Cluster anionic hydride

X neutral binary clusters cluster anions + neutral hydride clusters anionic hydride clusters... 

Saito and coworkers134 reported on the homogeneous reverse water-gas shift reaction catalyzed by Ru3(CO)i2. Conditions employed were 20 ml of N-methyl-2-pyrrolidone solution 0.2 mmol Ru3(CO)i2 1 mmol bis(triphenylphosphine)immi-nium chloride and C02-H2 1 3 under 80 kg/cm2 at 160 °C. The major products were CO (15.1 mmol), H20 (21.6 mmol), and methanol (0.8 mmol). As no formic acid was detected, and because the authors only detected Ru cluster anion species H3Ru4(CO)i2, H2Ru4(CO)i22, and HRu3(CO)n, they concluded that the mechanism did not involve formic acid as an intermediate. Rather, they proposed that the mechanism proceeds by dehydrogenation of a metal hydride, C02 addition, and electrophilic attack from the proton to yield H20, as outlined in Scheme 48. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

The synthetic methods used involve reaction of a cluster anion with [AuCIL], elimination of methane between a cluster hydride and [AuMeL] or addition of LAu+ units to metal-metal bonds. The emphasis here will be on structure and reactions of the complexes. Some examples of mixed gold clusters are given in Table 15, where it can be seen that most work has been on derivatives of clusters of iron, ruthenium and osmium. 

Some compounds and their reactions have been noted in Section 18-G-2. The homoleptic carbonyls are clusters such as M4(CO)i2 and M6(CO)i8. The hydride, HRh(CO)4, is very much less stable than HCo(CO)4 and has been made only under ca. 1400 atm pressure since it readily loses H2 to give clusters. Both Rh and Ir give anions [M(CO)4] and [M(CO)3]4 as R3NH+ salts as well as various cluster anions such as [Ir8(CO)22]2 and [Rh5(CO)i5] . Hydrido and other substituted polynuclear carbonyls are known. 

Transition-metal hydrides react with nitrogen compounds to form N—H bond-containing organometallic products. The [HFe3(CO),J cluster anion reacts with nitriles to form a coordinated RCNH species, along with the RCHN-coordinated isomer ... 

However, only alkyl formates are formed in the conventional reactions of alcohols, CO2 and H2 using transition metal complexes, because intermediary hydride complexes generally react with CO2 to give formate complexes. On the other hand, we have found that mthenium cluster anions effectively catalyze the hydrogenation of CO2 to CO, methanol, and methane without forming formate derivatives [2-4]. Ethanol was also directly formed from CO2 and H2 with ruthenium-cobalt bimetallic catalyst [5]. In this paper, we report that this bimetallic catalytic... 

Another interesting application is the selective reduction of aldehyde functions under water-gas shift reaction conditions [21]. Starting from Rh6(CO)i6 in the presence of an amine in aqueous media, the anionic cluster anion [Rh6(CO)i5H] forms via nucleophilic attack of hydroxide, followed by elimination of carbon dioxide. The anionic hydride cluster is thought to be the active species in the reduction of a number of aldehydes according to eq. (10). 

Reductive condensation of metal clusters to form larger cluster anions or hydrides is more extensively used than condensation of mononuclear complexes. In most systems examined a large number of cluster products can be obtained, but the reactions are sensitive to small changes in procedure. 

HCHO under carbonyl loss conditions (prolonged heating) to generate the cluster anion [Ru3lrH2(CO)i2] The hydride ligand is likely to be abstracted from the cluster by OH" (this step, of course, is not observed in the mass spectrometer). The resulting cluster will be short of one CO ligand, but as two have been lost, there will be plenty of CO present in solution for the unsaturated cluster to pick up. 

Several surface-mediated reactions leading to metal carbonyl clusters start from hydrated metal chlorides on wet silica it is also known that the presence of water can result in the formation of cluster anions at the expense of coordinated carbonylsJ l Hydridic cluster anions can be active in the water-gas shift reaction (WGSR), the Fischer-Tropsch and other reactions, as discussed belowJ ... 

Hydridic cluster anions are also important in the homogeneous WGSR cata-lysis.t The mechanism of WGSR reactions occurring on Ru3(CO)i2 with an acid cocatalyst (CF3COOH) has been fully elucidated.The radical anion [Fe3(CO)ii], obtained in the phase-transfer-catalyzed reaction of Fe3(CO)i2 with OH , catalyzes the reduction of nitrobenzene to aniline. 

Perhaps the most important development in polynuclear carbonyl hydride complexes was the observation by Kaesz et al. that good yields of hydridocarbonyls could be obtained by direct reaction of hydrogen with polynuclear carbonyls (82). This has been applied to a number of systems. Thus, the anion [Rh,2(00)39 yields the cluster anion... 

The formation of J-aggregate PIC in thin solid films. The Influence of the cluster anionic derivatives of high boron hydrides... 

A trinuclear cobalt(I) complex, PhCCo3(CO)9, can also catalyse the reduction of nitro compounds in the presence of hydroxide ion at room temperature under a normal pressure of CO [49]. Satisfactory results were obtained under phase transfer conditions. The catalyst and the aromatic nitro compounds were dissolved in benzene under carbon monoxide and an aqueous solution of sodium hydroxide containing cethyltrimethylammonium bromide was added. At a substrate/cat =10 ratio, ca. 60-80 % of amine was obtained in a 18 h reaction. The reaction also proceeded in a homogeneous phase (methanol-water, methanol, dioxane-water) but with lower conversions (less than 45 %). Cobalt complexes such as MeCCo3(CO)9 and MeCo(CO)4 were also active, but less effective. At the end of the reaction, the catalyst was recovered only in part (ca. 15 %). In the organic phase, an IR absorption at 1891 cm, attributable to [Co(CO)4] anion, was observed. Strangely enough, the preformed [Co(CO)4] anion has not been tested as catalyst. The active species was supposed to be the hydride cluster anion reported in Scheme 6. 

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