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The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.

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Dinitriles (5-7. 12, 13) react with enantiomerically pure 0-required for a conformational interconversion of zinc dichloramino alcohols (8 -11.17) under zinc chloride catalysis to give ide complex 23e was determined by variable-temperature 'Hoptically active C2-symmetric bis(oxazo1ines). 1,2-Bis(Z-ox-NMR studies. An X-ray structure analysis was performed with azolin-2-y1)benzenes 1 a -e are obtained under mild reaction the substituted [ 1.2-bis(2-oxazolinyl)benzene]zinc dichloride conditions. 'H-NMR spectroscopy indicates the formation of complex 23 a. 1 : 1 complexes 23 of these compounds with ZnC12. The energy Optically active oxazolines have been extensively used as valuable auxiliaries in asymmetric synthesis 2! They can effect efficient chirality transfer from the heterocycle to newly formed bonds, thereby generating new centers of chirality with high asymmetric induction. Oxazolines have also been found in many microbial metal chelators such as vibriobactin, mycobactin, and parabactin3! In these cases they are incorporated into extremely strong multidentate metal complexes, illustrating the high chelating ability of this moiety. Based on these properties, optically active oxazolines have been used as chiral ligands for transition metals in asymmetric catalysis4! During our studies of new bidentate ligands for enantioselective transition-metal catalysis5), we have envisioned that C2-symmetric homochiral bis(2-oxazoliny1)benzenes of type 1 and 2 might be effective ligands for affecting asymmetric catalysis.Compounds of type 2 have previously been prepared by dehydration of 1,3-bis(ben~oylamino)benzenes~~~~~ with thionyl chloride or by modified Pinner reactions (diimidate formation of 1,3-dinitriles, followed by reaction with amino alcohol^)^). However, ortho-substituted benzenes of type 1 are not easily accessible by these routes. They have only been synthesized under vigorous reaction conditions. For example, dehydration of 1,2-bis(benzoylamino) derivatives to 1,2-bis(2-oxazolin-2-yl)benzenes (type 1) requires high temperatures (100-170°C) and strongly acidic conditions (30% SO3 in 70% sulfuric acid)". The Pinner method fails because 1,2-dinitriles can only be converted to stable monoimidate salts (3). The second cyano group of 3 is inert, and bisimidates are not formed9). r OR 3 4In 1974 Witte and Seeliger reported on a procedure for the preparation of mono-and bis(2-oxazolines) by direct reaction of nitriles with amino alcohols in the presence of catalytic amounts of metal saltsloaJ. However, attempts to use phthalonitrile and 2-aminoethanol gave exclusively 2,3-dihydro-1,3-bis(2-hydroxyethylimino)-1H-isoindol (4); no 1,2-bis(2-oxazolinyl) derivatives could be obtained. The stereochemical course of this reaction was not examined. Synthesis of Bis(2-oxazolines)By a careful reinvestigation of Witte and Seeliger's metalcatalyzed oxazoline synthesis, we now demonstrate that a variety of substituted optically active bis(2-oxazolinyl) derivatives can readily be prepared under mild reaction conditions. We obtaine...

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