Helmuth G. L. Siebald

Crystal and molecular structures of transition metal complexes with N- and C-bonded diazoalkane ligands

Abstract The review covers structural and physicochemical studies on diazoalkanes N-coordinated to transition metals and encompasses all collected crystal structures. Our goal is to provide a classification of the complexes based on the metal, ranging from early to late transition metals, the nuclearity of the complex (mono, dinuclear, clusters), the electronic configuration of the metal (d 0 to d 10 ) and the bonding mode of the diazoalkanes. Interestingly, the variety of structures may be rationalized within the valence bond formalism, the reactions being essentially oxidative addition of diazoalkane on the metal complexes giving hydrazonido (-2- ligand). C-coordinated diazoalkyl complexes are still restricted to a few metals and a few diazosubstituents and their chemistry is not well developed.

Structural and spectral studies of thiosemicarbazones derived from 2-acetylthiophene

Abstract The reaction of 2-acetylthiophene with thiosemicarbazide and 4-phenylthiosemicarbazide yielded 2-acetylthiophene thiosemicarbazone ( 1 ) and 2-acetylthiophene 4-phenylthiosemicarbazone ( 2 ). Both compounds were fully characterised by 1 H and 13 C{ 1 H}-NMR and infrared spectroscopies and showed satisfactory elemental analysis. The X-ray crystallographic studies can be summarised as follows: ( 1 ) triclinic, P -1, a =5.6515(3), b =10.1401(6), c=11.7910(7) A , α =105.4260(10)°, β =94.202(2)° and γ =90.234(2)°, V=649.42(6) A 3 and Z =2; ( 2 ) triclinic, P -1, a =9.0352(4), b =9.7898(4), c=12.1839(5) A , α =104.6820(10)°, β =102.8180(10)° and γ =108.28(10)°, V=935.08(7) A 3 and Z =4.

Synthesis of methyl acetate from methanol catalyzed by [(η5-C5H5)(phosphine)2RuX] and [(η5-C5H5)(phosphine)2Ru(SnX3)] (X=F, Cl, Br): ligand effect

Abstract Monometallic Ru and heterobimetallic complexes containing RuSn bonds, [(η5-C5H5) P2RuX] and [(η5-C5H5)P2Ru(SnX3)], where P=PPh3, PPh2Me, P2=1,2-bis(diphenilphosphine) ethane (dppe), and X=F, Cl, Br, were synthesized and characterized. These complexes were tested as catalysts in a single-step methanol conversion to acetic acid (methyl acetate) in the absence of CO. All complexes showed a high selectivity with their catalytic activity being strongly dependent on the nature of the ligands P and X. The effect of the ligand P showed the order of PPh3>PPh2Me≅dppe and the halogen effect: F>Cl≅Br and SnF3>SnCl3≅SnBr3. Heterobimetallic complexes showed ca. doubled activities compared to their monometallic analogues, indicating the importance of the RuSn bond in a catalytic active specie. The order of catalytic activities followed the increase in the positive charge on the ruthenium atom, which was confirmed by 31P and 119Sn NMR spectroscopy and X-ray diffraction techniques. The obtained data support the mechanistic view of acetic acid formation by dehydrogenation of methanol giving formaldehyde via the rate-determining β-hydrogen abstraction in the Ru(II)–OMe intermediate, followed by formaldehyde dimerization into acetic acid.

Synthesis, characterisation and molecular structure of Ru–Sn(II) containing derivatives

Abstract A series of new ruthenium-based derivatives were obtained by reactions of [Ru(η-C5H5)(PPh3)2Cl]. They are as follows: [Ru(η-C5H5)(PPh3)2SnF3] (1), [Ru(η-C5H5)(PPh3)2SnCl3] (2), [Ru(η-C5H5)(PPh3)2SnBr3] (3), [Ru(η-C5H5)(dppe)SnF3] (4), [Ru(η-C5H5)(dppe)SnCl3] (5), and [Ru(η-C5H5)(dppe)SnBr3] (6). Compounds 1–6 were studied by IR, NMR (1H, 13C, 31P and 119Sn) and 119Sn Mossbauer spectroscopies. In addition, 1, 2, 3 and 6 were structurally authenticated by X-ray crystallographic studies. Finally all the derivatives were tested as catalysts in the methanol to acetic acid conversion process, showing promising activities.

Pyrolysis of organotin compounds: A preparative method for nanometric tin dioxide powders

Nanometric tin dioxide powders were obtained by pyrolysis of organotin oxide based compounds such as Sn3O3Bu6 (1) and Sn4O6Bu4 (2) (Bu = n-butyl). The thermal behaviour of 1 and 2 was studied by thermogravimetric analysis (TG) and with simultaneous differential thermal analysis (DTA). Pyrolysis experiments were carried out in three different atmospheres (N2, air and O2) and the residual powders were characterised by X-ray diffraction (XRD) and the morphology was investigated by scanning electron microscopy (SEM). The XRD data showed the formation of pure SnO2 when the decomposition process was accomplished in air or O2, however, in N2, and for Sn4O6Bu4, the X-ray study indicated the formation of a mixture of SnO/SnO2. The micrographs revealed grains of 30–40 nm, approximately.

Syntheses, characterization and structure determination of {[CpRu(X)]2(η2,μ2-dppe)2} complexes (X=Cl, N3; dppe=Ph2PCH2CH2PPh2): Chelating vs. bridging behavior of a classical bidentate ligand

Abstract Phosphine substitution reactions between (η5-C5H5)Ru(PPh3)2Cl (1) and 1,2-bis(diphenylphosphino)ethane (Ph2P(CH2)2PPh2, dppe), in refluxing benzene or in toluene at 80°C afforded a mixture of complexes where dppe behaves both as a bridging and as a chelating ligand. CpRu(η2-dppe)Cl (2) and {[CpRu(Cl)]2(η2,μ2-dppe)2} (3) were separated by fractional precipitation from the reaction mother-liquor, and were characterized by 1H, 13C, 31P NMR, elemental analysis and IR spectroscopy. The (2):(3) ratio in the composition of the reaction product was found to be independent of the reaction time. In solution and at room temperature, (3) exists in both boat and chair conformers of a 10-membered ring, while at lower temperatures, and in the solid-state, only the chair conformer is observed. Compounds (2) and (3) undergo halide-displacement upon reacting with NaN3 in the presence of ethanol to yield CpRu(η2-dppe)(N3) (4) and {[CpRu(N3)]2(η2,μ2-dppe)2} (5), respectively. The crystal structures of (3) and (5) were determined.

119Sn Mössbauer spectroscopic study of nanometric tin dioxide powders prepared by pyrolysis of organotin oxides

Abstract This paper reports the results of 119 Sn Mossbauer Spectroscopy of residues from the pyrolysis of Sn 3 O 3 Bu 6 ( 1 ) and Sn 4 O 6 Bu 4 ( 2 ) (Bu= n -butyl) in air, O 2 , and N 2 . The isomer shift and quadrupole splitting parameters of the samples allowed the identification of the tin oxidation states, as well as the number of non-equivalent coordinated tin sites. The result of the 119 Sn Mossbauer study correlates perfectly with those of X-ray electron probe microanalysis, scanning electron microscopy and X-ray powder diffraction for the formation of pure SnO 2 from the decomposition of ( 1 ) and ( 2 ) in air or O 2 . However, in N 2 , evidences suggest the formation of a mixture of SnO 2 and SnO.

Antimony and chromium determination in Brazilian sugar cane spirit, cachaça, by electrothermal atomic absorption spectrometry using matrix matching calibration and ruthenium as permanent modifier

This work reports a method for the determination of antimony and chromium in Brazilian sugar cane spirit, cachaca, by electrothermal atomic absorption spectrometry (ET-AAS) employing matrix matching calibration and ruthenium, thermally deposited (500 µg), as permanent modifier. The best pyrolysis and atomisation temperatures were 600 °C and 1400 °C for antimony while for chromium it was 700 °C and 2500 °C, respectively. For chromium, the peak returned to the baseline after 15 s in the absence of any modifier, whilst using Ru as permanent modifier, the peak returned to the baseline in 5 s, showing high symmetry. The characteristic mass (mo) obtained for chromium was 2.4 pg without modifier and 2.5 pg with Ru permanent (recommended 8.0 pg). For antimony it was 43.4 pg and 24.6 pg without modifier and with Ru permanent, respectively (recommended 200 pg). Matrix matching calibration curves (aqueous solutions 40% v/v in ethanol) gave a value of r (linear regression coefficient) higher than 0.999 for the two analytes. For antimony, two samples of cachaca spiked with 30.0, 60.0 and 90.0 µg l−1 showed a range of recovery from 98.8% to 110.0%, while for chromium it was from 101.7% to 107.9%. The detection limits (k = 3, n = 10) were 43 pg for antimony and 2 pg for chromium. The results obtained from analysis of fifty-two samples of cachaca, from Alto Vale do Jequitinhonha, Minas Gerais State, Brazil, varied from non-detectable to 39.1 µg l−1 for antimony and the RSDs, (n = 3), from 2.87% to 11.10%. For chromium, the same samples showed results from 0.64 to 1.53 µg l−1 (RSDs from 0.04% to 11.76%).

Preparation and crystal structure of trans-diazidotetrakis(trimethylphosphine)ruthenium(II)

Abstract The novel trimethylphosphine azido ruthenium(II) complex trans -Ru(N 3 ) 2 (PMe 3 ) 4 has been obtained and characterized by elemental analysis, IR and NMR spectroscopies, and electrochemistry. Its structure has been determined by single crystal X-ray diffraction methods. The complex consists of monomeric Ru(N 3 ) 2 (PMe 3 ) 4 units, in which the coordination geometry around the Ru atom is a distorted octahedron. The two azido ligand occupy trans positions and are oriented in two nearly orthogonal planes. Conversion into the cis isomer in CH 2 Cl 2 has been followed by 31 P NMR and cyclic voltammetry.

Alpha-metalated diazoalkanes: Synthesis of yttrium, lutetium and ytterbium trimethylsilyldiazomethyl complexes

Abstract Reaction of LiC(N2)SiMe3 with [MClCp2★] (M = Y, Lu, or Yb; Cp* = pentamethylcyclopentadienyl) gives rise to the three new compounds [MC(N2)SiMe3Cp2★(THF)] (M = Y, 1; Lu, 2; Yb, 3) with a metal carbon σ bond. They are thermally sensitive hygroscopic solids which have been characterized by IR (for 1, 2 and 3) and 1H NMR (for 1 and 2) spectroscopy.