Metal olefins

G. Paiaro Organometal. Chem. Optical activity in olefin-metal 17 ... 

As a typical case, olefin-metal complexation is described first. Alkene complexes of d° transition metals or ions have no d-electron available for the 7i-back donation, and thus their metal-alkene bonding is too weak for them to be isolated and characterized. One exception is CpfYCH2CH2C(CH3)2CH=CH2 (1), in which an intramolecular bonding interaction between a terminal olefinic moiety and a metal center is observed. However, this complex is thermally unstable above — 50 °C [11]. The MO calculation proves the presence of the weak metal-alkene bonding during the propagation step of the olefin polymerization [12,13]. 

The alcoholate is either dehydrogenated via (3-CH activation to afford an M-OH function and a hydrido (olefin) metal species or, to a minor extent, converted to alcohol. The hydrido (olefin) metal species can release 1-alkenes. The route toward alcohol is regarded as reversible, and thus allows the incorporation of co-fed alcohol, causing initiation of the FT synthesis via the alcoholate and the C,O-bridging aldehyde... 

The mechanism of this new reaction is shown in Scheme 14. Coordination of the diene to palladium(II) makes the diene double bond electrophilic enough to be attacked by the allylsilane. The attack by the allylsilane takes place on the face of the diene opposite to that of the palladium (anti). This is the first example of an anti attack by an allylsilane on a 7T-(olefin)metal complex. Benzoquinone (BQ)-induced anti attack by chloride ion produces the product 58. 

For a decade or so [CoH(CN)5] was another acclaimed catalyst for the selective hydrogenation of dienes to monoenes [2] and due to the exclusive solubility of this cobalt complex in water the studies were made either in biphasic systems or in homogeneous aqueous solutions using water soluble substrates, such as salts of sorbic add (2,4-hexadienoic acid). In the late nineteen-sixties olefin-metal and alkyl-metal complexes were observed in hydrogenation and hydration reactions of olefins and acetylenes with simple Rii(III)- and Ru(II)-chloride salts in aqueous hydrochloric acid [3,4]. No significance, however, was attributed to the water-solubility of these catalysts, and a new impetus had to come to trigger research specifically into water soluble organometallic catalysts. 

No distinction possible between olefin-metal ionizations. 

Investigation of Tt-olefin metal complexes with (Z)-2-butene or similar C2v olefins has shown that the energy barrier to the rotation is rather low67,69,70) and that therefore the two conformers must rapidly reach the equilibrium even at room temperature. 

A possible mechanism for the cleavage may involve the formation of an olefin-metal complex intermediate in which the silicon atom alpha to the vinyl group would be vulnerable to the attack of ethanol. 

E. Mass Spectra of Olefin Metal Carbonyl Derivatives. 103... 

The catalytic effect of platinum salts can be explained by the intermediate formation of an olefin-metal complex in which the electron density of the... 

Just as with neutral arene or olefin metal carbonyls, the cationic analogs are useful intermediates for the preparation of other substituted cations. This is because the organic moiety is often readily displaced by another ligand and, further, allows carbonyl derivatives to be prepared, which may not be readily accessible by direct reaction (dien = diethylene triamine). 

Because of the marked differences in reactivity of I, II, and III on palladium, Gault and co-workers prefer the metal-olefin/metal-alkyl insertion mechanism outlined above for this metal in contrast to platinum. It may be noted, incidentally, that the results described for reaction of I, II, and III on platinum would be consistent with the simplest possible mechanism of ring closure, namely through aco-diadsorption ... 

Laboratory in Oxford, and Geoffrey Ozin at the University of Toronto in the early 1970s. With the metal atom cocondensation technique (which as described in Chaps. 6 and 7 was also used to prepare a series of zerovalent arene and olefin metal complexes), they reported simultaneously that the elusive palladium and platinum tetracarbonyls, Pd(CO)4 and Pt(CO)4, as well as the coordinatively unsaturated fragments M(CO)3, M(CO)2, and M(CO) (M = Pd, Pt) were formed by cocondensation reactions of Pd and Pt atoms with CO in inert gas matrices at 4-10 K [119-122]. The comparison of the CO bond stretching force constants for Pd(CO)ra and Pt(CO)ra (n - 1-4) revealed that, in analogy to Ni(CO) , the most stable compounds were the tetracarbonyls. In a xenon matrix, Pd(CO)4 existed up to about 80 K [120]. Ozin s group as well as others... 

Although Walsh s proposal appeared convincing at first sight, Dewar considered it as unsatisfactory. Using molecular orbital theory, he developed a better concept in which the olefin-metal bond was divided in a a- and a re-component. The first was postulated to arise from an overlap of the filled bonding re-orbital of the olefin with an empty orbital of the metal, whereas the second was considered to be due to the interaction of a filled d-orbital of the... 

Pauson s work on the structure and bonding of butadiene iron tricarbonyl launched a series of studies making the chemistry of olefin metal carbonyls an... 

The photochemical route provided access not only to olefin metal carbonyls with coordinated ethene, propene, cyclooctene or styrene but also to those with... 

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