Η5 C5Me5 Research Articles

Manganese half-sandwich complexes as metal-organic chemical vapor deposition precursors for manganese-based thin films

The synthesis of compounds [Mn(η5–C5H4SiMe3)(CO)3] (1), [Mn(η5–C5H3-1-SiMe3-3-Me)(CO)3] (2), [Mn(η5–C5H4tBu)(CO)3] (3), [Mn(η5–C5Me5)(CO)3] (4) and [Mn(η5–C5H7)(CO)3] (5) and their potential use as metal-organic chemical vapor deposition (MOCVD) precursors for the deposition of manganese-based layers is reported. The thermal behavior of 1–5 was studied by thermogravimetry showing that these compounds evaporate in the temperature range of 363–498K depending on the cyclopentadienyl substituents and the type of pentadienyl used. Vapor pressure measurements indicate that all compounds possess vapor pressures between 60 and 630Pa at 353K. Compounds 1–5 could be successfully applied in manganese-based film deposition without activation steps prior to the MOCVD experiments. The as-deposited thin layers were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and X-ray powder diffraction. Under comparatively mild conditions, whereas 5 possesses the lowest deposition temperature (553K), dense and conformal layers with growth rates up to 7.0nmmin−1 (5) could be deposited. Metal carbonyls 1 and 2 featuring a SiMe3 group produced Si-containing manganese-based films. The as-deposited layers from 1, 2, 4 and 5 contain carbon impurities (5–8.9mol-%), while the films from 3 are carbon-free. The layers from 1 and 2 consist of mainly manganese silicate and manganese oxide, whereas those obtained from 3 to 5 are composed of manganese oxides.

The tri–μ–hydrido–bis[(η5–C5Me5)aluminum(III)] theoretical study, the assets of sandwiched M2H3 (M of 13th group elements) stability

The stability of the tri-mu-hydrido-bis[(eta(5)-C(5)Me(5))aluminum], Cp*(2)Al(2)H(3), 1 is studied at B3LYP/6-311+G(d,p), CCSD(T)//B3LYP/6-311+G(d,p) and MP4//B3LYP/6-311+G(d,p) levels. The coordination between Al(2)H(3) entity and both C(5)(CH(3))(5) groups is ensured by strong electrostatic and orbital interactions. The orbital analysis of the interacting fragments shows that Al(2)H(3) acceptor, which keeps its tribridged structure, implies the vacant [Formula: see text] and five antibonding ([Formula: see text], e' and e'') molecular orbitals to interact with two orbitals mixtures, b(1) and e" of the donors (C(5)Me(5)). When we take into account the solvent effect, the computation shows that 1 seems to be stable in condensed phase with a tribridged bond between the Al atoms [Cp*Al(micro-H)(3)AlCp*], whereas in the gas phase, the monobridged Cp*AlH(micro-H)AlHCp* 4 is slightly favored (4 kcal mol(-1)). We propose that 1 could be prepared thanks to Cp*Al (2) and Cp*AlH(2) (3) reaction in acidic medium. The experimental treatment of this type of metallocenes would contribute to the development of the organometallic chemistry of 13th group elements.

Electrochemical and spectral properties of some tantalocene derivatives with one pentamethylated cyclopentadienyl ligand: Cp*(Cp-R)TaCl2 , R = H, SiMe3 or (CH2)3NC4H4

Three tantalocene dichloride complexes, Cp*(Cp-R)Ta(IV)Cl2, with one pentamethylated cyclopentadienyl ligand, Cp* = η5–C5Me5, Me = CH3, and one monosubstituted cyclopentadienyl ligand, Cp-R, Cp = η5–C5H5, R = H, SiMe3 or (CH2)3NC4H4, have been studied in acetonitrile solutions with cyclic voltammetry in the ranges of the Ta(IV) oxidation to Ta(V) or of its reduction to Ta(III). The former transition is reversible, while the latter one gives an irreversible wave due to the dissociation of the reduced complex with the loss of one chloride ligand. The redox transformation from the initial state of complex Cp*CpSiMe3TaCl2 to its oxidized state, Cp*CpSiMe3TaCl2+, and back was monitored by spectroelectrochemical measurements in a thin-layer acetonitrile solution. Kinetic data for the evolution of the UV-visible spectrum of the system in the course of the double potential step experiment were treated on the basis of two theoretical models as the reactant diffusion across the solution layer without or with taking into account ohmic losses. The values of the diffusion coefficients of the complex in its initial and oxidized (cationic) states have been estimated. It was demonstrated that this complex in each of two oxidation states, Ta(IV) or Ta(V), is represented by a single molecular form. An attempt to deposit a conducting polymer film by oxidation of the tantalocene complex containing a pyrrole group attached to the Cp ring, Cp*Cp(CH2)3PyTaCl2, led to a thin insulating layer at the electrode surface because of an inhibiting effect of chloride anions.

LIGAND REACTIONS WITH UNSATURATED NICKEL – GROUP 6 COMPLEXES

The complexes [(η5–C5Me5)Ni–M(CO)3(η5–C5H5)] (Ni–M, M=Mo, W) can be considered to contain Ni=Mo or Ni=W double bonds and may be represented as [(η5–C5Me5)Ni=M(µ–CO)(CO)2(η5–C5H5)] (Ni=M, M=Mo, W). These species, and their closely related group 6 methylcyclopentadienyl congeners [(η5–C5Me5)Ni=M(µ–CO)(CO)2(η5–C5H4Me] (Ni=M, M=Mo, W), have a rich chemistry that stems from their unsaturation. This review relates their discovery, and summarizes the chemistry of these complexes with simple two-electron donor ligands, with alkynes, and with alkenes.

Synthesis, crystal structure and third-order nonlinear optical (NLO) properties of a novel tetranuclear organometallic cluster [(η5–C5Me5)WS3Au]2

Reactions of [PPh4][(η5–C5Me5)WS3] with equimolar AuI in MeCN gave rise to the title compound [(η5–C5Me5)WS3Au]2 (1) in high yield. Compound 1 crystallizes in the monoclinic space group P21/a with cell dimensions: a = 17.123(4), b = 9.373(3), c = 18.019(4) A, β = 107.43(2)°, V = 2759.2(13) A3 and Z = 4. The molecular structure of 1 contains a W2Au2 core in which two Au atoms are linked by two (η5–C5Me5)WS3 moieties. The nonlinear optical (NLO) properties of 1 were studied by 35 ps and 12 ns laser pulses. The third-order nonlinear susceptibility χ(3),, the nonlinear absorption, and optical limiting response are measured by degenerate four-wave mixing (DFWM), the Z-scan technique, and the transmission technique, respectively. The experimental data are theoretically fitted, and the mechanism for the third-order optical nonlinearities and the optical limiting properties are discussed, and the absorption cross sections of the ground state and the excited states are evaluated by a rate equation model.

Diastereomeric separations and crystal structures of rhodium(iii) and iridium(iii) complexes containing adenosine and related nucleosidesElectronic supplementary information (ESI) available: 1H NMR and CD spectra. See http://www.rsc.org/suppdata/dt/b2/b209148h/

Six C3 cyclic trinuclear complexes [{M(Cp*)(L)}3]3+ (M = RhIII and IrIII; Cp* = η5–C5Me5) containing adenosine nucleosides [L: adenosine (Hado), 2′-deoxyadenosine (Hdeoado) and 5′-acetyl-2′,3′-isopropylideneadenosine (Haipado)] were prepared and characterized by UV/Vis and circular dichroism (CD) spectra, NMR spectroscopy, electrospray ionization mass spectroscopy and X-ray crystal structure analysis. The isolations of one and/or two diastereomers were successfully carried out for the four systems by second-order asymmetric transformation and/or fractional crystallization. Interestingly, a striking kinetic difference was found between the present RhIII– and IrIII–ado systems. The crystal structure of CCC-[{Rh(Cp*)(ado)}3](CF3SO3)3·2.5H2O·CH3OH revealed that the ado ligand adopts a μ-1κN1:2κ2N6,N7 bridging mode and the three purine rings forming a triangle dome-like cavity can include one methanol molecule into its cavity. The absolute configurations were assigned to these complexes based on the crystal structural result and CD spectral arguments. The RhIII–N-methyl adenosine (HNMeado) system exceptionally gave a di-μ-hydroxy anti-dinuclear structure because of the weak coordination ability of the N(6) donor.

Heterodinuclear Complex Cp*Ru(CO)2Co(CO)4 (Cp* = η5–C5Me5) Induced Selective Dimerization of Terminal Alkynes

Abstract A heterobimetallic complex Cp*Ru(CO)2Co(CO)4 1 (Cp* = η5–C5Me5) and its selective reactions with alkynes are reported. Stoichiometric head-to-tail dimerization of tolylacetylene affords the dinuclear metallacyclopentadiene complex Cp*(CO)Ru{η2:η4–μ2–C(Tol)CHC(Tol)CH}Co(CO)2 2 whereas catalytic head-to-head coupling of methylpropiolate yields (E)-(MeO2C)CH=CH(C≡CCO2Me) 3. The structure of 2 has been determined by X-ray crystallography.

Sonoelectrochemistry in Highly Resistive Media:Mass Transport Effects

Sonovoltammetry methodology is studied for the enhancement of electrochemical processes in highly resistive media. As model systems the reduction of [FeCp*2]PF6 (with Cp* = η5–C5Me5) and the oxidation of FeCp*2 in acetonitrile are examined at a 25 μm diameter Pt microdisk electrode. Both in the presence and in the absence of supporting electrolyte ultrasound induces a strong increase in the observed limiting current in agreement with an increase in mass transport or, associated with this, a change in the average diffusion layer thickness. However, iR drop effects cause distortion of voltammetric waves, potential fluctuation, and ultrasonically induced current decrease under conditions of extremely low ionic strength.

A novel organometallic oxide cluster with multi-valley sites: synthesis and structure of [NBun4]2[{(η5-C 5Me5)Rh}2Mo6O20 (OMe)2] and its framework transformations

A novel organometallic oxide cluster [NBu n 4 ] 2 [{(η 5 -C 5 Me 5 )Rh} 2 Mo 6 O 20 (OMe) 2 ] 1 with multi-valley sites is synthesized by the reaction of [NBu n 4 ] 2 [Mo 2 O 7 ] and {(η 5 -C 5 Me 5 )RhCl(µ-Cl)} 2 ] in a molar ratio of 4:1 in methanol, and displays unique framework transformations upon treatment with organometallic and oxometalate compounds.

Synthesis and characterisation of the novel mixed-metal cluster [Ru5Rh(CO)12(μ-CO)(μ4-η 2-CO)2(η5-C5 Me5)

The reaction of the octahedral dianion [Ru 6 (CO) 18 ] 2- with the dication [Rh(η 5 -C 5 Me 5 )(MeCN) 3 ] 2+ afforded the novel mixed-metal cluster [Ru 5 Rh(CO) 12 (µ-CO)(µ 4 -η 2 -CO) 2 (η 5 -C 5 Me 5 )], which has been shown by an X-ray analysis to contain a bi-edge bridged tetrahedral framework, with the Rh(η 5 -C 5 Me 5 ) unit at the apex of the tetrahedron, and two µ 4 -η 2 -CO capping carbonyl ligands.

CHELATING PROPERTIES OF THE ANIONIC IRIDIUM(III) COMPLEX (η5—C5Me5)IrCl(PO(OMe)2}2]−, SYNTHESIS OF BI—AND TRINUCLEAR DERIVATIVES

Abstract The synthesis and properties of new neutral complexes of the type [(η5—C5Me5)IrX{PO(OMe)2} {P(OH)(OMe)2}] (X ─ C1, I) and their thallium derivatives. [(η5—C5Me5)IrX{PO(OMe)2)2T1] are described. The potentially bidentate or terdentate ligand being the anionic complex [(η5—C5Me5) IrCl{PO(OMe)2}2]− has been studied. It reacts with metal ions and with some organometallic fragments to yield trinuclear or binuclear complexes. Spectroscopy data for the isolated complexes are discussed.

Structure and Reactivity of C2 Species on Polymetallic Systems

Abstract A variety of polymetallic C2 (C2 and C2H) complexes are prepared by structure expansion of parent metal acetylide complexes, Fp*–C≡C–H (1) and Fp*–C≡C–Fp* (2) [Fp* = (η5–C5Me5)Fe(CO)2], and their structure and reactivity have been investigated as models for surface-bound C2 species formed during catalytic CO hydrogenation. The results summarized here involve (1) intramolecular 1,2-H shift of the C2H complexes relevant to the 1-alkyne-to-vinylidene rearrangement within a metal coordination sphere, (2) electronic influence of metal centers on the structure of dinuclear bridging alkynyl complexes, (3) conversion of the C2 moiety into various C2 functional groups, and (4) synthesis of higher nuclearity dicarbide (C2) cluster compounds with novel coordination structure by sequential addition reactions of metal fragments and direct coupling of a preformed low-nuclearity cluster structure.

Synthesis and Structure of Novel Organometallic Sulfide Cluster [(η5–C5Me5)MWO(μ–S2)(μ–S)2]2 (M = Rh, Ir) Containing High-Valent Tungsten Atoms

Abstract Novel transition metal sulfide cluster [(η5–C5Me5)MWO(μ–S2)(μ–S)2]2 (M = Rh, Ir) was synthesized and the crystal structure of iridium complex was analyzed. The cluster consists of two fused double incomplete-cubane frameworks made of tungsten(VI) and iridium(III) atoms. There are no metal–metal direct interactions within the cluster core in spite of short W–Ir contact of 2.816(1) Å.