A theoretical investigation into dimethylcarbene and its diamino and diphosphino analogs: effects of cyclization and unsaturation on the stability and multiplicity

Abstract

High levels of ab initio and DFT calculations (B3LYP/6-311RRG ** , B3LYP/AUG-cc-pVTZ, and CCSD(T)/6-311RRG ** levels) coupled with isodesmic reactions are used to compare and contrast the multiplicities and relative stabilities of singlet (s) and triplet (t) acyclic carbenes, including: dimethylcarbene, diaminocarbene, and diphosphinocarbene along with their saturated and unsaturated cyclic ones. Cyclization is unfavorable for all acyclic carbenes while unsaturation of cyclic analogs appears favorable. The simultaneous cyclization and unsaturation of dimethylcarbene increases the singlet-triplet energy gap (DE s-t ), while for diphosphinocarbene the situation is reversed. For diaminocarbene the increase of DE s-t is encountered only during cyclization.

Stable α-heteroatom-free dialkylcarbenes: a DFT study

“…Based on our recent works on singlet carbenes [15][16][17][18], we expect that: (i) the cyclization increases the singlettriplet energy separation (DE S-T ) of the species, (ii) the cyclic structure prohibits the probability of 1,2-H shift and hence increases the kinetic stability, and (iii) the unsaturation may increase the thermodynamic stability of the species by inducing pseoudoaromaticity to the ring. In addition, in a cyclic structure two adjacent cyclopropyls necessarily orient syn toward each other which is the most stable conformer for dicyclopropylcarbene (Scheme 2) [7].…”

Novel tetrazol‐5‐germavinylidenes with triplet monomeric, normal, and abnormal forms studied using DFT method

“…In our continued quest for novel divalent NH‐germavinylidene species, the question immediately arises whether stable normal and abnormal monomeric tetrazol‐5‐germavinylidenes are researchable and how H, CN, CF 3 , SH, NH 2 , OMe, and OH groups with different electronic effects may influence their stability, multiplicity (singlet [S] vs triplet [T]), Highest Occupied Molecular Orbital (HOMO) – Lowest Unoccupied Molecular Orbital (LUMO) band gap (Δ E HOMO‐LUMO ), aromaticity (NICS), Natural Bond Orbital (NBO), nucleophilicity ( N ), electrophilicity (ω), and geometrical parameters (Scheme ). The purpose of the present work is therefore to reach at novel triplet states of germylenes through alteration of the appropriate substitutions with different electronic effects in normal and abnormal forms of tetrazol‐5‐germavinylidenes and assess the influences of them on the singlet–triplet energy gaps (Δ E S‐T ).…”

Ylide stabilized carbenes: a computational study

“…Following our long quest for stable carbenes, here we intend to shed some light on the subject by comparing the effects of α ‐carbon, ammonium, sulfur, and phosphorus ylides on the stability of 24 acyclic, cyclic, and unsaturated cyclic singlet as well as triplet carbenes (Fig. ).…”