13C NMR spectra of phosphole–P(IV) dimers; ABX and AA′X 13C31P coupling in some derived structures

✍ Scribed by Louis D. Quin; Keith A. Mesch; Ryszard Bodalski; K. Michal Pietrusiewicz

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 814 KB
• Volume: 20
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270200205

✦ Synopsis

Abstract

The easily obtained dimers of phosphole oxides, sulfides and methiodides give ^13^C NMR spectra where carbons within three (sometimes four) bonds of each ^31^P nucleus are doublets of doublets and thus constitute X in an AMX spectrum. Most of the spectra have been completely interpreted with the aid of spectral measurements at two magnetic fields. Saturation of the double bonds in dimers of methylphosphole–P(IV) derivatives causes the ^31^P nuclei to have very similar chemical shifts, with Δν not adequately different from ^3^J(PP) to give first‐order coupling. When both ^31^P nuclei couple with a given ^13^C, a second‐order (ABX) ^31^C NMR spectrum is obtained. The presence of the effect is revealed by running the ^13^C NMR spectra at high magnetic field; J(AX)+J(BX) is constant at all fields, but spacing between the lines of the multiplet varies. The spectrum of the oxide, with Δν/J=1.44 for the ^31^P spectrum at 36.43 MHz, approaches first order character at 75 MHz; the methiodide spectrum (Δν/J=4.55) is second order at 15 MHz but clearly first order at 50 MHz, and the sulfide (Δν/J=5.6) is nearly first order at 15 MHz. [2 + 2]‐Photochemical intramolecular cyclization of the dimer oxides provides cage‐like structures where the ^31^P nuclei are chemically equivalent, but magnetically non‐equivalent, making the ^13^C signals have the characteristics of X in an AA′X coupling pattern.