Ambient reactions

The concentration of volatile compounds in the cavitation bubbles increases with temperature thus, faster degradation rates are observed at higher temperatures for those compounds [23]. Conversely, in the case of nonvolatile substrates (that react through radicals reactions in solution), the effect of temperature is somehow opposed to the chemical common sense. In these cases, an increase in the ambient reaction temperature results in an overall decrease in the sonochemical reaction rates [24]. The major effect of temperature on the cavitation phenomenon is achieved through the vapor pressure of the solvent. The presence of water vapor inside the cavity, although essential to the sonochemical phenomenon, reduces the amount of energy... 

Most rhodium catalysts for the enantioselective reduction of the C=N group are prepared in situ from a dimeric Rh-diene complex and a chiral diphosphine. Only few of the tested diphosphine ligands exhibit enantioselectivities >70% bdpp, cycphos, and phephos for imines and duphos for acylhydrazones. The activity of most Rh-diphosphine complexes for imine hydrogenation is low and therefore most of them are of limited practical use. Although some catalysts work already at ambient reaction conditions, most Rh-diphosphine complexes show low tof s even at elevated hydrogen pressures (>60 bar). 

The aldol condensation is a class of reactions widely used in organic synthesis for the production of various oxygenated compounds (Figme 1). The reactions may be conducted in the liquid or vapor phase with a variety of catalysts. We are interested in the application of CD to the aldol condensation of acetone (Ac) to examine the factors that determine the yield and selectivity in reactions involving a number of consecutive steps. Under ambient reaction conditions, diacetone alcohol (DAA) is readily formed. At higher temperatures DAA readily undergoes dehydration to mesityl oxide (MO) [2],... 

The goal of sustainable chemistry is to design reactions that incorporate catalysts and innocuous chemicals that reduce toxicity and provide eco-friendly reaction conditions. The chromium catalysts discussed in this chapter were designed to meet these ends. Future challenges in chromium-based catalysts need to focus on developing materials that do not require cocatalysts and can be performed at ambient reaction conditions to achieve high yields and stereoselectivities. 

Scheme 4.5). Potassium organotrifluoroborate salts are easily accessible, have attracted increased commercial availability, are air- and moisture-stable alternatives to boronic acids as well as their esters, and can be stored for long periods of time without decomposition under ambient reaction conditions. These aryl donors function brilhantly in arylations of phenols, albeit with the requirement for 2 equiv. of the potassium organotrifluoroborate salt being used to gain the best yields. However, the reactions function even at ambient temperature with molecular oxygen as a co-oxidant [20]. 

Diamine functionalized porous silica gel was used by Wang [81] as support for palladium complexes, which could be recycled up to 30 times. The copper-free reactions of aryl iodides and some aryl bromides were performed in EtOH as protic solvent with K2CO3 as base. Although these reactions could be conducted at ambient reaction temperature by immobilizing palladium on MCM-41 zeolites, they required the presence of Cu(I) additives and piperidine as the base of choice. 

But these protocols are not suitable for synthetic purposes. It was therefore a breakthrough when in 2015 Dong and coworkers [4] discovered the rhodium-catalyzed dehydroformylation of aldehydes in the presence of olefins, which corresponds to a net transfer hydroformylation. The new methodology operates at ambient reaction conditions and use a Rh(Xantphos) catalyst in low concentrations (Scheme 8.16). As formyl acceptors, NBD, norbornene, and benzonorbornadiene were screened, which were added in 1—6equiv relative to the aldehydic substrate. Benzonorbornadiene developed sufficient activity even at ambient temperature. A broad range of aldehydes could be so converted into olefins, among which were cychc and acyclic compounds with and without functional groups. 

Nishibayashi Y. Molybdenum-catalyzed reduction of molecular dinitrogen into ammonia imder ambient reaction conditions. C R Chim. 2015 18 776-784. 

Nishibayashi Y. Recent progress in transition-metal-catalyzed reduction of molecular dinitrogen under ambient reaction conditions. Inorg Chem. 2015 54 9234-9247. 

Imayoshi R, Tanaka H, Matsuo Y, et al. Cobalt-catalyzed transformation of molecular dinitrogen into silylamine under ambient reaction conditions. Chem Eur J. 2015 21 8905-8909. 

Abstract The in vitro enzyme-mediated polymerization of vinyl monomers is reviewed with a scope covering enzymatic polymerization of vitamin C functionalized vinyl monomers, styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible cosolvents. Vitamin C functionalized polymers were synthesized via a two-step biocatalytic approach where vitamin C was first regioselectively coupled to vinyl monomers and then subsequently polymerized. The analysis of this enzymatic cascade approach to functionalized vinyl polymers showed that the vitamin C in polymeric form retained its antioxidant property. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H2O2, initiator fS-diketone) was required for efficient polymerization and that the initiator controls the characteristics of the polymer. The main attributes of enzymatic approaches to vinyl polymerization when compared with more traditional synthetic approaches include facile ambient reaction environments of temperature and pressure, aqueous conditions, and direct control of selectivity to generate functionalized materials as described for the ascorbic acid modified polymers. 

Despite the mentioned successes, there are still plenty of challenges to face. Upon others, open questions are the electronic structure, reactivity and behavior towards more complex molecules/reactions and under realistic conditions. Within the scope of this thesis, using (exclusively) Pt clusters, under well defined (UHV) and applied (ambient) reaction conditions (see Fig. 1.1) different issues are tackled. 

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