The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

3.2. Thienothiophenes 1216 3.2.1. Thieno[3,4-b]thiophene Analogues 1216 3.2.2. Thieno[3,2-b]thiophene Analogues 1217 3.2.3. Thieno[2,3-b]thiophene Analogues 1218 3.3. , ′-Bridged Bithiophenes 1219 3.3.1. Dithienothiophene (DTT) Analogues 1220 3.3.2. Dithieno[3,2-b:2′3′-d]thiophene-4,4-dioxides 1221 3.3.3. Dithienosilole (DTS) Analogues 1221 3.3.4. Cyclopentadithiophene (CPDT) Analogues 1221 3.3.5. Nitrogen and Phosphor Atom Bridged Bithiophenes 1222

Functional oligothiophenes: molecular design for multidimensional nanoarchitectures and their applications.

Noble metal nanoparticles chemistry is a domain in rapid expansion, as those objects lead to interesting applications in the fields of catalysis, biosensing, electronics and optics. Because of their structure, intermediate between that of molecules and of bulk material, they enable to bridge the gap between molecular chemistry and surface science. In particular, their optical properties, known since antiquity, have already shown a part of their potential and further major discoveries can reasonably be expected. Their most insightful optical properties rely on a strong absorption in the visible spectrum, called the plasmon band, that colloidal solutions of gold, silver or copper feature. Herein we wish to present a comprehensible overview of the fundamentals of the theories explaining the phenomenon dedicated to chemists seeking an introduction to those features. We will also give a brief review of the recently published body of relevant literature with reference to the aforementioned theory.

The plasmon band in noble metal nanoparticles: an introduction to theory and applications

Novel heterogenized asymmetric catalysts were synthesized by immobilizing preformed Ru catalysts on magnetite nanoparticles via the phosphonate functionality and were characterized by a variety of techniques, including TEM, magnetization, and XRD. These nanoparticle-supported chiral catalysts were used for enantioselective heterogeneous asymmetric hydrogenation of aromatic ketones with very high enantiomeric excess values of up to 98.0%. The immobilized catalysts were easily recycled by magnetic decantation and reused for up to 14 times without loss of activity and enantioselectivity. Orthogonal nature of the present catalyst immobilization approach should allow the design of other superparamagnetic nanoparticle-supported asymmetric catalysts for a wide range of organic transformations.

Magnetically Recoverable Chiral Catalysts Immobilized on Magnetite Nanoparticles for Asymmetric Hydrogenation of Aromatic Ketones

The reduction of tetrachloroaurate or potassium tetrachloropalladate with sodium borohydride in the presence of optically active 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl [BINAP] gave the chiral (S)- or (R)-BINAP-stabilized gold or palladium nanoparticles which showed the small core (1.7 nm for BINAP−Au and 2.0 nm for BINAP−Pd) with narrow size distribution and remarkably high stability. Asymmetric hydrosilylation of styrene with trichlorosilane in the presence of chiral BINAP−Pd nanoparticles afforded an optically active 1-phenyl-1-trichlorosilylethane which was converted into an optically active 1-phenylethanol (95% enantiomeric excess) by oxidative cleavage of the carbon−silicon bond.

Masaru Tamura

Papers

Chiral bisphosphine BINAP-stabilized gold and palladium nanoparticles with small size and their palladium nanoparticle-catalyzed asymmetric reaction.