Transition metal complexes containing phosphine ligands have been widely studied as catalysts for hydroformylation and hydrogenation. General application of such complexes in reaction with carbon monoxide are discussed, e.g., in the monograph of Juergen Falbe, "Carbon Monoxide in Organic Synthesis, Springer Verlag, New York, 1970.
There were a number of all inclusive patent disclosures on the use of phosphine rhodium complexes as hydroformylation catalysts: German Offenlegungsschrift 2,758,473 by W. E. Smith (assigned to General Electric) disclosed them for allyl alcohol hydroformylation; U.S. Pat. No. 4,137,240 by M. L. Peterson (assigned to E. I. DuPont de Nemours and Co.) described them for 2-vinyl-4-methyl-1,3-dioxane batch hydroformylation; U.S. Pat. No. 3,965,192 by F. B. Booth (assigned to Union Oil Co. of California) disclosed them for the hydroformylation of monoolefins; U.S. Pat. No. 4,041,082 by T. Onoda and T. Masuyama (assigned to Mitsubishi Chemical Industries) defined such complexes broadly in a process for their reactivation; U.S. Pat. No. 3,821,311 by O. R. Hughes and M. E. D. Millman (assigned to Celanese Corp.) also disclosed the use of such complexes broadly when used with bases for combined hydroformylation, aldolization. Similarly, British Pat. No. 1,243,189 by M. J. Lawrenson and G. Foster (assigned to British Petroleum Co., Ltd.) provided an all inclusive definition of phosphines in such catalyst complexes also containing chelating diketones. Finally, U.S. Pat. No. 4,052,461 by H. B. Tinker and D. E. Morris (assigned to Monsanto Co.) disclosed rhodium containing cations which can include any tertiary phosphine.
Most of the prior art work was carried out with either triaryl phosphine or trialkyl phosphine complexes. The present study concentrated on an investigation of the complexes of some "mixed ligand structures," i.e., alkyl diphenyl phosphines. Prior to the present work, rhodium complexes of these ligands could not be used tp advantage.
The basic chemistry of hydroformylation and its catalysis by transition metal compounds, including phosphine-rhodium complexes is known and has been recently reviewed and summarized by R. L. Pruett in Vol. 17 of "Advances in Organo Metallic Chemistry" ed. S. G. Stone and R. West, Academic Press, New York, N.Y. 1979 in a chapter entitled Hydroformylation, Pruett concluded that, for a selective rhodium catalyzed hydroformylation of alpha-olefins to n-aldehydes, critical combinations of several reaction parameters were required. The author states that these parameters included low partial pressure of carbon monoxide, high concentration of excess phosphite or aryl phosphine ligands and low total gas pressure.
In U.S. Pat. Nos. 3,527,809 and 3,917,661; Pruett and Smith state that suitable ligands for rhodium catalysts for hydroformylation must be weakly basic, having a half neutralization potential (.DELTA.HMP) of at least 425 millivolts (preferably 500) above that of diphenyl guanidine. As such weakly basic ligands, Pruett and Smith mentioned among others phosphites and triaryl phosphines. They specifically indicate that stronger phosphines bases, such as diaryl alkyl phosphines, should be excluded as ligands for selective rhodium catalysis. Similar disclosures are also contained in Pruett and Smith's U.S. Pat. No. 4,148,830, where they additionally state that suitable ligands should be free of sterically hindered aromatic groups.
In German Offenlegungsschrift 2,802,922 (based on U.S. Ser. No. 762,335, filed on Jan. 25, 1977 in the names of D. G. Morrell and P. D. Sherman, Jr.), there is described a process including the addition of small amounts of diaryl alkyl phosphine ligands to a tris-triphenyl phosphine rhodium complex system. However, substantially all of the free ligand in the Morrell et al. system is a triaryl ligand, and it is specifically stated that the invention is not intended to include the use of diaryl alkyl phosphine ligands alone. Some of the diaryl alkyl phosphine ligands which are apparently disclosed in this German publication for use in that particular content include methyl diphenyl phosphine, ethyl diphenyl phosphine, propyl diphenyl phosphine, butyl diphenyl phosphine, ethyl-bis(p-methoxy phenyl) phosphine, ethyl-phenyl-p-biphenyl phosphine, methyl-phenyl-p(N,N-dimethylaminophenyl) phosphine, propyl-phenyl-p-(N,N dimethylaminophenyl) phosphine, and propyl-bis-(p-methoxy phenyl) phosphine.
Still other patents and publications also mention the use of certain other alkyl phosphines as ligands in rhodium catalyzed hydroformylation reactions. For example, ethyl ditolyl phosphine is mentioned as a possible ligand by Peterson in U.S. Pat. No. 4,137,240. Wilkinson, U.S. Pat. No. 4,108,905, discloses ethyl diphenyl phosphine as a ligand for a rhodium hydrido carbonyl complex, which he says may be used in the presence of molten triphenyl phosphine as reaction medium. British Pat. No. 2,014,138 discloses the use of, among others, alkyl diaryl phosphines, e.g., propyl diphenyl phosphine, in combination with certain diphosphino alkanes in rhodium hydrido carbonyl complex systems. Booth in U.S. Pat. No. 3,560,539 mentions as a ligand ethyl diphenyl phosphine, while Booth et al., U.S. Pat. No. 3,644,446, discloses as possible ligands ethyl diphenyl phosphine and methyl dixylyl phosphine. Slaugh et al., in U.S. Pat. No. 3,239,566 mentions diphenyl butyl phosphine, methyl diphenyl phosphine, ethyl diphenyl phosphine and diphenyl benzyl phosphine as possible ligands for rhodium or ruthenium catalysts. Chemistry Letters, (1972) pp. 483-488, refers to a rhodium complex bonded to (+)-diphenylneomenthyl phosphine.
Other Union Carbide researchers disclosed additional inventions mostly related to the commercial TPP-rhodium complex catalyzed process. German Offenlegungsschrift 2,715,685 by E. A. V. Brewster and R. L. Pruett described the continuous process in detail. Also, it showed the harmful effect of aldehydes having conjugated olefinic unsaturation. German Offenlegungsschrift 2,730,527 by R. W. Halstead and J. C. Chaty disclosed the addition of appropriate, minor amounts of oxygen to the reaction mixture of the continuous process to maintain activity.
Alkyl diaryl phosphine ligands were specifically disclosed as potential rhodium catalyst stabilizer ligands in a number of patents and journal articles on rhodium catalyzed hydroformylation, U.S. Pat. No. 4,108,905 by G. Wilkinson (assigned to Johnson Matthey & Co., Ltd.) disclosed ethyl diphenyl phosphine as a stabilizing ligand as a part of an all inclusive, but sparsely supported, disclosure on phosphine ligands. British Patent Application No. 2,014,138 (assigned to Kuraray Co., Ltd.) similarly disclosed bis-diarylphosphino alkanes, i.e., diaryl phosphine substituted alkyl diaryl phosphines, as stabilizing ligands. U.S. Pat. No. 4,151,209 by J. L. Paul, W. L. Pieper and L. W. Wade (assigned to Celanese Celanese Corp.) reported on the formation of propyl diphenyl phosphine ligand from the TPP-rhodium catalyst during propylene hydroformylation. U.S. Patent Nos. 3,560,539; 3,644,446 and 3,801,646 by F. B. Booth (assigned to Union Oil Co. of California) disclosed the derivation of undefined rhodium catalyst complexes by reduction, starting with a variety of phosphines including methyl diphenyl phosphine or propyl diphenyl phosphine. U.S. Pat. No. 3,239,566 by L. H. Slaugh and R. D. Mullineaux (assigned to Shell Oil Co.) disclosed methyl diphenyl phosphine, ethyl diphenyl phosphine and benzyl diphenyl phosphine as examples for an all inclusive definition of phosphine complexes of rhodium and ruthenium. Slaugh preferred the complexes of tributyl phosphine, started with rhodium chloride and emphasized the formation of alcohols as well as aldehydes in his process.
There are a number of patents which disclosed asymmetrical, optically active alkyl diaryl phosphines for the stereoselective hydroformylation of special olefins such as styrene, e.g., Canadian Pat. No. 1,027,141 by H. B. Tinker and A. J. Solodar (assigned to Monsanto Co.); British Pat. No. 1,402,832 by C. Botteghi, G. Consiglio and C. Salomon (assigned to P. Pino); U.S. Pat. No. 4,139,565 by J. D. Unruh and L. E. Wade (assigned to Celanese Corp.) and French Pat. No. 72.43479 by R. Stern, D. Commereuc, Y. Chavin and H. B. Kagan (assigned to the Institute Francais du Petrole, des Carburants et Lubrifiants). Although these ligands are structurally related to those of the present work, their properties and application is outside the scope of the present invention.
The most conclusive study regarding the effect on hydroformylation catalysis of an excess of a simple alkyl diphenyl phosphine, i.e., ethyl diphenyl phosphine, was published by A. R. Sanger in the Journal of Molecular Catalysis [3, pages 221-226, particularly page 222 (1977/1978)]. He reported that the addition of ethyl diphenyl phosphine to the TPP-rhodium catalyst resulted in less increase in catalyst activity at 20.degree. C. than that of excess TPP. He found similar effects when chelating di-alpha, .omega.-diphenylphosphino-alkanes were added. Using more than molar amounts of 1,4-diphenylphosphino-butane resulted in decreased catalyst activity.
There is much less information on hydroformylation catalysis by the rhodium complexes of substituted aliphatic phosphines, particularly substituted alkyl diaryl phosphines. Catalyst complexes of such phosphines are usually within the all inclusive scope of several patent applications already discussed. However, very few specific disclosures were made. In effect, no direct disclosure of any tris-(substituted alkyl diphenyl phosphine) rhodium carbonyl hydride was found prior to this invention.
In the area of trihydrocarbylsilyl substituted diphenyl phosphine rhodium complexes containing halogen, there are several disclosures by G. Chandra (British Pat. Nos. 1,419,769; 1,420,928 and 1,421,136, assigned to Dow Corning Ltd.). Tris-(trimethylsilyl-methyl diphenyl phosphine) rhodium carbonyl chloride is specifically disclosed. Relatively non-selective hydroformylation catalysis by this and similar complexes was recently reported by M. O Farrell, C. H. Van Dyke, L. J. Boucher and S. J. Metlin [J. Organomet. Chem., 169 (2) 199 (1979)].
Carboxy substituted t-phosphine rhodium and cobalt complexes of rhodium were disclosed in an all inclusive unspecified manner as hydroformylation catalysts in British Pat. No. 1,350,822 by BASF A.G. 2-Carboxyethyl diphenyl phosphine was disclosed as an exemplary phosphine ligand.
Halogen, aryloxy, alkoxy, hydroxy, nitro and phenyl substituted phosphine rhodium complexes were included in an all inclusive definition of phosphine rhodium complex hydroformylation catalysts in British Pat. No. 1,298,331 by G. Wilkinson (assigned to Johnson, Matthey & Co., Ltd). However, not a singly substituted alkyl diaryl phosphine compound was named. Similarly, amino, halo and alkyl substituted rhodium complex hydroformylation catalysts were generically disclosed by F. B. Booth in U.S. Pat. No., 3,965,192 (assigned to Union Oil Co. of California) which was already referred to. Again, no example of substituted alkyl diaryl phosphine was given.
As far as alkyl diphenyl phosphines are concerned, many compounds are known. However, few aryl or nonhydrocarbyl substituted compounds were disclosed. A complete list of characterized compounds and their preparation, up to 1969, is given in Volume 1, Chapter 1, pages 154 to 162 by L. Maier, as a part of the series of monographs, entitled "Organic Phosphorus Compounds" by G. M. Kosolapoff and L. Maier, J. Wiley & Sons, Inc., New York, N.Y., 1972. However, none of the heteroorganic substituted compounds of the present invention is disclosed. Chapter 3 by G. Booth of the same book also lists characterized phosphine metal complexes. However, no rhodium carbonyl hydrides are found.
With regard to the synthesis of alkyl diphenyl phosphines in general, Kosolapoff and Maier lists a number of displacement reactions as being frequently used (see page 2). However, there is little information on diphenyl phosphine to olefin addition. No substituted alkyl diphenyl phosphine derived via addition is disclosed. As far as the hydrido carbonyl rhodium complexes of phosphines are concerned, the known, obviously applicable syntheses, are reviewed in Booth's chapter. They do not include the presently recommended methods.
In the area of the silylalkylphosphine intermediates of the present invention, there are several disclosures related to the present invention. British Pat. No. 925,721 by H. Niebergall (assigned to Koppers Co., Inc.) broadly disclosed the addition of secondary phosphines to unsaturated silanes to provide silylalkyl phosphines. British Pat. No. 1,179,242 by W. J. Owen and B. E. Cooper, assigned to Midland Silicones, Ltd., disclosed the preparation of similar compounds via displacement reactions of chlorophosphines and silylalkyl Grignard compounds or sodium phosphines and silylalkyl halides. The preparation of related compounds, i.e., alkoxysilylalkylphosphines was described via an alternative addition method reacting alkoxysilances and unsaturated phosphines, by F. Fekete in U.S. Pat. No. 3,067,227, assigned to Union Carbide Corp. Silylalkylphosphine intermediates useful in the preparation of the complexes of the present invention were disclosed by J. K. Jacques and W. J. Owen in British Pat. No. 1,182,763 assigned to Albright and Wilson (MFG) Ltd., by B. E. Cooper and W. J. Owen in a journal article on oxidation potentials [see J. Organometal. Chem., 29, 33-40 (1971)].
In the area of insoluble, anchored phosphine-transition metal complex catalysts reactive silyl substituted alkyl diphenyl phosphines were utilized as intermediates for anchoring. For reference, see U.S. Pat. No. 3,726,809 by K. G. Allum, S. McKenzie and R. C. Pitkethly and U.S. Pat. No. 3,907,852 by A. A. Oswald and L. L. Murrell. Such phosphine anchoring agents had at least one reactive substituent on the silicon. As such, they reacted with the surface hydroxyl group of silica via siloxane formation.
In contrast to the prior art, it was found in the present invention that tris-(alkyl diaryl phosphine) rhodium carbonyl hydride complexes are attractive selective hydroformylation catalysts in the absence of TPP-rhodium, dependent on several unexpected conditions. Compared to the widely studied triphenyl phosphine rhodium complexes, the optimum catalysis temperature of the present complexes is higher. Higher hydroformylation temperatures using the present catalysts are possible because catalyst stability and selectivity are better maintained.
One of the key unexpected factors in process of the present invention is that the present catalysts can be employed in a large excess without a drastic loss of catalyst activity. The other factor, also important for high selectivity, is the high ratio H.sub.2 to CO. Unexpectedly, the excess of hydrogen does not result in the reduction of the aldehyde hydroformylation products to the corresponding alcohols. Coupled with the high H.sub.2 /CO ratios, it is essential in the present process to employ relatively low pressures, effectively limiting the CO partial pressure. Finally, the continuous process of the present invention is distinguished by relatively low olefin conversions. These are important for both catalysts stability and selectivity.
Due to the above characteristics, the present alkyl diaryl phosphine complex catalysts are uniquely suited for an operation wherein the aldehyde product is separated from the catalyst by distillation. Such a specifically advantageous operation is carried out in a continuous fashion wherein the olefin and synthesis gas feed are continuously introduced into the reactor comprising the catalyst solution and a mixture of the aldehyde product and the feed is continuously withdrawn in the gas phase.
The preferred selective process of the present invention, particularly the combination of the above features, is unique. It is not only unexpected in view of the prior art but was described as a process which should be inoperative due to the type of phosphine ligands employed.
When compared to the tris-(triphenyl phosphine) rhodium carbonyl hydride (TPP-rhodium) plus triphenyl phosphine based commercial, continuous process, the present process exhibits surprising advantages. The alkyl diaryl phosphines of the present process do not undergo P-C bond scission. The only catalyst by-products are the corresponding phosphine oxides. The latter are not inhibitors. The secondary by-products derived from the aldehyde products such as aldehyde trimers do not seriously inhibit the present catalytic system either. The present catalysts stand out with regard to long term activity maintenance in a continuous process. In contrast to the known process, no introduction of oxygen and/or chelating compounds or use of hydroxylic solvent is required for activity maintenance. As a consequence of higher catalyst stability, the present process can be operated at higher temperatures. This, in turn, can lead to an improved product to feed ratio in the distillate of the continuous product flash-off process. Also, it extends applicability to higher olefins and olefin derivatives. In addition, it provides unexpected advantages when employed for combined hydroformylation-aldolization-hydrogenation processes.
The applicability of the present phosphine ligands unexpectedly but understandably depends on their steric requirements, too. Substituents on the alkyl moiety close to the phosphorus were found to inhibit phosphine complexation with rhodium compounds for the first time. In contrast, substituents outside the immediate proximity of phosphorus resulted in improved complex catalysts. Such substituted phosphines could be surprisingly advantageously produced via the addition of diaryl phosphines to vinyl compounds having activated double bonds.
The alkyl diaryl phosphines of the present invention were found to complex with rhodium more strongly than triaryl phosphines. This finding led to a novel method of producing the present catalysts via ligand displacement, e.g., by the reaction of alkyl diaryl phosphines with tris-(triphenyl phosphine) rhodium carbonyl hydride. According to another novel method, the present complexes are produced from acetylacetonato dicarbonyl rhodium either prior to use or in situ under the reaction conditions.