Process for the alkoxycarbonylation of olefins in a medium having a low Brønsted acid concentration

Abstract

Process comprising the following process steps: a) introducing an ethylenically unsaturated compound; b) adding a ligand-metal complex comprising Pd and a bidentate phosphine ligand, or adding a bidentate phosphine ligand and a compound which comprises Pd; c) adding an alcohol; d) supplying CO; e) heating the reaction mixture, the ethylenically unsaturated compound being reacted to form an ester,
where the reaction mixture is admixed with less than 0.1 mol %, based on the amount of substance of the ethylenically unsaturated compound, of Brnsted acids having an acid strength of pKa3,
characterized in that the phosphine ligand is substituted on at least one phosphorus atom by at least one heteroaryl radical.

Claims

1. An acid-free alkoxycarbonylation process comprising the following process steps: a) introducing an ethylenically unsaturated compound; b) adding a ligand-metal complex comprising Pd and a bidentate phosphine ligand, or adding a bidentate phosphine ligand and a compound which comprises Pd; c) adding an alcohol; d) supplying CO; e) heating the reaction mixture, the ethylenically unsaturated compound being reacted to form an ester in the presence of a Brnsted acid at low concentration, where the reaction mixture has less than 0.1 mol %, based on the amount of substance of the ethylenically unsaturated compound, of Brnsted acids having an acid strength of pKa3 or an acid strength of a pKa5, where the Brnsted acid results from the reaction course and wherein the bidentate phosphine ligand is selected from a compound according to one of the formulae (I) and (II) ##STR00008## where R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.1, R.sup.2, R.sup.3, R.sup.4 are each independently selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.3-C.sub.20)-heteroaryl; at least one of the R.sup.1, R.sup.2, R.sup.3, R.sup.4 radicals or at least one of the R.sup.1, R.sup.2, R.sup.3, R.sup.4 radicals is a (C.sub.3-C.sub.20)-heteroaryl radical; and R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.1, R.sup.2, R.sup.3, R.sup.4, if they are (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl or (C.sub.3-C.sub.20)-heteroaryl, may each independently be substituted by one or more substituents selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl, O(C.sub.3-C.sub.12)-cycloalkyl, S(C.sub.1-C.sub.12)-alkyl, S(C.sub.3-C.sub.12)-cycloalkyl, COO(C.sub.1-C.sub.12)-alkyl, COO(C.sub.3-C.sub.12)-cycloalkyl, CONH(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.3-C.sub.12)-cycloalkyl, CO(C.sub.1-C.sub.12)-alkyl, CO(C.sub.3-C.sub.12)-cycloalkyl, N[(C.sub.1-C.sub.12)-alkyl].sub.2, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-O(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl, (C.sub.3-C.sub.20)-heteroaryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl-O(C.sub.1-C.sub.12)-alkyl, COOH, OH, SO.sub.3H, NH.sub.2 or halogen.

2. The process according to claim 1, where R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.1, R.sup.2, R.sup.3 and R.sup.4, if they are (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl or (C.sub.3-C.sub.20)-heteroaryl, may each independently be substituted by one or more substituents selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl, O(C.sub.3-C.sub.12)-cycloalkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-O(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl, (C.sub.3-C.sub.20)-heteroaryl-(C.sub.1-C.sub.12)-alkyl or (C.sub.3-C.sub.20)-heteroaryl-O(C.sub.1-C.sub.12)-alkyl.

3. The process according to claim 1, where at least two of the R.sup.1, R.sup.2, R.sup.3, R.sup.4 radicals or at least two of the R.sup.1, R.sup.2, R.sup.3, R.sup.4 radicals are a (C.sub.3-C.sub.20)-heteroaryl radical.

4. The process according to claim 3, where the R.sup.1 and R.sup.3 radicals or the R.sup.1 and R.sup.3 radicals are each a (C.sub.3-C.sub.20)-heteroaryl radical.

5. The process according to claim 4, where the R.sup.1 and R.sup.3 or R.sup.1 and R.sup.3 radicals are each a (C.sub.3-C.sub.20)-heteroaryl radical; and the R.sup.2 and R.sup.4 or R.sup.2 or R.sup.4 radicals are each independently selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl or (C.sub.6-C.sub.20)-aryl.

6. The process according to claim 1, where the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4 and/or R.sup.1, R.sup.2, R.sup.3 and R.sup.4, if they are a heteroaryl radical, are a heteroaryl radical having five or six ring atoms.

7. The process according to claim 1, where the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4 and/or R.sup.1, R.sup.2, R.sup.3 and R.sup.4, if they are a heteroaryl radical, are selected from 2-furyl, 2-thienyl, N-methyl-2-pyrrolyl, N-phenyl-2-pyrrolyl, N-(2-methoxyphenyl)-2-pyrrolyl, 2-pyrrolyl, N-methyl-2-imidazolyl, 2-imidazolyl, 2-pyridyl or 2-pyrimidyl, the stated heteroaryl radicals not being further substituted.

8. The process according to claim 1, where the bidentate phosphine ligand is selected from a compound according to one of the formulae (8) and (4) ##STR00009##

9. The process according to claim 1, wherein the ethylenically unsaturated compound is selected from the group consisting of ethene, propene, 1-butene, cis- and/or trans-2-butene, isobutene, 1,3-butadiene, 1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, hexene, tetramethylethylene, heptene, 1-octene, 2-octene, di-n-butene, and mixtures thereof.

10. The process according to claim 1, wherein the compound comprising Pd in process step b) is selected from palladium dichloride, palladium(II) acetylacetonate, palladium(II) acetate, dichloro(1,5-cyclooctadiene)palladium(II), bis(dibenzylideneacetone)palladium, bis(acetonitrile)dichloropalladium(II) or palladium(cinnamyl) dichloride.

11. The process according to claim 1, wherein the alcohol in process step c) is selected from the group consisting of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol, and mixtures thereof.

12. The process according to claim 1, where the reaction mixture is admixed with less than 0.1 mol %, based on the amount of substance of the ethylenically unsaturated compound, of Brnsted acids having an acid strength of pKa5.

Description

DESCRIPTION OF ILLUSTRATIONS

(1) FIG. 1: effect of the palladium precursor on the methoxycarbonylation of ethylene with ligands 3, 4 and 8.

(2) FIG. 2: acid-free methoxycarbonylation of ethene with ligands 3, 4 and 8

EXAMPLES

(3) The invention is described in more detail below by means of working examples

(4) General Procedures

(5) All the preparations which follow were carried out under protective gas using standard Schlenk techniques. The solvents were dried over suitable desiccants before use (Purification of Laboratory Chemicals, W. L. F. Armarego (Author), Christina Chai (Author), Butterworth Heinemann (Elsevier), 6th edition, Oxford 2009).

(6) Phosphorus trichloride (Aldrich) was distilled under argon before use. All preparative operations were effected in baked-out vessels. The products were characterized by means of NMR spectroscopy. Chemical shifts (6) are reported in ppm. The .sup.31P NMR signals were referenced as follows: SR.sub.31P=SR.sub.1H*(BF.sub.31P/BF.sub.1H)=SR.sub.1H*0.4048. (Robin K. Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Robin Goodfellow, and Pierre Granger, Pure Appl. Chem., 2001, 73, 1795-1818; Robin K. Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Pierre Granger, Roy E. Hoffman and Kurt W. Zilm, Pure Appl, Chem., 2008, 80, 59-84).

(7) The recording of nuclear resonance spectra was effected on Bruker Avance 300 or Bruker Avance 400, gas chromatography analysis on Agilent GC 7890A, elemental analysis on Leco TruSpec CHNS and Varian ICP-OES 715, and ESI-TOF mass spectrometry on Thermo Electron Finnigan MAT 95-XP and Agilent 6890 N/5973 instruments.

(8) Preparation of Precursor E

Preparation of chloro-2-pyridyl-tert-butylphosphine

(9) The Grignard for the synthesis of chloro-2-pyridyl-t-butylphosphine is prepared by the Knochel method with isopropylmagnesium chloride (Angew. Chem, 2004, 43, 2222-2226). The workup is effected according to the method of Budzelaar (Organometallics 1990, 9, 1222-1227).

(10) ##STR00004##

(11) 8.07 ml of a 1.3 M isopropylmagnesium chloride solution (Knochers reagent) are introduced into a 50 ml round-bottom flask with magnetic stirrer and septum, and cooled to 15 C. Thereafter, 953.5 l (10 mmol) of 2-bromopyridine are rapidly added dropwise. The solution immediately turns yellow. It is allowed to warm up to 10 C. The conversion of the reaction is determined as follows: about 100 l solution are taken and introduced into 1 ml of a saturated ammonium chloride solution. If the solution bubbles, not much Grignard has formed yet. The aqueous solution is extracted with a pipette of ether and the organic phase is dried over Na.sub.2SO.sub.4. A GC of the ethereal solution is recorded. When a large amount of pyridine has formed compared to 2-bromopyridine, conversions are high. At 10 C., there has been little conversion. After warming up to room temperature and stirring for 1-2 hours, the reaction solution turns brown-yellow. A GC test shows complete conversion. Now the Grignard solution can be slowly added dropwise with a syringe pump to a solution of 1.748 g (11 mmol) of dichloro-tert-butylphosphine in 10 ml of THF which has been cooled to 15 C. beforehand. It is important that the dichloro-tert-butylphosphine solution is cooled. At room temperature, considerable amounts of dipyridyl-tert-butylphosphine would be obtained. A clear yellow solution is initially formed, which then turns cloudy. The mixture is left to warm up to room temperature and to stir overnight. The solvent is removed under high vacuum and a whitish solid which is brown in places is obtained. The solid is suspended with 20 ml of heptane and the solid is comminuted in an ultrasound bath. After allowing the white solid to settle out, the solution is decanted. The operation is repeated twice with 10-20 ml each time of heptane. After concentration of the heptane solution under high vacuum, it is distilled under reduced pressure. At 4.6 mbar, oil bath 120 C. and distillation temperature 98 C., the product can be distilled. 1.08 g of a colourless oil are obtained. (50%).

(12) Analytical data: .sup.1H NMR (300 MHz, C.sub.6D.sub.6): 8.36 (m, 1H, Py), 7.67 (m, 1H, Py), 7.03-6.93 (m, 1H, Py), 6.55-6.46 (m, 1H, Py), 1.07 (d, J=13.3 Hz, 9H, t-Bu)

(13) .sup.13C NMR (75 MHz, C.sub.6D.sub.6): 162.9, 162.6, 148.8, 135.5, 125.8, 125.7, 122.8, 35.3, 34.8, 25.9 and 25.8.

(14) .sup.31P NMR (121 MHz, C.sub.6D.sub.6) 97.9,

(15) MS (EI) m:z (relative intensity) 201 (M.sup.+, 2), 147(32), 145 (100), 109 (17), 78 (8), 57.1 (17).

(16) Preparation of Compound 8

Preparation of 1,1-bis(tert-butyl-2-pyridylphosphino)ferrocene

(17) ##STR00005##
Variant A:

(18) 474.4 mg (2.55 mmol) of sublimed ferrocene are weighed out into a 50 ml round-bottom flask with magnetic stirrer and septum, and secured. Following addition of 15 ml of heptane, the ferrocene has completely dissolved. Then 841 l of tetramethylethylenediamine (1.1 eq, 5.61 mmol) are added in one go and 2.04 ml of BuLi (2.5 M in hexane, 2.0 eq, 5.1 mmol) are added dropwise. After 2-3 hours an orange precipitate is formed. The mixture is stirred overnight, the heptane solution is decanted, and the orange solid is washed twice with heptane. Then a further 10 ml of heptane are added and the suspension is cooled to 70 C. 1.08 g (2.1 eq, 5.36 mmol) of chloro-2-pyridyl-tert-butylphosphine are dissolved in 7 ml of heptane. The solution is cloudy and must be filtered over Celite. A little insoluble white solid has formed. This solution is added dropwise to the dilithium ferrocene solution. In the course of warming to room temperature, the orange suspension lightens. In order to complete the reaction, the reaction solution is heated under reflux for about 1 hour. A clear orange solution and white precipitate have formed.

(19) 7 ml of argon-saturated water are added to the suspension. The white precipitate dissolves. Following removal of the aqueous phase, the procedure is repeated twice. In the course of these operations, the heptane phase becomes cloudy. Following complete removal of the organic phase under a high vacuum, an oily orange residue is left. This residue is taken up in 10 ml of ether and dried over Na.sub.2SO.sub.4 (crude yield 913 mg). At 28 C., overnight, neither a precipitate nor crystals are formed. Even a mixture of diethyl ether and heptane at 28 C. does not result in crystallization. A .sup.31P NMR of the solution again shows the product peak, now at 7.39 ppm, and a signal at 40.4 ppm. The product can be purified by column chromatography. The ether solution is applied under argon to a short column eluted with diethyl ether. The orange product front runs away right at the front and can easily be collected. Removal of the ether gives 241 mg (16%) of a viscous orange oil in a purity of approximately 95%.

(20) Variant B:

(21) Batch size: 650.17 mg (3.495 mol) of ferrocene (sublimed), 2.8 ml (2 eq, 6.99 mmol) of 2.5 M BuLi (n-butyllithium), 1.1 ml (2.1 eq, 7.3 mmol) of tetramethylethylenediamine and 1.48 g (2.1 eq, 7.34 mmol) of chloro-2-pyridyl-tert-butylphosphine.

(22) The dilithium salt of the ferrocene is again prepared in 15 ml of heptane. The chloro-2-pyridyl-tert-butylphosphine is dissolved, instead of in heptane, in 10 ml of THF, since the chlorophosphine dissolves better in THF. The work-up procedure was likewise optimized: after the boiling under reflux, the reaction mixture is quenched with just 1 ml of H.sub.2O and the solvent (heptane and THF) is removed completely under a high vacuum. The dark-yellow-orange, tough solid is taken up in 8 ml of H.sub.2O and 15 ml of diethyl ether and stirred for 1 minute. Following phase separation, the aqueous phase is removed by syringe and the organic phase is washed three times with H.sub.2O. The organic phase is dried over Na.sub.2SO.sub.4 and filtered. The product is washed out of the Na.sub.2SO.sub.4 with three times 10 ml of diethyl ether until the solution is virtually colourless. The dark-orange solution is concentrated to a volume of 10 ml and passed under argon through a column containing silica gel 60. The eluent used is again diethyl ether. The filtrate is substantially lighter and orange. Removal of the solvent gives 1.16 g of a tough orange solid (64%).

Preparation of Compound 4 (,-bis(2-pyridyl(t-butyl)phosphino)o-xylene)

(23) ##STR00006##

(24) 675 mg (27.8 mmol, 4 eq) of Mg powder are weighed out in a glovebox in a 250 ml round-bottom flask with a nitrogen tap and magnetic stirrer bar, and the flask is sealed with a septum. High vacuum is applied to the round-bottom flask (about 510.sup.2 mbar) and it is heated to 90 C. for 45 minutes. After cooling down to room temperature, 2 grains of iodine are added and the mixture is dissolved in 20 ml of THF. The suspension is stirred for about 10 minutes until the yellow colour of the iodine has disappeared. After the magnesium powder has settled out, the cloudy THF solution is decanted and the activated magnesium powder is washed twice with 1-2 ml of THF. Then another 20 ml of fresh THF are added. At room temperature, a solution of 1.21 g (6.9 mmol) of ,-dichloro-o-xylene in 70 ml of THE is slowly added dropwise with a syringe pump. The THF solution gradually turns a darker colour. The next day, the THF suspension is filtered to remove the unconverted magnesium powder and the content of Grignard compound is determined as follows:

(25) 1 ml of Grignard solution is quenched in a saturated aqueous solution of NH.sub.4Cl and extracted with ether, and dried with Na.sub.2SO.sub.4.

(26) Quantitative Determination of the Content of the Grignard Solution:

(27) 1 ml of Grignard solution is quenched with 2 ml of 0.1 M HCl and the excess acid is titrated with 0.1 M NaOH. A suitable indicator is an aqueous 0.04% bromocresol solution. The colour change goes from yellow to blue. 0.74 ml of 0.1 M NaOH has been consumed. 2 ml-0.74 ml=1.26 ml, corresponding to 0.126 mmol of Grignard compound. Since a di-Grignard is present, the Grignard solution is 0.063 M. This is a yield exceeding 90%.

(28) In a 250 ml three-neck flask with reflux condenser and magnetic stirrer, under argon, 1.8 g (8.66 mmol) of chlorophosphine (2-Py(tBu)PCI) are dissolved in 10 ml of THF and cooled to 60 C. Then 55 ml of the above-stipulated Grignard solution (0.063 M, 3.46 mmol) are slowly added dropwise at this temperature with a syringe pump. The solution at first remains clear and then turns intense yellow. After 1.5 hours, the solution turns cloudy. The mixture is left to warm up to room temperature overnight and a clear yellow solution is obtained. To complete the reaction, the mixture is heated under reflux for 1 hour. After cooling, 1 ml of H.sub.2O is added and the solution loses colour and turns milky white. After removing THF under high vacuum, a stringy, pale yellow solid is obtained. 10 ml of water and 10 ml of ether are added thereto, and two homogeneous clear phases are obtained, which have good separability. The aqueous phase is extracted twice with ether. After the organic phase has been dried with Na.sub.2SO.sub.4, the ether is removed under high vacuum and a stringy, almost colourless solid is obtained. The latter is dissolved in 5 ml of MeOH while heating on a water bath and filtered through Celite. At 28 C., 772 mg of product are obtained in the form of white crystals overnight. (51%). After concentration, it was possible to isolate another 100 mg from the mother solution. The overall yield is 57.6%,

(29) .sup.1H NMR (300 MHz, C.sub.6D.sub.6): 8.58 (m, 2H, Py), 7.31-7.30 (m, 2H, benzene), 7.30-7.22 (m, 2H, Py), 6.85-6.77 (m, 2H, Py), 6.73 (m, 2H, benzene), 6.57-6.50 (m, 2H, py), 4.33 (dd, J=13.3 and 4.3 Hz, 2H, CH.sub.2), 3.72-3.62 (m, 2H, CH.sub.2), 121 (d, J=11.8 Hz, 18H, tBu).

(30) .sup.13C NMR (75 MHz, C.sub.6D.sub.6); 161.3, 161.1, 149.6, 137.8, 137.7, 134.5, 133.3, 132.7, 131.4, 131.3, 125.7, 122.9, 30.7, 30.5, 28.2, 28.0, 26.5, 26.4, 26.2, and 26.1.

(31) .sup.31P NMR (121 MHz, C.sub.6D.sub.6) 8.8.

(32) EA calculated for C.sub.26H.sub.34N.sub.2P.sub.2: C, 71.54; H, 7.85; N, 6.56; P, 14.35. Found: C, 71.21; H, 7.55; N, 6.56; P, 14.35.

(33) High-Pressure Experiments

(34) Feedstocks:

(35) Methanol (MeOH)

(36) Ethene (Also Referred to as Ethylene

(37) General Method for Performance of the High-Pressure Experiments

(38) General Experiment Description for Reactions in Batchwise Mode:

(39) Depending on the palladium precursor, 0.04 mol %, based on the ethylene, are weighed out under argon, and 0.16 mol % of the corresponding ligand are weighed out, into a 25 ml Parr reactor (Parr autoclave) which can be given gastight sealing. 5 ml of methanol are added. Then 1 g of ethylene (35.7 mmol) is transferred into the autoclave (monitored via weighing of the autoclave). The autoclave is heated to 80 C. The autogenous pressure of the ethylene at 80 C. is now 20 bar. 30 bar of CO are injected at this point. At this temperature, the autoclave is stirred for 20 h and the pressure drop is measured using a pressure sensor and the Specview software from Parr Instruments. The yields of product indicated in the diagram are in agreement with the consumption of gas. The autoclave is subsequently cooled to room temperature and the pressure is let off. The contents of the autoclave are transferred to a 50 ml Schlenk vessel, and 1 ml of isooctane is added as an internal standard. The yieid of methyl propionate is determined by GC analysis.

(40) Analysis:

(41) GC analysis of the products from ethene: for the GC analysis, an Agilent 7890A gas chromatograph having a 30 m HP column is used. Temperature profile: 35 C., 10 min: 10 C./min to 200 C., 16.5 min; the injection volume is 1 l with a split of 50:1. Retention time of methyl propionate: 6.158 min

(42) Methanol Analysis

(43) Methanol was pretreated in a solvent drying unit: Pure Solv MD-/Solvent purification system, Innovative Technology Inc. One Industrial Way, Amesbury Mass. 01013

(44) Water Values:

(45) Determined by Karl Fischer titration: TitraLab 580-TIM580, Radiometer Analytical SAS (Karl-Fischer Titration), water content: measurement ranges, 0.1-100% w/w, measured water content: 0.13889%

(46) The following were used:

(47) Technical methanol from Applichem: No. A2954,5000, batch number: LOT: 3L005446

(48) Water content max. 1%

(49) Methanol from Acros Organics (via molecular sieve): water content 0.005%, code number: 364390010, batch number: LOT 1370321

(50) TON: turnover number, defined as moles of product per mole of catalyst metal

(51) TOF: turnover frequency, defined as TON per unit time for the attainment of a particular conversion, e.g. 50%

(52) The n/iso ratio indicates the ratio of olefins converted terminally esters to olefins converted internally to esters.

(53) The n selectivities reported hereinafter relate to the proportion of terminal methoxycarbonylation based on the overall yield of methoxycarbonylation products.

Ethylene Example

(54) ##STR00007##

PdCl2/3 (Comparative Example)

(55) A 25 ml Parr autoclave is charged under argon with PdCl.sub.2 (2.53 mg, 0.04 mol % based on the amount of substance of ethylene) and 3 (22.5 mg, 0.16 mol % based on the amount of substance of ethylene) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis is carried out for determination of yield. The yield is 20%.

PdCl2/8

(56) A 25 ml Parr autoclave is charged under argon with PdCl.sub.2 (2.53 mg, 0.04 mol % based on the amount of substance of ethylene) and 8 (29.5 mg, 0.16 mol % based on the amount of substance of ethylene) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis is carried out for determination of yield. The yield is 100%.

PdCl2/4

(57) A 25 ml Parr autoclave is charged under argon with PdCl.sub.2 (2.53 mg, 0.04 mol %, here and always hereinafter, based on the amount of substance of ethylene) and 4 (29.5 mg, 0.16 mol %, here and always hereinafter, based on the amount of substance of ethylene) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis is carried out for determination of yield. The yield is 100%.

Pd(acac)2/3 (Comparative Example)

(58) A 25 ml Parr autoclave is charged under argon with Pd(acac).sub.2 (4.34 mg, 0.04 mol %) and 3 (22.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. Yield of product is not detectable.

Pd(acac)2/8

(59) A 25 ml Parr autoclave is charged under argon with Pd(acac).sub.2 (4.34 mg, 0.04 mol %) and 8 (29.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 60%.

Pd(acac)2/4

(60) A 25 ml Parr autoclave is charged under argon with Pd(acac).sub.2 (4.34 mg, 0.04 mol %) and 4 (24.9 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 29%.

Pd(OAc)2/8

(61) A 25 mi Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 8 (29.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. The autoclave is heated to 80 C. The pressure in the autoclave at this point is 20 bar at 80 C. Then 30 bar of CO are injected. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 58%.

(62) The results are shown in FIG. 1

(63) FIG. 1: Effect of the palladium precursor on the methoxycarbonylation of ethylene with ligands 3, 4 and 8.

(64) As is clearly apparent, with the PdCl.sub.2/ligand 8 combination without addition of an acid, a yield of >90% of methyl propionate is achieved after only around 2 hours, with a turnover frequency of 3700 mol of product/(mol Pd*h) based on a yield of 30%. Similarly good values are achieved with ligand 4. Here there is 90% yield after around 3 hours with a turnover frequency of 400. In comparison to this, the comparative ligand DTBPMB (3) shows a yield of around 20% with a turnover frequency of 27 only after 20 hours. Similarly, the use of Pd acetylacetonate or Pd acetate as a metal precursor in combination with the ligand for inventive use still leads to measurable yields in the acid-free system, whereas ligand 3 is no longer catalytically active.

(65) FIG. 2: Acid-free methoxycarbonylation of ethene with ligands 3, 4 and 8

(66) FIG. 2 shows results for the acid-free methoxycarbonylation of ethylene with ligands 3, 4 and 8. The reference point is the methoxycarbonylation with ligand 8 and the Pd compound palladium acetate Pd(OAc).sub.2 at 80 C. By raising the temperature to 120 C. it is possible to boost the yield of methyl propionate in 20 hours from 50% to 84%. With ligand 4 it is possible at 120 C. to achieve a yield of as much as 87% after 20 hours. The comparative ligand DTBPMB (3) gives a yield of only 3% in the acid-free system. The experiments are described in detail below.

Pd(OAc)2/8

(67) A 25 ml Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 8 (29.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. Then 30 bar of CO are injected. The autoclave is heated to 80 C. The contents are stirred at 80 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 50%.

Pd(OAc)2/8

(68) A 25 ml Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 8 (29.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. Then 30 bar of CO are injected. The autoclave is heated to 100 C. The contents are stirred at 100 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 64%.

Pd(OAc)2/8

(69) A 25 ml Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 8 (29.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. Then 30 bar of CO are injected. The autoclave is heated to 120 C. The contents are stirred at 120 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 84%.

Pd(OAc)2/3 (Comparative Example)

(70) A 25 ml Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 3 (22.5 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. Then 30 bar of CO are injected. The autoclave is heated to 120 C. The contents are stirred at 120 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 3%.

Pd(OAc)2/4

(71) A 25 ml Parr autoclave is charged under argon with Pd(OAc).sub.2 (3.2 mg, 0.04 mol %) and 4 (24.9 mg, 0.16 mol %) and 5 ml of methanol. Then 1 g (35.7 mmol) of ethylene is transferred into the autoclave. Mass is monitored via weighing of the autoclave. Then 30 bar of CO are injected. The autoclave is heated to 120 C. The contents are stirred at 120 C. for 20 h and the pressure drop in the autoclave is measured. The autoclave is then cooled and the residual pressure is let off. The contents of the autoclave are then transferred to a 50 ml Schlenk vessel and admixed with 1 ml of isooctane as an internal standard. A GC analysis takes place for determination of yield. The yield is 87%.