José L. Vidal

[Rh12Sb(CO)27]3-. an example of encapsulation of antimony by a transition metal carbonyl cluster

Abstract The reaction of Rh(CO)2acac with triphenylantimony in the presence of cesium benzoate in tetraethylene glycol/dimethyl ether solution resulted in the selective formation of [Rh12Sb(CO)27]3- (66% yield) after 3 h of contact time under ≈400 atm of carbon monixide and hydrogen (CO/H2  1) at 140–160°C. The cluster has been isolated as the [Cs(18-Crown-6)2]+, [(CH3)4]+, [(C2H5)4N]+, (Ph3P)2N]+ and [PhCH2N(C2H5)3]+ salts. The [(C2H5)4N]3 [Rh12Sb(CO)27] complex has been characterized via a complete three-dimensional X-ray diffraction study. The complex crystallizes in the space group R 3 c with a  23.258(13) A, c  22.811(4) A, V  10 686 A3 and p(calcd.)  2.334 g cm-3 for mol.wt. 2503.66 and Z  6. Diffraction data were collected with an Enraf-Nonius CAD 4 automated diffractometer using graphite-monochromatized Mo-Kα radiation. The structure was solved by direct methods and refined by difference-Fourier and least-squares techniques. All non-hydrogen atoms have been located and refined: final discrepancy indices are Rf  3.5% and Rwf  4.6% for 3011 reflections. The anions structure consists of twelve rhodium atoms situated at the corners of a distorted icosahedron with contacts of 2.807(1), 2.861(1), 2.874(1), 2.999(1), 3.017(1) and 3.334(1) A and rhodium—antimony contacts of 2.712(0) A. Rhodium—rhodium bond distances of 2.807 and 3.017 A are in the range usually found for these complexes although a distance of 3.334 A may be longer than expected from bonding interactions. The sum of the covalent radii of antimony and rhodium, 2.80 A, is intermediate between the two observed RhSb contacts. The anion cluster structure is that of distorted icosahedron. This polyhedron has previously been found in [B12H12]2- but not with transition metal clusters. A comparison between the structures of rhodium carbonyl clusters and boranes shows the occurrence of similar structural features. Applications of bonding theories based on the boranes, such as Wades rules, to rhodium carbonyl clusters shows the extent in which these rules are obeyed.

Carbon monoxide hydrogenation, preparation and characterization of model compounds

Abstract Polynuclear rhodium carbonyl complexes are present during the rhodium catalyzed conversion of carbon monoxide and hydrogen to alcohols. High pressure f.t.-i.r. analyses of reaction solutions containing [Rh17(CO)32-(S)2]3− suggest a catalyst manifold composed, almost exclusively, of that cluster. A related complex, [Rh17(CO)32−n(S)2(CHO)n](3 + n)−, has been prepared. The reactions of LiBH(C2H5)3 and LiBD(C2H5)3 with Os3(CO)12, Ru3-(CO)12, Ir4(CO)12, and Rh4(CO)12 have been studied by i.r., 1H and 2H n.m.r. and 13C n.m.r. With the exception of the rhodium containing system, results suggest the formation of formaldehyde and methanol in these reactions, as well as the existence of previously unreported polynuclear transition metal formyl complexes. Formyl complexes have been implicated as key intermediates in the manganese or cobalt catalyzed conversion of carbon monoxide and hydrogen to methanol. Mass spectral studies suggest that the reaction of acetic [13C] formic anhydride with sodium pentacarbonylmanganate, to give 13CO substituted pentacarbonylmanganese hydride, proceeds via formation of a short-lived neutral formyl complex, (CO)5Mn−13CHO.

Rhodium carbonyl cluster chemistry under high pressures of carbon monoxide and hydrogen : VIII. Synthesis and structure of [Rh15(CO)30]2− (bcc array) and its relationship to [Rhl4(CO)25]4− (incomplete bcc) and [Rh15(CO)27]3− (hcp-bcc)

Abstract The generation of [Rh 15 (CO) 27 ] 3− under high pressures of CO/H 2 (15 atm, 150°C, 3 h) from Rh(CO) 2 acac and CsPhCO 2 in 18-crown-6-alcohol solutions results in the formation, precipitation and isolation of single crystals of [Rh 15 (CO) 30 ] 3− with [Cs(18-crown-6) 2 ] + as a counterion. The new anion has a bcc array of metal atoms related to the distorted one in [Rh 15 (CO) 27 ] 3− (bcc-hcp) and derived from the incomplete bcc array in [Rh 14 (CO) 25 ] 4− by formal addition of a “Rh(CO) 5 + ” group. These results are potentially relevant to the modeling of surfaces by clusters and to the steps involved in the detachment of mononuclear fragments from clusters by either CO or CO/H 2 .

Formyl complexes of transition metal carbonyl clusters : II. Spectroscopic study by 2H NMR of the synthesis of [Ir4(CO)12-x(CHO)x]x−, [OS3(CO)11(CHO)]− and [Ru3(CO)11(CHO)]− (x = 1,2)☆

Abstract The reactions of LiHB(C2H5)3 and LiDB(C2H5)3 with Re2(CO)10, Ir4(CO)12, Os3(CO)12, Ru3(CO)12 and Rh4(CO)12 have been studied by 1H, 2H and 13C NMR techniques. Results suggest the formation of formaldehyde and methanol in these systems, as well as the existence of previously unreported formyl complexes. A 2H isotope effect is noted in the apparent increase in stability of cluster formyl complexes.

Metal formyl complexes. Hydride transfer to group VIII transition metal carbonyl clusters

Abstract The reaction of LiBH(C 2 H 5 ) 3 with Os 3 (CO) 12 or Ir 4 (CO) 12 leads to the formation of spectroscopically detectable formyl complexes. In the latter case, the complex is smoothly converted to [Ir 4 (CO) 11 H] − , an expected decompositioFn complex of the corresponding polynuclear formyl complex, [Ir 4 (CO) 11 CHO] − .

Rhodium Carbonyl Clusters with Encapsulated Main-Group Atom(s). Structures and Reactivity

Homogeneous catalysis by transition metal clusters is attracting increasing attention, (1,3) as well as the modeling of some heterogeneous catalysts by these complexes. (4) Cluster catalysis in homogeneous systems has been reported for some technologically relevant reactions such as hydr formylat ion, (5) water-shift, (6) oxidation (7) and Fisher-Tropsch. (8) In addition, rhodium carbonyl clusters are present during the catalytic synthesis of alcohols from carbon monoxide and hydrogen.(9)

On the thermal growth and decomposition of rhodium carbonyl clusters

Abstract The growth of anionic rhodium carbonyl clusters under pyrolytic conditions depends upon the counterion. The appearance of complexes of higher nuclearity was least favorable with the cesium salts while it occurred more readily with the ammonium salts following the trend: [R 4 N] + (R = alkyl) 3 R′N] + (R′ = benzyl) 3 NH] + 2 NH 2 ] + . A redox reaction between the rhodium carbonyl anion and the ammonium cation is implicated in the thermal growth of clusters. The electron-transfer process between these two moieties may involve the initial fragmentation of the clusters to form [Rh(CO) 4 ] − , and the reduction of the ammonium counterions by [Rh(CO) 4 ] − at high temperatures, although the direct electron transfer from the polynuclear species to the cation cannot be ruled out yet. It appears that electron transfer precedes or, that is parallel to, the fragmentation of the clusters while the aggregation reactions of the resulting fragments give the observed products. The formation of metallic rhodium from either mono- or poly-nuclear complexes, and the sequential transformations found for these species are in agreement with the expected thermodynamic preference for high nuclearity species. The existence of the independent effect of the amines and the alkali cations when both of them are present resulted in the inhibition of the formation of metallic rhodium and retarded the growth of the clusters. These results correlate with the enhanced rhodium solubility noted for some catalytic systems that are based on rhodium carbonyl clusters with amines and cesium salts added, and which are used to convert H 2 /CO mixtures into polyalcohols.

Rhodium carbonyl cluster chemistry under high pressure of carbon monoxide and hydrogen : VII. Conversion of [Rh15(CO)27]3− into other high nuclearity clusters: new high-yield syntheses for [Rh13(CO)24H2]3− an

Abstract The interconversions of [Rh13(CO)24H2]3-, [Rh15(CO)27]3-, and [Rh14(CO)25]4- have been studied under high press

Metal formyl complexes. The reaction of sodium pentacarbonylmanganate with acetic[13C]formic anhydride

The reaction of acetic [13C]formic anhydride with sodiumpentacarbonylmanganate proceeds rapidly at 0°C to give 13CO substituted pentacarbonylmanganese hydride as the predominant product. The results are consistent with the formation of a short-lived neutral formyl complex, (CO)5Mn13CHO.