Global energy consumption is projected to increase, even in the face of substantial declines in energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. This demand could be met, in principle, from fossil energy resources, particularly coal. However, the cumulative nature of CO2 emissions in the atmosphere demands that holding atmospheric CO2 levels to even twice their preanthropogenic values by midcentury will require invention, development, and deployment of schemes for carbon-neutral energy production on a scale commensurate with, or larger than, the entire present-day energy supply from all sources combined. Among renewable energy resources, solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user. An especially attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a photosynthetic process at a year-round average efficiency significantly higher than current plants or algae, to reduce land-area requirements. Scientific challenges involved with this process include schemes to capture and convert solar energy and then store the energy in the form of chemical bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or other hydrocarbon species.

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Powering the planet: Chemical challenges in solar energy utilization

Hydrogen Production by Molecular Photocatalysis

High oxidation state multiple metal-carbon bonds.

We have recently developed palladium-catalyzed methods for direct arylation of indoles (and other azoles) wherein high C-2 selectivity was observed for both free (NH)-indole and (NR)-indole. To provide a rationale for the observed selectivity ("nonelectrophilic" regioselectivity), mechanistic studies were conducted, using the phenylation of 1-methylindole as a model system. The reaction order was determined for iodobenzene (zero order), indole (first order), and the catalyst (first order). These kinetic studies, together with the Hammett plot, provided a strong support for the electrophilic palladation pathway. In addition, the kinetic isotope effect (KIE(H/D)) was determined for both C-2 and C-3 positions. A surprisingly large value of 1.6 was found for the C-3 position where the substitution does not occur (secondary KIE), while a smaller value of 1.2 was found at C-2 (apparent primary KIE). On the basis of these findings, a mechanistic interpretation is presented that features an electrophilic palladation of indole, accompanied by a 1,2-migration of an intermediate palladium species. This paradigm was used to design new catalytic conditions for the C-3 arylation of indole. In case of free (NH)-indole, regioselectivity of the arylation reaction (C-2 versus C-3) was achieved by the choice of magnesium base.

Direct palladium-catalyzed C-2 and C-3 arylation of indoles: a mechanistic rationale for regioselectivity.

Organometallic molecular wires and other nanoscale-sized devices: An approach using the organoiron (dppe)Cp*Fe building block

Synthesis of Molybdenum Complexes That Contain Silylated Triamidoamine Ligands. A .mu.-Dinitrogen Complex, Methyl and Acetylide Complexes, and Coupling of Acetylides

A variety of paramagnetic molybdenum complexes, [N3N]MoR ([N3N]3- = [(Me3SiNCH2CH2)3N]3-; R = Me, Et, Bu, CH2Ph, CH2SiMe3, CH2CMe3, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclopentenyl, phenyl), have been prepared from [N3N]MoCl. The several that have been examined all follow Curie−Weiss S = 1 behavior with a magnetic moment in the solid state between 2.4 and 2.9 μΒ down to 50 K. Below ∼50 K the effective moments undergo a sharp decrease as a consequence of what are proposed to be a combination of spin−orbit coupling and zero field splitting effects. NMR spectra are temperature dependent as a consequence of “locking” of the backbone into one C3-symmetric conformation and as a consequence of Curie−Weiss behavior. The cyclopentyl and cyclohexyl complexes show another type of temperature-dependent fluxional behavior that can be ascribed to a rapid and reversible α-elimination process. For the cyclopentyl complex the rate constant for α-elimination is ∼103 s-1 at room temperature, while the rate co...

Synthesis and Decomposition of Alkyl Complexes of Molybdenum(IV) That Contain a [(Me3SiNCH2CH2)3N]3- Ligand. Direct Detection of α-Elimination Processes That Are More than Six Orders of Magnitude Faster than β-Elimination Processes

.alpha.-Elimination Can Be Faster than .beta.-Elimination in d2 Alkyl Complexes of Molybdenum and Tungsten That Contain the Trimethylsilyl-Substituted Triamidoamine Ligand

Keng-Yu Shih

Papers

Synthesis of Molybdenum Complexes That Contain Silylated Triamidoamine Ligands. A .mu.-Dinitrogen Complex, Methyl and Acetylide Complexes, and Coupling of Acetylides

Synthesis and Decomposition of Alkyl Complexes of Molybdenum(IV) That Contain a [(Me3SiNCH2CH2)3N]3- Ligand. Direct Detection of α-Elimination Processes That Are More than Six Orders of Magnitude Faster than β-Elimination Processes

.alpha.-Elimination Can Be Faster than .beta.-Elimination in d2 Alkyl Complexes of Molybdenum and Tungsten That Contain the Trimethylsilyl-Substituted Triamidoamine Ligand

Synthesis and Decomposition of Alkyl Complexes of Tungsten(IV) That Contain a [(Me3SiNCH2CH2)3N]3- Ligand

Spontaneous loss of molecular hydrogen from tungsten(iv) alkyl complexes to give alkylidyne complexes