A counterintuitive, yet efficient synthesis of bis(indenyl)zirconium dihalides

The use of bisindenyl zirconium dimethyl in the synthesis of the corresponding dihalides is described. The synthesis of Ind₂ZrCl₂ has been carried out, cleanly and quantitatively, by chlorination of Ind₂ZrMe₂ (2) with a variety of inorganic chlorides, including BCl₃, SCl₂ in either toluene or methylene chloride, and HCl in Et₂O. The latter method is the preferred one, since it produces methane as the only byproduct, and the formed Ind₂ZrCl₂ precipitates quantitatively from the Et₂O solvent: a simple filtration then gives the analytically pure product in quantitative yield. Ind₂ZrBr₂ and Ind₂ZrI₂ are obtained by reacting 2 with Br₂ and I₂, respectively. The ‘inverse’ synthesis of metallocene dichlorides by chlorination of their dimethyl ‘derivatives’ has advantages compared to the classic method: first, Ind₂ZrCl₂ is obtained in higher yield (90-96%); second, it is easier to purify (at the dimethyl stage) and is obtained free from LiCl. Five bisindenyl zirconium complexes with different sigma ligands have been investigated in solution propylene polymerizations: it is found that the σ-ligands have no relevant influence on the catalyst activity, nor on the polymer properties.     

Indazole complexes of diorganotin(IV) dihalides. The crystal structures of dichloro and dibromodimethylbis(indazole) tin(IV)

Reaction of indazole (HInd) with diorganotin(IV) dihalides yielded compounds of the type [SnR₂X₂(HInd)₂] (R = Me, Et, Bu and Ph; X = Cl, Br). The structures of the dihalodimethylbis(indazole)tin(IV) complexes were determined by X-ray crystallography. These are trans-octahedral centrosymmetric compounds with the following bond lengths (Å) around the tin atom: Sn-Cl 2.590(2), Sn-N 2.377(6), Sn-C 2.12(1) in the chloride; and Sn-Br 2.733(1), Sn-N 2.370(5) and Sn-C 2.12(1) in the bromide. Mössbauer and vibrational spectra suggest similar trans stereochemistry for the other complexes prepared. The behaviour of these compounds in solution was studied by conductimetry and NMR techniques.     

Spectroscopic and structural studies on polyfluorophenyl tellurides and tellurium(IV) dihalides

Bis(fluorophenyl) tellurides R2Te (R = C6F2H3 (1), CF3C6F4 (2), CF3C6F4OC6F4 (3), and C6F5 (4)) are synthesized by the facile reaction of Na2Te with bromo-fluorobenzenes, RBr. The corresponding bis(fluorophenyl)tellurium(IV) dihalides, R2TeHal2 (Hal = F, Cl, and Br) (5-16), are obtained by the oxidation of 1-4 with mild halogenating agents (XeF2, SO2Cl2, and Br2). The dihalides show temperature-dependent NMR spectra. On the basis of the 19F NMR spectra of the two series, (C6F2H3)2TeHal2 (Hal = F (5), Cl (9), and Br (13)) and R2TeCl2 (R = C6F2H3 (9), CF3C6F4 (10), CF3C6F4OC6F4 (11), and C6F5 (12)), the coalescence temperatures, T(c), and free enthalpies, DeltaG, of rotation of the TeC bonds are determined. The activation enthalpies for the dichlorides/dibromide 9-13 are in the range of 14.4-15.2 kcal mol(-1) and that for the difluoride 5 is considerably lower at 10.7 kcal mol(-1). In addition to thorough spectroscopic characterization of 1-16, the crystal structures of the monotellurides 2 and 4 as well as of the tellurium(IV) dihalides 5, 6, 9, 10, and 13 were determined. The dihalides show interesting intermolecular Te...Hal contacts, significantly shorter than the sum of the van der Waals radii, leading to different networks of association.     

Methylene bis(aluminum dihalides)

Methylene bis(aluminum dichloride) and methylene bis(aluminum dibromide) have been synthesized in essentially quantitative yields. It is postulated that the reaction sequence which leads to these compounds requires aluminum monohalide as a transitory intermediate.     

A simplified synthesis of the hexamethylplatinate(IV) ion

Tetra-n-butylammonium hexachloroplatinate (IV) reacts with lithium methyl/lithium iodide in ether to give a solution containing lithium hexamethylplatinate (IV). With lithium methyl/lithium bromide in ether however, tetrabutylammonium hexamethylplatinate (IV) is precipitated together with lithium halides. Solid [Bu₄N)₂[Pt(Ch₃)₆] is stable under nitrogen at room temperature, but ether solutions of [Pt(Ch₃)₆]^2- decompose in a few minutes at room temperature in the absence of excess lithium methyl.     

A general modular method of azaindole and thienopyrrole synthesis via Pd-catalyzed tandem couplings of gem-dichloroolefins

A palladium-catalyzed reaction of gem-dichloroolefins and a boronic acid via a tandem intramolecular C-N and intermolecular Suzuki coupling process gave corresponding substituted azaindoles or thienopyrroles. This method is a very modular protocol to synthesize all four isomers of azaindole and two isomers of thienopyrroles in good to excellent yield.     

Preparation of di(n-butyl) tin and di(n-octyl) tin dihalides by the direct synthesis method

The direct synthesis of the two industrially important organotin intermediates, di(n-butyl)tin and di(n-octyl)tin dihalides, has been investigated by reacting the appropriate alkyl halide with metallic tin undervarying conditions. Observations were made on the influences of temperature, pressure, reaction time, nature of the tin metal, organic halide/tin reactant ratios and the presence of catalysts on the extent of tin conversion and yields of the organotin products. The efficacy of the onium halides, notably n-Bu₄NI, Me₃SI and Ph₃MeAsI, either singly or in binary combinations with iodine or inorganic iodine compounds, in catalysing the synthesis of the above dialkyltins as well as higher di(n-alkyl)tin analogues is described.     

A thermal synthesis of a new tin(IV) dithiocarbamate

A new tin dithiocarbamate containing sulphur bridges, di--sulphidobis [bis(N,N-diethyldithiocarbamato)tin(IV)], has been isolated from the thermal decomposition of tetrakis(N,N-diethyldithiocarbamato)tin(IV). A dimeric structure is proposed on the basis of results from mass spectrometry, infrared spectroscopy, thermal analysis and vapour pressure osmometry.

---

Zusammenfassung Ein neues, Schwefelbrücken enthaltendes Zinn-Dithiocarbamat, Di--sulfidobis[bis(N,N-diäthyldithiocarbamato)Zinn(IV)], wurde bei der Zersetzung von Tetrakis(N,N-diäthyl-dithiocarbamato)Zinn(IV) isoliert. Aufgrund der Ergebnisse der Massenspektrometrie, der Infrarotspektroskopie, der Thermoanalyse und der Dampfdruck-Osmometrie wird eine Dimerstruktur vorgeschlagen.

---

Résumé Un nouveau dithiocarbamate d'étain contenant des ponts de soufre, le di--sulfidobis[bis(N,N-diéthyl-dithiocarbamato)é tain(IV)], a été isolé lors de la décomposition thermique du tétrakis(N,N-diethyl-dithiocarbamato) étain(IV). Une structure dimère est proposéeà partir des résultats obtenus par spectrométrie de masse, spectroscopie infrarouge, analyse thermique et osmométrie sous pression de vapeur.

---

—-- [/N,N- (/IV)], [/N,N- (/IV)], , (N,N- ) (IV). - , , .

---

---

The authors gratefully acknowledge the assistance given by Dr. A. G. Wedd with the vacuum sublimation technique. One of us, G. K. B., is grateful for a research scholarship provided by La Trobe University.     

Parallel synthesis of modular chiral Schiff base ligands and evaluation in the titatium(IV) catalyzed asymmetric trimethylsilylcyanation of aldehydes

Highly modular tridentate Schiff base ligands arising from enantiopure epoxyalcohols have been prepared and evaluated in catalysis using parallel methods. The key structural motifs and experimental parameters have been identified, allowing enantioselectivities of up to 77% ee in the titatium-catalyzed trimethylsilyl cyanide addition to aldehydes.     

Oxidative-addition reactions of monocyclopentadienyltitanium(III) dihalides

Oxidative-addition reactions of CpTi^IIICl₂ are described, and, in particular, the reactions with compounds containing disulphide linkages.     

A concise and modular synthesis of pyranicin

A modular, 13-step synthesis of the tetrahydropyran-containing annonaceous acetogenin pyranicin is reported. Key features are the use of an Achmatowicz oxidation-Kishi reduction sequence for the assembly of a pyranone from a furan and the application of Fu's alkyl-alkyl Suzuki coupling for subunit union.     

A modular synthesis of unsymmetrical tetraarylazadipyrromethenes

[reaction: see text] A stepwise route to unsymmetrical tetraarylazadipyrromethenes by a condensation of 2,4-diaryl-5-nitroso-pyrroles with 2,4-diarylpyrroles is described. This modular building-block approach allows for the introduction of up to four different aryl substituents on the azadipyrromethene and is tolerant of a varied substituent set. An efficient synthesis of the 2,4-diarylpyrroles building blocks from 1,3-diaryl-4-nitro-butan-1-ones by nitro hydrolysis to a keto-aldehyde and subsequent ammonia condensation reaction has been achieved. The facile conversion of 2,4-diarylpyrroles into their alpha-nitroso analogues by their reaction with sodium nitrite generated the second building block required for the synthesis.     

A modular synthesis of annonaceous acetogenins

A synthesis of four Annonaceous acetogenins, asiminocin, asimicin, asimin, and bullanin, by a modular approach from seven fundamental subunits, A-G, is described. The approach employs a central core aldehyde segment, C, to which are appended an aliphatic terminus, A or B, a spacer subunit, D or E, and a butenolide terminus, F or G. Coupling of the A, B, D, and E segments to the core aldehyde unit is effected by highly diastereoselective additions of enantiopure allylic indium or tin reagents. The butenolide termini are attached to the ACD, BCE, or BCD intermediates by means of a Sonogashira coupling. The design of the core, spacer, and termini subunits is such that any of the C30, C10, or C4 natural acetogenins or stereoisomers thereof could be prepared. IC50 values for the four aforementioned acetogenins against H-116 human colon cancer cells were found to be in the 10(-3) to 10(-4) microM range. The IC90 activities were ca. 10(-3) microM for asimicin and asimin but only 0.1-1 microM for bullanin and asiminocin.     

A flexible and modular stereoselective synthesis of (9R,10S)-dihydrosterculic acid

(9R,10S)-Dihydrosterculic acid has been prepared from (S_S,S_S)-1,1-bis(p-tolylsulfinyl)methane in a sequence involving an asymmetric Corey–Chaykovsky cyclopropanation and two sulfoxide/lithium exchange reactions. In most steps, the reaction conditions had to be optimized for the unbranched alkyl substituents, which were prone to Evans–Mislow rearrangements and subsequent degradation.     

Synthesis and characterization of heavier dioxouranium(VI) dihalides

The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO(2)Br(2)x3H(2)O (1), [UO(2)Br(2)(OH(2))(2)](2) (2), and UO(2)I(2)x2H(2)Ox4Et(2)O (3), are reported. Moreover, adducts of UO(2)I(2) and UO(2)Br(2) with large, bulky OP(NMe(2))(3) and OPPh(3) ligands such as UO(2)I(2)(OP(NMe(2))(3))(2) (4), UO(2)Br(2)(OP(NMe(2))(3))(2) (5), and UO(2)I(2)(OPPh(3))(2)(6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P2(1)/c, a = 9.7376(8) A, b = 6.5471(5) A, c = 12.817(1) A, beta = 94.104(1) degrees , V = 815.0(1) A(3), Z = 4; (2) monoclinic, P2(1)/c, a = 6.0568(7) A, b = 10.5117(9) A, c = 10.362(1) A, beta = 99.62(1) degrees , V = 650.5(1) A(3), Z = 2; (4) tetragonal, P4(1)2(1)2, a = 10.6519(3) A, b = 10.6519(3) A, c = 24.0758(6) A, V = 2731.7(1) A(3), Z = 4; (5) tetragonal, P4(1)2(1)2, a = 10.4645(1) A, b = 10.4645(1) A, c = 23.7805(3) A, V = 2604.10(5) A(3), Z = 4, and (6) monoclinic, P2(1)/c, a = 9.6543(1) A, b = 18.8968(3) A, c = 10.9042(2) A, beta =115.2134(5) degrees , V = 1783.01(5) A(3), Z = 2. Whereas 1 and 2 are the first UO(2)Br(2) hydrates and the last missing members of the UO(2)X(2) hydrate (X = Cl --> I) series to be structurally characterized, 4 and 6 contain room-temperature stable U(VI)-I bonds with 4 being the first structurally characterized room temperature stable U(VI)-I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported.