Platinum metals, carbonyl halides carbonyls

A particularly interesting case is that of the platinum metal group which, in addition to platinum (Pt), comprises ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), and palladium (Pd). These carbonyl halides are usually the most practical precursors for metal deposition because of their high volatility at low temperature. Indeed two of them, palladium and platinum, do not form carbonyls but only carbonyl halides. So does gold. 

The hydrogen reduction of the metal halides, described in Sec. 1.2, is generally the favored reaction for metal deposition but is not suitable for the platinum-group metals since the volatilization and decomposition temperatures of their halides are too close to provide efficient vapor transport. 1 1 For that reason, the decomposition of the carbonyl halide is preferred. The exception is palladium which is much more readily deposited by hydrogen reduction than by the carbonyl-halide decomposition. 

These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

Recent literature describes the synthesis of vinyl esters in the presence of platinum metal complexes. Complexes which have proven particularly suitable in this context are those of ruthenium (eq. (15)), such as, for example, cyclooc-tadienylruthenium halides [36], ruthenium carbonyl complexes, and ruthenium acetate complexes [37]. A characteristic feature of these is their high selectivity with regard to acetylene, so that the production of acetylene polymers is reduced. 

The syntheses of RhHCPfCsH,),] and RhH(CO)[P(C H5)3]3 described herein are members of a group of preparations each involving addition of a platinum metal halide or halo complex and sources of hydride, carbonyl, and/or nitrosyl ligands to a briskly boiling solution of triphenylphosphine in an alcoholic solvent. ... 

The most stable carbonyl halides of group 10 metals are those of platinum. [PtX2(CO)2] and [PtX2(CO)]2 are prepared by reaction of PtX2 (X = C1, Br, I) with carbon monoxide under pressure. These compounds have the following structures ... 

Carbonyl halides of the platinum group metals, however, are often prepared by reacting the metal halide with carbon monoxide. [Ru(CO)3Cl,], and [Rh(CO),Cl], are mentioned above (p. 167). Platinum forms Pt(CO),X, and [Pt(CO)X,],. The latter were the first carbonyl complexes of any element to be described. They were reported by the French chemist, P. Schutzenberger, in 1870. 

More recently, methods based on the use of mild reductants, able to transfer a single electron to the polyhaloalkyl halide, have been described. Various metals or their derivatives have been employed ruthenium, platinum and their complexes in low oxidation state, iron" and its carbonyl complexes, or tetrakis(triphenylphosphane)palladium. Sodium arcncsul-finate, sodium dithionite" and various oxidants have also been used. Other examples of polyhaloalkyl halide additions to simple alkenes are summarized in Table 1. Typical examples are the formation of diiodide 6, chloro iodide 7, and iodo steroid 8. ... 

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 ... 

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