ABSTRACT
N-heterocyclic nitrogen Lewis acids are a recent addition to the field of organic chemistry. Based on nitrenium cations, these acids where previously shown to generate Lewis adducts when combined with the appropriate Lewis bases. Herein, a triazinium-based Lewis acid was combined with tBu3P to generate a frustrated Lewis pair (FLP) capable of cleaving, for the first time, Si-H bonds in silanes. Whereas low yields were initially encountered owing to insufficient Lewis acidity, a new nitrenium-based Lewis acid was synthesized, and its superior Lewis acidity was experimentally and computationally confirmed. A FLP based on this acid cleaved the Si-H bond in PhSiH3, generating the triazane product in a quantitative yield. This unprecedented N-H triazane was fully characterized by multinuclear NMR techniques and single-crystal X-ray crystallography. A new class of compounds, N-H triazanes display the potential capacity to participate in hydride transfer reactions.
ABSTRACT
Being a major conception of chemistry, Lewis acids have found countless applications throughout chemical enterprise. Although many chemical elements can serve as the central atom of Lewis acids, nitrogen is usually associated with Lewis bases. Here, we report on the first example of robust and modifiable Lewis acids centered on the nitrogen atom, which provide stable and well-characterized adducts with various Lewis bases. On the basis of the reactivity of nitrogen Lewis acids, we prepared, for the first time, cyclic triazanes, a class of cyclic organic compounds sequentially bearing three all-saturated nitrogen atoms (N-N-N motif). Reactivity abilities of these N-Lewis acids were explained by theoretical calculations. Properties and future applications of nitrogen Lewis acids are intriguing.
ABSTRACT
The Cu(I)-catalyzed Ullmann condensation reaction between aliphatic alcohols and sym-pentachlorocorannulene provides a convenient entry to 1,3,5,7,9-pentaalkoxycorannulenes. The latter are easily converted to novel deca-heterosubstituted derivatives, such as 1,3,5,7,9-penta-X-2,4,6,8,10-penta-Y-corannulenes by electrophilic aromatic substitution.
