Trinuclear clusters, transition metal

All these results indicate that one is just at the beginning of understanding the function of catalysts being deposited on a semiconductor. There is still quite a confusion in many papers published in this field. Therefore the catalytic properties depend so much on the procedure of deposition . It seems to be rather difficult to produce a catalyst for 02-formation, as shown by results obtained with Ti02 (see e.g.) . Rather recently new concepts for the synthesis of new catalysts have been developed applicable for multielectron transfer reactions. Examples are transition metal cluster compounds such as M04 2RU1 gSeg and di- and trinuclear Ru-complexes . 

Dinuclear Pt complexes of the type [ Pt(PR3) 2(p-S)2] are also known to serve as the good precursors to the trinuclear clusters. A series of triangular cluster cores M Pt2(p3-S)2 has been constructed therefrom (M = transition metals, main-group metals).50... 

Some post-transition elements (or the corresponding radicals) containing 3 or more electrons in their valence shell are able to assist the formation of clusters by bonding to several metal atoms. Typical examples of this behaviour are the extraordinarily easy syntheses of large series of compounds such as Co3 (CO)9 (p3-E) (E = Al, CR, CX, GeR, P, As, PS, S, Se, PR, SR) 201 209) and Fe3 (CO)9 (p3 -E)2 (E = S, Se, Te, NR, PR). This type of stabilization is usually found in trinuclear clusters although a few examples in tetranuclear clusters are known, for instance ... 

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... 

Several groups have been investigating the use of transition metal complexes for the catalytic conversion of hydrosilanes to silyl formates [Eq. (50)]. The anionic trinuclear cluster [HRu3(CO)M]-1 has been effective for... 

Trinuclear clusters play an important role in the chemistry of molybdenum and tungsten. Deep red, isostructural clusters containing both [M03O4F9]3- (148, 149) and [W304F9]5 (149-151) are later additions to this family of simplest types of cluster species. Their basic structures conform to the fii-type of trinuclear electron-poor transition-metal clusters where the metals are in a distorted octahedral environment. 

Figure 4. Coordination modes of thiolates bound to trinuclear transition metal carbonyl clusters.

Fe3(CO)i2] was expected, but whereas reactions of the iron cluster normally lead to cleavage of the trimeric unit, the ruthenium analog seems to give stable trinuclear species. This was correlated with an increase in the stability of metal-metal bonds on descending the transition metal triad. For instance, when R = Et, Bu" or -in the case of osmium, Ph, the reaction in benzene or toluene under reflux affords [M3(CO)io( -H)(//-SR)] (M = Ru, Os) complexes. The structure of [Os3(CO)io(//-H)(/i-SEt)], synthesized in octane under reflux, has been reported. ... 

Some other transition metal carbonyl compounds were also investigated instead of Ru3(CO)i2, such as Os3(CO)i2, Rh4(CO)i2, Re2(CO)io, but none of them showed any activity in this reaction. The mechanism behind this reaction was most likely the fact that a coordinatively unsaturated metal center of the trinuclear cluster is attacked and coordinated by pyridine, and subsequent ortho-metalation gives the key intermediate. Olefin insertion into a linear and branched alkyl species, followed by CO coordination and insertion, produces the acyl species, which reacts further to the acylated product by reductive elimination. 

Another approach using supported, early transition metals involves the use of tantalum clusters on oxide surfaces. Gates et al. reported the formation of trinuclear tantalum by exposing partially dehydroxylated silica treated with... 

An intercalation process under reflux conditions for 4 days has been performed by Ma et al. to prepare chromium oxide-pillared manganese oxides [38]. In this reaction chromium hydroxyl acetate clusters, Cr3(OAc)7(OH)2, are used as the pillaring species. Cr + self-polymerizes under reflux to form polynuclear clusters between the manganese oxide layers. Intercalation of this trinuclear chromium complex constitutes a challenge because redox reactions may occur between manganese oxide and the transition metal oxide during the process, which could destroy the layer structure. 

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