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Structures and Reactions of Compounds Containing Heavier Main Group Elements
Published in Takayuki Fueno, The Transition State, 2019
Heavier atoms form hypervalent (or hypercoordinate) compounds. These compounds have attracted considerable interest since they formally break the well-known octet rule.6) In order to show how the periodic trends of atomic orbitals are reflected in the bond formation, we consider the pentavalent compounds of group 15 atoms. The well-known trigonal-bipyramidal D3h structure of MH5 is shown in Fig. 8.3. In the trigonal part of MH5 the central M atom is forced to form sp2 hybrid orbitals so as to provide three equivalent equatorial M-Heq bonds; the p orbital remaining on M is used to form a three-center four-electron bond with two apical hydrogens (Hap).
The generation and reactions of sulfenate anions. An update
Published in Journal of Sulfur Chemistry, 2022
Adam B. Riddell, Matthew R. A. Smith, Adrian L. Schwan
The drive to reduce transition metal catalyzed reactions has prompted the exploration of novel transition metal free sulfenate reactions including arylations and alkenylations/alkynylations [50,110,111]. Recently, Zhang and coworkers [50], Bolm and coworkers [110], and Waser and coworkers [111] published their investigations into the functionalization of sulfenate anions with hypervalent iodine reagents. Hypervalent iodine reagents, in general, are reactive and environmentally benign compounds that tolerate various functional groups and possess low toxicity [110]. These characteristics of hypervalent iodine reagents, such as aryl iodonium salts, make their use in functionalization chemistry more attractive than the traditional transition metal-based protocols reported in this review.
Probing the basis set limit for thermochemical contributions of inner-shell correlation: balance of core-core and core-valence contributions*
Published in Molecular Physics, 2019
Nitai Sylvetsky, Jan M. L. Martin
Yockel and Wilson noted [77] that the ACVTZ basis set, which is used in the ccCA approach [7–9] for computing the core-valence correction, was inadequate for (pseudo)hypervalent systems of the type where tight d functions are essential in the valence basis set. They noted that the original cc-pCVTZ basis sets had core-valence functions optimised on top of the regular (aug-)cc-pVTZ basis sets and instead optimised aug-cc-pCV(n + d)Z basis sets where an extra d has been added to second-row elements. For the second-row subset of W4-17, ACV(T + d)Z does have a lower RMSD = 0.28 kcal/mol compared to 0.36 kcal/mol for ACVTZ, though awCVTZ actually attains marginally better RMSD = 0.26 kcal/mol. Between ACVQZ and ACV(Q + d)Z, however, the difference is quite small, 0.135–0.123 kcal/mol, both inferior to awCVQZ, 0.099 kcal/mol. We also obtained ACV(5 + d)Z results for a subset of the second-row molecules and found differences with regular ACV5Z of 0.001 kcal/mol or less. Again, awCV5Z is superior to either, 0.048 vs. 0.067 kcal/mol.
Organic superalkalis with closed-shell structure and aromaticity
Published in Molecular Physics, 2018
The species with lower IE than alkali atoms are referred to as superalkalis. According to Gutsev and Boldyrev [10], and confirmed by Wu et al. [11], such species can be designed by central electronegative atom with excess electropositive ligands. FLi2, OLi3, NLi4, etc. are typical examples of superalkalis. These are hypervalent clusters possessing an excess electron and hence, open-shell structure. Therefore, they possess strong reducing capability and can be employed in the formation of a variety of charge transfer species with unusual properties. For instance, the use of superalkalis in the design of superbases with strong basicity [12–14] and supersalts with tailored properties [15–19] has been extensively studied. Owing to interesting properties of superalkalis and their compounds, such species have been continuously explored [20–25]. In this paper, we show that the vertical ionisation energies (VIEs) of lithiated benzene (C6Li6) and its higher analogues such as C10Li8, C14Li10 and C24Li12 are lower than that of Li atom. Although the aromaticity of the rings is affected by substitution of Li-atoms, their planarity is retained. We have also studied the interaction of C6Li6 with BF4 superhalogen and compared that with that of OLi3 superalkali with BF4. Note that C6Li6 has been previously studied by several groups [26–29]. The application of C6Li6 in the hydrogen storage has also been reported [30,31]. We still believe that the low ionisation energy feature of C6Li6 is probably studied here for the first time.