Reactions of half-sandwich rhodium(III) and iridium(III) compounds with pyridinethiolate ligands: Mono-, di-, and tri-nuclear complexes

Neutral trinuclear metallomacrocycles, [Cp^*RhCl(μ-4-PyS)]₃ (3) and [Cp^*IrCl(μ-4-PyS)]₃ (4) [Cp^* = pentamethylcyclopentadienyl, 4-PyS = 4-pyridinethiolate], have been synthesized by self-assembly reactions of [Cp^*RhCl₂]₂ (1) and [Cp^*IrCl₂]₂ (2) with lithium 4-pyridinethiolate, respectively. In situ reaction of complex 3 with three equivalent of lithium 4-pyridinethiolate resulted in [Cp^*Rh(μ-4-PyS)(4-PyS)]₃ (5) containing both skeleton and pendent 4-PyS groups. Chelating coordination of 2-pyridinethiolate broke down the triangular skeleton to give mononuclear metalloligands Cp^*Rh(2-PyS)(4-PyS) (6) and Cp^*Ir(2-PyS)(4-PyS) (7) [2-PyS = 2-pyridinethiolate], which could also be synthesized from Cp^*RhCl(2-PyS) (10) and Cp^*IrCl(2-PyS) (11) with lithium 4-pyridinethiolate. The coordination reactions of 6 with complexes 1 and 2 gave dinuclear complexes [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*RhCl₂] (8) and [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*IrCl₂] (9), respectively. Molecular structures of 3, 4, 6 and 11 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Thermal Decomposition of bis(cyclopentadienyl)hafnium compounds and their deuterated analogues

Thermal decomposition ranges of Cp₂HfR_, (R = Me, Ph) have been found by the DTA method. The thermal stability of hafnium derivatives greatly exceeds the stability of analogous titanium and zirconium compounds. Decomposition of Cp₂HfR₂ occurs by abstraction of σ-bonded groups which convert into RH. Hydrogen donors for the RH formation are both π-cyclopentadienyl and σ-bonded groups. The initial π-Cp₂Hf structure rearranges to form the (η⁵-Cp)-(η⁵,η¹-C₅H₄)Hf fragment. These react with HCl to produce Cp₂HfCl₂. It has been established that hydrogen exchange between cyclopentadienyl rings and methyl groups occurs during the thermal decomposition of Cp₂HfMe₂. As a result of the exchange process on thermal decomposition of Cp₂HfMe₂-d6, deuterium insertion into the cyclopentadienyl ring has been shown. The participation of solvent during the decomposition process of the hafnium derivatives has been studied.     

Synthesis, characterization, and crystal structures of the osmium triflate complexes CpOs(P-P)(OTf) and [CpOs(P-P)(OH2)][OTf]

Treatment of the osmium(II) hydrides Cp^∗Os(P-P)H (Cp^∗ = pentamethylcyclopentadienyl) with methyl trifluoromethanesulfonate (MeOTf) affords osmium(II) triflate complexes with the general formula Cp^∗Os(P-P)(OTf), where P-P = bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), or 1,2-bis(dimethylphosphino)ethane (dmpe). The aqua complexes [Cp^∗Os(dmpm)(OH₂)][OTf] and [Cp^∗Os(dppm)(OH₂)][OTf] are synthesized by the addition of water to the corresponding anhydrous triflates. The complexes Cp^∗Os(dppm)(OTf) and [Cp^∗Os(dmpm)(OH₂)][OTf] have been examined crystallographically, and all compounds have been characterized by NMR spectroscopy.     

二茂锆羧酸配合物的合成——二茂锆氢化物与α,β—不饱和酸或钠盐反应的研究

本文研究了Cp₂ZrH₂与丙烯酸和Cp₂Zr(H)Cl与丙烯酸钠、巴豆酸钠的反应。产物由IR ¹H和¹³CNMR、ESR谱、气相色谱以及化学方法分析鉴定。产物水解得到与底物相应的饱和酸.用¹H NMR方法考察了Cp₂ZrH₂与丙烯酸的反应过程,用IR方法考察了Cp₂Zr(H)Cl与丙烯酸钠的反应过程。实验结果表明,上面两种反应首先消除H₂或NaCl,形成锆氧健,然后碳碳双键还原生成二茂锆羧酸盐配合物,其中羧酸根离子与二茂锆桥式双齿配位。     

C-H activation of benzene with CpRu(CO)2CH3

Irradiation of Cp^∗Ru(CO)₂CH₃ (1) in C₆D₆ at room temperature yields Cp^∗Ru(CO)₂C₆D₅ and CH₃D (where Cp^∗ = n⁵-C₅Me₅). Cp^∗Ru(CO)₂CD₃ (2) has also been prepared and similar irradiation in C₆H₆ yields Cp^∗Ru(CO)₂C₆H₅ (3) and CD₃H. This latter reaction confirms that it is the methyl group bonded to ruthenium that is involved in the C-H activation process and not the methyl groups on the Cp^∗ ligand system. The compound Cp^∗Ru(CO)₂C₆H₅ (3) has been prepared for the first time in good yield by the reaction of Cp^∗Ru(CO)₂Br with NaBPh₄. X-ray crystal structures of both Cp^∗Ru(CO)₂CH₃ (1) and Cp^∗Ru(CO)₂C₆H₅ (3) have been determined and the results are reported and discussed.     

Photochemie von pentamethylcyclopentadienyl-substituierten Diphosphenen und Phosphaarsenen

Under irradiation dimerization of the diphosphenes CpPPCp and Cp^*PPR (Cp  Pentamethylcyclopentadienyl, R  2,4,6-Tri-t-butylphenyl) and the phosphaarsene CpAsPR takes place. Further irradiation leads to homolytic cleavage of Cpelement bonds. Intramolecular recombination leads to the bicyclic butterfly-compounds P₄R₂ and P₂As₂R₂.     

The bis(η-cyclopentadienyl)titanium(IV) – salicylate system revisited and the characterisation of two 3,5-di-t-butylsalicylate analogues. The molecular structure of [Cp2Ti(sal)], (sal = O2CC6H4O2−)

The Cp₂Ti^IV – salicylate system has been re-examined and procedures for the syntheses of [Cp₂Ti(salH)₂] and [Cp₂Ti(sal)] explored, [salH = (O₂CC₆H₄OH-2)^–; sal = (O₂CC₆H₄O-2)^2–]. The new 3,5-di-t-butylsalicylate analogues have been prepared and characterised. An X-ray structure determination of [Cp₂Ti(sal)] confirms the chelating nature of the sal ligand which is bonded to the metal through the phenolic and one of the carboxylate oxygen atoms.     

Silyl-titanation of acetylenes and 1,3-dienes

A Ti^IIISi active species, Cp₂TiSiMe₂Ph, is formed either by the reaction of Cp₂TiCl₂ with two equivalents of PhMe₂SiLi or by the reaction of Cp₂TiCl with one equivalent of PhMe₂SiLi. Highly regio- and stereo-selective silyltitanation by this species has been observed with acetylenes and 1,3-dienes.     

Mechanism‐Based Condition Screening for Sustainable Catalysis in Single‐Electron Steps by Cyclic Voltammetry

A cyclic‐voltammetry‐based screening method for Cp₂TiX‐catalyzed reactions is introduced. Our mechanism‐based approach enables the study of the influence of various additives on the electrochemically generated active catalyst Cp₂TiX, which is in equilibrium with catalytically inactive [Cp₂TiX₂]^?. Thioureas and ureas are most efficient in the generation of Cp₂TiX in THF. Knowing the precise position of the equilibrium between Cp₂TiX and [Cp₂TiX₂]^? allowed us to identify reaction conditions for the bulk electrolysis of Cp₂TiX₂ complexes and for Cp₂TiX‐catayzed radical arylations without having to carry out the reactions. Our time‐ and resource‐efficient approach is of general interest for the design of catalytic reactions that proceed in single‐electron steps.     

Synthese und Charakterisierung von Metallocen-Chelaten heterocyclischer 1,2-Diselenolate

Synthesis and Characterization of Metallocene Chelates of Heterocyclic 1,2-Diselenolates Synthesis and properties of metallocen diselenolates Cp₂^RML (Cp^R = η⁵-C₅H₄CH₃ (Cp′); η⁵-C₅(CH₃)₄ C₂H₅ (Cp^o)) of titanium(IV) and vanadium(IV) with L = dsit (1,3-dithiole-2-thione-4,5-diselenolate), dsise (1,3-dithiole-2-selone-4,5-diselenolate) dsitse (1,3-thiaselenole-2-selone-4,5-diselenolate) and dsis (1,3-diselenole-2-selone-4,5-diselenolate) are described. The structures of these compounds in solution are discussed using ¹H, ¹³C, ⁷⁷Se NMR and EPR data. Their voltammetric behaviour is investigated in dichloromethane. The activation parameters of the chelate ring inversion of the titanocene diselenolates (Cp₂^RTiL) and the x-ray structures of Cp₂′Ti(dsit), Cp₂^oTi(dsit); Cp₂^oTi(dsise) (2 modifications) and Cp₂^oTi(dsis) are reported.     

Insertionsreaktionen von Bis(η-cyclopentadienyl)hydridorhenium mit monosubstituierten Acetylenen

Bis(η-cyclopentadienyl)hydridorhenium Cp₂ReH undergoes stereospecific trans insertion reactions when treated with monosubstituted acetylenes HCCR (R  CO₂Me, CN, CF₃). The cis alkenyl complexes Cp₂Re[η¹-(Z)-CHCHR] thus formed isomerize thermally or under acid catalysis to produce the trans isomers Cp₂Re[η¹-(E)-CHCHR]. When Cp₂ReH adds to HCCCOMe only the trans isomer is observed. The regiospecific β-addition of Cp₂ReH contrasts with the α-addition of Cp₂MoH₂ and Cp₂WH₂. The insertion of acetylenes HCCR′ into the metalcarbon bond of some alkenyl complexes Cp₂Re[η¹-(E)-CHCHR] affords butadienyl complexes Cp₂Re[η¹-{(1E,3E)-CHCHR′CHCHR&}] (R,R′  COMe, CO₂Me). The (E,E)-configuration of these compounds is deduced from ³J(¹³-C¹H) coupling constants.     

Interaction of chromocene with MgO and reactivity of the adsorbed species towards CO: An IR study

The interaction of chromocene with partially and totally dehydroxylated MgO and the reactivity of the adsorbed species towards CO have been studied by IR spectroscopy. Cp₂Cr is weakly adsorbed on residual surface MgOH groups, forming hydrogen bonded species and, on the extended (100) faces, forming clustered (Cp₂Cr)_n species. A stronger interaction is observed with the highly unsaturated ions located on the edges and corners of the MgO microcrystals. Upon dosage of CO at room temperature, Cp₂CrCO complexes are formed which are stabilized by interaction with the Mg²⁺ and O²⁻ ions of the surface. The occurrence of an activated process leading to [Cp₂Cr]⁺ and [CpCr(CO)₃]⁻ charged reaction products is also observed.     

Role of ion-pair equilibria in homogeneous Ziegler-Natta olefin polymerization catalysis

By means of a multinuclear NMR study of the complexes formed between AlCl₃ and either Cp₂TiCl₂ or Cp₂Ti(CH₂SiMe₃)Cl in methylene chloride solution, isomeric forms of the resulting 1:1 complexes have been detected. The influence of temperature, concentration, ratio of the titanocene chloride to aluminum chloride and nature of the solvent upon the ¹H, ¹³C and ²⁷Al NMR spectra has been investigated. The spectral changes caused by the foregoing factors give compelling evidence for a equilibrium in such Cp₂Ti(R)Cl · AlCl₃ complexes (R = Cl, CH₂SiMe₃) between contact ion pairs, Cp₂TiR · Cl · AlCl₃, and solvent-separated ion pairs, Cp₂TiR⁺ AlCl₄⁻. Upon experimental variations in temperature, concentration, solvent and ratio of R_nAlCl_3−n to the titanium catalyst, the polymerization activity of the catalyst system towards ethylene was markedly altered. Such changes in activity support the conclusion that the most active sites for polymerization in such systems are the solvent-separated ion pairs.     

Mechanism of the carbonylation of dicyclopentadienylmolybdenum dihydride

The carbonylation of Cp₂MoH₂ proceeds through the intermediates Cp₂MoCO, [Cp₂Mo(H)CO] [CpMo(CO)₃] (I) and CpMo(CO)₃ to the final products [CpMo(CO)₃]₂ and CpMo(η³-C₅H₇)(CO)₂. The formation of I in the carbonylation reaction has been shown to involve net hydride transfer, but an alternate synthesis has demonstrated the considerable proton basicity of Cp₂MoCO. Since the net hydride transfer between Cp₂MoH₂ and [CpMo(CO)₃]₂ can be accelerated by production of metal centered radicals, the actual mechanism is not a simple two-electron process (H^? transfer, but rather a sequence of one-electron steps.     

The first evidence for a stereostable centrometalled chirality in a dicyclopentadienyltantalum complex

Reaction of dichlorophenylphosphine with monohydrides Cp₂M(CO)H (M = Nb or Ta) gives the salts [Cp₂M(CO)(PPhClH(]⁺ Cl⁻ in good yields. In a basic medium these salts give the neutral complexes Cp₂M(CO) [P(O)(H)Ph]. In a reaction starting from the chiral hydride Cp^* CpTa(CO)H, (Cp^* = C₅Me₅), two diastereoisomers are obtained, and can be isolated as stereostable structures.     

Host-Guest Interactions between Calixarenes and Cp(2)NbCl(2)

The possible inclusion complexes of Cp₂NbCl₂ into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculations, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculations, ¹H NMR solution and solid state ¹³C CP-MAS NMR results demonstrated that p-sulfonic calix[6]arene does form an inclusion complex with Cp₂NbCl₂. Raman spectroscopy showed, for the inclusion compound of p-sulfonic calix[6]arene-Cp₂NbCl₂, a band between 500 and 850 cm⁻¹ characteristic of Nb-O vibration. This result suggests that Nb(V) may engage in coordination with the oxygen of the sulfonate group, as part of the host-guest interaction. However, it is important to mention that the niobocene dichloride (Cp₂NbCl₂) dissolves in water and undergoes oxidation and hydrolysis processes to yield Cp₂NbCl₂(OH) species. For that reason this band does not exclude that the Nb-O band belongs to Cp₂NbCl₂(OH). Solid State ¹³C CP-MAS NMR and solution ¹H NMR spectroscopies together with ab-initio results showed that Cp₂NbCl₂ is included in the p-sulfonic calix[6]arene cavity, with both Cp rings inside the cavity. In contrast, the solution ¹H NMR results demonstrated that calix[6]arene does not form inclusion complex with Cp₂NbCl₂ in CDCl₃ solution. Cp₂NbCl₂ is not included in the calix[6]arene cavity, possibly due to the lack of sulfonate heads which promote Nb-O interactions and assist the inclusion of Cp₂NbCl₂ into the cavity.     

A comparative study on the reaction mechanisms of Cp2MH2 (M = Cr,Mo, W) with HBF4

The reaction mechanisms of group 6 transition metal dihydride complexes, Cp₂MH₂ (M = Cr, Mo, and W), and HBF₄ were studied using M06‐L density functional theory. The chemical bond changes along the reaction pathway are analyzed by the topological analysis of electron density. The calculated results show that the interactions between the H atom of HBF₄ and Cp₂MH₂ are stronger than those between Cp₂MH₂ and BF₃; additionally, due to the low energy barriers in the subsequent reaction, all the title reactions can occur easily, and the yield rates of the Cp₂MH₂ + HBF₄ reactions are high. For M = Cr and Mo, the [Cp₂MH₃]⁺ in the product Cp₂MH₃·BF₄ is in the nonclassic dihydrogen‐hydride form ([Cp₂M(η²‐H₂)H]⁺). [Cp₂CrH₃]⁺ and [Cp₂MoH₃]⁺are unstable, and H₂ can be easily liberated from them. For M = W, the final product is Cp₂WH₃·BF₄, and [Cp₂WH₃]⁺ is stable in the classic trihydride form.     

Antifertility and biocidal activities of organometallics of silicon,germanium, titanium and zirconium derived from 2-acetylthiophene thiosemicarbazone

A comparative biochemical study of four Group IV element compounds with specific sulphur-containing organic substrates has been carried out and discussed. The structural characterizations of these organometallics, viz. Me₂SiLCl, Me₂SiL₂, Me₃SiL, Ph₂SiLCl, Ph₂SiL₂, Ph₃SiL, Ph₃GeL, Cp₂TiLCl, Cp₂TiL₂, Cp₂ZrLCl and Cp₂ZrL₂ (where LH?2-acetylthiophene thiosemicarbazone) had been deduced on the basis of various physico-chemical and instrumental techniques, viz., IR, UV, ¹H NMR, ¹³C NMR AND ²⁹SI NMR spectral studies. All the organometallics and the parent thiomine have been screened against a number of microbes and their sterilizing power in male mice tested. The results of these biocidal studies show that the organosilicon(IV) and organogermanium(IV) compounds are more active than the organotitanium(IV) and organozirconium(IV) derivatives. An attempt has also been made to correlate the structural aspects of the molecule with its biological activity.     

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH₃O₂CCH₂NH₃]⁺ (MeGlyH⁺) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonites [high‐purity montmorillonite (MMT)‐MeGlyH⁺] had larger interlayer spacing (12.69 Å) than montmorillonites without treatment (9.65 Å). The zirconocene catalyst system [Cp₂ZrCl₂/methylaluminoxane (MAO)/MMT‐MeGlyH⁺] had much higher Zr loading and higher activities than those of other zirconocene catalyst systems (Cp₂ZrCl₂/MMT, Cp₂ZrCl₂/MMT‐MeGlyH⁺, Cp₂ZrCl₂/MAO/MMT, [Cp₂ZrCl]⁺[BF₄]/MMT, [Cp₂ZrCl]⁺[BF₄]^?/MMT‐MeGlyH⁺, [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT‐MeGlyH⁺, and [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (Cp₂ZrCl₂/MAO/MMT‐MeGlyH⁺). MeGlyH⁺ and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1892–1898, 2002     

Ligand exchange reactions of the alkyluranium(III) complexes (η5-C5H5)3URLi

The Cp₃URLi compounds (Cp = η⁵-C₅H₅; R = Me, n-Bu, n-Pent) have been synthesized by reaction of CP₃U(THF) with 1 equivalent of RLi. Exchange of the R alkyl occurs on treatment with alkyllithium reagents or in hydrogenolysis in the presence of a terminal olefin. These reactions presumably involve the Cp₃U and Cp₂UR species which are in equilibrium with the Cp₃URLi complexes.