The synthesis and structures of a mononuclear copper(I) carbonyl complex [Cu(OClO3)(CO)(H2CPz2')] (3) and a dinuclear copper(I) carbonyl complex [{Cu(CO)(H2CPz2')}2(mu-pyrazine)](ClO4)2 (4), where H2CPz2' = bis(3,5-dimethylpyrazol-1-yl)methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H2CPz2')(MeCN)](ClO4) (1) and [{Cu(H2CPz2')(MeCN)}2(mu-pyrazine)](ClO4)2 (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu(I) complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(I) complex [Cu(PPh3)(H2CPz2')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu(I)-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi*(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu(I)-O(ClO4) = 2.240(3) A), is a potential precursor for polynuclear copper(I) carbonyl complexes.

The reactions of fert-butyl hydroperoxide with cyclohexene or cyclooctene, as catalyzed by a number of chelated diketonates of V02+, by (n-BuO)3VO, and by Mo02(acac)2, are highly selective and yield only tert-butyl alcohol and the corresponding epoxy cycloalkanes. Rate laws for the vanadium-catalyzed systems are consistent with reaction via rate-determining attack of olefin on a vanadium(V)-hydroperoxide complex. Association constants for the complexes and activation parameters associated with the various vanadium catalysts are different, indicating that these catalysts retain, at least in part, their ligand environments when converted to catálytically active species. Competitive inhibition by f-BuOH, reflecting the formation of catalyst-alcohol complexes, is observed in all cases; association constants for four of these alcohol complexes have been evaluated. Epoxidations of cyclohexene catalyzed by Mo02(acac)2 proceed approximately 102 as rapidly as those by the vanadium complexes under corresponding conditions. Kinetic behavior in the molybdenum system is consistent with the formation of molybdenum-hydroperoxide and molybdenum-olefin complexes, as well as a molybdenumhydroperoxide-olefin complex. Arguments are presented supporting the view that the molybdenum-catalyzed epoxidation, like those involving vanadium, proceeds by reaction of olefin with a metal-hydroperoxide complex, rather than through the ternary complex.The epoxidation of olefins using hydroperoxides or H2O2 in the presence of catalysts derived from vanadium, molybdenum, or tungsten2 \ / \ / is highly selective and, under favorable conditions, leads to quantitative yields of epoxides. Several workers2t)_d have suggested that this reaction is heterolytic, rather than free radical, in character, and an earlier study20 of the reaction in the presence of vanadyl acetylacetonate, VO(acac)2, provided evidence of the intervention of a hydroperoxide-vanadium-(V) complex and of severe competitive inhibition by alcohols, which are products when hydroperoxides are employed as oxidants. However, questions were left unanswered as to how the nature of the catalyzed reaction was affected by variation in the identity or oxidation state of the catalytic metal or by change in its ligand environment. The present report is directed toward partial resolution of these points; in addition, it presents further information concerning the changes occurring when VO(acac)2, a typical catalyst, is transformed to the principal active species during the early stages of reaction. Experimental SectionMaterials. Vanadyl acetylacetonate, VO(acac)2 (J. T. Baker), was recrystallized three times from anhydrous acetone; the purified chelate dissolved in benzene without leaving a residue. Since benzene solutions of this and other vanadyl chelates showed some deterioration on standing in air for several hours,20'3 each series of experiments employed a freshly prepared solution of metal chelate. Vanadium(III) acetylacetonate, V(acac)3 (J. T. Baker), was purified by dissolving in anhydrous...

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Photophysical properties such as absorption and emission spectra, lifetimes, and redox potentials of eight ruthenium complexes, Ru(LL)2(MebpyCOOH)2+, where LL represents bpy, phen, Me2bpy, Me4bpy, (MeO)2bpy, (EtO)2bpy, Cl2bpy, and NO2phen, have been measured. The acid dissociation constants of ground and excited states have been determined. The ground-state pKa values were obtained from the pH dependence of the complex absorbance changes. The excited-state pKa* values were extracted from the emission titration curve and corrected for the excited-state lifetime of both protonated and deprotonated species. The largest DeltapKa, pKa*-pKa, found for Ru(Me2bpy)2(MebpyCOOH)2+ and Ru(Me4bpy)2(MebpyCOOH)2+ of 1.7 indicate that MebpyCOOH gains most of the MLCT excited-state electron. The big negative DeltapKa found for Ru(Cl2bpy)2(MebpyCOOH)2+, -4.2, clearly indicates the metal-to-ligand charge transfer to the Cl2bpy ligands.

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A homochiral amino acid coordination network [{Ag3Cu3(l-methioninato)6(NO3)3(H2O)3}.7H2O]n, self-assembled from CuII, AgI, and l-methionine via a distinct soft-hard recognition process, shows interesting characteristics, in that it is constructed from 1D helical building blocks and contains homochiral channels in which 1D water chains are hosted. This result provides an effective and controllable strategy for the preparation of enantiopure heterometallic supramolecular structures that are relevant to biopolymers.

A reliable method for determining the mode of binding of ambidentate sulfoxide ligands to metals has been developed based upon a novel application of ESCA. Relative differences between S 2p3/, and O Is ionization potentials show a characteristic separation for oxygen-bound and sulfur-bound sulfoxides.