Giuliana Gervasio

An experimental (120 K) and theoretical electron- density study of KMnO4 and KClO4

The experimental electron density rho(r) of the two isomorphic salts KMnO(4) and KClO(4) was determined by a multipole analysis of accurate X-ray diffraction data at 120 K. The quantum theory of atoms in molecules was applied to rho(r) and to its Laplacian nabla(2)rho(r). The bonds were characterized using the topological parameters at the bond critical points of the density rho(r), nabla(2)rho(r), G(r) (kinetic energy density), V(r) (potential energy density) and H(r) (total energy density). According to the classification recently proposed by Espinosa, Alkorta, Elguero & Molins [J. Chem. Phys. (2002), 117, 5529-5542], the K-O and Cl-O bonds have a pure ionic and covalent character, respectively, while the Mn-O bonds show an intermediate behaviour. The results of the topological analysis of the experimental and theoretical (fully periodic Hartree-Fock and density functional calculations) electron density are in good agreement, even on a quantitative level. The atomic charges, determined by performing an integration over the topological basins, are about +2 e for Mn and Cl atoms. The ionic radius, estimated with the distance of the bond critical point from the nucleus, is in agreement with a charge of +2 e for the Mn atom.

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.

Neutron-diffraction study of a symmetrical ruthenium–hydrogen–ruthenium bond in nonacarbonylhydrido(t-butylethynyl)-triangulo-triruthenium

Neutron-diffraction investigation of the title compound has confirmed the presence of an hydridic hydrogen atom, as suggested by n.m.r. measurements. The compound crystallizes in the triclinic system, space group P with Z= 2 in a unit cell of dimensions a= 9.024(3), b= 12.893(4), c= 9.026(1)A, α= 105.25(7), β= 100.38(4), and γ= 92.20(8)°. Reflection intensities have been measured (λ 1.212 A) with a step-scan technique up to 2θ⩽ 68°. The anisotropic least-squares refinement, with 1 339 observed reflections, has led to R 0.028. The hydride atom lies on a pseudo-plane of symmetry out of the cluster plane, and forms a symmetrical bent Ru–H–Ru tricentric bond, confirmed by thermal-motion analysis. Extensions of the two axial Ru–C(carbonyl) bonds trans to the hydride atom clearly intersect at a point very close to the hydride atom : the Ru–H–Ru bond should thus be classified as ‘open’, unlike other W–H–W bonds previously studied. The observation that the Ru3 cluster has equilateral geometry shows that there is an exact balance between the lengthening effect of the hydride atom and the shortening effect of the organic ligand on the bridged Ru–Ru bond.

Reactions of [Fe3(CO)12] with asymmetrically substituted alkynes I. Chemical relationships between the [Fe3(CO) 9(μ3-η2-C2RR′)] and the carboxylato complexes [Fe2(CO) 6{RC2-R′(COO)}]. The splitting of a water molecule into its components favoured by TLC materials

Abstract The reactions of [Fe 3 (CO) 12 ] with RC 2 R′ asyymmetric alkynes lead to a variety of tri- an di-nuclear derivatives, each in two or three isomeric forms. Complexes [Fe 3 (CO) 9 (RC 2 R′)] ( 1 ) are among the first formed, with two isomers for each structure expected. The carboxylato complexes [Fe 2 (CO) 6 {RC 2 R′(COO)}] ( 2 ) are formed upon reaction of complexes 1 with moisture during the purification on silica TLC plates. In particular, the reaction of (hex-1-en-3-yne) leads to the diethylcarboxylato complex [Fe 2 (CO) 6 {EtC 2 Et(COO)} This process is probably promoted by the silica in the presence of moisture from the air or from the solvents used in the elution. The relationships between the isomers of complexes 1 and 2 are discussed. The formation of the carboxylato complexes presumably involves nucleophilic attack at a metal-coordinated carbonyl.

Formation of an allylic cluster in the reactions of [Ru3(CO)12] with diethylamino-propyne and trimethylsilyl propargyl alcohol. Crystal structure of [(μ-H)Ru3(CO)9(μ3-η3-C3H3)]

Abstract The title complex (μ-H)Ru3(CO)9(μ3-η3-C3H3) has been obtained following two different reaction pathways: one is the deamination of diethylaminopropyne, HCCCH2NEt2, in the presence of Ru3(CO)12 under thermal conditions. The other is the reaction of trimethylsilylpropargyl alcohol, (HO)H2CCC(SiMe3) (TSPA), with Ru3(CO)12. The complex is obtained both under thermal conditions and in the reaction of the carbonyl with TSPA in CH3OH/KOH (followed by acidification). Other reaction products, deriving from the loss of Me3Si and of HCHO fragments from TSPA, have also been characterized. Complex (μ-H)Ru3(CO)9(μ3-η3-C3H3) has been spectroscopically characterized and its crystal structure was determined by an X-ray analysis. An isosceles triangle of Ru atoms with an edge bridged by an H atom, is coordinated by an allylic moiety σ-bonded to two Ru atoms and π-interacting with the third Ru atom.

An Experimental Evidence of a Metal−Metal Bond in μ-Carbonylhexacarbonyl[μ-(5-oxofuran-2(5H)-ylidene-κC,κC)]-dicobalt(Co−Co)[Co2(CO)6(μ-CO)(μ-C4O2H2)]

The orthorhombic crystal structure of [Co2(CO)6(μ-CO)(μ-C4O2H2)] (1) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical-atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn2(CO)10], confirming our previously established bonding classification for organometallic and coordination compounds.

Synthesis of organic molecules from functionalized alkynes and metal carbonyls. Reaction pathways and intermediates. Crystal structure of Fe3(CO)6(μ-CO)2[(HC ≡ CCMe2)2NH]

The reactions of VIII Group metal carbonyls with dipropargylamines and other functionalized alkynes lead to new cluster and binuclear compounds: the ruthenium cluster derivatives may be considered as “models of intermediates” proposed in metal-mediated organic syntheses. The iron and cobalt carbonyls give metallacyclic derivatives which are intermediates in organic syntheses. The structure of Fe3(CO)6(μ-CO)2[(HC ≡ CCMe2)2NH] has been determined by an X-ray diffraction study.

HOMOGENEOUS HYDROGENATION OF DIPHENYLACETYLENE IN THE PRESENCE OF RU3(CO)9L3 (L = PPH3, PET3). THE CRYSTAL STRUCTURE OF RU3(CO)10(PET3)2 : A REACTION INTERMEDIATE?

Abstract The phosphine-substituted clusters Ru3(CO)9L3 (L=PPh3, 1; L=PEt3, 2) are active homogeneous catalysts for the hydrogenation of diphenylacetylene. In the catalytic reactions involving complex 2, formation of Ru3(CO)10(PEt3)2 (3) has been observed. This complex shows a hydrogenating activity greater than that of the parent complex 2. In the light of these results and of the observed effect of dihydrogen pressure and substrate/cluster ratio, reaction mechanisms are discussed. The structure of 3 has been characterized by X-ray diffraction and is compared with those of other phosphine-substituted triruthenium clusters. Compound 3 crystallizes in the monoclinic space group P21 with a=9.368(7), b=12.20(2), c=13.554(9) A, β=102.63(8)° and Z=2. Refinement of 4975 data gave R1=0.0417 and wR2=0.1105. The two phosphorus ligands occupy equatorial positions on adjacent metal atoms so that they are trans to each other at the ends of the RuRu vector. The presence of bent semi-bridging carbonyl groups makes the molecule chiral and its absolute structure was determined.

Structural and infrared spectroscopic characterization of Co6C(CO)12S2: a high-nuclearity carbido carbonyl cluster spontaneously formed from dicobalt octacarbonyl and carbon disulphide

Abstract Co6C(CO)12S2 (I) has been isolated in crystalline form from the mixture of more than a dozen of carbonyl products formed when Co2(CO)8 reacts at room temperature with CS2. Crystals of I are monoclinic with space group Cc, and lattice constants a  16.250(5), b  9.413(4), c  16.036(5) A, β  116.77(4)°. Structure refinement gave R  0.034 for 1974 reflections. The CCo6S2 core of the molecule possesses idealized D3h geometry. It is composed of a Co6 trigonal prism, enclosing a C atom in the centre, and the triangular faces are capped symmetrically by the two S atoms. The core contains two sorts od CoCo distances: short one (2.432 A) along the triangular edges, and long ones (2.669 A) along the lateral edges. The average CoC distance is 1.94 A, and the average CoS distance 2.192 A. 13CO-enriched samples were prepared photochemically and their IR spectra used in the assignment of the CO stretching frequencies. The CO stretching force constant was calculated to be 1670(2) Nm-1. By the use of 13CS2, I has also been obtained in a selectively carbido-13C-labelled form. The vibrational frequencies of the carbide atom were observed, and that at 819 cm-1 (13C: 790 cm-1) assigned to the species , and that at 548 cm-1 (13C: 535.5 cm-1) to species E′. For the Co-C(carbide) force constant a value of 155 Nm-1 was calculated. The cobalt—sulphur stretching frequencies were found at 309 cm-1 ( ) and 239 cm-1 (E′). The CoS stretching force constant, 78 Nm-1, is considerably lower than that obtained for SCo3-(CO)9, viz. 112 Nm-1.

Crystal and molecular structure of nonacarbonyl-µ-(1,2,3,4-tetraphenylbutadiene-1,4-diyl)-triangulo-triosmium, (Ph4C4)Os3(CO)9

Crystals of the title compound occur in two forms: (i) M-form, monoclinic, space group P21/c, Z= 4, a= 12·148(5), b= 9·796(4), c= 29·565(16)A, β= 91·79(5)°; and (ii) O-form, orthorhombic, space group Iba2, Z= 8, a= 38·45(8), b= 18·59(4), c= 9·80(2)A. The structures of both modifications were solved by Patterson and Fourier syntheses, and refined by least-squares methods to R 0·095 (4807 reflexions, M-form) and 0·080 (1916 reflexions, O-form); they have the same molecular structure. The molecule is built up of the organic ligand Ph4C4, with a cluster of three osmium atoms at the corners of an isosceles triangle, bonded to two, three, or four carbonyl groups. Co-ordination between Ph4C4 and the cluster is attained viaσ-bonds and the donation of four π-electrons of the osmacyclopentadiene ring. The cluster and the ligand configurations are discussed in relation to those of similar compounds.