Silyl Cations Stabilized by Pincer Type Ligands with Adjustable Donor Atoms

Abstract

Novel E,C,E'-pincer supported silyl cations (E, E' = O, S, Se, Au) were prepared in three steps starting from 2,6-F2C6H3SiMe2H (1a) and 2,6-Br2C6H3SiMe2H (1b), which were first converted in two complementary ways into 2,6-(Ph2P)2C6H3SiMe2H (2). The oxidation of 2 with H2O2·urea, S8, and Se8 afforded 2,6-(Ph2PE)2C6H3SiMe2H (3a, E = O; 3b, E = S; 3c, E = Se) and 2-(Ph2PE)-6-(Ph2P)-C6H3SiMe2H (4b, E = S; 4c, E = Se), which were reacted to the E,C,E-supported silyl cations [2,6-(Ph2PE)2C6H3SiMe2]+ (5a, E = O, counterion Br3–; 5b, E = S, counterion B(C6F5)4–; 5c, E = Se, counterion B(C6F5)4–), the E,C-supported silyl cations [2-(Ph2PE)-6-(Ph2P)C6H3SiMe2]+ (6b, E = S, not isolated; 6c, E = Se, not isolated), the O,C,S-supported silyl cation [2-(Ph2PS)-6-(Ph2PO)C6H3SiMe2]+ (7, counterion B(C6F5)4–) as well as the E,C,Au-supported silyl cations [2-(Ph2PAuC6F5)-6-(Ph2PE)C6H3SiMe2]+ (8b, E = S, counterion [B{3,5-(CF3)2C6H3}4]–; 8c, E = Se, [B{3,5-(CF3)2C6H3}4]–) using Br2, O2, S8, (tht)AuC6F5, Ph3C[B(C6F5)4] and Ph3C[B{3,5-(CF3)2C6H3}4]. All compounds were characterized by multinuclear (1H, 13C, 19F, 29Si, 31P, 77Se) NMR spectroscopy, ESI MS spectrometry and X-ray crystallography (2, 3a·H2O, 3b, 3c, 4b, 5a, 5c, 7, 8b, 8c). The gas phase structures of 2, 3a–c, 5a–c (fully optimized) and 8b, 8c (single-point calculations) were studied at the B3PW91/6-311+G(2df,p) level of theory. A set of real-space bonding indicators (RSBIs) derived from the theoretically calculated electron and pair densities were analyzed utilizing the atoms-in molecules (AIM) and electron-localizability indicator (ELI-D) space partitioning schemes.