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

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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.

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