Heterodinuclear titanium/zinc catalysis: synthesis, characterization and activity for CO2/epoxide copolymerization and cyclic ester polymerization. Issue 8 (3rd February 2017)

• Record Type: Journal Article
• Authors: Garden, Jennifer A.; White, Andrew J. P.; Williams, Charlotte K.
• Is Part Of: Dalton transactions. Volume 46:Issue 8(2017)
• Page Start: 2532
• Page End: 2541
• Publication Date: 2017-02-03
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt04193k
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The preparation of heterodinuclear complexes, especially those comprising early-late transition metals coordinated by a simple or symmetrical ancillary ligand, represents a fundamental challenge and an opportunity to prepare catalysts benefitting from synergic properties. Abstract : The preparation of heterodinuclear complexes, especially those comprising early-late transition metals coordinated by a simple or symmetrical ancillary ligand, represents a fundamental challenge and an opportunity to prepare catalysts benefitting from synergic properties. Here, two new mixed titanium(iv )–zinc(ii ) complexes, [LTi(O i Pr)2 ZnEt] and [LTi(O i Pr)2 ZnPh], both coordinated by a diphenolate tetra(amine) macrocyclic ligand (L), are prepared. The synthesis benefits from the discovery that reaction of the ligand with a single equivalent of titanium tetrakis(iso-propoxide) allows the efficient formation of a mono-Ti(iv ) complex, [LTi(O i Pr)2 ]. All new complexes are characterized by a combination of single crystal X-ray diffraction, multinuclear NMR spectroscopy and mass spectrometry techniques. The two heterobimetallic complexes, [LTi(O i Pr)2 ZnEt] and [LTi(O i Pr)2 ZnPh], feature trianionic coordination by the macrocyclic ligand and bridging alkoxide groups coordinate to both the different metal centres. The heterodinuclear catalysts are compared to the mono-titanium analogue, [LTi(O i Pr)2 ], in various polymerization reactions. In the alternating copolymerizations of carbon dioxide and cyclohexene oxide, the mono-titanium complex is totally inactive whilst the heterodinuclear complexes show moderate activity (TOF = 3 h −1 ); it should be noted the activity is measured using just 1 bar pressure of carbon dioxide. In the ring opening polymerization of lactide and ε-caprolactone, the mono-Ti(iv ) complex is totally inactive whilst the heterodinuclear complexes show moderate-high activities, qualified by comparison to other known titanium polymerization catalysts (l -lactide, k obs = 11 × 10 −4 s −1 at 70 °C, 1 M in [lactide]) and ε-caprolactone ( k obs = 5 × 10 −4 s −1 at 70 °C, 0.9 M in [ε-caprolactone]).