Hydride cluster , carbonyl

Conjugate reduction.1 This stable copper(I) hydride cluster can effect conjugate hydride addition to a,p-unsaturated carbonyl compounds, with apparent utilization of all six hydride equivalents per cluster. No 1,2-reduction of carbonyl groups or reduction of isolated double bonds is observed. Undesirable side reactions such as aldol condensation can be suppressed by addition of water. Reactions in the presence of chlorotrimethylsilane result in silyl enol ethers. The reduction is stereoselective, resulting in hydride delivery to the less-hindered face of the substrate. 

The interaction of Ru3(CO)i2 with Si02 seems to proceed via a hydride surface carbonyl species. An ulterior decomposition under vacuum mainly gives Ru particles of 1.4nm and Ru(II) carbonyl species ]90]. Similarly, [HRu3(CO)io( t-OSi)]surface specics are generated by the reachon of Ru3(CO)i2 with a porous Vycor glass at 65 °C under air ]103]. Above 130 °C it was reported that the surface cluster breaks down with formation of ]Ru(CO) (OSi)2]surface species (n = 2 and/or 3). When the initial surface species was heated in air at T> 250°C, decomposition of the cluster and formation of RUO2 nanoparticles were observed. 

Carbon tetrabromide, irradiation of, 5 152 Carbon tetrachloride, ionization, 9 230-231 Carbonyl anion and hydride clusters, 13 478-480, 482, 483... 

In some instances, particularly when the ruthenium trichloride sample contains more than the usual amount of water (this may occur, e.g., with old samples or on long exposure to moist air), the isolated product may be a mixture of Ru3(CO)12 and Ru4(/ -H)4(CO)12 (as indicated by the IR v(CO) spectrum). In such cases, depending upon the final product required (a) the product may be used directly as in the synthesis of Ru4( -H)4(CO)12 described below, when conversion to the cluster carbonyl hydride is completed by reaction with H2 or (b) treatment of the product with CO for 1 h while suspended in refluxing octane, using the apparatus depicted in Fig. 1, results in conversion of any Ru4(/i-H)4(CO)12 to Ru3(CO)12. 

Submitted by MICHAEL 1. BRUCE and MICHAEL L. WILLIAMS Checked by GUY LAVIGNE and TH RESE ARLIGUIEt This tetranuclear ruthenium carbonyl hydride was described on several occasions,5 but early preparations were usually contaminated with Ru3(CO)12, giving rise to suggestions of the existence of two isomeric forms. The situation was clarified by the work of Kaesz and coworkers,6 who discovered the direct route from Ru3(CO)12 and hydrogen, which is described below. The compound is often obtained from reactions between Ru3(CO)12 and substrates containing hydrogen (hydrocarbons, ethers, alcohols, water, etc.) and by acidification of anionic ruthenium cluster carbonyls.7... 

The already voluminous review literature on clusters will be considered as a basis for this review. The topics treated so far are clusters in general (109, 241) and in connection with metal-metal bonding (30, 338, 380), special types of clusters like those with TT-acceptor ligands (231), hydrides (233), carbonyls (85, 86) or methinyl tricobalt enneacarbonyls (313, 317) properties of clusters like structures (56, 316), fluxionality (110), mass spectra (226), vibrational spectra (365), and redox behavior (292). Clusters have been treated in the context of metal carbonyls (3, 4), metal sulfur complexes (2, 381), and in relation to coordination polyhedra (297). Reviews... 

Relationships between Carbonyl Hydride Clusters and Interstitial Hydrides... 

In the penta-, hexa-, and heptanuclear carbonyl hydride clusters, terminal hydrides are observed only in the less crowded species, and again no evidence for the presence of interstitial hydride is found. 

Early Studies on Rhenium-Carbonyl-Hydride Clusters and Related Species... 

Osmium-Carbonyl-Hydride Clusters and Related Ruthenium Complexes. Our investigation of these species began with a study of the species (/i2-H)(H)Os3(CO)n, prepared from Os3(CO)i2 via the unsaturated species (M2-H)20s3(CO)io (33) (see Reaction 1). 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

Flgure 2 Schematic metal framework of rhenium carbonyl hydride clusters, electron counts, and selected examples... 

Metal dimers containing cyclopentadienyl ligands also can be separated to monomers with Hj as for (h -CjH5)2Cr2(CO) at 150 atm (15 MPa) and 70°C to yield HCr(CjHj-h )(CO)3. Mixed-metal hydride clusters may be synthesized from the H -assisted condensation of two different metal carbonyls. When Os3(CO),2 Or Ru3(CO),2 reacts with Ni2(C5Hj-h )2(CO)2 in the presence of at atm P, the mixed-metal clusters M3(ja-H)3Ni(C5H5-h5)(CO), [M = Ru (39%), Os (70%)] are formed l... 

The stable, well-characterized copper(I) hydride cluster [(PPh3)CuH]6 is a useful reagent for conjugate reduction of a,p-unsaturated carbonyl compounds. o This hydride donor is chemically compatible with chlorotrimethylsilane, allowing formation of silyl enol ethers via a reductive silation process (Scheme 53). 

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