Noels’ vs. Grubbs’ Catalysts: Evidence for One Unique Active Species for Two Different Systems!

The catalytically active propagating species involved in the self‐metathesis of ethyl oleate obtained from the multi‐component Noels’ catalytic system {[RuCl₂(p‐cymene)(PCy₃)]+Me₃SiCHN₂} are probably the same as those of the single‐component well‐defined Grubbs’ 1st generation catalyst, [Cl₂RuCHPh(PCy₃)₂] ( 1‐Ph ). In the case of the Noels’ catalyst, it involves the de‐coordination of p‐cymene, and the redistribution of PCy₃ ligands to generate only 5–10 % of [Cl₂RuCHR(PCy₃)₂], where R=CH (CH₂)₆ CH₃ ( 1‐Oct ) and R=CH (CH₂)₆ COOEt ( 1‐E ), while 1‐Ph can generate 100 % of these species.     

Dimerization of Terminal Arylalkynes in Aqueous Medium by Ruthenium and Acid Promoted (RAP) Catalysis: Acetate‐ Assisted (sp)C?(sp2)C Bond Formation

The hexamethylbenzene ruthenium(II) dimer [{RuCl(μ‐Cl)(η⁶‐C₆Me₆)}]₂ (5 mol%), tested among a series of ruthenium(II) and ruthenium(IV) complexes, represents an efficient precatalyst source for the dimerization of terminal arylalkynes ArCCH [Ar=C₆H₅, 3,4,5‐(OMe)₃C₆H₂, 4‐MeOC₆H₄, 2‐MeOC₆H₄, 4‐MeC₆H₄, 2,4,5‐Me₃C₆H₂, 4‐BrC₆H₄, 4‐ClC₆H₄, 4‐FC₆H₄, 4‐HC(O)C₆H₄, 4‐CH₂CHC₆H₄, 3‐NCC₆H₄, 4‐O₂NC₆H₄, 4‐EtO₂C‐(CH₂)₃OC₆H₄, 4‐HO(CH₂CH₂O)₃C₆H₄, 3‐HO(CH₂CH₂O)₃‐C₆H₄] in acetic acid/water mixture (1:1, v/v). The reactions proceed for 24 h at room temperature under heterogeneous conditions and afford the dimeric enyne derivatives (E)‐Ar CHCH CC Ar in high yields and stereoselectivity. The preformed acetato complex [RuCl(η⁶‐C₆Me₆)(κ²‐OAc)] catalyzes the dimerization of phenylacetylene under analogous conditions, with rapid substrate conversion. The presence of cosolvents of acetic acid different from water reduces dramatically the efficiency and selectivity of the reaction. The aqueous medium facilitates the activation stage of the precatalyst by assisting the splitting of the ruthenium dimer. The addition or generation in situ of acetate salts results in shorter reactions times (0.5–3 h) and excellent yields, due to the rapid formation of active acetato complexes. Circumstantial evidence indicates that the π‐bound alkyne molecule is activated by intramolecular proton abstraction. This is currently the most efficient, E‐selective and wide‐scope catalytic system for the alkyne dimerization reaction in protic aqueous media.     

Investigation of Dynamic Intra‐ and Intermolecular Processes within a Tether‐Length Dependent Series of Group 4 Bimetallic Initiators for Stereomodulated Degenerative Transfer Living Ziegler–Natta Propene Polymerization

The series of bimetallic complexes, [(η⁵‐C₅Me₅)Zr(Me)₂]₂ [N(t‐Bu)C(Me)N (CH₂)_n NC(Me)N(t‐Bu)] 3 (n=8), 4 (n=6), and 5 (n=4) were prepared in high yield through a simple, one‐pot synthesis involving 2 equiv. of in situ generated (η⁵‐C₅Me₅)Zr(Me)₃ and the corresponding bis‐carbodiimide, (t‐Bu)NCN (CH₂)_n NCN(t‐Bu). Compounds 3 – 5 were found to be highly isoselective for the living Ziegler–Natta polymerization of propene upon 100% activation using 2 equiv. of the borate co‐initiator, [PhNHMe₂] [B(C₆F₅)₄] ( 2 ), with the degree of stereoselectivity decreasing slightly as the two metal centers are brought closer together [cf., 3 (σ=0.92)> 4 (σ=0.91)> 5 (σ=0.89)]. Under conditions of sub‐stoichiometric activation by 2 , all three bimetallic initiators, 3 – 5 , were found to engage in degenerative transfer living Ziegler–Natta polymerization involving rapid and reversible methyl group transfer between active, (cationic) and dormant, (neutral) methyl, polymeryl zirconium centers. Under these conditions, the frequency of mr triad stereoerror incorporation into the polypropene (PP) microstructure decreases as the two metal centers are brought closer together as a result of increasing barriers for metal‐centered epimerization within the neutral metal site due to correspondingly greater non‐bonded steric interactions vis‐à‐vis mononuclear 1 .     

Block copolymerizations of higher 1‐olefins with traditional polar monomers using metallocene‐type single component lanthanide initiators

Block copolymerizations of 1‐pentene or 1‐hexene with methyl methacrylate or ε‐caprolactone were explored using [Me₂Si(2‐SiMe₃‐4‐t‐BuMe₂SiC₅H₂)₂YH]₂ ( 1 ) or [Me₂Si(2‐SiMe₃‐4‐t‐BuC₅H₂)₂SmH]₂ ( 2 ) as an initiator in toluene or in neat mixtures by the successive additions of monomers in this order. Random copolymerizations of 1‐pentene with 1‐hexene, and random copolymerization of ethylene with 1‐hexene were also performed using 1 as an initiator. Copyright © 2004 Society of Chemical Industry     

NMR-study of the stereochemistry and dynamic behaviour of thioacrylamides

Several model thioacrylamides, Me₂N CH = C(R) C(S) NMe₂ (R = H, Ph — 2a, b ) and (p)MeO C₆H₄ NH CHC(R) C(S) NMe₂ (R = H, Ph — 3a, b ) have been synthesized. The ¹H-n.m.r. spectra have been taken for discussing the E/Z-isomerism of the thioacrylamides and the assignment further strengthened by an added LIS-study. The 2-unsubstituted compounds have been found to exist exclusively in preferred configurations/conformations: 2a — E(s-cis); 3a — Z(s-cis); the 2-phenylsubstituted analogs are of divergent behaviour: in 2b the C(S) NMe₂ moiety is found to be twisted out of the common plane, and 3b prefers the flat s-trans conformations (E(s-trans) ⇌ Z(s-trans)). The compounds show restricted rotations about C¹, N- and C³, N-partial double bonds. The corresponding rotational barriers, determined as ΔG-values by dynamic n.m.r. spectroscopy, are discussed with respect to (i) the resonance branch at C¹, (ii) the influence of substituents, and (iii) the effect of steric hindrance in the thioacrylamide moiety generally.     

Base‐Mediated Tandem Reaction Consisting of an Acyl Shift Strategy Leading to 4,5‐Disubstiuted Furan‐2(5H)‐ones

The first example of the synthesis of 4,5‐disubstiuted furan‐2(5H)‐ones by base‐mediated tandem acyl shift/cyclization/decarbonylation reactions of aroylmethyl 2‐alkynoates has been developed. This new and inexpensive tandem route allows both a C O bond and a Csp³ Csp² bond forming in one step involving an unprecedented acyl rearrangement process.     

On the Use of Non‐Symmetrical Mixed PCN and SCN Pincer Palladacycles as Catalyst Precursors for the Heck Reaction

The mixed pincer palladacycles (Me₂NCH₂(Cl)CCCH₂CH₂Y‐κN,κC,κY)PdCl ( 1 , Y=PPh₂; 2 , OPPh₂) and (t‐BuSCH₂CH₂CC(Cl)(o‐NC₅H₄)‐κS,κC,κN)PdCl 3 have been obtained in high yields by chloropalladation of heterosusbstituted alkynes Me₂NCH₂CCCH₂CH₂PPh₂, Me₂NCH₂CCCH₂CH₂OPPh₂ and t‐BuSCH₂CH₂CC(o‐NC₅H₄), respectively. The molecular structures of 1 and 3 have been ascertained by means of X‐ray diffraction analysis. The catalytic properties of these mixed donor group pincer‐type palladacycles have been evaluated in the arylation of olefins (Heck reaction). The pincer palladacycle 1 is highly active for the coupling of aryl iodides and aryl bromides with n‐butyl acrylate. In contrast it is only moderately active for the coupling of aryl chlorides substituted with electron‐withdrawing groups and inactive for the coupling of electron neutral and electron deactivated aryl chlorides.     

1,3-Diaza-2-azoniaallene Salts as Novel N3-Building Blocks: Preparation and cycloadditions to alkenes,alkynes, carbodiimides,and cyanamides

1,3-Diaza-2-azoniaallene salts R¹-NN⁺N R² 6 represent a new functional group. 1,3-Disubstituted triazenes 8 are oxidized with tert-butyl hypochlorite to stable open-chain N-chlorotriazenes R¹ NN NCl R² 9 , which at low temperatures with Lewis acids afford the reactive intermediates 6 . The salt 6a is stable below −50 °C and was characterized by spectroscopic and analytical data. Heterocumulenes 6 behave as positively charged 1,3-dipoles undergoing cycloadditions to many different multiple bonds to furnish 1,2,3-triazolium and tetrazolium salts, e.g. to both electron-rich and electron-deficient alkenes, alkynes, to one or both double bonds of 1,3-butadienes, to carbodiimides, and cyanamides (1,3-dipolar cycloaddition with inverse electron demand). With an allene, a butatriene and a pentatetraene the 4,5-dihydro-1H-1,2,3-triazolium salts 17–19 were obtained. The constitutions of four of the products were secured by X-ray structural analyses. 4,5-Dihydro-1H-1,2,3-triazolium salts 11 and 1H-1,2,3-triazolium salts 20 are aza analogues of Arduengo's and Wanzlick's nucleophilic carbenes.     

Syndio‐ and Isoselective Coordinative Chain Transfer Polymerization of Styrene Promoted by ansa‐Lanthanidocene/ Dialkylmagnesium Systems

Combinations of the discrete neutral allyl ansa‐lanthanidocenes {Me₂C(Cp)(Flu)}Nd[1,3‐ (SiMe₃)₂C₃H₃] and rac‐{Me₂C(Ind)₂}Y[1,3‐ (SiMe₃)₂C₃H₃] with di(n‐butyl)magnesium constitute efficient binary catalytic systems for the stereocontrolled coordinative chain transfer polymerization of styrene, yielding near‐perfect syndio‐ and isospecific polystyrenes, respectively, with high activities and productivities. By adjusting the amount of di(n‐butyl)magnesium, up to 200 polymer chains can be generated per lanthabide center, and good control of the molecular weight features enables the tailoring of low to medium molecular weight polymers.     

Adamantane Selective Hydroxylation by 2,6‐Dichloropyridine N‐Oxide and Organoruthenium(II) Polyoxometalates as Catalyst Precursors

Organoruthenium polyoxometalates with general formula [{Ru(C₆Me₆)}₃M₅O₁₈], M  Mo, W, serve as catalyst precursors, together with 2,6‐dichloropyridine N‐oxide, to effect the hydroxylation of adamantane with conversion up to 94%, and C³‐H/C²‐H selectivity >100. Under analogous conditions, hydroxylation of cis‐decalin occurred with complete stereoretention. Control experiments and kinetic evidence suggest the in‐situ formation of a high valent Ru‐oxo species as the competent oxidant.     

Vinyl‐addition copolymerization of norbornene and polar norbornene derivatives using novel bis(β‐ketoamino)Ni(II)/B(C6F5)3/AlEt3 catalytic systems

Copolymerization of norbornene (NBE) and polar norbornene derivatives undergoes vinyl polymerization by using novel catalyst systems formed in situ by combining bis(β‐ketoamino)Ni(II) complexes {Ni[R₁C(O)CHC(NR₃)R₂]₂ (R_l = R₂ = CH₃, R₃ = naphthyl, 1 ; R₁ = R₂ = CH₃, R₃ = C₆H₅, 2 ; R₁ = C₆H₅, R₂ = CH₃, R₃ = naphthyl, 3 ; R_l = R₂ = CH₃, R₃ = 2, 6‐(CH₃)₂C₆H₃, 4 ; R₁ = R₂ = CH₃, R₃ = 2, 6‐′Pr₂C₆H₃ 5 ; R₁ = C₆H₅, R₂ = CH₃, R₃ = 2, 6‐′Pr₂C₆H₃, 6 )} and B(C₆F₅)₃/AlEt₃ in toluene. The 1 /B(C₆F₅)₃/AlEt₃ catalytic system is effective for copolymerization of NBE with NBE OCOCH₃ and NBE CH₂OH, respectively, and copolymerization activity is followed in the order of NBE CH₂OH > NBE OCOCH₃ > NBE CN. The molecular weights of the obtained poly(NBE/NBE CH₂OH) reached 5.97 × 10⁴ to 2.07 × 10⁵ g/mol and the NBE CH₂OH incorporation ratios reached 7.0–55.4 mol % by adjusting the comonomer feedstock composition. The copolymerization of NBE and NBE CH₂OH also depend on catalyst structures and activity of catalyst followed in the order of 2 > 1 > 3 > 5 > 4 > 6 . The molecular weights and NBE CH₂OH incorporation ratios of poly(NBE/NBE CH₂OH) were adjustable to be 1.91–5.37 × 10⁵ g/mol and 9.5–41.1 mol %  OH units by using catalysts 1 – 6 . The achieved copolymers were confirmed to be vinyl‐addition type, noncrystalline and have good thermal stability (T_d = 380–410°C). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Metallkomplexe mit biologisch wichtigen Liganden. CXXIII. Darstellung von Isophthaloyl‐ und Terephthaloyl‐di‐[(β,γ,δ)‐amino‐α‐aminocarboxylat]‐verbrückten zweikernigen Ruthenium‐, Rhodium‐ und Iridium‐Halbsandwich‐Komplexen

The reaction of the Cu(II) bis N,O‐chelate‐complexes of L‐2,4‐diaminobutyric acid, L‐ornithine and L‐lysine {Cu[H₂N–CH(COO)(CH₂)_nNH₃]₂}²⁺(Cl^–)₂ (n = 2–4) with terephthaloyl dichloride or isophthaloyl dichloride gives the polymeric complexes {‐OC–C₆H₄–CO–NH–(CH₂)_n–CH(nh₂)(COO)Cu(OOC)(NH₂)CH–CH₂)_n–NH‐}_x 1 – 5 . From these the metal can be removed by precipitation of Cu(II) with H₂S. The liberated ω,ω′‐N,N′‐diterephthaloyl (or iso‐phthaloyl)‐diaminoacids 6 – 10 react with [Ru(cymene)Cl₂]₂, [Ru(C₆Me₆)Cl₂]₂, [Cp*RhCl₂]₂ or [Cp*IrCl₂]₂ to the ligand bridged bis‐amino acidate complexes [L_n(Cl)M–(OOC)(NH₂)CH–(CH₂)_nNH–CO]₂–C₆H₄ 11 – 14 .     

Synthesis and Characterization of Energetic 1,2‐Bis(Oxyamino)Ethane Salts

The synthesis, characterization, theoretical calculations, and safety studies of energetic salts based on 1,2‐bis(oxyamino)ethane, (H₂N O CH₂ CH₂ O NH₂), were carried out. The salts were characterized by vibrational (infrared, Raman), multinuclear NMR studies (¹H, ¹³C), differential scanning calorimetry (DSC), elemental analysis, and initial safety testing (impact and friction sensitivity). Single crystal X‐ray diffraction studies were carried out on the mono‐perchlorate and the double nitrate salts, revealing the expected structures.     

Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ onto O,N‐carboxymethyl chitosan

The chelation of zinc ions onto O,N‐carboxymethyl chitosan (ONCMCh) was characterized using a Fourier transform infrared (FTIR) spectrophotometer and a scanning electron microscope (SEM). From the FTIR spectra, little change in the absorption intensities and frequencies at 3300–3600 cm⁻¹ of Zn²⁺ ONCMCh chelated specimens suggested that  OH and  NH₂ groups were not participating in the chelation reaction. The absence of absorption bands at 1755–1700 cm⁻¹ suggested that the carboxyl group CO was not ionized, and the ionized CO bands were observed at 1400–1600 cm⁻¹ for chelated specimens. Thus, the chelation sites took place at the carboxyl group rather than at the  OH and NH₂ groups. It also confirmed that water‐insoluble chelates, which were formed through the Zn O and Zn N bonds, presented a tetrahedral structure. The water‐soluble complexes where zinc ions connected with oxygen of CO and water molecules were only due to electron attraction. Formation of different microstructures on the surfaces, as revealed by SEM, provided evidence to distinguish different chelating mechanisms between water‐soluble and water‐insoluble complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1476–1485, 2001     

Synthese und Reaktivität von tert-Butyl-(2-aryl-3-methyl-but-2-yl)-peroxiden

Synthesis and Reactivity of tert-Butyl-(2-aryl-3-methyl-but-2-yl) Peroxides tert-Butyl-(2-aryl-3-methyl-but-2-yl) peroxides (2a–d) were prepared from t-BuOOH and corresponding 2-aryl-methyl-butan-2-ols (1a–d) (Ar:p-MeO C₆H₄ (a) ; Ph (b) ; p-Cl C₆H₄ (c) ; m-CF₃ C₆H₄ (d) ) and characterized by NMR, MS and elemental analysis. Kinetic data for the thermolysis of 2a–d in cumene as the solvent were determined at 110–140 °C and the products analyzed. The rate constants satisfy the Hammett equation with σ giving a ρ-value of −0.73. Oxidation of 2a–d at 80 °C gives the corresponding acetophenones 4 , epoxides 6 and hydroperoxides 8 . The products of the oxidation of 2a–2d were analysed after reduction of the reaction mixtures with LiAlH₄. Relative reactivities of the tertiary C H bonds of peroxides 2 were determined by competitive oxidations. They amount to 0.115–0.275 (with respect to the tertiary C H bond of cumene)     

Vinyloge Acylverbindungen. XX. Reaktivität und Toxizität arylsubstituierter β-Chlorvinylketone, β-Chlorvinylaldehyde und β-Chlorvinylmethyleniminiumsalze

Vinylogous Acyl Compounds. XX. Reactivity and Toxicity of Aryl-substituted β-Chlorovinyl Ketones, β-Chlorovinyl Aldehydes, and β-Chlorovinyl Methyleniminium Salts Based on kinetic measurements, the nucleophilic replaceability of the chlorine in aromatic β-chlorovinyl ketones ArCO-CH  CH-Cl ( 1 ), isomeric β-chlorovinyl aldehydes OCH CHC(Cl)Ar( 2 ), and corresponding β-chlorovinyl methyleniminium salts Me₂N^⊕;CH CHC(Cl)Ar X^⊖ ( 3 ) is compared and related to toxicological findings. The chemical reactivity of these important synthetic building blocks increases in the order 2 < 1 < 3 , the acute toxicity (24 h LD₅₀ i. p. in the mouse) shows the graduation 2 < 3 < 1 . Compounds of type 1 prove to be relatively toxic (LD₅₀ 24–42 mg/kg) and display a marked necrotic action after percutaneous absorption, whereas the aldehydes 2 have not only a minor acute toxicity (LD₅₀ 158–298 mg/kg) but also a somewhat less marked skin damaging activity. In addition, the LD₅₀ values of selected β-chlorovinyl carbonyl compounds are compared with those of corresponding halogen-free compounds as well as of vinylogous carbonamidium salts ArCO CHCH N^⊕R₃X^⊖. The latter, which can be used as synthetic equivalents of 1 , differ in both the reduced acute toxicity and missing skin damaging properties.     

Asymmetric 1,3‐Dipolar Cycloaddition Reaction between α,β‐Unsaturated Aldehydes and Nitrones Catalyzed by Well‐Defined Iridium or Rhodium Catalysts

Reaction of the complexes (S_M,R_C)‐[(η⁵‐C₅Me₅)M{(R)‐Prophos}(H₂O)](SbF₆)₂ (M=Rh, Ir) with α,β‐unsaturated aldehydes diastereoselectively gave complexes (S_M,R_C)‐[(η⁵‐C₅Me₅)M{(R)‐Prophos}(enal)](SbF₆)₂ which have been fully characterized, including an X‐ray molecular structure determination of the complex (S_Rh,R_C)‐[(η⁵‐C₅Me₅)Rh{(R)‐Prophos}(trans‐2‐methyl‐2‐pentenal)](SbF₆)₂. These enal complexes efficiently catalyze the enantioselective 1,3‐dipolar cycloaddition of the nitrones N‐benzylideneaniline N‐oxide and 3,4‐dihydroisoquinoline N‐oxide to the corresponding enals. Reactions occur with excellent regioselectivity, perfect endo selectivity and with enantiomeric excesses up to 94 %. The absolute configuration of the adduct 5‐methyl‐2,3‐diphenylisoxazolidine‐4‐carboxaldehyde was determined through its (R)‐(−)‐α‐methylbenzylamine derivative.     

Facile,Efficient Copolymerization of Ethylene with Bicyclic,Non‐Conjugated Dienes by Titanium Complexes Bearing Bis(β‐Enaminoketonato) Ligands

Copolymerizations of ethylene with 5‐vinyl‐2‐norbornene or 5‐ethylidene‐2‐norbornene under the action of various titanium complexes bearing bis(β‐enaminoketonato) chelate ligands of the type, [R¹NC(R²)CHC(R³)O]₂TiCl₂ ( 1 , R¹=Ph, R²=CF₃, R³=Ph; 2 , R¹=C₆H₄F‐p, R²=CF₃, R³=Ph; 3 , R¹=Ph, R²=CF₃, R³=t‐Bu; 4 , R¹=C₆H₄F‐p, R²=CF₃, R³=t‐Bu; 5 , R¹=Ph, R²=CH₃, R³=CF₃; 6 , R¹=C₆H₄F‐p, R²=CH₃, R³=CF₃), have been shown to occur with the regioselective insertion of the endocyclic double bond of the monomer into the copolymer chain, leaving the exocyclic vinyl double bond as a pendant unsaturation. The ligand modification strongly affects the copolymerization behaviour. High catalytic activities and efficient co‐monomer incorporation can be easily obtained by optimizing the catalyst structures and polymerization conditions.     

Über die Säuren HOOCCH(SX)CH(SX)COOH (X  CH2COOH,C6H5) und ihre Methylester

The Acids HOOCCH(SX)CH(SX)COOH (X  CH₂COOH, C₆H₅) and their Methyl Esters The acids HOOCCH(SX)CH(SX)COOH with X  CH₂COOH and C₆H₅ and their methyl esters have been prepared by addition of thiols to acetylene dicarboxylic acid as salt and methyl ester. The structures and configurations have been discussed.     

Regioselective Cleavage of Unstrained C?C Bond and C?H Bond: Palladium–Copper Catalyzed Deacetophenonylative Arylation of Coumarin Derivatives

A C_α C_β bond activation of the carbonyl group in unstrained ketones catalyzed cooperatively by palladium and copper(II) with the departure of the acetophenone has been developed, and the subsequent coupling with a variety of aromatics via the formal C H activation similar to the Friedel–Crafts reaction affords the skeleton‐reconstructed coumarin derivatives with high regioselectivity.