Analysis of Non‐innocence of Phosphaquinodimethane Ligands when Charge and Aromaticity Come into Play

Abstract

Several phosphaquinodimethanes and their M(CO) 5 complexes (M = Cr, Mo, W) and model derivatives have been theoretically investigated regarding the quest of non-innocence. Computed structural and electronic properties of the P-Me/NH 2 substituted phosphaquinodimethanes and tungsten complexes revealed an interesting non-innocent ligand behaviour for the radical anion complexes with distonic ion character and a strong rearomatization of the middle phenyl ring. The latter was further probed taking also geometric aromaticity (HOMA) and quinoid distortion parameters (HOMQc) into account, as well as NICS(1). Furthermore, the effect of the P-substitution was investigated for real (or plausible) complexes and their free ligands focusing on the resulting aromaticity at the middle phenyl ring and vertical one-electron redox processes. The best picture of ligand engagement in redox changes was provided by representing NICS(1) values versus HOMA and the new geometric distortion parameter HOMQc8.

1,3,2-Diheterophospholane complexes: access to new tuneable precursors of phosphanoxyl complexes and P-functional polymers

“…This observation is in agreement with reports from King 44 and others 45 who found that the steric bulk at the N at the α-position to phosphorus is mandatory for a clear reduction of chlorobis (dialkylamino)phosphanes. However, on treating 5 with tetraethylammonium pentacarbonyl hydrido tungstate(I) the desired complex 6a formed quantitatively, as confirmed by 31 P NMR spectroscopy (Scheme 2). Complex 6a exhibits a larger 1 J W,P of 305 Hz and a 1 J P,H of 321.5 Hz, compared to complex 3 ( 1 J W,P : 295 Hz; 1 J P,H : 272.9 Hz), and a lowfield shift of the phosphorus resonance (δ = 121; 3: 78.7 ppm).…”

“…It should be pointed out that complexation to transition metals has shown an increase in the stability of low valent open-shell phosphorus species without losing reactivity. [28][29][30][31] Using this concept, we have synthesised a potential precursor transition metal complex and, in 2016, we showed that the transient diphenyl phosphanoxyl tungsten complex VIII is formed. Its chemistry was explored thereafter, 32,33 and DFT calculations suggested a rapid equilibrium between VI and VIII.…”

On metal coordination of neutral open-shell P-ligands focusing on phosphanoxyls, their electron residence and reactivity

“…27 Heterocoupling of the P-chloro complex and the (formed) Gomberg radical led to the first described phosphaquinomethane complex, and their chemistry has since then been further explored. [26][27][28][29] A P-chloro complex IV was also formed as a transient species in the SET oxidation of Li/Cl phosphinidenoid complexes by hexafluoro acetone, also in these cases heterocoupling products of the radical pairs were observed. 30 Our attempts to implement TEMPO as SET oxidant and trapping reagent of P-fluoro substituted type IV radicals did not yield the expected heterocoupling products, but products of further redox processes.…”

“…27 Heterocoupling of the P-chloro complex and the (formed) Gomberg radical led to the first described phosphaquinomethane complex, and their chemistry has since then been further explored. 26–29 A P-chloro complex IV was also formed as a transient species in the SET oxidation of Li/Cl phosphinidenoid complexes by hexafluoro acetone, also in these cases heterocoupling products of the radical pairs were observed. 30…”

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics

“…As our purpose is to scrutinize the stability of phosphinyl radicals, in the following, a selection of the most important examples is presented; however, we note that further derivatives are also known. 33 − 35 , 46 − 52 …”