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The carbonyl hydride cluster Ir4H8(CO)(4)(PPh3)(4) (1) has been formed in hig(31)P NMR spectra, two isomeric forms (1A and 1B) of the cluster are present in CD2Cl2 solution at room temperature, and they do not interconvert in the explored temperature range. However, if a solid sample of the cluster is dissolved at 188 K, only 1A is detected by NMR spectroscopy. The structure of 1B could be proposed on the basis of the T-1 relaxation times of the various hydrides: it results by localised exchange of H and CO around two vertices of the tetrahedral frame.h yield and purity by heating a mixture of Ir-4(CO)(12) and PPh3 in toluene at 90 degreesC under hydrogen at atmospheric pressure. The product has been characterised by microanalysis, spectroscopy (IR, H-1 and P-31 NMR) and X-ray diffraction. In the solid state one hydrogen, one CO and one triphenylphosphane ligand are terminally bonded to each iridium atom, whereas four hydride ligands are bridging. All the hydrogen atoms were directly located by X-ray analysis at an average H-Ir distance of 1.55 Angstrom. (for the terminal H) and 1.75 Angstrom (for the p-H). As shown by H-1 and P-31 NMR spectra, two isomeric forms (1A and 1B) of the cluster are present in CD2Cl2 solution at room temperature, and they do not interconvert in the explored temperature range. However, if a solid sample of the cluster is dissolved at 188 K, only 1A is detected by NMR spectroscopy. The structure of 1B could be proposed on the basis of the T-1 relaxation times of the various hydrides: it results by localised exchange of H and CO around two vertices of the tetrahedral frame

The cluster [FeNi5(CO)(13)] (2-) (1) was obtained by reaction of Fe(CO)(5) and [Ni-6(CO)(12)](2-) (2), in acetonitrile at room temperature. Its solid state structure was determined on the [NEt4]() salt, and consists of a trigonally distorted octahedron, with six edge-bridging ligands. This assembly strictly recalls the architecture of the prototypical [Ni-6(CO)(12)](2-) anion, by formal replacement of one Ni(CO) unit with the Fe(CO)(2) fragment. However, the requirements of the additional ligand have sterical consequences on the other carbonyl groups, which can not be coplanar as in the all-nickel cluster. [FeNi5(CO)(13)](2-) reacts readily with acids, to yield the already known [HFe3Ni(CO)(12)](-) (3), and with CO, being stepwise fragmented to species of lower nuclearity, ending with [Fe3Ni(CO)(12)](2-) (4) or [Fe-2(CO)(8)](2-). The solid state structure of the tetranuclear [Fe3Ni(CO)(12)](2-) was also determined, and is reported here. (C) 2002 Elsevier Science B.V. All rights reserved.

The cluster [Ir-6(CO)(13)(C7H8)] (1) was synthesized from [Ir-6(CO)(16)] and excess cycloheptatriene in refluxing toluene. In the solid state, the six iridium atoms define an octahedral metal cage, and one face is capped by the mu(3)-eta(2):eta(2):eta(2)-C7H8 ligand, which is a six-electrondonor, through the three C C double bonds. Reaction of 1 with Na2CO3 in THF yields [Ir-6(CO)(12)(C7H7)](-) (2). In this octahedral anion, the cycloheptatrienyl ring is almost planar and is coordinated to a triangular face in the mu(3)-eta(2):eta(3):eta(2)-C7H8 fashion. Reaction of 1 or 2 with NaOH in THF yields [Ir-6(CO)(12)(C7H8)(2-) (3), in which a mu(3)-eta(3):eta(3):eta(3)-C7H8 is also present. The H-1 NMR spectra of 1 and 3 show five signals, which were assigned to the nonequivalent hydrogen atoms by bidimensional experiments. The spectrum of 2 shows a singlet, even at low temperature, in agreement with a highly fluxional ligand. The interconversions of 1 to the anions 2 and 3, respectively, have been followed by electrochemical investigations. The neutral [Ir-6(CO)(13)(C7H8)] proves to undergo a two-electron reduction, which, being accompanied by decarbonylation, affords the dianion [Ir-6(CO)(12)(C7H8)](2-). In turn, the latter undergoes a two-electron oxidation, which followed by deprotonation affords the monoanion [Ir-6(CO)(12)(C7H7)](-)

The cluster [HIr5(CO)(12)](2-) (1) was prepared by condensation of [HIr4(CO)(11)](-) and [Ir(CO)(4)](-) (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh3CH2Ph](2)[HIr5(CO)(12)]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr4(CO)(10)PPh3](-) (2) was synthetized by CO displacement on [HIr4(CO)(11)], in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir-H distance of 1.57(9) Angstrom. On the contrary, two isomers are present in THF solution, and they interconvert tepidly at room temperature, as shown by H-1 and P-31 NMR spectra

The cluster [Fe5MnN(CO)16]2 (1) was synthesized from [Fe6N(CO)15]3- and Mn2(CO)10, in refluxing EtCN, or [Fe4N(CO)12]- and [FeMn(CO)9] -. Its solid state structure was determined on the [Me3NCH2Ph] + salt, and consists of an octahedral metal cage, enclosing a six-coordinated nitrido ligand. The position of the manganese atom in the solid state could be established, despite some crystallographic disorder, by considering the local stereochemistry of the ligands. The cluster [Fe6N(CO)14NO]2- (2) was obtained in moderate yields by the reaction of [Fe4N(CO12] with Mo(CO)3(EtCN)3. The nitrosyl is formed by oxidation of the starting nitride, and the source of the oxygen is presumably a carbonyl, whose splitting is mediated by the molybdenum complex. This process is the first example of an oxidation of a nitride in a carbonyl cluster. The solid state structure of the iron cluster is also octahedral, and the linear nitrosyl ligand was unambiguously located from the short Fe–N bond distance, and from dishomogeneous distribution of ligands. Cyclic voltammetric studies have shown that electron transfer processes are followed by chemical reactions thus testifying that no stable redox congeners exist for these two nitride clusters.

The anionic clusters [Fe5MN(CO)14Cp]2- [M = Mo (1) or W (2)] were synthesized from [Fe4N(CO)12]- and [MCp(CO)3]- in refluxing acetonitrile. The clusters [Fe3M3N(CO)18]3- [M = Mo (3) orW(4)] were prepared by reaction of [Fe4N(CO)12]- with [M2(CO)10]2- under the same conditions. The molybdenum- containing anions 1 and 3 are obtained in higher yields than 2 and 4. The reaction of the tetranuclear iron cluster with [Mo(ç6-Me3C6H3)(CO)3] affords a mixture of [Fe3Mo3N(CO)18]3- and [HFe5MoN(CO)16]2- (5). The solid state structures of the clusters 1, 2 and 3 have been determined; they consist of six metal atoms, arranged in octahedral metal cages encapsulating a ì6-N ligand. The cyclo- Introduction The interest in heterometallic clusters is still growing, and several examples of their application in catalysis can be found in the literature.[1] In homogeneous catalysis, mixed metal species are preferred, due to the presence of polar metal2metal bonds which can tune electron density at the metal centres, thus modifying the reactivity of the coordinated ligands.[2] In the field of heterogeneous catalysis, mixed-metal species can be exploited for the formation of bimetallic particles which are extraordinarily uniform in their morphology and composition.[3] In this context, the stability of the cage due to the interstitial atoms can avoid [a] Dipartimento di Scienze dell’ Ambiente e del Territorio, Universita` di Milano-Bicocca Piazza della Scienza 1, 20126 Milano, Italy rpergola@mailserver.unimi.it Fax: (internat.) 1 39-02/236-2748 [b] Dipartimento di Chimica Inorganica, Metallorganica ed Analitica and Centro del CNR Universita` di Milano, via G. Venezian 21, 20133 Milano, Italy [c] Dipartimento di Biologia Strutturale e Funzionale, Universita` degli studi dell’Insubria, via J. H. Dunant 3, 21100 Varese, Italy [d] Dipartimento di Chimica Strutturale e Stereochimica Inorganica and Centro del CNR 2 Universita` di Milano via G. Venezian 21, 20133 Milano, Italy E-mail: m.manasser

The cluster [Ir4(CO)11(CPh CHPh)] was obtained by reaction of [HIr4(CO)11] and diphenylacetylene by refluxing in tetrahydrofuran (THF), with yields approaching 80%. The solid state structure was determined on the [NEt4] salt; the cluster possesses a tetrahedral metallic framework, with three edge bridging carbonyls. The vinyl fragment, having two phenyl rings in cis, is bound in axial position and donates only one electron to the cluster, since the C C double bond (1.34 A, ) does not interact with any iridium atom. The 13C-NMR of the cluster, recorded at 90°C, allows full assignment of the signals. The cluster [Ir6(CO)14(COOMe)2]2- was obtained by nucleophilic attack of MeONa on [Ir6(CO)16], in anhydrous methanol at room temperature. The solid state structure was determined on its [N(PPh3)2] salt. Two methoxycarbonyl fragments are on adjacent metal vertices of the octahedral framework.

The neutral cluster [Ir6(CO)15(AuPPh3)21 has been obtained by reaction of [IrdC0)15I2- with [AuPPh3]+. The iridium atoms of the cluster define an octahedral frame capped by one gold-phosphine group. The second AuPPh3 unit spans one Ir-Au edge. The metal skeleton of C1 symmetry is coordinated by twelve terminal and three edge-bridging carbonyl groups. The dianionic [IrdcO)14(Hgc1)21~- has been prepared from [Irs(C0)15l2- and Hg2C12, HgC12 + Hg, or HgClz in the presence of Na2C03. The metallic framework forms an octahedron of iridium atoms bearing, on four non-adjacent faces, two ,u3-HgC1 fragments and two ,u3-C0 groups. The chemical shift of the lg9Hg NMR was found at +1508 ppm.

The compound [Felr3(CO)12]- can be obtained by degradation of [Felr4(C0)l5]2- under a carbon monoxide atmosphere as well as by reduction of an equimolar mixture of [Fe(CO)5] and [Ir4(CO)12] in alcoholic NaOH under 1 atm of carbon monoxide. The molecular structure of the anion consists of a tetrahedron of metal atoms surrounded by twelve carbonyl groups: nine are terminally bound whereas three are bridging the edges of the Felr2 basal face. The dianion [Fe2lr2(C0)l2]2- was obtained by several different ways, the most selective being the condensation of [Fe2(CO)9] with [Ir(CO)4]-. The molecular structure of the dianion is based on a tetrahedral cluster of metal atoms and consists of an apical Ir(CO)3 group co-ordinated by three metal-metal bonds to a basal Fe2lr(CO)9 fragment containing two Fe(CO)2 units and one Ir(CO)2 group linked to each other by a metal-metal bond and bridging carbonyl groups.The salt [PPh4]2[Fe2lr2(CO)12] reacts with [Au(PPh3)CI] to give [PPh4][Fe2lr2(CO)12{m3-Au(PPh3)}]. The metal framework of the anion is a trigonal bipyramid with the Au(PPh3) moiety in one of the apical positions, the other being occupied by a Fe(CO)3 group. Each edge of the equatorial triangle, formed by one iron and two iridium atoms, is spanned by a bridging carbonyl ligand, and two terminal CO groups are attached to each metal of this triangle.

The synthesis and the structure of the novel trianion [fe3Rh3(CO)17]3- is reported; the metal framework of this 88 valence electron bimetallic cluster is unusual, and consists of an Fe2Rh3 trigonal bipyramid with iron and rhodium atoms in apical sites and a dangling Fe atom attached to the apical Rh.

The dark brown [Ir3Ni6(m-CO)6(m3-CO)2(CO)9]3- trianion has been obtained by redox condensation between [Ni(CO)4] and [Ir(CO)4]-. This new mixed-metal cluster is rapidly degraded, at room temperature and atmospheric pressure, by carbon monoxide to form the [Ni(CO)4] and [Ir(CO)4]- parent mononuclear compounds. The metal framework consists of a face-sharing bioctahedron, with the three iridium atoms located in the inner triangle.

In the title compound two C‐atoms are located in the cavity of a cluster. The CċC distance in very short—only 1.49 Å (for comparison: CC single bond 1.54 Å)—but, as deduced from a consideration of the number of cluster valence electrons, a delocalized CC interaction is more probable than a localized one. (Figure Presented.) Copyright © 1984 by Verlag Chemie, GmbH, Germany

Reaction of [lr4(CO)12] or [lr6(CO)16] in tetrahydrofuran with SCN-, SeCN-, or polysulphides in MeOH gives the trinuclear anions [Ir3(m3-X)2(CO)6]- (X = S or Se) which have been isolated and investigated by X-ray analysis. The anions consist of an Ir3 triangle bicapped by triply bridging chalcogenide atoms. Each iridium atom, bearing two terminal CO groups, displays an almost square-planar geometry with respect to the ligands.

The synthesis and properties of the new dicarbidocarbonyl bimetallic clusters [Co3Ni7(CO)16C2]2- and [Co3Ni7(co)15C2]3- are described. Anion I is paramagnetic, and has a metal frame based on a 3,4,3-C2h stack of metal atoms. The resulting deca-vertces metal polyhedron encapsulates a c2 fragment showing a short C-C interatomic separation of 1.48 Å

The syntheses and interconversions of mixed iron-rhodium carbonyl clusters are described; a combination of X-ray analysis and multinuclear n.m.r. measurements allowed the structural characterisation of [FeRh4(CO)15]2-, [FeRh5(CO)16]-, and [Fe2Rh4(C0)16]2- which can all be obtained from the unstable cluster, [Fe2Rh(CO)x]

Reaction of [Co3(CO)9CCl] with [Ni6(CO)12]2- results in a complicated mixture of mixed Co-Ni carbide carbonyl clusters, among which the [Co3Ni9C(CO)21]3- trianion has been isolated in a pure crystalline state and fully characterized by X-ray crystallography. The metal framework of this compound is unprecedented in cluster geometries and may be described as a square antiprism of metal atoms tetra-capped on two alternate pairs of adjacent triangular faces. Despite the presence of a caged carbon atom in the square-antiprismatic cavity, the compound is readily degraded by carbon monoxide (25 "C, 1 atm) mainly to a mixture of [Co(CO)4]- and [Ni(CO)4]. Corresponding degradation of the cluster under a mixture of carbon monoxide and hydrogen yields, in addition, trace amounts of organics, mainly C1 and C2 hydrocarbons, probably derived from the carbide atom.