Niobium and tantalum mesityl complexes and the role of the mesityl ligand in α- and γ-hydrogen abstraction reactions

The Ta and Nb complexes M(Mes)_nX_5?n (Mes = Mesityl; XCl or Br; n = 1, 2 or 3) and several derivatives can be prepared in high yield. They are considerably more stable than their phenyl analogues. 1H NMR data indicate that a mesityl ligand most likely occupies an equatorial site in a trigonal bipyramidal molecule but cannot rotate freely because its ortho methyl groups cannot pass by the axial chloride ligands. TaMes(CH₂CMe₃)X3 reacts with PMe₃ ( L) to give the known alkylidene complexes, Ta(CHCMe₃)L2X3, but TaMes(CH₃)X₃ reacts with PMe₃ to give the benzylidene complexes, Ta(CHC₆H₃Me₂)L₂X₃ (by γ-abstraction from the mesityl ligand), instead of the hoped for analogous methylene complex.     

Transition metal complexes of azo compounds V. Complexation and cleavage of the NN bond of diazirines by iron carbonyls

3,3-Dimethyldiazirine and 3,3-pentamethylenediazirine, R₂CN₂, react with enneacarbonyldiiron initially via N-tetracarbonyl intermediates to give dark blue μ-1,2-diazirine-bis(tetracarbonyliron) complexes and small amounts of an Fe₃(CO)₉-cluster of the diazirine. Depending upon the solvent, further reaction may take place by splitting of the NN bond to yield orange (R₂CN)Fe₂(CO)₆(NCR₂) and red (R₂CN)Fe₂(CO)₆(NCO), which contain bridging ketiminato and isocyanato groups. Formation of the latter complexes probably involves “nitrenic” intermediates. A general scheme is proposed for the reactions of the cis-azo group of cyclic azo compounds with iron carbonyls which permits estimation of the product ratio as a function of the ring size of the parent azo ligand. (R₂CN)Fe₂(CO)₆(NCO) adds methanol at room temperature to give (R₂CN)Fe₂(CO)₆(NHCO₂Me).     

Transition metal promoted alkylations of unsaturated alcohols: the methylation and ethylation of 3-buten-1-ol using titanium tetrachloride-organoaluminum systems

The ethylation and methylation of the olefinic linkage in 3-buten 1-ol by incorporating the alkenol into a titanium-organoaluminum system was studied under a variety of conditions. Systems were derived from titanium tetrachloride and the organoaluminum compounds Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(CH₃)₃, and Al(CH₃)₂Cl. With diethylaluminum chloride the major products obtained were 1-hexanol, 3-methyl-1-pentanol, trans-3-hexen-1-ol, and 1-butan I. Triethylaluminum gave no alkylation products. Dimethylaluminum chloride and trimethylaluminum gave product distributions similar to the analogous diethylaluminum chloride system.     

Structural studies on osmium carbonyl hydrides: XXXI. Crystal and molecular structure of CpWOs3(CO)9(μ-H)(μ-O)(μ-CHCH2C6H4Me), a hydrido-alkylidene produced by hydrogenation of a μ3-alkylidyne

The complex CpWOs₃(CO)₉(μ-H)(μ-O)(μ-CHCH₂C₆H₄Me), previously prepared by hydrogenation of CpWOs₃(CO)₉(μ-O)(μ₃-CCH₂C₆H₄Me), has been subjected to a single-crystal X-ray diffraction study. The complex crystallizes in the non-centrosymmetric monoclinic space group Cc(C_s⁴; No. 9) with a 14.1510(27), b 13.9257(22), c 13.3179(19) Å, β 92.023(13)°, V 2622.8(7) ų and D(calcd) 3.06 g cm^?3 for Z = 4 and mol. wt. 1206.8. Single-crystal X-ray diffraction data were collected with a Syntex P2₁ automated four-circle diffractometer and the structure was refined to R 3.5% for all 2476 independent observations (Mo-K_α radiation, 2θ = 4.5–40.0°) and R 3.4% for those 2430 data with | F₀| > 3.0σ(| F₀|). The molecule contains a tetrahedral WOs₃ core associated with 60 valence electrons. Each osmium atom is associated with three terminal carbonyl ligands and the tungsten atom is linked to an η⁵-C₅H₅ ligand. In addition, the μ-oxo ligand is involved in a WO: → Os bridge (in which WO(B) 1.737(17), Os(3)← :O(B) 2.167(16) Å and WO(B)Os(3) 96.0(7)°), the μ-hydride ligand spans the Os(1)Os(3) linkage and the μ-CHCH₂C₆H₄Me ligand bridges the WOs(2) linkage (WC(1) 2.068(26) and Os(2)C(1) 2.281(26) Å).     

Catalytic hydrogenation of propene over polymer supported rhodium complexes

Hydrogenation of propene and other substrates has been studied in flow and batch reactors using various rhodium catalysts. The results show that in some cases rhodium metal is probably formed, but only if solvent is present. A possible explanation is given.     

Complexes of silver(III) with oxoanions

Silver(III) has a half-life at pH 11 of several hundred seconds in aqueous solutions in the presence of 0.1–1.0 M concentrations of certain basic oxoanions (Oxo) (phosphate, carbonate, borate, pyrophosphate, and arsenate). This compares with a lifetime of a few seconds at pH 11 in the absence of these oxoanions. UV-visible spectra and kinetic data for these solutions are interpreted as evidence for the following equilibria in the pH range 9–13.Ag(OH)₄^?1 + H₂O ? Ag(OH)₃H₂O + OH^? (1)Ag(OH)₄^?1 + Oxo ? Ag(OH)₃Oxo + OH^? (2)Ag(OH)₃Oxo + H₂O ? Ag(OH)₂(Oxo)H₂O + OH^? (3) Values of K₃ lie in the range 10^?3 < K₃ <10⁴ M for the systems studied. K₂ is estimated to be ～10² for phosphate and slightly smaller for the other systems. Ag(OH)₄^? undergoes an unusual reaction with pyrophosphate at pH ～ 8 to form a novel silver(II) complex, [Ag(P₂O₇)₂]^6?, for which EPR and electronic absorption spectral parameters are reported.     

The chemistry of sulfines. 9. A novel synthesis of α-chloroalkyl alkanethiosulfonate esters

Sulfines react with sulfinyl chlorides giving α-chloroalkyl alkanethiosulfonate esters and with thionyl chloride giving α-chloroalkanesulfenyl chlorides, both in good yields.     

The preparation of di- and tri-phenylstannyl esters of aromatic dithio acids,and some of their reactions

Some crystalline di- and tri-phenylstannyl esters [ArCS₂SnPh₃ and (ArCS₂)₂SnPh₂] of aromatic dithio acids have been prepared in good yields and characterized. Preferential cleavage of the SnS bond of the ester was observed by treating them with primary and secondary amines as well as with phenacylidenetetramethylenesulfurane.     

A CNDO study of the electronic structure of oxyanions XO4n− with X = Si,P, S,Cl, Ge,As, Se and Br

The orbital order, the bonding properties of the orbitals and the orbital populations are discussed. It is concluded that the orbital order in the valence shell in all the ions is 1a₁, 1t₂, 2a₁, 2t₂, 1e, 3t₂ and 1t₁. The results are compared when possible with experimental data and ab initio results.     

Magnetic behavior of copper diethyldithiocarbamate at low temperatures: A reinvestigation

The title compound, Cu(S₂CNEt₂)₂, behaves at low temperatures (1–20 K) as a normal spin-1/2 molecule, with 〈g〉 =2.06 and the Curie-Weiss θ = +0.25 K. This result contradicts an earlier investigation that led to the suggestion that the crystallographically-occurring dimers are coupled ferromagnetically.     

Magnetic susceptibility of ruthenium(III) in tris-ethylenediamine salts. Effect of outer sphere ligands

The paramagnetic susceptibility of Ru(III) in tris-ethylenediamine salts has been measured as a function of temperature. In all cases the iodide salt exhibits a greater susceptibility than the bromide salt. This difference may be attributed to a larger degree of temperature independent paramagnetism in the iodide complex due to the presence of low lying charge transfer states.     

Crystal structure of dimeric p-phenoxyphenyltellurium(IV) trichloride

p-PhOC₆H₄TeCl₃ crystallises with a dimeric molecular unit. The two approximately square pyramidal coordination polyhedra are linked trans to each other through two bridging chlorine atoms. The dimeric units are further connected through Te…Cl secondary interactions producing a distorted octahedral geometry about each tellurium atom. The crystals are triclinic, space group P$\text{1}$, with unit cell dimensions a 8.521(2), b 10.917(2), c 14.813(2) Å, α 81.84(1), β 83.38(1), γ 88.41(1)°, V 1353.4(4) ų and Z = 2(dimers) from 3887 observed reflections [I > 3σ(I)], R = 0.0359.     

Total synthesis of (±) zoapatanol: a stereospecific synthesis of a key intermediate

The development of a stereospecific synthesis of a key intermediate in the synthesis of (±)-zoapatanol from the Weiland-Miescher ketone is described.     

Studies on terpenes—7: A Short route to a pentalenolactone e precursor

The bicyclic enone 6 was converted into the adduct 13 by photochemical addition of aliene, and then elaborated through a fragmentation sequence into the -methylene ketone 17.