Preparation, characterization and X-ray crystallographic analysis of eta(5)- and eta(6)-mono-ruthenium(II) complexes of 2,3-bis(2,2 '-bipyridyl)quinoxaline

The reaction of 2,3-bis(2,2'-bipyridyl)quinoxaline (L) with ruthenium terpy ridine (tpy) trichloride in ethanol containing N-ethylmorpholine afforded [ LRu(tpy), PF6](2) (1) and the eta(5)-mu-chloro complex [LRu(Cl)tpy, PF6] (2 )1 as major and minor products, respectively, and recovered L. The structur e of 1 was confirmed by H-1 NMR spectroscopic and X-ray crystallographic st udies, and compared to that of L. The precise structure of 2 was distinguis hed between several possible isomers through a combination of H-1 NMR and U V/vis spectroscopy. Together, all of these studies suggest that steric inte ractions between the quinoxaline fragment and the orthogonal tpy ring syste m, rather than between the bipyridyl groups of L, are responsible for the f ormation of 2. (C) 1998 Elsevier Science Ltd. All rights reserved.