SYNTHESIS AND DYNAMIC NMR-STUDIES OF RHENIUM(I) TRICARBONYL BROMIDE COMPLEXES OF BENZIMIDAZOLYLPYRIDINE LIGANDS - CRYSTAL-STRUCTURE OF IS(1',5',6'-TRIMETHYLBENZIMIDAZOL-2'-YL)PYRIDINE)]

Pentacarbonylbromorhenium(I) reacted with 2,6-bis(benzimidazol-2'-yl)p yridine (bbip), 2,6-bis(1'-methylbenzimidazol-2'-yl)pyridine (bmbip), 2,6-bis(5',6'-dimethylbenzimidazol-2'-yl)pyridine (bdmbip), and -bis(1 ',5',6'-trimethylbenzimidazol-2'-yl)pyridine (btmbip) to form stable o ctahedral complexes of type fac[ReBr(CO)(3)L] (L = bbip, bmbip, bdmbip or btmbip) in which L is acting as a bidentate chelate ligand. At abo ve-ambient temperatures in solution the complexes are fluxional with t he nitrogen ligand oscillating between equivalent bidentate bonding mo des. Rates and activation energies for these fluxions have been invest igated by NMR methods. At low temperatures rotation of the uncoordinat ed benzimidazolyl unit is restricted and for fac-[ReBr(CO)(3)(btmbip)] in CD2Cl2 solution, two preferred rotamers exist in 89:11% relative a bundances. A rotational energy barrier has been estimated. The X-ray c rystal structure of fac-[ReBr(CO)(3))(btmbip)] confirms the bidentate chelate bonding of btmbip with a N-Re-N angle of 74.2 degrees. The pen dant benzimidazole unit is inclined at an angle of 60.7 degrees to the pyridine ring. (C) 1998 Elsevier Science Ltd. All rights reserved.