Carbon-13 nuclear magnetic resonance spectra of some polyphosphines with ethane bridges between trivalent phosphorus atoms

Abstract

The proton noise-decoupled pulsed Fourier transform ¹³C n.m.r. spectra of (C₆H₅)₂PCH₂CH₂PR₂(R = CH₃ and C₆H₅), R₂PCH₂CH₂P(H)C₆H₅(R = CH₃ and C₆H₅), (CH₃)₂PCH₂CH₂PH₂, n-C₆H₁₃PHCH₂CH₂PH₂, R′P(CH₂CH₂PR₂)₂(R′= CH₃, R = CH₃; R′= C₆H₅, R = CH₃ or C₆H₅), (CH₃)₂PCH₂CH₂P(R)CH₂CH₂PH₂(R = H and C₆H₅), and P(CH₂CH₂PH₂)₃ have been examined. Replacement of alkyls by hydrogen in R₂P units consistently raises the ¹³C n.m.r. chemical shifts (i.e., lowers the δ values) of CH₂ groups attached to this phosphorus. The spin–spin splittings in the ¹³C n.m.r. spectra by the phosphorus atoms in (C₆H₅)₂PCH₂CH₂ P(C₆H₅)₂ and C₆H₅P[CH₂CH₂P-(C₆H₅)₂]₂ must be analysed as second-order ABX systems whereas those in the remaining polyphosphines can be analysed as first-order AMX systems. The range of significant phosphorus-carbon coupling in these compounds is limited to three bonds. In most cases, the coupling constants ¹J(C–P) and ²J(C–P) have nearly equal magnitudes but opposite signs. However, direct bonding of hydrogen to a trivalent phosphorus atom appears to decrease markedly its |²J(C–P)| while having much less effect on its |¹J(C–P)|. This indicates that substitution on phosphorus of alkyls or aryls by hydrogens has a major effect on the conformation of the PCH₂CH₂P chain.