Halogeno Ligands Research Articles

(2-Acetylpyridine-κN4-phenylthiosemicarbazonato-κ2N1,S)halogeno-trans-dimethyltin(IV) (halogeno = chloro and bromo)

A thio­semicarbazone derivative, 2-acetyl­pyridine 4-phenyl­thio­semicarbazone, was prepared and complexed to Lewis acids, Sn(CH3)2X2, X = Cl and Br. The products, [SnX(C14H13N4S)(CH3)2], were characterized by single-crystal X-ray diffraction, and IR, NMR and Mossbauer spectroscopies. They are isomorphous and crystallize in the monoclinic space group P21/n. The structure determination revealed discrete neutral complexes with the SnIV atom in a distorted octahedral coordination geometry, with the halogeno ligand and the thio­semicarbazone derivative in the equatorial plane and the methyl groups in axial positions.

Lewis base adducts of bis-(halogeno)dioxomolybdenum(VI): syntheses, structures, and catalytic applications

Reaction of solvent substituted MoO 2X 2(Solv) 2 complexes ((Solv)=THF, CH 3CN) with mono- and bidentate nitrogen and oxygen donor ligands leads to complexes of the type MoO 2X 2L 2 in nearly quantitative yields at room temperature within a few minutes. The 95 Mo and 17 O NMR data of selected complexes as well as the MoO IR vibrations were used to probe the influence of the ligands on the electronic properties of the metal and the MoO bond. Two complexes have additionally been examined by single crystal X-ray analysis. The activity of the MoO 2X 2L 2 complexes as catalysts in olefin epoxidation with t-butylhydroperoxide as oxidizing agent depends on both the nature of the organic ligand L and the halogeno ligand X. The difference in activity observed between Cl and Br substituted complexes is not very pronounced. In general, the Cl derivatives are more active than their Br analogues. The organic ligands L display a significant influence on the catalytic performance. Complexes with ligands bearing aromatic substituents at N are in all cases, much more active than those bearing aliphatic substituents. The less active complexes can be activated by raising the temperature and extending the reaction time. In all observed cases, these changes produce a significant increase of the product yield.

Ruthenium(II) complexes with the tetradentate 6,6′-bis(oxazolinyl or benzimidazolyl)-2,2′-bipyridine ligand: synthesis, electrochemical properties, and catalytic reactivities

New ruthenium complexes, trans-[RuX 2(L)] (L = tetradentate 6,6′-bis(oxazolinyl or benzimidazolyl)-2,2′-bipyridine; X=halide or cyanide ion) have been synthesized. The present Ru complexes reveal a stable Ru(II/III) oxidation process and exhibit strong MLCT bands around 450–600 nm. The oxidation potential depends on the axial halogeno ligand; the potential increases in the order of X=Cl<Br<CN. The complexes possess catalytic activity for oxidation of styrene and 1-phenylethanol. The bis(benzimidazolyl)bipyridine complex has stronger oxidizing power compared to the analogous bis(oxazolinyl)bipyridine complex.

Facile Alkylation of Cobalt(III) Porphyrins by Organosilicon Compounds

(σ-Alkyl)cobalt(III) porphyrins were easily synthesized and isolated as stable crystalline compounds by the reaction of halogenocobalt(III) porphyrins with silyl enol ethers and ketene silyl acetals. The yields depended on the solvent (CH2Cl2 > MeOH), the substituent of the porphyrin periphery (meso-tetraphenylporphyrin > octaethylporphyrin), and the axial halogeno ligand of cobalt(III) porphyrins (F ≥ Cl ≫ Br ≈ I ≈ ClO4). 1-((Trimethylsilyl)oxy)-1,3-butadiene afforded (σ-4-oxobut-2-enyl)cobalt(III) porphyrins, which showed very broad 1H NMR signals at 25 °C. The temperature-dependent dynamic behavior of this complex was explained in terms of the rotation around the C(α)−C(β) bond but not of the σ−π rearrangement in the 4-oxobut-2-enyl ligand.

Wismutverbindungen mit voluminösen, mehrfach alkylierten Cyclopentadienyl‐Liganden

Bismuth Compounds with Crowded Multiply Alkylated Cyclopentadienyl LigandsHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet. Bismuth complexes of alkylated cyclopentadienyl ligands are obtained in good yield on treating bismuth(III) halides with tetraisopropylcyclopentadienylsodium or 1,2,4‐tri‐tert‐butyl‐cyclopentadienyllithium. A 1:1 stoichiometric ratio gives the complexes [Cp4iBiCl2] (1), [Cp3tBiCl2] (2), and [Cp4iBiI2] (3) (Cp4i = C5iPr4H, Cp3t = C5H2tBu3‐1,2,4). According to X‐ray crystal structure analyses, 1 and 3 display dimeric structures with two bridging and two terminal halogeno ligands and η3‐coordination of the cyclopentadienyl rings. With half an equivalent of tetraisopropylcyclopentadienylsodium BiCl3 forms [Cp4iBi2Cl5] (4). An X‐ray crystal structure analysis of 3 reveals a central Bi2Cl10 core of two edge‐sharing BiCl6 octahedra coordinated to two Bi(η5‐Cp4i) fragments generating a framework of two face‐sharing cubes. Reaction of two equivalents of 1,2,4‐tri‐tert‐butylcyclopentadienyllithium with BiCl3 yields deep purple [Cp3t2BiCl] (5), a bent sandwich complex with an η3,η2‐bonding mode of the cyclopentadienyl ligands. Attempted formation of the octaisopropyl analogue of 5 from BiCl3 and two equivalents of tetraisopropylcyclo‐pentadienylsodium with elimination of propene gives [Cp4iCp3iBiCl] (6) (Cp3i = C5H2iPr3). Use of monodeuterated tetraisopropylcyclopentadienylsodium in the second substitution step gave pure [Cp4i([D1]Cp3i)BiCl] ([D1]6) proving the absence of ring exchange reactions under the reaction conditions employed and elimination of propene from the second incoming sterically crowded tetraisopropylcyclopentadienyl ring system. The importance of proper choice of solvent and reaction conditions on the formation of alkylated cyclopentadienyl bismuth derivatives is demonstrated by extensive formation of 1,1′,3,3′,5,5′‐hexa‐tert‐butyldihydrofulvalene (7) from 1,2,4‐tri‐tert‐butylcyclopentadienylsodium and BiCl3.

Schwingungsspektren und Normalkoordinatenanalyse der Acetatohalogenodimetallate M2(O2CCH3)4X2, M = Re, Tc; X = CI, Br/Vibrational Spectra and Normal Coordinate Analysis of Acetatohalogenodimetalates M2(O2CCH3)4X2, M = Re, Tc; X = Cl, Br

Abstract The orange-red Tc2(O2CCH3)4Br2 has been prepared for the first time by reaction of [Tc2Br8]2- with glacial acetic acid and acetic anhydride. The IR and Raman spectra have been recorded at 80 K and are compared with those of the analogous compounds Tc2(O2CCH3)4Cl2, Re2(O2CCH3)4Cl2 and Re2(O2CCH3)4Br2. The assignment according to the point group D4h is supported by normal coordinate analysis based on a general valence force field. The quadruple M - M bond is stabilized by the bridging acetato and destabilized by the axial halogeno ligands. The valence force constants fd(MM) are determined to 3,96-4,08 mdyn/Å. The interaction constants fdd(MM/MX), fdd(MM/MO) and fdα (MM/MMO) are about three times higher for the technetates as compared with the rhenates. The stronger interaction between oppo­site bonds in the equatorial ligand sphere is revealed by the stretching interaction constants fdd', which are about two times higher than fdd for M - O bonds at right angles. The strong coupling of the ring co-ordinates implies extensive mixing of the M - O valence and deformation modes. The electronic spectra of Tc2(O2CCH3)4X2, agree with those of the corresponding Re compounds.

Doubly charged ions in the mass spectra of mono- and binuclear metal carbonyl derivatives

Doubly charged ions produced in the mass spectra of mono- and bimetallic carbonyl compounds at 40, 70 and 100 eV electron beam energies are reported. Fe 2(CO) 9 and Mn 2(CO) 10 give very weak doubly charged ions, whilst a strong increase of the relative abundances of these species is observed in the mass spectra of Re 2(CO) 10. The presence of the halogeno ligands in Mn(CO) 5X and Re(CO) 5X (X=Cl, Br, I) produces a stabilizing effect on the doubly charged ions. A higher ion current is transported by doubly charged fragments of Mn(CO) 5X with respect to Mn 2(CO) 10, while [M] 2+ accompanied by doubly charged high mass fragments are originated by Re(CO) 5X. The strong increase of the relative abundances of doubly charged ions observed in the mass spectra of Fe 2(CO) 6C 4(C 2H 5) 4 and Os 2(CO) 6C 4(C 2H 5) 4 suggests a significant effect of the unsaturated organic ligands, which adds to that of the nature of the metal atom on the stabilization of multiply charged ions.

Chemical stability and reactivity of the 1?1 and 2:1 halobis(N,N-dialkyldithiocarbamato)iron(III): Molecular halogen loose associations

EHMO-SCCC calculations have been used to probe the molecular orbital interactions of 1:1 and 2∶1 charge-transfer complexes of halobis(N,N-dialkyldithiocarbamato)iron(III) complexes with molecular halogens, treated as “super molecules.” The molecular orbital structure of the compounds is being described in essentially the same way to that successfully applied in the cases ofπ-π, π-gs, and n-σ CT complexes. It is found that all types of orbital interactions (σ- and/orπ type) have a destabilizing effect on the complexes; hence, the forces of attachment have to be of the charge-transfer and van der Waals type, to offset this “molecular orbital-based” repulsion. The relative stability of the compounds is broadly discussed in terms of the calculated binding energies, which are found to depend on the nature of both constituent molecules. Moreover, orbital populations, two-center energy terms, and computed atomic charges of the “super molecules,” as compared to those of the constituent molecules, provide adequate information on the mechanism of the charge-transfer processes occurring upon complexation. It is important that weak bonding interactions between the constituent molecules do exist, but surprisingly directly, between the molecular halogens and the iron(III) central atoms, and not via the apical halogeno ligands. These bonding interactions, although not responsible for the stability of the compounds, account well for the observed magnetic behavior of the dimeric (2∶1) complexes and are of key importance in promoting intramolecular electron-transfer reactions responsible for the oxidation of half of the dithio ligands into the thiuram disulfides observed in some of the reactions of the iron(III) halobisdithiocarbamates with molecular halogens.