botteghi, R. Ganzerla, M. Lenarda and G. Moretti, J. Mol. Catal., 40 (1987) 129. A. Scrivanti, A. Berton, L. Toniolo and C. Botteghi, J. Organometall. Chem., 314 (1986) 369. M. Orchin,Acc. Chem. Res., 14 (1981) 259. P. Parrinello, R. Deschenaux and J. K. Stille, J. Org. Chem., 51 (1986) 4189. P. Escaffre, A. Thorez and P. Kalck, J. Chem. Sot., Chem. Commun., (1987) 146. W. R. Jackson, P. Perlmutter and G. H. Suh, J. Chem. Sot., Chem. Commun., (1987)
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36
(1979) 1356. See: M. I. Bruce,
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T. Venalainen, (1985) 1348. See for example:
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and S. I. Richter,
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