Viability of aromatic all-pnictogen anions

Abstract

Aromaticity in novel cyclic all-pnictogen heterocyclic anions, P2N3(-) and P3N2(-), and in their heavier analogues is studied using quantum mechanical computations. All geometrical parameters from optimized geometry, bonding, electron density analysis from quantum theory of atoms in molecules, nucleus-independent chemical shift, and ring current density plots support their aromaticity. The aromatic nature of these molecules closely resembles that of the prototypical aromatic anion, C5H5(-). These singlet C2v symmetric molecules are comprised of five distinct canonical structures and are stable up to at least 1000 fs without any significant distortion. Mechanistic study revealed a plausible synthetic pathway for P3N2(-) - a click reaction between N2 and P3(-), through a C2v symmetric transition state. Besides this, the possibility of P3N2(-) as a η(5)-ligand in metallocenes is studied and the nature of bonding in metallocenes is discussed through the energy decomposition analysis.

Pentapnictogen heterocyclic monoanions: Structure, stability, and aromaticity

“…The aromaticities of these five‐membered ring anions were investigated first by scanning the NICS values (both NICS iso and NICS zz ) at distances ranging from 0.0 (i.e., in the molecular plane) to 5.0 Å (step size: 0.1 Å) in the direction perpendicular to the ring plane. The scan of NICS values was suggested to be more suitable to probe the aromaticity of a planar system than a single NICS value, and it becomes even critical for the heterocycles due to the varied size of p orbitals . For comparison, we also calculated the NICS profile for Cp − at the same level of theory.…”

“…The short bond distances and perfect planarity suggest the presence of multiple bonding and strong 6π‐electron delocalization in these rings. Our computed structural parameters and relative energies for different isomers confirm Nizovtsev's recent results on P 2 E 3 − (E = N, As, Sb, Bi) and Mandal et al's results for P 2 N 3 − , As 2 P 3 − , Sb 2 As 3 − , Bi 2 Sb 3 − , P 3 N 2 − , As 3 P 2 − , Sb 3 As 2 − , and Bi 3 Sb 2 − (only configuration I was considered in the latter) …”

“…DFT has been widely used in recent works to study the structures, energies, and aromaticities of several pentapnictogen ring anions, yielding rather reasonable results comparable with the expensive coupled‐cluster calculations . It is thus the best choice of theory for current work because there is a large number of ring systems to compute (vide infra).…”

“…Accordingly, full geometry optimizations were carried out by using the M06‐2X functional and the def2‐TZVPPD basis set for all the elements, with the corresponding efficient core potentials for heavier Sb and Bi . The current level of theory has been successfully employed to study some binary all‐pnictogen pentagon anions in Mandal et al's recent work . To characterize the nature of stationary points, harmonic vibrational frequencies were calculated at the same theoretical levels after the optimization.…”

“…Its high aromaticity and stability were confirmed by the calculations and observed large adiabatic detachment energy . Recently, Mandal et al selectively investigated eight all‐pnictogen heterocyclic anions (ie, P 2 N 3 − , As 2 P 3 − , Sb 2 As 3 − , Bi 2 Sb 3 − , P 3 N 2 − , As 3 P 2 − , Sb 3 As 2 − , and Bi 3 Sb 2 − ) by means of density functional theory (DFT) calculations and demonstrated their stability and aromaticity . Nizovtsev searched the stable structures of P 2 E 3 − (E = N, P, As, Sb, Bi) and found that they are all planar and aromatic …”