Sterically controlled mechanochemistry under hydrostatic pressure

• Published in: Nature (London) 2018-02, Vol.554 (7693), p.505-510
• Main Authors: Yan, Hao, Yang, Fan, Pan, Ding, Lin, Yu, Hohman, J. Nathan, Solis-Ibarra, Diego, Li, Fei Hua, Dahl, Jeremy E. P., Carlson, Robert M. K., Tkachenko, Boryslav A., Fokin, Andrey A., Schreiner, Peter R., Galli, Giulia, Mao, Wendy L., Shen, Zhi-Xun, Melosh, Nicholas A.
• Format: Article
• Language: English
• Subjects: 119/118; 140/146; 639/638/263/910; 639/638/298/303; 639/638/440/947; Anvils; Carbon; Chalcogen bonds; Chemical bonds; Chemical reactions; Compressibility; Compression; Compressive properties; Computational fluid dynamics; Control; Copper; Deformation mechanisms; Humanities and Social Sciences; Hydrostatic pressure; letter; Ligands; Mechanical stimuli; Mechanochemistry; multidisciplinary; Observations; Observatories; Polymers; Pressure; Reaction mechanisms; Redox reactions; Science; Shearing; Spectrum analysis; Strain; Stresses; Sulfur
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature25765

‘Molecular anvil’ molecules consisting of a compressible mechanophore and incompressible ligands react under hydrostatic pressure to produce elemental metal via an unexplored mechanism. Controlled chemistry under pressure Mechanochemistry is the activation of bonds using mechanical force rather than the addition of reactants. It typically takes advantage of applied tensile stress to break specific bonds in a mechanophore—a compound that reacts when mechanical force is applied. Bond formation or breaking in response to an applied compressive force is much rarer. Here, Nicholas Melosh and colleagues show that, for a metal–organic solid-state compound, compressing the whole sample causes anisotropic strain and redox reactions at the molecular level, which are transmitted by bulky ligand groups in one direction but adsorbed by flexible mechanophores in another. Further development of combinations of flexible and rigid components to dissipate or transmit stress could open up routes to more sophisticated mechanochemical reactions, or perhaps sequential reactions, simply by applying pressure to the sample. Mechanical stimuli can modify the energy landscape of chemical reactions and enable reaction pathways, offering a synthetic strategy that complements conventional chemistry 1 , 2 , 3 . These mechanochemical mechanisms have been studied extensively in one-dimensional polymers under tensile stress 4 , 5 , 6 , 7 , 8 , 9 using ring-opening 10 and reorganization 11 , polymer unzipping 6 , 12 and disulfide reduction 13 , 14 as model reactions. In these systems, the pulling force stretches chemical bonds, initiating the reaction. Additionally, it has been shown that forces orthogonal to the chemical bonds can alter the rate of bond dissociation 15 . However, these bond activation mechanisms have not been possible under isotropic, compressive stress (that is, hydrostatic pressure). Here we show that mechanochemistry through isotropic compression is possible by molecularly engineering structures that can translate macroscopic isotropic stress into molecular-level anisotropic strain. We engineer molecules with mechanically heterogeneous components—a compressible (‘soft’) mechanophore and incompressible (‘hard’) ligands. In these ‘molecular anvils’, isotropic stress leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. Conversely, rigid ligands in steric contact impede relative motion, blocking reacti