Electrocatalytic reduction of CO(2) by [Ru(tpy)(bpy)(solvent)](2+) (tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine) and its structural analogs is initiated by sequential 1e(-) reductions at the tpy and bpy ligands followed by rate limiting CO(2) addition to give a metallocarboxylate intermediate. It undergoes further reduction and loss of CO.

The oxidative stability of the molecular components of dye-sensitized photoelectrosynthesis cells for solar water splitting remains to be explored systematically. We report here the results of an electrochemical study on the oxidative stability of ruthenium(II) polypyridyl complexes surface-bound to fluorine-doped tin oxide electrodes in acidic solutions and, to a lesser extent, as a function of pH and solvent with electrochemical monitoring. Desorption occurs for the Ru(II) forms of the surface-bound complexes with oxidation to Ru(III) enhancing both desorption and decomposition. Based on the results of long-term potential hold experiments with cyclic voltammetry monitoring, electrochemical oxidation to Ru(III) results in slow decomposition of the complex by 2,2'-bipyridine ligand loss and aquation and/or anation. A similar pattern of ligand loss was also observed for a known chromophore-catalyst assembly for both electrochemical water oxidation and photoelectrochemical water splitting. Our results are significant in identifying the importance of enhancing chromophore stability, or at least transient stability, in oxidized forms in order to achieve stable performance in aqueous environments in photoelectrochemical devices.

A series of complexes of the form TpW(NO)(PMe3)(η2-arene) (where arene = benzene, anisole, dimethoxybenzene, trifluorotoluene, and naphthalene) are evaluated as practical synthons for the versatile dearomatization agent {TpW(NO)(PMe3)}, considering air stability, synthetic scalability, and substitution lability. Large-scale syntheses (9−30 g) are reported for several of these complexes as well as their precursors (TpW(NO)(CO2), TpW(NO)Br2, and TpW(NO)(PMe3)Br), and methods for spectroscopic characterization of composition and stereochemistry for the arene complexes (including J PW correlations) are summarized.

A general electropolymerization/electro-oligomerization strategy is described for preparing spatially controlled, multicomponent films and surface assemblies having both light harvesting chromophores and water oxidation catalysts on metal oxide electrodes for applications in dye-sensitized photoelectrosynthesis cells (DSPECs). The chromophore/catalyst ratio is controlled by the number of reductive electrochemical cycles. Catalytic rate constants for water oxidation by the polymer films are similar to those for the phosphonated molecular catalyst on metal oxide electrodes, indicating that the physical properties of the catalysts are not significantly altered in the polymer films. Controlled potential electrolysis shows sustained water oxidation over multiple hours with no decrease in the catalytic current.

The synthesis, characterization, and redox properties are described for a new ruthenium-based chromophore-catalyst assembly, [(bpy)(2)Ru(4-Mebpy-4'-bimpy)Ru(tpy)(OH(2))](4+) (1, [Ru(a)(II)-Ru(b)(II)-OH(2)](4+); bpy = 2,2'-bipyridine; 4-Mebpy-4'-bimpy = 4-(methylbipyridin-4'-yl)-N-benzimid-N'-pyridine; tpy = 2,2':6',2"-terpyridine), as its chloride salt. The assembly incorporates both a visible light absorber and a catalyst for water oxidation. With added ceric ammonium nitrate (Ce(IV), or CAN), both 1 and 2, [Ru(tpy)(Mebim-py)(OH(2))](2+) (Mebim-py = 2-pyridyl-N-methylbenzimidazole), catalyze water oxidation. Time-dependent UV/vis spectral monitoring following addition of 30 equiv of Ce(IV) reveals that the rate of Ce(IV) consumption is first order both in Ce(IV) and in an oxidized form of the assembly. The rate-limiting step appears to arise from slow oxidation of this intermediate followed by rapid release of O(2). This is similar to isolated catalyst 2, with redox potentials comparable to the [-Ru(b)-OH(2)](2+) site in 1, but 1 is more reactive than 2 by a factor of 8 due to a redox mediator effect.

Several π-allyl complexes of {TpW(NO)(PMe 3 )} are investigated as possible sources of η 2 -diene complexes. In order to prepare the diene complex as a single diastereomer, the allyl complex must undergo deprotonation stereoselectively. Allyl complexes of this tungsten system are highly distorted, with the difference between the WÀC bond lengths for the two allyl termini being as much as 0.69 Å. DFT calculations and several crystal structures are presented that collectively suggest that one terminus, C1, distal to the PMe 3 group, tends toward an sp 2 carbocation. Consistent with this interpretation, deprotonation preferentially occurs at a carbon adjacent to this allyl terminus for six-membered rings. However, in the presence of base the five-membered cyclic analogue [TpW(NO)(PMe 3 )(C 5 H 7 )] þ fails to form either isomer of the corresponding η 2 -diene complex.

The synthesis and analysis of a new amide-linked, dinuclear [Ru(bpy)(2)(bpy-ph-NH-CO-trpy)Ru(bpy)(OH(2))](4+) (bpy = 2,2'-bipyridine; bpy-ph-NH-CO-trpy = 4-(2,2':6',2"-terpyridin-4'-yl)-N-[(4'-methyl-2,2'-bipyridin-4-yl)methyl]benzamide) assembly that incorporates both a light-harvesting chromophore and a water oxidation catalyst are described. With the saturated methylene linker present, the individual properties of both the chromophore and catalyst are retained including water oxidation catalysis and relatively slow energy transfer from the chromophore excited state to the catalyst.

The N-acetylpyridinium complex of {TpW(NO)(PMe3)} undergoes regio- and stereoselective reactions with a broad range of common organic nucleophiles, providing a family of 1,2-dihydropyridine (DHP) complexes of the form TpW(NO)(PMe3)(3,4-η(2)-DHP). The present study explores the elaboration of these systems into novel piperidines. The addition of an acid to the DHP complexes generates highly asymmetric π-allyl complexes that in turn react with a second nucleophile at either C3 or C5. The subsequent oxidative decomplexation of these materials yields several piperidinamides with unconventional substitution patterns.