Reactions of Complex Hydrides

The reaction of complex hydrides with carbonyl compounds can be exemplified by the reduction of an aldehyde with lithium aluminum hydride. The reduction is assumed to involve a hydride transfer from a nucleophile -tetrahydroaluminate ion onto the carbonyl carbon as a place of the lowest electron density. The alkoxide ion thus generated complexes the remaining aluminum hydride and forms an alkoxytrihydroaluminate ion. This intermediate reacts with a second molecule of the aldehyde and forms a dialkoxy-dihydroaluminate ion which reacts with the third molecule of the aldehyde and forms a trialkoxyhydroaluminate ion. Finally the fourth molecule of the aldehyde converts the aluminate to the ultimate stage of tetraalkoxyaluminate ion that on contact with water liberates four molecules of an alcohol, aluminum hydroxide and lithium hydroxide. Four molecules of water are needed to hydrolyze the tetraalkoxyaluminate. The individual intermediates really exist and can also be prepared by a reaction of lithium aluminum hydride... 

Reactions of complex hydrides with Sb compounds are effective for stibine syntheses. Metal tetrahydroborate reductions of Sb compounds in both HjO and nonaqueous media occur. Dropwise addition of a basic [Sb(OH) ] -KBH, soln to aqueous acid forms SbHj in 95% yield ... 

Plumbane, because of its low thermal stability, is not isolated from reactions of complex hydride with Pb halides. Alkylplumbanes (RjPbH, R PbHp form in reactions of dialkyl- or trialkylhaloplumbanes with LiAlH in ethers (MejO or monoglyme) at —60 to — 110°C in up to 90% yield, e.g. ... 

Another important research for dehydrogenation and rehydrogenation is for multicomponent (or mixed) system. For example, the dehydrogenation and rehydrogenation reactions of complex hydride-metal hydride e.g. M(BH4) -M Hm have been recently investigated ... 

Reaction of metal hydride complexes with N-nitrosoamides, e.g. Af-methyl-7V-nitrosourea ... 

Reaction of Carbonyl Hydrides with Complexes of Group-IB. 

S.3.2.2.2. Reaction of Carbonyl Hydrides with Complexes of Group-IB Metals. 

The reactions of silicon hydrides with low-valent phosphine complexes of Fe, Co, and Ni have led to the isolation of a number of products in some of which the silicon moiety may be present as an [SiXj] anion (177). Examples are given in Eqs. (102)-(103). Definitive confirmation of these formulations... 

However, there is evidence that reactions of aluminium hydride produced in situ involve single-electron-transfer (SET) processesThe reactions described by Trost and Ghadiri have most likely not been studied in sufficient detail to permit an adequate description of the reaction mechanism to be given at this stage. It is, however, quite likely that the Grignard reactions catalyzed by copper(II) and nickel(II) complexes , as developed by julia - and by Masaki , do involve SET processes, although, if this is so, the preservation of stereochemistry in some of the examples described by these workers is quite remarkable. (In this context, the reader s attention is drawn to Reference 196, end of this section.)... 

Reactions of Complex Metal Hydrides with Borate Esters. J. Organo-metal. Chem. 3, 371 (1965). 

A similar involvement of palladium hydride, palladium alkyl, and palladium acyl complexes as intermediates in the catalytic cycle of the Pd-catalyzed hydroxycarbonylation of alkenes was reported for the aqueous-phase analogs. The cationic hydride PdH(TPPTS)3]+ was formed via the reduction of the Pd11 complex with CO and H20 to [Pd(TPPTS)3] and subsequent protonation in the acidic medium. The reaction of the hydride complex with ethene produced two new compounds, [Pd(Et)(TPPTS)3]+ and Pd(Et)(solvent)(TPPTS)2]+. The sample containing the mixture of palladium alkyl complexes reacted readily with CO to afford trans-[Pd(C(Q)Et)(TPPTS)2]+.665... 

An important contribution to an understanding of the mechanism of propene dimerization has been obtained by studying the reaction of nickel-hydride model complexes (55). The formation of the propyl- and isopropyl-nickel complexes 48 and 49 has been observed in the reactions of HNi(PR3)Cl complexes (50) with propene at -78°C [Eq. (15)] ... 

In related studies, Cp2ZrCl2 has been found to catalyze at room temperature an aluminum hydride (i-Bu2AlH) reduction of CO to linear Ci-C5 alcohols (430). The system involves reaction of complex 55 with CO, which precipitates the starting zirconium(IV) complex and leaves a yellow solution, that on hydrolysis yields the alcohols. Toluene solutions of Cp2Ti(CO)2 complex under H2/CO effect Eq.(69), i.e., a homogeneous stoichiometric hydrogenation of carbon monoxide to methane (426). 

These ate complexes are prepared by reaction of potassium hydride with a 9-alkyl-9-borabicyclo[3.3. l]nonane (9-R-9-BBN). 

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