Intramolecular P–H···H–Si Dihydrogen Bonding in the 5‑Dimethylsilyl-9,9-dimethylxanthen-4-yl-diphenylphosphonium Cation

The synthesis of
4-bromo-5-diphenylphosphino-9,9-dimethylxanthene
(1a), 4-bromo-6-diphenylphosphinodibenzofuran (1b), 4-diphenylphosphino-5-dimethylsilyl-9,9-dimethylxanthene
(2a), 4-diphenylphosphino-6-dimethylsilyldibenzofuran
(2b), 5-dimethylsilyl-9,9-dimethylxanthen-4-yl-diphenylphosphonium
tetrakis­(pentafluorophenyl)­borate [3a]­[B­(C6F5)4], and 6-dimethylsilyldibenzofuran-4-yl-diphenylphosphonium
tetrakis­(pentafluorophenyl)­borate [3b]­[B­(C6F5)4] was reported. Unlike the benzofuran derivate
[3b]+, the xanthene derivative [3a]+ shows an intramolecular dihydrogen bond of the type
P–H···H–Si, which was studied by DFT
calculation using a set of real-space bond indicators (RSBIs) derived
from the Atoms-In-Molecules (AIM), Non-Covalent Interactions (NCI)
indicator, and Electron Localizability Indicator (ELI-D) methods.
Neither [3a]+ nor [3b]+ shows any propensity to release dihydrogen to give the 4-diphenylphosphino-9,9-dimethylxanthen-5-yl-dimethylsilyl
cation [4a]+ or the 4-diphenylphosphino-dibenzofuran-5-yl-dimethylsilyl
cation [4b]+, respectively.