Organometallics 1986, 5 , 460-466
460
the top and bottom of each line of the triplet (Figure 1G). This allows only a rough estimation of the 57Fecoupling (ca. 4.5 G ) . However, the lack of another pair of weaker shoulders near the base of each line, i.e., the outermost lines of the 1:6:11:6:1 quintets mentioned above, seems more consistent with a species with a single iron atom than with two equivalent ones.
Acknowledgment. We thank Drs. Keith F. Preston, John R. Morton, and Mr. R. Duttrisac for a sample of
57Fe-enrichedFe(CO),. We are also grateful to Dr. K. F. Preston, Dr. David Thorn, and Professor Robert Bergman for helpful discussions. Registry No. I, 91199-15-4;I-13C4,99546-49-3;I-d, 99546-51-7; 11,78005-17-1;II-I3C8,99546-50-6;11-d, 99546-52-8;111,12002-28-7; IV, 71500-60-2;V,77024-06-7;V-I3Cll,99546-53-9;V-d, 99546-55-1; VI, 99546-47-1; VI13C,, 99546-54-0; VI-d,, 99546-56-2; VII, ~~, Fe(CO),, 13463-40-6; HP, 99546-48-2; V I I - ~ , - ' ~99546-57-3; 1333-74-0; D2, 7782-39-0; CO, 630-08-0; 13C0, 1641-69-6.
Cobalt Hydroformylation Catalyst Supported on a Phosphinated Polyphosphazene. Identification of Phosphorus-Carbon Bond Cleavage as Mode of Catalyst Deactivation' Robert A. Dubois,+ Philip E. Garrou,*+ Karen D. Lavin,' and Harry R. Allcock*$ Dow Chemical Company, Wayland, Massachusetts 0 1778, and the Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 Received June 18, 7985
The interaction of C O ~ ( C Owith ) ~ [NP(OPh)1.7(OCSH4PPh2)0.3]n ( l ) , N3P3(0Ph),(OC6H,PPh2)(2), PPh,-linked polystyrene (3), or triarylphosphine [PPh,, P(p-CH3C6H,)3]yielded species of the type Co2(CO);PR3,[Co(C0),PR3I2,and [CO(CO)~(PR~),]+CO(CO),as identified by infrared spectroscopy and 31PNMR. Catalysts derived from 1 were expected to have higher thermal stability based on the inherent thermal stability of 1 vs. 3. A study of the catalyst system 1/Co2(CO)8for 1-hexene hydroformylation revealed an initial activity equal to its homogeneous analogue. This has been rationalized as due to cleavage of cross-linking P-Co-P sites during reaction with CO/H2 to give soluble hydride HCO(CO)~PR~ type species. All of the catalysts also revealed a time-dependent decrease in catalytic activity, due to a cobalt-mediated phosphorus-carbon bond cleavage. Benzene, toluene, benzyl alcohol, and p-MeCGH,CH20Hwere detected as primary cleavage products. When olefin was omitted from these reactions, R2PH was observed.
Introduction Homogeneous transition-metal catalysts have been the focus of much fundamental research during the past decade. However, their use in large scale catalytic transformations has been limited, mainly because of the difficulties encountered in their recovery from the reaction products and unused starting materials. A possible solution to this problem that has been explored in a number of laboratories is to link transitionmetal catalysts to organic macromolecules. Such hybrid polymer-catalyst systems should be easy to recover from reaction media, especially if the macromolecules are lightly cross-linked to form three-dimensional matrices that can be used as solvent-swelled, permeable particles.' The main impediment to the development of this idea lies in the instability of most organic polymers under the sometimes severe reaction conditions employed in important catalytic reactions. Thus, an ideal carrier polymer must be thermally and oxidatively stable and be chemically resistant to substrate and products under the reaction conditions. Not only must the polymer itself be stable under such conditions but so too must be the linkage between the transition metal and the macromolecule. Largely because of their dominant role in the history of homogeneous c a t a l y ~ i s ,tricoordinate ~,~ phosphorus units have been used widely as sites for the linkage of metals 'Daw Chemical Company.
* T h ePennsylvania State University
0276-7333/86/2305-0460$01.50/0
to macromolecules.2~5 In particular, cross-linked phosphinated polystyrene has been the main support material, largely because of its ease of synthesis and its commercial availability.6 (Ary1oxy)phosphazenes are expected to possess a higher thermooxidative stability than many of the organic polymers studied previously. In this paper, we describe our studies of phosphine-bearing phosphazenes 1 and 2 as carriers for cobalt hydroformylation catalysts, and we compare them to their homogeneous and polystyrenebound analogues 3. Compound 4 was studied as a control compound.
Results and Discussion Polymer 1 and the cyclic model compound 2 were examined as functionalized supports for cobalt catalysts with a view to assessing their catalytic activity and stability. Cobalt catalysts derived from 1 and 2 were catalytically (1) Some of these results have been published in a preliminary communication, see: Dubois, R. A,; Garrou, P. E.1 Lavin, K. D.; Allcock, H. R. Organometallics 1984, 3, 649. (2) Bailey, D. C.; Langer, S. H. Chem. Reu. 1981, 81, 109. (3) Heck, R. F. "Organotransition Metal Chemistry"; Academic Press: New York, 1974. (4) Parshall, G. W. "Homogeneous Catalysis"; Wiley-Interscience: New York, 1980. (5) Hodge, P.; Sherrington, D. C., Eds. "Polymer Supported Reactions in Organic Synthesis"; Wiley: New York, 1980. (6) Polymer-bound triphenylphosphine or styrene-divinylbenzene is made by the Strem Chemical Co. and sold under license of U S . Patent 3 708 462 owned by the Dow Chemical Co.
0 1986 American Chemical Society
Organometallics, Vol. 5, No. 3, 1986 461
Cobalt Hydroformylation Catalyst
QP
Table I 31P
o b
NMR, IR (CO), cm-' 2079 (m), 2026 (m), 1996 (s), 1964 (m)n [CO(CO)~PP~,], (B) 1960 ( s ) ~ [Co(CO),(PPh3),]+- 1995 (s), 1978 (m), 1890 (s)' ~CO(CO)*I(C) H C O ( C O ) ~ P P ~ , 2041 (m), 1952 (4' 2075 (w), 2000 (s), 1980 (sh), co2(co)8+ 1 1955 (s), 1890 (s) Co2(C0)*+ 2 comDd Co2(C0)7PPh3(A)
~~
2
1
Reference 7. in ref 7.
-
3
4
active for the hydroformylation of 1-hexene. However, a decline in catalytic activity with use was detected for both species. We attribute this both to loss of cobalt species from the phosphine unit and to cleavage of phosphine units from the polymeric or cyclic phosphazenes. We believe that this cleavage reaction is a general problem with triarylphosphine-modified catalytic systems. Consequently, a reinterpretation of the industrial viability of phosphinated organic supports for hydroformylation reactions may be needed. Reaction of CO,(CO)8 with Phosphine-Bearing Polyphosphazenes. The reaction of Co2(CO)8 with tertiary phosphines is k n o w 7 to yield three types of compounds, illustrated as species A-C. Each of these is distinguishable Co2k017PR3
A
LolCO13PR3
B
l2
k o k O l @ R 3 . ) ~ ColC0I4+
C
by its characteristic infrared spectrum in the carbonyl region. The known stretching frequencies of the three species, together with those observed for the polyphosphazene-cobalt system, are shown in Table I. The relative concentrations of the three species under hydroformylation conditions depend on temperature, partial pressure of CO/H2, and on the phosphine/cobalt ratio.7 The soluble phosphine-bearing polyphosphazenes [NP(OPh)l,7(OC6H4PPh2)a,3]n reacted with CO2(CO)8 in T H F or toluene solution to yield an insoluble brown complex. An infrared spectrum of this material was consistent with the presence of all three cobalt complexes, A, B, and C. It was reported earlier8 that only species B and C were present in the cobalt carbonyl complexes with (dipheny1phosphino)methylated polystyrene. The presence of all three species in the present system is probably a consequence of the higher cobalt to phosphorus ratio. Cobalt carbonyl is known to react with tertiary phosphines to yield bis(phosphine) complexe~,~ and we attribute the insolubility of the polyphosphazene-cobalt system to cross-linking through P-Co-P sites. This type of crosslinking has been described previously for [RhCl(CO),], and Fe(CO),(PhCH=CHC(O)CH,) coordinated to this polymer.g No evidence was obtained for linkage of cobalt to (7) Wood, C. W.; Garrou, P. E. "Catalytic Convenion of Synthesis-Gas and Alcohols to Chemicals"; Herman, R. G., Ed.; Plenum Press: New York, 1984; p 203. (8) Evans, G. 0.; Pittman, C. U.; McMillan, R.; Beach, R. T.; Jones, R. J.; J. Organomet. Chem. 1974, 67, 298.
DDm 82.4" 71.65" 64.4b 81.2, 70.7
Assigned by analogy to PCy3 and PEt3 systems
the nitrogen atoms of the polymer backbone. Poly(bisphenoxyphosphazene) did not react with CO2(CO)8 under similar conditions. Catalyst Activity. The cobalt-phosphine catalyzed hydroformylation of olefins to aldehydes and alcohols has been studied e x t e n s i ~ e l y . ~ Hydroformylation ~~~~J~~~ of 1-hexene in the presence of cobalt/phosphine catalysts yields hexenes, hexane, heptanal, heptanol, heptyl formate, and higher molecular weight species. From an industrial standpoint, the alcohols are the more desirable products. The initial product of hydroformylation is the linear and branched isomer mixture of heptanal, which is reduced under the reaction conditions to the corresponding isomers of heptanol. The first step to yield heptanal takes place readily at moderate temperatures (110 "C). Alcohol (heptanol) is the main product of hydroformylation at the higher temperatures (170-200 OC). Two complicating side reactions also occur: namely, aldol condensation to higher molecular weight species and formate production." Both of these products are generated from the initial aldehyde.'J1J3 Product distributions in this study are reported as normalized percentage yields excluding these higher molecular weight species (which normally constituted 7.5 f 2.5% of the final products). The results of this study are summarized in Table II.I4 In general, polymer-supported catalysts are less active than their homogeneous analogues, presumably because of mass transfer limitations. However, this was not found to be the case for the polyphosphazene system 1. The cobaltbound polyphosphazene gave heptanol in 85% yield (reaction 2 in Table 11), while the homogeneous cobalt-triphenylphosphine system gave an 87% yield (reaction 4 in Table 11) under identical reaction conditions. In addition, the polyphosphazene-cobalt system brought about the reaction of all the initial substrate, 1-hexene. Only a few examples are known where a homogeneous catalyst retains its activity or shows increased activity on an insoluble support, e.g., cobalt-bound 2-vinylpyridine and 2-vinylpyridine-styrene polymer system^.'^ We propose then that, under these reaction conditions, the cross-linked P-Co-P sites are broken to give the known hydrido HCO(CO)~PR~ type species. With this now soluble (9) Allcock, H. R.; Lavin, K. D.; Tollefson, N. M.; Evans, T. L. Organometallics 1983, 2, 267. (10) Paulik, F. E. Catal. Reu. 1972, 6 , 49. (11) Wender, I.; Pino, P. "Organic Synthesis Via Metal Carbonyls";
Wiley-Interscience: New York, 1977; Vol. 2, p 43. (12) Pruett, R. L. "Advances in Organometallic Chemistry"; West, R., Stone, F. G. A., Eds.; Academic Press: New York, 1979; Vol. 17, p 1. (13) Marko, L.; Szabo, P. Chem. Technol. 1961, 13, 482. (14) Complex reaction profiles which would have given a more quantitative picture of the relative reaction rates were not obtained since it was observed that all of the catalyst systems were degrading with time. (15) Moffat, A. J. J. Catal. 1970, 18, 143, 322.
462 Organometallics, Vol. 5, No. 3, 1986
Dubois e t al. Table I1
reactn 1 2 3 1
5 6
Co, mmol
molar P/Co ratio
1
0.10
3.0
1
0.18
PPh, PPh,
0.06 0.18
3' 3' 31
0.17 0.31 0.42
4.0 3.8 3.9 2.7
phosphine source
hexenes* 3.0
1.9 I .2
hexane
12.8
6.1
18.2d 4.8
14.7d 38.0d 20.gd
product distributiono heptanalc heptanolc 21.3 62.4 3.3 84.7 62.4 17.3 87.2 33.4 52.1 30.0 31.9 30.7 47.4
heptyl formate'
3.7 1.7 2.5 8.5
