Platinum synthesis activity

Of the platinum group metals only ruthenium and osmium show significant ammonia synthesis activity, though only in the presence of alkali promoters. This can be seen from the performance of the potassium metal promoted carbon-supported catalysts in Table Although osmium was one of the earliest and... 

A.n log ue Synthesis. Two notable examples, in which analogues have greater therapeutic indexes than the parent dmgs, have been identified in Phase I trials. These are carboplatin (29) and ado2elesin (37) (35). Carboplatin s approval was based on its comparable efficacy to cis-platinum (28) and its more favorable toxicity profile, ie, reduced and delayed episodes of emesis, reduced ototoxicity, etc. On the other hand, ado2elesin, a totally synthetic analogue of natural product CC1065, has demonstrated a similar potency and antitumor activity profile as its natural prototype but is devoid of the delayed death UabiUty associated with the parent dmg in animals (36). 

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

A review9 with more than 37 references includes an examination of symmetry groups and chirality conditions for C60 and C70 bonded to one or two metals in rf and/or rf fashion. Palladium and platinum rf complexes of C6o and C70 are described (novel synthesis, NMR spectra, electrochemistry) as well as first optically active organometallic fullerene derivatives. 

Zhu et al. [94] reported the synthesis of Sn02 semiconductor nanoparticles by ultrasonic irradiation of an aqueous solution of SnCLj and azodicarbonamide under ambient air. They found that the sonochemically synthesized Sn02 nanoparticles improved remarkably the performance of Li ion batteries such that there was about threefold increase (from 300 to 800 mAh/g) in the reversible capacity in the first lithiation to delithiation cycles. Similarly the irreversible capacity also increased by about 70% (from 800 to 1400 mA h/g). Wang et al. [95] reported the synthesis of positively charged tin porphyrin adsorbed onto the surface of silica and used as photochemically active templates to synthesise platinum and palladium shell and... 

Platinum complexes with chiral phosphorus ligands have been extensively used in asymmetric hydroformylation. In most cases, styrene has been used as the substrate to evaluate the efficiency of the catalyst systems. In addition, styrere was of interest as a model intermediate in the synthesis of arylpropionic acids, a family of anti-inflammatory drugs.308,309 Until 1993 the best enantio-selectivities in asymmetric hydroformylation were provided by platinum complexes, although the activities and regioselectivities were, in many cases, far from the obtained for rhodium catalysts. A report on asymmetric carbonylation was published in 1993.310 Two reviews dedicated to asymmetric hydroformylation, which appeared in 1995, include the most important studies and results on platinum-catalogued asymmetric hydroformylation.80,81 A report appeared in 1999 about hydrocarbonylation of carbon-carbon double bonds catalyzed by Ptn complexes, including a proposal for a mechanism for this process.311... 

Balthis and Bailar6 obtained tris (ethylenediamine) chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt (III) com plexes. Mori7 described the preparation of hexaamminechromium(III) salts from the oxidation of chromium (II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic.8,9 Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer,100 in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product.106 The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

A stoichiometric dehydrogenation reaction has been utilized for the synthesis of the natural product Rhazinilam in which the key step was a platinum-mediated C-H activation, followed by P-elimination (213,214). This step is shown in Scheme 50. 

This elegant organic transformation is, along with the recent development of a Pt(II)-based derivatization procedure for amino acids (221), an impressive example that platinum-mediated C-H activation offers great potential for not only the functionalization of simple small molecules but also the synthesis of complicated organic targets. 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

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