Hydride production

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

Still another type of an intramolecular reaction is the ring enlargement by the insertion of a carbene. When 1-formylhexahelicene tosylhydrazone (105a) is heated in benzene, especially in the presence of sodium hydride, product (106) can be isolated 168). Presumably, the reaction proceeds via the intermediates (105b) and (105c) (Scheme 29). 

Reagents such as LiAlH4 and KH are not effective for the synthesis of formyl complexes. LiAlH4 does react with many metal carbonyl compounds, but it can transfer more than one and usually effects the formation of metal hydride products (50). Similar results are usually found with NaBH4(50), although some neutral formyl complexes (vide infra) can be obtained under special conditions. KH will also react with some metal carbonyls. However, rates are not very rapid, and any formyl intermediates are likely to decompose faster than they form (51). 

The kinetics of this reaction have been studied in detail and a hydroxy-carbonyl is specifically proposed as an intermediate consistent with the kinetic data. Decomposition of this intermediate hydroxycarbonyl may proceed by -elimination of the platinum hydride product since the hydroxycarbonyl is a 16-electron coordinatively unsaturated complex. Another well-known example of metal hydride formation from CO and H20 is the reaction of iron carbonyl in aqueous alkali (55) (36). 

The above results are consistent with a steric specific syn 1,2-addition-elimination of metal hydride intermediate which is formed fast in a pre-equilibrium [MH] [MD] and adds to the olefinic substrate to form the metal alkyl intermediate (equation 261). The /1-hydride elimination of the most stable rotamer (equation 262) is the RDS in the rearrangement, leading to a metal hydride-product complex, which starts a new cycle faster than uncoordinated metal hydride. The protonated catalyst, 434, produces a precursor... 

Allyl hydride complexes of osmium are isolated from treatment of phosphine-substituted osmacyclobutane complex 114 with a thallium salt (Scheme 21). The reaction initially provides a mixture of an unstable -benzyl hydride complex 115 and the rf -allyl hydride complex 116 the -benzyl intermediate ultimately isomerizes to the latter complex, a very rare instance of isolable allylic hydride products generated from a starting metallacyclobutane <2004OM4858>. 

Stereochemical studies by Morandini and Consiglio and colleagues, on the reaction of Grignard reagents with the separate epimers of (tj5-C5H5)-[(R)-PROPHOS]RuC1 (34 and 35) support the mechanisms shown in Scheme 1 since they indicate that the formation of both alkyl and hydride products proceeds with retention of configuration at the ruthenium center [Eqs. (37) and (38)] (35). It should be noted, however, that dissociative pathways to the alkyl complexes via coordinatively unsaturated ruthenium... 

This compound was shown by neutron powder diffraction to adopt an unprecedented structure in which chains of C0O4 squares share comers to form chains that are linked to form a layer by H-bridges. The average cobalt oxidation state is 1.1+ and the C0O2 sheets in the starting material have been replaced with CoOHo,7 sheets in the oxide hydride product, which is consistent with a mechanism in which oxide vacancies created by oxide ion deintercalation are filled by intercalation of hydride ions. 

Pyrolysis of germane-silane mixtures by their rapid passage through a 350-370 C hot zone yields mixtures of binary and ternary hydrides . Typical pyrolysis mixtures and the major ternary hydride products obtained are SiH -GeH, SiGeH ... 

Caution, The boron hydride -products should be concentrated at as louo a temperature as possible under vacuum to avoid the possibility of an explosion. A safely shield is recommended. 

The dihydroxy-ketal (240), previously prepared from ( —)-santonin, has been used to synthesize a number of related sesquiterpenoids. Thus the diacetate of (240) was converted in six steps into (241), which was then treated with iso-propenyl acetate-sulphuric acid the derived enol-acetate was cleaved to the triol (242) by ozonolysis and lithium aluminium hydride reduction. The triol (242) was then converted into the di-iodo acetate (243) in a number of steps and thence to shyobunone (244) by dehydroiodination, reduction, and oxidation. Thermolysis of shyobunone at 160—180 °C gave preisocalamendiol (245) in about 30% yield. More recently, Iguchi et al. have shown that preisocalamendiol (245) can be cyclized to isocalamendiol (246) in aqueous acetic acid no trace of calamendiol (247) was found. A number of other interesting acid-catalysed cyclizations have been observed in this area, e.g. the formation of (248 R = OH) and (248 R = OAc) from (249) and the formation of (250) from (251). Finally, e-cadinene (252) has been obtained from (253), the lithium aluminium hydride product of preisocalamendiol (245). 

That the ethene complex was the thermodynamic product, precludes it being an intermediate en route to the carbon-hydrogen activation product (the vinyl, hydride product ). Matrix isolation studies of CpIr(C2H4)PMe3 under photolysis showed isomerization to the vinyl, hydride complex . 

Use Powder metallurgy, production of pure hydrogen (can contain 1800 cc (STP) H/cc of hydride), production of foamed metals, solder for metal-glass composites, electronic getter, reducing atmosphere for furnaces, hydrogenation agent, refractories. 

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