Olefins, complexes with

The use of silver fluoroborate as a catalyst or reagent often depends on the precipitation of a silver haUde. Thus the silver ion abstracts a CU from a rhodium chloride complex, ((CgH )2As)2(CO)RhCl, yielding the cationic rhodium fluoroborate [30935-54-7] hydrogenation catalyst (99). The complexing tendency of olefins for AgBF has led to the development of chemisorption methods for ethylene separation (100,101). Copper(I) fluoroborate [14708-11-3] also forms complexes with olefins hydrocarbon separations are effected by similar means (102). 

Olefin Complexes. Silver ion forms complexes with olefins and many aromatic compounds. As a general rule, the stabihty of olefin complexes decreases as alkyl groups are substituted for the hydrogen bonded to the ethylene carbon atoms (19). 

Tetracyanoethylene is colorless but forms intensely colored complexes with olefins or aromatic hydrocarbons, eg, benzene solutions are yellow, xylene solutions are orange, and mesitylene solutions are red. The colors arise from complexes of a Lewis acid—base type, with partial transfer of a TT-electron from the aromatic hydrocarbon to TCNE (8). TCNE is conveniendy prepared in the laboratory from malononitrile [109-77-3] (1) by debromination of dibromoma1 ononitrile [1855-23-0] (2) with copper powder (9). The debromination can also be done by pyrolysis at ca 500°C (10). 

Scheme 60 Reaction of a diruthenium disulfido complex with olefins...

Scheme 61 Plausible mechanism for the reaction of diruthenium disulfido complexes with olefins...

Iron hydride complexes can be synthesized by many routes. Some typical methods are listed in Scheme 2. Protonation of an anionic iron complex or substitution of hydride for one electron donor ligands, such as halides, affords hydride complexes. NaBH4 and L1A1H4 are generally used as the hydride source for the latter transformation. Oxidative addition of H2 and E-H to a low valent and unsaturated iron complex gives a hydride complex. Furthermore, p-hydride abstraction from an alkyl iron complex affords a hydride complex with olefin coordination. The last two reactions are frequently involved in catalytic cycles. 

These ions, with the exception of Pb(IV), form complexes with olefins and this process is a preliminary to oxidation when this occurs. A recent review of the action of Pd(II) covers aspects of structure and bonding as well as kinetics, and a similar but older, review exists for Hg(II) . The oxidation of olefins by thallic... 

The dihalogen complexes with olefin donors were first identified spectroscopically in the mid-1960s [42-45] and extensive experimental and computational studies have been carried out by Chiappe, Lenoir and coworkers in recent years [46 - 48 ]. These systems are highly unstable, since the complexation of dihalogens with olefins is followed rapidly by the formation of ionic intermediates and further chemical transformations. Therefore, attention in the corresponding work has mostly focused on hindered olefins, although the spectral characteristics of complexes with less sterically crowded and alkyl- as well as chloro-substituted and cyclic olefins are also reported [44]. The absorption maxima for the dihalogen complexes with olefins (evaluated by the subtraction... 

The same difference in regioselectivity holds for cyclopropanation with ethyl diazoacetate 25 K It is assumed that Cu(OTf)2 or Cu(BF4)2 are reduced to the Cu(I) salts by the diazo compound the ability of CuOTf to form stable complexes with olefins may then explain why, with these catalysts, cyclopropanation is governed by the steric environment around a double bond rather than by its electron-richness. 

The simplest mechanism includes stages of catalyst oxidation to its highest valence state, the formation of a complex with ROOH, and the reaction (bimolecular) of this complex with olefin [240]. 

Finally, binuclear lanthanide(III)-silver(I) shift reagents are noteworthy. These form complexes with olefins, aromatic rings, halogenated saturated hydrocarbons, and phosphines. Due to the lack of polar groups, these functionalities do not give significant LIS with common mononuclear LSR. Applications of this binuclear technique have been reviewed261 for example, the Z- and E-isomers of 2-octene can be differentiated. 

Mercury(II) forms either coordination complexes or organometallic complexes with olefins, depending on the reaction conditions 19, 34). In solutions of suitable pH and purity of reagents the following equilibria are established ... 

From the encouraging results obtained in the reactions of a series of gold(III) oxo complexes with olefins [56], Cinellu et al. tried to achieve the supposed oxametalla-cyclic intermediate, which had never been isolated before [25]. In the reaction of 8 and norbornene 56, if the - atoms were considered to be equivalents of coordinated water, and it was therefore possible to talk about the gold-catalyzed addition of water to an alkene. The metallaoxetane 58 was separated from the gold-alkene complex 57 and characterized by X-ray crystal structure analysis. The subsequent stoichiometric reaction yielded epoxide 59 (Scheme 8.5). 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

Frequently substantially more than catalytic amounts of a Lewis acid metal halide are required to effect Friedel-Crafts alkylation. This is due partly to complex formation between the metal halide and the reagents or products, especially if they contain oxygen or other donor atoms. Another reason is the formation of red oils. Red oils consist of protonated (alkylated) aromatics (i.e., arenium ions) containing metal halides in the counterions or complexed with olefin oligomers. This considerable drawback, however, can be eliminated when using solid acids such as clays,97 98 zeolites (H-ZSM-5),99,100 acidic cation-exchange resins, and perfluoro-alkanesulfonic acid resins (Nafion-H).101-104... 

Fig. 7 Photoinduced cis-trans isomerization of complexes with olefin or azo linkages...

Their view that cobalt hydrotricarbonyl, instead of die hydrotetra-carbonyl, is the reactive species is based on evidence that the formation of alkylcobalt tetracarbonyl is inhibited by carbon monoxide more fundamentally, initial complexing with olefin would presumably require the participation of a coordinately unsaturated carbonyl. 

Molybdenum -peroxo complexes give oxiranes in high yields. " For anhydrous hydrogen peroxide, a three-step mechanism is assumed, with an a-hydroxyhydroperoxide intermediate. Detailed studies have been made on the mechanism of the reaction of the MoO(02)2-HMPT complex with olefins (Eq. 27). 2 ... 

The reactions of Cp2Zr(H)(THF) hydride complexes with olefins and other substrates were noted in Section III,D. Cationic alkyl complexes also exhibit a rich insertion chemistry. In this section simple single insertion reactions are reviewed reactions with olefins are discussed in Section V,F. 

Deuterium might adsorb by heterolytic ligand displacement adsorption at Cr3+ complexed with olefin where the Cr3+(cus) was initially five-coordinate. Adsorption at Cr +D- with accompanying displacement of seems less likely. It is difficult to evaluate this possibility. We have no molecular analogies since tri- and tetracoordinate are almost unknown as ligands in molecular coordination chemistry. There is one compound of Cr(III) whose study could be of interest which involves 82)... 

The inability of normal shift reagents to complex with olefinic double bonds has been overcome by the use of a mixture of silver heptafluorobutyrate and europium or praeseodymium heptafluoro-octanedionate, the silver interacting with the olefin and the lanthanide with the carboxylate group. (5) The shifts observed are, however, rather small, as expected in view of the distance of the lanthanide from the hydrogens. 

Diazo ester/rhodium(II) carboxylate combinations other than EDA/Rh2(OAc)4 have been tested It turned out that the solubility of the rhodium(II) carboxylate greatly influenced the efficiency of cyclopropanation. For the reaction of monoolefins with ethyl diazoacetate, markedly higher yields than with Rh(II) acetate were obtained with the better soluble rhodium(II) butanoate and rhodium(II) pivalate, the latter one being soluble even in pentane. However, only poor yields resulted from the use of rhodium(Il) trifluoroacetate, even though this compound is readily soluble, Rh CCFjCOO), in contrast to the other rhodium(II) carboxylates, is able to form 1 1 complexes with olefins particularly with electron-rich ones thus, competition of olefin and diazo compound for the only available coordination site at the metal atom could be responsible for the reduced catalytic action of Rh2(CF3COO)4 (as will be seen in Section 4.1, this complex is an excellent catalyst for cyclopropanation of aromatic substrates). The diazoester substituent also has some influence on the yields. Increasing yields were obtained in the series methyl ester, ethyl ester, n-butyl... 

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