In situ system

Some other enantioselective approaches have been attempted, still with moderate enantioselectivities, by making use of in situ systems containing a chiral NHC precursor. Luo and co-workers reported on the use of the bidentate chiral imidazo-lium salt 16, derived from L-proUne, in combination with [RhCia-COCcod)], leading to an enantiometic excess of around 20% [30]. The use of chiral imidazolium salt 17 in combination with [RhCl(CH2=CHj)j]j by Aoyama afforded slightly better ee (Fig. 7.3) [31 ]. So far, Bohn and co-workers have obtained the best enantioselectivities (up to 38% ee) for the catalytic addition of phenylboronic acid to aromatic aldehydes by using planar chiral imidazolium salts 18, derived from paracyclophane, in combination with [Rh(OAc)2]2 [32]. 

Austin, W.A., 1998. Development of an In-Situ System for Measuring Ground Thermal Properties, MSc. Thesis, Oklahoma State University, USA, 164 pp. 

Austin, W.A., C. Yazuzturk, and J.D. Spitler, 2000. Development of an in-situ system for measuring ground thermal properties, ASHRAE Trans., 106 (1) 365-379. 

In situ systems create minimal disruption and/or disturbance to ongoing site activities. 

The chiral ligand was in all cases (2S,4S)-N-tert-butoxycarbonyl-4-diphenylphos-phino-2-diphenylphosphinomethylpyrrolidine (BPPM) and the catalyst was formed in an in situ system of [Rh(COD)2] BFT The asymmetric hydrogenation is well investigated in organic solvents like methanol, but the presence of water usually causes loss of activity and enantioselectivity because of the low solubility of both the catalyst and the substrate in water [27, 29]. The addition of low-molecular surfactants or commercially available polymeric amphiphiles increases the activity (here given as time of consumption of half the stoichiometric volume of hydrogen, t/2) as well as the enantioselectivity [4]. Tab. 6.1 summarizes selected experiments with different polymeric amphiphiles. 

The Mizoroki-Heck reaction in liquid imidazolium salts as the solvent is a special case of an in situ system Under the reaction conditions NHC complexes of palladium are formed as the active catalyst from the solvent and the ligand-free palladium precursor. In general, ionic liquids are novel reaction media for homogeneous catalysis. They allow easy separation of product and catalyst after the reaction. ... 

Comparison of the different types of cobalt catalysts shows that the in situ system [Eq.(2)] is most accessible while the Rep-, R(ind)-, and bori-ninato ligands having electron-withdrawing substitutents are the most active. The difference between the 14e" and the 12e core complexes makes itself apparent in the chemoselectivity of the reaction. Catalysts containing a 14-electron core favor pyridine formation, whereas those containing a 12-electron core (i.e., the rj -allylcobalt systems) favor the formation of benzene derivatives by cyclotrimerization of the alkynes. For example, in the reaction of propyne and propionitrile at 140°C in the presence of a 12-electron system (5), a 2 1 ratio of benzene to pyridine product is formed, whereas a catalyst containing the cpCo moiety (a 14-electron system) leads (under identical conditions) to the predominant formation of pyridine derivatives (84HCA1616). 

The marked advantage of an in situ detection system is that it does not ingest the molecules hence it does not disturb the area, does not require as close approach to an explosive device, and it should produce a faster response time than ingesting systems. The disadvantage of in situ systems is also that they do not ingest the molecules hence they have no means of concentrating the sample... 

In 1996, the vendor stated that the average price of an in situ system, based on 60 cost estimates, was 450,000 for construction costs, 225,000 for media costs, and 775,000 for the average total cost. The vendor stated that the following factors affected treatment costs ... 

An in situ system operating at a former semiconductor facility in Cahfomia has a net present value (NPV) over a 30-year lifetime of approximately 4.4 million. This represents a 3.4 million savings over the estimated 30-year NPV for the pump-and-treat system that was formerly operating at the site. Both estimates of NPV include capital as well as operations and maintenance costs (D12777P). 

The Heck arylation of ethene with iodoarenes was investigated with a preformed [PdCl2(tppms)2] catalyst and gave the product styrenes in 60-100% yield (115). In contrast, when the in situ system Pd(OAc)2 -T 2tppms was used as a precursor, the conversion was less effective and yielded the hydration products. 

The amendments may vary for soil and groundwater treatments and in on-site and in situ systems and are, therefore, discussed in detail in sections 8.4 and 8.5. 

Park, K. Ch ng, H.S. Robinson, J.R. Alternative approaches to oral controlled drug delivery bioadhesives and in situ systems. In Recent Advances in Drug Delivery Systems Anderson, J.M., Kim, S.W., Eds. Plenum Press NY, 1984 163. 

Particle size distributions are important information for evaluating the synthesis, growth and kinetics of formation of nanoparticles and nanoparticle aggregates. The main contrasting techniques are imaging via TEM, and SAXS analysis. TEM analysis is independent of the type of aggregation, shape and size of nanoparticles, whereas SAXS interpretation requires assumptions about the nature of the sample. On the other hand, SAXS can be done on in situ systems, and often in real time during particle formation. 

After the first report in 1998 [5], Pd complexes of A -heterocyclic complexes demonstrated their high catalyst efficiency in the Suzuki coupling [6-8]. Both isolated Pd /Pd -complexes such as Structures 4-6 [5-7] and in situ systems like 7 and 8 [9, 10] have been used. A -Heterocyclic carbenes as ligands in transition-metal catalysis were also described [11]. 

The concept of electron-rich P(f catalysts is based on the analogy between nucleophilic aromatic substitution (eq. (12a)) and Pd° insertion (cf. eq. (12b)) [42 c, d]. It had previously been applied in the carbonylation of aryl chlorides [38 a, b]. Related work by Milstein [42] and Basset [43] should be consulted. High-pressure conditions seem to enhance the aryl chloride reactivity, too [44]. Meanwhile, various other methods have been developed for the selective activation of aryl chlorides with defined Pd complexes as well as in situ systems (cf. Section 3.1.6.4). 

Crane, M., Higman, M., Olsen, K., Simpson, P., Callaghan, A., Fisher, T. and Kheir, R. (2000) An in situ system for exposing aquatic invertebrates to contaminated sediments. Environ. Toxicol. Chem., 19, 2715-2719. 

Figure 4.14 Schematic drawing of the intestinal perfusion technique. The intestine of the animal is catheterised in both ends and a flow of buffer solution of 37°C is perfused using a pump. For in vitro studies in which only the absorption over the intestine is to be measured, the vascular support can be cannulated, and a separate buffer solution can be perfused through the intestine. If the influence of the liver on drug absorption is to be studied, an in situ system with an intact anaesthetised animal can be used by only perfusion of the intestine, keeping the blood flow of the vascular support intact.

Polymerization of butadiene by modified cobalt catalysts, such as the in situ system [CoIII(acac)3]/AlEt3/H20/CS2, can yield highly crystalline syndiotactic 1,2-poly-butadiene (Tm 205 °C) [35, 36], Such stereospecific polymerizations can be carried out in aqueous emulsion [37-39], and polymer latexes can be obtained (Eq. 3) [38]. A prepolymerization with a small portion of butadiene monomer in the presence of only trace amounts of water is required. A hydrocarbon solution of this prepolymerized catalyst mixture is subsequently dispersed in water together with further butadiene, and polymerization proceeds. It has been speculated that... 

Ismail MI, A New In-situ system for monitoring phase and property change in chemical engineering system, 3rd world Congress Chem Eng, Tokyo, Sep. 1986, Vol IV, 119-203, 446-449. ... 

Tsoureas et al. [61] employed a closely related system bearing an NHC/phosphine ligand in well-defined catalysts of LPdX2 formulation (X=Br,Me) or their corresponding cationic complexes. The results in the Heck coupling of aryl bromides and methyl acrylate were lower than the results using the in situ system. A maximum TON of 2,242 was achieved when the reaction was performed in NMP as solvent and NEt3 as base. 

The rat dorsal root ganglion (Minchin and Iversen, 1974), spinal ganglia (Roberts, 1974), and superior cervical ganglion (Bowery and Brown, 1972) represent in situ systems with certain advantages. They can be used for the analysis of some aspects of GABA uptake and release Radiolabeled GABA is exclusively accumulated into glial cells Thus, these preparations consist of in situ systems with normal connections intact and, therefore, little... 

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