Asymmetric, regio‐ and stereo‐selective alternating copolymerization of CO₂ and propylene oxide catalyzed by chiral chromium Salan complexes

Abstract

Chiral chromium complexes of tetradentate N,N′‐disubstituted bis(aminophenoxide) (designated as Salan, a saturated version of Schiff‐base Salen ligand) in conjunction with an ionic quaternary ammonium salt can efficiently catalyze the copolymerization of CO2 with racemic propylene oxide (rac‐PO) at mild conditions to selectively afford completely alternating poly(propylene carbonate) (PPC) with ∼ 95% head‐to‐tail linkages and moderate enantioselectivity. These new catalyst systems predominantly exceed the previously much‐studied SalenCr(III) systems in catalytic activity, polymer enantioselectivity, and stereochemistry control. The chiral diamine backbone, sterically hindered substitute groups on the aromatic rings, and the presence of sp3‐hydridized amino donors and its N,N′‐disubstituted groups in chiral SalanCr(III) complexes all play significant roles in controlling polymer stereochemistry and enantioselectivity. Furthermore, a relationship between polycarbonate enantioselectivity and its head‐to‐tail linkages in relation to regioselective ring‐opening of the epoxide was also discussed on the basis of stereochemical studies of PPCs derived from the copolymerization of CO2 with chiral PO at various conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6102–6113, 2008

Chromium(iii) amine-bis(phenolate) complexes as catalysts for copolymerization of cyclohexene oxide and CO2

“…1-6 Carbon dioxide is an appealing C1 feedstock because it is widely available, inexpensive, and nontoxic. 7 Many homogeneous catalysts containing metals such as Mg, 8 Al, [9][10][11][12][13] Zn, [14][15][16][17][18][19][20][21][22] Cr, [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Co 6,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]…”

Stabilization of the Thermal Decomposition of Poly(Propylene Carbonate) Through Copper Ion Incorporation and Use in Self-Patterning

“…PPC decomposes by chain scission and unzipping. 11,[19][20][21] Decomposition propagates via chain unzipping at low temperatures because the cyclic monomer is thermodynamically more favored than the straight chain polymer. At higher temperatures, chain scission competes with the unzipping decomposition mechanism.…”

“…Efforts to improve the thermal stability of PPC involve increasing the molecular weight, 23 changing the backbone structure, 10,14,18,19 adding crosslinking, 24,25 and use of additives that prevent decomposition. Enhancement of the thermal stability of PPC has been reported by end-capping the polymer chains 21,[26][27][28] to inhibit initiation of the decomposition mechanism or hydrogen bonding to carbonyl oxygens to suppress propagation of the degradation reaction.…”

Highly regio- and stereo-selective copolymerization of CO2 with racemic propylene oxide catalyzed by unsymmetrical (S,S,S)-salenCo(III) complexes

“…Recently, we succeeded in tuning salenCr(III) complexes into regular catalysts for the copolymerization of CO 2 and aliphatic epoxides by designing sterically hindered coordination environment around the central metal ion [14,17]. Based on the understanding of stereochemistry control mechanism of coordination catalysis polymerization, herein we report highly active catalyst systems based on unsymmetrical chiral salenCo(III) complexes ( Figure 2, 1a-c, 2) containing a derived chiral-BINOL for asymmetric copolymerization of CO 2 and racemic propylene oxide (PO), with emphasis on precise control of polycarbonate regio-and stereo-chemistry.…”

“…Particularly, some well-defined homogeneous metal complexes have been reported to be highly active and/or selective catalysts. The representatives are discrete -diiminate zinc alkoxides [4], and binary or bifunctional catalyst systems based on metal-salen or -salan complexes [5][6][7][8][9][10][11][12][13][14].…”