Hydride compounds reactions

Field and Lampe (23) established the occurrence of the hydride transfer reaction in the gas phase in 1958 by detecting secondary ions of mass one unit lower than the parent compound. Subsequently, Futrell (24, 25) attempted to account for most lower hydrocarbon products formed in the radiolysis of hexane and pentane by assuming that hydride transfer reactions play a dominant role in radiolysis. More recently, Ausloos and Lias (2) presented experimental evidence which indicated that some of the products in the radiolysis of propane are, in... 

Carbanions derived from phosphine oxides also add to carbonyl compounds. The adducts are stable but undergo elimination to form alkene on heating with a base such as sodium hydride. This reaction is known as the Horner-Wittig reaction.268... 

The difficulty in controlling the regiochemistry during radical-denitration of allylic nitro compounds is well known. The migration of the double bond is a serious problem, as shown in Eq. 7.96. This problem is overcome by a hydride transfer reaction in the presence of a palladium catalyst (Eq. 7.97).140... 

The regiochemical control of Pd-catalyzed hydride transfer reaction is much more effective than that of the radical denitration, as shown in Eq. 7.98. The base-catalyzed reaction of nitroolefins with aldehydes followed by denitration provides a new synthetic method of homoallyl alcohols (Eq. 7.99).140 Exomethylene compounds are obtained by denitration of cyclic allylic nitro compounds with Pd(0), HC02H and Et3N (Eq. 7.100).140b... 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

Only scant information is available about the influence of coke formation on the alkylation mechanism. It has been proposed that, similar to the conjunct polymers in liquid acids, heavy unsaturated molecules participate in hydride transfer reactions. However, no direct evidence was given for this proposition (69). In another study, the hydride transfer from unsaturated cyclic hydrocarbons was deduced from an initiation period in the activity of NaHY zeolites complete conversion of butene was achieved only after sufficient formation of such compounds (73). 

Certain volatile elements must be analyzed by special analytical procedures as irreproducible losses may occur during sample preparation and atomization. Arsenic, antimony, selenium, and tellurium are determined via the generation of their covalent hydrides by reaction with sodium borohydride. The resulting volatile hydrides are trapped in a liquid nitrogen trap and then passed into an electrically heated silica tube. This tube thermally decomposes these compounds into atoms that can be quantified by AAS. Mercury is determined via the cold-vapor... 

Dications 222+ and 232+ were synthesized by hydride abstraction reaction of the corresponding hydro derivatives as stable dark-brown powder. The p/CR+ values for these dications are also extremely high for doubly-charged systems (222+ 11.7 and 232+ 11.7). The electrochemical reduction of 222+ and 232+ exhibited a reduction wave at less negative potentials than that of dication 212+. This wave corresponds to the reduction of two cation units by a one-step, two-electron reduction to form thienoquinoid products. Chemical reduction of 222+ and 232+ afforded the closed-shell thienoquinoid compounds (22 and 23), which exhibited high electron-donating ability. The formation of the closed-shell molecules is in contrast with the result from reduction of dication 212+connected via a / -phenylenediyl spacer. 

The data for the four compounds [83]—[86] show a good linear relationship (correlation coefficient r = 0.995) between the (C-)H" C( = 0) distance and the activation energy for hydride transfer reaction of the alkoxide anion (Fig. 16). Here also there is a simple and strong correlation between geometry and reactivity ground state structures closer to the presumed transition state structure give faster reactions. 

Fig. 16 Relationship between activation energy for the hydride transfer reaction of compounds [83-86] and the distance the hydrogen atom has to travel. The data are taken from Cernik et al. (1982, 1984).

In an attempt to prepare alkylamines by asymmetric reduction of imines with chiral hydride reagents, diphenylphosphinyl imines (38), prepared by reaction of ketoximes (39) with chlorodiphenylphosphine [(Cg 115)2 PCI], were reduced in the presence of a variety of chiral aluminum and boron hydride reagents43. Among the most promising reagents was BINAHL-H44 (40), a chiral hydride compound prepared by the modification of lithium... 

X.L. Yeh, K. Samwer, W.L. Johnson, Formation of an amorphous metallic hydride by reaction of hydrogen with crystalline intermetallic compounds - a new method of synthesizing metallic glasses, Appl. Phys. Lett. 42 (1983) 242-244. 

The Bartlett Condon-Schneider hydride transfer reaction, first employed in silicon chemistry by Corey in 1975, " developed since then to be the most popular synthetic approach to silylium ions in the condensed phase. Subsequently, it was also used for the generation of germylium and stannylium compounds." ... 

The major obstacle of the hydride transfer reaction is the steric bulk of the trityl cation as the reagent of choice. Substrates that will allow the isolation of cations RsE, free from intramolecular and/or intermolecular interactions with solvent molecules or anions, need to have bulky substituents and therefore the hydride transfer reaction between the hydride and trityl cation is severely hampered or it is even impossible. Another drawback of this method is the limited availability of the starting hydrido compound, which for example, is not available for lead compounds, due to the high reactivity of lead(IV) hydrides. 

Catalytic reduction of olefins by heavy metal catalysts probably involves metal hydride addition reactions also. If this is correct, the observed inhibition of the reduction by carbon monoxide, phosphines, sulfur compounds, and other materials with unshared electrons is exactly what would be expected if a vacant orbital on the hydride is required before addition can take place. 

The compounds obtained by the replacement of ring sulfur by carbon, as in the case of penicillins, show somewhat improved antibiotic properties. A free radical— based route has been described for the conversion of fermentation derived cephalosporins to their carbocyclic derivatives. The first step in this sequence consists of the condensation of the cephalosporin sulfone (36-1) with formaldehyde and dimethyla-mine the initial product from the Mannich-like reaction consists of the exomethylene derivative at the position adjacent to the activating sulfone. The product is treated in situ with phenylselenol to give the Michael adduct (36-2). This fragments with an extmsion of sulfur dioxide when heated with the free radical initiator AIBN in the presence of tributyltin hydride the reaction can be envisaged as leading to the... 

The ke[ values of photoinduced electron transfer reactions from [Ru(bpy)3]2 + to various nitrobenzene derivatives in the presence of 2.0 mol dm-3 HC104 are listed in Table 1, where the substituent effect is rather small irrespective of electron-withdrawing or donating substituents. A similar insensitivity to the substituent effect is also observed in the acid-catalyzed photoinduced electron transfer from [Ru(bpy)3]2+ to acetophenone derivatives [46,47]. The stronger the electron acceptor ability is, the weaker is the protonation ability, and vice versa. Thus, the reactivity of substrates in the acid-catalyzed electron transfer may be determined by two reverse effects, i.e., the proton and electron acceptor abilities, and they are largely canceled out. Such an insensitive substituent effect shows a sharp contrast with the substituent effect on the acid-catalyzed hydride transfer reactions from Et3SiH to carbonyl compounds, in which the reactivity of substrates is determined mainly by the protonation ability rather than the electron acceptor ability. 

The catalytic effect of metal ions such as Mg2+ and Zn2+ on the reduction of carbonyl compounds has extensively been studied in connection with the involvement of metal ions in the oxidation-reduction reactions of nicotinamide coenzymes [144-149]. Acceleration effects of Mg2+ on hydride transfer from NADH model compounds to carbonyl compounds have been shown to be ascribed to the catalysis on the initial electron transfer process, which is the rate-determining step of the overall hydride transfer reactions [16,87,149]. The Mg2+ ion has also been shown to accelerate electron transfer from cis-dialkylcobalt(III) complexes to p-ben-zoquinone derivatives [150,151]. In this context, a remarkable catalytic effect of Mg2+ was also found on photoinduced electron transfer reactions from various electron donors to flavin analogs in 1984 [152], The Mg2+ (or Zn2+) ion forms complexes with a flavin analog la and 5-deazaflavins 2a-c with a 1 1 stoichiometry in dry MeCN at 298 K [153] ... 

Several recent examples of this technique are outlined in Scheme 70.l99 20li20S 206 The starting cobalt complexes are highly colored, air stable compounds that require no special precautions in handling. The process is relatively cost effective most cobalt precursors are less expensive per mole than tributyltin hydride. The reactions are conducted by visible light irradiation in a variety of solvents and can often be followed by color changes characteristic of the different oxidation states of cobalt. A disadvantage is that... 

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