@article{oai:nagoya.repo.nii.ac.jp:02001601,
 author = {Ousaka, Naoki and Itakura, Manabu and Nagasaka, Akira and Ito, Masaki and Hattori, Tomonari and Taura, Daisuke and Ikai, Tomoyuki and Yashima, Eiji},
 issue = {11},
 journal = {Journal of the American Chemical Society},
 month = {Mar},
 note = {A stimuli-responsible reversible structural transformation is of key importance in biological systems. We now report a unique water-mediated reversible transformation among three discrete double-stranded dinuclear titanium(IV) achiral meso- and chiral rac-helicates linked by a mono(μ-oxo) or a bis(μ-hydroxo) bridge between the titanium ions through hydration/dehydration or its combination with a water-mediated dynamic cleavage/re-formation of the titanium-phenoxide (Ti–OPh) bonds. The bis(μ-hydroxo) bridged titanium(IV) meso-helicate prepared from two tetraphenol strands with titanium(IV) oxide was readily dehydrated in CD3CN containing a small amount of water upon heating, accompanied by Ti–OPh bond cleavage/re-formation catalyzed by water, resulting in the formation of the mono(μ-oxo)-bridged rac-helicate, which reverted back to the original bis(μ-hydroxo)-bridged meso-helicate upon hydration in aqueous CD3CN. These reversible transformations between the meso- and rac-helicates were also promoted in the presence of a catalytic amount of an acid, which remarkably accelerated the reactions at lower temperature. Interestingly, in anhydrous CD3CN, the bis(μ-hydroxo)-bridged meso-helicate was further slowly converted to a different helicate, while its meso-helicate framework was maintained, namely the mono(μ-oxo)-bridged meso-helicate, through dehydration upon heating and its meso to meso transformation was significantly accelerated in the presence of cryptand[2.2.1], which contributes to removing Na^+ ions coordinated to the helicate. Upon cooling, the backward meso to meso transformation took place via hydration. Hence, three different, discrete double-stranded chiral rac- and achiral meso-titanium(IV) helicates linked by a mono(μ-oxo) or a bis(μ-hydroxo) bridge were successfully generated in a controllable manner by a change in the water content of the reaction media.},
 pages = {4346--4358},
 title = {Water-Mediated Reversible Control of Three-State Double-Stranded Titanium(IV) Helicates},
 volume = {143},
 year = {2021}
}