Fused Tricyclic Phosphiranes—Analysis of Phosphorus Chemical Shieldings

Abstract

1,2‐Addition of transient W(CO)5‐complexed phosphinidenes exo to hexamethyl Dewar benzene affords the novel 3‐phosphatricyclo[3.2.0.02,4]hept‐6‐ene complexes. The fused tricyclic phosphiranes are obtained as both the Z and the thermally less stable E isomers, the 31P NMR chemical shifts of which differ by about 60 ppm. A computational investigation shows that the phosphorus pyramidalization and the presence of the γ double bond are responsible for this effect. The semiquantitative results contribute to a more systematic understanding of the structural influences on 31P chemical shieldings. The congested double bond of the Z isomer can be epoxidized with m‐chloroperbenzoic acid (MCPBA) to afford a fused tetracyclic P,O bis‐adduct.

Aspects of Phosphaallene Chemistry: Heat-Induced Formation of 1,2-Dihydrophosphetes by Intramolecular Nucleophilic Aromatic Substitution and Photochemical Generation of Tricyclic Phosphiranes

“…Complexes 11 and 12 were isolated after column chromatography (SiO 2 , n -hexane) and recrystallization from n -hexane or CH 2 Cl 2 in 53% ( 11c ) to 78% yield ( 12 ). The 31 P NMR signals of the colorless or yellow ( 11a ), air-stable products (Cr: δ −143.6; Mo: δ −170.0; W: δ −190.2 ppm) are shifted significantly downfield relative to the free ligand and compare well to corresponding complexes and the decreasing ability of the metal atoms for backbonding. , The 1 J PC coupling constants in the PC 2 heterocycle are as expected , significantly smaller in the complexes (11–24 Hz versus 39 Hz; 5–11 Hz versus 31 Hz). The CO stretching vibrations of compounds 11 are found between 1925 and 2073 cm –1 . , The mass spectra show the molecular ion peaks and fragments resulting from the loss of two to four CO groups.…”

“…Detailed closed shell mechanistic studies did not lead to a convincing reaction pathway and indicate the photochemical nature of this conversion involving open shell states. 10 shows a high field signal in the 31 P NMR spectrum (δ −207.8 ppm) that is typical of phosphiranes. − The 1 J PC coupling constants in the PC 2 heterocycle are with 31 and 39 Hz at the lower end of expected values. − …”

Insight into fragmentation of a phosphirane to form phosphinidene complexes: an illustration with the 1-phenylselenylphosphirane W(CO)5 complex

“…O or Se atom) of phosphorus plays a major role in the decomposition of the phosphirane complex to a phosphinidene complex. No decomposition was observed with the 1-methylphosphirane complex 21 a ,25 at 140 °C, which demonstrates the importance of the vicinal lone pair in phosphirane fragmentation again.…”

Phosphines and related C–P bonded compounds

“…384 A route to fused tricyclic phosphiranes is afforded by the reactions of W(CO) 5 complexed phosphinidenes to hexamethyl Dewar benzene. 385 Stable syn-substituted methylenediphosphirane complexes have been obtained from the reaction of transient electrophilic phosphinidene complexes [RP ¼ W(CO) 5 ] (R ¼ Me or Ph), thermally generated from complexed benzophosphepines, with 1-phosphaallene. 386 Related to the phosphinidene area is a study of the reactions of the triply bonded molecule P 2 with stable carbenes, giving bis(phosphinidene) complexes of the type R 2 C-P-P'CR 2 , involving a phosphorus-phosphorus single bond.…”