Effects of Substituents on Arsenic−Tin Triple Bonds: A Theoretical Study

The heterocubane [TerSnAs]4

The synthesis of a novel heterocubane [RSnE]4 was successful for E = As, while for E = P differing behaviour was observed. Aryl-substituted chlorostannylenes were treated with salts of heavy cyanate homologues PCO- and AsCO-. The reaction with AsCO- salts afforded primarily [TerSnAs]4 (Ter = 2,6-dimesitylphenyl). In contrast, the reaction of TerSnCl with NaPCO proceeded considerably less cleanly affording a mixture of products. The main product was putatively a neutral [Ter4Sn4P4] compound, however, it is not a cubane. A variety of by-products of this reaction could be characterised crystallographically.

Tailoring the electronic properties among oxoarsine, arsinoyl and arsine oxide isomers: the simplest molecular systems with an arsenic–oxygen bond

The main goal of this investigation is to understand the reaction pathways and the electronic and spectroscopy properties of AsOH_n radicals (n = 0–3), which are some of the simplest compound models with an arsenic–oxygen bond.

5-Endo-Dig Radical Cyclizations: “The Poor Cousins” of the Radical Cyclizations Family

Kinetics and thermodynamics of 5-endo-dig radical cyclizations were studied using a combination of DFT computations and Marcus theory. When the reactant is stabilized by conjugation of the radical center with the bridge pi-system, the cyclization starts with reorientation of the radical orbital needed to reach the in-plane acetylene pi-orbital in the bond-forming step. This reorientation leads to loss of the above conjugative stabilization, increases the activation energy, and renders such cyclizations less exothermic. As a result, even when the radical needed for the 5-endo cyclization is formed efficiently, it undergoes either H-abstraction or equilibration with an isomeric radical. Only when the bridging moiety is saturated or when intramolecular constraints prevent the overlap of the bridge pi-orbital and the radical center, 5-endo cyclizations may be able to proceed with moderate efficiency under conditions when H-abstraction is slow. The main remaining caveat in designing such geometrically constrained 5-endo-dig cyclizations is their sensitivity to strain effects, especially when polycyclic systems are formed. The strain effects can be counterbalanced by increasing the stabilization of the product (e.g., by introducing heteroatoms into the bridging moiety). Electronic effects of such substitutions can be manifested in various ways, ranging from aromatic stabilization to a hyperconjugative beta-Si effect. The 4-exo-dig cyclization is kinetically competitive with the 5-endo-dig process but less favorable thermodynamically. As a result, by proper design of reaction conditions, 5-endo-dig radical cyclizations should be experimentally feasible.