Olefin complexes ratio

Internal RCH=CHR 2-Hexene MeCH=CHC3H7 is not isomerized by complex 1 to 1- or 3-hexene, nor is its cis trans ratio changed. No olefin complexes or coupling products are obtained. The corresponding zirconocene complexes 2 likewise did not show any isomerization activity [15]. 

The proton-olefin complex is probably responsible for the unusually high cisjtrans ratio 47, 92). These intermediates have to be considered as hydrogen bond-like structures and evidence has been presented for an extremely high mobility of the proton in these structures 98, 99). 

From i CO) spectra of [M(CO)5 E=C(Aryl)H ] (M = Cr, W E = S, Se) it follows that the heteroaldehyde ligand acts essentially as a coordination mode. The acceptor properties and thus v(CO) spectra are similar to those of [M(CO)s(thioether)] and [M(CO)s (phosphine)] complexes. In the 7/2-bonding mode the heteroaldehyde ligands are strong rr acceptors and their IR spectra resemble those of, e.g., alkyne and olefin complexes. Because [W(CO)5 Se = C(Aryl)H ] complexes are present in solution as rapidly interconverting mixtures of the 771 isomers and the if isomer their IR spectra are composed of both types of i CO) spectra. The intensity ratio of the v(CO) absorptions depends on the temperature due to the temperature dependence of the 17V172 equilibrium. 

As we mentioned earlier (Sect. 2.1.5.), a further complication arises from the fact that, with the exception of the C2v or C2h olefinic substrates, two isomeric reaction products could be formed by cis attack of the metal hydride to one face of the prochiral substrate. In principle, if rc-olefin complexes are intermediates, the isomeric ratio could be determined in the re-complex formation, two non-interconvertible conformers of each of the two diastereomeric rc-complexes being formed. Each conformer then gives rise to a different structural isomer of the reaction products (Fig. 14, paths a, c and a, c ). 

The oxidation catalyst is believed to be ruthenium tetraoxide based on work by Engle,149 who showed that alkenes could be cleaved with stoichiometric amounts of ruthenium tetraoxide. Suitable solvents for the Ru/peracid systems are water and hexane, the alkene (if liquid) and aromatic compounds. Complex-ing solvents like dimethylformamide, acetonitrile and ethers, and the addition of nitrogen-complexing agents decrease the catalytic system s activity. It has also been found that the system has to be carefully buffered otherwise the yield of the resulting carboxylic acid drops drastically.150 The influence of various ruthenium compounds has also been studied, and generally most simple and complex ruthenium salts are active. The two exceptions are Ru-red and Ru-metal, which are both inferior to the others. Ruthenium to olefin molar ratios as low as 1/20000 will afford excellent cleavage yields (> 70%). vic-Diols are also... 

All the examples to be discussed are of square-planar platinum(II) complexes, recorded in Scheme 2. Thus Boucher and Bosnich (8) have prepared a series of olefin complexes derived from ( -tolylmethylsulfoxide)dichloroplatinum(II) in which the ligand is S-bonded. The S-methyl protons provide a convenient and sensitive NMR probe for the determination of diastereomer ratios. In the cases of but-l-ene, 3-methylbut-l-ene, styrene and 3,3-dimethylbut-l-ene crystals of a single diastereomer can be isolated in all but the last of these, however, there is rapid equilibration between diastereomers in solution, with relatively little discrimination between them (typically 55-75% of the major species). Since several rotamers are possible in the sulfoxide ligand it is not easy to specify the origin of chiral discrimination. 

A number of unexplained factors warrant mention. Orientation of elimination differs for secondary and tertiary structures. The peculiar predominance of cis- rather than /ra/ii-olefin may arise from the relative stabilities of the proton-olefin complexes. but a more certain conclusion would be possible if the stereochemistry of the dehydration in the acyclic series had been determined. Assumption of the anti stereospecificity known to be favoured by the cyclohexyl systems may be unsound especially in the light of the recent stereochemical findings in base-catalysed elimination reactions (Section 2..1.1(e)). The solution of the problem of the cis/trans ratios may lie in the duality of mechanism, namely the syn-clinallanti complexity. Certainly recent results on the dehydration of threo- and eo t/iro-2-methyl-4-deutero-3-pentanols on thoria show syn-clinal rather than anti stereospecificity as indicated by deuterium analysis of the cis- and /rn/iJ-4-methyl-2-pentenes, but in these cases the trans isomer was formed in a three-fold excess over the m-olefin . Of course, the dehydration reactions on the less acidic thoria may not be good models for alumina but a knowledge of stereochemistry in the acyclic series might prove an invaluable aid in the elucidation of the mechanism. There is obviously plenty of scope for future kinetic investigations which at the moment sadly lag behind preparative studies. 

From alkyl complex Po, the olefin can be captured to form the rt-complex tto, and inserted via 1,2- or 2,1-insertion route. In the model apphed here we consider the olefin capture and its insertion as one reactive event, i.e., we assume a pre-equihbrium between the alkyl and olefin complexes, described by an equilibrium constant =[Tto]/[Po]=exp (AG ,p ./RT). This corresponds to neglecting the barrier for the monomer capture. Such an approach is valid for the late-transition metal complexes, e.g., the diimine catalysts studied in the present work, where the resting state of the catalyst is a very stable olefin Ti-complex [16] and the olefin capture barrier and the related n-complex dissociation barrier is much lower than the insertion barriers. This assumption allows one to speed up the simulation otherwise many olefin capture/dissocia-tion steps, not important for the final result of the simulation, would be happening before insertion takes place. It follows from the above considerations that the insertion rate is given by Eq. (8), and the equation for the isomerisation vs insertion relative probability (Eq. 4) includes the isomerisation and insertion rate constants, the equilibrium constant, K omph <>nd the olefin pressure, polefin,- Finally, the relative probability for the two alternative insertions is given by Eq. (4) it depends on the two rate constants ratio only. 

Although reaction rate and selectivities of heterogeneous catalysis do depend on ligand dimensions ligand/metal complex ratios, these values are in most cases unknown. In order to clarify this, the hydrogenation of olefins on rhodium/phosphine catalysts has been studied [231]. The compounds />-/i-butyl- and p- -dodecylphenyl-diphenylphosphine as well as triphenylphosphine have been used as models of triphenylphosphine polymeric ligands... 

With added CO, but not in its absence, ethylene reacts rapidly with HRh(CO)L3 solutions to give the acyl complex EtCORh(CO)2iL2- With 1 atm of H2 and CO (in a 2 1 ratio) propionaldehyde forms with a half-life of 5 minutes. Using a 1 2 mixture of H2 and CO instead of 2 1 increases the half-life to an hour, suggesting that CO dissociation from the 18-electron acyl complex is necessary before oxidative addition of H2. Isomerization and hydrogenation are much slower under hydroformylation conditions (with H2 and CO) than under H2 alone. These reactions are typically only 1-2% of the hydroformylation rate. The reason must be high rates of capture of 16-electron alkyl rhodium complexes by CO compared to rates of H2 capture or jS -hydride abstraction to form isomerized hydrido-olefin complexes. 

In this work, 1-hexene was extracted from its mixtures with n-hexane in vaiying ratios using a task specific ionic liquid. Herein, the ionic liquid (IL) 1-butyl-3-methylimidazolium nitrate, [BMIM][N03], was used and examined with and without the addition of a metal salt. The impact of water on both selectivity and distribution coefficient was also tested. Four potential metal salts were investigated, the results of which demonstrate that the dissolution of transition-metal salts in the IL improves the separation of 1-hexene from n-hexane tinongh metal-olefin complexation. Additionally, the presence of water in IL solntions containing metal salt enhances this selectivity. Finally, UNIFAC was nsed to correlate the experimental LLE data with good accnracy. ... 

Exchange reactions of one olefin for another is a particular case of substitution reaction. The possibility of obtaining a new olefin complex in this way depends on the ratio of the formation constants of two alkene complexes remaining in the equilibrium... 

An earlier study (1) of the stoichiometry and stability of crystalline complexes of some mono-olefins with anhydrous silver fluoroborate established that these were quite stable by comparison with those silver ion-olefin complexes which had been known and that, with the exception of ethylene, the most stable complex in every instance had a silver ionrolefin stoichiometric ratio of 1 2. The study established as well an essentially linear correlation between the ionization potential of the olefin and the infrared shift in the double bond stretch vibration frequency upon complexation with the silver salt. 

Derivatives Containing the iT- C-i)M System. The parent radical for this type of olefin complex is the 7t-C3H5 group, for which three major resonances are observed in the intensity ratio 1 2 2, i.e. for the protons labeled H, H, ... 

Despite thdr lability, many of the silver-olefin complexes may be isolated as thdr nitrate or perchlorate salts and, in most cases, the ratio of co-ordinated C=C groups to the metal atom is 1 1. However, the stoicheiometry of the isolated olefin complexes does not necessarily indicate the nature of the species in solution. For example, in solution norbomadiene forms a 1 1 complex with Ag(I), whilst the solids isolated from the solution may have the stoicheiometry C7H8(AgNOj)2 [30] or C7H AgNOj [53,30]. 

Attention should be paid to the fact that the ratio of Pd and phosphine ligand in active catalysts is crucial for determining the reaction paths. It is believed that dba is displaced completely with phosphines when Pd2(dba)3 is mixed with phosphines in solution. However the displacement is not eom-plcte[16]. Also, it should be considered that dba itself is a monodentate alkene ligand, and it may inhibit the coordination of a sterically hindered olefinic bond in substrates. In such a case, no reaction takes place, and it is recommended to prepare Pd(0) catalysts by the reaction of Pd(OAc)2 with a definite amount of phosphinesflO]. In this way a coordinatively unsaturated Pd(0) catalyst can be generated. Preparation of Pd3(tbaa)3 tbaa == tribenzylidene-acetylacetone) was reported[17], but the complex actually obtained was Pd(dba)2[l8],... 

The reaction mechanisms by which the VOCs are oxidized are analogous to, but much more complex than, the CH oxidation mechanism. The fastest reacting species are the natural VOCs emitted from vegetation. However, natural VOCs also react rapidly with O, and whether they are a net source or sink is determined by the natural VOC to NO ratio and the sunlight intensity. At high VOC/NO ratios, there is insufficient NO2 formed to offset the O loss. However, when O reacts with the internally bonded olefinic compounds, carbonyls are formed and, the greater the sunshine, the better the chance the carbonyls will photolyze and produce OH which initiates the O.-forming chain reactions. 

---