Diolefins, carbonylation

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. 

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. 

Both conjugated and nonconjugated olefins form complexes with the transition-metal carbonyls. Despite the fact that the first known complex, Zeises salt K(PtC2H4Cl3), discovered in 1827, was that of a simple olefin, complexes of monoolefins are rather limited in number. However, nonconjugated diolefins (L) react with group-VI carbonyls to form complexes of the type LM(CO)4 an example is provided by tetracarbonyl-bicyclo-(2,2, l)hepta-2,5-diene chromium (2) (Fig. 1). In contrast, the iron carbonyls... 

Linear and cyclic diolefins form a variety of clusters with trirutheniumdodeca-carbonyl or the tetraruthenium carbonyl hydrides. These belong to the compound types H2Ru3(CO)9L [56] or HRu3(C0)gl/ [55]. Type [56] complexes are obtained from cyclopentadienes (27 7), cyclooctadienes (74), or bicyclooctadiene (146). 

This reaction could explain the decomposition of alkylcobalt tetra-carbonyls under nitrogen and also the reactions observed by Bertrand et al. (14) in which 1-butene gave various nonanones, and some diolefins gave cyclic ketones. 

Kranemann CL, Eilbracht P (1998) One-pot synthesis of tertiary a,catalyst precursor. Synthesis 1998(01) 71—77, 10.1055/s-1998-4481... 

Among the complexes which may function in this way are pentacyano-cobaltate ion, iron pentacarbonyl, the platinum-tin complex, and iridium and rhodium carbonyl phosphines. It has been suggested that with tristriphenylphosphine Rh(I) chloride, a dihydride is formed and that concerted addition of the two hydrogen atoms to the coordinated olefin occurs (16). There are few examples of the homogeneous reduction of other functional groups besides C=C, C=C, and C=C—C=C penta-cyanocobaltate incidentally is specific in reducing diolefins to monoolefins. 

Displacement of weakly coordinating ligands is also very effective. Common ligands that form weakly stabilized complexes with metals include acetonitrile, ethylene, and other mono- and diolefins. The metal nucleophile may be a metal carbonyl anion, a metal hydride, or a neutral, low-valent metal complex ... 

The controlled synthesis of Ti-d8 early-late heteropolynuclear diolefin and carbonyl clusters has been reported. The synthetic approach was based on deprotonation reactions involving Gp2Ti(SH)2 and appropriate rhodium and iridium diolefin and carbonyl compounds. The catalytic activity of some representative Ti-Rh compounds toward alkene hydroformylation has been explored.1778... 

The anion [(CpTiS)2(/x-S)]22 obtained by monodeprotonation of Cp2Ti(SH)2 with LiBuc in THF reacts with complexes [M(/i-Cl)(diolefin)]2 (M = Rh, Ir) to give the tetranuclear derivatives CpTi(/i3-S)3M3(diolefin)3. Carbonylation reactions and further treatment with P-donor ligands afford Rh- and Ir-substituted complexes CpTi(/i3-S)3M3Lx (Scheme 712). Spectrocopic data indicate fluxional behaviour in solution. Structural studies and... 

The fragment CpTi(acac)S2 is considered as an S-donor metalloligand that supports the binuclear moiety Ir2(CO)4 in the complex CpTi(acac)(/i3-S)2[Ir(CO)2]2, which is obtained upon carbonylation of CpTi(acac)(//3-S)2[Ir(diolefin)2]2. In this Tilr2 system the titanium fragment, as a metalloligand, exerts important steric and electronic influences on the reactivity of the Ir metal toward electrophiles. Thus, the reactivity of this complex with iodine, alkyl iodides, and activated acetylenes has been studied.1798... 

Wittig-oiefination.1 The N-bridgehead bicyclic amides (1) and (2) react with (ethoxycarbonylmethylene)triphenylphosphorane or (cyanomethylene)triphenylphos-phorane to form mono- and diolefins. The reaction takes place preferentially at a five-membered carbonyl group. 

Cobalt forms few complexes of monoolefins, although diolefins react with Co2(CO)g without cleavage of the Co( t-CO)2Co bridge . Similarly, monoolefins do not displace CO from rhodium carbonyl, although diolefins react with Rh6(CO)ig to form a complex series of products . 

A number of chelating diolefin complexes of group-VIA metal carbonyls have been prepared by refluxing the hexacarbonyl in a hydrocarbon solvent " ... 

Acetonitrile complexes of the group-VIA metals are useful intermediates in the development of the chemistry of those metals. Three carbonyl ligands of M(CO)s, where M = Cr, Mo or W, are replaced by acetonitrile when the hexacarbonyls are refluxed in that solvent . When [M(CO)3(CH3CN)j] is treated with chelating diolefins the three acetonitrile ligands together with one carbonyl ligand are displaced to form M(diolefin)2(CO)2 ... 

Neutral and anionic organoimidoimido clusters of rhodium)I) with diolefin and carbonyl ligands are accessible and stable. The diolefin neutral compounds [Rh4(/i-N-/7-tolyl)2(diolefin)4] are a convenient entry into this chemistry for which the synthetic route is an apparently simple replacement reaction, but the reproducibility of the results requires a careful technique. These tetranuclear compounds contain a trimetallic triangular cluster face capped on both sides by two pnra-toly-limido ligands and a further rhodium fragment coordinated to a para-to y ring in a 7 -fashion, giving an overall valence electron count of 64e. 

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