Platinum carbonyl compounds

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

We were able to prepare (63) iron carbonyl halides of lower carbon monoxide content, Fe(CO)2X2, which are formally related to the long-known platinum carbonyl compounds (62), e.g.,... 

No kinetic studies have been made on platinum carbonyl compounds however, the carbonylation reaction of the tetrasubstituted phosphine derivatives of platinum (0) is slow enough for the tricoordinated compounds to isolate. The following steps have been proposed (38). 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

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 palladium and platinum metals also form carbonyl compounds. Of the expected compounds Pd(CO)4, Pt(CO)4, Ru(CO)5, Os (CO) 5, Mo-(CO)e, and W(CO)6 only Mo(CO)e has been prepared, although some unsaturated ruthenium carbonyls have been prepared. The compounds Pd(CO)2Cl2, Pt(CO)2Cl2, K[PtCOCl3], etc., show the stability of the four dsp2 bonds. It would be interesting to determine whether or not each CO is bonded to two metal atoms in compounds such as [Pt(CO)Cl2]2, whose structure is predicted to be... 

As mentioned in Section 3.2, hydrogenation is by far the most investigated catalytic reaction and palladium the most commonly employed metal, followed by platinum. The most common substrates for catalytic hydrogenation tests are simple alkenes, cyclic alkenes and unsaturated carbonylic compounds. In the latter case, conjugated substrates (a,P-unsaturated aldehydes, acrylic acid) have received particular attention. 

Consequently, by choosing proper conditions, especially the ratios of the carbonyl compound to the amino compound, very good yields of the desired amines can be obtained [322, 953]. In catalytic hydrogenations alkylation of amines was also achieved by alcohols under the conditions when they may be dehydrogenated to the carbonyl compounds [803]. The reaction of aldehydes and ketones with ammonia and amines in the presence of hydrogen is carried out on catalysts platinum oxide [957], nickel [803, 958] or Raney nickel [956, 959,960]. Yields range from low (23-35%) to very high (93%). An alternative route is the use of complex borohydrides sodium borohydride [954], lithium cyanoborohydride [955] and sodium cyanoborohydride [103] in aqueous-alcoholic solutions of pH 5-8. 

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. 

The transformation of alcohols to the corresponding carbonyl compounds or carboxylic acids is one of the few examples in which a heterogeneous (solid) catalyst is used in a selective, liquid phase oxidation (7,2). The process, which is usually carried out in an aqueous slurry, with supported platinum or palladium catalysts and with dioxygen as oxidant, has limited industrial application due to deactivation problems. 

This section on platinum carbonyl complexes should be read in conjunction with the comparable chapter by Hartley in Comprehensive Organometallic Chemistry , Volume 6, Chapter 39. This section will emphasize very recent work and will omit compounds which are completely organometallic in nature. 

Lower aliphatic amines are widely used as intermediates for the synthesis of herbicides, insecticides and drugs or can be applied as rubber accelerators, corrosion inhibitors, surface active agents etc. [l]. The most widespread method for the preparation of lower aliphatic amines involves the reaction of ammonia with an alcohol or a carbonyl compound in the presence of hydrogen. The most common catalysts used for reductive amination of alcohols, aldehydes and ketones contain nickel, platinum, palladium or copper as active component [ I — 3 ]. One of the most important issues in the reductive amination is the selectivity control as the product distribution, i.e. the ratio of primary to secondary or tertiary amines, is strongly affected by thermodynamics. 

The palladium peroxometallic adducts were found to be less stable than the platinum analogs and decompose mainly by C—C bond cleavage to carbonyl compounds (equation 49).143 A similar decomposition may occur in the oxidation of ketoximes to ketones by Pd02(Ph3P)2 (equation 50).195... 

Cluster Compounds.—An interesting new series of platinum carbonyl dianions of formula [Pt3(CO)3(p2-CO)3]2 n = 2—5) have been synthesized by reduction of [PtClg]2" with CO and methanolic NaOH.107 Species with decreasing n were isolated with increasing concentration of reducing agent (equation 18). The X-ray... 

The allylation of carbonyl compounds with allyltin reagents is still an active area of organotin chemistry from the methodological point of view, and also for synthetic applications. For completeness we should add several alternative techniques, such as the development of trifluoromethanesulphonic acid as a Bronsted acid catalyst for the allylation of aldehydes in water123, or the design of fluorous allyltin reagents for the platinum-catalysed allylation of aldehydes124. 

The characteristics of the electrooxidation of fluorosulfate anions in the electrolysis of a potassium fluorosulfate solution in fluorosulfonic acid have been investigated. The formation of oxide layers on platinum and the modification of glassy carbon with fluorosulfate groups during anodic polarization in fluorosulfonic acid are studied. The reactions of fiuoroolefin fluorosulfation are considered and a mechanism is suggested223. Trifluoromethylation of carbonyl compounds can be achieved using bromo-trifluoromethane and a sacrificial electrode in solvents such as DMF/pyridine, and DMF/TMEDA, as seen in equation 126224. 

Carbon monoxide has been found to be surprisingly reactive toward the metals in Group VIII, in both their oxidized and unoxidized states. A sizable number of compounds exist in which one or more CO molecules are attached to a metal atom through the carbon typical of these are nickel tetracarbonyl, Ni(CO)4, iron pentacarbonyl, Fe(CO) cobalt carbonyl hydride, Co(CO)4H platinum carbonyl chloride, Pt(CO)2Cl2 and more complicated molecules such as Co4(CO)i2. 

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