Anionic States of Six-Membered Aromatic Phosphorus Heterocycles As Studied by Electron Transmission Spectroscopy and ab Initio Methods

Abstract

The electron transmission spectra of 1,3,5-tri-tert-butylbenzene, 2,4,6-tri-tert-butylpyridine, 2,4,6-tri-tertbutylphosphabenzene, and 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene have been investigated and interpreted by means of quantum chemical calculations. Scaled virtual orbital energies obtained from calculations without employing diffuse functions provide good numerical values for the vertical electron attachment energies (VAEs). B3LYP/6-311+G* VAEs, calculated as the energy difference between the anion and the neutral molecule, were in good agreement with experiment, with the molecules investigated here having VAEs of less than about 1 eV. The first anion state of phosphabenzene is predicted to lie at the edge of stability. The gradual replacement of CH units by phosphorus in π systems results in a significant stabilization of the anionic states, which contrasts with the relative invariance of the electron donor properties. This behavior can be explained by considering that for the PdC π system both the interaction between the atomic levels ( ) and the overlap are smaller than for the CdC π system.

Exceptional Coordination Mode of Unsaturated PNP Ligands (Me3Si)2C=PN(R)PPh2 with Palladium and Platinum Dichlorides: Insertion of Phosphaalkene Phosphorus Atoms into Metal–Chlorine Bonds

“…On the basis of these results, the known strong electronacceptor behaviour of the π*(C=P) unit [4] is remarkably increased by the silyl groups (the LUMO energy drops). The effect is enhanced by attaching phenyl groups on the σ 3 ,λ 3 -P instead of methyl groups.…”

“…[2,3] The electronegative nitrogen substituent is expected to enhance the π-acceptor properties of the P=C bond in type C ligands. [4][5][6] On subjecting this concept to experimental investigation by reacting type C ligands with halides of nickel(II), palladium(II) and platinum(II), in the case of Pd II and Pt II we unexpectedly observed the crystallisation of 2:1 chelate complexes of the composition MCl 2 [(Me 3 Si) 2 C=PN(R)-PPh 2 ] 2 , which proved to contain chlorine atoms covalently bonded to phosphorus and not to palladium or platinum.…”

Synthesis of the 2,4,5‐Tri‐tert‐butyl‐1,3‐diphospholide Anion by Phosphinidene Elimination from 2,4,6‐Tri‐tert‐butyl‐1,3,5‐triphosphabenzene on Treatment with the Amide Li[NPh(SiMe3)]

“…[17] Addition of TMEDA to 3 a afforded [LiA C H T U N G T R E N N U N G (TMEDA)]-A C H T U N G T R E N N U N G [P 2 C 3 tBu 3 ] (3 A) as a pale orange powder that was purified by vacuum sublimation and subsequently crystallised. Compounds 3 A and 4 a were both characterised by their 31 P, 13 C, 7 Li and 1 H NMR spectra, their mass spectra and by singlecrystal X-ray diffraction studies. The 31 P{ 1 H} NMR spectrum of 3 A exhibited a singlet at d = 186.8 ppm which is in excellent agreement with literature values reported for both Na-…”

“…[12] (Scheme 1). In these reactions the reactant is a nucleophile that attacks the low-lying [13] LUMO of the triphosphabenzene. ]hept-3-ene.…”

Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis, Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds

“…In contrast, the LUMO (see Figure S13 and S14 in the Supporting Information) is localised at the ligand core, and is stabilised by 0.5 eV in 7a with respect to 8a.F urthermore, the LUMO exhibits significant pyridine character for complex 8a and triazaphosphole character for complex 7a.T his behaviour is in accordance with the known stabilisation of the p* P=C energy levels with respectt ot heir p* C=C counterparts, as shown by ac omparative investigation of the electron transmission spectra of the corresponding benzene, phosphabenzene andt riphosphabenzene derivatives. [23,24] The TD-DFTcomputations performed on complexes 7a and 8a predict 15 transitions for both complexes at wavelengths highert han l = 250 nm. Most of these transitions are of low intensity( f = 0.0001-0.02);t hus having only as mall contribution to the spectrum.T here are three features, however,t hat have higheri ntensity and we assign those to the observed band maxima.…”