Electronic effect of η5-cyclopentadienyl and η3-allyl ligands on the nature of the metal—olefin bond: Reversal of the relative olefin affinity of palladium(II) and platinum(II) ions

The barrier to olefin rotation in [Pt(η³-CH₂CMeCH₂)(olefin)(PPh₃)]PF₆ (3) (olefin = CH₂CH₂, E-MeCHCHMe) has been found to be extremely low compared to those in the other known, 4-coordinate olefin complexes of Pt^II. This can be ascribed to the smaller steric congestion around the olefin in 3. The corresponding barrier in [Pt(η⁵-C₅H₅)(CH₂CH₂)(PPh₃]ClO₄ (2), possessing likewise small steric congestion, was substantially higher than that in 3 (olefin = CH₂CH₂). The ¹³C and ³¹P NMR measurements have revealed much larger J(Pt-C(olefin)) in 2 than that in 3 (olefin = CH₂CH₂), while J(Pt-P) are comparable in these two. Stability constant data suggested that Pd^II ion in the Pd(η⁵-C₅H₅)(PPh₃)⁺ moiety is a better π-donor to olefins than Pt^II ion in the Pt(η³-CH₂CMeCH₂)(PPh₃)⁺ moiety, a reversal of the normal trend in the relative olefin affinity of these metal ions. The above spectral and stability features have been related to the electronic effect of the Cp ligand in enhancing the π back-bond interaction in one particular orientation of the CC bond.     

Catalytic olefin hydrogenation with the application of a new water soluble rhodium catalyst

The catalyst precursor preparedin situ from rhodium dimer [Rh(cod)Cl]₂ and a new water-soluble phosphine Ph₂PCH₂CH₂CONHC(CH₃)₂CH₂SO₃H (in Li⁺ salt form) has been found to act as an effective olefin hydrogenation catalyst. Catalytic hydrogenation reactions have been tested in either two phase: aqueous catalyst/insoluble olefin or methanolic catalyst/olefin systems. The observed reaction rates were higher for terminal than for internal olefins. 1-Hexene in methanolic solution has been hydrogenated with a turnover frequency of about 8000 h^–1. This system has also been applied in the form of a supported aqueous phase catalyst.     

Thermal decomposition of η5-cyclopentadienyl-η2-propenealkylnickel complexes

Thermolysis of compounds of the type CpNiR (η²-propene) (R = CH₃ (1), CD₃ (2), CH₂CH₃ (3), CH₂CH₂CH₃ (4) and CH₂SiMe₃ (5)) was studied. The methyl complex 1 gives mainly methane, ethane and (CpNi)₃CH. Toluene-d₈ has no effect on the composition of the gaseous products and does not yield gases containing deuterium. In the CD₃ complex 2 a HD exchange reaction between the complexed propene and the CD) group takes place. Decomposition of the trimethylsilylmethyl complex 5 gave tetramethylsilane. The complexes 3 and 4 containing a β-hydrogen atom, decompose via a β-elimination reaction giving the corresponding olefin. The unstable {CpNiH} formed in the reaction reacts with {CpNiR} giving the corresponding alkane and a mixture of non-isolated cyclopentadienylnickel clusters. The complexes studied undergo insertion of the coordinated olefin into the NiC σ-bond, which results in the formation of higher hydrocarbons.     

New Synthetic Methodology and Biologically Active Substances

The η⁵-cyclopentadienyl-η²-propenealkylnickel complexes 4–9 (alkyl  CH₃, CD₃, CH₂SiMe₃, CH₂ CH₃, CH₂ CH₂ CH₃ and CH(CH₃)₂) have been prepared by treating nickelocene (1) with the appropriate organomagnesium halides 2a–2f and propene at ?20 to ?10°C. Temperature dependent ¹H-NMR spectra result from rotation of the propene molecule around the nickel—olefin axis; in the case of 4 and 8, two rotamers a and b can be distinguished below ca. ?60°C. The decomposition pathways for 4 and 8 are discussed.     

Synthesis of diversely functionalized pyrrolizidines and indolizidines using olefin ring-closing metathesis

Various nitrogen-fused tricyclic compounds, having benzoindolizidine and benzopyrrolizidines ring systems were synthesized via ene-ene metathesis using the first and second-generation Grubbs catalyst. The ene-ene metathesis proceeded smoothly in refluxing CH₂Cl₂ with 3.0 mol % of G₁, giving good yields (78-86%) of the benzoindolizidine products 12a,b. The benzopyrrolizidine 6 was prepared after optimization in 64% yield by using 5.0+5.0 mol % of G₂. The resulting olefin moiety of the indolizidine framework is a suitable precursor for polyhydroxy structures via the Sharpless process. The structures of the polyhydroxylated adducts were determined by ¹H NMR spectra and single-crystal X-ray analysis.     

Reactivity differences between molecular and surface silanols in the preparation of homogeneous and heterogeneous olefin metathesis catalysts

The reaction of Mo(N)(CH₂tBu)₃ (1) and SiO_2-(700) generates (SiO)Mo(NH)(CHtBu)(CH₂tBu) (2) when performed in C₆H₆ (material [1/SiO_2-(700)]_C6H6). The grafting occurs presumably by protonation of the nitrido ligand to form an intermediate (SiO)Mo(NH)(CH₂tBu)₃ (3), a pentacoordinated complex, which decomposes into 2 and 2,2-dimethylpropane. While [1/SiO_2-(700)]_C6H6 is highly active in olefin metathesis, [1/SiO_2-(700)]_CH2Cl2 and [1/SiO_2-(700)]_THF are poorly active or inactive catalysts respectively. In contrast, when Mo(N)(CH₂tBu)₃ reacts with a molecular silanol derivative, a soluble model of the surface of SiO_2-(700), it yields a very stable complex, (c-C₅H₉)₇Si₇O₁₂SiO-Mo(NH)(CH₂tBu)₃ (3m), which does not spontaneously generate 2,2-dimethylpropane and an alkylidene complex in contrast to the surface complex. Moreover, 3m does not catalyse olefin metathesis at room temperature as it does not already contain the initiating carbene ligand, and it is necessary to heat up the reaction mixture to 110 °C to obtain low catalytic activity. Nevertheless, the complex 3m generates well-defined metallocarbenes when heated in the presence of PMe₃: (c-C₅H₉)₇Si₇O₁₂SiO-Mo(N)(CHtBu)(P(CH₃)₃)₂ (4m) as a 10:1 mixture of its syn and anti rotamers with the loss of 2 equiv. of 2,2-dimethylpropane.     

Chlorosulfonic acid as a convenient electrophilic olefin cyclization agent

Among several sulfonic acids studied (MeSO₃H, p-TsOH, H₂SO₄, ClSO₃H, FSO₃H), the scarcely used chlorosulfonic acid showed to be an efficient agent for electrophilic olefin cyclizations with internal nucleophilic termination, in a similar manner that is well-established with fluorosulfonic acid. Its availability, lower price and relatively lesser handling problems makes ClSO₃H an advantageous cyclizing agent particularly for high-scale applications. The stereochemical outcome of these cyclizations has been rationalized.     

A comment on “crystallinity” in poly (olefin sulphones)

It is suggested that seemingly crystalline structures which have been observed in films of poly(olefin sulphones) cast from solution in liquid SO₂ are voids that replicate (in three dimensions) dendritic crystals which originally formed as a consequence of the condensation of moisture on the cold rapidly-evaporating solution and which subsequently evanesced by sublimation or melting and evaporation. This has been shown directly in the case of poly(butene-l-sulphone) and also simulated in an indisputably non-crystallizable polymer (atactic poly(methyl methacrylate)). At least two crystalline species are produced by condensing moisture under these conditions, one with hexagonal symmetry (presumably ice I_h) and one with cubic symmetry (apparently a known clathrate hydrate of SO₂). It is further suggested that similar “crystalline” structures observed by Brady and O'Donnell [1] in films of poly(3-methyl-1-butene sulphone) cast from SO₂ rich mixtures, and assumed by them to be a crystalline phase of the polymer, have a similar origin. This assumption formed the basis of their explanation of a thermodynamic anomaly in the formation of insoluble poly(olefin sulphones), an explanation which is now open to serious question.     

Radiation Degradation of Poly(olefin Sulfone)s: A Volatile Product Study

The predominant degradation reaction in the γ-irradiation of nine poly(olefin sulfone)s was found to be C-S bond scission with elimination of SO₂ and olefin. The extent of depolymerization, measured by the yields of the two comonomers, increased over five irradiation temperatures from 0 to 150° C and could be correlated with the ceiling temperature. Thus G (total volatile products) increased from 10 to 10,000 over this temperature range. Minor radiolysis products included the alkanes corresponding to (1) loss of the side chain group and (2) scavenging of the side chain radical by monomer olefin. There was a deficiency of olefin relative to SO₂, except at high temperatures, and isomerization of the product olefin in some cases. These observations are attributed to reactions of radiation-induced polymeric cations.     

The role of non-coordinating anions in homogeneous olefin polymerization

We present an overview of homogeneous olefin polymerization catalysts in which chain initiation and propagation involves a metallocenium ion (e.g. Cp₂ZrMe⁺) that can be produced by equilibrium or irreversible CH₃⁻ transfer. The Kaminsky catalyst is an example of the former. Complexes of (C₆F₅)₃B with water, alcohols, mercaptans, silanols and oximes are strong acids which can protonate dialkylmetallocenes to produce weakly-coordinated metallocenium salts that are hydrocarbon soluble and which produce high molecular weight poly-1-olefins. Polymer molecular weight is correlated with the steric and electronic effects of the ligands attached to the metal.     

The resistance to hydrolysis of N,N-dimethyl-N-phenylammoniomethanesulfonate and the improbability of a recently-proposed mechanism of hydrolysis of anilinomethanesulfonates

The hydrolysis of PhN⁺Me₂CH₂SO₃^? (2) is so slow that a proposed mechanism of hydrolysis of PhNHCH₂SO₃^? Na⁺ involving S_N2 attack of H₂O on PhN₂⁺CH₂SO₃^? may be discounted.     

Synthesis of copper(I) bis(3,5-dimethylpyrazolyl)methane olefin complexes and their reactivity towards carbon monoxide

The chemistry of bis(3,5-dimethylpyrazolyl)methane complexes of copper(I) has been investigated and a dinuclear copper(I) derivative of formula {Cu₂[μ-CH₂(3,5-Me₂Pz)₂]₂}(TfO)₂ [TfO = trifluoromethanesulphonate anion, ], characterized by an uncommon bridging coordination of the bis(pyrazolyl)methane ligands, has been isolated and characterized by X-ray diffraction methods. Moreover, new olefin derivatives of general formula [Cu[CH₂(3,5-Me₂Pz)₂](olefin)]TfO have been prepared (olefin: coe = cyclooctene, van = 4-vinylanisole, nbe = norbornene), their carbonylation reactions, {Cu[CH₂(3,5-Me₂Pz)₂](olefin)}TfO + CO ? {Cu[CH₂(3,5-Me₂Pz)₂](CO)}TfO + olefin, have been studied gas volumetrically and the thermodynamical parameters of the equilibria for the displacement of the coordinated olefin by carbon monoxide have been determined.     

Mechanism of olefin polymerization by a soluble zirconium catalyst

A mechanistic study has been carried out on the homogeneous olefin polymerization/oligomerization catalyst formed from Cp₂ZrMe₂ and methylaluminoxane, (MeAlO)_x, in toluene. Formal transfer of CH₃ from Zr to Al yields low concentrations of Cp₂ZrMe⁺ solvated by [(Me₂AlO)_y(MeAlO)_x−y]_y. The cationic Zr species initiates ethylene oligomerization by olefin coordination followed by insertion into the Zr–CH₃ bond. Chain transfer occurs by one of two competing pathways. The predominant one involves exchange of Cp₂Zr–P⁺ (P=growing ethylene oligomer) with Al–CH₃ to produce another Cp₂ZrMe⁺ initiator plus an Al-bound oligomer. Terminal Al–C bonds in the latter are ultimately cleaved on hydrolytic workup to produce materials with saturated end groups. Concomitant chain transfer occurs by sigma bond metathesis of Cp₂Zr–P⁺ with ethylene. Metathesis results in cleavage of the Zr–C bond of the growing oligomer to produce materials also having saturated end groups; and a new initiating species, Cp₂Zr-CHCH₂⁺. The two chain transfer pathways afford structurally different oligomers distinguishable by carbon number and end group structure. Oligomers derived from the Cp₂ZrMe⁺ channel are C_n (n=odd) alkanes; those derived from Cp₂Zr–CHCH₂⁺ are terminally mono-unsaturated C_n (n=even) alkenes. Chain transfer by beta hydride elimination is detectable but relatively insignificant under the conditions employed. Propylene and 1-hexene react similarly but beta hydride elimination is the predominant chain transfer step. The initial Zr-alkyl species produces a Cp₂ZrH⁺ complex that is the principle chain initiator. Chain transfer is fast relative to propagation and the products are low molecular weight oligomers.     

Supported silica-molybdena catalysts for olefin metathesis activated by photoreduction

Cyclopropane (CP) or methylcyclopropane (MCP) chemisorption on silica-molybdena catalysts photoreduced in CO was found to result in a sharp increase (by one order of magnitude) of specific activities for olefin metathesis (propene, 1-hexene, ethyl oleate). IR and UV-VIS spectroscopic studies revealed that promoting effect of CP and MCP treatment was associated with the formation of the thermally stable carbene complexes Mo = CH₂ and Mo=CH-CH₃, arising from CP and MCP interaction with low coordinated MO⁴⁺ ions in photoreduced Mo/SiO₂ IR data showed fast reversible transformation of Mo=CH₂ to Mo=CH-CH₃ thus providing the first direct spectroscopic confirmation of a chain carbene mechanism of propene metathesis. A general scheme for CP and MCP interaction with photoreduced Mo/SiO₂ was proposed.     

A new effective method for the resolution of prochiral olefins : Stereoselective coordination in [PtCl3 (olefin)]− induced by crystallization

Crystallization of [PtCl₃(olefin)]^? [($\text{S}$-C₆H₅CH(CH₃)N(CH₃)₃]⁺ compounds (olefin = prochiral olefins) affords a single diastereoisomer through a second-order asymmetric transformation.     

New copper(I) and silver(I) triazolato-complexes: Synthesis, reactivity and catalytic activity in olefin cyclopropanation

A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H₃L¹) and o-anisaldehyde (H₃L²) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N,N′-exobidentate conformation. The copper derivative [Cu(H₂L¹)(CH₃CN)]₂ (1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular, it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H₂L¹)(CO)]₂ (4), by substitution of the nitrile with carbon monoxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH₂Cl₂ afforded a mono-carbene product, as established by ¹³C NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence of ethyl diazoacetate. In the case of internal alkenes a trans:cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I) complex, namely [Ag(H₂L¹)(PPh₃)]₂ (3), obtained by reacting the polymeric [Ag(H₂L¹)]_n (2), with triphenylphosphine, is also reported.     

Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand

The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy₃)((^κN,O)-picolinate)₂RuCHPh (5) and (H₂IMes)((^κN,O)-picolinate)₂RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.     

A novel alkenyl-substituted ansa-zirconocene complex with dual application as olefin polymerization catalyst and anticancer drug

The alkenyl substituted fulvene compound, (C₅H₄)CMe(CH₂CH₂CHCMe₂) (1), reacts with one equivalent of LiMe to give the lithium derivative Li{C₅H₄(CMe₂CH₂CH₂CHCMe₂)} (2). The reaction of 2 with Me₂Si(C₅Me₄H)Cl gave the ansa-ligand precursor Me₂Si(C₅Me₄H)(C₅H₄(CMe₂CH₂CH₂CHCMe₂)) (3), which after the subsequent reaction with 2 equivalents of LiBuⁿ yielded the dilithium salt Li₂{Me₂Si(C₅Me₄)(C₅H₃(CMe₂CH₂CH₂CHCMe₂))} (4). The alkenyl-substituted zirconocene complex [Zr{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃(CMe₂CH₂CH₂CHCMe₂))}Cl₂] (5) was synthesized by the equimolar reaction of 4 and ZrCl₄. 5 was characterized by spectroscopic methods and by single crystal X-ray diffraction studies. The zirconocene compound 5 has been tested as a catalyst in the polymerization of ethylene at different temperatures and Al:Zr ratios, and also in the co-polymerization of ethylene and 1-octene, observing modest co-monomer incorporations. In addition, the cytotoxic activity of 5 was tested against tumour cell lines 8505C anaplastic thyroid cancer, A253 head and neck tumour, A549 lung carcinoma, A2780 ovarian cancer and DLD-1 colon carcinoma. Complex 5 showed the best cytotoxic activity on A2780 ovarian cancer (IC₅₀ value of 36.8 ± 5.9 μM). This represents the highest reported cytotoxic activity of a zirconocene complex on A2780 ovarian cancer. In addition, the cytotoxic activities of 5, have been compared with those obtained using cisplatin.     

Removal of an olefin metathesis catalyst using 4-nitrophenyl acrylate based polymer supports

A polymer-supported 1,4-butanediolvinyl ether derivative was used for removal of an olefin metathesis catalyst (PCy₃)₂(Cl)₂Ru(3-phenyl-indenylid-1-ene) (M1, PCy₃ = tricyclohexylphosphine) from the reaction solution. Poly(styrene-co-4-nitrophenyl acrylate), cross-linked with either ethylene glycol dimethacrylate or divinylbenzene was prepared via suspension polymerisation and modified chemically to yield a supported acid chloride and subsequently a 1,4-butanediolvinyl ether derivative. A batch reaction of supported vinyl ether with M1 resulted in binding of the catalyst onto the polymer. A high accessibility of up to 43% of reactive sites in the polymer matrix could be achieved.     

Lithiated γ-O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SOxPh)CH2CH2OR] (x = 0, 2). [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH₂CH₂CH₂OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh₃, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH₂CH₂OR}(tmeda)] (α-2a–d) and [Li{o-C₆H₄SCH₂CH₂CH₂OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu₃SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu₃SnCH(SPh)CH₂CH₂OR (α-3a–d) and n-Bu₃Sn(o-C₆H₄SCH₂CH₂CH₂OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH₂CH₂OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH₂CH₂Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO₂CH₂CH₂CH₂OR (R = Me, 5a; i-Pr, 5b; CPh₃, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO₂Ph)CH₂CH₂OR] (6a–c) that were found to react with n-Bu₃SnCl yielding the requisite α-stannylated compounds n-Bu₃SnCH(SO₂Ph)CH₂CH₂OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn).