Metal Olefin Complexes

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 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. 

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. 

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... 

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... 

He received his Ph.D. in summer 1940 and firmly wished to stay in fundamental research. He was offered a post at St. Andrews University which he could not take up because of World War II. Instead he was assigned to a war problem at Cambridge involving the synthesis of the then unknown 1,3,5,7-tetranitro-naphthalene, which Sir Robert Robinson anticipated to be an exceptionally effective explosive. In 8 months he managed to make 100 g of the compound but was then dispatched to the Research Department of Woolwich Arsenal, at that time evacuated to the University College at Swansea. There he spent most of his time in the library where he eventually found R. N. Keller s review on olefin metal complexes [3]. He remembered that Mann had mentioned in his lectures that olefins were the only ligating species that did not possess a lone pair of electrons, which prompted him to work on their complexes as soon as he was free to do so. 

For the reader desiring more information on mono-olefin complexes of the transition metals, a number of excellent reviews are available. Early studies on olefin-metal complexes (primarily of Pt, Pd, Ag, and Hg) have been reviewed by Keller Chatt 27), and Douglas 70). Two more... 

There is one further area in which the properties of olefin-metal complexes and adsorbed olefins show common behavior. The olefin is often readily displaced by diolefins and alkynes many other ligands, including phosphines, amines, nitriles, cyanide ion, and carbon monoxide, can however cause olefin displacement, and these include molecules which are notorious catalyst poisons. Again no quantitative information is available, but a causal connection is strongly suggested. 

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