Olefin complexes, homogeneous

The seminal report of an asymmetric homogeneous metal-catalyzed reaction described the copper-catalyzed group-transfer reaction from a diazoester to an alkene, Eq. 3 (2). This article provided experimental verification of the intervention of copper carbenoid olefin complexes in the catalytic decomposition of diazo com-... 

In homogeneous systems, a- and > 3-alkylallyl complexes, as well as alkylallyl carbanions, have been prepared. Furthermore, a reversible interconversion of the /3-allyl complex to the corresponding olefin complex was demonstrated by using NMR spectroscopy. Equation (9) shows an equilibration between the /3-allylhydridotrifluorophosphinenickel complex and n-bonded propene complex (20). Brennemann affirmed also that the >/3-allyldeuterio nickel complex changes exclusively to propene-l-d, or propene-3-rf, by the reversible operation of Eq. (9). 

Such examples have shown that the role of the cationic group 4 metal complexes in the coordination polymerisation of ethylene and oc-olefins with homogeneous single-site Ziegler-Natta catalysts must not be limited to those containing cyclopentadienyl-like ligands. 

To obtain the HMC as an active component zero-valent nickel complexes of the general formula - Ni[PRj] (n=2-4), where R was Ph or EtjN, characterized by high activity in oligomerization of lower olefins in homogeneous conditions were taken. Heterogenization of these complexes was conducted by method of ligand exchange. In the Literature there are examples of carbonyl complexes of palladium prepared by this method, which show activity in propylene dimerization [8], However, we have failed to find data on such nickel catalysts in the literature. 

Ruthenium (II) Chloride. The homogeneous catalysis of the hydrogenation of fumaric acid in aqueous solution by ruthenium (II) chloride has been interpreted (36) in terms of the following mechanism in which the heterolytic splitting of H2 by a Ru -olefin complex is the rate-determining step. 

This somewhat incomplete picture can be coordinated with known facts of homogeneous catalysis. We may say that the monoolefin complexes of Ni are too unstable to be reactive, while the simple analogues of Pt are too stable optimum reactivity therefore resides in complexes of Pd and Rh where these opposing effects balance properly. We must defer for the present a discussion of the effects which other coordinated groups e.g., PR3, GO, SnGl.r) have on the reactivity of coordinated olefins since much more systematic information is needed for this to be feasible. The limited catalytic activity of olefin complexes e.g., Gu Ag ) is presumably caused by the absence from these complexes of any vacant orbitals at which attack by another reactant can occur. 

William Christopher Zeise (1789-1847) was a Danish apothecary and professor in Copenhagen, Denmark. He synthesized the first metal-olefin complex by serendipity (this term is explained in Chapter 4), when he treated platinum(IV) chloride with ethanol and potassium chloride K[PtCl3( -C2H4)], sal kalico-platinicus inflammabilis , cf [73], TT-Complexation of olefins at transition metals nowadays comprises a key feature of homogeneous catalysis in terms of olefin activation, with the Wacker-Hoechst process being a prominent example (cf. Section 2.4.1). 

Ojima and co-workers have undertaken extensive research into the formation of AT-acyl-a-amino acids via amidocarbonylation chemistry [5]. Their focus includes the generation of A -acyl-a-amino acids directly from allyl alcohols, oxiranes, or olefins using homogeneous binary catalyst systems, particularly cobalt octacarbo-nyl - Group VIII transition-metal complex combinations. New catalytic processes feature ... 

Iron pentacarbonyl and some ruthenium(III) complexes, such as RuCls 3 H2O or Ru(NH3)4(OH)Cl2, are claimed in a patent as catalysts for the hydroamination of ethylene and higher olefins in homogeneous solution [13]. 

So far as possible, the same order has been used for the fluoroalkyl derivatives in each group of transition metals a-bonded alkyl, alkenyl, and alkynyl derivatives, 7r-bonded derivatives, and then derivatives bonded via N, P, O, or S in that order. In some cases, notably olefin complexes, there is ambiguity about the bonding and this should be borne in mind when searching for particular compounds. Fluoroaryl and heteroaryl derivatives form a more homogeneous group of compounds, and their parameters are considered together across the transition series. 

Nickel(O)—olefin complexes sueh as tris(ethylene)nickel(0) and tris(bicyelohep-tene)nickel(O) are highly active homogeneous catalysts for the transalkylation of tri-alkylaluminum with terminal olefins [25]. After completion of the reaction, the naked nickel(O) can be removed in the form of Ni(CO)4 by reaction with carbon monoxide. 

Transition-metal complexes of olefins have been extensively studied as possible intermediates in homogeneous catalysis. However, in recent years, it has been recognized that olefin complexes are extremely useful intermediates for synthesis of many other transition-metal complexes. The olefin ligand is often labile and is easily replaced by a phosphine or by carbon monoxide. 

Ruthenium-hydridophosphine complexes are well-known homogeneous hydrogenation catalysts . In some cases stable >/ -olefin complexes can be isolated. Thus ethylene and styrene react with RuH2(PPh3)4 to yield the Ru(0) complexes, Ru(PPh3)3(olefin). These reactions are accompanied by olefin hydrogenation " ... 

Table I. Olefin polymerization results with selected vanadium complexes (Homogeneous conditions) ...

Asymmetric epoxidation of olefins with homogeneous chiral (salen) Mn(III) complex 13COC2936. 

Oxo Synthesis. Ad of the synthesis gas reactions discussed to this point are heterogeneous catalytic reactions. The oxo process (qv) is an example of an industriady important class of reactions cataly2ed by homogeneous metal complexes. In the oxo reaction, carbon monoxide and hydrogen add to an olefin to produce an aldehyde with one more carbon atom than the original olefin, eg, for propjiene ... 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

A new homogeneous process for hydroformylation of olefins using a water-soluble catalyst has been developed (40). The catalyst is based on a rhodium complex and utilizes a water-soluble phosphine such as tri(M-sulfophenyl)phosphine. The use of an aqueous phase simplifies the separation of the catalyst and products (see Oxo process). 

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