Metal halides, condensation with carbonyl

Just as for group 5, 6, and 7 ( -CsF MCU species, Fehlner has shown that BH3-THF or Li[BH4] react with group 8 and 9 cyclopentadienyl metal halides to result in metallaborane clusters, many of them having a metal boron ratio of 1 3 and 1 4, and much of the synthetic chemistry and reactivity shows close connections with the earlier transition metals. The main difference between the early and later transition metallaboranes that result is that the latter are generally electron precise cluster species, while as has been shown, the former often adopt condensed structures. Indeed, as has been pointed out by King, many of the later transition metallaborane clusters that result from these syntheses have structures closely related to binary boranes and, in some cases, metal carbonyl clusters such as H2Os6(CO)18.159... 

Related synthetic routes include the redox condensation reaction of carbonylate anions with neutral carbonyls, e.g., Eq. (12) (55), metal exchange reactions between carbonylate anions, e.g., Eq. (13) (56), and direct reductive carbonylation of metal halides, e.g., Eq. (14) (57). The stoichiometry of the products are not rational, and the mechanisms clearly are very complicated, though once again these reactions, under experimental optimization, can provide very useful synthetic routes. 

Polymerization of olefins such as styrene is promoted by acid or base or sodium catalysts, and polyethylene is made with homogeneous peroxides. Condensation polymerization is catalyzed by acid-type catalysts such as metal oxides and sulfonic acids. Addition polymerization is used mainly for olefins, diolefins, and some carbonyl compounds. For these processes, initiators are coordination compounds such as Ziegler-type catalysts, of which halides of transition metals Ti, V, Mo, and W are important examples. 

Reaction XLIV. (b) Condensation of Alkyl and Aryl Halogen Compounds with the Sodio- and other Metallo-derivatives of Ethyl Aceto-acetate and its Homolognes. (A., 186, 214 201, 143 213, 143.)—Like malonic ester, acetoacetic ester contains two 1 3-carbonyl groups with a methylene group in position 2. It is only to be expected then that it yields with metallic sodium or sodium alcoholate sodio-derivatives from which mono- and di-, alkyl and aryl homologues can be obtained by treatment with a suitable halide, including halogen esters. Acetoacetic acid... 

The reaction occurs well below the temperature at which most of the parent metal carbonyls exchange with free CO and so is a direct nucleophilic attack on coordinated CO, although it may alternatively proceed via a prior electron path. The resulting acyl anions can be isolated as their [R4N] " or [ (C6H5)3P 2N] salts but are reactive and are used directly in subsequent alkylations with organic halides, acetylenes, a-/i-unsaturated carbonyls and alkyloxonium salts to form organic condensation products or metal-carbene complexes. 

The intermediate metal hydride has been isolated on occasion for Co and Mn , and Eq. (b) has actually been used to prepare silicon-metal bonds (see 5.2.3.2.2.). Inspection of Table 1 reveals the ease of reaction of Co2(CO)g compared with the other carbonyls. Normally this reaction is performed simply by condensing volatile silane onto the carbonyl in the absence of solvent and then allowing rapid reaction in the liquid phase at room temperature, but for the remaining carbonyls it is necessary to use elevated temperatures and sealed, evacuated tubes. The products are volatile and readily purified by vacuum fractionation or sublimation, but are often oxygen and moisture sensitive. The route is most efficient for RjSi derivatives of Co, Mn and Re, which are not generally obtainable by the reactions of silicon halides with metal carbonyl anions (see S.8.3.3.I.). In this way lCo(SiR,)(CO -] = Et, Phj, Clj -, (OEt)j, F/, ... 

---