Catalysts

Abstract

The present invention relates to the field of polymerisation catalysts, and systems comprising these catalysts for polymerising carbon dioxide and an epoxide, a lactide and/or lactone, and/or an epoxide and an anhydride. The catalyst is of formula (I):

##STR00001##

wherein at least one of M.sub.1 or M.sub.2 is selected from Ni(II) and Ni(III)-X. A process for the reaction of carbon dioxide with an epoxide; an epoxide and an anhydride; and/or a lactide and/or a lactone in the presence of the catalyst is also described.

Claims

1. A catalyst of formula (I): ##STR00033## wherein: M.sub.1 and M.sub.2 are independently selected from Zn(II), Cr(II), Co(II), Cu(II), Mn(II), Mg(II), Ni(II), Fe(II), Ti(II), V(II), Cr(III)-X, Co(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II), Al(III)-X, Ti(III)-X, V(III)-X, Ge(IV)-(X).sub.2 or Ti(IV)-(X).sub.2; wherein at least one of M.sub.1 or M.sub.2 is selected from Ni(II) and Ni(III)-X; R.sub.1 and R.sub.2 are independently selected from hydrogen, halide, a nitro group, a nitrile group, an imine, an amine, an ether group, a silyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, a sulfinate group or an acetylide group or an optionally substituted alkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio, arylthio, alicyclic or heteroalicyclic group; R.sub.3 is independently selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, heteroarylene or cycloalkylene, wherein alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, may optionally be interrupted by aryl, heteroaryl, alicyclic or heteroalicyclic; R.sub.5 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; E.sub.1 is C, E.sub.2 is O, S or NH or E.sub.1 is N and E.sub.2 is O; E3, E4, E5 and E6 are selected from N, NR.sub.4, O and S, wherein when E3, E4, E5 or E6 are N, is , and wherein when E3, E4, E5 or E6 are NR.sub.4, O or S, is ; R.sub.4 is independently selected from hydrogen, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; X is independently selected from OC(O)R.sup.X, OSO.sub.2R.sup.X, OSOR.sup.X, OSO(R.sup.X).sub.2, S(O)R.sup.X, OR.sup.X, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, nitro, amido or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl; R.sub.x is independently hydrogen, or optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and G is absent or independently selected from a neutral or anionic donor ligand which is a Lewis base.

2. The catalyst of claim 1, wherein at least one of M.sub.1 or M.sub.2 is Ni(II).

3. The catalyst of claim 1, wherein one of M.sub.1 or M.sub.2 is selected from Ni(II) and Ni(III)-X and the remaining occurrence of M.sub.1 and M.sub.2 is selected from Zn(II), Cr(III)-X, Cu(II), Co(III)-X, Co(II), Cu(II), Mn(III)-X, Mn(II), Mg(II), Ni(II), Ni(III)-X, Fe(II), Fe(III)-X, Ti(II), Ti(III)-X, V(II), V(III)-X, Ge(IV)-(X).sub.2 and Ti(IV)-(X).sub.2.

4. The catalyst of claim 3, wherein the remaining occurrence of M.sub.1 and M.sub.2 is selected from Zn(II), Cr(III)-X, Co(II), Ni(II), Fe(II), Fe(III)-X and V(II).

5. The catalyst of claim 3, wherein the remaining occurrence of M.sub.1 and M.sub.2 is selected from Zn(II), Cr(III)-X, Co(II), Mn(II), Mg(II), Ni(II), Ni(III)-X, Fe(II), and Fe(III)-X.

6. The catalyst of claim 3, wherein the remaining occurrence of M.sub.1 and M.sub.2 is selected from any of: Zn(II), Mg(II), Ni(II), Co(II), Co(III)-X and Ni(III)-X.

7. The catalyst of claim 1, wherein both M.sub.1 and M.sub.2 are Ni(II).

8. The catalyst of claim 1, wherein R.sub.3 is selected from substituted or unsubstituted alkylene and substituted or unsubstituted arylene.

9. The catalyst of claim 1, wherein R.sub.3 is selected from substituted or unsubstituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, and cycloalkylene, cycloalkylene.

10. The catalyst of claim 1, wherein R.sub.3 is selected from 2,2-dimethylpropylenyl, CH.sub.2 CH.sub.2 CH.sub.2, CH.sub.2CH(CH.sub.3)CH.sub.2, CH.sub.2C(CH.sub.2C.sub.6H.sub.5).sub.2CH.sub.2, phenylene, CH.sub.2 CH.sub.2, CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2, CH.sub.2 CH.sub.2N (CH.sub.3) CH.sub.2 CH.sub.2, 1,4-cyclohexandiyl, CH.sub.2CH.sub.2CH (C.sub.2H.sub.5) or CH.sub.2C(C.sub.2H.sub.5).sub.2CH.sub.2.

11. The catalyst of claim 1, wherein R.sub.3 is selected from is selected from 2,2-dimethylpropylenyl, CH.sub.2 CH.sub.2 CH.sub.2, CH.sub.2CH(CH.sub.3)CH.sub.2, CH.sub.2C(CH.sub.2C.sub.6H.sub.5).sub.2CH.sub.2, CH.sub.2CH.sub.2CH (C.sub.2H.sub.5), CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2.

12. The catalyst of claim 1, wherein R.sub.3 is selected from a 2,2-dimethylpropylenyl, CH.sub.2C(CH.sub.2C.sub.6H.sub.5).sub.2CH.sub.2, CH.sub.2C(C.sub.2H.sub.5).sub.2CH.sub.2 and CH.sub.2CH.sub.2CH (C.sub.2H.sub.5).

13. The catalyst of claim 1, wherein R.sub.3 is a 2,2-dialkylpropylenyl.

14. The catalyst of claim 1, wherein both occurrences of R.sub.3 are the same.

15. The catalyst of claim 1, wherein E.sub.1 is C and E.sub.2 is O, S, or NH.

16. The catalyst of claim 1, wherein E3, E4, E5 and E6 are NR.sub.4.

17. The catalyst of claim 1, wherein R.sub.4 is selected from hydrogen or an optionally substituted alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, aryl or heteroaryl.

18. The catalyst of claim 1, wherein each occurrence of R.sub.4 is the same.

19. The catalyst of claim 1, wherein E3, E4, E5 and E6 are the same.

20. The catalyst of claim 1, wherein R.sub.1 is selected from hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl, silyl ether, and optionally substituted alkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxy, arylthio or alkylthio.

21. The catalyst of claim 1, wherein R.sub.1 is selected from halide, sulfoxide, silyl, and an optionally substituted alkyl, heteroaryl or alkoxy.

22. The catalyst of claim 1, wherein R.sub.1 is selected from t-butyl, methoxy, triethylsilyl, bromide, SO.sub.2CH.sub.3, or piperidinyl.

23. The catalyst of claim 22, wherein R.sub.1 is selected from t-butyl or triethylsilyl.

24. The catalyst of claim 1, wherein both occurrences of R.sub.1 are the same.

25. The catalyst of claim 1, wherein X is selected from OC(O)R.sup.X, OSO.sub.2R.sup.X, OS(O)R.sup.X, OSO(R.sup.X).sub.2, S(O)R.sup.X, ORX, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, nitro, amido, and optionally substituted alkyl, heteroalkyl, alicyclic, heteroalicyclic, aryl or heteroaryl.

26. The catalyst of claim 1, wherein X is selected from OC(O)R.sup.X, ORX, halide, carbonate, amino, nitro, alkyl, aryl, heteroaryl, phosphinate or OSO.sub.2R.sup.X.

27. The catalyst of claim 1, wherein X is selected from OC(O)R.sup.X, ORX, halide, alkyl, aryl, heteroaryl, phosphinate or OSO.sub.2R.sup.X.

28. The catalyst of claim 1, wherein X is OC(O)R.sup.X.

29. The catalyst of claim 1, wherein X is selected from OAc, O.sub.2CCF.sub.3, or C.sub.2C(CH.sub.2)3Cy.

30. The catalyst of claim 1, wherein both occurrences of X are the same.

31. The catalyst of claim 1, wherein R.sup.X is an optionally substituted alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl, cycloalkyl or alkylaryl.

32. The catalyst of claim 1, wherein R.sup.X is selected from hydrogen, or an optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl.

33. The catalyst of claim 1, wherein R.sup.X is selected from an optionally substituted alkyl, alkenyl, heteroalkyl, or cycloalkyl.

34. The catalyst of claim 1, wherein R.sup.X is selected from an optionally substituted alkyl, heteroalkyl, or cycloalkyl.

35. The catalyst of claim 1, wherein R.sup.X is an optionally substituted alkyl.

36. The catalyst of claim 1, wherein both occurrences of R.sup.X are the same.

37. The catalyst of claim 1, wherein each occurrence of R.sub.2 and R.sub.5 is hydrogen.

38. The catalyst of claim 1, wherein both occurrences of R.sub.1 are the same, and are selected from hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl, silyl ether and an optionally substituted alkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxy or alkylthio; R.sub.2 is hydrogen; both occurrences of R.sub.3 are the same, and are selected from substituted or unsubstituted alkylene and substituted or unsubstituted arylene; E.sub.1 is C and E.sub.2 is O; E3, E4, E5 and E6 are NR.sub.4, R.sub.4 is hydrogen; each X is the same, and is selected from OC(O)R.sup.X, OR.sup.X, halide, carbonate, amino, nitro, alkyl, aryl, heteroaryl, phosphinate or OSO.sub.2R.sup.X, each R.sup.X is the same and is selected from alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; each G, where present, is the same and is selected from halide; water; a heteroaryl optionally substituted by alkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitro or nitrile; and one of M.sub.1 and M.sub.2 is Ni(II) or Ni(III)-X, and the remaining M.sub.1 or M.sub.2 is selected from Mg(II), Zn(II), Cr(III)-X, Co(II), Co-(III)-X Mn(II), Ni(II), Ni(III)-X, Fe(II), and Fe(III)-X.

39. The catalyst of claim 38, wherein both occurrences of M.sub.1 and M.sub.2 are selected from Ni(II) and Ni(III)-X.

40. The catalyst of claim 38, wherein R.sub.1 is hydrogen, halide, silyl, silyl ether, sulfonyl or optionally substituted alkyl or alkoxyl.

41. The catalyst of claim 1, of the formula (Ib): ##STR00034## wherein: both occurrences of R.sub.1 are the same, and are selected from hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl, silyl ether and an optionally substituted alkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxy or alkylthio; R.sub.3 is selected from substituted or unsubstituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene or heteroalkynylene, cycloalkylene or aryl ene; each X is the same, and is selected from OC(O)R.sup.X, OR.sup.X, halide, carbonate, amino, nitro, alkyl, aryl, heteroaryl, phosphinate or OSO.sub.2R.sup.X, R.sup.X is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; R.sup.X is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; each G, where present, is independently selected from halide; water; a heteroaryl optionally substituted by alkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitro or nitrile; and one occurrence of M.sub.1 and M.sub.2 is Ni(II) or Ni(III)-X, and the remaining occurrence of M.sub.1 or M.sub.2 is selected from Mg(II), Zn(II), Cr(III)-X, Co(II), Co(III)-X, Mn(II), Ni(II), Ni(III)-X, Fe(II), and Fe(III)-X.

42. The catalyst of claim 41, wherein R.sub.1 is hydrogen, halide, silyl, silyl ether, sulfonyl, and optionally substituted alkyl or alkoxy.

43. The catalyst of claim 41, wherein R.sub.3 is selected from propylenyl, 2,2-dimethylpropylenyl, and substituted or unsubstituted phenylenyl or biphenylenyl.

44. The catalyst of claim 41, wherein M.sub.1 and M.sub.2 are selected from Ni(II) and Ni(III)-X.

45. The catalyst of claim 41, wherein X is OC(O)R.sup.X, OR.sup.X, halide, alkyl, aryl, heteroaryl, phosphinate or OSC.sub.2R.sup.X.

46. The catalyst of claim 41, wherein R.sup.X is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl, or alkylaryl.

47. The catalyst of claim 41, wherein G is absent.

48. The catalyst of claim 1 of the formula: ##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042##

49. A process for the reaction of: a. carbon dioxide with an epoxide; b. an epoxide and an anhydride; and/or c. a lactide and/or a lactone, in the presence of the catalyst of claim 1.

50. The process of claim 49, wherein the epoxide is ethylene oxide, butylene oxide, propylene oxide or cyclohexene oxide.

51. (canceled)

52. (canceled)

53. (canceled)

54. (canceled)

55. (canceled)

Description

[0140] Embodiments of the invention will now be described with reference to accompanying examples and figures in which:-

[0141] FIG. 1 shows the selectivity of various catalysts.

[0142] FIG. 2 shows the activity of various catalysts.

[0143] FIG. 3 is a close up from FIG. 2.

EXAMPLES

Example 1

Synthesis of Nickel-Containing Catalysts

[0144] Ligands H.sub.2L.sup.1-18 were synthesised by the method previously described by Kember et al, Angew. Chem. Int. Ed., 2009, 48, 931-933.

##STR00030##

[0145] Ligands H.sub.2L.sup.1, H.sub.2L.sup.3 H.sub.2L.sup.5, H.sub.2L.sup.6, H.sub.212 and H.sub.2L.sup.8 (2 mmol) were dissolved in MeOH (50 mL), Ni(OAc).sub.2.4H.sub.2O (0.498 g, 4 mmol) was added portionwise over 15 minutes and the solution stirred overnight. The solvent was removed under vacuum and excess water/AcOH was removed by azeotrope with toluene (340 mL) to give a green or blue solid. [0146] [L.sup.1Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1581 and 1413. MALDI-TOF MS: m/z: 727.6 ([M -OAc)].sup.+, 100%); [0147] [L.sup.3Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1577 and 1413. [0148] [L.sup.5Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1585 and 1413. APCI-MS: m/z: 829 ([M-2 .sup.OAc+.sup.O.sub.2CH].sup.+, 100%); [0149] [L.sup.6Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1577 and 1439. APCI-MS: m/z: 754 ([M-2 .sup.OAc+.sup.O.sub.2CH].sup.+, 100%); [0150] [L.sup.7Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1581 and 1413. APCI-MS: m/z: 757 ([M-2 .sup.OAc+.sup.O.sub.2CH].sup.+, 100%). [0151] [L.sup.8Ni.sub.2(OAc).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1581 and 1413. APCI-MS: m/z: 779.2 ([M-.sup.OAc].sup.+, 75%), 765.2 ([M-2 .sup.OAC+.sup.O.sub.2CH].sup.+, 95%).

##STR00031##

[0152] Ligand H.sub.2L.sup.x (2 mmol) was dissolved in MeOH (50 mL), Ni(X).sub.2.xH.sub.2O (4 mmol) was added portionwise over 15 minutes and the solution stirred overnight. The solvent was removed under vacuum and excess water/acid was removed by azeotrope with toluene (340 mL) to give a green or blue solid. [0153] [L.sup.1Ni.sub.2(C.sub.2CCF.sub.3).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1674 and 1480. ESI-MS: m/z =779.3 (100%, [M-O.sub.2CCF.sub.3].sup.+). [0154] [L.sup.1Ni.sub.2(C.sub.2C(CH.sub.2).sub.3Cy).sub.2]: IR (.sub.CO, cm.sup.1, neat): 1581 and 1406: ESI-MS: m/z=835.2 (100%, [M-(O.sub.2C(CH.sub.2).sub.3Cy)].sup.+). [0155] L.sup.14Ni.sub.2(C.sub.2CCF.sub.3).sub.2: IR (.sub.CO, cm.sup.1, neat): 1678 and 1480. ESI-MS: m/z: 711.2 ([M-2 .sup. OAc+.sup.O.sub.2CH].sup.+, 100%);

##STR00032##

[0156] Ligand H.sub.2L.sup.X (2 mmol) was dissolved in MeOH (50 mL), Ni(OAc).sub.2.4H.sub.2O (0.498 g, 4 mmol) was added portionwise over 15 minutes and the solution stirred overnight. The solvent was removed under vacuum and excess water/acid was removed by azeotrope with toluene (340 mL) to give a green or blue solid. [0157] L.sup.9Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1573 and 1421. APCI-MS: m/z: 655.1 ([M-2 .sup. OAc+.sup.C.sub.2CH].sup.+, 85%); [0158] L.sup.10Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1577 and 1421. APCI-MS: m/z: 685.1 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 70%); [0159] L.sup.11Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1581, 1413. APCI-MS: m/z: 1017.2 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 70%), 969.2 ([M-2 .sup.OAc].sup.+, 100%); [0160] L.sup.12Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1559 and 1417. APCI-MS: m/z: 725.1 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 50%); [0161] L.sup.13Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1551 and 1436. APCI-MS: m/z: 629.1 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 50%); [0162] L.sup.14Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1573 and 1410. APCI-MS: m/z: 725.2 ([M - .sup.OAc].sup.+, 100%). [0163] L.sup.15Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1566, 1413. APCI-MS: m/z: 685.1 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 100%); [0164] L.sup.16Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1577 and 1402. ESI-MS: m/z: 741.3 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 55%) ; 755.3 ([M-.sup.OAc].sup.+, 20%). [0165] L.sup.17Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1566, 1454. APCI-MS: m/z: 735.2 ([M-2 .sup.OAc +.sup.C.sub.2CH].sup.+, 100%); [0166] L.sup.18Ni.sub.2(OAc).sub.2: IR (.sub.CO, cm.sup.1, neat): 1585, 1424. APCI-MS: m/z: 769.2 ([M - 2 .sup.OAc +.sup.C.sub.2CH].sup.+, 95%);

Example 2

1 atm Copolymerisation of CHO with CO.SUB.2 .Using Ni Catalysts

[0167] The catalyst (0.0247 or 0.00494 mmol) was added to a dried Schlenk tube and dried under vacuum for 30 minutes. CHO (2.5 mL, 24.7 mmol) was added under CO.sub.2 via a syringe, the vessel was heated to 100 C. and stirred for 2-16 hours, after which the heating was removed and a sample taken for GPC/NMR analysis.

[0168] The catalysts show over 90% selectivity for polymer towards the reactant cyclohexene oxide, >99% selectivity for polycarbonate over polyether (that is >99% carbonate incorporation), high activities and activity under low pressures (1 atm).

Example 3

Polymerisation of CO.SUB.2 .and PO at 90 C. and 0.21 mmol [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.]

[0169] [L.sup.1Ni.sub.2(OAc).sub.2] (0.21 mmol) was dissolved in propylene oxide (214 mmol) in a Schlenk tube and the solution transferred into a pre-dried 100 mL stainless steel Parr pressure vessel using a syringe. The vessel was charged with CO.sub.2 (3.0 MPa) and heated to 90 C. The solution was stirred mechanically for 6 hours, giving 7.5g of poly(propylene carbonate) (Mn 19000/9700, PDI 1.03/1.04) as a white solid with a high selectivity for polymer and >99% carbonate linkages.

Example 4

Polymerisation of CO.SUB.2 .and PO at 80 C. and 0.11 mmol [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.]

[0170] [L.sup.1Ni.sub.2(OAc).sub.2] (0.11 mmol) was dissolved in propylene oxide (214 mmol) in a Schlenk tube and the solution transferred into a pre-dried 100 mL stainless steel Parr pressure vessel using a syringe. The vessel was charged with CO.sub.2 (4.0 MPa) and heated to 80 C. The solution was stirred mechanically for 16 hours, giving 7.4 g of poly(propylene carbonate) (Mn 23000/11400, PDI 1.03/1.05) as a white solid with a high selectivity for polymer and >99% carbonate linkages.

Example 5

Polymerisation of CO.SUB.2 .and PO at 90 C. and 0.11 mmol of [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.]

[0171] [L.sup.1Ni.sub.2(OAc).sub.2] (0.11 mmol) was dissolved in propylene oxide (214 mmol) in a Schlenk tube and the solution transferred into a pre-dried 100 mL stainless steel Parr pressure vessel using a syringe. The vessel was charged with CO.sub.2 (4.0 MPa) and heated to 90 C. The solution was stirred mechanically for 17 hours, giving 11.5 g of poly(propylene carbonate) (Mn 39900/17600, PDI 1.03/1.09) as a white solid with a high selectivity for polymer and >99% carbonate linkages.

Example 6

Polymerisation of CO.SUB.2 .and CHO at 100 C. and 0.05 mmol of [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.]

[0172] [L.sup.1Ni.sub.2(OAc).sub.2] (0.05 mmol) was dissolved in cyclohexene oxide (50 mmol) in a Schlenk. The vessel was degassed, charged with CO.sub.2 (0.1 MPa) and heated at 100 C. with magnetic stirring for 3 hours, giving 2.9g of poly(cyclohexene carbonate). The polymer contained >99% carbonate linkages and was produced with >99% selectivity (Mn 12000/5000, PDI 1.04/1.11).

Example 7

Polymerisation of CO.SUB.2 .and CHO at 80 C. and 0.09 mmol of [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.]

[0173] [L.sup.1Ni.sub.2(OAc).sub.2] (0.09 mmol) was dissolved in cyclohexene oxide (0.9 mmol) and propylene oxide (0.9 mmol) and the solution transferred into a pre-dried 100 mL stainless steel Parr pressure vessel using a syringe. The vessel was charged with CO.sub.2 (1.5 MPa) and heated to 80 C. The solution was stirred mechanically for 7 hours, giving 13.1 g poly(cyclohexene-co-propylene) carbonate containing >99% carbonate linkages with a very high selectivity for polymer formation.

Example 8

Comparison of Polymerisation of CO.SUB.2 .and PO with [L.SUP.1.Ni.SUB.2.(OAc).SUB.2.], [L.SUP.5.Ni.SUB.2.(OAc).SUB.2.], and [L.SUP.1.Mg.SUB.2.(OAc).SUB.2.] at a Range of Temperatures

[0174] The catalyst ([L.sup.5Ni.sub.2(OAc).sub.2]/[L.sup.1Ni.sub.2(OAc).sub.2]/[L.sup.1Mg.sub.2(OAc).sub.2]) (0.21 mmol) was dissolved in propylene oxide (214 mmol) in a Schlenk tube and the solution transferred into a pre-dried 100 mL stainless steel Parr pressure vessel using a syringe. The vessel was charged with 0.4-0.5 MPa CO.sub.2 pressure and heated to temperature. Once at temperature the CO.sub.2 pressure was topped up to 4.0 MPa. The solution was stirred mechanically for the desired reaction time and the reaction followed by in-situ ATR-FT-IR spectroscopy. The selectivity and activity of the reaction was determined by ATR-FT-IR spectroscopy and confirmed with .sup.1H NMR spectroscopy of the crude product. Results are set out in FIG. 1 and FIG. 2.

[0175] FIG. 1 shows that the selectivity of the catalyst having a Magnesium centre [L.sup.1Mg.sub.2(OAc).sub.2] is much lower than compared with a catalyst having the same ligand structure but with a Nickel metal centre [L.sup.1Ni.sub.2(OAc).sub.2]. Furthermore, FIG. 1 shows that the selectivity of catalysts having nickel metal centres remains high over a broad temperature range, at 100C, the selectivity of the nickel centred catalysts, [L.sup.1Ni.sub.2(OAc).sub.2], [L.sup.5Ni.sub.2(OAc).sub.2], is still at least 55%, whereas at 100C the selectivity of the magnesium centred catalyst, [L.sup.1Mg.sub.2(OAc).sub.2], has fallen to 0%.

[0176] FIG. 2 shows that the activity of the catalyst having a Magnesium centre [L.sup.1Mg.sub.2(OAc).sub.2] is much lower than compared with a catalyst having the same ligand structure but with a Nickel metal centre [L.sup.1Ni.sub.2(OAc).sub.2] across a temperature range. Furthermore, FIG. 2 shows that the activity of the nickel centred catalyst significantly increases at higher temperature, whilst retaining selectivity for PPC, unlike the magnesium centred catalyst which shows less activity and no selectivity at higher temperatures (see FIG. 1).

[0177] FIG. 3 is a close up from FIG. 2 in the window 65-85 C. and shows more closely the comparative activities of [L.sup.1Ni.sub.2(OAc).sub.2] and [L.sup.1Mg.sub.2(OAc).sub.2] in this temperature range. It demonstrates more clearly that [L.sup.1Ni.sub.2(OAc).sub.2] is surprisingly twice as active as it's magnesium analogue.

Example 9

Comparison of 1 atm Copolymerisation of CHO and CO2 with Equivalent Ni and Mg Complexes under Identical Conditions

[0178]

[0179] The catalysts having nickel metal centres show over 99% selectivity to the reactant cyclohexene oxide. The catalysts having nickel metal centres also display a higher turnover number and a higher turnover frequency when compared to catalysts having the same ligand structure but with magnesium metal centres and when tested under identical reaction conditions. In particular, the turnover frequency of the catalysts having nickel metal centres is in some cases double that shown with catalysts having magnesium metal centres.

[0180] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0181] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0182] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.