Palladium complexes clusters

There has been great interest in the preparation of bimetallic transition metal cluster complexes containing palladium.899-902 Bimetallic palladium-ruthenium clusters have been shown to be good precursors to supported bimetallic catalysts.903,904... 

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... 

Other electron-poor clusters include the 44-electron Pt3(CO)3(PPh3)4 and the 42-electron species Pd3(CO)3(PPh3)3 and [Re3Cl12p. For the 44-electron system, the 18-electron rule predicts two double bonds within the M3 triangle and for the 42-electron complexes, three double bonds. The structures of the platinum and palladium complexes are unknown, but the Re-Re distances of 2.47-2.49 A in the anion [Re l ]3- are regarded (20) as short and consistent with a formal bond order of two. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Complex compounds obtained on the basis of phosphoranimine 409 [712a] and diaminophosphine 410 [520] ligands are of considerable interest. Complex compounds of the types 408 and 410 are represented in general by chelates, and 409 by cluster structures. N,P-Bidentate ligands and their rhodium and palladium complexes are described in a recent review [712b],... 

The heterometallic cluster compounds [Pt(AuPPh3)8](N03)2 and [Pd(AuPPh3)8](N03)2, synthesized by the coreduction of platinum or palladium complexes and Au(PPh3)N03 (117, 123, 124), both adopt a... 

Pyridyldiphenylphosphine forms a number of homo-and heteronuclear palladium dinuclear clusters with short Pd-M bonds (about 260 pm). They are usually made by comproportionation of a Pd(II) complex and a second complex in a low oxidation state, for example, Pd(0), Rh(I), Ru(0). For these derivatives, head-to-head and head-to-tail isomers are possible, but the latter seems to be preferred (Figure 2). The metal-metal bonds in these derivatives are not as reactive as in the corresponding dppm complexes and insertion reactions do not occur. Some single-bridged complexes, such as [Cp(CNR)Rh(/u.-PPh2Py)Pd(CNR)Cl]+ (Pd-Rh distance 263.1 pm) are also known. 

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. ... 

The reactivity of palladium and copper cluster models toward diazirine has been compared using the LCGTO-MCP-LSD method <1996SUS11> such calculations were performed to give an insight into the differential bond scission experimentally observed in the thermal decomposition of diazirine on palladium and copper surfaces. Stronger chemisorption was evident with palladium and furthermore, partial diazirine lowest-unoccupied molecular orbital (LUMO) occupation only occurred for the copper cluster model systems. The calculated N-N bond order was significantly decreased in the copper complexes of excited state diazirines, whereas palladium complexes remained unperturbed. 

By this time, substantial experience in the synthesis of low-valence noble metal complexes in the form of non-crystalline, colloid-like samples has been accumulated. For instance, a series of amorphous, high-molecular weight palladium complexes, which had remarkable catalytic capability, had been obtained starting from low-nuclearity Pd(I) clusters and Pd(II) complexes. ... 

The palladium complex Pd(MeCN)2Cl2 is actually decomposed under the reaction conditions to form catalytically active nano-sized palladium clusters. However, in the case of less reactive aryl halides bearing electron-donating groups, e.g. 4-bromo toluene, addition of 10 mol% of P(0/-Pr)3 as stabilizing ligand for zero-valent palladium was necessary to rich high conversions. 

Ferrocene was the first organometallic guest incorporated and numerous spectroscopic and electrochemical studies have been performed on ferrocene, substituted ferrocene, and related metallocene (e.g. cobaltocene) inclusion complexes (444-469]. Half-sandwich cyclopentadienyl- and benzene-metal carbonyl complexes have also been studied quite extensively [470-479] as have // -allyl metal (palladium) complexes [480], diene metal (rhodium) complexes [481-484], acetylene cobalt carbonyl cluster complexes [485], and complexes with metal carbonyls, e.g. Fe(CO)5, Mn2(CO)io, and CoNO(CO)3 [485a]. 

Complexes of other transition metals have been reported to catalyze Pauson-Khand reactions. Buchwald reported intramolecular PKRs with 1.2 atm of CO at 90 °C in the presence of CpjTi(CO)2. " However, most other catalytic Pauson-Khand reactions have been conducted with late transition metal catalysts. Murai and Mitsudo simultaneously reported intramolecular PKRs catalyzed by ruthenium carbonyl clusters in dioxane or DMAc at 140-160 °C under 10-15 atm of CO. The first Rli-catalyzed PKR was reported by Narasaka. ° In this case, the reaction occurred with acceptable rates, even with CO pressures less than 1 atm. Shibata reported PKRs in refluxing xylenes under 1 atm of CO in the presence of catalytic amounts of PPli and [Ir(COD)Cl]2. Adrio and Carretero showed that the solvated molybdenum carbonyl complex Mo(DMF)3(CO)3 catalyzed intramolecular PKRs with monosubstituted olefins, as well as with disubstituted electron-poor olefins, and Hoye showed that W(CO)5(THF) catalyzes intramolecular PKRs. Iron and palladium complexes have also been reported to catalyze the PKR. 

Under different experimental conditions, the reaction of [PdQ2(PPh3)2] with E(SiMc3)2 (E = S, Se, lb) can also lead to other multinuclear palladium complexes. It is quite remarkable, however, that these complexes bear no relationship to the nickel complexes already mentioned. For example, there is no indication that a [PdgE6(PR3)s] cluster having a cubic Pdg framework, or an octahedral... 

---