STEREOCHEMICALLY NONRIGID TRANSITION-METAL COMPLEXES OF 2,6-BIS[(1-PHENYLIMINO)ETHYL]PYRIDINE (BIP) .2. DYNAMIC NMR-STUDIES OF FAC-[REX(CO)(3)(BIP)] (X=CL, BR, OR I) - CRYSTAL-STRUCTURE OF FAC-[REBR(CO)(3)(BIP)]

The complexes fac-[ReX(CO)(3)(BIP)] (X = Ck, Br or I; BIP = 2,6-bis[(1 -phenylimino)ethyl]pyridine) have been synthesised and characterised a s involving BIP as a bidentate chelate ligand. In solution the ligand exists in three conformational forms, namely E,E- and both distal and proximal E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallo tropic shifts of the ReX(CO)(3) moiety between equivalent E,E forms, E ,Z-isomerisation of the pendant imine function and restricted C-C rota tion of the pendant arm of the BIP ligand. Activation energies Delta G (not equal) (298.15 K) for all these processes are of comparable magni tude, in the range 79-88 kJ mol(-1) , and are essentially halogen inde pendent. Restricted rotation of the phenyl ring attached to the Re-coo rdinated nitrogen was also detected with Delta G(not equal) = = 67.3 /- 0.2 kJ mol(-1). A crystal structure of fac-[ReBr(CO)(3)(BTP)] confi rms the E-conformation of the pendant imine function with its N atom c is to the pyridyl nitrogen.