Cluster Build-up Research Articles

Thermolytic reaction of 1,4-diisopropenylbenzene with [Ru3(CO)12]: an arene ligand as a template for cluster formation

The reaction of [Ru3(CO)12] with 1,4-diisopropenylbenzene in refluxing octane led to the isolation of a series of clusters with nuclearities from 2 to 7: [Ru4(CO)10(C12H14)]1, [Ru3(CO)8(C12H12)]2, [Ru6H(CO)15(C12H11)]3, [Ru6H(CO)15(C12H13)]4, [Ru2(CO)6(C12H12)]5, [Ru7C(CO)16(C12H12)]6, [Ru3H(CO)9(C12H11)]7, [Ru5H(CO)14(C12H11)]8 and [Ru6C(CO)15(C11H10)]9. The molecular structures of 1 and the three metallacycle compounds 2–4 have been determined by X-ray crystallography. The hexaruthenium species 3 and 4 represent a new category of arene cluster. The six ruthenium atoms describe an edge-bridged tetrahedron with a ruthenium spike bound to the edge-bridging atom. The arene ligand acts as an eleven-electron donor via both σ and π bonds. The pathway of the reaction has been established and provides evidence for ligand-moderated modular cluster build-up in which the ligand acts as a template.

Syntheses, structures and chemistry of the high-nuclearity ruthenium hydrido cluster anions [Ru10H2(CO)25]2? and [Ru11H(CO)27]3?

Thermolysis of [Ru3(CO)12] in ethanol yielded the decanuclear hydridoruthenium cluster dianion [Ru10H2(CO)25]2–1. When a mixture of methanol and water is employed as thermolysis solvent the undecaruthenium hydridoruthenium trianion [Ru11H(CO)27]3–2 is also formed. Crystal structure analysis of 1 as its [N(PPh3)2]+ salt and 2 as its [NEt3(CH2Ph)]+ salt showed their metal core structures to be related, 2 being a square-faced capped congener of 1. Cluster 2 was alternatively formed in near-quantitative yields when [Ru3(CO)12] was thermolysed in acetonitrile containing traces of water for several days. It was not possible to locate the hydride ligands in the structures by potential-energy-minimisation calculations, but strong signals were seen in the 1H NMR spectra at δ–14.2 (s, 2 H) for 1 and at –5.47 (s, 1 H) for 2. On treatment of 1 and 2 with [Au(PPh3)Cl] in the presence of TlPF6, 1 showed no reactivity, but 2 reacted smoothly adding one [Au(PPh3)]+ moiety and giving a product characterised as [Ru11H(CO)27{Au(PPh3)}]2–3. The structural relationships between the known high-nuclearity ruthenium hydrido carbonyl clusters are discussed, and their implications for a possible cluster build-up sequence considered.

Systematic build-up of high-nuclearity osmium–mercury clusters

The cluster dianion [Os10C(CO)24]2–1 has been studied as a substrate for redox condensations with mercury(II) electrophiles. Its reaction with HgX2(X = Cl, Br or I) initially generates the halogenomercury-capped clusters [Os10C(CO)24(HgX)]–(X = Cl 2a, Br 2b or I 2c) which undergo redistribution reactions in solution. This can be prevented by blocking one co-ordination site of the Hg atom with a CF3 group, thus producing the stable monoanion [Os10C(CO)24(HgCF3)]–2d. The structures of the [N(PPh3)2]+ salt of 2b and the [PPh4]+ salt of 2d were established by single-crystal X-ray structure analysis. The reaction of 1 with 0.5–0.7 equivalent of Hg(O3SCF3)2 leads to selective formation of the Hg-linked cluster dianion [{Os10C(CO)24}2Hg]2– the structure of which was determined by X-ray crystallography as its [N(PPh3)2]+ salt. The limits of this synthetic concept are set by the redox behaviour of the cluster. The cluster build-up achieved with 1 does not take place with its tetrahydrido analogue [Os10H4(CO)24]2–, which is instead oxidised by mercury salts to yield the radical monoanion.

Azoalkan‐ und Nitren‐verbrückte Carbonylmetall‐Cluster des Eisens und Rutheniums

Azoalkane‐ und Nitrene‐Bridged Carbonyl Metal Clusters of Iron and RutheniumBy using cluster buildup reactions, the new azoalkane‐bridged clusters Ru3(CO)9(RNNR) (3a, RMe, 3b, REt), Fe2Ru(CO)9(EtNNEt) (4), Ru4(CO)12(RNNR) (5a, RMe, 5b, REt), and FeRu3(CO)12(EtNNEt) (6) were obtained. Upon attempts to prepare further such compounds, the N‐N bond was cleaved resulting in nitrene‐bridged clusters including the new compound Fe4(CO)11(μ4‐NEt)2 (9). Cluster buildup starting from Ru3(CO)9(μ3‐NPh)2 resulted in Ru4(CO)11(μ4‐NPh)2 (10) and FeRu3(CO)11(μ4‐NPh)2 (11). The crystal structures of 5b and 9 as well as some reactions of the nitrene‐bridged clusters are described.

Synthesis of metal-rich metallaborane clusters. Evidence for a mechanism involving fragment condensation

A mechanistic hypothesis of metallaborane cluster build-up by the condensation of metal and boron containing fragments, which is supported by circumstantial evidence from previous work, suggests improved routes to the synthesis of ferraboranes. This work describes two new approaches consisting of the examination of two precursors with properties consistent with such a hypothesis. The first precursor, a neutral mononuclear dimethyl sulfide substituted iron tetracarbonyl, Fe(CO) 4SMe 2, is a new compound and the high yield synthesis and structural characterization of it are reported. This compound provides a better route to the ferraborane Fe 2(CO) 6B 2H 6 than those presently known and is an isolatable, alternate source of the Fe(CO) 4 fragment. The second precursor, Fe(CO) 3(cco) 2, where cco is η 2- cis-cyclooctene, is a known, ready source of the Fe(CO) 3 fragment. The reaction of Fe(CO) 3(cco) 2 with BH 3 sources at low temperatures results in good yields of known ferraboranes and a product distribution that depends primarily on the ratio of boron to iron in the reactants. Both of these results support a mechanism for metallaborane cluster formation involving rapid metal carbonyl fragment condensation as a principal mechanistic component.

ChemInform Abstract: Silylalkyne‐ and Silylvinylidene‐Bridged Mixed Metal Clusters.

AbstractAttempts to incorporate silylalkynes into FeCo2 or RuCo2 clusters by means of cluster buildup or capping reactions are reported.

Silylalkin‐ und Silylvinyliden‐verbrückte Heterometallcluster

Silylalkyne‐ and Silylvinylidene‐Bridged Mixed Metal ClustersAttempts to incorporate silylalkynes into FeCo2 or RuCo2 clusters by means of cluster buildup or capping reactions are reported. From RuCo2(CO)11 and Me3SiC≡CMe were obtained RuCo2(CO)9(μ3‐Me3SiC≡CMe) (5) and its more stable isomer RuCo2(CO)9(μ3‐C=C(Me)SiMe3) (6). Of the latter the isonitrile derivative 8 was characterized by structure determination. The silylalkyne‐bridged cluster 5 is very prone to desilylation forming RuCo2(CO)9(μ3‐HC≡CMe) (11). The silylvinylidenebridged cluster 6 undergoes cluster expansion with CpRh(CO)2 to form RuCo2RhCp(CO)8(μ4‐Me3siC≡CMe) (12), which again bears the silylalkyne ligand.

Carbide forming and cluster build-up reactions in ruthenium carbonyl cluster chemistry

The reinvestigation of an early synthesis of hexaruthenium carbido clusters has lead to the isolation of a number of new clusters which have been fully characterised by spectroscopic and crystallographic techniques. The thermolysis of Ru 3(CO) 12 in the presence of mesitylene (1,3,5-trimethylbenzene) at moderate temperatures yields two new clusters, [Ru 6(μ 4-η 2-CO) 2(CO) 13(η 6-C 6H 3Me 3)] (I) and [HRu 6(μ 4-η 2-CO)(CO) 13(μ 2-η 7-C 6H 3Me 2CH 2)] (II), the structures and reactivity of which indicate the origin and mechanism of formation of the carbido-carbon in the hexaruthenium carbido clusters [Ru 6C(CO) 14(η 6-C 6H 3Me 3)] (III) and [Ru 6C(CO) 17] (IV). A further product of the reaction is the decaruthenium carbido cluster dianion [Ru 10C(CO) 24] 2− (V) which has the tetracapped octahedral geometry. The monohydrido-cluster anion [HRu 10C(CO) 24] − (VI) may be synthesised quantitatively from V by protonation. The nature of the hydrido-ligand in VI has been investigated in the solid state by NMR spectroscopy and it has been found to be fluxional, its location being temperature dependent. The decanuclear dianion V has been found to react with mercury salts to yield the 21 metal atom cluster dianion [Ru 18Hg 3C 2(CO) 42] 2− (VII) which consists of two tricapped octahedral nonaruthenium “subclusters” fused by a bi-facecapping (Hg 3) 2+ unit.