CRYSTAL-STRUCTURE, AND VARIABLE-TEMPERATURE PROTON AND C-13 NMR-SPECTRA OF THE 9-MEMBERED RING COMPLEX [CR(CO)(4)(E,Z-PPH(2)CH(2)C((T)BU)=N-N=C((T)BU)CH(2)PPH(2))]

Treatment of [Cr(CO)(4)(nbd)] (nbd = norbornadiene) with Z,Z-PPh(2)CH(2)C((t)Bu)=N-N=C((t)Bu)CH(2)PPh(2) gave the title compound 2b, the structure of which was determined by a single crystal X-ray diffraction study. The proton NMR spectrum of 26 at 308 K and 400 MHz showed that for each of the methylene groups the protons are equivalent, but the spectrum is temperature dependent and at 188 K the slow exchange limiting spectrum is obtained, with all methylene hydrogens chemically non-equivalent; corresponding changes were observed in the C-13-(H-1) NMR spectrum. The behaviour is due to the fluxionality of the 9-membered ring.