Abstract:
Hydrogenation of a polyene to a monoene using a ruthenium catalyst that is promoted with a sterically-hindered tertiary amine.

Description:
FIELD OF THE INVENTION 
     This invention relates to the hydrogenation of a polyene to produce a monoene using a ruthenium catalyst that is promoted by a sterically-hindered tertiary amine or a sterically-hindered pyridine. 
     BACKGROUND OF THE INVENTION 
     The hydrogenation of polyenes to produce monoenes using ruthenium complex catalysts is disclosed in Fahey&#39;s U.S. Pat. No. 3,925,494. Fahey&#39;s U.S. Pat. No. 3,804,914, in Example II shows hydrogenation of polyenes using a ruthenium complex catalyst and excess triphenylphosphine. Fahey discloses in Journal of Organic Chemistry, Vol. 38, No. 1, 1973, pages 80-87 that Lewis Bases, including diethylamine were tested in the hydrogenation of cyclododecatriene. No bases were found to be more effective at enhancing selectivity than triphenylphosphine. No other effects were noted. 
     The rate of hydrogenation of a particular polyene using a ruthenium catalyst is taught to be increased by adding certain specific amines in an article titled &#34;Selective Homogeneous Hydrogenation of 3-Oxo-1,4-diene Steroids. II. Effects of Basic Additives and para Substituents on the Hydrogenation with Dichlorotris(triphenylphosphine) ruthenium&#34;, by Nishimura et al, appearing in Bulletin of the Chemical Society of Japan, Vol. 46, 279-283 (1973). 
     The process disclosed by the Fahey patents suffers from the difficulty that there is an induction period of considerable length between the time the ingredients of the reaction mixture are combined under reaction conditions, and the time that the mixture actually begins to react at a significant rate. 
     An object of the present invention is to shorten this induction period. 
     SUMMARY OF THE INVENTION 
     The present invention is a process for the hydrogenation of a polyene to a monoene which comprises forming a reaction mixture containing the polyene, hydrogen, a ruthenium-ligand complex hydrogenation catalyst, free triarylphosphine, and a sterically-hindered tertiary amine of the formula NR 3  where R is alkyl or aryl or a sterically-hindered pyridine having an alkyl or aryl substitutent in the 2 and/or 6 position, and reacting the mixture under hydrogenation conditions. The presence of the sterically-hindered tertiary amine or pyridine promotes the reaction, i.e., it reduces the induction period. Preferred sterically-hindered tertiary amines have cone angles of greater than 200 degrees. The term &#34;cone angle&#34; is used in accordance with the Seligson et al. article, J. Am. Chem. Soc., 1991, Vol. 113, No. 7, page 2520. Cone angle describes the amount of space taken up by a particular amine ligand on the metal i.e., ruthenium atom. 
    
    
     DETAILED DESCRIPTION 
     It is preferred that the ruthenium-ligand complex hydrogenation catalyst have the formula: Ru(PAr 3 ) 2  (CO) 2  Cl 2  (in which the triarylphosphine ligand P(Ar) 3  is from the group consisting of P(C 6  H 5 ) 3 , P(p-tolyl) 3 , P(p-F-C 6  H 4 ) 3 , P(p-OMe-C 6  H 4 ) 3  or P-(p-F-(C 6  H 5 ) 3 ) 
     The process is particularly effective in converting cyclododecatriene to cyclododecene. 
     The preferred sterically-hindered tertiary amines are those in which the R groups have 2 to 18 carbon atoms, and in which the total number of carbon atoms on all R groups is between 7 and 48. The preferred stericallyhindered pyridines are those in which the alkyl groups have 1 to 18 carbon atoms, or aryl groups having 6 to 14 carbon atoms. Examples are ethyldiiso-propylamine, tritolueneamine, N,N,N,N-tetramethyethylene-diamine, and 2,6-di-tert-butyl-4-methylpyridine. The tertiary amines may be used in lieu of other promoters such as lithium aluminum hydride, water, water-containing basic compounds like sodium hydroxide, or calcium carbonate. Normally the amount of sterically-hindered tertiary amine or pyridine in the reaction mixture should be in the amount of about 2 to 10 moles per mole of catalyst. 
     The amount of free triarylphosphine present in the reaction mixture should normally be in the range of about 5 to 50 moles per mole of catalyst. Suitable triarylphosphines include: triphenylphosphine, tris-paratolylphosphine, tris-para-fluorophenylphosphine, tris-para-methoxyphenylphosphine. It is desirable that the excess triarylphosphine be the same compound as the phosphine ligand on the ruthenium catalyst. 
     The amount of catalyst in the reaction mixture may vary widely, but is usually in the range set forth in the Fahey patent 3,925,494, i.e., 0.00001 to about 0.5 mole of ruthenium-ligand complex per mole of polyene. In addition to 1,5,9-cyclododecatriene the process operates on 1,5-cyclooctadiene, and linoleic acid ethyl ester. The Fahey patent ,494 indicates that such catalysts are satisfactory for cyclic and acyclic polyenes of up to 20 carbon atoms including 1,3-cyclopentadiene, 1,3-pentadiene, and 1,3,7,9-octa-decatetraene. 
     The process is normally operated at a pressure in the range of about 100 to about 600 psi and at a temperature in the range of about 130 to about 150° C. 
     Suitable solvents include benzene, toluene, cumene, isooctane, cyclohexane, ethanol, 1-butanol, ethylacetate, tetrahydrofuran. The reaction can be conducted without a solvent. 
     EXAMPLES 
     Table 1 below sets forth the ingredients, the amounts of the ingredients, and the results obtained when the reaction is run in a quartz Fischer-Porter tube at 120 psi H 2  and 150° C. All of the catalysts had the form Ru(PAr 3 ) 2  (CO) 2  Cl 2 . The percent conversion is after 4 hours. 
     
                                           TABLE I__________________________________________________________________________Pu Complex       CDDT                PAr.sub.3 **                    Toluene                                                     % Conv(mg)             (ml)                (g)  Promotor      NR.sub.3     (ml) (4__________________________________________________________________________                                                     h)Control 1 PPh.sub.3 50 mg            12  1.102                     --            --           8    7%Control 2 PPh.sub.3 50 mg            12  1.102                     LiAlH.sub.4 2.5 mg                                   --           8    11.9Example 1 PPh.sub.3 50 mg            12  1.102                     LiAlH.sub.4 2.5 mg                                   60 μL NEt(i-Pr).sub.2                                                18   47.5Example 2 PPh.sub.3 50 mg            12  1.102                     LiAlH.sub.4 2.5 mg                                   95 mg (N)(CH.sub.2 Ph).sub.3                                                15   37.9Example 3 PPh.sub.3 50 mg            12  1.18 --            50 μL NEt(i-Pr).sub.2                                                15   85.9Example 4 PPh.sub.3 50 mg            12  1.18 --            68 μL 2,5-di-tert-                                                18   56.3                                   butyl-4-methylpyridineExample 5 PPh.sub.3 50 mg            12  1.18 --            71 mg*       15   32.8Example 6 PPh.sub.3 50 mg            12  1.18 --            14 mg*       15   32Example 7 PPh.sub.3 50 mg            12  1.18 --            46 L TMEDA** 15   76.5Example 8 PPh.sub.3 50 mg            12  1.18 --            46 L NEt.sub.3                                                15   25Example 9 PPh.sub.3 50 mg            12  1.18 --            27 L Pyridine                                                15   2.2Example 10 P(p-F--C.sub.6 H.sub.4)            11.3                0.196                     --            54 μL NEt(i-Pr).sub.2                                                8.7  92.7Example 11 P(p-F--C.sub.6 H.sub.4).sub.3            11.3                0.196                     --            --           18.7 8.6Example 12 P(p-OMe--C.sub.6 H.sub.4).sub.3            10.8                0.209                     --            52 μL NEt(i-Pr).sub.2                                                19.2 55.4Example 13 P(p-OMe--C.sub.6 H.sub.4).sub.3            10.8                0.209                     --            --           19.2 22.7Example 14 PPh.sub.2 (p-Me--C.sub.6 H.sub.4)            11.9                1.18 --            57 μL NEt(i-Pr).sub.2                                                18.1 93.9Example 15 PPh.sub.2 (p-Me--C.sub.6 H.sub.4)            11.9                1.18 --            --           18.1 64.2Control 3 PPh.sub.3 50 mg            12  1.18 50 μL H.sub.2 O                                   --           18   2.0Control 4 PPh.sub.3 50 mg            12  1.18 50 μL 10%/NaOH aq                                   --           18   1.9Control 5 PPh.sub.3 50 mg            12  1.18 50 μL H.sub.2 O/7 mg CaCO.sub.3                                   --           18   2.8__________________________________________________________________________ *1,-8-bis(dimethylamino)napthalene **N,N,N,Ntetramethylethyldiamine ***Triphenylphosphine 
    
     Table 2 below sets forth the ingredients, the amount of ingredients, and the results obtained when the reaction is run in a Fischer-Porter tube at 150° C. and at 500 psi. All catalysts had the form Ru(PAr 3 ) 2  (CO) 2  Cl 2 . 
     
                                           TABLE 2__________________________________________________________________________Ru complex  CDDT           PAr.sub.3 *      % Conv(mg)        (ml)           (g) Promoter                    NR.sub.3                            (4 H)__________________________________________________________________________Control PPh.sub.3 25 mg       32  0.174               --   --      2.8Example 16 PPh.sub.3 25 mg       32  0.174               --   29 l NEt(i-Pr).sub.2                            24.2Control 8 PPh.sub.3 25 mg       32  0.174               --   9 l NEt.sub.3                            2.9__________________________________________________________________________ *Triphenylphosphine