Isolable Silicon‐Based Polycations with Lewis Superacidity

Abstract

Molecular silicon polycations of the types R 2 Si 2+ and RSi 3+ (R = H, organic groups) are elusive Lewis superacids and currently unknown in the condensed phase. Here, we report the synthesis of a series of isolable terpyridine-stabilized R 2 Si 2+ and RSi 3+ complexes, [R 2 Si(terpy)] 2+ (R = Ph 1 2+ ; R 2 = C 12 H 8 2 2+ , (CH 2) 3 3 2+) and [RSi(terpy)] 3+ (R = Ph 4 3+ , cyclohexyl 5 3+ , m-xylyl 6 3+), in form of their triflate salts. The stabilization of the latter is achieved through higher coordination and to the expense of reduced fluoride-ion affinities, but a significant level of Lewis superacidity is nonetheless retained as verified by theory and experiment. The complexes activate C(sp 3) À F bonds, as showcased by stoichiometric fluoride abstraction from 1-fluoroadamantane (AdF) and the catalytic hydrodefluorination of AdF. The formation of the crystalline adducts [2(F)] + and [5(H)] 2+ documents in particular the high reactivity towards fluoride and hydride donors.

Cationic Carbene Analogues: Donor‐Free Phosphenium and Arsenium Ions

“…The acceptor numbers calculated based on this change (CD 2 Cl 2 ) for 6 (132), 7 (117) and 8 (137) are, as expected, considerably larger than for B(C 6 F 5 ) 3 (82, CD 2 Cl 2 ), [31] [Et 3 Si] + (105, C 6 D 6 ) [32] or [Fc 2 P] + (116, CD 2 Cl 2 , Supporting information). The phosphenium ions 6 and 8 have marginally larger acceptor numbers than some recently reported doubly charged phosphorandiylium species (117, 129, CD 2 Cl 2 ) [33] and are only surpassed by [Me 5 C 5 P] 2+ (163, 1,2‐F 2 C 6 H 4 ) [34, 35] and the triply cationic salt [2,6‐Me 2 C 6 H 3 SiTerPy][OTf] 3 (154, CD 3 CN; TerPy=terpyridine) [36] . We note that the Lewis acidity of phenyl substituted 8 is slightly larger than that of 6 in agreement with smaller stabilizing inductive effects present in the phenyl‐substituted 8 .…”

Synthesis and Catalytic Activity of Atrane‐type Hard and Soft Lewis Superacids with a Silyl, Germyl, or Stannyl Cationic Center

“…Driess et al . demonstrated facile access to pristine LSA, Si(OTf) 4 , in which the OTf substituents work as excellent leaving groups and modulate reactivity towards hard and soft Lewis bases [13] . In these systems that activated a variety of substrates, the hard and soft Lewis acidities result from the formation of the highly coordinated Si and Ge centers.…”

“…In order to assess the characters of 1 E + with no adducts of solvents, we considered the Lewis acidity of 1 E + by quantum chemical calculations. The values of FIA and HIA were estimated according to the reported method [13] (Table 2 and see Supporting Information). The gas phase FIAs of 1 E + were obviously larger than that of SbF 5 , meeting the criteria for hard LSAs.…”

Kationische Carben‐Analoga: Donorfreie Phosphenium‐ und Arsenium‐Ionen

“…Die berechneten Akzeptornummern basierend auf diesen Änderungen (CD 2 Cl 2 ) für 6 (132), 7 (117) und 8 (137) sind, wie erwartet, beträchtlich größer als für B(C 6 F 5 ) 3 (82, CD 2 Cl 2 ), [31] [Et 3 Si] + (105, C 6 D 6 ) [32] oder [Fc 2 P] + (116, CD 2 Cl 2 , siehe Hintergrundinformationen). Die Phosphenium‐Ionen 6 und 8 haben etwas größere Akzeptorzahlen als einige kürzlich berichtete doppelt‐geladene Phosphorandiylium Spezies (117, 129, CD 2 Cl 2 ) [33] und werden nur übertroffen von [Me 5 C 5 P] 2+ (163, 1,2‐F 2 C 6 H 4 ) [34, 35] und dem dreifach‐geladenen Salz [2,6‐Me 2 C 6 H 3 SiTerPy][OTf] 3 (154, CD 3 CN; TerPy=terpyridine) [36] . Wir stellen fest, dass die Lewis‐Azidität des Phenyl‐substituierten 8 geringfügig größer ist als die von 6 , was im Einklang steht mit dem geringeren induktiven Effekt der Phenylgruppe.…”