Phenanthroline based pincer complexes useful as catalysts for the preparation of methanol from carbondioxide

Abstract

The present invention relates to a novel phenonthroline based pincer complexes and process for preparation thereof. The present invention also provides a one pot process for the conversion of carbon dioxide to methanol in the presence of a molecularly defined pincer-type single-site Ru-catalyst and secondary amine. Further the present invention provides the use of phenonthroline based pincer complexes for the esterification of alcohols and hydrogenation of esters under mild conditions.

Claims

1. A process for the preparation of methanol from carbon dioxide catalysed by phenanthroline complex pincer complexes, comprising the steps of: i. mixing a catalyst and a secondary amine in a ratio of (1:500) in tetrahydrofuran to obtain a solution; ii. adding potassium tert-butoxide to the solution obtained in step (a) to obtain a solution; iii. pressurizing the solution as obtained in step (ii) with carbon dioxide at 10 atmosphere followed by H.sub.2 atmosphere at 30-40 atm to obtain a solution; iv. heating the solution as obtained in step (iii) at 110-120 C. and stirring for 12-14 hrs to obtain a solution; v. removing excess gases from the solution as obtained in step (iv) to obtain N-formylated product of secondary amine; vi. adding the catalyst and potassium tert-butoxide to the N-formylated product of secondary amine as obtained in step (v) to obtain solution (vi); vii. pressurizing the solution as obtained in step (vi) with H.sub.2 at 40-45 atmosphere followed by heating the solution at 110-120 C. and stirring for 18-20 hrs to obtain methanol and recyclable secondary amine, wherein the catalyst used in step (i) and step (vi) is selected from HCl(CO)Ru(Phen-(tBu)PNN) (3); H(CO)Ru-(Phen-(tBu)PNN) (4); and H(CO)Ru(IBH4)(Phen-(tBu)PNN) (5) ##STR00168##

2. The process as claimed in claim 1, wherein the secondary amine used in step (i) is selected from A or B ##STR00169## wherein; X is selected from the group consisting of NH, CH.sub.2, and O, R.sup.1 and R.sup.2 are the same or different and are selected from the group consisting of linear alkyl, branched alkyl, substituted or unsubstituted cyclo, wherein said cyclo is optionally up to a seven membered cyclo, wherein said substituted cyclo is mono, di, tri or tetra substituted and said substitution is independently and selected from the group consisting of linear alkyl, branched alkyl, substituted aryl, cycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl, halogen, trifluoromethyl, nitro, alkoxy, dialkylamino, diarylamino, and SR, wherein R is alkyl, cycloalkyl, or aryl, which is optionally further substituted with heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, or alkylheteroaryl, cycloalkyl, substituted or unsubstituted aryl, wherein said substituted aryl is mono, di, tri or tetra substituted, heterocyclyl, and heteroaryl.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 depicts the schematic representation of synthesis of Milstein ligand.

(2) FIG. 2 depicts the schematic representation of synthesis of Phen-.sup.tBuPNN

(3) FIG. 3 depicts the schematic representation of hydrogenation of esters to alcohols, lactones to diols, alcohol to esters, diols to lactones and secondary alcohols to ketones.

(4) FIG. 4 depicts the schematic representation of process for preparation of methanol from carbon dioxide using catalyst of formula 1 and secondary amine

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention provides novel phenanthroline based pincer complexes of formula (I) as shown below:

(6) ##STR00010##
wherein
M is a noble metal, transition metal (1.sup.st, 2.sup.nd and 3.sup.rd row of elements), alkaline-earth- or rare-earth elements;
Y is selected from the group consisting of phosphine (PR.sup.aR.sup.b), phosphite P(OR.sup.a)(OR.sup.b), phosphinite P(OR.sup.a)(R.sup.b), amine (NR.sup.aR.sup.b), imine, sulphide SR.sup.a, oxide OR.sup.a, sulfoxide S(O)R.sup.a, sulphone SO.sub.2R.sup.a, oxazoline, N-heterocyclic carbine, heteroaryl containing at least one heteroatom selected from nitrogen or Sulphur;
L is selected from the group consisting of CO, BH.sub.3, BH.sub.2, PR.sup.aR.sup.bR.sup.c, P(OR.sup.a)(OR.sup.b)(OR.sup.c), nitrile (RCN) or isonitrile (RNC);
R, R.sup.a, R.sup.b, and R.sup.c are selected from the group consisting of alkyl, cycloalkyl, aryl which may be further substituted heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl.

(7) A ligand used is aromatic or dearomatic is selected from the group consisting of H, halogen, OCOR, OCOCF.sub.3, OSO.sub.2R, OSO.sub.2CF.sub.3, CN, OR, N(R).sub.2 and RS;

(8) R.sup.1, represents hydrogen or one or two substituents wherein each such substituent is independently selected from the group consisting of alkyl (linear and branched), cycloalkyl, aryl, substituted aryl, heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl, halogen, triflurometyl, nitro, amide, ester (CO.sub.2R), OC(O)R, OC(O)CF.sub.3, OSO.sub.2R, OSO.sub.2CF.sub.3) cyano, alkoxy, alkylamino (mono or di), arylamino (mono or di), SR, an inorganic support or a polymeric moiety.

(9) R.sup.2 and R.sup.3 form a 6 membered aromatic ring which is further substituted with one or two substituents wherein each such substituent is independently selected from the group consisting of alkyl (linear and branched), cycloalkyl, aryl, substituted aryl, heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl, halogen, triflurometyl, nitro, amide, ester (CO.sub.2R), OC(O)R, OC(O)CF.sub.3, OSO.sub.2R, OSO.sub.2CF.sub.3) cyano, alkoxy, alkylamino (mono or di), arylamino (mono or di), SR, an inorganic support or a polymeric moiety.

(10) R.sup.3 and R.sup.4 form a six member aromatic ring which is further substituted with one or two substituents wherein each such substituent is independently selected from the group consisting of alkyl (linear and branched), cycloalkyl, aryl, substituted aryl, heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl, halogen, triflurometyl, nitro, amide, ester (CO.sub.2R), OC(O)R, OC(O)CF.sub.3, OSO.sub.2R, OSO.sub.2CF.sub.3) cyano, alkoxy, alkylamino (mono or di), arylamino (mono or di), SR, an inorganic support or a polymeric moiety.

(11) The phenanthroline based pincer complexes of formula (I) is selected from HCl(CO)Ru(Phen-(tBu)PNN) (3), H(CO)Ru-(Phen-(tBu)PNN) (4) and H(CO)Ru(1BH4)(Phen-(tBu)PNN) (5a).

(12) The present invention provides a process for the preparation of novel phenanthroline based pincer complexes of formula (I) comprising the steps of: a) Adding solution of Lithium diisopropylamide and tBuOK in suitable solvent to a solution of 2-methyl-1,10-phenanthroline (1) in ether at temperature in the range of 0 to 5 C. followed by stirring the reaction mixture for the period ranging from 30 to 40 min at the same temperature; b) Adding a solution of di-tert-butylchlorophosphine in ether with constant stirring for further 1 to 2 hr at temperature in the range of 50 to 78 C. followed by stirring at temperature ranging from 25 to 30 C. for the period in the range of 12 to 14 hrs to obtain Phen-PNN(tBu) (2); c) Heating the reaction mixture of compound of step (b), RuHCl(CO)(PPh.sub.3).sub.3 in THF at temperature in the range of 60 to 70 C. for the period ranging from 5 to 6 hr to afford HCl(CO)Ru(Phen-(tBu)PNN) (3); d) Adding Sodium bis(trimethylsilyl)amide to a solution of compound of step (c) in C.sub.6H.sub.6 to obtain phenanthroline based pincer complexes of formula H(CO)Ru-(Phen-(tBu)PNN) (4); e) Stirring the reaction mixture comprising compound of step (c) and NaBH.sub.4 in toluene and ethanol at temperature in the ranging from 50 to 70 C. for the period ranging from 10 to 15 min then at room temperature for the period in the range of 4 to 6 hr to afford H(CO)Ru(.sup.1BH.sub.4)(Phen-(tBu)PNN) (5a).

(13) The solvent in step (a) is selected from hexane heptane, tetrahydrofuran (THF) diethyl ether, toluene and etheylbenzene.

(14) The step (c) is carried out under argon atmosphere.

(15) The N arm in the Milstein catalyst is hemilabile in nature and it can dissociate during the course of catalysis. Thus, under extreme conditions and by use of early transition elements (Fe, Co, Ni etc.,) metal can come out from the ligand core and generates inactive metal particles (data not available). However in the phenanthroline based system the dissociation is restricted and thus gives the unique stability to the metal centre. Py-.sup.tBuPNN ligand (liquid state) is highly moisture and air sensitive, due to this complexation has been achieved under extremely inert atmosphere (glove-box), however phenanthroline ligand (solid state) is very much stable and can handled without any special care under an ordinary atmosphere.

(16) The catalyst are stable at normal atmospheric pressure, higher temperatures too [stable up to 180 C. without any decomposition for about 30 min in solid state and stable up to 200 C. for about 1 hr in solution state (2 mL of mesitylene)].

(17) The phenanthroline based pincer complexes have unique metal stability resistant towards oxygen and moisture.

(18) The pincer based phenanthroline catalyst is used to catalyze hydrogenation and dehydrogenation reactions.

(19) The pincer based phenanthroline catalyst catalyses reactions selected from, but not limited to hydrogenation of esters to alcohols, lactones to diols, alcohol to esters, diols to lactones and secondary alcohols to ketones, as shown in FIG. 2 and Tables 1-4.

(20) The said catalyst is used for hydrogenation of esters to alcohols as shown in table 1.

(21) TABLE-US-00001 TABLE 1 Catalytic hydrogenation of esters to alcohols. Entry Catalyst esters products Yield (%).sup.b 1 3 86 2.sup.a 5a 92 3 3 89 4 3 91 5 3 0 95 6 3 98 7 3 92 8 3 94 9 3 90 10 5a HCO.sub.2Me CH.sub.3OH 89 .sup.awithout .sup.tBuOK. .sup.byields are based on aromatic alcohols (entries 4-9).

(22) The said catalyst is used for hydrogenation of lactones to diols as shown in table 2.

(23) TABLE-US-00002 TABLE 2 Catalytic hydrogenation of lactones to diols. 0 Entry Catalyst lactones diols (yield %) 1 3 (72) 2 5a (81) 3 5a (79) 4 5a (68)

(24) The said catalyst is used for dehydrogenation of alcohols to esters as shown in table 3.

(25) TABLE-US-00003 TABLE 3 Catalytic dehydrogenation of alcohols to esters and dihydrogen. 0 Entry Catalyst.sup.a alcohols esters (yield %) 1 3 (59) 2 3 (78) 3 3 (92) 4 3 (97) 5 5a 0 (81) ain case of Cat. 3 one equiv. of .sup.tBuOK (w.r.t Cat. 3) was used.

(26) In another preferred embodiment, said catalyst is used for dehydrogenation of diols to lactones as shown in table 4.

(27) TABLE-US-00004 TABLE 4 Catalytic dehydrogenation of diols to lactones and dihydrogen. Entry Catalyst diols lactones (yield %) 1 3 (72) 2 3 (78) 3 3 (66)

(28) The said catalyst is used for dehydrogenation of secondary alcohols to ketones as shown table 5.

(29) TABLE-US-00005 TABLE 5 Catalytic dehydrogenation of sec. alcohols to ketones. Entry Catalyst sec. alcohols ketones (yield %) 1 3 0 (43) 2 3 (74) 3 5a 87 4 3 (80 5 3 (72) 6 3 0 (76)

(30) The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

EXAMPLES

(31) Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1: Synthesis of Phen-PNN(.SUP.t.Bu)

(32) ##STR00072##

(33) An oven-dried 250 mL two-necked round bottom flask equipped with an argon inlet, a stirring bar and dropping funnel is cooled under a stream of argon. The flask is then charged with 1.94 g (10.0 mmol) of 2-methyl-1,10-phenanthroline (1) in 50 mL dry ether. The solution was cooled to 0 C. and a 1.8 M solution of LDA in heptane/THF/etheylbenzene (6.2 mL, 11.0 mmol) was added via a syringe (15 min) followed by addition of tBuOK (2 mmol). The resulting brown coloured mixture was stirred for 30 min at the same temperature and a solution of di-tert-butylchlorophosphine (1.99 g, 11.0 mmol) in 10 mL dry ether was added dropwise (10 min). Continue the stirring for further 1 hr at 78 C. and the mixture was allowed slowly to warm up to 30 C. and continue the stirring for 12 hrs at the temperature. To this reaction mixture was added 20 mL of degassed water and the ether phase was separated under N.sub.2 atmosphere. The aqueous phase was extracted with ether (220 mL). The combined ether solutions were dried over anhydrous Na.sub.2SO.sub.4, filtered, and the solvent was removed under vacuum to get yellowish-white solid. This was crystallized from mixture of toluene:ether (1:2) at ca. 0 C. to yield 2.27 g (67%) of 2-((di-tert-butylphosphanyl)methyl)-1,10-phenanthroline [Phen-(.sup.tBu)PNN] (2) as a white solid.

(34) .sup.31P{.sup.1H}NMR (120 MHz, CDCl.sub.3): 38.13. .sup.1H NMR (300 MHz, CDCl.sub.3): 1.19 (d, J.sub.PH=10.0 Hz, 18H, P(C(CH.sub.3).sub.3).sub.2), 3.15 (d, J.sub.PH=3.0 Hz, 2H, PCH.sub.2), 7.43-7.50 (m, 1H), 7.59-7.64 (m, 1H), 7.73 (d, J.sub.HH=9.0 Hz, 2H), 8.06 (d, J.sub.HH=9.0 Hz, 1H), 8.25 (dd, J.sub.HH=3.0 Hz and J.sub.HH=9.0 Hz 1H), 9.21 (dd, J.sub.HH=3.0 Hz and J.sub.HH=9.0 Hz 1H). .sup.13C{.sup.1H} NMR (75 MHz, CDCl.sub.3): 25.62 (s, P(C(CH.sub.3).sub.3), 25.70 (s, P(C(CH.sub.3).sub.3), 31.25 (d, J.sub.PC=21.0 Hz, PCH.sub.2), 31.56 (d, J.sub.PC=23.2 Hz, P(C(CH.sub.3).sub.3).sub.2), 122.59 (s), 123.53 (s), 125.37 (s), 126.33 (s), 126.33 (s), 128.76 (s), 135.79 (s), 136.00 (s), 145.80 (s), 146.09 (s), 150.16 (s), 159.46 (d, J.sub.PC=14.0 Hz). HRMS (FAB) Calculated for C.sub.21H.sub.27N.sub.2P [MH.sup.+]: 338.4348. Found: 238.4361.

Example 2: Synthesis of HCl(CO)Ru(Phen-(.SUP.t.Bu)PNN) (3)

(35) ##STR00073##

(36) To an oven dried 25 mL pressure vessel equipped with magnetic stirring bar was added Phen-(.sup.tBu)PNN (2) (199 mg, 0.52 mmol), RuHCl(CO)(PPh.sub.3).sub.3 (476 mg, 0.5 mmol), and 10 mL dry THF under argon atmosphere. The flask was sealed and heated at 65 C. (bath temperature) for 5 hr with constant stirring, then cooled to room temperature to lead to reddish-orange solid. Then the solvent was decanted and the solid thus obtained was washed with diethyl ether (33 mL), followed by dried under vacuum to give analytically pure complex 3 (212 mg, 88%). IR (KBr pellet, cm.sup.1): 1995, 1900. .sup.31P{.sup.1H}NMR (120 MHz, CD.sub.2Cl.sub.2): 108.21 (s). .sup.1H NMR (300 MHz, CD.sub.2Cl.sub.2): 15.30 (d, J.sub.PH=24.0 Hz, RuH), 1.29 (d, J.sub.PH=15.0 Hz, 9H, P(C(CH.sup.a.sub.3).sub.3), 1.58 (d, J.sub.PH=6.0 Hz, 9H, P(C(CH.sup.b.sub.3).sub.3), AB system centered at 3.82 and 3.97 (ABq, J.sub.HH=18.0 Hz and J.sub.PH=12.0 Hz, 2H, PCH.sup.aH.sup.b), 7.78 (dd, 1H, J.sub.HH=9.0 Hz and J.sub.HH=7.89 (d, J.sub.HH=9.0 Hz, 1H), 7.93-7.98 (m, 2H), 8.39 (dd.fwdarw.t, J.sub.HH=9.0 Hz, 1H), 9.43 (br m, 1H). .sup.13C{.sup.1H}NMR (75 MHz, CD.sub.2Cl.sub.2): 28.50 (d, J.sub.PC=3.0 Hz, P(C(C.sup.aH.sub.3).sub.3), 29.96 (d, J.sub.PC=3.0 Hz, P(C(C.sup.bH.sub.3).sub.3), 36.49 (d, J.sub.PC=23.0 Hz, PCH.sub.2), 37.40 (d, J.sub.PC=15.0 Hz, P(C.sup.a(CH.sub.3).sub.3), 37.76 (d, J.sub.PC=16.5 Hz, P(C.sup.b(CH.sub.3).sub.3), 122.23 (d, J=8.0 Hz), 125.15 (d, J=2.3 Hz), 126.17 (s), 126.36 (s), 127.78 (s), 130.08 (s), 135.42 (s), 135.86 (s), 153.19 (d, J=1.0 Hz), 161.49 (d, J=5.0 Hz), 208.31 (d, J.sub.PC=14.8 Hz, RuCO). HRMS (FAB) Calculated for C.sub.22H.sub.28N.sub.2OPRu [M-Cl].sup.+: 468.5228. Found: 468.5239.

Example 3: Synthesis of H(CO)Ru.SUP..(Phen-(.SUP.t.Bu)PNN) (4)

(37) ##STR00074##

(38) 5.0 mg. of HCl(CO)Ru(Phen-(.sup.tBu)PNN) (3) (0.01 mmol) were placed into a J. Young NMR tube, dissolved in 0.5 mL of C.sub.6H.sub.6 and 1 eq. of NaHMDS (2.5 mg) was added to generate dark yellowish-brown complex 4. The resulting complex 4 exhibits a broad singlet at 91.53 in .sup.31P {.sup.1H}NMR.

Example 4: Synthesis of H(CO)Ru(.SUP.1.BH.SUB.4.)(Phen-(.SUP.t.Bu)PNN) (5a)

(39) ##STR00075##

(40) 50 mg of HCl(CO)Ru(Phen-(tBu)PNN) (3) (0.1 mmol) and NaBH.sub.4 (19 mg, 0.5 mmol) were placed in a 15 mL Schlenk flask equipped with a Teflon-coated magnetic stirring bar. A 1:1 mixture of toluene and ethanol (2 mL) was added to the flask. It was then stirred at 60 C. for 15 min then at room temperature for 5 hr. Solvent was removed in vacuo and the resulted residue was dissolved in dry CH.sub.2Cl.sub.2 (5 mL) and the remaining insoluble materials were removed by filtration through a celite pad. The filtrate was concentrated to ca. 0.3 mL and 3 mL of hexane was added to cause precipitation of a orange-yellow solid, which was filtered, dried under vacuum to give 40 mg (81%) of RuH(CO)(.sup.1BH.sub.4)Phen-(.sup.tBu)PNN (5a).

(41) .sup.31P{.sup.1H}NMR (200 MHz, CD.sub.2Cl.sub.2): 113.8 (s). .sup.1H NMR (300 MHz, CD.sub.2Cl.sub.2): 12.60 (d, .sup.2J.sub.PH=22.0 Hz, 1H, RuH), 2.28 to 1.86 (br d, 4H, RuHBH.sub.3), 1.31 (d, J.sub.PH=14.0 Hz, 9H, P(C(CH.sup.a.sub.3).sub.3), 1.56 (d, J.sub.PH=10.5 Hz, 9H, P(C(CH.sup.b.sub.3).sub.3), 3.58-3.72 (m, 2H, PCH.sup.aH.sup.b), 7.68-7.71 (m, 1H), 7.85 (d, J.sub.HH=8.0 Hz, 1H), 7.90-7.97 (m, 2H), 8.42 (m, 1H), 9.46-9.49 (br m, 1H).

Example 5: Hydrogenation Process Experimental Details

(42) A 90 mL Fischer-Porter tube was charged under argon with catalyst 3 (0.02 mmol), .sup.tBuOK (0.02 mmol), ester (4.0 mmol), and THF (2 mL). The Fischer-Porter tube was purged by three successive cycles of pressurization/venting with H.sub.2 (15 psi), then pressurized with H.sub.2 (150 psi). The solution was heated at 110 C. (bath temperature) with stirring for 16 hr. After cooling to room temperature, the excess H.sub.2 was vented carefully and the products were analyzed by GC-MS and determined by GC using m-xylene as an internal standard.

Example 6: Hydrogenation of Lactones to Diols

(43) A 90 mL Fischer-Porter tube was charged under argon with catalyst (0.02 mmol), .sup.tBuOK (0.02 mmol; in case of Cat. 3), ester (4.0 mmol), and THF (2 mL). The Fischer-Porter tube was purged by three successive cycles of pressurization/venting with H.sub.2 (15 psi), then pressurized with H.sub.2 (150 psi). The solution was heated at 110 C. (bath temperature) with stirring for 16 hr. After cooling to room temperature, the excess H.sub.2 was vented carefully and the products were determined by GC using m-xylene as an internal standard.

(44) TABLE-US-00006 TABLE 2 Catalytic hydrogenation of lactones to diols. Entry Catalyst lactones diols (yield %) 1 3 (72) 2 5a 0 (81) 3 5a (79) 4 5a (68)

Example 7: Dehydrogenation of Alcohols to Esters

(45) Complex 3 or 5a (0.02 mmol) and primary alcohol (5 mmol) were added to a 15 mL Schlenk flask under an atmosphere of argon. The flask was equipped with a reflux condenser and the neat solution was heated with stirring in an open system under argon for 14 hr (Table 3) at the boiling point of the respective alcohols. The reaction products were analyzed by GC-MS. After cooling to room temperature, m-xylene (1 mmol) was added as internal standard to the reaction mixture and the products were quantitatively analyzed by GC.

(46) TABLE-US-00007 TABLE 3 Catalytic dehydrogenation of alcohols to esters and dihydrogen. Entry Catalyst.sup.a alcohols esters (yield %) 1 3 (59) 2 3 0 (78) 3 3 (92) 4 3 (97) 5 5a (81) .sup.ain case of Cat. 3 one equiv. of .sup.tBuOK (w.r.t Cat. 3) was used.

Example 8: Dehydrogenation of Diols to Lactones

(47) Complex 3 (0.02 mmol), .sup.tBuOK (0.02 mmol), diol (2 mmol), and m-xylene (2 mL) were added to a 15 mL Schlenk flask under an atmosphere of argon. The flask was equipped with a reflux condenser and the solution was heated with stirring in an open system under argon at 155 C. (bath temperature). After cooling to room temperature the products were analyzed by GC-MS.

(48) TABLE-US-00008 TABLE 4 Catalytic dehydrogenation of diols to lactones and dihydrogen. Entry Catalyst diols lactones (yield %) 1 3 00 (72) 2 3 01 02 (78) 3 3 03 04 (66)

Example 9: Dehydrogenation of Sec.Alcohols to Ketones and Dihydrogen

(49) Complex 3 or 5a (0.02 mmol), .sup.tBuOK (in case of cat. 3; 0.02 mmol), sec. alcohols (2.5 mmol), and m-xylene (2 mL) were added to a 15 mL Schlenk flask under an atmosphere of argon. The flask was equipped with a reflux condenser and the solution was heated with stirring in an open system under argon at 155 C. (bath temperature) for about 24 hr. After cooling to room temperature, the products were analyzed by GC.

(50) TABLE-US-00009 TABLE 5 Catalytic dehydrogenation of sec. alcohols to ketones. 05 Entry Catalyst sec. alcohols ketones (yield %) 1 3 06 07 (43) 2 3 08 09 (74) 3 5a 0 87 4 3 (80) 5 3 (72) 6 3 (76)

Example 10: Process for the Synthesis of Methanol from Carbon Dioxide Using Ruthenium (II) Based Pincer-Type Complexes Catalyst

(51) The process for the synthesis of methanol from carbon dioxide by using single catalytic system comprising the steps of: a) mixing catalyst, secondary amine and solvent to obtain a solution; b) adding potassium tert-butoxide (if applicable) to the solution obtained in step (a) to obtain a solution; c) pressurizing the solution as obtained in step (b) with carbon dioxide at 10 atmosphere followed by H.sub.2 atmosphere in the range of 30-40 atm to obtain a solution; d) heating the solution as obtained in step (c) in the range of 110 C.120 C. with stirring for 12-14 hrs to obtain a solution; e) removing excess gases from the solution as obtained in step (d) to obtain N-formylated product of secondary amine; f) adding catalyst and potassium tert-butoxide (if applicable) g) and pressurizing with H.sub.2 in the range of 40-45 atmosphere followed by heating the solution in the range of 110-120 C. with stirring for 18-20 hrs to obtain methanol and secondary amine.

(52) The solvent used is tetrahydrofuran, 1,4-dioxane, toluene, mesitylene, xylene etc., The ruthenium (II) based pincer-type complexes catalyst is selected from HCl(CO)Ru(Phen(tBu)PNN), H(CO)Ru-(Phen-(tBu)PNN), HCl(CO)Ru(BPy-tPNN), [H(CO)Ru.sup.(BPy-tPNN)], and HCl(CO)Ru(Py-.sup.tPNN)].

(53) The said secondary amine may be reused and is selected from:

(54) ##STR00118##
Wherein;
X is selected from the group consisting of NH, CH.sub.2 and O
R.sup.1 and R.sup.2 are the same or different and each such substituent is independently selected from the group consisting of alkyl (linear, branched), cyclo (up to 7 membered, which may be further mono, di, tri or tetra substituted and selected from the group consisting of alkyl (linear and branced), aryl (further substituted), cycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl, halogen, triflurometyl, nitro, alkoxy, dialkylamino, diarylamino,and SR), cycloalkyl, aryl (which may be further mono, di, tri or tetra substituted), heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, and alkylheteroaryl.

(55) The cascade hydrogenation of carbon dioxide to methanol by a single molecular catalyst involves two steps, a) conversion of carbon dioxide to formamide, b) effective formamide hydrogenation to methanol and corresponding amine. The reaction is very selective and operates under mild conditions such as low pressure and temperature without the need of any strong acid.

(56) According to the present invention, the schematic representation of instant process is given in FIG. 1.

Example 11

(57) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 3 (0.01 mmol), .sup.tBuOK (0.011 mmol), morpholine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 120 C. (bath temperature) with stirring for 12 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 3 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 120 C. (bath temperature) with stirring for 18 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and morpholine) were analysed by GC-MS and determined by GC using m-xylene as an internal standard. The methanol was distilled from the reaction mixture.

Example 12

(58) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 3 (0.01 mmol), .sup.tBuOK (0.011 mmol), piperidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 120 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl piperidine). Fresh catalyst 3 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (45 atm). The solution was heated at 120 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and piperidine) were analysed by GC using m-xylene as an internal standard. The methanol was distilled from the reaction mixture.

Example 13

(59) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 4 (0.01 mmol), morpholine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 110 C. (bath temperature) with stirring for 12 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 4 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 18 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and morpholine) were analysed by GC using m-xylene as an internal standard. The methanol was distilled from the reaction mixture.

Example 14

(60) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 4 (0.01 mmol), piperidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 120 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl piperidine). Fresh catalyst 4 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 18 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and methanol was distilled from the reaction mixture.

Example 15

(61) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 4 (0.01 mmol), pyrrolidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (35 atm). The solution was heated at 110 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl pyrrolidine). Fresh catalyst 4 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and pyrrolidine) were analysed by GC using m-xylene as an internal standard.

Example 16

(62) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 4 (0.01 mmol), morpholine (5.0 mmol), and 1,4-dioxane (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 120 C. (bath temperature) with stirring for 12 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 4 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 18 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and morpholine) were analysed by GC using m-xylene as an internal standard.

Example 17

(63) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 5 (0.01 mmol), .sup.tBuOK (0.011 mmol), morpholine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 110 C. (bath temperature) with stirring for 12 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 5 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 18 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and methanol was distilled from the reaction mixture.

Example 18

(64) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 5 (0.01 mmol), .sup.tBuOK (0.011 mmol), piperidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (40 atm). The solution was heated at 120 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl piperidine). Fresh catalyst 5 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (40 atm). The solution was heated at 120 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and piperidine) were analysed by GC using m-xylene as an internal standard.

Example 19

(65) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 6 (0.01 mmol), morpholine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (30 atm). The solution was heated at 110 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 6 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (45 atm). The solution was heated at 110 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products were analysed by GC.

Example 20

(66) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 6 (0.01 mmol), piperidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (40 atm). The solution was heated at 110 C. (bath temperature) with stirring for 12 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl piperidine). Fresh catalyst 6 (0.01 mmol) was once again added and the autoclave was pressurized with H.sub.2 (45 atm). The solution was heated at 110 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and methanol was distilled from the reaction mixture.

Example 21

(67) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 7 (0.01 mmol), .sup.tBuOK (0.011 mmol), morpholine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (40 atm). The solution was heated at 120 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl morpholine). Fresh catalyst 7 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (45 atm). The solution was heated at 120 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and morpholine) were analysed by GC using m-xylene as an internal standard.

Example 22

(68) A 30 mL autoclave equipped with a magnetic stirring was charged under argon with catalyst 7 (0.01 mmol), .sup.tBuOK (0.011 mmol), piperidine (5.0 mmol), and THF (5 mL). The autoclave was pressurized with CO.sub.2 (10 atm) followed by H.sub.2 (40 atm). The solution was heated at 120 C. (bath temperature) with stirring for 14 hrs. After cooling to 30 C., the excess gases were vented carefully (the obtained product is N-formyl piperidine). Fresh catalyst 7 (0.01 mmol) and .sup.tBuOK (0.011 mmol) were once again added and the autoclave was pressurized with H.sub.2 (45 atm). The solution was heated at 120 C. (bath temperature) with stirring for 20 hrs. After cooling to 30 C., the excess H.sub.2 was vented carefully and the products (methanol and piperidine) were analysed by GC.

(69) The pincer catalysts used for the hydrogenation of CO.sub.2 to MeOH are shown in FIG. 1.

(70) ##STR00119##

FIG. 1. Pincer Catalysts Used for the Hydrogenation of CO.SUB.2 .to MeOH

(71) The result of catalytic hydrogenation of CO.sub.2 to methanol is summarized in table 1:

(72) TABLE-US-00010 TABLE 6 Catalytic hydrogenation of CO.sub.2 to MeOH. Yield (%) of Entry Catalyst Amine Formamide Yield (%) Formamide Products methanol 1.sup.st stage 2.sup.nd stage 1 3 + .sup.tBuOK 0 quantitative 91 2 5 + .sup.tBuOK 93 84 3 3 + .sup.tBuOK quantitative 0 93 4 5+ .sup.tBuOK 95 88 5 6 96 88 6 7 + .sup.tBuOK 0 62 35 7 4 quantitative 97 8 4 (in 1,4- dioxane) 96 0 89 9 4 99 90 10 4 94 81 11 6 0 81 42 12 7 + .sup.tBuOK 50 28

Advantages of the Invention

(73) 1. Environmentally benign conditions 2. Operationally simple synthetic process 3. solvent-free reaction conditions 4. Direct conversion of alcohols to esters with liberation of hydrogen gas 5. Efficient hydrogenation of esters including lactones to the corresponding alcohols 6. One-pot process catalyzed by a single-site molecularly defined Ru-catalyst 7. Operationally simple synthetic process (low temperature and pressure) 8. Amine acts as auto-catalyst and can be reused 9. Improved yield