On Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions

Abstract

Attempts have been made to prepares alts with the labile tris(trimethylsilyl)chalconium ions, [(Me 3 Si) 3 E] + (E = O, S), by reacting[ Me 3 Si-H-SiMe 3 ][B(C 6 F 5 ) 4 ]a nd Me 3 Si[CB] (CB À = carborate = [CHB 11 H 5 Cl 6 ] À ,[ CHB 11 Cl 11 ] À )w ith Me 3 Si-E-SiMe 3 .I nt he reaction of Me 3 Si-O-SiMe 3 with [Me 3 Si-H-SiMe 3 ] [B(C 6 F 5 ) 4 ], al igand exchange was observed in the [Me 3 Si-H-SiMe 3 ] + cation leadingt ot he surprising formation of the persilylated [(Me 3 Si) 2 (Me 2 (H)Si)O] + oxonium ion in af ormal [Me 2 (H)Si] + instead of the desired [Me 3 Si] + transferr eaction. In contrast, the expected homoleptic persilylated [(Me 3 Si) 3 S] + ion was formed and isolated as [B(C 6 F 5 ) 4 ] À and [CB] À salt, when Me 3 Si-S-SiMe 3 was treated with either [Me 3 Si-H-SiMe 3 ] [B(C 6 F 5 ) 4 ]o rM e 3 Si[CB]. However, the addition of Me 3 Si[CB] to Me 3 Si-O-SiMe 3 unexpectedly led to the release of Me 4 Si with simultaneous formation of ac yclic dioxonium dicationo ft he type [Me 3 Si-mO-SiMe 2 ] 2 [CB] 2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamicso f the [(Me 3 Si) 3 E] + and [(Me 3 Si) 2 (Me 2 (H)Si)E] + ion formation are presented as well as mechanistic investigationso nt he template-driven transformation of the [(Me 3 Si) 3 E] + ion into a cyclic dichalconium dication [Me 3 Si-mE-SiMe 2 ] 2 2 + . Scheme1.Synthesis of silylated chalconium salts with [B(C 6 F 5 ) 4 ] À as counterion (E = O, S; T= Me 3 Si, R = alkyl).

Activation of CS2 and CO2 by Silylium Cations

“…Hexaethyldisilathiane reacts as base and forms with another [Et 3 Si] + cation the tris(triethylsilyl)sulfonium cation [(Et 3 Si) 3 S] + (step 3), which was identified by multinuclear NMR spectroscopy and crystal structure determination. This reaction is energetically favored by −130 kJ mol −1 and has already been reported by Olah and Prakash and Schulz for R=Me [16, 17] …”

“…From a reaction starting with ethyldimethylsilane the methylated cation [(Me 3 Si) 2 SMe] + was isolated due to alkyl‐alkyl exchange. Related alkyl‐alkyl exchange reactions are known and were reported before by Müller [8] and Schulz [17] …”

“…Trisilylated sulfonium ions were detected for the first time by Olah and Prakash in 2000 in a low temperature NMR study, in which [Me 3 Si] + was reacted with the thiosilylether Me 3 Si−S−SiMe 3 in dichloromethane [16] . Based on this approach very recently Schulz and co‐workers have succeeded in the synthesis of the chalconium salts [(Me 3 Si) 3 Ch][B(C 6 F 5 ) 4 ] (Ch=S, O) [17] …”

“…The structures of the mono‐, di‐ and tri‐silylated sulfonium cations with R=Et are shown in Figure 3. The structure of the [(Et 3 Si) 3 S] + cation can be compared to the recently published structure of the [(Me 3 Si) 3 S] + cation [17] . While the averaged S−Si distances are very similar (225.8 pm vs. 225.1 pm), the [(Et 3 Si) 3 S] + is less pyramidal (the sum of Si‐S‐Si bond angles is 331.3° vs. 326.6°) due to the higher sterical demand of the longer alkyl chains.…”

Chiral Chalcogenyl‐Substituted Naphthyl‐ and Acenaphthyl‐Silanes and Their Cations

“…This causes a syn / anti relation of the substituents at the silicon atom relative to the aryl substituent at the chalcogen atom. This coordination environment is expected based on a fundamental VSEPR treatment and it was confirmed recently by the results of XRD analysis of related dimethyl‐substituted silylselenonium borates and trisilylsulfonium borates and carborates [38, 39, 53] The stereochemistry of cations 13 c – f and 14 was determined by 1 H NMR Nuclear Overhauser Effect (NOE) difference spectroscopy. Saturation of the 1 H NMR resonance of the silylmethyl groups leads in the case of the trans ‐isomers to an enhancement of the signals of the ortho ‐H‐atoms of the phenyl substituent at the chalcogen atom (Figure 5).…”