Olefin hydrogenation neutral

Catalysts prepared from iridium neutral binary carbonyl compounds and several supports have been studied extensively. Small Ir (x = 4, 6) clusters supported on several oxides and caged in zeolite, and their characterization by EXAFS, have been prepared [159, 179, 180, 194-196]. The nuclearity of the resulting metallic clusters has been related with their catalytic behavior in olefin hydrogenation reactions [197]. This reaction is structure insensitive, which means that the rate of the reac-hon does not depend on the size of the metallic particle. Usually, the metallic parhcles are larger than 1 nm and consequently they have bulk-like metallic behavior. However, if the size of the particles is small enough to lose their bulk-like metallic behavior, the rate of the catalytic reaction can depend on the size of the metal cluster frame used as catalyst. 

Some of the first NMR spectroscopic applications in humic substance research involved the use of NMR for the examination of soluble humic substances.(5) The information obtained from NMR spectra of humic and fulvic acids dissolved in alkaline or neutral aqueous solutions has been quite useful in characterizing the aromatic and aliphatic structures of these complex materials. In as much as humic materials are inherently complex, the spectra show only broad signals with some fine structure which can be related to specific methyl, methylene, methine, and aromatic/olefinic hydrogens. Because NMR spectroscopy contains inherently more structural information for humic substances, the use of NMR has been limited since much of the work conducted prior to 1987. This is... 

The synthesis and characterization of enantiomerically pure ansa-cyclopentadienyl organolanthanides Me2Si(ButCp)[(+)- i o-Men-Cp]Ln(CH(SiMe3)2 and their use as precatalysts for asymmetric olefin hydrogenation have been reported. In a one-pot reaction starting from 6,6-dimethylfulvene, methyllithium, and dimethyldichloro-silane the desired product Me2Si(ButCp)Cl was obtained, which was alkylated with Na[(+)-row-Men-Cp] to afford the neutral ligand. Reaction with BunLi afforded the dilithium salt as a colorless crystalline solid (Scheme 161). 

This explanation indicates that the action of sodium upon alcohol is really the action of sodium upon water, partially olefinated. The action of ethyl iodide upon sodium ethoxide is not the replacement of the sodium by ethyl so much as the action of olefinated hydrogen iodide upon olefinated sodium hydroxide. It is the same type of reaction as the neutralization of sodium hydroxide by hydriodic acid in aqueous solution. The hydrated hydrogen iodide reacts with hydrated sodium hydroxide. The water bears the same relation to the latter reaction that the olefin does to the former. 

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

In general, hydroboration—protonolysis is a stereoselective noncatalytic method of cis-hydrogenation providing access to alkanes, alkenes, dienes, and enynes from olefinic and acetylenic precursors (108,212). Procedures for the protonolysis of alkenylboranes containing acid-sensitive functional groups under neutral or basic conditions have been developed (213,214). 

A benzylidene acetal is a commonly used protective group for 1,2- and 1,3-diols. In the case of a 1,2,3-triol the 1,3-acetal is the preferred product. It has the advantage that it can be removed under neutral conditions by hydrogenolysis or by acid hydrolysis. Benzyl groups and isolated olefins have been hydrogenated in the presence of 1,3-benzylidene acetals. Benzylidene acetals of 1,2-diols are more susceptible to hydrogenolysis than are those of 1,3-diols. In fact, the former can be removed in the presence of the latter. A polymer-bound benzylidene acetal has also been prepared." ... 

An important feature of sulfation chemistry is the thermal instability of the acid sulfate, which breaks down to a mixture of products including the parent alcohol, the dialkyl sulfate (R0S020R), the dialkyl ether (ROR), isomeric alcohols, olefins (R CH=CH2), and esters (R0S03R). Because of the thermal instability of the acid sulfate it is necessary to avoid high sulfation temperatures and to neutralize the acid sulfation product soon after its formation. An aging time of about 1 min at 30-50°C is adequate for the second reaction whereby the desired alkyl hydrogen sulfate is formed. In practice the minimum sulfation feasible temperature is determined by the need for the feedstock and reaction mixture to be mobile liquids (Table 3). 

Although non-covalent interactions of anions are one of the most actively explored areas of supramolecular chemistry [15], the anion sensing and recognition have up to now relied primarily on electrostatic binding or hydrogen bonding to the receptor [16,54-61]. However, recent UV-Vis and NMR spectral studies clearly reveal that complex formation takes place in the solutions between halides and neutral olefinic and aromatic it-acceptors such as those in Fig. 3 [23,62],... 

A chiral diphosphine ligand was bound to silica via carbamate links and was used for enantioselective hydrogenation.178 The activity of the neutral catalyst decreased when the loading was increased. It clearly indicates the formation of catalytically inactive chlorine-bridged dimers. At the same time, the cationic diphosphine-Rh catalysts had no tendency to interact with each other (site isolation).179 New cross-linked chiral transition-metal-complexing polymers were used for the chemo- and enantioselective epoxidation of olefins.180... 

The reaction is complicated in aprotic media by polymerization of the olefin at the electrode 132> apparently because anions such as 134 or 136 can initiate anionic polymerization of the activated olefin. Steric hindrance about the double bond can retard polymerization yields of hydrodimer from 132 in di-methylformamide as a function of the size of R are R = hydrogen or methyl, 0%, R % n-propyl, 25% R % i-propyl, 65% R % /-butyl, 95%, 32). Saturation of the double bond to produce, e.g., 136 from 132, is a side reaction in neutral... 

Successive hydrogen transfers within 60, followed by coordination of olefin and then H2 (an unsaturate route), constitute the catalytic cycle, while isomerization is effected through HFe(CO)3(7r-allyl) formed from 59. Loss of H2 from 60 was also considered to be photoinduced, and several hydrides, including neutral and cationic dihydrides of iridium(III) (385, 450, 451), ruthenium(II) (452) and a bis(7j-cyclopentadienyltungsten) dihydride (453), have been shown to undergo such reductive elimination of hydrogen. Photoassisted oxidative addition of H2 has also been dem-... 

The addition of a cation to an olefin to produce a carbonium ion or ion pair need not end there but may go through many cycles of olefin addition before the chain is eventually terminated by neutralization of the end carbonium ion. Simple addition to the double bond is essentially the same reaction stopped at the end of the first cycle. The addition of mineral acids to produce alkyl halides or sulfates, for example, may be prolonged into a polymerization reaction. However, simple addition or dimerization is the usual result with olefins and hydrogen acids. The polymerization which occurs with a-methyl-styrene and sulfuric acid or styrene and hydrochloric acid at low temperatures in polar solvents is exceptional.291 Polymerization may also be initiated by a carbonium ion formed by the dissociation of an alkyl halide as in the reaction of octyl vinyl ether with trityl chloride in ionizing solvents.292... 

This stearolic acid has been thoroughly characterized 3 6 by the freezing-point curve, ultraviolet and infrared spectra, ozonization, and hydrogenation. It has been shown to be free both of positional isomers and of olefinic acids such as oleic and elaidic acids. Its properties include m.p. 46-46.5°, iodine number (Wijs titration, 30 minutes) 89.5, d 5 1.4510, d 5 1.4484, neutral equivalent 279.2-279.6 (theory 280.4), hydrogen uptake 95-100% of theory for a triple bond. The last trace of color is difficult to remove by recrystallization from petroleum ether. It can be removed, however, by crystallization from a 20-30% solution in acetone at —5 to —8°, or from an 8-10% solution at —20°, or by distillation (b.p. 189-190°/2mm.). 

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