Poly(lactic acid) (PLA) is by far the most commonly produced biodegradable polyester. Metal-mediated ring opening polymerization of lactide is the most studied route for the synthesis of PLA, with hundreds of catalysts reported to date. Discrete metal initiators are comprised of an electropositive metal center, an ancillary ligand, and an initiating group such as an amide or an alkoxide. This difference in polarity between the electrophilic metal centers and the nucleophlic initiators often leads to catalyst aggregation. Partially due to this phenomenon, bimetallic catalysts, either dimeric, tethered, or dinucleating, are gaining attention as catalysts. The involvement of two metals in each of these motifs can affect the mechanism, and thus the activity, of the catalytic systems differently. This review is divided into three main segments: A) Dinuclear or dimeric species arising from aggregation of two discrete metal centers through bridging ligands; B) Tethered species involving two non-bridged metal centers on the same ligand architecture that can react independently and C) Dinucleating catalysts involving a multidentate ligand platform bound to two different metals, which are also bridged by a secondary ligand and can react in tandem. This review explores the structure-function relationship for each of these motifs by examining the effect of ligand design on various modes of bimetallic cooperativity in the ring opening polymerization mechanism of lactide.
Publications
(59) Phys. Fluids 2021, 33, 043102
(58) Phys. Fluids 2021, 33, 032010
(57) Polym. Chem. 2021, 12, 783 - 806
(56) Catal. Sci. Technol. 2021, 11, 2119–2129
(55) Catal. Sci. Technol. 2021, 11, 62-91
(54) ACS Appl. Mater. Interfaces 2020, 12, 52182−52191
(53) Macromolecules 2020, 53(20), 8819-8828
(52) ACS Catal. 2020, 10, 6488−6496
(51) Chem. Sci. 2020, 11, 6485−6491
(50) Inorg. Chem. 2020, 59, 5546−5557
(49) Chem. Commun. 2019, 55, 3347-3350
(48) Coord. Chem. Rev. 2019 380, 35–57
(47) ChemCatChem 2018, 10, 3219 – 3222
(46) ACS Sustainable Chem. Eng., 2018, 6, 1650–1661
(45) Acc. Chem. Res. 2017, 50, 2861−2869
(44) J. Rheol. 2017 61(6), 1137-1148
(43) ACS Catal. 2017, 7, 6413−6418
(42) Dalton Trans. 2017 46, 6723–6733
(41) Macromolecules 2017 50 (6), 2535–2546
(40) Inorg. Chem. 2017 56 (3), 1375–1385
(39) Macromolecules 2016 49 (23), 8812–8824
(38) Inorg. Chem. 2016, 55(18), 9445–9453
(37) Inorg. Chem. 2016, 55(11), 5365–5374
(36) Macromolecules 2016, 49(3), 909–919
(35) Macromolecules 2015, 48(18), 6672-6681
(34) Chem. Sci., 2015, 6, 5284–5292
(33) Dalton Trans. 2015, 44, 14248 - 14254
(32) Dalton Trans. 2015, 44, 6126 - 6139
(31) Inorg. Chem. 2014, 53(18), 9897−9906
(30) J. Am. Chem. Soc. 2014, 136(32), 11264–11267
(29) Inorg. Chem. 2014, 53(13), 6828–6836
(28) Organometallics 2013, 32(23), 6950–6956
(27) Macromolecules 2013, 46, 3965−3974
(26) Chem. Commun. 2013, 49, 4295-4297
(25) J. Am. Chem. Soc. 2012, 134(30), 12758–12773
(24) Chem. Commun. 2012, 48(54), 6806-6808
(23) Polymer 2012, 53(12), 2443-2452
(22) Dalton Trans. 2012, 41(26), 8123-8134.
(21) Rheol. Acta 2012, 51(4), 357-369
(20) J. Am. Chem. Soc. 2011, 133(24), 9278–9281
(19) J. Rheol. 2011, 55(5), 987-1004
(18) Organometallics 2010, 29(22), 6065–6076
(17) Inorg. Chem. 2010, 49(12), 5444–5452
(16) Dalton Trans. 2010, 39(2), 541–547
(15) J. Supercrit. Fluids 2010, 51(3), 376-383
(14) Organometallics 2009, 28(21), 6370–6373
(13) Organometallics 2009, 28(13), 3889–3895
(12) Organometallics, 2009, 28(5), 1309-1319
(11) Angew. Chem. Int. Ed. 2008, 47(12), 2290-2293