Palladium carbonyl clusters

Relatively few investigations involving palladium carbonyl clusters have been carried out, partly because palladium per se does not form stable, discrete homometallic carbonyl clusters at room temperature in either solid or solution states.114,917-922 Nevertheless, solution-phase palladium carbonyl complexes have been synthesized with other stabilizing ligands (e.g., phosphines),105,923 and carbon monoxide readily absorbs on palladium surfaces.924 Moreover, gas-phase [Pd3(CO)n]-anions (n = 1-6) have been generated and their binding energies determined via the collision-induced dissociation method.925... 

Polynuclear platinum and palladium carbonyl clusters containing the bulky tri-ferf-butylphosphine ligand are inherently electron-deficient at the metal centers. The trigonal bipyramidal cluster [Pt3Re2(CO)6(P Bu3)3], as shown in Fig. 11.4.4(a), is electronically unsaturated with a deficit of 10 valence electrons, as it needs 72 valence electrons to satisfy an 18-electron configuration at... 

Under conditions similar to those used for the formation of this palladium carbonyl cluster, another palladium carbonyl cluster was formed in zeolite 5A. It has been suggested to be [Pd6(CO)j,], where y is unknown. Again, the suggestion [49] is speculative but the synthesis and the compound are novel. 

Formation of palladium carbonyl clusters entrapped in faujasites and consistent with the geometric constraints in the supercages are reported by Sachtler et al. [110]. Terminal, doubly and triply bridged CO species could be distinguished. After argon purging they were able to classify the terminal complexes into Pd +-CO, Pd -CO and Pd°-CO in the sequence of decreasing CO frequency. 

Phosphine palladium and phosphine platinum carbonyl cluster compounds. N. K. Eremenko, E. G. Mednikov and S. S. Kurasov, Russ. Chem. Rev. (Engl Transl.), 1985, 54, 394 (69). 

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... 

The dominant role of copper catalysts has been challenged by the introduction of powerful group VIII metal catalysts. From a systematic screening, palladium(II) and rhodium(II) derivatives, especially the respective carboxylates62)63)64-, have emerged as catalysts of choice. In addition, rhodium and ruthenium carbonyl clusters, Rh COJjg 65> and Ru3(CO)12 e6), seem to work well. Tables 3 and 4 present a comparison of the efficiency of different catalysts in cyclopropanation reactions with ethyl diazoacetate under standardized conditions. 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

Comparing these results for CO bonded to Ni(lOO) and Pd(lOO) to the structure of metal carbonyl clusters, one finds that the multiply-coordinated CO on palladium has... 

A number of reports of high nuclearity palladium clusters have been made in recent years. Palladium halocarbonyl clusters of unspecified nuclearity [PdX(CO)] (X = C1, Br) have been prepared by several groups of workers through the carbonylation of [PdCl2(MeCN)2] or PdX2 (X = Cl, Br).112-114 These decompose in solution to give Pdn and Pd°. When Na PdClJ was used as a precursor, then an anionic palladium(II) dimer (22) resulted.113... 

Their number, however, is small compared to the rich cluster chemistry found for other transition metals, possibly because of the lower stability of palladium carbonyls. High nuclearity clusters are dealt with in another article (see Polynuclear Organometallic Cluster Complexes). 

Carbonylation of different palladium complexes, often in the presence of phosphines, led to the synthesis of a variety of clusters including halocarbonyl clusters of unknown nucle-arity [PdX(CO)] (X = Cl, Br), and phosphine-carbonyl clusters from tetrameric [Pd4(CO)s(PR3)4] to high nuclear-ity compounds such as [Pd38(/r -CO)4(/u. -CO)24(PEt3)i2]. From these preformed clusters, nanosized cluster compounds of higher nuclearity such as [Pd69(CO)36(PEt3)ig] can be prepared. ... 

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