Silylium-Arene Adducts: An Experimental and Theoretical Study

The solvent-coordinated [Me3Si center dot arene][B(C6F5)(4)] salts (arene = benzene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, o-xylene, m-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene) are prepared and fully characterized. As an interesting decomposition product the formation of bissilylated fluoronium ion [Me3Si-F-SiMe3](+) was observed and even cocrystallized with [Me3Si center dot arene][B(C6F5)(4)] (arene = benzene and toluene). Investigation of the degradation of [Me3Si center dot arene][B(C6F5)(4)] reveals the formation of fluoronium salt [Me3Si-F-SiMe3] [B(C6F5)(4)], B(C6F5)(3), and a reactive C6F4 species which could be trapped with CS2. Upon addition of CS2, the formation of a formal S-heterocyclic carbene adduct, C6F4CS2-B(C6F5)(3), was observed. The structure and bonding of substituted [Me3Si center dot arene][B(C6F5)(4)] with arene = RnC6H6-n (R = H, Me, Et, Pr, and Bu; n = 0-6) is discussed on the basis of experimental and theoretical data. X-ray data of [Me3Si center dot arene][B(C6F5)(4)] salts reveal nonplanar arene species with significant cation center dot center dot center dot anion interactions. As shown by different theoretical approaches (charge transfer, partial charges, trimethylsilyl affinity values) stabilizing inductive effects occur; however, the magnitude of such effects differs depending on the degree of substitution and the substitution pattern.