Hydrides preparation

Reduction of a-trimethylsily1niethylacrylic acid by lithium aluminum hydride prepared according to Hosomi, A. Hashimoto, H. Sakurai, H. Tetrahedron Lett. 1980, 951. Trost, B. M. Curran, 0. P., unpublished results. 

Reduction of l-methyl-2-alkyl-.d -pyrroline and l-methyl-2-alkyl-.d -piperideine perchlorates with complex hydrides prepared in situ by partial decomposition of lithium aluminum hydride with the optically active alcohols (—)-menthol and (—)-borneol affords partially optically active l-methyl-2-alkyl pyrrolidines (153, n = 1) and 1-methy 1-2-alkyl piperideines (153, n = 2), respectively (241,242). 

Scheme 8-5 Zirconocene hydrides prepared in situ alternative to the Schwartz s reagent, ...

The hydride, prepared at —78°C, suddenly decomposes during slow warming at... 

Sodium hydride ignites in oxygen at 230°C, and finely divided uranium hydride ignites on contact. Lithium hydride, sodium hydride and potassium hydride react slowly in dry air, while rubidium and caesium hydrides ignite. Reaction is accelerated in moist air, and even finely divided lithium hydride ignites then [1], Finely divided magnesium hydride, prepared by pyrolysis, ignites immediately in air [2], See also COMPLEX HYDRIDES... 

E,E)-1,3-Dienes. A cobalt hydride prepared from these three reagents (1 4 1) in THF at -20° converts 1-alkynes into (E,E)-1,3-dienes ... 

In the 1950 s and 1960 s a number of new boron hydrides and boron hydride anions were prepared. Although particular emphasis was placed upon stable higher borane entitles derived from BioHm, significant progress was made in the preparation of new, smaller boron hydrides. Unfortunately, at this period of time, most of these materials could be obtained only in small amounts. (A comprehensive treatment of all boron hydrides prepared through 1978 is given in references (51) and (52). 

Another hydride, magnesium hydride prepared in situ from lithium aluminum hydride and diethylmagnesium, reduced terminal alkynes to 1-alkenes in 78-98% yields in the presence of cuprous iodide or cuprous r rt-butoxide, and 2-hexyne to pure cij-2-hexene in 80-81% yields [///]. Reduction of alkynes by lithium aluminum hydride in the presence of transition metals gave alkenes with small amounts of alkanes. Internal acetylenes were reduced predominantly but not exclusively to cis alkenes [377,378]. 

Triphenylstannane reduced the double bond in dehydro-)J-ionone in 84% yield [872], Complex copper hydrides prepared in situ from lithium aluminum hydride and cuprous iodide in tetrahydrofuran at 0° [873], or from lithium trimethoxyaluminum hydride or sodium bis(methoxy-ethoxy)aluminum hydride and cuprous bromide [874] in tetrahydrofuran at 0° reduced the a,p double bonds selectively in yields from 40 to 100%. Similar selectivity was found with a complex sodium bis(iron tetracarbonyl)hydride NaHFe2(CO)g [875]. 

Since sodium borohydride usually does not reduce the nitrile function it may be used for selective reductions of conjugated double bonds in oc,/l-un-saturated nitriles in fair to good yields [7069,1070]. In addition some special reagents were found effective for reducing carbon-carbon double bonds preferentially copper hydride prepared from cuprous bromide and sodium bis(2-methoxyethoxy)aluminum hydride [7766], magnesium in methanol [7767], zinc and zinc chloride in ethanol or isopropyl alcohol [7765], and triethylam-monium formate in dimethyl formamide [317]. Lithium aluminum hydride reduced 1-cyanocyclohexene at —15° to cyclohexanecarboxaldehyde and under normal conditions to aminomethylcyclohexane, both in 60% yields [777]. 

Calcium acetylide, 11 182-183 Calcium aluminum hydride, preparation and properties of, 8 327-329 Calcium borates, 25 218-219 stability ranges, 25 209-210 structures, 25 190-195, 197-199 in water, 25 218... 

Cesium acetylide, 11 195 Cesium aluminum hydride, preparation and properties of, 8 323 Cesium carbide, 11 195 Cesium chloride, 2 5-6 gaseous metal halide complexes, 26 204-206... 

Chromium-based reagent systems, for pinacol coupling, 11, 63 Chromium carbenes, in ene-yne metathesis, 11, 272 Chromium carbonyl compounds with bridging hydrides, 5, 206 computational studies and spectroscopy, 5, 203 experimentally determined structures, 5, 204 nitro and nitroso compounds, 5, 205 silatropic migrations, 5, 249 with very weakly bonded ligands, 5, 205 Chromium carbonyl hydrides, preparation and characteristics,... 

Fluorous organometallic chemistry, examples, 1, 842 Fluorous solubles, in organometallic synthesis, 1, 81 Fluorous solvents, for hydroformylations, 11, 450 Fluorous tin hydrides, preparation and applications, 9, 346 Fluorovinyl groups, vinylic C-F bond activation, 1, 753 Fluoro vinyltitanocenes, synthesis, 4, 546 g tfZ-Fluorovinyltributylstannane, in carbonylative cross-coupling, 11,413... 

Iron carbonyl hydrides, preparation and properties, 6, 7 Iron cations, acyclic (rj5-pentadienyl) Fe, 6, 153-154 Iron clusters... 

Reduction of l-methyl-2-alkyl-J2-piperideine perchlorates with complex hydrides prepared in situ by partial decomposition of... 

The reaction described here of methylzinc iodide with sodium hydride, to produce Na[Zn2(CH3)2H3], may be pictured as a combination of the two reaction types named above. Unlike many hydride preparations, the synthesis of sodium trihydridodimethyldizincate(l —) is easily performed using ordinary Schlenk-type bench-top techniques and commercially available starting materials.4 Sodium trihydridozincate( 1 —) is easily prepared by exposing Na[Zn2(CH3)2H3]-xTHF to high vacuum.4... 

More recently, a related reaction has been reported, in which active forms of magnesium hydride, prepared in situ or pre-prepared, undergo addition to alkenes, catalysed by titanium or zirconium(iv) halides, to give dialkylmagnesium compounds [56, 59, 64] ... 

Whereas pure lithium hydride prepared from lithium and H2 does not add to C=C double bonds, the lithium hydride bond in 22 proves to be more reactive, for example, with norbomene, propylene, or ethylene. 

Reduction of -acylpyridinium salts. These salts are reduced regiospecifically in moderate yield to 1 -acyl-1,4-dihydropyridines by a copper hydride prepared from lithium tri-r-butoxyaluminum (3 equiv.) and CuBr (4.4 cquiv.) (equation I). 

A synthetically useful and convenient method for the B(C6F5)3-catalyzed hydro-stannylation of alkynes with tributyltin hydride, prepared in situ from easily handled and inexpensive chlorostannane and hydrosilane, has been developed by Yamamoto and his colleagues [155]. The hydrostannylation of monosubstituted alkynes proceeds in a regiospecific manner to give the /3-hydrostannylation products exclusively (Eq. 100). The reaction is trans stereoselective. This method can also be applied to the hydrostannylation of allenes and alkenes (Eqs 101 and 102). 

Beryllium hydride prepared by these methods is an amorphous polymer, and IR spectra indicate long-chain bridge bonding. 

The formaldehyde in some of these reactions is not only the source of the carbonyl ligands, but is also a potential alternative to the alcohol solvent as source of the hydride ligands. A similar ambiguity exists in the many hydride preparations in which H,0 and [OH] are present as well as ROH and [RO] , e.g., in ... 

A comparison of four tri-f-alkoxyaluminum hydrides revealed that lithium tris[(3-ethyl-3-pen-tyl)oxy]aluminum hydride, prepared from LAH and 3-ethyl-3-pentanol, was the most selective for reduction of aldehydes over ketones of all types. Even the less reactive benzaldehyde was reduced in THE at -78 C faster than cyclohexanone (97.7 2.3). A good correlation between the steric demands of the reducing agent and the observed chemoselectivity was observed. 

Lithium hydride, prepared by hydrogenolysis of /-butyllithium under pressure, was observed to reduce aldehydes and cyclohexanones to the corresponding alcohols in the presence of transition metal halides.An equimolar quantity of vanadium trichloride was found to be the most effective catalyst, but the identity of the active reducing species was not established. 

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