Acyl complexes of molybdenum: structural and reactivity studies

The following structural peculiarities of the agostic acyl structure ₂R) (R = H, SiMe₃) and some characteristic chemical reactivity of the M-η²-acyl and iminoacyl linkage are described. (i) A structural comparison of the bonding parameters within three agostic acetyl Mo complexes containing the dithioacid ligand, indicates that the agostic interaction strengthens upon increasing the electron-releasing properties of the S-chelating ligand. (ii) The acyl-xanthate complex Mo(C(O)Me)(S₂COR)(CO)(PMe₃)₂ undergoes loss of a sulfur atom from the coordinated xanthate and coupling with the acyl ligand to form complexes containing coordinated alkoxythiocarbonyl and monothioacetate ligands. The latter can be metathetically replaced by KS₂COR. (iii) Upon heating at 70°C η²-acyl-dicarbonyl bispirazolilborate complexes of molybdenum of the type Mo(H₂B(pz^*)₂)(η²-C(O)Me)(CO)₂(PMe₃) (pz^* = 3,5-dimethyl-pyrazol-1-yl) yield functionalized acyl ligands derived from the stereo- and regioselective intramolecular addition of one of the B---H bonds of the H₂B(pz^*)₂ group across the C=O moiety of the η²-acyl group. (iv) The η²-acyl-isocyanide complexes {Mo}(η²-C(O)R)(CNR′) ({Mo} = Mo(H₂B(pz^*)₂)(CO)(PMe₃)) undergo irreversible thermal isomerization to the corresponding η²-iminoacyl-carbonyl derivatives {MO}(η²-C(NR′)R)(CO). This isomerization reaction follows first-order kinetics.     

Diazapolycyclic compounds—XIII : Reactions of diazaquinone adducts with N-bromosuccinimide

The action of N-bromosuccinimide on adducts obtained by Diels-Alder reaction of benzo(g)phthalazin-1,4-dione with substituted 1,3-butadienes is reported. Different addition or substitution products are formed depending on the solvent and reaction conditions. The stereochemistry of the most interesting among these compounds has been studied, and a possible mechanism for their formation is proposed.     

Copper(II) thiocyanide complexes extractable with [dibenzo-18-crown-6-K] + in chloroform

Summary Cu^II can be extracted from aqueous KSCN solutions using 2,3,11,12-dibenzo-1,7,10,13,16-hexaoxacyclooctadiene (di-benzo-18-crown-6) in CHCl₃. Raman and i.r. spectroscopies establish that the species present in the organic phase after extraction corresponds to [Cu₂OH(SCN)₅]-[dibenzo-18-crown-6-K ⁺]₂, where the Cu^II thiocyanide complex and the K⁺ crown complex are ionically associated.     

Synthesis and characterisation of new triple halide-bridged mixed valence binuclear complexes of ruthenium and osmium

Several isomers of the type [M₂Cl₅L₄] (M = Ru, L = AsPh₃, As(p-tol)₃, As(p-PhCl)₃, PEt₂Ph, PMe₂Ph; L₂ = Ph₂As(CH₂)₂AsPh₂; M = Os, L = PPh₃, AsPh₃) have been synthesised by various routes and characterised by magnetic, ESR and electrochemical measurements, and for [(PEt₂Ph)Cl₂RuCl₃Ru(PEt₂Ph)₃] by X-ray structural analysis.     

Unrestricted Hartree-Fock instabilities in semiempirical CNDO/S and INDO/S calculations of spin-spin coupling constants

It is shown that non-convergent calculations of the Fermi contact term of spin-spin coupling constants within the self-consistent and finite perturbation schemes used to solve the coupled Hartree-Fock equations, are originated in non-singlet Hartree-Fock instabilities of the closed-shell restricted Hartree-Fock wavefunction. In CNDO/S and INDO/S wavefunctions, where the electronic system response has been successfully reproduced, all investigated molecules containing MOs were found to be unstable. Results of spin-spin coupling constants are given and compared with experimental as well as FP and SOS INDO values.Part of a Ph.D. thesis (G.E.S.) to be presented to the University of Buenos Aires.Comisión de Investigaciones Científicas (CIC, Pcia. de Bs. As.) fellow.     

Hydroformylation of naphthas with a rhodium complex in biphasic medium

The chlorocarbonyl bis-[butylphenyl (meta-sulfonate-phenyl)phosphine] rhodium (I) complex shows catalytic hydroformylation activity in toluene/water biphasic medium for 1-hexene, cyclohexene, 2,3-dimethyl-2-butene and 2-methyl-2-pentene, their binary mixtures and a real Venezuelan naphtha, under standardized reaction conditions (1000 psi of syngas (1:1 H₂/CO), 100°C, substrate/catalyst molar ratio (600:1) and 4 h reaction time), obtaining high percent conversion to oxygenated products.     

Theoretical studies of physicochemical properties of aniline oligomers: analysis of counterion influence

We present some semiempirical quantum chemistry calculations, geometric structures, charge distribution, gap energy, and enthalpy of formation (H _f ) for aniline oligomers in the different oxidation states using the AM1 method. A linear relationship between calculated optical transition values and the experimental reported ones was found. The effect of the interaction between the chloride counterion and these molecules was analyzed and indicates a decrease both in H _f of the aniline oligomers in the radical cation state and in E(SOMO-LUMO). The withdrawal of one electron from the reduced aniline tetramer to form a radical cation in the presence of chloride (Cl^–) yields to the radical cation band, similar to the polaron band in the polyaniline case. Contrary to the expected results, our calculations show that Cl^– was able to transfer about 80% of its charge to the oligomers.