Nonsymmetric Bis Research Articles

Congestion of steric and electronic factors in α-diimine nickel precatalysts for high-temperature ethylene polymerization in accessing direct PE elastomer

In α-diimine-nickel catalysts mediated ethylene polymerization, the synergistic impact of steric and electronic factors plays an instrumental role in fine-tuning catalytic activity, polymer molecular weights, microstructure, as well as mechanical and elastic properties. In this study, a new series of nonsymmetrical bis(arylimino)-acenaphthene-nickel complexes was prepared and investigated for ethylene polymerization. These complexes feature both bulky N-2,6-dibenzhydryl-3,4,5-fluorophenyl imine and smaller N-2,6-di(R)-4-(R1)phenyl imine units [Ni2Me (R, = Me, R1 = H), Ni2Et (R, = Et, R1 = H) and Ni2iPr (R, = iPr, R1 = H), Ni3Me (R, R1 = Me), Ni2Et,Me (R, = Et, R1 = Me)]. The incorporation of both steric congestion and strong electronic withdrawal groups into the catalyst structure resulted in significantly improved catalytic performance: high thermal stability and exceptional activity were observed at both ambient temperature (21.24 × 106 at 30 °C) and industrially relevant temperatures (1.65 × 106 at 100 °C). Polymer molecular weights and branching degree were tunable by adjusting the ligand structure and reaction conditions. This correlation extended to mechanical and elastic properties, demonstrating high tensile strength at low temperatures and good elastic recovery at high reaction temperatures, consistent with typical polyolefin elastomers.

Unusual Effect of α-olefins as Chain Transfer Agents in Ethylene Polymerization over the Catalyst with Nonsymmetrical Bis(imino)pyridine Complex of Fe(II) and Modified Methylalumoxane (MMAO) Cocatalyst.

Ethylene polymerization with bis(imino)pyridlyiron precatalysts generally produces linear polyethylene (PE) even with the presence of α-olefins because α-olefins are not incorporated into polymeric products. Interestingly, α-olefins, such as hexene-1 or butene-1, have been found to act as effective chain transfer agents in the ethylene polymerization promoted by nonsymmetrical bis(imino)pyridyliron complexes with modified methylalumoxane (MMAO), resulting in higher catalytic activities with higher amounts of polymers with lower molecular weights, and, more importantly, narrower molecular weight distributions of the resultant polyethylenes (PE). This phenomenon confirms the assistance of α-olefins in the chain-termination reaction of iron-initiated polymerization and regeneration of the active species for further polymerization. Besides higher activities of the catalytic system, the formation of linear PE with trans-vinylene terminal groups and lower molecular weights are explained. The observation will provide a new pathway for enhancing catalytic activity and improving the quality of polyethylenes obtained by regulation of molecular weights and molecular weight distribution.

Expedient Access to Indolyl-Substituted Tri- and Diarylmethanes and (±)-Colletotryptin E by Silica Sulfuric Acid Catalyzed Transindolylation

AbstractAn expedient access to a series of nonsymmetrical bis(indolyl)methanes (BIMs) through transindolylation of readily available symmetrical 3,3′-BIMs with various indoles catalyzed by silica-supported sulfuric acid has been established. This approach not only provides a useful strategy for the synthesis of structurally diverse BIMs, but also provides examples of nucleophilic substitution of BIMs with aromatic and nonaromatic π-systems, leading to a library of indolyl-substituted tri- and diarylmethanes. Moreover, this method was successfully applied in the first total synthesis of the 2,3′-BIM alkaloid (±)-colletotryptin E in three steps with an overall yield of 46%. The features of this procedure include a metal-free process, an inexpensive and environmentally friendly catalyst, mild reaction conditions, broad functional-group tolerance, good yields, and gram-scalable preparations.

Non-symmetrical bis(aminoalkyl)phosphinates: new ligands with enhanced binding of Cu(ii) ions

Novel, non-symmetrical bis(aminoalkyl)phosphinic acids exhibit enhanced efficiency in Cu(ii) ion binding.

Palladium‐Catalyzed Ethylene/Methyl Acrylate Co‐Oligomerization: The Effect of a New Nonsymmetrical α‐Diimine with the 1,4‐Diazabutadiene Skeleton

AbstractPdII complexes with a nonsymmetrical bis(aryl‐imino)diazabutadiene ligand (ArDAB) have been synthesized and characterized. The new ligand features one aryl ring substituted in the ortho positions with a methyl group and the other ring that bears a trifluoromethyl group on the meta positions, which leads to subtle steric and electronic differences at the two N donor atoms. This peculiar substitution makes the direct synthesis of the ligand unfeasible, and the relevant PdII complex, [Pd(CH3)Cl(ArDAB)], is obtained directly through a template reaction. The corresponding cationic complexes with either acetonitrile or DMSO were synthesized and characterized. The X‐ray crystal structure of a Pd complex with an α‐diimine and DMSO is reported. The monocationic complexes were tested as precatalysts in ethylene/methyl acrylate co‐oligomerization under mild reaction temperature and pressure conditions. A comparison of the catalytic behavior of the precatalysts with the corresponding nonsymmetrical aryl α‐diimines with an acenaphthene skeleton indicated that the active species with the new ligand is more productive and leads to the formation of ethylene oligomers and ethylene/methyl acrylate co‐oligomers.

Enantioselective Conjunctive Cross-Coupling of Bis(alkenyl)borates: A General Synthesis of Chiral Allylboron Reagents.

Palladium-catalyzed conjunctive cross-coupling is used for the synthesis of enantioenriched allylboron reagents. This reaction employs nonsymmetric bis(alkenyl)borates as substrates and appears to occur by a mechanism that involves selective activation of the less substituted alkene followed by migration of the more substituted alkene during the course of a Pd-induced metalate rearrangement.

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms.

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis(urea)s and tris(urea)s decorated by two incompatible polymer arms, namely, poly(styrene) (PS) and poly(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis(urea)s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris(urea)s (Nagg ∼ 50) which developed six cooperative hydrogen bonds per molecule. (1)H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders.

Synthesis, Theoretical Analysis, and Experimental pKa Determination of a Fluorescent, Nonsymmetric, In-Out Proton Sponge.

Herein, we report the synthesis and theoretical investigation of a nonsymmetric bis(diisopropylamino)cyclopropenimine (DAC)-functionalized proton sponge derivative, coined the "Janus" sponge. The reported sponge was isolated as a monoprotonated salt, though no intramolecular hydrogen bond was observed. Homodesmotic equations supported the absence of a N-HN intramolecular hydrogen bond and a relatively low freebase strain, while DFT calculations and X-ray crystallography revealed the presence of a hydrogen bond to the Cl(-) counterion. Associated with this fact was the rare in-out geometry of the basic nitrogens, which represents the first such instance in a proton sponge not having an ortho-substituent and/or being in a protonated state. Furthermore, NLP donation into the cyclopropenium cation was found to stabilize this unprecedented in-out geometry. The measured pKa was determined to be 23.8, in good agreement with the computed value of 23.9. Lastly, the Janus sponge was found to have fluorescent properties both in the solid state and in solution, which notably represents the first example of a cyclopropenimine-based fluorescent organic compound.

Catalyst activity or stability: the dilemma in Pd-catalyzed polyketone synthesis

A series of Pd-complexes containing nonsymmetrical bis(aryl-imino)acenaphthene (Ar-BIAN) ligands, characterized by substituents on the meta positions of the aryl rings, have been synthesized, characterized and applied in CO/vinyl arene copolymerization reactions. Crystal structures of two neutral Pd-complexes have been solved allowing comparison of the bonding properties of the ligand. Kinetic and mechanistic investigations on these complexes have been performed. The kinetic investigations indicate that in general ligands with electron-withdrawing substituents give more active, but less stable, catalytic systems, although steric effects also play a role. The good performance observed with nonsymmetrical ligands is at least in part due to a compromise between catalyst activity and lifetime, leading to a higher overall productivity with respect to catalysts based on their symmetrical counterparts. Additionally, careful analysis of the reaction profiles provided information on the catalyst deactivation pathway. The latter begins with the reduction of a Pd(II) Ar-BIAN complex to the corresponding Pd(0) species, a reaction that can be reverted by the action of benzoquinone. Then the ligand is lost, a process that appears to be facilitated by the contemporary coordination of an olefin or a CO molecule. The so formed Pd(0) complex immediately reacts with another molecule of the initial Pd(II) complex to give a Pd(I) dimeric species that irreversibly evolves to metallic palladium. Mechanistic investigations performed on the complex with a nonsymmetrical Ar-BIAN probe evidence that the detected intermediates are characterized by the Pd-C bond trans to the Pd-N bond of the aryl ring bearing electron-withdrawing substituents. In addition, the intermediate resulting from the insertion of 4-methylstyrene into the Pd-acyl bond is a five-member palladacycle and not the open-chain η(3)-allylic species observed for complexes with Ar-BIANs substituted in ortho position.

Switching with orthogonal stimuli: electrochemical ring-closure and photochemical ring-opening of bis(thiazolyl)maleimides

The photochemistry as well as electrochemistry of novel donor–acceptor bis(morpholinothiazolyl)–maleimides has been investigated. Proper substitution of these diarylethene-type molecular switches leads to the unique situation in which their ring-closure can only be accomplished electrochemically, while ring-opening can only be achieved photochemically. Hence, these switches operate with orthogonal stimuli, i.e. redox potential and light, respectively. The switch system could be optimized by introducing trifluoromethyl groups at the reactive carbon atoms in order to avoid by-product formation during oxidative ring closure. Both photochemical and electrochemical pathways were investigated for methylated, trifluoromethylated, and nonsymmetrical bis(morpholinothiazolyl)maleimides as well as the bis(morpholinothiazolyl)cyclopentene reference compound. With the aid of the nonsymmetrical “mixed” derivative, the mechanism of electrochemically driven ring closure could be elucidated and seems to proceed via a dicationic intermediate generated by two-fold oxidation. All experimental work has been complemented by density functional theory that provides detailed insights into the thermodynamics of the ring-open and closed forms, the nature of their excited states, and the reactivity of their neutral as well as ionized species in different electronic configurations. The particular diarylethene systems described herein could serve in multifunctional (logic) devices operated by different stimuli (inputs) and may pave the way to converting light into electrical energy via photoinduced “pumping” of redox-active meta-stable states.

Palladium‐Catalyzed Ethylene/Methyl Acrylate Cooligomerization: Effect of a New Nonsymmetric α‐Diimine

AbstractA new nonsymmetric bis(aryl‐imino)acenaphthene (Ar‐BIAN) ligand, featured by a subtle steric and electronic unbalance of the N‐donor atoms, is reported. With the new ligand and the corresponding symmetrically substituted derivatives, both neutral and monocationic PdCH3 compounds have been synthesized and characterized. The series of the monocationic complexes [Pd(CH3)(L)(Ar‐BIAN)][PF6] (L=CH3CN, dmso) has been extended to dimethyl sulfoxide derivatives. The monocationic complexes are tested as precatalysts for the ethylene/methyl acrylate cooligomerization under mild reaction conditions of temperature and ethylene pressure. The catalytic product is a mixture of ethylene/acrylate cooligomers and higher alkenes. The catalysts containing the new nonsymmetric ligand are found to be more productive than those with the symmetric Ar‐BIANs. The Pd–dmso catalysts are more productive and show a longer lifetime than their Pd–NCCH3 counterparts.

New bis(macrocyclic) dinickel(II) complexes obtained by oxidation of bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,7-dien-6-yl)dinickel(II) perchlorate

New bis(macrocyclic) dinickel(II) complexes with bis(Me 2[14]-4,7-dien-6-ylidene), 2a and 2b, were synthesized by oxidation of a dinickel(II) complex with an unsaturated bis(macrocyclic) ligand containing four C N bonds, bis(Me 2[14]-4,7-dien-6-yl) ( 1). Complex 2a was found to undergo intramolecular cyclization between the methyl group of one macrocycle and the carbon atom of the C N group of the other macrocycle to produce a bis(macrocyclic) dinickel(II) complex bridged by a fivemembered ring ( 3). The structures of 2b and 3 were determined by X-ray crystallography. The nonsymmetrical bis(macrocyclic) structure of the dinickel(II) complex 3 was reflected in its cyclic voltammogram and 1H and 13C NMR spectra. The catalytic capabilities of these bis(macrocyclic) nickel(II) complexes in the reductive debromination of 1-bromo-4- tert-butylbenzene were also investigated.

A Modular Approach Towards Nonsymmetrical Bis(metallosalen) Building Blocks

AbstractNew bis(metallosalen) building blocks are described that can be accessed through di‐ or tetraimine precursors derived from the 3,3′‐diaminobenzidine backbone. A selective procedure for the introduction of two imine groups in 3,3′‐diaminobenzidine was developed to furnish starting materials for nonsymmetrical metallosalen complexes. The procedure proved to be widely applicable and several diimine derivatives were isolated and fully characterized. The diimine compounds were used to prepare the first nonsymmetrical bis(salen) complexes (M = Zn, Ni) with different peripheral groups upon treatment with various salicylaldehydes in a one‐pot procedure. The identity of the bis(metallosalen)s was verified by a range of analytical techniques, and for two of these derivatives the X‐ray molecular structures are described. The crystallographic data revealed that the biphenylene linker between the two N2O2 donor sets can adopt conformations with different dihedral angles. The supramolecular potential of the bis[Zn(salen)] derivatives was investigated by combining two of these complexes with a ditopic ligand to yield supramolecular assemblies with nanoscale dimensions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

( N, N) vs. ( N, S) chelation of palladium in asymmetric allylic substitution using bis(thiazoline) ligands: A theoretical and experimental study

New thiazoline-containing ligands including non-symmetric bis(thiazolines) and oxazoline–thiazolines were synthesized and then compared to C 2-symmetric bis(thiazolines) in the palladium-catalyzed allylic substitution. The experimental results obtained in this study support the hypothesis of a competition between the ( N, N) and the ( N, S) palladium chelation, when sterically hindered bis(thiazolines) are used as ligands. A quantum chemical study performed on the Pd-complexes derived from three selected ligands, two C 2-symmetric bis(thiazolines) and one oxazoline–thiazoline, also supports this hypothesis.

Subtle Balance of Steric and Electronic Effects for the Synthesis of Atactic Polyketones Catalyzed by Pd Complexes with Meta-Substituted Aryl-BIAN Ligands

Both symmetric and nonsymmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladium-catalyzed CO/vinyl arene copolymerization. The nature and the number of substituents affect both the productivity and the molecular weight of the synthesized copolymers. Palladium complexes containing the nonsymmetric ligands are the most efficient catalysts reported so far for the synthesis of atactic polyketones.

Synthesis of non-symmetric bis(oxazoline)-containing ligands and their application in the catalytic enantioselective Nozaki–Hiyama–Kishi allylation of benzaldehyde

We report the good to high-yielding three-step synthesis of non-symmetrical bis(oxazoline)-containing ligands possessing an N-thienylaniline unit. The convergent synthesis employed a palladium-catalysed aryl amination of 2-(2'-bromothiophene)nitrile as the key step, with sixteen ligands prepared in total. These ligands were subsequently applied in the chromium-catalysed enantioselective Nozaki-Hiyama-Kishi allylation of benzaldehyde with an optimal enantioselectivity of 73%.

The application of bis(oxazoline) ligands in the catalytic enantioselective methallylation of aldehydes

A series of symmetric and non-symmetric bis(oxazoline) ligands were applied in the Nozaki-Hiyama-Kishi methallylation of a range of aromatic and aliphatic aldehydes. A non-symmetrical ligand with tert-butyl/benzyl-substituted oxazolines provided the highest enantioselectivity of 99.5% for the methallylation of benzaldehyde.

Novel ferrocenyl-oxazoline ligands: first preparation of non-symmetrical bis(oxazoline)

New ferrocenyl-arenylethenyl-oxazoline derivatives have been prepared ( 5– 10) from the mono- and (1,1 ′)-disubstituted (nitrile-ethenylaryl)ferrocene compounds ( 1 and 2) and the appropriated β-aminoalcohol ( 3 and 4) in one step synthesis. The X-ray crystal structure of one of the ferrocenyl-ethenylaryl-oxazoline ( 5) is described, revealing the unusual quasi-planarity of the oxazoline ring with the phenyl and cyclopentadienyl cycles. Two compounds end-capped ( 9 and 10) with both, nitrile and oxazoline groups, are the key intermediates to obtain the non-symmetrical bis(oxazoline) 11, containing two different substituted heterocycles.

Symmetric and Non-Symmetric Dinuclear Alkenyl-Bridged Carbene Complexes of Chromium and Tungsten

Treatment of (CO)5W=C(NMe2)CH=CH−Ar−(OH)(H)C≡CH (1a−b) [a: −Ar− =1,4-C6H4−; b: −Ar− = 2,5-C4H2S−] with W(CO)5(THF) in methanol yields the nonsymmetrical bis(alkenylcarbene)-bridged ditungsten complexes (CO)5W=C(NMe2)CH=CH−Ar−CH=CH(OMe)C=W(CO)5 (3a−b). Similarly, the symmetrical bis(methoxycarbene)ditungsten derivative [(CO)5W=C(OMe)CH=CH−]2(1,4-C6H4−) (4a) is obtained in a low yield from the precursor (CO)5W=C(OMe)CH=CH−C6H4−(OH)(H)C≡CH (2a). Complexes 3a and 3b undergo aminolysis reactions with diamines such as piperazine and ethylenediamine to produce the corresponding bis[alkenyl(amino)carbene]ditungsten complexes 5a−b and 6a−b. The reaction of 1a with Cr(CO)5(THF) affords the heterobimetallic (W−Cr) bis(carbene) complex (CO)5W=C(NMe2)CH=CH−Ar−CH=CH(OMe)C=Cr(CO)5 (3′a). This complex, as well as the bis(methoxycarbene) derivative 4′a, can also be obtained by treatment of (CO)5W=C(XR)CH=CH−C6H4−CHO [1c: XR = NMe2; 2c: XR = OMe] with (CO)5Cr=C(OMe)CH2−Li+. All the new compounds have been characterized by analytical and spectroscopic methods, and the single-crystal structures of 3a, 4a−b, and 4′a have been established.

チアツオール誘導体の研究 (第14報)

Decomposition of the hydrochloride of bis (2-thiazolyl) sulfide compounds by heating in carbon disulfide is affected by the substituent in 5-position of the thiazole ring. While CH3 and CH2CH2OH have no effect on the 2-position, COOC2H5 group in 5-position results in selective formation of ethyl 2-chloro-4-methyl-5-thiazolecarboxylate (IX), and this was proved by reaction between bis (2-thiazolyl) sulfide hydrochloride (or hydrobromide) and 2-chlorothiazole derivatives. The reason for formation of two kinds of symmetric bis (2-thiazolyl) sulfides by reaction of ethyl 2-mercapto-4-methyl-5-thiazolecarboxylate (VIII) and 2-chlorothiazole derivatives, 2-mercapto-4, 5-dimethylthiazole (XIV) and 2-(2-chloro-4-methyl-5-thiazolyl) ethanol (IV), or 2-(2-mercapto-4-methyl-5-thiazolyl) ethanol (I) and 2-chloro-4, 5-dimethylthiazole (XV), during syntheses of non-symmetric bis (2-thiazolyl) sulfide compounds, was assumed to be due to the similar decomposition reaction of an intermediary produced hydrochloride and subsequent reaction of the decomposition products or starting materials with each other to fix hydrochloric acid or to form bis (4-methyl-5-ethoxycarbonyl-2-thiazolyl) sulfide (X) which does not form a hydrochloride.