Complexes with Unsaturated Hydrocarbons

Zeise had formulated this salt as a compound of ethylene, namely KCl-PtCl2 -H20. Liebig disagreed, considering it rather to contain an ethoxide group (165, 252). Since the compound usually formed as a monohydrate and since the water of hydration could be removed fairly easily, analytical results could be used to justify either viewpoint. Zeise s view prevailed, and was verified by later work. Zeise s last paper (295), by an ironical juxtaposition, appeared right next to Bunsen s first paper on cacodyl (39)  

Anderson showed that ethylene could be displaced from Zeise s salt by various other ligands (5). However, the nature of the olefin-metal linkage was puzzling. Winstein and Lucas (282) proposed that the linkage in olefin-silver complexes involved resonance between three canonical forms  

Complete understanding of bonding in these systems would not be developed until after the discovery of ferrocene. 

Attempts to prepare aromatic derivatives of other transition metals generally failed a typical reaction would be 

Only the elements of Group IB gave isolable phenyl derivatives CgHgCu (217), (C0H5Ag)2-AgNO3 (113, 157, 217), (C0H5) AuCl3 (n = 1,2) (145). These are o-bonded compounds. 

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Several attempts have been made to replace silver ion with ions of other elements [74, 75]. Of particular practical and theoretical interest is the possibility of using thallium salts [74]. The physical and chemical properties of silver(I) and thallium(I) compounds are similar. Thallium(I) salts are stable up to 150°C in the absence of oxygen, but thallium(I) complexes with unsaturated hydrocarbons have not been studied before. The results of the separation are given in Table 6.1 [74]. 

Organometallic chemistry (see p. 1199) is not particularly extensive even though gold alkyls were amongst the first organo-transition metal compounds to be prepared. Those of Au are the most stable in this group, while Cu and Ag (but not Au ) form complexes, of lower stability, with unsaturated hydrocarbons. 

Metal vapor chemistry showed that the lanthanides had quite an extensive chemistry with unsaturated hydrocarbons. Some of the early surveys of metal vapor reactions with unsaturated hydrocarbons included some lanthanide metals and showed that reactivity was present for these metals (14-18). Subsequent synthetic studies in which the products were isolated and characterized led to some of the most unusual organolanthanide complexes currently known (19-28). 

Therefore, the measurement of the relative reactivities in separate and in competitive experiments will permit the evaluation of either K jK or KiK IK K depending upon whether the principal surface species are the TT-complexed multiply unsaturated hydrocarbons or the respective half-hydrogenated states. If the former situation exists, the evaluated ratios might be expected to correlate with the association constants of the hydrocarbons with silver ion (78), but not if the main surface species are the half-hydrogenated states. Apparently, it is the latter condition which prevails. 

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. 

Effectively penta-coordinated complexes are found among the ir-com-plexes of these metals with unsaturated hydrocarbon derivatives these are described in Section IV,F. 

Halogenoboranes are capable of giving weak complexes even with unsaturated hydrocarbons.55 Similarly, weak van der Waals complexes are produced from BF3 by supersonic expansion with CO, N2 and Ar.56... 

For example the total pentane extracts of the web and cuticle from two European Agelenidae and Amaurobiidae comprised a complex mixture of fatty acids, alcohols and long-chain aliphatic hydrocarbons (Prouvost et al., 1999 Trabalon et al., 1996, 1997 Trabalon and Assi-Bessekon, 2008 Tables 16.1 and 16.2). The qualitative composition of cuticular extract obtained was similar to that reported for most insects and scorpions. Hydrocarbons in spiders form complex and varied mixtures with unsaturated hydrocarbons. In those species, the hydrocarbon fraction consists of n-, monomethyl- and... 

Polymerisations and copolymerisations of heterounsaturated and heterocyclic monomers in the presence of coordination catalysts constitute a distinct group of coordination polymerisation processes. Considering the nature of the coordination bond of the a type between the monomer heteroatom (beyond carbon monoxide [60]) and the metal atom, the complexes formed differ essentially from the re complexes of unsaturated hydrocarbon monomers with transition metals. 

Mechanism. The ability of S02 to participate in complex formation with unsaturated hydrocarbons and a host of other compounds such as amines, ethers, phenols, and aromatic hydrocarbons is known (2, 6, 11, 22). SO has been found to initiate polymerization of some monomers... 

Finally, in this catalogue of recent achievements, mention must be made of the measurements, by a variety of techniques, of the energy partitioning in reactions that involve long-lived, association-dissociation complexes. Examples are provided by the reactions of F atoms with unsaturated hydrocarbons, such as... 

The reactivity of osmium with terminal alkynes can be used to prepare bimetallic complexes. When an osmium hydride reacts with a terminal aUcyne that is part of a ruthenium complex, the product is a Ru-Os bimetallic complex with a hydrocarbon bridge (Scheme 16). Another bimetallic complex, [Cp(PPh3 )20s=C=C=CH-C=C-0s(PPh3)2Cp]+, resulted from the reaction between [CpOs(PPh3)2]+ with HC=CCH(OH)C=CH followed by alumina. The unsaturated C5 bridging group is V-shaped. 

The most common mode of reactivity of Y—H with unsaturated hydrocarbons in the absence of acidic hydrogens is 1,2-addition as shown in Scheme 5. The hydrides react with alkenes to form alkyl complexes, with 1,2-propadiene to form allyl systems, and with alkynes to form cis-alkenyl complexes (45). Crystallographic confirmation of the 1,2-addition mode of Y—H with unsaturated hydrocarbons was obtained using terf-butylnitrile as a substrate. The structure of the alkylideneamido product, [(C5Hs)2Y(/Li-N==CHCMe3)]2, was determined by X-ray crystallography. 

Dichlorobis(triethylphosphine)nickel(II) is an effective catalyst for the reaction of symmetrical tetramethyldisilane with unsaturated hydrocarbons (237). A hydronickel complex was postulated as being involved in the reaction, although the mechanism may involve the intermediacy of a dimethylsilylene compound formed by Si—Si bond cleavage rather than the silyl-nickel bond being formed by Si—H bond cleavage. The complex was an effective catalyst for formation of the... 

Finally all our results concerning reactions of complex reducing agents with unsaturated hydrocarbons can be interpreted by the mechanism pictured in Scheme 17. 

Certain well-defined trends in the ability of metals to form complexes of a specified type with unsaturated hydrocarbons are now becoming apparent and will be briefly summarized in this section. There is, however, the difficulty that the failure to discover a particular complex to date is not evidence that its preparation is impossible, so that the con-... 

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