In silico capture and activation of methane with light atom molecules

Methane (CH4) can be captured in silico with a light atom molecule containing only C, H, Si, O, and B atoms, respectively. A tripodal peri-substituted ligand system was employed, namely, [(5-Ph2B-xan-4-)(3)Si]H (1, xan = xanthene), which after hydride abstraction (1(+)) carries four Lewis acidic sites within the cationic cage structure. In a previous study, this system was shown to be able to capture noble gas atoms He-Kr (Mebs & Beckmann 2022). In the corresponding methane complex, 1(+)CH(4), a polarized Si+MIDLINE HORIZONTAL ELLIPSISCH4 contact of 2.289 & ANGS; as well as series of (H-3)CHMIDLINE HORIZONTAL ELLIPSISO/C-Ph hydrogen bonds enforce spatial CH4 fixation (the molecule obeys C-3-symmetry) and slight activation. A trigonal-pyramidal Si-CH3eq-H-ax local geometry is thereby approached with H-ax-C-H-eq angles decreased to 103.7 & DEG;. All attempts to replace the Lews acidic -BPh2 fragments in 1 with basic -PR2 (R = Ph, tBu) fragments indeed increased intra-molecular hydrogen bonding between host molecule and CH4, and thus caused stronger activation of the latter, however ultimately resulted in the formation of energetically favorable quenched structures with short P-Si contacts, making CH4 binding hard to achieve. The electronic situation of two hypothetic methane complexes, 1(+)CH(4) and [(5-tBu(2)P-xan-4-)(3)SiCH4](+) (2(+)CH(4)), was determined by a set of calculated real-space bonding indicators (RSBIs) including the Atoms-In-Molecules (AIM), non-covalent interactions index (NCI), and electron localizability indicator (ELI-D) methods, highlighting crucial differences in the level of activation. The proposed ligand systems serve as blueprints for a more general structural design with adjustable trigonal ligand systems in which central atom, spacer fragment, and functional peri-partner can be varied to facilitate different chemical tasks.

Automated summary

A study found that methane can be captured with a light atom molecule containing C, H, Si, O, and B atoms. By using a specific ligand system, it was possible to create Lewis acidic sites within a cationic cage structure, allowing the methane to be captured and activated.