摘要:
[Ru-II(Me(2)edda)(H2O)(2)] (1), Me(2)edda(2-)=N,N'-dimethylethylenediaminediacetate, exhibits a sterically-controlled molecular recognition in forming eta(2) and eta(4) olefin complexes. 1 exists with an N2O2 in-plane set of chelate donors and axial H2O ligands. The two CH3 functionalities of Me(2)edda(2-) are poised above and below the N2O2 plane of the glycinato rings. Studies herein of the 2,2'-bipyridine complex, [Ru-II(Me(2)edda)(bpy)], with bidentate bpy chelation as established via H-1 NMR and electrochemical methods show 1 to be ligated in the S,S configuration with the glycinato rings in-plane as a cis-O form. 1 is sterically discriminating in forming eta(2) complexes with smaller olefins (ethylene, 2-propene, cis-2-butene, methyl vinyl ketone and 3-cyclohexene-1-methanol), but rejects larger decorated ring structures and branched olefins (1,2-dimethyluracil, cyclohexene-1-one and 2-methyl-2-propene). eta(2) complexes of 1 have characteristic Ru-II/III DPP waves near 0.55 V which vary slightly with olefin structure. Potentially bidentate dienes (1,3-butadiene, 1,3-cyclohexadiene and 2,5-norbornadiene (nbd)) form eta(4) complexes as shown by RU(II/III) waves between 0.94 and 1.30 V, indicative of a highly stabilized Ru-II center by bis pi-backbonding. An eta(2)=eta(4) 'equilibrium' with apparent K=22 at 25 degrees C is observed for nbd coordinated to 1. (The eta(2) and eta(4) distribution may be a kinetic one and not a thermodynamic one.) To allow formation of the cia eta(4) complexes, 1 must undergo a shift of one or both glycinato donors from the N2O2 plane into the axial site away from the dimethyl functionalities. eta(4) chelation by 1,3-butadiene has been confirmed by H-1 NMR spectral assignments of two [Ru-II(Me(2)edda)] isomers, one in the axial trans-O glycinato configuration, e.g. 1,3-butadiene is bidentate in the original N2O2 plane and a second unsymmetrical glycinato arrangement with in-plane and axial glycinato as well as in-plane and axial eta(4)-1,3-butadiene coordination. [Ru-II(hedta)(H2O)](-) (2), hedta(3-)=N-hydroxyethylethylenediaminetriacetate is less discriminating for olefin structures, forming eta(2) complexes with all eleven olefins and dienes mentioned for studies with 1. However, 2 does not undergo displacement of a carboxylate donor by the second olefin unit of a diene [Ru-II(hedta)(diene)](-) complexes possess a pendant non-coordinated olefin and one eta(2)-bound olefin in the complex, indicated by a normal Ru-II(pac)(olefin)Ru-II/III wave near 0.55 V.