Copper hydride CuH

The existence of copper hydride (CuH ) as a chemical compound has been questioned. It may actually be an adsorption mixture, a solid solution or an interstitial compound. Ephraun, "Inorganic Chemistry, third English edition, p. 866, Nordeman Publishing Co., New York, 1939. 

They have compositions corresponding to EcHg, structures are unknown. Copper hydride, CuH, has been made recently by mixing lithium aluminium hydride, dissolved in pyridine and ether, with copper (I) iodide in pyridine ... 

A further example of a bifunctional base-hydrogenation catalyst for methanol has recently been reported by Union Carbide (ref. 44). Their homogeneous catalyst consists of a Cu+ compound and an alkali methoxide, and the hydrogenation component is believed to be the copper hydride CuH. The alkali methoxide may then serve as a base that activates CO by a nucleophilic attack analogous to reaction (9)... 

Among its salient features, this copper hydride (written for simplicity from now on as the monomer (Ph3 P)CuH) can be prepared in multi-gram quantities from four precursor compounds (CuCl, NaO-t-Bu, PPh3, and H2) that are not only readily available but also very inexpensive (Eq. 5.5) [15]. It is also noteworthy that the byproducts of formation (NaCl and t-BuOH) are especially environmentally friendly . 

A fascinating study on the surface science of copper hydride on Si02, as well as on AI2O3, ceria (cerium oxide), and ZnO, has appeared [50]. Pure, yet thermally unstable, CuH can be precipitated as a red-brown solid from aqueous cupric sulfate and hypophosphorous acid in the presence of H2SO4, and has been characterized by powder X-ray diffraction (PXRD) (Eq. 5.25). Transmission electron microscopy (TEM) data suggest that it is most stable when deposited on acidic Si02. 

Reduction to a saturated ketone raises the potential problem of competition between 1,2 and 1,4 reduction. Based on the HSAB principle, soft nucleophiles (e.g cuprates) lead to 1,4 products. On the other hand, hard nucleophiles (alkyllithium compounds, LiAlH4) react preferentially to give 1,2 products. Two alternatives to the copper hydride complex [PPh>CuH]6 were investigated - reduction with either NaBII3 or Na2S20i4 - but both failed to produce the desired results. 

The chief avason for utilizing the reaction sequence described is the fact that formation of the a,p-unsaturated ketone in II makes it possible to dilTea ntiate between the two double bonds, because the copper hydride complex [PPh CuH], reduces only the conjugated double bond... 

Another, albeit less-frequently employed option for a copper-mediated reduction of propargylic electrophiles to allenes relies upon the use of a copper hydride, for example, Stryker s reagent [(Ph3P)CuH]6. This reagent was applied by Brummond and Lu147 to the synthesis of the structurally complex precursor 197 for a potent antitumor agent, ( )-hydroxymethylacylfulvalene, from propargyl acetate 196 (Equation (11)). 

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