Olefin complexes preparation

One example of a bonafide bis(alkyne) complex has recently been prepared. Reaction of the in situ generated olefin complex prepared by alkylation of ( -CsHs ZrC 50 with the diaryl alkyne in Equation (7) yields 253.130 In this structure, C-C coupling has not occurred, presumably a result of the steric strain associated with the zirconacyclo-pentadienyl fragment (Equation (7)). The solid-state structure further establishes the compound as a bis(alkyne) complex. Computational studies suggest that a Zr(iv) resonance structure is the most suitable representation of the compound. However, reaction of 253 with iodine in THF yields ( -CsHs Zrle 254 and the dialkyne starting material, suggesting that the zirconium center can act as a source of Zr(n) (Equation (8)). 

Contains a detailed survey of olefin complexes prepared firom acetylenes. M. A. Bennett, Chem. Rev. 62, 1962, 611 R. G. Guy and B. L. Shaw, Advances in Inorganic Chemistry and RmUochemistry 4, 1962, 78. Slightly out-of-date reviews of olefin and acetylene complexes of transition metals. 

Asymmetric versions of the cyclopropanation reaction of electron-deficient olefins using chirally modified Fischer carbene complexes, prepared by exchange of CO ligands with chiral bisphosphites [21a] or phosphines [21b], have been tested. However, the asymmetric inductions are rather modest [21a] or not quantified (only the observation that the cyclopropane is optically active is reported) [21b]. Much better facial selectivities are reached in the cyclopropanation of enantiopure alkenyl oxazolines with aryl- or alkyl-substituted alkoxy-carbene complexes of chromium [22] (Scheme 5). 

The coordinated ethylene is readily expelled at 25 °C by the attack of a conjugated diene and the hydride is transferred to the sterically less crowded diene terminus. Thus the niobium hydrido-olefin complexes serve as convenient reagents for the preparation of 1,2- or 1,3-dialkyl-substituted allylniobium compounds starting from butadiene, (E,E) and (/i,Z)-2,4-hcxadicnc, (E)- and (Z)-l,3-pentadiene (equation 1), 3-methyl-l,3-pentadiene and isoprene (equation 2). All the allyl niobium compounds synthesized were isolated as air-sensitive pale-yellow crystals by crystallization from hexane. 

The protonation of the a-allylic cyanocobaltate complexes has been reported by Kwiatek and Seyler 50) to proceed with the liberation of the corresponding olefin. Thus the complex prepared from butadiene [Eq. (35)] on treatment with aqueous HCl liberates 1-butene. The carbonium ion which probably forms first can cleave directly to 1-butene or it may first rearrange to a Tr-olefin complex, from which the olefin is then displaced with either HgO or chloride ... 

Internal olefins (2-butene, 2-hexene) were also successfully hydroformylated in water with complexes prepared in situ from [PtCbCCOD)] and the tetrasulfonated diphosphines 37 at 100 °C and 80 bar syngas [148,149]. The same catalysts were suitable for the hydroformylation of 2- and 3-pentenoic acids and trans-2-pentenenitiile, too [150]. The -... 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

There is often a striking similarity between olefins and carbon monoxide as ligands, and one of the most common ways of preparing olefin complexes is by replacement of one or more carbon monoxide ligands in a metal carbonyl by olefins. Both olefin and carbonyl complexes frequently obey the simple E.A.N. rule, each CO ligand and C C bond contributing two ir-electrons to the metal atom, to enable it to attain the electronic configuration of the next inert gas in the Periodic Table. 

Anhydrous silver-olefin complexes are readily dissociable, low-melting, and variable in composition 92a, 176, 183). Cyclic olefins and polyolefins form stable complexes with silver nitrate or perchlorate, but again the Stoichiometry of the complexes varies considerably, sometimes depending on the conditions of preparation. The following types have been isolated [Ag(un)2]X (un = e.g., cyclohexene, a- and /3-pinene) ISO), [Ag(diene)]X diene = e.g., dicyclopentadiene 220), cyclo-octa-1,5-diene 50, 130), bi-cyclop, 2,1 ]hepta-2,5-diene 207), and cyclo-octa-1,3,5-triene 52), and [Ag2(diene)]X2 (diene = e.g., cyclo-octa-1,3- and -1,4-diene 180), bi-cyclo[2,2,l]hepta-2,5-diene 1) and tricyclo[4,2,2,0]-decatriene 10)). Cyclo-octatetraene (cot) forms three adducts with silver nitrate 52), viz., [Ag(cot)]NOs, [Ag(cot)2]N03, and [Ag3(cot)2](N03)3. On heating, the first two lose cyclo-octatetraene and all three decompose at the same temperature. From the stoichiometry of the above complexes it appears that the... 

The acetylenic diol Me2C(OH)-C C-C(OH)Me2 (ac) forms complexes of the types K PtCl3ac] and cis- and 2mns-[PtCl2(ac)(am)] (am = amine), by reactions commonly used in the preparation of olefin complexes 23, 25,... 

Several attempts to prepare palladium(II)-olefin complexes have failed. Thus, organosilicon groups from /3-trimethylsilylstyrene were cleaved (as chlorotrimethylsilane) by palladium(II) chloride (164) with formation of trans,tran.s-1,4-diphenyl-1,3-butadiene. 

Another example has been found in the author s laboratory. In the course of studies on the synthesis of metal-olefin complexes by means of cathodic reduction in dry organic mediums, a variety of linear oligomers were prepared on the nickel atom formed at the platinum cathode in electrolytic solution (32). The solution contained tetracispyridine nickel perchlorate or nickel dichloride and butadiene in ethanol or dimethoxye-thane, using tetrabutylammonium perchlorate as an electrolyte. 

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). 

Several gold(I) olefin complexes have been prepared, although the exact constitution was often in some doubt. The first olefin complex was reported (73) in 1964, when white crystals were obtained from the reaction of cycloocta- 1,5-diene (cod) with AuCl or HAuC14. These products were believed to be a dimeric aurous complex [Au2Cl2(cod)]. Subsequent reports, however, showed that although gold(I) chloride reacted (74) to give... 

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