Estudio computacional de la reactividad de heterociclos organofosforados de tres y cuatro miembros

Resumen

The main goal of this work is to carry out a theoretical study about the structural and electronic properties, as well as the synthesis and reactivity of three- and four-membered organophosphorus heterocycles, namely azaphosphiridines, oxaphosphiranes, azadiphosphiridines, tiaphosphiranes and 1,2-oxaphosphetanes. In particular, the study is focused on: The study of the inversion process in group 15 derivatives. The study of ring strain energies of four-membered rings with one group 13-16 elements and azaphosphiridines. The study of the formation mechanism of some derivatives: ligated oxaphosphiranes, ligated azaphosphiridines, tiaphosphiranes and ligated 1.2-oxaphosphetanes. The study of the reactivity of oxaphosphiranes and unligated 1,2-oxaphosphetanes. All data were calculated using ORCA y Gaussian16 software. In general, compounds were optimized in redundant internal coordinates with tight convergence criteria, using Density Functional Theory (DFT). A frequency calculation was conducted in all optimized geometries to check whether a minimum (none imaginary frequency) or a transition state (one imaginary frequency) was obtained. All the transition states were confirmed by Intrinsic Reaction Coordinate (IRC) calculations. The general conclusions that can be drawn from all the work carried out are: σ3λ3-Pnictogen derivatives invert through five different structures, called vertex, edge, turnstile and Dewar-Chatt-Duncanson (type 1 and 2). The presence of electronegative substituents or small-sized rings increases while unsaturated substituents lower the pnictogen inversion barriers. Four-membered heterocycles containing an element of groups 13-16 show ring strain energies between 14 and 25 kcal mol-1, depending on the element and period. Of particular interest is the higher RSE exhibited by some four-membered heterocycles compared to their three-membered analogues. The different studied azaphosphiridine derivatives have shown RSEs between 23 and 47 kcal mol-1 depending on the substituents. These values have also been related to different structural and electronic parameters. The study of the mechanism of the formation of complexed oxaphosphiranes has proved that they can be obtained by the reaction of carbonyl groups with phosphinidenoid Li/Cl complexes, as well as with complexed terminal phosphinidenes. Inspection of the mechanism of the formation of complexed azadiphosphiridines from aminophosphanes has revealed that it is a kinetically and thermodynamically favourable process. This study has also shown that the experimentally found planarity of the nitrogen in an azadiphosphiridine arises from electronic effects induced by particular groups and steric hindrance around the three-membered ring. The mechanistic study of the formation of tetrathiafulvalenes from 1,3-dithiol-2-thiones with P-substituents revealed the existence of thiaphosphiranes as intermediates. The mechanistic study of formation of complexed 1,2-oxaphosphetanes revealed that it is a favourable process that can occur by the attack of phosphorus from a phosphinidenoid Li/Cl complex at the epoxide carbon atoms or, alternatively, by formation of an adduct between a complexed terminal phosphinidene and the epoxide oxygen atom. σ3λ3-Oxaphosphiranes have shown enormous versatility in their reactivity with other species. The reactivity of 1,2-oxaphosphetanes involving retro-cycloaddition reactions was studied in detail, demonstrating the enormous versatility of these compounds when it comes to isomerising to five-membered rings or exchange between the exocyclic chalcogen and the ring oxygen.