Nuclear magnetic resonance studies of scrambling reactions in solutions of tetra-alkyl- and tetra-aryl-diphosphanes

The chemistry of cationic polyphosphorus cages – syntheses, structure and reactivity

“…This trend was previously termed γ-effect. 46 In contrast, the chemical shifts of tetra-coordinated P atoms (marked in red, Fig. 8 ) exhibit an almost inverse trend (from 99 ppm ( 32a + ) to 69 ppm ( 32e + )).…”

“…This can be explained in terms of a combination of a -effect and γ-effect ( vide infra ). 46 , 47 The resonances of the tetra-coordinated P atoms in aryl-substituted cations 36e–h + are shifted to higher field compared to those of the corresponding P atoms in cages 36a–d + . This is due to a positive mesomeric effect, namely the donation of π-electron density from the aryl substituents to the lobes of the anti-bonding σ*(P–P) orbitals at the phosphonium moiety.…”

PP-Rotation, P-Inversion and Metathesis in Diphosphines Studied by DFT Calculations: Comments on Some Literature Conflicts

“…Scheme 1. Symmetrical (1,2,3,4), unsymmetrical (5,6) and P-stereogenic diphosphines (7,8) studied in this work. Scheme 1.…”

“…An apparent aggregation of diphosphines in high concentration polar solvents and the formation of unsymmetrical diphosphines in mixtures of symmetrical diphosphines supported an active metathesis pathway previously dismissed by LJM. This scrambling reaction typically results in a mixture of symmetrical and unsymmetrical diphosphines [8] but some polarized diphosphines were found to be "metathesis stable" and select mixtures yielded complete conversion to unsymmetrical diphosphine [3,[9][10][11]. The use of the scrambling reaction fell out of favour because the stable unsymmetrical diphosphines could be more readily prepared by direct cross coupling of monophosphorus species.…”

PHOSPHORSUBSTITUIERTE N, N′ -DIMETHYLTHIOHARNSTOFFVERBINDUNGEN. III. UNSYMMETRISCH BISPHOSPHORYLIERTE DERIVATE

“…(3) beobachtet. Vergleicht man 5 mit der Diphosphorverbindung Ph,P-PMe,, so wird die Stabilitat von Ph,P-PMe, in Losung* damit begrundet, darj der elektronenziehende Effekt der Phenylgruppen die Aciditat des Phosphoratoms der PMe,-Gruppe erhoht 9. Die Symmetrisierung von unsymmetrisch substituierten Diphosphorverbindungen wurde sogar im festen Zustand beobachtet ; ihre Geschwindigkeit nimmt in Losung und bei hoherer Temperatur rasch zu.…”