A 7-BOND COUPLING, (7)J(PP) OR THROUGH-SPACE COUPLING IN THE AZINE DIPHOSPHINE Z,Z-PPH2CH2C(BU(T))=N-N=(BU(T))CCH2PPH2 - CRYSTAL-STRUCTURE OF Z,Z-P(=O)PH2CH2(BU(T))=N-N=(BU(T))-CCH2P(=O)PH2

Analysis of the (C{H})-C-13-H-1 NMR spectrum of ZZ-PPh2CH2C(But)=N-N=C(But)CH2PPh2 (1) gives second order patterns for the C(ipso), C(ortho), C(meta), PCH2 and C=N carbons caused by a non-zero seven-bond coupling, 7J(PP). Simulation of the spectra gives 7J(PP)=4.8 Hz. The corresponding diphosphine dioxide 2 gives first order (C{H})-C-13-H-1 spectra, i.e. 7J(PP) approximately 0 Hz. Possible explanations for this unusually large value of 7J(PP) are discussed. Crystals of 2 are orthorhombic, space group Pbca, with a=1592.2(3), b=1196.1(2), c=1663.0(3) pm and Z=4; final R factor 0.0381 for 1780 observed reflections.