Phenylphosphoranyl radicals: are they tetrahedral or trigonal bipyramidal?

Abstract

The e.s.r. spectra of phenylphosphoranyl radicals [Ph,PX,-,Y]-show that, depending on the nature of X and Y, these radicals fall into two types in which the unpaired electron is centred mainly on phosphorus or on the aromatic ring.

Electron spin resonance studies of thiophosphoranyl radicals. The mechanism of ligand permutation in phosphoranyl radicals

“…However, hydrogen sulphide proved to be a good co-solvent for Ph,P and permitted the spectrum of [ButOPPh,] *, which has a ligand-x electronic structure, * to be observed a t lower temperatures than before. 19 a(lH), 7.9, a ( 2 H ) 4.4 G, g 2.0031, as expected if the unpaired electron is located on one ring rather than delocalised over all three (see Figure 3). A t higher temperatures lineshape effects indicated that electron exchange between the rings was taking place on the e.s.r.…”

A study of transient phenomena in the reactions of alkoxy radicals with triphenylphosphine and triphenylborane

“…Alkoxytriphenylphosphoranyl radicals show strong absorption bands in the visible region of the spectrum (Xmax 430 nm, emax ~6200 M-1 cm-1 for 1) which extend well into the near-IR region; these characteristics probably reflect an extensive delocalization of the unpaired electron on the aromatic rings and are consistent with the low values of the 3IP hyperfine coupling constants. 5 Our results for triphenylborane provide conclusive evidence for the stepwise nature of the reaction with Zezv-butoxy radicals. In fact, the behavior of triphenylborane parallels that of phosphorus compounds, though it is clear that the tetracoordinate boranyl radical intermediate is considerably less stable than its phosphorus counterpart.…”

Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

“…An analogous case of a nearly complete transfer of spin density away from a heteroatom occurs in the phosphorus-centered radical cPPh(OEt) 2 (OBu-t), where the spin density is delocalized onto the aromatic ring. 13 The hyperfine coupling of germanium in 3a, a( 73 Ge) ¼ 15.0, is much smaller than that in the stable pyramidal radical [(Me 3 Si) 2 N] 3 Gec (171.0 G), 14 and in fact even smaller than reported for the planar radical (t-Bu 2 MeSi) 3 Gec (20.0 G). 15 The relatively low 73 Ge hyperfine coupling constant in radical 3a is consistent with delocalization of the unpaired electron away from the Ge atom.…”

“…2c: 1 H NMR (benzene, DMSO-d 6 capillary): d 5.71 (2H, s), 4.52 (4H, m, J H-P ¼ 6.3 Hz, J H-H ¼ 6.2 Hz), 1.41 (18H, s), 1.19 (24H, dd, J H-P ¼ 2.0 Hz, J H-H ¼ 6.2 Hz); 29 Si NMR: d À71.2 (t, J Si-P ¼ 1.3 Hz); 31 P NMR: d 126.2; 13 C NMR: d 110.4, 65.5 (d, J C-P ¼ 11.1 Hz), 51. 3, 30.6, 24.5. 5b: 1 H NMR (benzene, DMSO-d 6 capillary): d 4.94 (4H, m, J H-H ¼ 6.0 Hz), 2.94 (8H, s), 1.39 (36H, s), 1.33 (24H, d, J H-H ¼ 6.0 Hz); 29 Si NMR: d 67.9 (d, J Si-P 16.4 Hz); 31 P NMR: d 129.7; 13 C NMR: 65.0 (d, J C-P ¼ 10.9 Hz), 51. 2, 44.1, 30.8, 24.8. 5c: 1 H NMR (benzene, DMSO-d 6 capillary): d 4.55 (4H, m, J H-P ¼ 6.0 Hz, J H-H ¼ 6.3 Hz), 2.90 (4H, s), 1.66 (18H, s), 1.22 (24H, dd, J H-P ¼ 5.2 Hz, J H-H ¼ 6.3 Hz); 29 Si NMR: d À69.1 (t, J Si-P ¼ 3.2 Hz); 31 P NMR: d 126.0; 13 C NMR: d 65.2 (d, J C-P ¼ 10.8 Hz), 50.9, 41.5, 29.3, 25.0.…”