Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

Abstract

Anionic hypercoordinated silicates with weak donors were proposed as key intermediates in numerous silicon‐based reactions. However, their short‐lived nature rendered even spectroscopic observations highly challenging. Here, we characterize hypercoordinated silicon anions, including the first bromido‐, iodido‐, formato‐, acetato‐, triflato‐ and sulfato‐silicates. This is enabled by a new, donor‐free polymeric form of Lewis superacidic bis(perchlorocatecholato)silane 1. Spectroscopic, structural, and computational insights allow a reassessment of Gutmann's empirical rules for the role of silicon hypercoordination in synthesis and catalysis. The electronic perturbations of 1 exerted on the bound anions indicate pronounced substrate activation.

Silicon Carbamates by CO2 Fixation: Brønsted Acid Labile Precursor of a Lewis Superacid

“…1 H– 29 Si HMBC-NMR experiments excluded a coupling between HNPh 2 and the silicon center, which might form adduct 1 -HNPh 2 (see sections 2 and 5 of the Supporting Information). Instead, spectroscopic signatures suggested the formation of anionic triflate adduct [TfO- 1 ] − . Using HNTf 2 as the Brønsted acid, the release of CO 2 and [H 2 TMP]­[NTf 2 ] and the precipitation of polymeric [ 1 ] n were noted, because the bistriflimide anion is insufficiently coordinating.…”

“…Instead, spectroscopic signatures suggested the formation of anionic triflate adduct [TfO-1] − . 48 Using HNTf 2 as the Brønsted acid, the release of CO 2 and [H 2 TMP][NTf 2 ] and the precipitation of polymeric [1] n were noted, 49 because the bistriflimide anion is insufficiently coordinating.…”

p-Block Element Catecholates: Lewis Superacidic, Constitutionally Dynamic, and Redox Active

“…This was achieved as part of our study on various new hypercoordinated silicates. 47 The synthesis was initiated by adding a small amount of butylsulfone to a mixture of HSiCl 3 and perchlorocatechol in dichloromethane (DCM). This donor is nucleophilic enough to induce H 2 /HCl release and Si-O bond formation, but weak enough to be removed from the final product by liquid-phase extraction (Figure 5a).…”

“…A first insight was provided upon sublimation of Si(cat F ) 2 from its bis(acetonitrile) adduct and crystallization of the sublimate in CH 2 Cl 2 . 28 Dynamic constitutional self-assembly of 14 units of Si(cat F ) 2 led to [Si(O 2 C 6 F 4 ) 2 ] 14 , the first giant perfluorinated macrocycle (Figure 4a ). The oligomerization process was monitored spectroscopically, and the macrocycle was analyzed by scXRD.…”

Azobenzene-Functionalized UiO-66-NH2: Solid Base Catalysts with Photocontrollable Activity

“…To satisfy the requirements of environmental protection and sustainable development, the use of heterogeneous catalysts instead of traditional homogeneous catalysts has attracted much attention. − As widely used heterogeneous catalysts, solid bases are extremely valuable for applications in resource-saving and environmentally friendly catalytic reactions because of their obvious advantages including low corrosiveness, easy reutilization, and trivial byproducts. − These solid base catalysts have made great progress for different catalytic reactions, for example, Knoevenagel condensation, − Michael addition, , halogenation, and transesterification reaction, , indicating good catalytic activity. , Conventional solid base catalysts have fixed properties, and the catalytic activity is regulated by external factors such as temperature and pressure. Regulation of the activity by in situ changing their own properties has never been reported.…”