Vitor Rosa

Trimethylsilyl-substituted ligands as solubilizers of metal complexes in supercritical carbon dioxide

The SiMe3 group (TMS), introduced as a substituent at the cyclopentadienyl ligand, is found to magnify the solubility of the corresponding metal complexes in supercritical carbon dioxide (scCO2). This is verified from comparative solubility measurements of the species (η5-Me3SiC5H4)MoO2Cl, 1a, (η5-Me3SiC5H4)2ZrCl2, 2a, and (η5-Me3SiC5H4)Co(CO)I2·0.5(I2), 3a (newly synthesised), and of their unsubstituted precursors 1b–3b, respectively. In spite of the increased solubility, the chemical, structural and reactivity properties of the TMS derivatives are scarcely affected. Confirmation comes from a detailed study of the cobalt complex 3a that includes X-ray structural determination. The geometry is most similar to that of the precursor 3b while an apparently different Co–CO interaction is observed in the carboxylated analogue [(η5–PhCH2CO2C5H4)Co(CO)I2, 3c]. The problem is computationally tackled by using the DFT B3LYP method. The optimised geometries of the simplified models of 3a–3c are all very similar. In particular, the computed stretching frequency of the unique CO ligand is consistent with the insignificant influence of the TMS group while it suggests a reduced amount of metal back-donation in 3c. It is inferred that the TMS complexes 1a–3a, while having higher solubility in scCO2, maintain almost unaltered the electronic and chemical features of their parent compounds. In particular, the role of 1a–3a as catalysts, that is well documented for homogeneous solutions, remains unaltered in the very different scCO2 environment. The assumption is experimentally validated for 1a by performing with the latter two classic catalytic processes. The first process is the oxidation of PPh3 that is achieved by using molecular oxygen as an oxidant. The second example concerns the epoxidation of cyclohexene achieved in presence of tert-butyl hydroperoxide (TBHP).

Janus Microspheres for Visual Assessment of Molecular Interconnects

A rigid S-functionalized metalloligand is used to pair Janus Au-coated silica microspheres and the resulting assemblies are assessed with optical microscopy. New Pd complexes provide stable molecular interconnects, and the metal centre controls the structure of the linker and provides the desired rigidity, by virtue of its well-established coordination chemistry.

Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding.

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe–P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P′R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe–P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe–P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Mononuclear and dinuclear complexes of manganese(III) and Iron(III) supported by 2-salicyloylhydrazono-1,3-dithiane ligand: synthesis, characterization and magnetic properties

The coordination chemistry of 2-salicyloylhydrazono-1,3-dithiane (H2L) was studied with manganese and iron ions. The following complexes have been isolated as crystalline materials, and their crystal structures have been determined by single crystal X-Ray crystallography: MnIII(acac)(HL)2 (1) (acac = acetylacetonate), MnIII(HL)3·CH2Cl2 (2), FeIII(HL)3·2CHCl3 (3), FeII(H2L)2Cl2·2CH3OH (4), FeIII2(μ-OMe)2(HL)4·0.5CH3OH (5), FeIII2(μ-O) (HL)4·3CH2Cl2 (6). All attempts to synthesize the dinuclear μ-methoxo complex [MnIII2(μ-OMe)2(HL)4] have so far failed, even when the procedure used in the case of 2-salicyloylhydrazono-1,3-dithiolane (H2L′) ligand, which worked very efficiently, was employed. The new iron dinuclear μ-methoxo complex (5) presented in this study shows antiferromagnetic intramolecular coupling (J = −21.1 cm−1), which is in agreement with the theoretical study proposed previously for its manganese analogue.

Imine Ligands Based on Ferrocene: Synthesis, Structural and Mössbauer Characterization and Evaluation as Chromogenic and Electrochemical Sensors for Hg+2

The compounds 1-naphthyliminoferrocene, 1, and 2-methyl-1-naphthyliminoferrocene, 2, were prepared by the reaction of ferrocenecarboxaldehyde and the corresponding amine, 1-naphthylamine and 2-methyl-1-naphthylamine with one drop of pyrrolidine as the catalyst, in CH2Cl2, under an inert atmosphere. The compounds were fully characterized by elemental analyses, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF), FT-IR, 1H and 13C NMR as well as two-dimensional, NOESY, COSY and HSQC, NMR spectroscopy. Mossbauer spectroscopic studies were performed to characterize iron species in both compounds. The solid-state molecular structures of compounds 1 and 2 were determined by single crystal X-ray diffraction. Analysis of the electrochemical behaviour of complexes 1 and 2 was performed by cyclic and square wave voltammetry. Compounds 1 and 2 were tested as chromogenic and electrochemical sensors for Hg2+.