Schiff base ligands are considered "privileged ligands" because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.

The enantioselective hydrogenation of N-(1-phenylethylidene)aniline using cationic iridium complexes with chiral phosphinooxazoline ligands was studied as a chemical probe to assess the potential of ionic liquid/carbon dioxide (IL/CO2) media for, multiphase catalysis. The biphasic system leads to activation, tuning, and immobilization of the catalyst that would be impossible in classical organic solvent systems or in either of the two unconventional media separately. In particular it is demonstrated that (i) the presence of CO2 can be beneficial or even mandatory for efficient hydrogenation in the IL; (ii) the precursor is activated in the IL by anion exchange allowing one to use in situ catalysts; (iii) the anion of the IL greatly influences the selectivity of the catalyst; (iv) the products are readily isolated from the catalyst solution by CO2 extraction without cross contamination of IL or catalyst; and (v) the IL leads to enhanced stability of the catalyst. These results are corroborated and rationalized on the basis of the physicochemical properties of the biphasic medium and the chemical characteristics of the catalytic systems.

BODIPYs offer a versatile platform to build organic triplet photosensitisers for PDT, TTA upconversion and photocatalysis. Tuning their properties provides the opportunity of replacing heavy-metal complexes and can lead to improved sustainability.

In 2005, the ACS Green Chemistry Institute (GCI) and the global pharmaceutical corporations developed the ACS GCI Pharmaceutical Roundtable to encourage the development of green chemistry and green engineering in the pharmaceutical industry. The Roundtable has established a list of key research areas including the direct nucleophilic reactions of alcohols. The substitution of activated alcohols is a frequently used approach for the preparation of active pharmaceutical ingredients. Alcohols are transformed into the reactive halides or sulfonate esters, thereby allowing their reaction with nucleophiles. Although the direct nucleophilic substitution of an alcohol should be an attractive process, as one of the byproducts from the reaction yields water, hydroxide is a poor leaving group that hinders the reaction. Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through an SN1 reaction with catalytic amounts of Brønsted or Lewis acids. In this review, the approaches leading to a greener process are examined in detail, and the advances achieved to date in this important transformation are presented.

Enantioselective catalytic formation of tertiary stereogenic centers has nowadays reached an impressive level of maturity, as is reflected in the large variety of available methods that afford high yields and high stereoselectivities. However, the development of stereoselective approaches for the formation of quaternary stereogenic centers still represents an enormous challenge for synthetic chemists. On the other hand, biologically active molecules containing quaternary stereogenic centers provide an incentive for the development of new, selective, and useful processes. Over the last few years, breakthrough work relating to the formation of fully substituted carbon centers has appeared in the literature. In this review we discuss recent highlights of this new direction in catalysis research: the formation of quaternary stereogenic centers by enantioselective catalytic methodologies.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

A mechanism based on the sequential absorption of two photons by the components of a redox couple has been recently proposed for catalysis of the energetically demanding reduction of aryl halides. Here, we analyze the suggested photochemical mechanism of this reaction, which employs perylenediimide (PDI) as a photocatalyst, on the basis of spectroscopic, electrochemical and electron paramagnetic resonance data. Our results indicate that the photoexcited PDI radical anion (*PDI˙) cannot play the role of a photosensitizer in the aforementioned process. Instead, the reduction of 4'-bromoacetophenone likely involves *PDI˙ decomposition products. The extremely short lifetime of the photoexcited transient species, as *PDI˙, is a major general limitation for photocatalytic schemes based on sequential two-photon excitation. In order to better understand the potential of such schemes, we discuss them in the context of the Z-scheme in natural photosynthesis.

General methods S3Materials S3Optimization of the enantioselective photo alkylation of aldehydes S4Light/dark effect S7 Synthesis of catalyst 3 S8 Synthesys of aldehydes 1g,h S8General procedure for enantioselective photo alkylation of aldehydes. S9General procedure for determination of enantiomeric excesses of compounds 6-9. S10 Characterization data of compounds 4-15 S11Synthesis of (-)-isodeoxypodophyllotoxin S14 Mechanistic insights. S15Synthesis of aldehyde (±)-trans 1i. S15 Synthesis of aldehyde (±)-cis 1i. S16 Photoalkylation of aldehyde (±)-trans-1i. S17Photoalkylation of aldehyde (±)-cis-1i. S24 Photophysical measurements. S28Emission profile of the 23W Compact Fluorescent lamp used to irradiate the solutions. S32EPR studies S33 References. S34Copies of NMR spectra. S36Copies of HPLC, GC traces and NMR spectra for the determination of enantiomeric excess. S56S3

Work-alcoholic! The elusive enantioselective catalytic alpha-alkylation of aldehydes, a widely sought transformation, was brought to execution by the use of alcohols capable of forming stabilized carbocations (see scheme, TFA = trifluoroacetic acid).