NEW TRANSITION METAL CATALYST

Abstract

The present invention relates to specific transition metal catalysts and their use in chemical reactions.

Claims

1. A transition metal catalyst of the formula (I)
[M(III)QX(Y).sub.n]  (I), wherein M is a transition metal chosen from the list of Ru, Rh and Ir, preferably Ir, and Q is the ligand L or an anion of the ligand L, wherein the ligand L has the following formula (II) ##STR00013## wherein R.sub.1 is H, CH.sub.3 or OH, R.sub.2 is H, CH.sub.3 or OH, R.sub.3 is H or CH.sub.3 R.sub.4 is a C.sub.2-C.sub.4 alkyl group, which is substituted by at least one OH group and which is optionally further substituted, with the provisos that when R.sub.1 is OH or CH.sub.3, then R.sub.2 is H and when R.sub.2 is OH or CH.sub.3, then R.sub.1 is H, and X is cyclopentadienyl, or a substituted cyclopenadienyl group, preferably indenyl or pentamethylcyclopentadienyl, and Y is an anion and n is 1 or 2, with the proviso that the value of n is chosen such that the overall metal complex is a neutral species.

2. Transition metal catalyst according to claim 1, wherein M is Ir.

3. Transition metal catalyst according to claim 1, wherein L is a ligand of formula (IIa) ##STR00014##

4. Transition metal catalyst according to claim 1, wherein L is a ligand of formula (IIb) ##STR00015##

5. Transition metal catalyst according to claim 1, wherein L is a mixture of ligands of formula (IIa) ##STR00016## and of formula (IIb) ##STR00017##

6. Transition metal catalyst according to claim 1, wherein L is a ligand of formula (II′a)-(II′″″a) or (II′b)-(II′″″b): ##STR00018## ##STR00019##

7. Transition metal catalyst according to claim 1, wherein L is a ligand of formula (II′a) ##STR00020##

8. Transition metal catalyst according to claim 1, wherein Y is chosen from the group consisting of a halide, carboxylate, formate, hydride, borohydride, borate, BF.sub.4.sup.−, PF.sub.6.sup.−SbF.sub.6.sup.−and BAr.sup.F.sub.4.sup.−.

9. Transition metal catalyst according to claim 1, wherein Y is chosen from the group consisting of hydride and halide.

10. Transition metal catalyst according to claim 1, wherein Y is Cl.sup.−.

11. Use of at least one transition metal catalyst according to claim 1 in a chemical process.

12. Use according to claim 11, which is reduction reaction.

Description

EXAMPLES

[0033] The ligands used are either commercially available or can be prepared using known methods. One method to prepare a range of ligands is described below.

General Procedure for Preparation of Ligands

[0034] An oven-dried flask was charged with Cbz-D-proline or Cbz-L-proline (1.00 eq.) or a proline derivative and dry dichloromethane (0.20 mol/L). The solution was cooled to 0° C. and triethylamine (1.00 eq.) and isobutyl chloroformate (1.00 eq.) were added. The mixture was stirred for 0.5 h, and the relevant amine (1.00 eq.) was added. The mixture was warmed to room temperature and stirred until complete conversion (monitored by TLC). The mixture was washed with aq. sat. NH.sub.4Cl, aq. sat. NaHCO.sub.3 and brine. Each aqueous layer was re-extracted with dichloromethane. The combined organic layers were dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The crude intermediate could be purified or used in the following step without further purification. The intermediate (1.00 eq.) was dissolved in MeOH (0.40 mol/L), the flask was flushed with argon three times and Pd/C (10.0 wt. %, 5.00 mol %) was added in one portion. The mixture was evacuated and flushed with hydrogen five times. The black suspension was stirred at room temperature under a hydrogen atmosphere until complete conversion (monitored by TLC). The reaction mixture was filtered over a plug of celite and rinsed with methanol.

Example 1 - (R)-N-(2-Hydroxyethyl)Pyrrolidine-2-Carboxamide (Ligand II′b)

[0035] According to the procedure above: Cbz-D-proline (2.49 g,10.0 mmol, 1.00 eq.), triethylamine (1.41 mL, 10.0 mmol, 1.00 eq.), isobutyl chloroformate (1.30 mL, 10.0 mmol, 1.00 eq.) and ethanolamine (1.21 mL, 10.0 mmol, 1.00 eq.) were reacted to form the intermediate (2.08 g).

[0036] The intermediate (2.03 g, 6.94 mmol, 1.00 eq.) and Pd/C (10.0 wt. %, 368 mg, 347 μmol, 5.00 mol %) yielded ligand (II′b) as a colorless liquid (1.10 g, quant.).

Example 2: Preparation of Ethyl (R)-2-Hydroxy-3,3-Dimethyl-4-Oxobutanoate

[0037] To a solution of (R)-N-(2-hydroxyethyl)pyrrolidine-2-carboxamide (II′b, 79.1 mg, 500 μmol, 5.00 mol%) in t-BuOH (10.0 mL), isobutanal (910 pL,10.0 mmol, 1.00 eq.) and ethyl glyoxalate (50.0% in toluene, 1.98 mL,10.0 mmol, 1.00 eq.) were added. The mixture was stirred at room temperature for 24 h. The solvent was removed in vacuo and the residue purified by column chromatography (cyclohexane/ethyl acetate, 4:1) yielding ethyl (R)-2-hydroxy-3,3-dimethyl-4-oxobutanoate (VI) (1.47 g, 84%, 72% ee) as a colorless oil. 1H NMR (400 MHz, CDCl3) δ=9.57 (1H, s), 4.32 (1H, s), 4.30-4.18 (2H, m), 3.06 (1H, br), 1.27 (3H, t), 1.14 (3H,s), 1.05 (3H, s). The analytical data was in agreement with an authentic sample.

Example 3: Preparation of Catalyst [IrCl(Cp*)(Anion of Ligand II′b)]

[0038] To a solution of (IrCl.sub.2(Cp*)).sub.2 (19.9 mg, 25.0 μmol, 1.00 eq.) in dry toluene was added (R)-N-(2-hydroxyethyl)pyrrolidine-2-carboxamide (II′b, 7.91 mg, 50.0 μmol, 2.00 eq.) and triethylamine (11.0 μL, 75.0 μmol, 3.00 eq.). The solution was stirred at room temperature for 4 h. The solvent was decanted with a syringe to obtain a yellow precipitate. The catalyst could be recrystallised from hexane/chloroform. 1H NMR (500 MHz, CDCl3)β=5.63 (1H, br), 4.33 (1H, br), 3.98 (1H, m), 3.79 (2H, m), 3.64 (1H, m), 3.58 (1H, br), 3.44 (1H, m), 3.13 (1H, m), 2.14 (1H, m), 2.02 (1H, m), 1.85 (1H, m), 1.78 (1H, m), 1.67 (15H, s); 13C NMR (126 MHz, CDCl3) β=181.5, 85.5, 65.1, 64.0, 54.3, 52.4, 29.8, 26.7, 9.5.

General Procedure for Transfer Hydrogenation Ethyl (R)-2-Hydroxy-3,3-Dimethyl-4-Oxobutanoate to Yield (R)-2-Hydroxy-3,3-Dimethyl-γ-Butyrolactone

[0039] The preformed transition metal catalyst or the transition metal salt and the ligand were added to a solution of ethyl (R)-2-hydroxy-3,3-dimethyl-4-oxobutanoate (from example 2) in water:tert-butanol (2:1). The mixture was degassed, sodium formate (5 eq.) was added and the mixture was stirred at the desired temperature for the stated time. The reaction mixture extracted with MTBE or dichloromethane and the combined organic phases were dried, filtered and concentrated in vacuo.

TABLE-US-00001 T T Conv. Example Ligand Metal precursor and loading [° C.] [h] [%] 3a II′b (RuCl.sub.2(p-cymene)).sub.2 0.50 mol % rt 26 98 3b II′b (IrCl.sub.2Cp*).sub.20.50 mol % 40 1 99 3c II′b (IrCl.sub.2Cp*).sub.2 0.50 mol % rt 4 99 3d II′b (IrCl.sub.2Cp*).sub.2 0.25 mol % 40 2 93 3e II′b (IrCl.sub.2Cp*).sub.2 0.10 mol % 40 5 99 3f II′b (RhCl.sub.2Cp*).sub.2 0.50 mol % 40 2.5 97

[0040] Examples 3b to 3f are the examples claimed by the present patent claims, whereas 3a is a comparison example.