Abstract

The complexes fac-[ReX(CO)3(BIP)] (X = CI, Br or I; BIP = 2,6-bis[(1-phenylimino)ethyl]pyridine) have been synthesised andcharacterised as involving BIP as a bidentate chelate ligand. In solution the ligand exists in three conformational forms, namely E,E- andboth distal and proximal E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallotropic shifts of the ReX(CO) 3 moietybetween equivalent E,E forms, E,Z-isomerisation of the pendant imine function and restricted C-C rotation of the pendant arm of theBIP ligand. Activation energies AG * (298.15 K) for all these processes are of comparable magnitude, in the range 79-88 kJmol-J, andare essentially halogen independent. Restricted rotation of the phenyl ring attached to the Re-coordinated nitrogen was also detected withAG * = 67.3 + 0.2 kJ mol- i. A crystal structure of fac-[ReBr(CO)3(BIP)] confirms the E-conformation of the pendant imine functionwith its N atom cis to the pyridyl nitrogen.