Kinetische und mechanistische untersuchungen von übergangsmetallkomplex-reaktionen : IX. Substitution von CO durch PPh3 in aminocarbinkomplexen: Präparative und kinetische untersuchungen

Pentacarbonyl(diethylaminocarbyne)chromium tetrafluoroborate, [(CO)₅₋ CrCNEt₂]BF₄ (I), reacts with PPh₃ with substitution of CO and formation of trans-tetracarbonyl(diethylaminocarbyne)triphenylphosphanechromium tetra-fluoroborate, trans-[PPh₃(CO)₄CrCNEt₂]BF₄ (III). Substitution of CO by PPh₃ in neutral trans-tetracarbonyl(halo)(diethylaminocarbyne)chromium complexes, trans-X(CO)₄CrCNEt₂ (IVa: X = Br, IVb: X = I), leads in a reversible reaction to the corresponding tricarbonyl complexes, mer-X(PPh₃)(CO)₃₋ CrNEt₂ (V), PPh₃ occupying the cis-position to the carbyne ligand. With PPh₃ in large excess both reactions follow a first-order rate law. This as well as the activation parameters (ΔH≠ = 104–113 kJ mol⁻¹, ΔS≠ = 64–71 J mol⁻¹ K⁻¹) indicate a dissociative mechanism.     

Ein- und zweikernige Dinitrosylkomplexe von Molybdän und Wolfram. Die Kristallstrukturen von (PPh3Me)2[WCl4(NO)2], (PPh3Me)2[MoCl3(NO)2]2 und von (PPh3Me)2[WCl3(NO)2]2

Mono- and Binuclear Dinitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of (PPh₃Me)₂[WCl₄(NO)₂], (PPh₃Me)₂[MoCl₃(NO)₂]₂, and (PPh₃Me)₂[WCl₃(NO)₂]₂ The complexes (PPh₃Me)₂[MCl₄(NO)₂] (M = Mo, W), and (PPh₃Me)₂[MCl₃(NO)₂]₂, respectively, are prepared by reactions of the polymeric compounds MCl₂(NO)₂ with triphenylmethylphosphonium chloride in CH₂Cl₂, forming green crystals. According to the IR spectra the nitrosyl groups are in cis-position in all cases. The tungsten compounds as well as (PPh₃Me)₂[MoCl₃(NO)₂]₂ were characterized by structure determinations with X-ray methods. (PPh₃Me)₂[WCl₄(NO)₂]: space group C2/c, Z = 4. a = 1874, b = 1046, c = 2263 pm, β = 119.99°. Structure determination with 3492 independent reflexions, R = 0.057. The compound consists of PPh₃Me^⊕ ions, and anions [WCl₄(NO)₂]^2? with the nitrosyl groups in cis-position (symmetry C_2v). (PPh₃Me)₂[WCl₃(NO)₂]₂: Space group C2/c, Z = 4. Structure determination with 2947 independent reflexions, R = 0.059. (PPH₃Me)₂[MoCl₃(NO)₂]₂: Space group P1 , Z = 1. a = 989, b = 1134, c = 1186 pm; α = 63.25°, β = 80.69°, γ = 69.94°. Structure determination with 3326 independent reflexions, R = 0.046. The compounds consist of PPh₃Me^⊕ ions, and centrosymmetric anions [MCl₃(NO)₂]₂^2?, in which the metal atoms are associated via MCl₂M bridges of slightly different lengths. One of the NO groups is in an axial position, the other one in equatorial position (symmetry C_2h).     

Dioxomolybdenum(VI) complexes containing 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones

Dioxomolybdenum(VI) complexes derived from ethyl maltol (2-ethyl-3-hydroxy-4-pyrone) and 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones have been prepared and characterized using physical methods including ¹H- and ¹³C-n.m.r. spectroscopy, i.r., elemental analysis, and X-ray diffraction for the pyrone and 3-methylpyridine pyridinone derivatives. The octahedral complexes have the general formula cis-MoO₂L₂ where L = the deprotonated pyrone or pyridinone ligand.     

Deprotonated and non-deprotonated cobalt(II) complexes of the bis-amide tetradentate ligand N,N′-(dipicolyl)-1,8-naphthylene diamine. Three different modes of coordination by the ligand

The preparation and some properties of the cobalt(II) complexes Co(LH₂)Cl₂·2H₂O, Co(LH₂(NCS)₂ and CoL·H₂O (whereLH₂=N,N-(dipicolyl)-1,8-naphthylenediamine) are reported. On the basis of magnetic moments, visible reflectance and IR data, the structure is proposed to be pseudo-octahedral for Co(LH₂)Cl₂·2 H₂O, pseudo-tetrahedral for Co(LH₂)(NCS)₂ and square planar for CoL·H₂O.

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Deprotonierte und Nicht-deprotonierte Co(II)-Komplexe des vierzähnigen Bisamid-Liganden N,N-(Dipicolyl)-1,8-naphthyldiamin. Drei verschiedene Koordinationstypen

Zusammenfassung Es werden die Darstellung und einige Eigenschaften der Kobalt(II)-Komplexe Co(LH₂)Cl₂·2 H₂O, Co(LH₂)(NCS)₂ und CoL·H₂O [LH₂=N,N-(dipicolyl)-1,8-naphthylendiamin] diskutiert. Auf der Grundlage von magnetischen Momenten, von Daten der sichtbaren Reflektions-und IR-Spektren wird eine pseudooctaedrische Struktur für Co(LH₂)Cl₂·2H₂O, eine pseudotetraedrische für Co(LH₂)(NCS)₂ und eine planar-quadratische für CoL·H₂O vorgeschlagen.

     

Synthesis of carbaalane halogen derivatives

The carbaalane halogen derivatives [(AlX)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (X = F (9), Cl (7), Br (10), I (11)) were prepared in toluene from [(AlH)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (6) and BF(3).OEt(2), BX(3) (X = Br, I), Me(3)SnF, and Me(3)SiX (X = Cl, Br, I), respectively. A partially halogenated product [(AlH)(2)(AlX)(4)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (12) (X = Cl (approximately 40%), Br (approximately 60%)) was obtained from 5 and impure BBr(3). [(AlH)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (5) was converted to [(AlX)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (X = F (13), Cl (14), Br (15), I (16)) using BF(3).OEt(2) and Me(3)SiX (X = Cl, Br, I), respectively. The X-ray single-crystal structures of 11.C(6)H(6), 12.3C(7)H(8), 13.6C(7)H(8), and 15.4C(7)H(8) were determined. Compounds 7 and 9-11 are soluble in benzene/toluene and could be well characterized by NMR spectroscopy and MS (EI) spectrometry. The results demonstrate the facile substitution of the hydridic hydrogen atoms in 5 and 6 by the halides with different reagents.     

Some new aspects of a HPLC-method for the determination of traces of formaldehyde in air

Summary A practicable method was developed for the routine determination of formaldehyde in air. Formaldehyde is sampled in small sampling tubes filled with Chromosorb P, coated with 2,4-dinitrophenylhydrazine (= DNPH). The sorbent is extracted with acetonitrile, and the different DNPhydrazones were separated by reversed-phase HPLC. UV-detection at = 345 nm was compared with electrochemical detection. The detection limit was 100 pg for UV- and 50 pg for electrochemical detection with a linear range of more than 3 decades, respectively. For the determination of formaldehyde in air the detection limit is 10 ppb with an average recovery of 99.3% and an estimated relative standard deviation S of 1.5%. This method was compared with the sampling by impingers using the same separation and detection method.

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Einige neue Aspekte einer HPLC-Methode zur Spurenbestimmung von Formaldehyd in Luft

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

A Quantitative Assessment of „Through-space”︁ and „Through-bond”︁ Interactions. Application to Semi-empirical SCF Models

The scheme of ‘through-space’ and ‘through-bond’ interaction of (semi)localized orbitals, originally proposed by Hoffmann, is reexamined in terms of SCF many-electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off-diagonal matrix elements of the Hartree-Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalized Hartree-Fock matrices referring to ‘precanonical orbitals’. The procedure outlined is applied to three practical examples using the semiempirical many-electron treatments SPINDO, MINDO/2 and CNDO/2:

• a A reassessment of ‘through-space’ and ‘through-bond’ interaction in norbornadiene indicates, that the latter type of interaction is also of importance for the orbital based mainly on the antisymmetric combination of the localized x-orbitals. The differences in the predictions derived from the three models are critically examined.
• b The competition between ‘through-space’ and ‘through-bond’ interaction in the series of bicyclic dienes from norbornadiene to bicyclo[4.2.2]-dcca-7,9-diene and in cyclohexa-1,4-diene, i. e. their dependence on the dihedral angle UI is reexamined. It is found that the rationalization for the orbital crossing near ω = 130° deduccd from PE. spectroscopic data can not be as simple as originally suggested and that the relay’ orbitals responsible for ‘through-bond interaction affecting both the symmetric and the antisymmetric combination of the π-orbitals extend over the whole CC-σ-system of the six membered ring.
• c ‘Through-bond’ interaction of the two lone pair orbitals in 1,4-diazabicyclo[2.2.2]octane is found to be large for their symmetric and the antisymmetric linear combination.

The analysis quoted, draws attention to some of the dangers involved in using semiempirical treatments for the interpretation of PE. data in terms of Koopmans′ theorem, without due caution.     

Influence of moderate Joule heating on electroosmotic flow velocity, retention, and efficiency in capillary electrochromatography

The influence of Joule heating on electroosmotic flow velocity, the retention factor of neutral analytes, and separation efficiency in capillary electrochromatography was investigated theoretically and experimentally. A plot of electrical current against the applied electrical field strength was used to evaluate the Joule heating effect. When the mobile phase concentration of Tris buffer exceeded 5.0 mM in the studied capillary electrochromatography systems using particulate and monolithic columns (with an accompanying power level of heat dissipation higher than 0.35 W/m), the Joule heating effect became clearly noticeable. Theoretical models for describing the variation of electroosmotic flow velocity with increasing applied field strength and the change of retention factors for neutral analytes with electrical field strength at higher Tris buffer concentrations were analyzed to explain consequences of Joule heating in capillary electrochromatography. Qualitative agreement between experimental data and implications of the theoretical model analysis was observed. The decrease of separation efficiency in capillary electrochromatography with macroporous octadecylsilica particles at high buffer concentration can be also attributed to Joule heating mainly via the increased axial diffusion of the analyte molecules and dispersion of solute bands by a nonuniform electroosmotic flow profile over the column cross-section. However, within a moderate temperature range, the contribution of the macroscopic velocity profile in the column arising from radial temperature gradients is insignificant.