Copper halides complex hydrides

The procedures described below have consistently given stable, crystalline products for a number of tertiary phosphine copper hydride complexes. These complexes can be prepared by the careful reaction of lithium tetrahydrido-aluminate(l-) with tertiary phosphine copper halide complexes. The reactions are run in etheral solvents under an inert atmosphere. The resultant products are... 

There are many examples of borohydride compounds of these metals, e.g., Cu, Ag, Zn and Cd-BH as neutral and anionic complexes in which the mode of bonding of BH is dependent on the coordination number of the metaP. Higher borane anions also combine with Cu and Ag, yielding both neutral and anionic complexes. Although no borohydrides of Au are isolated, treatment of Au-halide complexes with, e.g., NaBH, is a standard method for the preparation of Au-cluster compounds Copper(I) hydride, first reported in 1844, has the ZnS structure [d(Cn-H) = 0.173 nm (1.73 A) d(Cu-Cu) = 0.289 nm (2.89 A)] and decomposes to the elements when heated. At >100°C the decomposition is explosive. 

The paper reports preparation of two new copper hydride complexes. The lithium complex (1) is prepared from CuBr and 2 equiv. of lithium trimethoxy-aluminum hydride (cf. 5, 168) the sodium complex (2) is prepared from CuBr and 1 equiv. of sodium bis(2-methoxyethoxy)aluminum hydride. Both complexes are useful for selective reduction of the double bond of conjugated cnones 1 is more efficient for reduction of cyclohexenones and 2 is more efficient for reduction of acyclic enones. Aldehydes, ketones, and halides are also reduced nitrile and ester units are inert. The effective stoichiometry of both reagents is consistent with the structures LiCuHj and NaCuHs, but complex 1 is clearly different from a reagent assigned the structure LiCuHa by Ashby et al. ... 

Reactions.—New systems for the reduction of alkyl halides to alkanes include mixtures of lithium aluminium hydride with transition-metal chlorides (such as Ni or Co" chlorides) and some complex metal hydrides of copper, especially the THF-soluble Li4CuHs. Details of the application of sodium cyanoborohydride to the reduction of halides (and sulphonate esters) in dipolar aprotic solvents have been published. Virtually all other functional groups are inert to this convenient, mild, and efficient system, which has been used to develop a one-pot deoxygenation of primary alcohols (Scheme 39) via the iodides. The alternative cyanoborohydride reagents (55) and the polymeric (56) are also discussed. ... 

Copper-metal bonds have been synthesized by the condensation of (NHC)CuOFt with the acidic metal hydride CpMo(H)(CO)3 [171], or by halide displacement from (NHC)copper(l) using anions such as CpFe(CO)2 and CpMo(CO)3" (Cp = ri -CjHj Scheme 11.6) [172]. The net metal-metal interaction in these complexes is a a-bond In (lDipp)Cu-Fe(CO)2Cp, with a Cu-Fe distance of only 2.3462(5) A, the HOMO—1 and HOMO are Fe- Cu ic orbitals, and the LUMO is the a orbital. Natural population analysis indicates significant ionic character, consistent with unequal sharing of an... 

Other metals can catalyze Heck-type reactions, although none thus far match the versatility of palladium. Copper salts have been shown to mediate the arylation of olefins, however this reaction most probably differs from the Heck mechanistically. Likewise, complexes of platinum(II), cobalt(I), rhodium(I) and iridium(I) have all been employed in analogous arylation chemistry, although often with disappointing results. Perhaps the most useful alternative is the application of nickel catalysis. Unfortunately, due to the persistence of the nickel(II) hydride complex in the catalytic cycle, the employment of a stoichiometric reductant, such as zinc dust is necessary, however the nickel-catalyzed Heck reaction does offer one distinct advantage. Unlike its palladium counterpart, it is possible to use aliphatic halides. For example, cyclohexyl bromide (108) was coupled to styrene to yield product 110. 

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