Silylium–Arene Adducts: An Experimental and Theoretical Study

The solvent-coordinated [Me3Si·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·arene][B(C6F5)4] (arene = benzene and toluene). Investigation of the degradation of [Me3Si·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·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·arene][B(C6F5)4] salts reveal nonplanar arene species with significant cation···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.