Engineering titania nanostructure to tune and improve its photocatalytic activity.

Photocatalytic pathways could prove crucial to the sustainable production of fuels and chemicals required for a carbon-neutral society. Electron-hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, we show the efficacy of anisotropy in improving charge separation and thereby boosting the activity of a titania (TiO2) photocatalytic system. Specifically, we show that H2 production in uniform, one-dimensional brookite titania nanorods is highly enhanced by engineering their length. By using complimentary characterization techniques to separately probe excited electrons and holes, we link the high observed reaction rates to the anisotropic structure, which favors efficient carrier utilization. Quantum yield values for hydrogen production from ethanol, glycerol, and glucose as high as 65%, 35%, and 6%, respectively, demonstrate the promise and generality of this approach for improving the photoactivity of semiconducting nanostructures for a wide range of reacting systems.

Cyclic Group 15 Radical Cations.

Singlet cyclo-1,3-dipnicta-2,4-diazane-1,3-diyls of the type [E(µ-NTer)2 E] (2, E=P, As, Ter=2,6-dimesitylphenyl) can undergo a one-electron-oxidation utilizing silver salts of weakly coordinating anions such as [AgLn][B(C6F5)4 ] (L=donor solvents) to afford the novel cyclic radical cations, [E(µ-NTer)2E](+·) (3(+·)). When smaller and more basic anions were employed in the reaction, the anions were found to form covalent bonds to the radical centers yielding dipnictadiazanes, [FP(µ-NTer)2PF] (5) and [(CF3CO2)P(µ-NTer)2P(CF3CO2)] (6). A two-electron oxidation process, resulting in the formation of dications of the type [E(µ-NTer)2E](2+), could not be observed. Computational and EPR data revealed that the spin density is almost completely localized at the two heavier pnictogen centers E of the former 1,3-dipnictadiazane-1,3-diyls. The bonding situation in the radical cations features a rare example of a transannular one-electron π bond without having a σ bond.

Four-membered heterometallacyclic d° and d¹ complexes of Group†4 metallocenes with amidato ligands.

A study of the coordination chemistry of different amidato ligands [(R)N-C(Ph)O] (R=Ph, 2,6-diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp2M(Cl){κ(2)-N,O-(R)N-C(Ph)O}] M=Zr, R=Dipp (1 a), Ph (1 b); M=Hf, R=Ph (2)) were synthesized by reaction of [Cp2MCl2] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp2Zr(H)Cl]. Salt metathesis reaction of [Cp2Zr(H)Cl] with deprotonated amide [(Dipp)N-C(Ph)O] gave the zirconocene hydrido complex [Cp2M(H){κ(2)-N,O-(Dipp)N-C(Ph)O}] (3). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)3Mg(Cl) {κ(2)-N,O-(Dipp)N-C(Ph)O}] (4; py=pyridine). The paramagnetic complexes [Cp'2Ti{κ(2)-N,O-(R)N-C(Ph)O}] (Cp'=Cp, R=Ph (7 a); Cp'=Cp, R=Dipp (7 b); Cp'=Cp*, R=Ph (8)) were prepared by the reaction of the known titanocene alkyne complexes [Cp2'Ti(η(2)-Me3SiC2SiMe3)] (Cp'=Cp (5), Cp'=Cp* (6)) with the corresponding amides. Complexes 1 a, 2, 3, 4, 7 a, 7 b, and 8 were characterized by X-ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.

Water reduction with visible light: synergy between optical transitions and electron transfer in Au-TiO(2) catalysts visualized by in†situ EPR spectroscopy.

Golden electrons: Visible light excites conduction electron transfer from gold particles to support vacancies where they are taken up by protons to produce hydrogen. This transfer process was visualized by in situ EPR spectroscopy.

Highly strained heterometallacycles of Group†4 metallocenes with bis(diphenylphosphino)methanide ligands.

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph2PC(X)PPh2] (X = H, SiMe3) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp2Ti{κ(2)-P,P-Ph2PC(X)PPh2}] (X = H (3 a), X = SiMe3 (3 b)) have been prepared by the reactions of [(Cp2TiCl)2] with [Li{C(X)PPh2}2(thf)3]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp2Ti(η(2)-Me3SiC2SiMe3)] with Ph2PC(H)(SiMe3)PPh2 (2 b). The heterometallacyclic complex [Cp2Zr(H){κ(2)-P,P-Ph2PC(H)PPh2}] (4 aH) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh2}2(thf)3]. Reactions of [Cp2HfCl2] with [Li{C(X)PPh2}2(thf)3] gave the highly strained corresponding metallacycles [Cp2M(Cl){κ(2)-P,P-Ph2PC(X)PPh2}] (5 aCl and 5 bCl) in very good yields. Complexes 3 a, 4 aH, and 5 aCl have been characterized by X-ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH, 5 aCl, and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta-2,3-dienes.