NOVEL BIMETALLIC CATALYTIC COMPLEXES FOR THE POLYMERISATION OF CARBON DIOXIDE AND AN EPOXIDE

Abstract

The present invention provides a novel catalyst of formula (I): wherein M is selected from Zn(H), Co(II), Mn(II), Mg(II), Fe(II), Cr(III)—X or Fe(III)—X, and the use thereof in polymerising carbon dioxide and an epoxide.

Claims

1-6. (canceled)

7. A dimeric catalyst wherein said dimeric catalyst comprises two monomeric subunits, wherein each monomeric subunit is a catalyst of formula (I): ##STR00010## wherein each R.sub.1 and R.sub.2 are independently hydrogen, alkyl, haloalkyl, aryl, halide, amine, a nitro group, an ether group, a silyl ether group, a nitrile group or an acetylide group; each R.sub.3 is independently alkylene, arylene or cycloalkylene; each R.sub.4 is independently H, alkyl, aryl or alkylaryl; each E.sub.1 is C, each E.sub.2 is independently O, S or NH; or each E.sub.1 is N and each E.sub.2 is O; X is OCOCH.sub.3, OCOCF.sub.3, OSO.sub.2C.sub.7H.sub.7, OSO(CH.sub.3).sub.2 or halide; M is Zn(II), Cr(II), Co(II), Mn(II), Mg (II), Fe(II), Cr (III)—X, Co (III)—X, Mn (III)—X or Fe(III)—X; and wherein the two monomeric subunits are linked by a bridging ligand X.

8. The dimeric catalyst as claimed in claim 7, wherein said catalyst has the structure: ##STR00011## wherein: X is OCOCH.sub.3, OCOCF.sub.3, OSO.sub.2C.sub.7H.sub.7, OSO(CH.sub.3).sub.2, or halide.

9. The dimeric catalyst as claimed in claim 7, wherein said catalyst has the structure: ##STR00012##

10. A mixture comprising the dimeric catalyst of claim 7, wherein the monomeric subunits forming the dimeric catalyst have the same structure.

11. A process for the reaction of carbon dioxide with an epoxide in the presence of a catalyst as claimed in claim 7.

12. The process as claimed in claim 11, wherein the epoxide is selected from cyclohexene oxide, an alkylene oxide, or a substituted oxirane.

13. The process as claimed in claim 11, wherein said process is carried out at 1 atmosphere.

14. A product of the process of claim 11.

15. (canceled)

16. A process for the production of a dimeric catalyst as claimed in claim 7, said process comprising reaction of a compound of formula (III) ##STR00013## with a metal complex comprising the groups M and X in the presence of water, wherein the groups X, R.sub.1, R.sub.2, R.sub.3, R.sub.4, M, E.sub.1 and E.sub.2 are as defined in claim 7.

17. The process as claimed in claim 16, wherein said reaction occurs in the presence of base.

18-21. (canceled)

22. The dimeric catalyst as claimed in claim 7, wherein each R.sub.1 and R.sub.2 are independently selected from hydrogen, tBu, Me, CF.sub.3, phenyl, F, Cl, Br, I, NMe.sub.2, NEt.sub.2, NO.sub.2, OMe, OSiEt.sub.3, CNMe, CN, or CCPh.

23. The dimeric catalyst as claimed in claim 7, wherein each R.sub.1 and R.sub.2 are independently selected from hydrogen, tBu, Me, F, Cl, Br, I, or OMe.

24. The dimeric catalyst as claimed in claim 7, wherein R.sub.3 is ethylene, 2,2-dimethylpropylene, propylene, butylene, phenylene, cyclohexylene, or biphenylene.

25. The dimeric catalyst as claimed in claim 7, wherein R.sub.3 is 2,2-dimethylpropylene or propylene.

26. The dimeric catalyst as claimed in claim 7, wherein R.sub.4 is H, Me, Et, Bn, iPr, nBu, tBu, or Ph.

27. The dimeric catalyst as claimed in claim 7, wherein R.sub.4 is H.

28. The dimeric catalyst as claimed in claim 7, wherein X is OCOCH.sub.3, OCOCF.sub.3, OSO.sub.2C.sub.7H.sub.7, OSO(CH.sub.3).sub.2, Cl, Br, or I.

29. The dimeric catalyst as claimed in claim 7, wherein X is OCOCH.sub.3.

30. The dimeric catalyst as claimed in claim 7, wherein each E.sub.1 is C, and each E.sub.2 is O.

31. The dimeric catalyst as claimed in claim 7, wherein M is Zn(II), Cr(II), Co(II), Mg (II), Fe(II), Cr (III)—X, Co (III)—X, or Fe(III)—X.

32. The dimeric catalyst as claimed in claim 7, wherein said dimeric catalyst comprises a bound water molecule.

Description

[0050] The invention may be put into practice in various ways and a number of specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying drawings, in which:

[0051] FIG. 1 shows the copolymerization of carbon dioxide and cyclohexene oxide, where [cat]=catalyst, frequently a Zn(II), Cr(III) or Co(III) complex;

[0052] FIG. 2 shows the synthesis of the dizinc complex [L.sup.1Zn.sub.2(OAc).sub.2]. Reagents and conditions: i) KH, THF, −78° C..fwdarw.RT, 1 hour. ii) Zn(OAc).sub.2, THF, RT, 16 hours.

[0053] FIG. 3 shows a plot showing the M.sub.n of the polycarbonate, as determined by GPC, versus the percentage conversion, as determined by .sup.1H NMR. The values in parentheses represent the polydispersity index; and

[0054] FIG. 4 shows a .sup.1H NMR spectrum, at 110° C. of the dizinc complex [L.sup.1Zn.sub.2(OAc).sub.2].

[0055] FIG. 5 shows an X-ray crystallography structure for the dimeric catalyst complex [L.sup.1.sub.2Mg.sub.4(OAc).sub.4(H.sub.2O)]

[0056] The present invention will now be illustrated by reference to one or more of the following non-limiting examples.

EXAMPLES

Example 1

[0057] Reaction of a number of epoxides with carbon dioxide were carried out using a bimetallic zinc complex [L.sup.1Zn.sub.2(OAc).sub.2] as illustrated in FIG. 2. The macrocyclic ligand, H.sub.2L.sup.1, was prepared two steps, in 84% overall yield, from commercial reagents as described below. The bimetallic zinc complex, [L.sup.1Zn.sub.2(OAc).sub.2], was prepared by the double deprotonation of the H.sub.2L.sup.1, using potassium hydride, and the subsequent reaction with zinc acetate. The complex was isolated, as a white solid, in 70% yield.

[0058] The complex stoichiometry was confirmed by the elemental analysis being in excellent agreement with the calculated values and a daughter peak in the FAB mass spectrum for the molecular ion less an acetate group. The .sup.1H NMR spectrum, at 25° C., shows several broadened resonances, consistent with the several diastereoisomers being present, which are fluxional on the NMR timescale. When the sample was heated to 110° C., coalescence was observed as illustrated in FIG. 4. A single resonance was observed for the aromatic protons and the NH groups showed a broadened resonance at 4.78 ppm. The methylene groups are diastereotopic and so, four broadened resonances were observed from 3.32-2.46 ppm, each with an integral of 4H. The tert-butyl and acetate methyl groups resonate as singlets with integrals of 18H and 6H, respectively. The methyl groups on the ligand backbone are also diastereotopic and are observed as two singlets, each with a relative integral of 6H.

[0059] The complex was tested, under very mild conditions, for the copolymerization of carbon dioxide and cyclohexene oxide as illustrated in FIG. 1. Results of the copolymerization are set out in table 1 below. Thus, at only 1 atm pressure of carbon dioxide and at 70° C., poly(cyclohexene carbonate) was produced with a TON of 300 and a TOF of 12 h.sup.−1. On increasing the temperature to 100° C. (Table 1, 1-4), the TON increased to 530 and the TOF to 26 h.sup.−1. There are very few catalysts which are effective at such low pressure, the most active of these is a dizinc complex with a TON of 20 and TOF of 3.3 h.sup.−1 (Table 1, entry 9). [L.sup.1Zn.sub.2(OAc).sub.2] is also tolerant, it operates effectively at a loading of 0.01 mol % (Table 1, entries 5-9). The catalyst shows much enhanced activity at 1 atm compared to any previously reported catalysts; it has TONs which are up to 35 times greater and TOFs up to 10 times greater (entry 10). Indeed [L.sup.1Zn.sub.2(OAc).sub.2] displays comparable TONs and TOFs to Darensbourg's bis(phenoxide)zinc catalysts (entry 12), but at 1/60 of the pressure of carbon dioxide. When the pressure of CO.sub.2 was increased (entries 7-9), the TONs and TOFs increased to a maximum of 3400 and 140 h.sup.−1, respectively. Indeed, under comparable conditions (70° C., 7 atm), [L.sup.1Zn.sub.2OAc.sub.2] has a slightly higher TON (entry 7) than Coates β-diiminate catalysts (entry 11).

TABLE-US-00001 TABLE 1 The copolymerization of carbon dioxide and cyclohexene oxide, catalysed by [L.sup.1Zn.sub.2(OAc).sub.2]. The copolymerizations were conducted in a Schlenk tube for 20-24 h, at a loading of [L.sup.1Zn.sub.2(OAc).sub.2]:cyclohexene oxide of 1:1000 (unless otherwise stated), or in a Parr reactor at 7-10 atm for 24 h (entries 7-9). p(CO.sub.2) TOF.sup.b) Entry # T (° C.) [atm] TON.sup.a) [h.sup.−1] % carbonate.sup.c) % polymer.sup.d) M.sub.n.sup.e) PDI.sup.e) 1 70 1 292 12.2 >99 >99.6 3518 1.22 2 80 1 439 18.3 >99 96 6193 1.19 3 90 1 567 23.6 >99 95 6519 1.21 4 100 1 527 25.1 >99 94 7358 1.21 5.sup.f) 70 1 321 13.4 >99 >99 N/A N/A 6.sup.f) 100 1 708 29.5 >99 89 1395 1.19 7.sup.f) 70 7 728 30.3 >99 >99 1861 1.23 8.sup.f) 70 10 760 31.6 >99 >99 2585 1.24 9.sup.f) 100 10 3347 139.5 >99 95 14100.sup.g) 1.03 10) Comparative 60 1 20 3.3 >99 N/A 19200  1.56 example 12) Comparative 50 7 494 247 90 N/A 31000  1.10 example 11) Comparative 80 60 774 32.2 >99 N/A 8900 1.2  example .sup.a)the turn over number (TON) = number of moles of cyclohexene oxide consumed/number of moles of [L.sup.1Zn.sub.2(OAc).sub.2]. .sup.b)the turn over frequency (TOF) = TON/reaction period. .sup.c)determined by integration of the signal at 3.45 ppm assigned to poly(cyclohexene ether) in the .sup.1H NMR spectrum. .sup.d)assigned by integration of the signal at 4.65 ppm assigned to cyclohexene carbonate. .sup.e)determined by GPC in THF, using narrow M.sub.w polystyrene standards. .sup.f)carried out at a loading of [L.sup.1Zn.sub.2(OAc).sub.2]:cyclohexene oxide of 1:10000. .sup.g)a bimodal peak was observed with M.sub.n of 14100 and 6600. The catalyst is also selective, yielding a polymer with >99% polycarbonate linkages. In contrast to previous literature catalysts, [L.sup.1Zn.sub.2(OAc).sub.2] is remarkably robust, it is still active after 24 h of reaction and at loadings of 0.01 mol %. It is also stable in air; indeed comparable TONs and TOFs are obtained for polymerizations when [L.sup.1Zn.sub.2(OAc).sub.2] is handled in air. The polymerization is well controlled, giving polycarbonate with a narrow polydispersity index (Table 1) and a linear relationship between the M.sub.n and percentage conversion (as illustrated in FIG. 3).

[0060] Materials and Methods

[0061] All reactions were conducted under a nitrogen atmosphere, using either standard anaerobic techniques or in a nitrogen filled glovebox. High-pressure reactions were carried out in a Parr 5513 100 mL bench reactor. 4-tert-butyl-2,6-diformylphenol was synthesised according to a literature procedure. All solvents and reagents were obtained from commercial sources (Aldrich and Merck). THF was distilled from sodium and stored under nitrogen. Cyclohexene oxide, methylene chloride and d.sub.2-TCE were distilled from CaH.sub.2 and stored under nitrogen. CP grade carbon dioxide was used for polymerisation studies.

[0062] .sup.1H and .sup.13C {.sup.1H} NMR spectra were performed on a Bruker AV-400 instrument, unless otherwise stated. All mass spectrometry measurements were performed using a Fisons Analytical (VG) Autospec spectrometer. Elemental analyses were determined by Mr Stephen Boyer at London Metropolitan University, North Campus, Holloway Road, London, N7. SEC data were collected using a Polymer labs PL GPC-50 instrument with THF as the eluent, at a flow rate of 1 mLmin.sup.−1. Two Polymer labs Mixed D columns were used in series. Narrow M.sub.w polystyrene standards were used to calibrate the instrument.

[0063] Synthesis of [H.sub.4L.sup.1′](ClO.sub.4).sub.2

##STR00008##

[0064] To a round-bottomed flask was added 4-tert-butyl-2,6-diformylphenol (1.20 g, 5.80 mmol), NaClO.sub.4 (2.81 g, 23.2 mmol), acetic acid (0.66 mL, 11.6 mmol) and methanol (90 mL). This solution was heated to 70° C. whilst stirring, as the solution started to boil, 2,2-dimethyl-1,3-propanediamine (0.70 mL, 5.8 mmol) was added slowly in methanol (30 mL). The yellow reaction mixture was allowed to cool to room temperature, and left stirring for 72 hours, after which a bright orange precipitate was filtered and washed with cold (−78° C.) methanol (1.85 g, 95%). δ.sub.H(400 MHz; d.sup.6-dmso) 13.61 (4H, br s, NH/OH), 8.68 (4H, d, N═CH), 7.66 (4H, s, Ar—H), 3.87 (8H, s, CH.sub.2), 1.28 (12H, s, CH.sub.3), 1.15 (18H, s, CH.sub.3); δ.sub.C(400 MHz; d.sup.6-dmso) 176.5, 169.3, 142.5, 136.2, 116.6, 60.7, 35.2, 34.0, 31.2 and 23.6.

[0065] Synthesis of H.sub.2L.sup.1

[0066] [H.sub.4L.sup.1′](ClO.sub.4).sub.2 (1.80 g, 2.69 mmol) was suspended in methanol (180 mL). The suspension was cooled to 0° C. and NaBH.sub.4 (2.65 g, 69.9 mmol) was added slowly. As NaBH.sub.4 was added, the red-orange suspension turned to a clear solution. Water was added slowly, and the solution turned cloudy. Once precipitate started to form, the mixture was left overnight and H.sub.2L.sup.1 was filtered off as a white solid (1.21 g, 88%).

[0067] Mp 162° C. (from methanol); Anal. Calc. for C.sub.34H.sub.56N.sub.4O.sub.2: C, 73.87; H, 10.21; N, 10.13. Found: C, 73.87; H, 10.26; N, 10.18; δ.sub.H(400 MHz; CDCl.sub.3): 6.95 (s, 4H, Ar—H), 3.76 (s, 8H, CH.sub.2), 2.53 (s, 8H, CH.sub.2), 1.27 (s, 18H, CH.sub.3), 1.02 (s, 12H, CH.sub.3); δ.sub.C (400 MHz; CDCl.sub.3) 154.7, 140.7, 124.9, 124.3, 59.9, 53.4, 34.7, 34.1, 33.9, 31.7, and 25.2; m/z (ES) 553 (M.sup.+, 75%), 277 (100), 216 (8), 175 (7).

[0068] Synthesis of [L.sup.1Zn.sub.2OAc.sub.2]

[0069] H.sub.2L.sup.1 (0.40 g, 0.72 mmol) was dissolved in dry THF (10 mL) and transferred into a Schlenk tube containing KH (0.04 g, 1.08 mmol), and cooled to −78° C., under nitrogen. This suspension was allowed to warm to room temperature and left to stir for 1 hour. The excess KH was filtered off and the solution transferred to a Schlenk tube containing Zn(OAc).sub.2 (0.27 g, 1.48 mmol). The reaction was left to stir for 16 hours overnight, after which the THF was removed in vacuo, and the product taken up in dry CH.sub.2Cl.sub.2 (10 mL). This was then filtered and the CH.sub.2Cl.sub.2 removed in vacuo to yield the title compound as a white powder (0.40 g, 69.5%).

[0070] Anal. Calc. for C.sub.36H.sub.60N.sub.4O.sub.2Zn.sub.2: C, 57.07; H, 7.56; N, 7.01; Found: C, 56.91; H, 7.46; N, 6.92; δ.sub.H (400 MHz, d.sup.2-tce, 383 K) 7.00 (4H, s, Ar—H), 4.78 (4H, br s, NH), 3.32 (4H, br d, CH.sub.2), 2.95 (4H, br s, CH.sub.2), 2.84 (4H, br s, CH.sub.2) 2.46 (˜4H, br s, CH.sub.2), 2.08 (˜6H, s, OAc), 1.35 (18H, s, Ar—C—CH.sub.3), 1.29 (6H, s, CH.sub.2—C—CH.sub.3), 1.05 (6H, s, CH.sub.2—C—CH.sub.3); δ.sub.C (400 MHz, d.sup.2-tce, 383 K) 174.7, 159.5 (br), 139.5 (br), 127.4, 124.4, 63.2, 56.3, 33.5, 31.4, 27.9, 21.1 and 20.7; m/z (FAB) 739 ([M−OAc].sup.+, 100%).

[0071] Polymerization Conditions

[0072] Cyclohexene oxide (5 mL, 49.4 mmol) and [L.sup.1Zn.sub.2(OAc).sub.2] (0.049 mmol) were added to a Schlenk tube. The cyclohexene oxide was degassed, before being left stirring under 1 atm CO.sub.2, at a certain temperature, for 24 hours. The crude reaction mixture was then taken up in CH.sub.2Cl.sub.2 and evaporated in air, after which the product was dried in vacuo overnight.

[0073] For high-pressure reactions, [L.sup.1Zn.sub.2(OAc).sub.2] (0.0198 mmol) was dissolved in cyclohexene oxide (20 mL, 197.6 mmol) in a Schlenk tube. This was transferred into the Parr reaction vessel, (which was dried in an oven at 140° C. overnight) under nitrogen. The reactor was brought up to temperature under 2 atm CO.sub.2 before being left at a certain pressure and temperature for 24 hours. Work-up as above.

[0074] Turn-over-number calculated as [(isolated yield−weight catalyst)/142.1]/moles catalyst.

Example 2

[0075] Complexes [L.sup.2Zn.sub.2(OAc).sub.2] and [L.sup.3Zn.sub.2(OAc).sub.2] were prepared in the same manner as [L.sup.1Zn.sub.2(OAc).sub.2].

##STR00009##

[0076] Both complexes were found to react with cyclohexene oxide in the same manner as [L.sup.1Zn.sub.2(OAc).sub.2]. The nature of the complexes was confirmed by very similar features in the .sup.1H and .sup.13C NMR spectra, elemental analysis and FAB mass spectra to [L.sup.1Zn.sub.2(OAc).sub.2].

[0077] Both [L.sup.2Zn.sub.2(OAc).sub.2] and [L.sup.3Zn.sub.2(OAc).sub.2] were tested under mild conditions (80° C., 1 atm CO.sub.2, 24 hours), for the copolymerisation of carbon dioxide and cyclohexene oxide. Results showed both complexes to have similar activity to [L.sup.1Zn.sub.2(OAc).sub.2]. Results of the copolymerisation are set out in table 2.

TABLE-US-00002 TABLE 2 Comparison of catalytic activity between [L.sup.1,2,3Zn.sub.2(OAc).sub.2] at 80° C., 1 atm CO.sub.2, 24 hours. Molar ratio of catalyst:cyclohexene oxide - 1:1000 [L.sup.2Zn.sub.2(OAc).sub.2] was also tested at a higher temperature and pressure (100° C., 10 atm CO.sub.2, 24 hours) and was found to exhibit very similar activities to [L.sup.1Zn.sub.2(OAc).sub.2] under these conditions. TOF Catalyst TON [h.sup.−1] % carbonate % polymer Mn PDI % conversion L.sup.1Zn.sub.2OAc.sub.2 439 18.4 >99 96 6200 1.20 45 L.sup.2Zn.sub.2OAc.sub.2 398 16.6 >99 96 5800 1.21 40 L.sup.3Zn.sub.2OAc.sub.2 288 12 >99 97 2800 1.21 29

[0078] These results are outlined in table 3 below.

TABLE-US-00003 TABLE 3 Comparison of catalytic activity between [L.sup.1,2Zn.sub.2(OAc).sub.2] at 100° C., 10 atm CO.sub.2, 24 hours. Molar ratio of catalyst:cyclohexane oxide - 1:10000 TOF % % Catalyst TON [h.sup.−1] carbonate polymer Mn PDI L.sup.1Zn.sub.2(OAc).sub.2 3347 140 >99 96 14100 1.03 L.sup.2Zn.sub.2(OAc).sub.2 2839 118 >99 96 13000 1.04

[0079] General Procedure for the Synthesis of [H.sub.4L.sup.n′](ClO.sub.4).sub.2

[0080] To a round-bottomed flask was added 4-R.sub.1-2,6-diformylphenol, wherein R.sub.1 is as defined for formula (I), (5.80 mmol), NaClO.sub.4 (2.81 g, 23.2 mmol), acetic acid (0.66 mL, 11.6 mmol) and methanol (90 mL). This solution was heated to 70° C. whilst stirring, as the solution started to boil, 2,2-dimethyl-1,3-propanediamine (0.70 mL, 5.8 mmol) was added slowly in methanol (30 mL). The reaction mixture was allowed to cool to room temperature, and left stirring for 24 hours, after which a precipitate was filtered and washed with cold (−78° C.) methanol.

[0081] This procedure was carried out to produce [H.sub.4L.sup.2′](ClO.sub.4).sub.2 wherein R.sub.1 is methyl, and to produce [H.sub.4L.sup.3′](ClO.sub.4).sub.2 wherein R.sub.1 is methoxy.

[0082] [H.sub.4L.sup.2′](ClO.sub.4).sub.2 (orange crystals; 1.72 g, 2.26 mmol, 76%): .sup.1H NMR (d.sub.6-DMSO): δ 8.63 (d, J=13.5 Hz, 4H, N═CH), 7.34 (s, 4H, Ar—H), 3.90 (d, 8H, N—CH.sub.2—C), 2.13 (s, 6H, Ar—CH.sub.3), 1.28 (s, 12H, C—CH.sub.3). .sup.13C{.sup.1H} NMR (d.sub.6-DMSO): δ 176.1, 168.1, 145.2, 122.5, 116.3, 60.2, 33.7, 30.4, 18.7. Anal. Calc. for C.sub.28H.sub.38Cl.sub.2N.sub.4O.sub.10: C, 50.84; H, 5.79; N, 8.47. Found: C, 50.79; H, 5.77; N, 8.41.

[0083] [H.sub.4L.sup.3′](ClO.sub.4).sub.2 (brick red powder; 0.63 g, 0.90 mmol, 31%): .sup.1H NMR (d.sub.6-DMSO): δ 13.83 (s, 4H, OH/NH), 8.67 (d, 4H, N═CH), 7.22 (s, 4H, Ar—H), 3.90 (s, 8H, N—CH.sub.2—C), 3.69 (s, 6H, Ar—O—CH.sub.3), 1.29 (s, 12H, C—CH.sub.3). .sup.13C{.sup.1H} NMR ((d.sub.6-DMSO): δ 174.3, 168.5, 147.3, 130.7, 116.9, 61.2, 56.4, 34.4, 23.5. Anal. Calc. for C.sub.28H.sub.38Cl.sub.2N.sub.4O.sub.12: C, 48.49; H, 5.52; N, 8.08. Found: C, 48.47; H, 5.46; N, 8.12.

[0084] Synthesis of H.sub.2L.sup.2

[0085] [H.sub.4L.sup.2′](ClO.sub.4).sub.2 (2.7 mmol) was suspended in methanol (180 mL). The suspension was cooled to 0° C. and NaBH.sub.4 (2.65 g, 70 mmol) was added slowly. As NaBH.sub.4 was added, the red-orange suspension turned to a clear solution. The solution was allowed to stir at room temperature for 1 hour, after which water was added slowly, and the solution turned cloudy. Once precipitate started to form, the mixture was left overnight. The product was filtered, washed with water and dried under vacuum to yield white crystals of the title compound.

[0086] H.sub.2L.sup.2 (0.75 g, 1.6 mmol, 59%): Mp 154° C. .sup.1H NMR (CDCl.sub.3): δ 6.74 (s, 4H, Ar—H), 3.74 (s, 8H, N—CH.sub.2—Ar), 2.51 (s, 8H, N—CH.sub.2—C), 2.22 (s, 6H, Ar—CH.sub.3), 1.03 (s, 12H, C—CH.sub.3). .sup.13C{.sup.1H} NMR (CDCl.sub.3): δ 154.6, 128.7, 127.2, 124.7, 59.7, 52.7, 34.7, 25.0, 20.4. m/z (ES): 469 ([M+H].sup.+, 100%), 235 (14%). Anal. Calc. for C.sub.28H.sub.44N.sub.4O.sub.2: C, 71.76; H, 9.46; N, 11.95. Found: C, 71.60; H, 9.52; N, 11.88.

[0087] Synthesis of H.sub.2L.sup.3

[0088] [H.sub.4L.sup.3′](ClO.sub.4).sub.2 (1.40 g, 2.02 mmol) was suspended in MeOH (110 mL). The suspension was cooled to 0° C. and NaBH.sub.4 (1.99 g, 52.6 mmol) was added slowly. As NaBH.sub.4 was added, the brick-red suspension turned to a light brown, clear solution. The solvent was removed in vacuo and the crude product taken up in a minimal amount of CHCl.sub.3. After an hour a brown precipitate was filtered off, and the solvent removed in vacuo. The product was recrystallised from MeOH/H.sub.2O and dried under vacuum.

[0089] H.sub.2L.sup.3 (White crystals, 0.340 g, 0.68 mmol, 34% yield): Mp 74° C. (from CHCl.sub.3). .sup.1H NMR (CDCl.sub.3): δ 6.52 (s, 4H, Ar—H), 3.74 (m, 14H, N—CH.sub.2—Ar and Ar—O—CH.sub.3), 2.50 (s, 8H, N—CH.sub.3—C), 1.02 (s, 12H, C—CH.sub.3). .sup.13C{.sup.1H} NMR (CDCl.sub.3): δ 151.7, 150.5, 125.6, 113.5, 59.4, 55.7, 52.6, 34.6, 24.9; m/z (ES): 501 (100%, [M+H].sup.+), 251 (25%). Anal. Calc. for C.sub.28H.sub.44N.sub.4O.sub.4: C, 67.17; H, 8.86; N, 11.19. Found: C, 67.28; H, 8.98; N, 11.06.

[0090] General Procedure for the synthesis of [L.sup.nZn.sub.2(OAc).sub.2]

[0091] H.sub.2L.sup.n (0.72 mmol) was dissolved in dry THF (10 mL) in a Schlenk tube. The solution was transferred to another Schlenk tube containing Zn(OAc).sub.2 (0.27 g, 1.48 mmol). The reaction was left to stir for 16 hours overnight, after which the THF was removed in vacuo, and the product taken up in dry CH.sub.2Cl.sub.2 (10 mL). The solution was then filtered, the solvent removed in vacuo and the white powdery product dried under vacuum overnight.

[0092] [L.sup.2Zn.sub.2(OAc).sub.2] (0.37 g, 0.52 mmol, 72%): .sup.1H NMR (d.sub.2-TCE, 383 K): δ 6.83 (s, 4H, Ar—H), 4.76 (br s, 4H, NH), 3.26 (br s, 4H, CH.sub.2), 2.96 (br s, 4H, CH.sub.2), 2.79 (br s, 4H, CH.sub.2), 2.44 (br s, 4H, CH.sub.2), 2.27 (s, 6H, Ar—CH.sub.3), 2.09 (s, 6H, OAc), 1.26 (s, 6H, C—CH.sub.3), 1.04 (s, 6H, C—CH.sub.3). .sup.13C{.sup.1H} NMR (d.sub.2-TCE, 383 K): δ 175.1, 159.0 (br), 139.0 (br), 131.0, 124.7, 63.4, 56.1, 33.4, 27.9, 21.3, 19.7. m/z (FAB): 656 ([M−OAc].sup.+, 100%). Anal. Calc. for C.sub.32H.sub.48N.sub.4O.sub.6Zn.sub.2: C, 53.71; H, 6.76; N, 7.83. Found: C, 53.60; H, 6.74; N, 7.82.

[0093] [L.sup.3Zn.sub.2(OAc).sub.2] (0.40 g, 0.54 mmol, 75%): .sup.1H NMR (d.sub.2-TCE, 383 K): δ 6.61 (s, 4H, Ar—H), 4.68 (s, br, 4H, NH), 3.77 (s, 6H, Ar—OCH.sub.3), 3.21 (s, br, 4H, CH.sub.2), 2.98 (s, br, 4H, CH.sub.2), 2.76 (s, br, 4H, CH.sub.2), 2.49 (s, br, ˜4H, CH.sub.2), 2.01 (s, 6H, OAc), 1.25 (s, 6H, C—CH.sub.3), 1.03 (s, 6H, C—CH.sub.3). .sup.13C{.sup.1H} NMR (d.sub.2-TCE, 383 K): δ 174.5, 155.2, 150.4, 125.5, 116.2, 63.2, 56.8, 33.4, 27.8, 21.4, 20.8. m/z (FAB): 687 ([M−OAc].sup.+, 98%). Anal. Calc. for C.sub.32H.sub.48N.sub.4O.sub.8Zn.sub.2: C, 51.42; H, 6.47; N, 7.49. Found: C, 51.36; H, 6.56; N, 7.49.

Example 3

[0094] A complex of H.sub.2L.sup.1 and Mg(OAc).sub.2 was prepared in the same manner as [L.sup.1Zn.sub.2(OAc).sub.2]. X-ray crystallography, .sup.1H and .sup.13C NMR data suggest that the bimetallic magnesium complex produced is a mixture of two different structures, one containing two acetate groups ([L.sup.1Mg.sub.2(OAc).sub.2]) and one being a dimeric structure containing two ligand moieties linked by a bridging acetate group, with one bound water molecule ([L.sup.1.sub.2Mg.sub.4(OAc).sub.3(H.sub.2O)]. The dimeric structure is shown in FIG. 5. The dimeric structure is formed due to the presence of an impurity of water during the complexation of the macrocyclic ligand H.sub.2L.sup.1 with Mg(OAc).sub.2. Unlike Zn(OAc).sub.2, Mg(OAc).sub.2 is not commercially available in anhydrous form. Commercially available Mg(OAc).sub.2.4H.sub.2O was dried under vacuum at 100° C., prior to use in the complexation reaction. It has been found that this drying was insufficient to remove all of the water, and therefore provides a source of water to allow the formation of a dimeric complex.

[0095] Other catalyst complexes of formula (I) of the present invention may form a dimeric structure or mixture of monomer and dimer where catalyst synthesis is carried out in the presence of water. Dimer formation is avoided when the synthesis is anhydrous.

[0096] The mixture of the [L.sup.1Mg.sub.2(OAc).sub.2] complex and dimeric structure thereof was tested under mild conditions for the copolymerisation of carbon dioxide and cyclohexane oxide. Results of the copolymerisation are set out in table 4. Data shows that the magnesium complex mixture shows excellent activity under identical conditions as used for [L.sup.1Zn.sub.2(OAc).sub.2].

TABLE-US-00004 TABLE 4 Comparison of [L.sup.1Zn.sub.2(OAc).sub.2] and magnesium complex activities for copolymerization of cyclohexene oxide and CO.sub.2. Where [L.sup.1Mg.sub.2(OAc).sub.2] represents a mixture of [L.sup.1Mg.sub.2(OAc).sub.2] and [L.sup.1.sub.2Mg.sub.4(OAc).sub.3(H.sub.2O)]. The molar catalyst loading is 1:1000 (catalyst:epoxide) at 1 atm CO.sub.2 and 1:10000 (catalyst:epoxide) at 10 atm CO.sub.2. Time T P TOF Catalyst (h) (° C.) (atm) TON [h.sup.−1] % carbonate % polymer Mn PDI L.sup.1Zn.sub.2(OAc).sub.2 24 80 1 439 18.3 >99 96 6200 1.19 L.sup.1Mg.sub.2(OAc).sub.2 16 80 1 527 33.3 >99 >99 7200 1.23 L.sup.1Zn.sub.2(OAc).sub.2 24 100 1 527 25.1 >99 94 7400 1.21 L.sup.1Mg.sub.2(OAc).sub.2 5 100 1 482 96.4 >99 >99 6400 1.24 L.sup.1Zn.sub.2(OAc).sub.2 24 100 10 3347 140 >99 96 14100 1.03 L.sup.1Mg.sub.2(OAc).sub.2 5 100 10 3660 732 >99 >99 14300 1.05

[0097] As can be seen from table 4, the magnesium catalyst mixture shows a TOF of almost 34 h.sup.−1 at 80° C. and 1 atm CO.sub.2, this value increases to almost 97 h.sup.−1 when the temperature is increased to 100° C. (entries 2 and 4). If the pressure is increased to 10 atm, the activity is increased further still (entry 6). In addition, there is no evidence for the formation of any cyclic carbonate in the .sup.1H NMR spectra. This is observed for all copolymerisations using the magnesium catalyst and is very unusual, as the formation of cyclic carbonate is generally held to be under thermodynamic control, increasing with temperature. The polymer properties are very similar to those produced by [L.sup.1Zn.sub.2(OAc).sub.2], with similar polydispersities, molecular weights and no observable ether linkages.

[0098] Synthesis of the Mixed Magnesium Complex

[0099] H.sub.2L.sup.1 (0.40 g, 0.72 mmol) was dissolved in dry THF (10 mL) in a Schlenk tube The solution was transferred to another Schlenk tube containing Mg(OAc).sub.2 (0.21 g, 1.48 mmol). The reaction was left to stir for 16 hours overnight, after which the THF was removed in vacuo, and the product taken up in dry CH.sub.2Cl.sub.2 (10 mL). The solution was then filtered, the solvent removed in vacuo and the white powdery product dried under vacuum overnight.

[0100] .sup.1H NMR (CD.sub.3OD): δ Complex A (monomeric [L.sup.1Mg.sub.2(OAc).sub.2]): 7.03 (s, 4H, Ar—H), 4.03 (d, J=11.8 Hz, 4H, CH.sub.2), 3.22 (d, J=11.8 Hz, 4H, CH.sub.2). 2.79 (d, J=11.6 Hz, 4H, CH.sub.2), 2.65 (d, J=11.5 Hz, 4H, CH.sub.2), 1.91 (s, ˜6H, OAc), 1.28 (s, 18H, Ar—C—CH.sub.3), 1.26 (s, 6H, C—C—CH.sub.3), 1.03 (s, 6H, C—C—CH.sub.3). Complex B (dimeric complex [L.sup.1.sub.2Mg.sub.4(OAc).sub.4(H.sub.2O)]): 7.14 (s, 4H, Ar—H), 3.97 (s, 8H, Ar—CH.sub.2—N), 2.73 (s, 8H, N—CH.sub.2—C), 1.91 (s, ˜6H, OAc), 1.29 (s, 18H, Ar—C—CH.sub.3), 1.26 (s, ˜6H, C—C—CH.sub.3), 1.06 (s, 6H, C—C—CH.sub.3). m/z (FAB): 657 ([M−OAc].sup.+, 100%).