1,10-Phenanthroline ring-opening mediated by cis-{Re(CO)2} complexes

Abstract

Pyridine ring-opening of a metal-coordinated 1,10-phenanthroline has been demonstrated for the first time. The reaction of stable, well-defined cis,trans-[Re(CO)₂(N–N)(N-RIm)(PMe₃)]OTf [N–N = 2,2′-bipyridine (bipy), N-RIm = N-alkylimidazole] compounds with KN(SiMe₃)₂ followed by the addition of an excess of electrophile (MeOTf) afforded bipy ring-opening products easily at room temperature. The new, electron rich analogous 1,10-phenanthroline (phen) cis-{Re(CO)₂} complexes allowed also, under mild conditions, the ring-opening of phen, which can be regarded as a model of coordinated quinoline, one of the impurities in fuels most difficult to eliminate by the hydrodenitrogenation (HDN) process. The phenanthroline ring-opening products are regiochemically different from those obtained with bipy, and the results of computational calculations suggest that the difference can be traced to the avoidance of a larger loss of aromaticity. The new ring-opening products have been spectroscopically characterized in solution and by means of X-ray diffraction in the solid state.