Synthesis, Characterization and Theoretical Calculations of Novel Five Membered Rings Containing Phosphorus and Arsenic Atoms

Abstract

A síntese de dois novos arsadifosfóis de fórmula (AsP 2 C 2 Bu t 2 )CH(SiMe 3 ) 2 , a partir dos anéis aniônicos 4-arsa-1,2-difosfaciclopentadienil e 2-arsa-1,4-difosfaciclopentadienil é reportada, junto com suas caracterizações utilizando RMN de 31 P. Cálculos ab initio no nível MP2/6-31G(d) de teoria foram realizados para se investigar as barreiras de inversão piramidal, estabilidade relativa e o caráter aromático de todos os possíveis isômeros dos arsadifosfóis, em fase gasosa. A distribuição termodinâmica dos isômeros está em completo acordo com os resultados experimentais. O caráter de aromaticidade obtido para os três isômeros contendo um fósforo sp 3 é maior quando comparado com o 1,2,4-trifosfol, sintetizado previamente. Os efeitos dos grupos substituintes volumosos sobre a aromaticidade e as barreiras de inversão piramidal são também discutidos.The synthesis of two new arsadiphospholes of formula (AsP 2 C 2 Bu t 2 )CH(SiMe 3 ) 2 , from 4-arsa-1,2-diphosphacyclopentadienyl and 2-arsa-1,4-diphosphacyclopentadienyl ring anions are reported together with their characterization by 31 P NMR. Ab initio calculations at the MP2/6-31G(d) level of theory were carried out to investigate the energy barrier for pyramidal inversion about the pyramidal P and As atoms, relative stability and aromaticity character of all possible isomers in the gas phase. The thermodynamic isomers distribution is in agreement with the experimental results. The inversion barrier at the sp 3 phosphorus compared to the inversion barrier found for the arsenic atom is low. This fact is directly related with the aromaticity of the rings and shows the preference of the side group for the phosphorus atom, which leads to a more aromatic ring structure. The aromaticity character found for three isomers containing a sp 3 -phosphorus is greater if compared with that of 1,2,4-triphosphole synthesized previously. The effects of bulky R substituents on the aromaticity and on the energy barrier for pyramidal inversion are also discussed.

Structure and Nature of the Metal−Ligand Interactions in Mixed Iron(II) Phosphametallocenes

“…The NICS is indeed a consistent aromaticity probe 35 and has been applied recently to study the aromaticity of poplyphosphaphospholes 36 and arsadiphospholes. 37 We have applied the NICS index to investigate the aromatic character of the free ligands 1a-1d, which is also shown in Figure 1. With the cyclopentadienyl ligand (1a), which is a well-known aromatic five-membered ring, the NICS value of -14.5 ppm computed for the phospholyl ligand 1b is 84% of the NICS value of -17.2 computed for 1a.…”

“…Negative NICS values denote aromaticity, whereas small and positive NICS values indicate nonaromaticity. The NICS is indeed a consistent aromaticity probe 35 and has been applied recently to study the aromaticity of poplyphosphaphospholes and arsadiphospholes . We have applied the NICS index to investigate the aromatic character of the free ligands 1a − 1d , which is also shown in Figure .…”