Lead compounds, redistribution reaction

These, to some extent, are related to redistribution reactions but, of course, do not lie within the scope of this review. Probably one of the first redistribution reactions of ir-bonded compounds is the exchange of carbonyl groups with 7r-bonded benzene (85) on chromium leading to the mixed compound, benzenechromium tricarbonyl. 

Many such redistribution reactions are known between organome-tallic compounds the discovery of this type of reaction is due to Calin-gaert et al 70 71>. Redistribution reactions involving lead and other Group IVb metals have been reviewed by Moedritzer224>, who calculated equilibrium constants for several of the reactions. The enthalpy change for reactions on the same metal is nearly zero, and the entropy of the system is then the principal driving force. 

The redistribution reaction in lead compounds is straightforward and there are no appreciable side reactions. It is normally carried out commercially in the liquid phase at substantially room temperature. However, a catalyst is required to effect the reaction with lead compounds. A number of catalysts have been patented, but the exact procedure as practiced commercially has never been revealed. Among the effective catalysts are activated alumina and other activated metal oxides, triethyllead chloride, triethyllead iodide, phosphorus trichloride, arsenic trichloride, bismuth trichloride, iron(III)chloride, zirconium(IV)-chloride, tin(IV)chloride, zinc chloride, zinc fluoride, mercury(II)chloride, boron trifluoride, aluminum chloride, aluminum bromide, dimethyl-aluminum chloride, and platinum(IV)chloride 43,70-72,79,80,97,117, 131,31s) A separate catalyst compound is not required for the exchange between R.jPb and R3PbX compounds however, this type of uncatalyzed exchange is rather slow. Again, the products are practically a random mixture. 

Recently, redistribution reactions between phenyllead compounds have been used to prepare triphenyllead chloride from tetraphenyllead and diphenyllead dichloride 202>, and, using mercury acetate in acetic acid as a catalyst, phenyllead triacetate from diphenyllead diacetate and lead tetraacetate, and diphenyllead diacetate from tetraphenyllead and lead tetraacetate 325>. The mercury acetate catalyst is notable in that it does not catalyze the redistribution of alkyllead compounds. 

The redistribution reaction is done at a temperature up to 150 °C. In this way, low-molecular-weight resins with an intrinsic viscosity (IV) between about 0.08 dl g and 0.16 dl g are obtained. If no additional functionalized phenolic compound is added at the redistribution step, the TMDQ is incorporated into the PPE, which leads to a PPE with a high hydroxyl content. 

The borders between the three stages are, of course, not sharp and even today the improvement of methods of preparation for simple lead alkyls such as tetraethyllead or tetrabutyllead is of great importance. But the following remarks are meant to deal mainly with the third and newest part of the development. This decision is an easy one because the developments until 1936 149), until 1952 161), and to the middle of 1963 273, 274) are treated in excellent reviews. Also there are critical reports on some topics, for instance, Catenated Organic Compounds of. .. Pb (77), redistribution reactions 185, 190), molecular complexes (76), and sulfur-containing alkyllead compounds ). The literature up to 1964 has been compiled by Dub (52). For 1964, 1965, and 1966 annual surveys 250) are available. 

Protonolysis of Pb(C2H5)4 leads to cleavage of one or two Pb-C bonds, depending on the acid and the reaction conditions, and formation of tri- or diethyllead compounds. These primary products tend to redistribute or to decompose, and in many instances, especially at elevated temperatures, lead(II) derivatives of the acid are the secondary final products, either alone or as contaminants of the primary products. No acidolytic cleavage of a third Pb-C bond or even of all four Pb-C bonds of Pb(C2Hs)4 has been observed, thus, monoethyl-lead compounds or inorganic lead(IV) compounds cannot be obtained by acidolysis of... 

Mbedritzer, K., "Redistribution reactions of organometallic compounds of silicon, germanium, tin and lead," Organometal. Chem. Rev. 1 179-278 (I966) CA 16997. 

Only two compounds containing Au-In bonds have been structurally characterized to date. They were prepared following reactions which include ligand redistribution and redox processes. Thus, the treatment of Au(PPh3)Cl with InCl (molar ratio 1 1) in THF leads only to isolation of (THF)2Cl2In-InCl2(THF)2 and no gold species were... 

Olefin metathesis has emerged as a powerful tool for the preparation of cyclic organic compounds. Metathesis involves the redistribution of carbon-carbon double bonds in the presence of metal carbene complexes ([M]=CR2). The reaction of these metal carbenes with a,co-dienes leads to well-defined carbocyclic systems in what is termed ring-closing olefin metathesis (RCM). ... 

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