Dihydride

There are four general methods for preparing magnesium dihydride.1 

The tetrahydrofuran used in the synthesis is dried immediately prior to use and is purified by atmospheric-pressure distillation over sodium tetrahydridoaluminate(l — ) under a nitrogen atmosphere. The use of lithium tetrahydridoaluminate(l —) is to be avoided because of reports that it explodes on distillation. The following precautions should be observed when distilling tetrahydrofuran over sodium tetrahydridoaluminate(l —). 

Predry fresh tetrahydrofuran with calcium dihydride. 

Do not use a large excess of sodium tetrahydridoaluminate(l —) (10 g of sodium tetrahydridoaluminate(l —) per liter of tetrahydrofuran is recommended). 

Do not continue the distillation beyond the point where the flask is one-third full. 

When the evaporation is complete, the 0°C. trap will contain a few milliliters of diglyme the — 196°C. trap will have trapped-out diborane (caution) and the — 126°C. trap will have retained the dimethyltin dihydride together with traces of diglyme and diborane. The crude product is accordingly subjected to a second vacuum fractionation through clean, 0°C. and — 126°C. vacuum traps into the same — 196°C. trap. The diborane collected in the — 196°C. trap is destroyed as described in Sec. A. The colorless, volatile liquid product is identified from its vapor-phase infrared spectrum14 and from its refractive index, nf 1.4475, literature,2 n 1.4480, as dimethyltin dihydride. The yield is 8.25 g. (0.055 mole, 96%). 

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Methanol Beryllium dihydride, chloroform, oxidants, potassium r rf-butoxide... 

The relative abundance of neutral SiH and H2 species have been measured as a function of power, pressure, flow rate, and dilution. For low power levels, eg, 5 W, up to 50% of the SiH gas is dissociated and the percentage increases to 80% for a power of 50 W. The decomposition of SiH gas proceeds more readily with lower flow rates. These observations, coupled with infrared (ir) measurements performed on the films, suggest that deposition under conditions in which the silane gas is not entirely decomposed leads to a majority of SiH units, whereas those deposited under conditions in which silane is strongly dissociated contain a majority of dihydride units leading to a deterioration of the semiconductor. Also, when the dwell time of SiH in the plasma region increases, the resultant film exhibits a pronounced peak at 2090 cm from the ir spectra corresponding to S1H2 inclusion. 

RhCl(P(C3H3)3)2(solv) +H2 Rh(H)2Cl(P(C3H3)3)2(solv) where solvis solvent. An olefin, R, such as cyclohexene, substitutes for the solvent on the dihydride. 

In the face-centred cubic structure tirere are four atoms per unit cell, 8x1/8 cube corners and 6x1/2 face centres. There are also four octahedral holes, one body centre and 12 x 1 /4 on each cube edge. When all of the holes are filled the overall composition is thus 1 1, metal to interstitial. In the same metal structure there are eight cube corners where tetrahedral sites occur at the 1/4, 1/4, 1/4 positions. When these are all filled there is a 1 2 metal to interstititial ratio. The transition metals can therefore form monocarbides, niU ides and oxides with the octahedrally coordinated interstitial atoms, and dihydrides with the tetrahedral coordination of the hydrogen atoms. 

Figure 2 SEM (left) and REELM (right) micrographs of a hydrogenated scandium sample. Only the REELM image correctly identifies the scandium solid solution phase (bright) in the presence of the scandium dihydride phase (black).

In view of the fact that the conversion of tertiary into quaternary base other hand, hydrogenation in this series ma have 110 effect on activity (cf. erythraline and its dihydro-derivative ery thramine) or may enhance it (cf. -erythroidine and its dihydride) or mai diminish it (cf. erythramine and its dihydride). 

Clusters Ru3(CO)l2 and Os3(CO)l2 as well as their substitution products, e.g. [Os3(CO)lo(AN)2], activate pyrrole and its derivatives in many different ways. Thus, dihydrides 43 (R = H, Me) follow from triosmium dodecacarbonyl and pyrrole or 1-methylpyrrole [82JCS(D)2563 84P1175 86JOM(311)371]. Complex 43 (R = H) isomerizes as a result of proton transfer to the more stable species 44 and... 

In the previous Sections, bulk specimens were alloyed with hydrogen from the gas phase. It was interesting to see whether hydrogen affects the mechanical properties of titanium in a similar way if metal is in a powder state and hydrogen is introduced by mechanical mixing of the metal powder with titanium dihydride, or the interparticle boundaries axe an insurmountable obstacle for hydrogen an eliminate the effects observed in bulk specimens. 

Compacted powder mixtures of titanium and titanium dihydride demonstrate the hydrogen-enhanced plasticity effects on deformation over 500 C, like titanium alloys hydrogenated from the gas phase. 

The halide groups can be replaced by other substituents like hydride or alkyl [86]. When the naphthyl (np) RuHnp(dmpe)2 is heated, the ligand undergoes an internal metallation to afford a dimer [87] (it was originally believed to be a monomer), though Ru(dmpe)2 has been isolated by photolysis of its dihydride, in matrixes at 12K (Figure 1.29) [88],... 

Both cis- and (rans-structures are possible RuH2(PMe3)4 is cis (Ru-H 1.507, 1.659 A, Ru-P 2.276-2.306 A) [90] while spectra show that RuH2(PF3)4 and others have this configuration. RuH2[PPh(OEt)2]4 is definitely trans (X-ray) with Ru-H 1.6 A, Ru-P 2.272 A. Many diphosphines form dihydrides. Ru(dmpe)2H2 has been a useful starting material for the synthesis of thiolate complexes [91] such as fra s-Ru(SPh)2(dmpe)2. 

Reaction of OsH4(PR3)3 with tertiary phosphines gives dihydrides OsH2(PR3)4 (PR3 = PMePh2, PMe2Ph, PEt2Ph, etc.) [163] ... 

RhCl(PPhi)i as a homogenous hydrogenation catalyst [44, 45, 52]. The mechanism of this reaction has been the source of controversy for many years. One interpretation of the catalytic cycle is shown in Figure 2.15 this concentrates on a route where hydride coordination occurs first, rather than alkene coordination, and in which dimeric species are unimportant. (Recent NMR study indicates the presence of binuclear dihydrides in low amount in the catalyst system [47].)... 

Figure 2.68) while 5-coordinate (tbp) dihydrides have also been synthesized [119b],... 

Several m-platinum(II) dihydrides lose H2 reversibly in solution, forming dinuclear platinum(I) hydrides [(diphosphine)PtH]2 [62],... 

Dihydrides are more difficult to prepare but are most easily obtained with very bulky tertiary phosphines [101a]... 

Tetraphenylmolybdenocene dihydride Mo(r 5-C5HPh4)CpH2 (45) was formed by addition of diphenylacetylene to MoCpL(PhC CPh)CH3 (L = P(OMe)3) (Eq. 15), presumably via an ot-hydrogen abstraction to an intermediate methylidene hydrido complex, followed by addition of two equivalents of diphenylacetylene and C — H insertion with concomitant elimination of L [57 b],... 

Auch Diphenyl-zinn-dihydrid (Herstellungs.ds. Handb. Bd. XIII/6, S. 258 u. S. 451) und auf Polystyrol auf-getragcnes Dibntyl-zinn-dihydrid1 wird zu Reduktionen eingesctzt. 

Bis-[pentafluor-phenyl]- -dibromid 486 Bis-[pentafIuor-phenyl]- -dihydrid 486 Dicblor-dipbenyl- 702 Diphenyl- 702 Propyl- -trichlorid 486 Propyl- -trihydrid 486 Tris-[pentafluor-phenyI]- -bromid 486 Tris-[pentafluor-phenyI]- -hydrid 486... 

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