Platinum-sulfur clusters

Platinum-ruthenium carbonyl clusters, characteristics, 8, 419 Platinum-sulfur bonds, in platinacycles, 8, 505 Platinum-thallium carbonyl clusters, characteristics,... 

Thus the Shell workers conclude that Pt-Re bonds are present at the surface in platinum-rhenium catalysts, whether or not chemisorbed sulfur is present. A platinum-rhenium entity of the type envisioned by these investigators, if it indeed exists, could also be called a bimetallic cluster. 

Reactions between the sulfur-containing amino acids cysteine and methionine (Fig. 2.18) and rufhenium(II) arene anticancer complexes are of much interest in view of the strong influence of sulfur amino acids on the intracellular chemistry of platinum drugs, their involvement in detoxification and resistance mechanisms [100]. We found [101] that [(ri -biphenyl)Ru(en)Cl][PF 5] reacts slowly with the thiol amino add L-cysteine in aqueous solution at 310 K, pH 2-5, and only to about 50% completion at a 1 2 mM ratio. Reactions appeared to involve aquation as the first step followed by initial formation of 1 1 adducts via substitution of water by S-bound or O-bound cysteine. Two dinuclear complexes were also detected as products from the reaction. In these reactions half or all of the chelated ethylene-diamine had been displaced and one or two bridging cysteines were present The unusual cluster species (biphenyl) Ru g was also formed espedaUy at higher cysteine concentrations. The reaction was suppressed in 50 mM triethylammo-nium acetate solution at pH > 5 or in 100 mM NaCl suggesting that thiols may not readily inactivate Ru(II)-en arene complexes in blood plasma or in cells. Similarly, reactions with the thioether sulfur of methionine appeared to be relatively weak. Only 27% of [(r -biphenyl)Ru(en)Cl][PF5] reacted with L-methionine (L-MetH) at an initial pH of 5.7 after 48 h at 310 K, and gave rise to only one adduct [(ri -biphenyl) Ru(en) (i-MetH -S)]. ... 

The dehydrocyclization of n-hexane catalyzed by platinum-loaded alkali L zeolite reported by Bernard [34] became the subject of recent industrial development [35]. In contrast to the acidic commercial reforming catalyst, the new L zeolite catalyst reported by Hughes et al. [35] is nonacidic Pt-BaK-L zeolite. Prestimably, the properties of platinum clusters by themselves account for all the catalytic activity. The catalyst is extremely sensitive to poisoning by sulfur, but with a thoroughly desulfurized feed, a one-year run has been successfully completed with refinery light naphta. 

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