Electrochemical and EPR studies of the corannulene ruthenium(II) sandwich complex [(eta6-C6Me6)Ru(eta6-C20H10)](SbF6)(2)

The dication [(eta6-C6Me6)Ru(eta6-C20H10)]2+ in propylene carbonate solution exhibits a sequence of reduction processes that is either metal-centered [Ru(II)/Ru(I)/Ru(0)] or ligand-centered. The marginally stable Ru(I) monocation [(eta6-C6Me6)Ru(eta6-C20H10)]+ has been characterized by EPR spectroscopy. The electrochemistry of C20H10 and EPR features of its stable monoanion [C20H10]- have also been revisited.     

Reassessment of the electronic absorption spectra of Cr(η6-C6H6)2, Cr(CO)6 and Cr(η6-C6H6)(CO)3

The UV absorption bands between approximately 330 and 200 nm have been assigned to Rydberg transitions for the d⁶ complexes Cr(η⁶-C₆H₆)₂, Cr(CO)₆ and Cr(η⁶-C₆H₆)(CO)₃     

Synthesis and structural characterization of Be(eta 5-C5Me5)(eta 1-C5Me4H). Evidence for ring-inversion leading to Be(eta 5-C5Me4H)(eta 1-C5Me5)

The mixed-ring beryllocene Be(C5Me5)(C5Me4H), that contains eta 5-C5Me5 and eta 1-C5Me4H rings, the latter bonded to the metal through the CH carbon atom (X-ray crystal structure) reacts at room temperature with CNXyl (Xyl = C6H3-2,6-Me2) to give an iminoacyl product, Be(eta 5-C5Me4H)[C(NXyl)C5Me5] derived from the inverted beryllocene structure Be (eta 5-C5Me4H)(eta 1-C5Me5).     

Addition of Pt(PBu(t)(3)) groups to Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(5)-C). Synthesis, structures, and dynamical activity

The reaction of Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(5)-C), 7, with Pt(PBu(t)(3))(2) yielded two products Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))], 8, and Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))](2), 9. Compound 8 contains a Ru(5)Pt metal core in an open octahedral structure. In solution, 8 exists as a mixture of two isomers that interconvert rapidly on the NMR time scale at 20 degrees C, DeltaH() = 7.1(1) kcal mol(-1), DeltaS() = -5.1(6) cal mol(-)(1) K(-)(1), and DeltaG(298)(#) = 8.6(3) kcal mol(-1). Compound 9 is structurally similar to 8, but has an additional Pt(PBu(t)(3)) group bridging an Ru-Ru edge of the cluster. The two Pt(PBu(t)(3)) groups in 9 rapidly exchange on the NMR time scale at 70 degrees C, DeltaH(#) = 9.2(3) kcal mol(-)(1), DeltaS(#) = -5(1) cal mol(-)(1) K(-)(1), and DeltaG(298)(#) = 10.7(7) kcal mol(-1). Compound 8 reacts with hydrogen to give the dihydrido complex Ru(5)(CO)(11)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))](mu-H)(2), 10, in 59% yield. This compound consists of a closed Ru(5)Pt octahedron with two hydride ligands bridging two of the four Pt-Ru bonds.     

Isolation of the novel dirhodium(II/II) thiolate compound Rh(2)(eta(1)-C(6)H(5)S)(2)(mu-C(6)H(5)S)(2)(bpy)(2)

The reaction of the anticancer active compound [Rh(2)(mu-O(2)CCH(3))(2)(bpy)(2)(CH(3)CN)(2)][BF(4)](2) (1) (bpy = 2,2'-bipyridine) with NaC(6)H(5)S under anaerobic conditions yields Rh(2)(eta(1)-C(6)H(5)S)(2)(mu-C(6)H(5)S)(2)(bpy)(2).CH(3)OH (2), which was characterized by UV-visible, IR, and (1)H NMR spectroscopies as well as single-crystal X-ray crystallography. Compound 2 crystallizes as dark red platelets in the monoclinic space group C2/c with cell parameters a = 20.398(4) A, b = 11.861(2) A, c = 17.417(4) A, beta = 108.98 degrees, V = 3984.9(14) A(3), Z = 4. The main structural features are the presence of a [Rh(2)](4+) core with a Rh-Rh distance of 2.549(2) A bridged by two benzene thiolate ligands in a butterfly-type arrangement. The axial positions of the [Rh(2)](4+) core are occupied by two terminal benzene thiolates. Cyclic voltammetric studies of 2 reveal that the compound exhibits an irreversible oxidation at +0.046 V in CH(3)CN, which is in accord with the fact that the compound readily oxidizes in the presence of O(2). The fact that this unusual dirhodium(II/II) thiolate compound is formed under these conditions is an important first step in understanding the metabolism of dirhodium anticancer active compounds with thiol-containing peptides and proteins.     

Synthesis and structural characterization of the first unsymmetrical diarylpalladium complex trans-Pd(C6F5)(2,4,6-C6F3H2)(PEt3)2, derived from transmetallation between 2,4,6-trifluorophenylboronic acid and trans-Pd(C6F5)I(PEt3)2

The reactions of 2,4,6-trifluorophenylboronic acid with aryl(iodo)palladium(ii) complexes, trans-Pd(C(6)F(5))I(PR(3))(2)(PR(3)= PEt(3), PMe(2)Ph, PMePh(2)) in the presence of Ag(2)O afforded trans-Pd(C(6)F(5))(2,4,6-C(6)F(3)H(2))(PR(3))(2) which are stabilized by fluorine atoms in the ortho positions.     

Condensed metallaborane clusters: synthesis and structure of Fe2(CO)6(eta5-C5Me5RuCO)(eta5-C5Me5Ru)B6H10

Mild pyrolysis of (eta5-C5Me5Ru)2B6H12 with Fe2(CO)9 yields the 12 skeletal electron pair (sep) Fe2(CO)6(eta5-C5Me5RuCO)(eta5-C5Me5Ru)B6H10 cluster; the title compound represents a novel class of hybrid multiple cluster in which a Fe2B2 tetrahedron has been fused to a ruthenaborane substrate.     

Syntheses,reactivity, and crystal structures of molybdenum complexes with pyridine-2-thionate (pyS)-containing ligands: crystal structures of [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2), exo-[Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-dppe)], [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)], and [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)

The doubly bridged pyridine-2-thionate (pyS) dimolybdenum complex [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2) (1) is accessible by the reaction of [Mo(eta(3)-C(3)H(5))(CO)(2)(CH(3)CN)(2)Br] with pySK in methanol at room temperature. Complex 1 reacts with piperidine in acetonitrile to give the complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(2)-pyS)(C(5)H(10)NH)] (2). Treatment of 1 with 1,10-phenanthroline (phen) results in the formation of complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(1)-pyS)(phen)] (3), in which the pyS ligand is coordinated to Mo through the sulfur atom. Four conformational isomers, endo,exo-complexes [Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-diphos)] (diphos = dppm, 4a-4d; dppe, 5a-5d), are accessible by the reactions of 1 with dppm and dppe in refluxing acetonitrile. Homonuclear shift-correlated 2-D (31)P((1)H)-(31)P((1)H) NMR experiments of the mixtures 4a-4d have been employed to elucidate the four stereoisomers. The reaction of 4 and pySK or [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)] (6) and O(2) affords allyl-displaced seven-coordinate bis(pyridine-2-thionate) complex [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)] (7). All of the complexes are identified by spectroscopic methods, and complexes 1, 5d, 6, and 7 are determined by single-crystal X-ray diffraction. Complexes 1 and 5d crystallize in the orthorhombic space groups Pbcn and Pbca with Z = 4 and 8, respectively, whereas 6 belongs to the monoclinic space group C2/c with Z = 8 and 7 belongs to the triclinic space group Ponemacr; with Z = 2. The cell dimensions are as follows: for 1, a = 8.3128(1) A, b = 16.1704(2) A, c = 16.6140(2) A; for 5d, a = 17.8309(10) A, b = 17.3324(10) A, c = 20.3716(11) A; for 6, a = 18.618(4) A, b = 16.062(2) A, c = 27.456(6) A, beta = 96.31(3) degrees; for 7, a = 9.1660(2) A, b = 12.0854(3) A, c = 15.9478(4) A, alpha = 78.4811(10) degrees, beta = 80.3894(10) degrees, gamma = 68.7089(11) degrees.     

Supramolecular gas-solid reaction between formic acid vapours and solid [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)

Exposure of the solid zwitterion [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)] to vapours of formic acid quantitatively produces the co-crystal [CoIII(eta 5-C5H4COOH)(eta 5-C5H4COO)] [HCOOH] without proton transfer from formic acid to the deprotonated -COO- group on the zwitterion; formic acid can be quantitatively removed by mild thermal treatment, regenerating the starting material.     

Experimental and molecular dynamics simulation study of the sublimation and vaporization energetics of iron metalocenes. crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)

The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and alpha-methylferrocenemethanol, and the enthalpy of vaporization of N,N-dimethyl(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudsen effusion method. The obtained values were used to assess and refine our previously developed force field for metallocenes. The modified force field was able to reproduce the deltasubHdegreesm and deltavapHdegreesm values of the test-set with an accuracy better than 5 kJ.mol-1, except for decamethylferrocene, in which case the deviation between the calculated and experimental deltasubHdegreesm values was 16.1 kJ.mol-1. The origin of the larger error found in the prediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimation of structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)] at 293 and 150 K, respectively, are reported.     

Stereospecific and chemospecific interconversions of the rhenium alkylidene [(η-C5H5)Re(NO)(PPh3)(CHC6H5)]+PF6− and the alkylrhenium (η-C5H5)Re(NO)(PPh3)(CH(OCH3)C6H5)

Addition of methoxide to either geometric isomer of the benzylidene complex [(η-C₅H₅)Re(NO)(PPh₃)(CHC₆H₅)]⁺PF₆^? (1t, 1k) affords (η-C₅H₅)Re(NO)(PPh₃)(CH(OCH₃)C₆H₅ (2t, 2k) in which a new chiral center has been generated stereospecifically or with high stereoselectivity. Reaction of 2t and 2k with Ph₃C⁺PF₆^? results in the chemospecific abstraction of a methoxy group and the stereospecific regeneration of 1t and 1k, respectively.     

IR and Raman characterization of the zincocenes (eta(5)-C5Me5)2Zn2 and (eta(5)-C5Me5)(eta(1)-C5Me5)Zn

The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (eta(5)-C5Me5)2Zn2, 1, and bis(pentamethylcyclopentadienyl)monozinc, (eta(5)-C5Me5)(eta(1)-C5Me5)Zn, 8, are reported in some detail. The IR spectra of the vapors of 1 and 8 each trapped in a solid Ar matrix at 12 K confirm the essentially molecular character of the solids. The experimental results have been interpreted with particular reference (i) to the corresponding spectra of (68)Zn-enriched samples of the compounds, and (ii) to the spectra simulated by density functional theory (DFT) calculations at the B3LYP level. The marked differences of structure of 1 and 8 contrast with the relatively close similarity of their vibrational spectra, disparities being revealed only on detailed scrutiny, including the effects of (68)Zn enrichment, and primarily at wavenumbers below 1000 cm(-1). The Zn-Zn stretching motion of 1 features not as a single, well-defined mode identifiable with intense Raman scattering but in several normal modes which respond in varying degrees to (68)Zn substitution. A stretching force constant of 1.42 mdyne A(-1) has been estimated for the Zn-Zn bond of 1.     

Synthesis,structure, and dissociation equilibrium of [Co(eta5-C5H5)(Se2C6H4)]2, a novel metalladiselenolene complex

A (phenylenediselenolato)cobalt complex dimer, [Co(eta(5)-C(5)H(5))(Se(2)C(6)H(4))](2) (1), was synthesized by a reaction of carbonyl(eta(5)-cyclopentadienyl)diiodocobalt(III) ([Co(eta(5)-C(5)H(5))I(2)(CO)]) with poly(o-diselenobenzene). The structure of 1, determined by single-crystal X-ray crystallography, was found to be located in the space group of P2(1)/c (No. 14), with a = 9.3346(5) A, b = 11.6477(9) A, c = 10.2179(5) A, beta = 111.491(1) degrees, and Z = 2. Covalent Co-Se bonds bridge the metal centers. In solution, dimers and monomers coexist at equilibrium. The dissociation equilibrium constant of 1 in solution was evaluated by (1)H NMR spectra at several temperatures between 20 and 80 degrees C. Dissociation enthalpies/entropies were found to be 50/110, 60/120, and 88 kJ mol(-1)/200 J K(-1) mol(-1) in dimethyl sulfoxide-d(6), benzene-d(6), and chloroform-d(1), respectively.     

Reaction of nido-7,8-C(2)B(9)H(13) with Dicobalt Octacarbonyl: Crystal Structures of the Complexes [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)], [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)], and [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))

The compounds [Co(2)(CO)(8)] and nido-7,8-C(2)B(9)H(13) react in CH(2)Cl(2) to give a complex mixture of products consisting primarily of two isomers of the dicobalt species [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (1), together with small amounts of a mononuclear cobalt compound [Co(CO)(2)(eta(5)-10-CO-7,8-C(2)B(9)H(10))] (5) and a charge-compensated carborane nido-9-CO-7,8-C(2)B(9)H(11) (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C(2)B(9)H(11) cage framework. The two Co(CO)(eta(5)-7,8-C(2)B(9)H(11)) units are linked by a Co-Co bond [2.503(2) ?], which is supported by two three-center two-electron B-H right harpoon-up Co bonds. The latter employ B-H vertices in each cage which lie in alpha-sites with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe(2)Ph to a CH(2)Cl(2) solution of a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)] (2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that of 1a but differs in that whereas one B-H right harpoon-up Co bridge involves a boron atom in an alpha-site of a CCBBB ring coordinated to cobalt, the other uses a boron atom in the beta-site. Reaction between 1b and an excess of PMe(2)Ph in CH(2)Cl(2) gave the complex [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))] (3), the structure of which was established by X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic Co(II) species of formulation [Co(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))]. Addition of 2 molar equiv of CNBu(t) to solutions of either 1a or 1b gave a mixture of two isomers of the complex [Co(2)(CNBu(t))(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (4). NMR data for the new compounds are reported and discussed.     

Homoleptic coordination of arsenine C5H5As to molybdenum(0) and tungsten(0): further observations on the eta1,eta6-dilemma

By means of metal-atom ligand-vapor cocondensation (CC) hexa(eta1-arsenine)molybdenum (11) and hexa(eta1-arsenine)tungsten (12) have been prepared; in the molybdenum case, the sandwich complex bis(eta6-arsenine)molybdenum (10) has been isolated as the primary product. The structure of 12 follows from a single-crystal X-ray diffraction study. Based on the results of CC synthesis, chromium binds to arsenine in the eta6-mode exclusively, molybdenum features both options eta1 and eta6, and for tungsten only eta1 coordination is observed.     

Kinetics of hydrogen atom transfer from (eta(5)-C(5)H(5))Cr(CO)(3)H to various olefins: influence of olefin structure

Treating (etha(5)-C(5)H(5))Cr(CO)3H (1) or (etha(5)-C(5)H(5))Cr(CO)3D (1-d(1)) with an excess of olefin containing the opposite isotope generally leads to H/D exchange, although hydrogenation is also observed in some cases. Application of an appropriate statistical correction to the observed exchange rate gives kH and kD, the rate constants for H* (D*) transfer from (etha(5)-C(5)H(5))Cr(CO)(3)H (D) to various olefins. The values of kH and kD vary appreciably with the substituents on the double bond. Phenyl-substituted olefins accept H* more readily than do carbomethoxy-substituted olefins, although the latter accept H* more readily than do alkyl-substituted olefins. A methyl substituent on the incipient radical site increases k(H) at 323 K by a factor between 5 and 50. A methyl substituent on the carbon to which the H* is being transferred decreases kH substantially. On the whole, the rate constants for H* transfer reflect steric effects as well as the stability of the resulting carbon-centered radicals.     

Synthesis of chromium(0) and molybdenum(0) bis (eta(6)-arene) derivatives and their monoelectronic oxidation to [M(eta(6)-arene)(2)](+) cations

M(eta(6)-arene)(2) species (M = Cr, arene = 1,3,5-Me(3)C(6)H(3); M = Mo, arene = 1,3,5-Me(3)C(6)H(3), 1,3,5-(i)Pr(3)C(6)H(3)), have been prepared by a modified Fischer-Hafner synthesis or by metal vapour techniques. The reaction of Cr(eta(6)-1,3,5-Me(3)C(6)H(3))(2) with the fulvene derivatives pentacarbomethoxycyclopentadiene (pcmcpH), 1-benzoyl-6-hydroxy-6-phenylfulvene (dbcpH), or 1-benzoyl-3-nitro-6-hydroxy-6-phenylfulvene (dbncpH) proceeds with evolution of dihydrogen and formation of the ionic derivatives [Cr(eta(6)-1,3,5-Me(3)C(6)H(3))(2)][E], where E = pcmcp, dbcp, or dbncp. Mo(eta(6)-arene)(2) derivatives (arene = toluene, 1,3,5-Me(3)C(6)H(3), 1,3,5-(i)Pr(3)C(6)H(3)) are oxidized to [Mo(eta(6)-arene)(2)](+) by pcmcpH. The crystal and molecular structures of [M(eta(6)-1,3,5-R(3)C(6)H(3))(2)][pcmcp] (M = Cr, R = Me; M = Mo, R = Me, (i)Pr) have been solved by X-ray single crystal diffraction.