Journal
INORGANIC CHEMISTRY
Volume 62, Issue 37, Pages 14873-14887Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.3c01249
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In this study, a detailed route for the formation of titanium(III) orthophenylendiamido (PDA) species using [LiBHEt3] as a reducing agent is provided. These low-valent compounds in combination with [PPN]Cl are highly selective catalysts for the copolymerization of CO2 and cyclohexene epoxide.
Titanium compounds in low oxidation states are highly reducing species and hence powerful tools for the functionalization of small molecules. However, their potential has not yet been fully realized because harnessing these highly reactive complexes for productive reactivity is generally challenging. Advancing this field, herein we provide a detailed route for the formation of titanium(III) orthophenylendiamido (PDA) species using [LiBHEt3] as a reducing agent. Initially, the corresponding lithium PDA compounds [Li-2((Ar)PDA)(thf)(3)] (Ar = 2,4,6-trimethylphenyl ((Mes)PDA), 2,6-diisopropylphenyl ((iPr)PDA)) are combined with [TiCl4( thf)(2)] to form the heterobimetallic complexes [{TiCl((Ar)PDA)}(mu-(Ar)PDA){Li(thf)(n)}] (n = 1, Ar = iPr 3 and n = 2, Ar = Mes 4). Compound 4 evolves to species [Ti((Mes)PDA)(2)] (6) via thermal treatment. In contrast, the transformation of 3 into [Ti((iPr)PDA)(2)] (5) only occurs in the presence of [LiNMe2], through a lithium-assisted process, as revealed by density functional theory (DFT). Finally, the Ti(IV) compounds 3-6 react with [LiBHEt3] to give rise to the Ti(III) species [Li(thf)(4)][Ti((Ar)PDA)(2)] (Ar = iPr 8, Mes 9). These low-valent compounds in combination with [PPN]Cl (PPN = bis(triphenylphosphine)iminium) are proved to be highly selective catalysts for the copolymerization of CO2 and cyclohexene epoxide. Reactions occur at 1 bar pressure with activity/selectivity levels similar to Salen-Cr(III) compounds.
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