Metallocene Bis Research Articles

A Metallocene Bis(phosphoranocarbene) of Uranium and a Probe of Its Reactivity with Alcohols.

The addition of 2 equiv of the phosphaylide H2C═PPh3 to the dimethyl uranium metallocene Cp*2UMe2 (Cp* = η5-C5Me5) in toluene with gentle heating at 40 °C generates the phosphorano-stabilized bis(carbene) Cp*2U[C(H)PPh3]2 (1) in good yield. Characterization of 1 by X-ray crystallographic analysis reveals two short uranium-carbon bonds, ranging from 2.301(5) to 2.322(5) Å, consistent with the presence of U═C carbene-type bonds. Monitoring the reaction by NMR spectroscopy suggests that it proceeds through the intermediate formation of the methyl carbene complex Cp*2U[C(H)PPh3](Me) (1Int); however, prolonged heating of these solutions leads to the ortho-cyclometalated carbene species Cp*2U{κ2-[C(H)PPh2(C6H4)]} (2) via intramolecular C-H activation. Rapid conversion from 1 to 2 occurs within hours upon heating its toluene solutions to 100 °C. Preliminary reactivity studies of 1 show that it readily reacts with alcohols, such as HODipp (Dipp = 2,6-diisopropylphenyl) and HOC(CF3)3, to give the mixed carbene alkoxide compounds Cp*2U[C(H)PPh3](OR) (R = Dipp (4Dipp), C(CF3)3 (5CF3)). In one case, the reaction of 1 with HODipp in the presence of adventitious water led to the formation of a few crystals of the terminal U(IV) oxo complex, [Ph3PCH3][Cp*2U(O)(ODipp)] (3oxo). The isolation of 1 marks the first instance of an unchelated, heteroatom-stabilized bis(carbene) complex of uranium that also provides an entryway to the synthesis of its monocarbene derivatives through protonolysis.

Latest News: Reactions of Group 4 Bis(trimethylsilyl)acetylene Metallocene Complexes and Applications of the Obtained Products

Recently published reactions of group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complexes from the last two years are reviewed. Complexes like Cp’2Ti(η2‐Me3SiC2SiMe3) and Cp2Zr(py)(η2‐Me3SiC2SiMe3) with Cp’ as Cp (cyclopentadienyl) and Cp* (pentamethylcyclopentadienyl) have been considered (py=pyridine). These complexes can liberate a reactive low‐valent titanium or zirconium center by dissociation of the ligands and act as ‘‘masked’’ MII complexes (M=Ti, Zr). They represent excellent sources for the clean generation of the reactive coordinatively and electronically unsaturated complex fragments [Cp’2M]. This is the reason why they were used for many synthetic and catalytic reactions during the last years. As an update to several review articles on this topic, this contribution provides an update with recent examples of preparative organometallic and organic chemistry of these complexes, acting as reagents for a wide range of coordinating and coupling reactions. In addition, applications and investigations concerning reaction products derived from this chemistry are mentioned, too.

Update for Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes: A Never-Ending Story?

Recently reported reactions of group 4 metallocene bis(trimethylsilyl)acetylene complexes from the last two years are summarized. This could be considered as a never-ending story. A recently report...

Advantages of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes as Metallocene Sources Towards Other Synthetically used Systems.

Active species for synthetic and catalytic applications are formed from well defined complexes or mixtures of compounds. For group 4 metallocenes, three pathways for the formation of the reactive complex fragment [Cp′2M] are known: (i) reductive mixtures and well defined complexes which are able to form the metallocene fragments either by (ii) addition or (iii) substitution reactions. In this account for each of theses systems (i)–(iii) a prominent example will be discussed in detail, (i) the Negishi reagent Cp2ZrCl2/n‐BuLi, (ii) bis(η5 : η1‐pentafulvene) complexes and (iii) metallocene bis(trimethylsilyl)acetylene complexes, to show the advantages and the disadvantages for each of these methods for synthetic applications. This account summarizes some main advantages of group 4 metallocene bis(trimethylsilyl)acetylene complexes as metallocene generating agents over other synthetically used systems. For each of the special purposes, all described systems have advantages as well as disadvantages. The aim of this overview is to help synthetic chemists in selecting the most effective system on the basis of [Cp′2M] (M=Ti, Zr) for synthetic or catalytic puposes.

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

With the 30 years old first example of a stable group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complex Cp2Ti(η2‐btmsa) a series of similar complexes like Cp′2M(η2‐btmsa) (M = Ti, Zr; Cp′ = Cp, Cp* as η5‐pentamethylcyclopentadienyl and Cp′2 = rac‐(ebthi) as rac‐1,2‐ethylene‐1,1′‐bis(η5‐tetrahydroindenyl) ) represent excellent sources for the generation of the very reactive coordinatively and electronically unsaturated complex fragments [Cp'2M], which were used in many synthetic and catalytic reactions. Examples for this were oresented in several papers and summarized in some reviews. In this update new reactions of group 4 metallocene bis(trimethylsilyl)acetylene complexes towards symmetrically and unsymmetrically α‐dihetero‐substituted alkynes, reactions with other alkynes, di‐ and polyynes to metallacyclopentadienes as well as the conversions of the formed products are summarized. Additionally, novel synthetic applications of the formed metallacyclopentadienes on the basis of the zirconocene bis(trimethylsilyl)acetylene complex Cp2Zr(py)(η2‐btmsa) are highlighted. Reactions with imines, neutral N‐donor ligands, E‐H compounds (E = N, O, P), molecular hydrogen, water, phosphino‐ and aminoboranes, E‐Cl compounds (E = C, P), disilylated germylenes and aryloxy ketones were described. Different self‐assembly reactions to multinuclear complexes by using group 4 metallocene bis(trimethylsilyl)acetylene complexes in C‐C coupling reactions with or without C‐H bond activation to tri‐ or tetranuclear complexes are considered, too. These examples are discussed following the general L‐M‐S principle for stoichiometric and catalytic reactions, whereby different ligands L (L = Cp′ = Cp, Cp*, rac‐ebthi), metals M (M = Ti, Zr, Hf) and substrate substituents S influence the reactivity and the obtained products.

Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes with Nitriles and Isonitriles.

This Review summarizes reactions of Group 4 metallocene bis(trimethylsilyl)acetylene complexes with nitriles and isonitriles. Selected examples of reactions of Group 4 metallocene alkyne complexes of the type Cp'2 M(η2 -Me3 SiC2 SiMe3 ) with different nitriles and isonitriles are described following the general L-M-S principle, in which stoichiometric and catalytic reactions are influenced by ligands L, metals M, and substrate substituents S. The influence of all these parameters is highlighted. The basic reactions with nitriles and in some cases with isonitriles were investigated in detail and are summarized. Selected further reactions of the products again depend on L, M, and S. Most interesting feature for this is the formation of mono- and polynuclear 1-metalla-2,5-diazacyclopenta-2,4-dienes, which show great potential for the synthesis of complex heterocycles.

Structure and properties of ethylene/propylene copolymers synthesized with bis(2,4,7-trimethylindenyl)zirconium dichloride activated by methyl aluminoxanes containing different amount of trimethylaluminum

Ethylene/propylene copolymerization was catalyzed under the same conditions with unbridged metallocene bis(2,4,7-trimethylindenyl)zirconium dichloride (Cat.1) activated by aluminoxane type cocatalysts having different content of trimethylaluminum (TMA). Chain structure of the copolymers was characterized by 13C NMR and thermal analysis on copolymer fractions separated based on crystallinity. Changing the cocatalyst from commercial methylaluminoxane (MAO, containing both free TMA and bond TMA) to dried MAO (dMAO, containing only bond TMA) and BHT-treated MAO (BMAO, containing almost no TMA) caused only slight differences in polymerization activity and moderate increase in copolymer molecular weight, but marked differences in copolymer chain structure. The copolymers produced using MAO (sample 1) and dMAO (sample 2) as cocatalysts contain high amount of fractions with very low propylene content and almost isolated propylene units. The copolymer produced using BMAO as cocatalyst (sample 3) has very broad composition distribution, but its fraction with the highest crystallinity has much higher content of PP dyads than the crystalline fractions of the other two samples. This sample has the lowest crystallinity among the three samples. Phase morphology and tensile properties of the copolymer changed markedly when different cocatalyst was used. Tensile properties of sample 1 and 2 were similar to mixtures of elastomer and crystalline plastic materials, but tensile properties of sample 3 were more or less like a thermoplastic elastomer. Influences of TMA on the micro scale environment of active centers were considered the main reason for the effects of cocatalyst on copolymer structure and properties.

Chain structure, aggregation state structure, and tensile behavior of segmented ethylene-propylene copolymers produced by an oscillating unbridged metallocene catalyst.

Segmented ethylene-propylene copolymers (SEPs) with different propylene contents were prepared by an unbridged metallocene bis(2,4,6-trimethylindenyl)zirconium dichloride [(2,4,6-Me3Ind)2ZrCl2] catalyst. Due to oscillation of the unbridged ligands in the catalyst, the SEPs are composed of segments with low propylene contents, alternated by the segments with high propylene contents. Such a chain structure was verified by (13)C NMR and successive self-nucleation and annealing (SSA). As the propylene/ethylene feed ratio during copolymerization increases, the comonomer contents in both segments are increased, leading to noncrystallizability of the high propylene segments and smaller crystallinity of the low propylene segments. Consequently, SEPs may be used as thermoplastic elastomers (TPEs). The aggregation state structures at nano- and micro-scales were characterized with small angle X-ray scattering, transmission electron microscopy and polarized optical microscopy, and compared with those of ethylene-octene multiblocky copolymers (OBCs) with similar crystallinity. It is found that SEPs form thinner lamellar crystals with a lower melting temperature due to shorter length and higher comonomer content of the low propylene segments. Moreover, the short length of the high propylene segments in SEPs results in an evidently thinner amorphous layer among the lamellar crystals, thus lots of amorphous phases are excluded out of the interlamellae. Accordingly, ill-developed spherulites or even bundle crystals are formed in SEPs, as compared with the well-developed spherulites in OBCs. SEPs exhibit the tensile property of typical TPEs with diffused yielding and large strain at break.

Synthesis, Characterization and Reactivity of Group 4 Metallocene Bis(diphenylphosphino)acetylene Complexes—A Reactivity and Bonding Study

A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C≡C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'2M(L)(η(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged η(5)-cyclopentadienyl), the expected mononuclear complexes Cp*2Ti(η(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(η(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(η(2)-Me3SiC2SiMe3) with Ph2P-C≡C-PPh2, the dinuclear complex [Cp2Zr(η(2)-Ph2PC2PPh2)]2 (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C≡C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)2Ni(η(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(μ-PPh2)]2 (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C≡C-PR2 ligand. For compound 7b, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.

Phosphonothioate Hydrolysis by Molybdocene Dichlorides: Importance of Metal Interaction with the Sulfur of the Thiolate Leaving Group

The metallocene bis(cyclopentadienyl)molybdenum(IV) dichloride Cp2MoCl2 hydrolyzes O,S-diethyl phenylphosphonothioate (1) with only P–S scission to yield a phosphonate under mild aqueous conditions. In terms of degrading phosphonothioate neurotoxins, exclusive cleavage of the P–S linkage is preferred, for P–O scission yields another toxic phosphonothioate. Structure–activity relationship studies were undertaken with various phosphonothioates to test the hypothesis for the exclusive P–S scission by Cp2Mo(aq). Kinetics data show that the rates of phosphonothioate hydrolysis correspond to the size of the alkanethiolate leaving group on treatment with Cp2MoCl2. This suggests that the exclusive P–S scission of 1 is due to the interaction between the thiophilic Cp2Mo with the sulfur site of the P–SR linkage.

ChemInform Abstract: Strong Lewis Acids of Air‐Stable Metallocene Bis(perfluorooctanesulfonate)s as High‐Efficiency Catalysts for Carbonyl‐Group Transformation Reactions.

AbstractCationic mononuclear zirconocene and titanocene perfluorooctanesulfonate complexes are successfully applied in various transformation reactions of carbonyl compounds.

Phosphonothioate Hydrolysis Turnover by Cp2MoCl2 and Silver Nanoparticles

The metallocene bis(cyclopentadienyl)molybdenum(IV) dichloride (Cp2MoCl2; Cp = η5-C5H5) is the first organometallic compound to promote the hydrolysis of phosphonothioates with selective P–S scission in a stoichiometric fashion. This report shows that silver nanoparticles capped with borohydride ions promote turnover in this hydrolytic process, as indicated by 31P NMR studies on the reaction of O,S-diethyl phenylphosphonothioate (DEPP) with Cp2MoCl2 (pH 7). This is the first example of the joint use of nanoparticles and molybdenum metallocenes to promote phosphonothioate hydrolysis. Initial results indicate the turnover may be due to free Ag+(aq) ions present in the solution that arise either from the slow dissolution of the nanoparticles or from interactions with the Ag nanoparticle surface.

Strong Lewis Acids of Air‐Stable Metallocene Bis(perfluorooctanesulfonate)s as High‐Efficiency Catalysts for Carbonyl‐Group Transformation Reactions

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)(2)][OSO(2)C(8)F(17)](2)⋅nH(2)O⋅THF (M = Zr (2 a⋅3 H(2)O⋅THF), M = Ti (2 b⋅2 H(2)O⋅THF)) were synthesized by the reaction of [M(Cp)(2)]Cl(2) (M = Zr (1 a), M = Ti (1 b)) with nBuLi and C(8)F(17)SO(3)H (2 equiv) or with C(8)F(17)SO(3)Ag (2 equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry-differential scanning calorimetry (TG-DSC) analysis showed that 2 a and 2 b were thermally stable at 300 and 180 °C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2 a and 2 b) were ionic dissociation in CH(3)CN solution. X-ray analysis result confirmed 2 a⋅3 H(2)O⋅THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2 a. Fluorescence spectra showed that the Lewis acidity of 2 a fell between those of Sc(3+) (λ(em)=474 nm) and Fe(3+) (λ(em)=478 nm). ESR spectra showed the Lewis acidity of 2 a (0.91 eV) was at the same level as that of Sc(3+) (1.00 eV) and Y(3+) (0.85 eV), while the Lewis acidity of 2 b (1.06 eV) was larger than that of Sc(3+) (1.00 eV) and Y(3+) (0.85 eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel-Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis.

In situ stereocomplexing polymerization of methyl methacrylate by diastereospecific metallocene catalyst pairs

This contribution reports the first in situ stereocomplexing polymerization of methyl methacrylate (MMA) using a pair of diastereospecific coordination polymerization catalysts for rapid, high-yield, ambient-temperature production of crystalline stereocomplex poly(methyl methacrylate), sc-PMMA, with high Tm up to 217 °C. The diastereospecific catalyst pair is conveniently generated by in situ activation of a mixture of C2- and Cs-ligated metallocene bis(ester enolate)s with [Ph3C][B(C6F5)4], which is highly active, stereospecific, and controlled for coordination–addition polymerization of MMA to afford crystalline sc-PMMA in typically high to quantitative yields within only minutes of reaction. The isotactic/syndiotactic (it/st) composition of the sc-PMMA materials can be modulated by simply adjusting the relative ratio of the diastereospecific catalysts derived from pre-catalysts such as C2-ligated rac-(EBI)ZrMe[OC(OiPr)CMe2] and Cs-ligated [Ph2C(Cp)(2,7-tBu2-Flu)]Zr[OC(OiPr)CMe2]2; such catalysts have also been used separately to produce highly stereoregular it- and st-PMMAs and their corresponding sc-PMMA transparent film that exhibits nearly idealized characteristics: Mn = 44.2 kDa (vs. the calculated 40.1 kDa), PDI = 1.14, Tg = 96 °C, Tm = 213 °C, mm = 29.2%, rr = 62.3% (it/st ≈ 1/2), and visible transmittance = 92–95%. The in situ PMMA stereocomplexation can also occur in an it/st ratio deviating from the commonly recognized ratio of 1/2. Analysis of two such sc-PMMA materials with it/st ≈ 1/1 and ≈ 1/3 by wide-angle X-ray scattering (WAXS) has revealed essentially the same WAXS profile with nearly identical crystalline diffraction peaks attributed to sc-PMMA. The dynamic light scattering (DLS) results of the in situ stereocomplexing polymerization by a diastereospecific catalyst pair, obtained by monitoring the reaction in real time with DLS, indicate that stereocomplexation occurs as the diastereomeric PMMA chains are continuously growing. The presence of nanocages such as POSS and C60, which can be encapsulated by st-PMMA, in the stereocomplexing MMA polymerization system can completely disrupt or have no effect on the stereocomplexation, or enable both stereocomplexation and inclusion complexation processes to occur, depending on the type of nanocage employed.

Experimental and Theoretical Studies of Unusual Four‐Membered Metallacycles from Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes with the Sulfurdiimide Me3SiN=S=NSiMe3

AbstractThe use of the sulfurdiimide RN=S=NR′ (R = R′ = SiMe3, 3) in reactions with group 4 metallocene bis(trimethylsilyl)acetylene complexes of the type [Cp2M(L)(η2‐Me3SiC2SiMe3)] (1: M = Ti, no L; 2: M = Zr, L = pyridine) has led to the formation of four‐membered metallacycles 4M containing the group 4 metal, nitrogen and sulfur. DFT calculations performed on compound 4Ti indicate that this complex is best described as a σ‐complex with cyclic delocalisation of the ring electrons. Moreover, pseudo‐Jahn–Teller distortion plays a significant role in stabilising this complex.

Hydride-Shuttling Chain-Transfer Polymerization of Methacrylates Catalyzed by Metallocenium Enolate Metallacycle−Hydridoborate Ion Pairs

Activation of 12 group IV metallocene bis(ester enolate) complexes with B(C(6)F(5))(3) at room temperature (RT) affords quantitatively the corresponding isolable cationic eight-membered ester enolate metallacycles. This rapid two-step reaction consists of vinylogous hydride abstraction to form the anion [HB(C(6)F(5))(3)](-), and nucleophilic addition of the second enolate ligand to the methacrylate resulted from loss of a hydride in the first enolate ligand to form the chelating cation. This activation methodology for generating the active species (structural models for resting intermediates involved in methacrylate polymerization) is rather general, as demonstrated by a broad substrate scope examined in this study, including group IV metallocene bis(ester enolate) complexes that varied metals (Ti, Zr, Hf), bridging atoms (Ph(2)C<, Ph(2)Si<, Me(2)C<, -CH(2)CH(2)-), substituents ((t)Bu, Et(3)Si), substitution patterns (on 3-Cp and 2,7-Flu ring positions), and ligand symmetries (C(2), C(2v), C(1), and C(s)), all of which lead to the clean formation of their corresponding cationic metallacycles. Comparative methyl methacrylate (MMA) polymerization studies have identified metallacycle 4, {[Ph(2)C(Cp)(2,7-(t)Bu(2)-Flu)]Zr[OC(O(i)Pr)═CMeCH(2)C(Me(2))C(O(i)Pr)═O]}(+)[HB(C(6)F(5))(3)](-), as being the most active, efficient, and syndiospecific catalyst within the C(s)-ligated catalysts. Kinetic experiments at room temperature show that the MMA polymerization by 4 follows first-order kinetics in both [MMA] and [Zr], consistent with a monometallic, intramolecular coordination-addition mechanism that involves the eight-membered ester enolate chelate resting state. Thermodynamic experiments at varied temperatures yield activation parameters of ΔH(double dagger) = 6.23 kcal/mol, ΔS(double dagger) = -41.7 eu, and ΔG(double dagger) = 17.6 kcal/mol (273 K). As compared to ansa-Flu-Cp ligated chelating cations paired with more commonly used weakly coordinating anions such as [MeB(C(6)F(5))(3)](-) and [B(C(6)F(5))(4)](-), the same cations paired with the anion [HB(C(6)F(5))(3)](-) behave differently in MMA polymerization in terms of activity, stereospecificity, and sensitivity to solvent polarity. Most uniquely, [HB(C(6)F(5))(3)](-)-based catalysts effect substantial internal chain-transfer reactions, especially for polymerizations carried out in toluene and in the presence of excess B(C(6)F(5))(3), thus releasing polymer chains with a terminal double bond and achieving a catalytic polymerization. Computational results show the thermodynamics feasibility of the activation steps and the reversibility of the hydride abstraction step during activation, thus indicating that [HB(C(6)F(5))(3)](-) can uniquely act as a weak hydride donor. The picture emerging from the combined experimental and theoretical study has led to a new hydride-shuttling chain-transfer mechanism promoted by the hydridoborate anion, involving a hydride addition and abstraction sequence through the borane center.

Phosphonothioate hydrolysis through selective P-S bond scission by molybdenum metallocenes

We present an overview of the phosphonothioate hydrolytic chemistry promoted by molybdenum organometallics as well as new results on solvent effects. The metallocene bis(� 5 -cyclopentadienyl) molybdenum(IV) dichloride (Cp2MoCl2 Cp = � 5 -C5H5) and the methylated analog, (CH3Cp)2MoCl2 hydrolyzes the compoundO, S-diethyl phenylphosphonothioate (DEPP) whose core functional group mimics the neurotoxin VX. This is one of the few examples of phosphonothioate degradation yielding exclusively the desired P-S bond scission under mild aqueous conditions (pH 7, 25 � C). The solvent composition affects the monomer-dimer equilibrium of aquated molybdocenes which in turn dictates the rate of DEPP hydrolysis. Kinetic and equilibrium results are presented to show that the monomer is the active species. Moreover, photoelectron spectroscopy data indicate that while the methylated (CH3Cp)2MoCl2 has a higher monomer concentration compared to Cp2MoCl2, the former has a diminished electrophilic molybdenum center that is key in phosphonothioate hydrolysis.

Metallocene bis(perfluoroalkanesulfonate)s as air-stable cationic Lewis acids

Zirconocene and titanocene bis(perfluorooctanesulfonate)s were synthesized. In contrast to the corresponding triflates and perchlorates, these compounds are air- and water-stable. They were proved to be ionic on the basis of conductivity measurements and X-ray analysis, allowing these complexes to be stored for months. The strong Lewis acidity of these cationic metallocene species, which was proved by ESR study, enabled catalytic glycosylation.

Degradation of a VX Analogue: First Organometallic Reagent To Promote Phosphonothioate Hydrolysis Through Selective P−S Bond Scission

We report the first case of a metal complex that degrades a neurotoxin mimic under extremely mild conditions (pH 6.8, room temperature). The metallocene bis(η5-cyclopentadienyl)molybdenum(IV) dichloride (Cp2MoCl2; Cp = η5-C5H5) efficiently hydrolyzes the compound O,S-diethyl phenylphosphonothioate (DEPP), whose core functional group mimics the neurotoxin VX. Moreover, this is one of the few examples where phosphonothioate degradation yields exclusively the desired P−S bond scission under mild aqueous conditions (pH 7.2, 30 °C). Activation parameters for DEPP hydrolysis by Cp2MoCl2 in aqueous THF/acetone indicate (Ea = 86 kJ/mol, ΔH⧧= 83 kJ/mol, and ΔS⧧ = −10 J/(mol K)) an intramolecular hydrolytic process that goes through an ordered transition state. Alteration of the cyclopentadienyl ligand showed that ansa-Cp2MoCl2 with enhanced Mo(IV) electrophilicity significantly decreased DEPP hydrolysis, while (CpMe)2MoCl2 with increased Mo(IV) electron density had the opposite effect. These structure–activity relationships as well as the activation parameters indicate DEPP hydrolysis is achieved by nucleophilic attack of a Cp2Mo-bound hydroxide on the phosphonothioate.

Thermal decomposition studies of the polyhedral oligomeric silsesquioxane, POSS h, and when it is impregnated with the metallocene bis(η 5-cyclopentadienyl)zirconium (IV) dichloride or immobilized on silica

Thermal decomposition studies of the free polyhedral oligomeric silsesquioxane, POSS h, and when this compound has been impregnated with Cp 2ZrCl 2 (Cp = η 5-C 5H 5) or immobilized on SiO 2 were conducted using infrared emission spectroscopy (IES) over a 100–1000 °C temperature range and by thermogravimetric analysis (TGA). The organic groups in POSS h apparently decompose thermally into Si–CH 3, Si–H and other fragments. Upon impregnation with Cp 2ZrCl 2, however, a different thermal decomposition pathway was followed and new infrared emission bands appeared in the 1000–900 cm −1 region suggesting the formation of Si–O–Zr moieties. When immobilized on SiO 2 and subjected to thermal decomposition, the POSS h compound lost its organic groups and the inorganic structure remaining was incorporated into the SiO 2 framework.