Mario Castiglioni

Simple, high-yields syntheses of nickel-osmium clusters. spectroscopic characterization of the new (η-C5H5)NiOs3(CO)9(μ2-H)3. The reactivity of (η-C5H5)NiOs3(CO)9(μ2-H)3 and (η-C5H5)3Ni3Os3(CO)9 towards H2, CO, alkynes and alkenes

Abstract The complexes (η-C5H5)NiOs3(CO)9(μ2-H)3 and (η-C5H5)3 Ni3Os3(CO)9 can be obtained in high yield by treating Os3(CO)12 or H2Os3(CO)10 with [(η-C5H5)-Ni(CO)]2 in refluxing hydrocarbons. The course of the reactions and the yields of the products can be modified by carrying out the reaction under nitrogen, hydrogen or carbon monoxide atmospheres. A preliminary report of an X-ray study of the hexametallic, 87 e− cluster was presented. The new tetrametallic derivative was characterized by spectroscopic techniques; a tetrahedral, tri-hydridic structure is proposed for this complex. The reactions of the heterometallic nickel-osmium complexes towards ligands, in particular alkenes and alkynes, are discussed. A preliminary investigation of homogeneous hydrogenation of these substrates is reported.

The reactivity of HRu3(CO)9C2·CMe3. The hydrogenation of coordinated t-butyl-acetylene to neo-hexane and the crystal structure of the intermediate trihydride H3Ru3(CO)9C·CH2·CMe3

Abstract The reaction of Ru 3 (CO) 12 with 3-2dimethybut-1-yne (t-Butylacetylene) gives the mono-hydride HRu 3 (CO) 9 C 2 Bu t in good yields. This complex reacts in hydrocarbon solvents with molecular hydrogen, to give the tri-hydride H 3 Ru 3 (CO) 9 C·CH 2 ·CMe 3 which, upon further hydrogenation, affords H 4 Ru 4 (CO) 12 and neo-hexane. In this way, a full hydrogenation cycle can be obtained; however, low yields of the hydrogenated product, and some decomposition to metal powder are also observed. The probable intermediate steps of these reactions are discussed. The strcuture of the intermediate H 3 Ru 3 (CO) 9 C· CH 2 CMe 3 has been studied by X-ray diffraction; the complex crystallizes in the triclinic system, space group P 1 with a = 8.781(3), b = 9.253(3), c = 14.910(4) A , α = 86.17(5), β = 85.69(5), γ = 63.50(4)°. The ruthenium atoms were located by the Patterson method and the remaining carbon and oxygen atoms by Fourier-difference maps. A least-squares anisotropic refinement led to R = 0.0385 for 4028 observed reflections with 1 ⩾ 3σ(I). The title compound belongs to the series of methylidine complexes with a ‘tetrahedral’ Ru 3 C core; each ruthenium atom links three terminal carbonyl groups and a chainCH 2 C(CH 3 ) 3 is bonded to the apical carbon atom of the core. The presence of the three bridging hydridic atoms is discussed and a comparison with the parent HRu 3 (CO) 9 C 2 C(CH 3 ) 3 complex is made. complex is made.

Homogeneous catalytic hydrogenation and isomerization of linear and cyclic monoenes and dienes in the presence of the heterometallic cluster (η5-C5H5)NiRu3(μ-H)3(CO)9

Abstract The complex (η 5 -C 5 H 5 )NiRu 3 (μ-H) 3 (CO) 9 catalyses the selective hydrogenation of the terminal double bond of conjugated linear dienes in homogeneous conditions; isomerization of non-conjugated to conjugated dienes and of pent-1-ene to pent-2-enes also occurs. Selective hydrogenation and isomerization of cyclic hexenes and hexadienes takes place without opening of the ring; a reaction scheme is proposed, and the activity of the cluster itself relative to that of its decomposition products is discussed. Its behaviour is compared with the analogous complex (η 5 -C 5 H 5 )NiOs 3 (μ-H) 3 (CO) 9 .

Metal carbonyl clusters in homogeneous catalysis. Hydrogenation and isomerization of cyclic dienes in the presence of [H4Ru4(CO)12], [H2Ru4(CO)13], [H2FeRu3(CO)13] and [Fe2Ru(CO)12]. Identification of organometallic products and a discussion of their role

The hydridic tetrahedral clusters [H4Ru4(CO)12] (1), [H2Ru4(CO)13] (2) and [H2FeRu3(CO)13] (3), and the related [Fe2Ru(CO)12] (4), have been tested as homogeneous catalysts for the hydrogen ation-isomerization of 1,3- and 1,4-cyclohexadiene. Catalytic activity was found but there is evidence for metal species rather than intact clusters to account for the observed behaviour. After the hydrogenation experiments, diene- and arene-substituted clusters and organometallic derivatives were found in solution. Their nature was confirmed by spectroscopic analyses, mass spectrometry and, in some instances, by independent synthesis. Their role in the hydrogenation reactions is discussed. Deuteration experiments showed that hydrogen adds first to the cluster metals and is then transferred to the coordinated substrate.

Phosphine-substituted and phosphido-bridged metal clusters in homogeneous catalysis: IV. Selective hydrogenation of diphenylacetylene and isomerization of cis-stilbene in the presence of Ru3(CO)12−n (PPh2H)n (n = 2, 3), HRu3(CO)10(μ-PPh2), HRu3(CO)9(μ-PPh2) and HRu3(CO)7(μ-PPh2)3

The clusters Ru3(CO)12−n(PPh2H)n (n = 2, 3), HRu3(CO)10(μ-PPh2), HRu3-(CO)9(μ-PPh2) and HRu3(CO)7(μ-PPh2)3 show considerable activity in the selective hydrogenation of diphenylacetylene to stilbenes; the phosphine-substituted derivatives are also very efficient in the isomerization of cis-stilbene to trans-stilbene. The latter product is often found as a precipitate in the vials after the hydrogenation or isomerization experiments. Different cis/trans-stilbene ratios in the hydrogenation solutions have been found for the phosphine-substituted and the phosphido-bridged clusters; this points to different reaction patterns and/or intermediates. A comparison of the behaviour of C2Ph2, C2Et2 and HC2But under the same conditions and in the presence of the same phosphido-bridged cluster has been made; the nature of the alkyne has an important influence on the hydrogenation rate and the formation of reaction intermediates

Thermolysis and mass spectra of polymeric germanium hydride produced by γ-radiolysis

Abstract TGA, MS and DSC of a solid polymeric Ge hydride, obtained by γ-radiolysis of GeH 4 , are reported. Upon heating, it undergoes two successive weight losses at 463 and 1173 K. At 948 K two crystal phases are formed, one of them is pure germanium. Some comparisons with a-Ge: H produced via RF sputtering or glow discharge are reported.

Metal clusters in catalysis. The reactivity of alkyne- and vinylidene-substituted homo- and hetero-metallic clusters towards molecular hydrogen in homogeneous conditions

Abstract The reactivity of alkyne- and vinylidene-substituted clusters towards molecular hydrogen in homogeneous conditions has been studied by means of GC and GC/MS techniques. The reactivity of the homo- and hetero-metallic cluster frames (containing nickel and one of the iron triad metals) is discussed, as well as that of the coordinated ligands. Under hydrogen the cluster cores are modified, sometimes as a part of a catalytic cycle. The products obtainable from the coordinated small molecules seem to depend mainly on the overall electronic situation of the clusters or on the CC distances in the alkynes, and to a lesser extent on the number of coordinating metal centres. In some instances it was observed that when both free alkynes and substituted clusters were present, only the coordinated alkynes were hydrogenated.

Homogeneous catalysis on metal clusters. The isomerization and selective hydrogenation of dienes, alkenes, and alkynes in the presence of [(η-C5H5)NiOs3(µ-H)3(CO)9] and [(η-C5H5)NiOs3(µ-H)3(CO)8L][L = PPh2H or P(C6H4Me-o)3]. Spectroscopic identification of the reaction intermediates and X-ray structure of [Os3(µ-H)(CO)9(MeCCHCMe)]

The complexes [(η-C5H5)NiOs3(µ-H)3(CO)9] and [(η-C5H5)NiOs3(µ-H)3(CO)8L][L = PPh2H or P(C6H4Me-o)3] catalyze under homogeneous conditions the hydrogenation of one double bond of dienes and show selectivity in the hydrogenation of triple and double C–C bonds; non-conjugated dienes are isomerized. Experimental evidence suggests that the cluster acts as a catalyst. Complexes [(η-C5H5)NiOs3(µ-H)3(CO)8(diene)] and [Os3(µ-H)(CO)9(MeCCHCMe)] have been isolated in the reaction solutions. The former complexes have been identified by spectroscopy and the latter by X-ray diffraction methods. A reaction path is proposed. Crystals of [Os3(µ-H)(CO)9(MeCCHCMe)] are monoclinic, space group P21/n, with unit-cell dimensions a= 10.960(7), b= 17.064(8), c= 10.162(5)A, β= 106.07(2)°, and Z= 4. The structure was determined from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.048. In the complex an allylic ligand (derived from a pentadiene) co-ordinated to a triangular osmium cluster has been found; although this type of structure has already been reported, this is the first osmium complex obtained by reaction with a diene.

“Olefin metathesis” reactions of (η5-C5H5)NiRu3(μ-H)(CO)9-(μ4-η2)-(CCHBut) and related complexes

Abstract The complex (η 5 -C 5 H 5 )NiRu 3 (μ-H)(CO) 9 (μ 4 -η 2 -CCHBu t ) ( 1a ) reacts with olefins to give several organic products, including species derived from the coupling of the vinylidene ligand with an olefin-derived =CRR′ fragment, representing the first example of a (non catalytic) olefin metathesis reaction involving a metal cluster; other complexes structurally or chemically related to the compound 1a have also been treated with olefins and alkynes.

Homogeneous hydrogenation of alkynes and of 1,4-cyclohexadiene in the presence of the clusters Ru3(CO)7(μ-PPh2)2(C6H4), Ru4(CO)11(μ4-PPh)(C6H4), Ru3(CO)7(μ-PPh2)2(HC2Ph) and Ru4(CO)11(μ4-PPh)(C2Ph2)

Abstract The title complexes, containing phosphido or phosphinidene bridges, catalyze the hydrogenation of alkynes and of 1,4-cyclohexadiene (1,4-CHD). The benzyne-substituted clusters Ru 3 (CO) 7 (PPh 2 ) 2 (C 6 H 4 ) ( 1 ) and Ru 4 (CO) 11 (PPh)(C 6 H 4 ) ( 2 ) show the highest hydrogenation activity yet observed for substituted metal carbonyl clusters towards alkynes; the activity is related to the nature of the alkyne substrate, C 2 Et 2 2 Ph 2 Ph 2 . The alkyne complexes Ru 3 (CO) 7 (PPh 2 ) 2 (HC 2 Ph) ( 3 ) and Ru 4 (CO) 11 (PPh)(C 2 Ph 2 ) ( 4 ), structurally closely related to 1 and 2 , have also been examined in comparable reactions; complex 3 shows very high activity, especially towards 1,4-CHD. Organometallic intermediates could not be isolated but direct and indirect evidence supporting a reaction pathway based on cluster catalysis was obtained; this will require the formation of an active site, dihydrogen activation and insertion of the substrate into M–H bonds. Possible alternative mechanisms are also discussed.