In silico capture and activation of methane with light atom molecules.

Methane (CH 4 ) 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-Ph 2 B-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+CH4, a polarized Si + ⋯CH 4 contact of 2.289 Å as well as series of (H 3 )CH⋯O/C Ph hydrogen bonds enforce spatial CH 4 fixation (the molecule obeys C 3 -symmetry) and slight activation. A trigonal-pyramidal Si-CH eq 3 -H ax local geometry is thereby approached with H ax -C-H eq angles decreased to 103.7°. All attempts to replace the Lews acidic -BPh 2 fragments in 1 with basic -PR 2 (R = Ph, t Bu) fragments indeed increased intra-molecular hydrogen bonding between host molecule and CH 4 , 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 CH 4 binding hard to achieve. The electronic situation of two hypothetic methane complexes, 1+CH4 and [(5- t Bu 2 P-xan-4-) 3 SiCH 4 ] + (2+CH4), 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.