Carbonyl complexes of palladium

It has been suggested (162) that there exists only negligible 7r-backbonding in [AuCl(CO>], and a number of displacement reactions have been described (162, 163). Vibrational and NMR spectroscopic studies have been made of this complex (164), and the results have been compared with those for carbonyl complexes of palladium, platinum, rhodium, and iridium. 

To obtain the HMC as an active component zero-valent nickel complexes of the general formula - Ni[PRj] (n=2-4), where R was Ph or EtjN, characterized by high activity in oligomerization of lower olefins in homogeneous conditions were taken. Heterogenization of these complexes was conducted by method of ligand exchange. In the Literature there are examples of carbonyl complexes of palladium prepared by this method, which show activity in propylene dimerization [8], However, we have failed to find data on such nickel catalysts in the literature. 

Rivetti, F. Romano, U. Alkoxy carbonyl complexes of palladium and their role in alcohol carbonylation. J. Organomet. Chem. 1979, 154 (3), 323-326. 

No reactions of complexes 62 and 63 have been reported. Palladium and platinum form no well-defined dinitrogen complexes. However, until relatively recently there were few carbonyl complexes of palladium and platinum. This has changed rapidly with the preparation of a wide variety of compounds such as dinuclear complexes, e.g., [M2Cl2(ju,-CO)-(ju. -dppm)2] where M = Pd, Pt, and neutral and anionic polynuclear complexes such as [Os2(CO)6 /t-Pt-(CO)(PPh3) 2] and [Pt9(CO)i8]. The absence of simple, mononuclear palladium and platinum dinitrogen complexes should not be construed as evidence that this is a barren area for research. 

The chemistry of palladium-carbonyl complexes has experienced extensive recent developments due to an increased interest in the role of palladium in surface catalysis especially in automobile exhaust catalysts. Palladium-carbonyl complexes are nevertheless stiU relatively rare, which is probably due to their relative instability in comparision with that of Ni complexes. The homoleptic Pd(CO)4 only exists at low temperatures (<80 K) in noble gas or CO matrices, in sharp contrast with isoleptic Ni(CO)4, which is stable at ambient temperature. Table 1 compiles some of the known and representative carbonyl complexes of palladium. 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

The hydrocarboxylation of styrene (Scheme 5.12) and styrene derivatives results in the formation of arylpropionic acids. Members of the a-arylpropionic acid family are potent non-steroidal anti-inflammatory dmgs (Ibuprofen, Naproxen etc.), therefore a direct and simple route to such compounds is of considerable industrial interest. In fact, there are several patents describing the production of a-arylpropionic acids by hydroxycarbonylation [51,53] (several more listed in [52]). The carbonylation of styrene itself serves as a useful test reaction in order to learn the properties of new catalytic systems, such as activity, selectivity to acids, regioselectivity (1/b ratio) and enantioselectivity (e.e.) in the branched product. In aqueous or in aqueous/organic biphasic systems complexes of palladium were studied exclusively, and the results are summarized in Table 5.2. 

A pyridine-2-carboxylato (N-0) complex of palladium(II) with a labile tosylato ligand has been shown to act as an efficient carbonylation catalyst for a series of alcohols and olefins. The catalyst precursor, [Pd(N-0)(0Ts)(PPh3)] (24), in conjunction with promoters (e.g. Lil, LiCl, TsOH), is active for the carbonylation of primary, secondary and tertiary alcohols as well as functionahzed terminal olefins with good selectivity and turnover frequency. This reaction has been further discussed in a report dealing with the kinetic modeling of this and other catalytic-carbonylation reactions. 

A homoleptic square-planar palladium(II) carbonyl complex [Pd(CO)4](Sb2Fii)2 that displays v(CO) at 2259 cm (the value for free CO is 2143 cm ) has been recently prepared. This is an exceptional complex, dubbed by the authors as superelectrophilic metal carbonyl . The very high value of v(CO) shows that the carbonyl hgands behave as a-donors (see Carbonyl Complexes of the Transition Metals). Additional data (e g. v(M )) and stability data support that this ligand is very weakly coordinated as only a a-donor. ... 

Interaction of the dibenzylideneacetone complex of palladium with a high surface area carbon gave a supported complex which on heating produced a Pd/C catalyst having a uniform distribution of palladium metal particle sizes. The rhodium carbonyls, Rh4(CO) 2 and Rh6(CO) 6, were adsorbed on silica to give... 

Hegedus and Tamura (66) postulated that reactions of acyliron, acyl-nickel, and cobalt carbonyl anions with ij -allyl complexes of palladium proceed via unstable bimetallic intermediates with bridging o-,7r-alkenyl ligands, L (RC(0))M T7 T7--CH=CHR PdL . Products isolated from the acylation of rr-allyl ligands were a,/3- and a,y-unsaturated ketones. 

Pure carbonyl compounds of palladium are not known complexes of palladium and CO have to contain further ligands to stabilize the whole complex. 

Consistent with low stability for compounds of this type, loss of carbon monoxide has been observed when metal complexes containing two adjacent carbonyl functions have been prepared by an indirect route. For example, a-ketohydrocarbyl complexes of palladium(II) or platinum(II) have been prepared by oxidative addition of the appropriate organic halide to palladium(O) or platinum(O) triphenylphosphine complexes ... 

Cy3P, i-Pr3P [201], and t-Bu3P [202]. These findings are of exceptional importance since electron-rich complexes of palladium have never been successfully used before for catalysis of SN reactions of nonactivated chloroarenes. It is also remarkable that the Pd/t-Bu3P system exhibited catalytic activity in the animation reaction [202], while failing to catalyze the carbonylation of chlorobenzene [59]. 

Cavinato, G. Toniolo, L.J. New aspects of the synthesis of dimethyl carbonate via carbonylation of methyl alcohol promoted by methoxycarbonyl complexes of palladium(II). J. Organomet. Chem. 1993, 444 C65-C66. 

E5.4 Formation of platinum and palladium clusters with carbonyl and phosphine ligands E5.5 Reactivity and flexibility in platinum metal clusters E5.6 Excited state properties of the low-valent bi- and trinuclear complexes of palladium and platinum E5.7 Interstitial nickel carbonyl clusters... 

Palladium(O) compounds have a configuration and unlike most transition metals this oxidation state is dominated by phosphine complexes rather than carbonyls. In fact binary carbonyl complexes with palladium are unstable at room temperature. The highest coordination number known for Pd is four and [PdLj complexes adopt a square planar structure. Dissociation of ligands from [PdLJ occurs readily to generate the 16- and 14-electron species [PdLs] and [Pdl ] these are trigonal planar and linear respectively. Another notable feature of Pd° is that facile oxidation to cr Pd occurs. 

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