Palladium mixed-metal clusters

The reaction with [Mn(CO)5]2 or [Co(CO)4]2 also led to mixed-metal clusters.962,963 Osmium-palladium mixed-metal carbonyl clusters were made using the unsaturated cluster [Os3(CO)io(/r-H)2] and the carbido cluster [Os5(/U5-C)(CO)15].964 970 Treatment of [Os3(CO)10Gu-H)2] with [Pd2(/u-dppm)2Cl2] afforded the novel high-nuclearity osmium-palladium mixed-metal carbonyl clusters [Os5Pd6(CO)13( -CO)5(/u-H)2(/u-dppm)2], [Os5Pd6(CO)13(//-CO)6(/u-dppm)2], and... 

Imido dialkyl complexes, with tantalum, 5, 120 Imido-dicarbenes, with palladium, 8, 228-229 Imido groups, in Ru-Os mixed-metal clusters, 6, 1078 Imido hydrocarbyl complexes, with Re(VII), 5, 945 Imido ligands... 

The first mixed-metal cluster of Os-Pd, [Os6Pd(bipy)(CO)i8], was reported in 1994, and since then a variety of mixed-metal cluster that contain various Os Pd ratios have been created. Palladium-pyridine complexes appear to be useful reagents in the synthesis of mixed-metal clusters with osmium carbonyl compounds. " The reaction of the coordinately unsaturated cluster [Os3(yu-H)2(CO)io] with [Pd(NH3)2l2] afforded a number of Os-Pd clusters with a high hydride content. " Both palladium phosphine and bidentate phosphine complexes are useful in the preparation of high-nuclearity mixed-metal clusters. The reaction of [Os3(/i-H)2(CO)io] with [Pd2(/i-dppm)2Cl2] gave 258 and 259, in addition to 260, with the same metal core, " in which the molecule contains a twofold symmetry axis. " " ... 

Supported mixed metal catalysts are also prepared by other means such as the deposition of bimetallic colloids onto a support O and the decomposition of supported bimetallic cluster compounds.208 The photocatalytic codeposition of metals onto titania was also attempted with mixed results.209 with a mixture of chloroplatinic acid and rhodium chloride, very little rhodium was deposited on the titania. With aqueous solutions of silver nitrate and rhodium chloride, more rhodium was deposited but deposition was not complete. In aqueous ammonia, though, deposition of both silver and rhodium was complete but the titania surface was covered with small rhodium crystallites and larger silver particles containing some rhodium. With a mixture of chloroplatinic acid and palladium nitrate both metals were deposited but, while most of the resulting crystallites were bimetallic, the composition varied from particle to particle.209... 

Other metallic clusters that have been demonstrated to show the QDL effect are palladium [116, 117], silver [118] and copper [119]. Palladium MFCs capped with mixed monolayers of hexanethiolate/dodecanethiolate and ferrocene thiolate ligands are prepared in a manner similar to that employed for gold MFCs. The DPV studies exhibit a quantized charging effect but the current peaks are not as well defined as those observed for Au-MPCs. Capacitance values of the order of 0.35 aF are obtained, indicating smaller core sizes or thicker monolayer dielectrics [116]. 

It is noteworthy that besides highly dispersed palladium clusters, ionic Pd was also detected by ESR in Pd/Li-AbOa catalysts prepared by anchoring PdCb onto alumina modified with butyl lithium. These catalysts were highly active and selective in the hydrodechlorination of substituted aromatic compounds. The coexistence of Pd and Pd° in the Pd/Li-AbOa catalysts suggests the possible formation of mixed metal ion - metal nanocluster ensemble sites. 

The activity of [PPN][Rh(CO)4] is higher than that of all other rhodium-based catalytic systems (although lower than the one of several palladium-based ones) and a catalytic ratio of 300 was used in order to avoid to reach complete conversion in 1.5 h. As for the mixed-metal anionic clusters, [Rh(CO)4] is active even in the absence of any added base (run 1), but the addition of Bipy greatly enhances its activity, with the ideal Bipy/Rh molar ratio being 3 (runs 2-5). Use of Phen in place of Bipy gave worse results (run 6) whereas use of the tridentate Terpy (2,2 ,6 ,2 -terpyridine) gave a somewhat higher conversion, but a lower... 

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