Carbonylation of platinum

By Carbonylation of Platinum(II) Derivatives in Presence of Reducing Agents. Recently, some polymeric platinum (0) derivatives of the... 

Platinum(II) iodo carbonyl derivatives were first prepared by carbonylation of platinum iodides at high pressure and temperature. ... 

The same cluster, [PtRh5(CO)i5], may also be obtained from anionic metal carbonyls of platinum and rhodium ... 

The great majority of platinum(I) complexes are binuclear with monofunctional or bifunctional bridging groups. However, there is also a series of unsupported dimers with the general structure shown in (12). These are generally stabilized by phosphine, carbonyl, and isocyanide ligands.17 Dimeric hydride complexes can have terminal or bridging hydrides and these are discussed above in Section 6.5.2.1.4. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

While cobalt and rhodium have been the focus of most research and are the metals of choice for commercial hydroformylation reactions, numerous other metals have been disclosed as catalysts in the patent literature. However, only some of the carbonyl-forming metals can be seriously considered. Even of these, a comparison of relative reactivity (118) based on cobalt as the standard indicates a decided preference for only two or three metals. This listing may be considered incomplete without the inclusion of platinum and copper, which have recently received significant attention (vide infra). 

In Table II are listed the neutral homonuclear carbonyls of the Group VIII metals that have been identified to date. Although palladium and platinum do not have any stable neutral carbonyls, a large... 

For example, the results in Table 3 suggest that binary carbonyls of copper, silver and gold which have been detected spectrometrically in matrices at very low temperatures27, contain metal-CO bonds which are approximately of the same strength as those in Mn2(CO)i0. Similar considerations apply to carbonyls of palladium and platinum which have also been detected by matrix isolation spectrometry28. All of these binary compounds are unstable with respect to [M(c) + CO(g)J at room temperature. 

Other works related to the use of platinum carbonyl species in the preparation of catalysts, which lie beyond the scope of this chapter, refer to the synthesis in situ of supported platinum carbonylate species. For this purpose, the impregnation or exchanging of Pt precursors as [Pt(NH3)4], [Ptcy and [PtCLt] " on an appropriate support is carried out. Then, the carbonylation renders a carbonylate species that could be naked to metal frameworks by appropriate decarbonylation. 

Scheme 16.14 Convenient syntheses of platinum carbonyl compounds on the surface of Si02 (under 1 atm CO at 25°C).

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

An HP IR study of the platinum catalysed carbonylation of methanol to methyl formate, revealed that the catalyst precursor, ds-[Pt(PEt3)2Cl2] is converted into cis-[Pt(PEt3)2(CO)2] along with a cluster species, [Pt3(PEt3)3(CO) ] (n = 3 or 4) [95]. A mechanism involving oxidative addition of methanol to Pt(0) followed by CO insertion into the Pt-OMe bond was suggested. 

Platinum also is used extensively as a catalyst in hydrogenation, dehydrogenation, oxidation, isomerization, carbonylation, and hydrocracking. Also, it is used in organic synthesis and petroleum refining. Like palladium, platinum also exhibits remarkable abdity to absorb hydrogen. An important application of platinum is in the catalytic oxidation of ammonia in Ostwald s process in the manufacture of nitric acid. Platinum is installed in the catalytic converters in automobile engines for pollution control. 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

Carbonyl halide complexes of platinum(IV) are less common. The reaction of [Pt(CO)2]s with chloride ion in an aqueous solution of iron(HI) ions gives Pt(CO)H2Cl2, which adds chloride to give Pt(CO)H2ClJ.313,314 Addition of chlorine to a thionyl chloride solution of Pt(CO)2Cl2 at room temperature results in the rapid formation of Pt(CO)Cl (equation 106), which shows a carbonyl stretch at 2191 cm-1. The yellow-orange compound is stable toward Cl- but reacts with water to form C02.315... 

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