Pyrrolyl Ligands Research Articles

Synthesis and styrene polymerisation catalysis of η5- and η1-pyrrolyl-ligated cationic rare earth metal aminobenzyl complexes

The cationic rare earth metal aminobenzyl complexes bearing mono(pyrrolyl) ligands are synthesised and structurally characterised, and the coordination mode of the pyrrolyl ligands is found to show significant influence on the polymerisation of styrene.

Aluminum Alkyl Complexes Containing Bidentate, Mono‐ or di‐anionic Pyrrolyl Ligands: Intramolecular Elimination of Methane and 1‐Hexene Polymerization

AbstractA series of aluminum alkyl complexes were synthesized and their catalytic polymerization reactivity toward 1‐hexene was studied. Aluminum complexes, [C4H3N(CH2NHMe)‐2]AlR2 (1a, R = Me; 1b, R = Et), containing substituted pyrrolyl ligand can be prepared by reacting AlR3 with one equiv of C4H3NH(CH2NHMe)‐2 in diethyl ether at room temperature. Dimeric aluminum complexes, {[C4H3N‐(CH2NMe)‐2]AlR}2 (2a, R = Me; 2b, R = Et), can be obtained via metathesis by heating AlR3 and with one equiv of [C4H3NH(CH2NHMe)‐2] in toluene for 24 h or via intramolecular methane elimination by heating 1 and 2 at 90 °C in toluene. Complexes 1a, 1b, 2a, and 2b have been characterized by NMR spectroscopy and by X‐ray crystallography. Complexes 1a and 2a have shown moderate reactivity for 1‐hexene polymerization in the presence of MAO.

A robust dimethylgold(III) complex stabilized by a 2-pyridyl-2-pyrrolide ligand

Reaction of isopropyl[(2-pyridyl)alkyl]amines such as N-isopropyl- N-2-methylpyridine or N-isopropyl- N-2-ethylpyridine with aqueous solutions of NaAuCl 4 led to the formation of [LAuCl 2][AuCl 4] in low yields, where L = pyridyl amine bound to gold in a bidentate fashion. Reaction of 2-(3,5-diphenyl-1H-pyrrol-2-yl)pyridine with aqueous NaAuCl 4, however, proceeded with formal loss of HCl and direct formation of the gold(III) amido complex L′AuCl 2, where L′ = deprotonated pyrrolyl ligand. Optimization of the reaction conditions to make the new amido complex identified MeCN:H 2O (1:2) as the best choice of solvent, affording product in 92% yield. This dichloro amido complex is a convenient precursor to L′AuMe 2, which was found to be air-stable and thermally robust.

Synthesis and Characterization of Zirconium and Hafnium Aryloxide Compounds and Their Reactivity Towards Lactide and ϵ‐Caprolactone Polymerization

AbstractReactions of 2 equiv. pyrrole with [C4H3N(CH2NMe2)‐2]2M(NEt2)2 in toluene generated tetra‐pyrrolyl metal compounds [C4H3N(CH2NMe2)‐2]2M(C4H4N)2 (3, M = Zr; 4, M = Hf) in moderate yields. Similarly, treatment of metal amides [C4H3N(CH2NMe2)‐2]2M(NEt2)2 with 2,6‐dimethylphenol or 2,6‐diisopropylphenol in heptane resulted in the elimination of diethylamine along with the formation of the corresponding metal alkoxides [C4H3N(CH2NMe2)‐2]2M(OR)2 (5, M = Zr, R = C6H3‐2,6‐Me2; 6, M = Hf, R = C6H3‐2,6‐Me2; 7, M = Zr, R = C6H3‐2,6‐iPr2; 8, M = Hf, R = C6H3‐2,6‐iPr2) in moderate yields. All the new compounds were characterized by 1H and 13C NMR spectroscopy and the structures of 3, 4, 6, 7, and 8 have also been determined by X‐ray crystallographic studies. The aryloxides and the substituted pyrrolyl ligands in both compounds 5 and 6 show fluxionality as observed by 1H NMR signals. A kinetic study on the ring‐opening polymerization of lactide exhibits a first‐order reaction of lactide monomer with compound 8. The catalytic properties of all the metal complexes have been studied for the ring‐opening polymerization of ϵ‐caprolactone. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Insertion, Reduction, and Carbon–Carbon Coupling Induced by Monomeric Aluminum Hydride Compounds Bearing Substituted Pyrrolyl Ligands

A monomeric aluminum hydride complex bearing substituted pyrrolyl ligands, AlH[C(4)H(3)N(CH(2)NMe(2))-2](2) (1), was synthesized and structurally characterized. To further confirm the presence of Al--H bonds, the compound AlD[C(4)H(3)N(CH(2)NMe(2))-2](2) ([D]1) was synthesized by reacting LiAlD(4) with [C(4)H(4)N(CH(2)NMe(2))-2]. Compound 1 and [D]1 react with phenyl isothiocyanate yielding Al[C(4)H(3)N(CH(2)NMe(2))-2](2)[eta(3)-SCHNPh] (2) and Al[C(4)H(3)N(CH(2)NMe(2))-2](2)[eta(3)-SCDNPh] ([D]2) by insertion. The reactions of 1 with 9-fluorenone and benzophenone generated the unusual aluminum alkoxide complexes 3 and 4, respectively, through intramolecular proton abstraction and C-C coupling. A mechanistic study shows that 9-fluorenone coordinates to [D]1 and releases one equivalent of HD followed by C-C coupling and hydride transfer to yield the final product. Reduction of benzil with 1 affords aluminum enediolate complex 5 in moderate yield. Mechanistic studies also showed that the benzil was inserted into the aluminum hydride bond of [D]1 through hydroalumination followed by proton transfer to generate the final product [D]5. All new complexes have been characterized by (1)H and (13)C NMR spectroscopy and X-ray crystallography.

Synthesis and characterization of lithium and yttrium complexes containing tridentate pyrrolyl ligands. Single-crystal X-ray structures of {Li[C 4H 2N(CH 2NMe 2) 2-2,5]} 2 ( 1) and {[C 4H 2N(CH 2NMe 2) 2-2,5]YCl 2(μ-Cl) · Li(OEt 2) 2} 2 ( 2) and ring-opening polymerization of ε-caprolactone

The lithiated pyrrolyl ligand, {Li[C 4H 2N(CH 2NMe 2) 2-2,5]} 2 ( 1) was synthesized and structurally characterized. Reaction of 1 with YCl 3 in the molar ratio 1:1 in diethyl ether at room temperature afforded a di-yttrium di-lithium tetranuclear complex, {[C 4H 2N(CH 2NMe 2) 2-2,5]YCl 2(μ-Cl) · Li(OEt 2) 2} 2 ( 2) in 87% yield. Compounds 1 and 2 were characterized by NMR spectroscopy and single crystal X-ray crystallography. Compound 1 shows high reactivity for the ring-opening polymerization of ε-caprolactone.

Isoselective Living Polymerization of 1-Hexene Catalyzed by Half-Metallocene Dimethyl Complexes of Hafnium with Bidentate N-Substituted (Iminomethyl)pyrrolyl Ligands

The nonbridged half-metallocene dimethylhafnium complexes 3a−c with N-substituted (iminomethyl)pyrrolyl ligands 2a−c have been synthesized and characterized by NMR spectroscopy as well as X-ray ana...

New C—N and C—C Bond Forming Reactions Catalyzed by Titanium Complexes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Bonding and fluxionality in group-4 metal complexes with pyrrolyl ligands

Abstract The bonding of pyrrolyl ligands (pyr′) in group-4 metal complexes, [M(pyr′)Cl 3 ], is studied by means of DFT/B3LYP calculations with a VDZP basis set. Two metals (M = Ti, Hf) and two pyrrolyl ligands are addressed, pyr′ = pyrrolyl (pyr), and 2,5-dimethylpyrrolyl (dmp). The study allowed the characterization of the π-pyr′ complexes with a η 5 coordination of this ligand, the σ complexes with the pyr′ bonding established by the nitrogen lone pair, and the transition states for the interconversion between the two isomers. A comparative analysis of the pyr′ bonding to the metal in all the species is provided, as well as a detailed study of the mechanism for the interconversion between the two pyr′ coordination modes. This is a slippage process without significant folding of the pyr′ ring and the activation energies obtained ( E a –1 ) suggest the possible fluxionality between the two coordination modes, in solution. Calculated pyr′–M bond enthalpies show an increase in the bond strength going down the group, allowing a rationalization of the differences in stability of the two coordination modes observed for the various metals and, consequently, of the associated ring slippage process. To cite this article: A.R. Dias et al., C. R. Chimie 8 (2005) . Resume Les liaisons des ligands pyrrolyl dans les complexes metalliques du groupe 4, [M(pyr′)Cl 3 ], ont ete etudiees a l'aide de calculs de fonctionnelle de densite DFT/B3LYP avec une base VDZP. Les deux metaux (M = Ti, Hf) et deux ligands pyrroles pyr′ = pyrrolyl (pyr), et 2,5-dimethylpyrrolyl (dmp) ont ete etudies. L'etude a permis la caracterisation des complexes π-pyr′ avec une coordination η 5 du ligand, des complexes σ avec liaison pyr′ par la paire azote unique et de l'etat de transition pour l'interconversion entre ces deux isomeres. Une analyse comparative de la liaison pyr′–metal dans toutes les especes est donnee, ainsi qu'une etude detaillee du mecanisme de l'interconversion entre les deux modes de coordinaiton des pyr′. Il s'agit d'un processus de glissement sans effet sur le cycle pyr′ ; les energies d'activation ( E a –1 ) amenent a envisager une possible fluxionalite entre les deux modes de coordination en solution. Les enthalpies des liaisons pyr′–M calculees montre une augmentation de la force des liaisons a mesure que l'on descend dans la colonne, ce qui permet de rationaliser les differences de stabilite entre les deux modes de coordination observes pour des metaux varies et, par consequent, le processus de glissement de cycles associe. Pour citer cet article : A.R. Dias et al., C. R. Chimie 8 (2005) .

New C–N and C–C bond forming reactions catalyzed by titanium complexes

Titanium(IV) complexes with two basic dimethylamido ligands can be efficient catalysts for alkyne hydroamination by primary amines. Readily prepared pyrrolyl ligands have proven to be especially useful in generating active catalysts for hydroamination and hydrohydrazination. From these reactions, new methodologies for the synthesis of imines, hydrazones, alpha,beta-unsaturated imines, pyridines, indoles, and pyrroles have developed. In addition, a new reaction that is mechanistically related to hydroamination, alkyne iminoamination, has been discovered. Iminoamination, which is a multicomponent coupling between an amine, alkyne, and isonitrile, provides unsymmetrical alpha, beta-unsaturated beta-iminoamines in a single, titanium-catalyzed step.

Insertion reactions of phenyl isocyanate into hafnium nitrogen bonds: synthesis and reactivity of hafnium complexes bearing substituted pyrrolyl ligands

A bis(diethylamido)hafnium compound [C 4H 3N(CH 2NMe 2)-2] 2Hf(NEt 2) 2 ( 1) has been prepared in 79% yield by reacting Hf(NEt 2) 4 with 2 equiv. of [C 4H 3NH(CH 2NMe 2)-2] in heptane via deamination. Reacting compound 1 with 2 equiv. of phenyl isocyanate at room temperature in diethyl ether results in the PhNCO being inserted seletively into hafnium–NEt 2 bonds to generate [C 4H 3N(CH 2NMe 2)-2] 2Hf[PhNC(NEt 2)O] 2 ( 2) in 56% yield. Similarly, while reacting 1 with 2 equiv. of phenyl isocyanate for a week in toluene produces a mixture of 2 and [C 4H 3N(CH 2NMe 2)-2]Hf[PhNC(NEt 2)O] 3 ( 3). For comparison, reacting Hf(NEt 2) 4 with 4 equiv. of PhNCO in a toluene solution at room temperature results in the PhNCO inserted into Hf–N bonds, and forms a tetrakis-ureato hafnium compound Hf[PhNC(NEt 2)O] 4 ( 4) in 88% yield. A theoretical calculation found that the unpaired electrons of the ureato fragments of 2 are resonance delocalized between the C–O, C–NPh, and C–NEt 2 bonds, which are all partially doubly bonded.

Hafnium chloride and hafnium methyl complexes bearing substituted pyrrolyl ligands: synthesis, characterization, and ethylene polymerization

Reactions of HfCl 4 with 2 and 3 equiv. of Li[C 4H 3N(CH 2NMe 2)-2] in toluene afford HfCl 2[C 4H 3N(CH 2NMe 2)-2] 2 ( 1) and HfCl[C 4H 3N(CH 2NMe 2)-2] 3 ( 2), respectively. Transmetallation reaction of 1 with 2 equiv. of MeLi results in a hafnium dimethyl compound HfMe 2[C 4H 3N(CH 2NMe 2)-2] 2 ( 3). A variable-temperature 1H NMR spectroscopic study shows that the activation energy for the dissociation/association of the NMe 2 units of compound 2 in solution is ca. 13.6 kcal/mol. Compounds 1– 3 are characterized by NMR spectroscopy and single crystal X-ray diffraction. A polymerization study shows that compounds 1 and 3 exhibit moderate activity toward ethylene in the presence of TIBA and MAO.

Bonding Geometry of Pyrrolyl in Zirconium Complexes: Fluxionality between σ and π Coordination

The bonding geometry of pyrrolyl ligands (pyr') in zirconium complexes was studied by means of DFT/Β3LYP calculations with a DZVP basis set. Monopyrrolyl complexes, [Zr-(pyr')L 3 ], and bispyrrolyl species, [Zr(pyr') 2 L 2 ], were addressed, with different pyrrolyl ligands, pyr' = pyrrolyl (pyr), 2,5-dimethylpyrrolyl (dmp), 2,4-dimethyl-3-ethylpyrrolyl (dmep), and ancillary ligands, L = chloride, methyl. Two coordination modes of pyr' were considered. The first is the π coordination of pyr', with the bonding to the metal established by means of the ring π orbitals. Slightly distorted η 5 coordination results, with the nitrogen tending to approach the metal. The second corresponds to a σ-pyr', with the nitrogen lone pair used to establish a a bond to the metal. The slippage from a π to a δ-pyr' produces an electronically poorer metal center and results, normally, in a less stable complex, although this effect is partially compensated by a strengthening of the Zr-N in the a coordination mode, when compared with the one existing in a π-pyr'. The σ-pyr' coordination and the π-σ slippage were found to be disfavored by substituents in the a carbon atoms of pyr', confirming a known empirical rule. The interconversion between the two coordination modes of the pyr' ligand was studied in all the complexes and determined to correspond to a slippage process without any significant ring folding. In the corresponding transition states the Zr-C bond breaking process is completed for the two β carbon atoms, and the slipping pyr' ring coordinates in a flat η 3 mode. The activation energies calculated for the slippage process in the various species (<10 kcal mol - 1 ) suggest the possibility of fluxionality in solution, even at room temperature. The mechanism for the rac/meso isomerization of [Zr(π-dmep) 2 (CH 3 ) 2 ] was also studied and determined to proceed via consecutive slippage and rotation of the dmep ring, the rate-determining step corresponding to the first slippage of that ligand. The calculated activation energy (E a < 7 kcal mol - 1 ) corroborates the experimental observation of fluxionality in solution, at room temperature.

Unusual Enhancement of Ethylene Polymerization Activity of Benzyl Zirconium Complexes by Benzylation of the Imino Moiety of 2-(N-Aryliminomethyl)pyrrolyl Ligand

Abstract Reaction of Zr(CH2Ph)4 (1) with one equiv. of 2-(N-aryliminomethyl)pyrrolyl ligands (2a–e) in toluene afforded two types of products, depending upon the bulkiness of the aryl moiety. The reactions of 1 with two equiv. of the most sterically bulky 2e afforded complex 5e, whose pseudo octahedral geometry around the zirconium atom and totally dissymmetric cis-dibenzyl structure were elucidated. The high catalytic activity for ethylene polymerization was obtained by using complexes 3a and 3b.

Synthesis and characterization of [W(NC 4Me 4) 2Cl 2] and [W(NC 4Me 4) 2(CH 3) 2], the first azametallocene tungsten complexes with pyrrolyl ligands. Electronic structure and bonding of tungsten bispyrrolyl complexes

The synthesis of the first tungsten azametallocene complexes with pyrrolyl ligands, [W(NC 4Me 4) 2L 2], is reported. The dichloro complex (L=Cl) was obtained from the reaction of WCl 4DME (DME=1,2-dimethoxyethane) with Li(NC 4Me 4) in poor yield (6.5%). A small amount (ca. 0.063 g, yield: 15.8%) of the dimethyl complex, [W(NC 4Me 4) 2(CH 3) 2], resulted from the reaction of the dichloro species (L=Cl) with LiCH 3. Both complexes were characterised by 1H, 13C{ 1H} NMR and mass spectroscopy. Molecular orbital studies based on B3LYP/DFT calculations were performed in order to study the complexes electronic structure, focusing the pyrrolyl coordination mode. Equivalent bond strengths were found for the two extreme coordination modes of that ligand: π coordination (η 5) through the pyrrolyl π system, and N-σ coordination established by the nitrogen lone pair. The relative stability of the isomers originated by the different pyrrolyl coordination modes, results from a delicate balance between electronic and stereochemical factors, on each case. The calculations suggest the existence of a fluxional process in solution, involving the π/π and the σ/π isomers of [W(NC 4Me 4) 2(CH 3) 2].

Seven-coordinated tantalum trichloride complex containing substituted pyrrolyl ligand: synthesis and characterization of [NC 4H 3(CH 2NMe 2)-2] 2TaCl 3

bis[2-(Dimethylaminomethyl)pyrrolyl]tantalum chloride ( 1) was prepared by treatment of the TaCl 5 with 2 equiv. of [2-(dimethylaminomethyl)pyrrolyl]lithium. The solid state structure of 1 shows the seven-coordinated tantalum atom, with a geometry corresponding to a pentagonal bipyramidal structure, in which two chlorine atoms occupy the axial position with the angle of 174.8(2)°. Furthermore, variable-temperature 1H NMR spectra infer the fluxionality of the two chelating pyrrolyl ligands with an estimated energy barrier of 13.8 kcal mol −1. Compound 1 shows no catalytic activity toward ethylene polymerization even activated with MAO.

SYNTHESIS AND CHARACTERIZATION OF ANTIBACTERIAL Co(II), Cu(II), Ni(II), AND Zn(II) COMPLEXES OF ACYLHYDRAZINE DERIVED PYRROLYL COMPOUNDS

ABSTRACT Acylhydrazine derived pyrrolyl ligands and their metal [Co(II), Cu(II), Ni(II), and Zn(II)] complexes have been prepared and characterized on the basis of elemental analyses, magnetic moments, molar conductances and spectroscopic (electronic, IR, 1H and 13C NMR) data. All of these compounds function as tridentate ligands, with their deprotonated enolic form being preferred in the coordination to the metal ions. The title synthesized ligands and their metal(II) complexes have been screened for bactericidal activity against the pathogenic bacterial species Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, and it is shown that the metal complexes act as more active antibacterial agents than the uncomplexed ligands from which they derive.

Coordinating properties of mixed pyrrolyl/dicarbollide cobalt metallocene-type complexes

Mixed-sandwich Co(III) complexes incorporating an η5 pyrrolyl unit [η5-NC4H4]− are very stable when the second η5 moiety is a dicarbollide [η5-C2B9H11]2−. The existence of a lone pair on N in the neutral closo-[3-Co(η5-NC4H4)-1,2-C2B9H11] (1) has allowed for the first time a study of the N-σ bonding capacity of a pyrrolyl ligand η5 bonded to a metal in an oxidation state higher than two. This capacity has been proven by reacting closo-[3-Co(η5-NC4H4)-1,2-C2B9H11] with Lewis acids (BH3, BF3 and Ag+) and a Co(III) macrocycle. In all cases the reaction went to completion proving the strength of the σ bond generated. The stability of the [3-Co(η5-NC4H4)-1,2-C2B9H11] complexes vs. oxidation state Co(III)/Co(II) was studied by cyclic voltammetry. It was found that [3-Co(η5-NC4H4)-1,2-C2B9H11]− is not as stable as [3-Co(η5-NC4H4)-1,2-C2B9H11]; however, when coordinated to cobalt(III), both [3-Co(η5-NC4H4)-1,2-C2B9H11]− and [3-Co(η5-NC4H4)-1,2-C2B9H11] are of comparable stability. The stability of the reduced form Co(II) in the mixed pyrrolyl/dicarbollide is enhanced when an electron withdrawing group is bonded to the cluster carbon atom in the dicarbollide.

Synthesis and structure of ansa-cyclopentadienyl pyrrolyl titanium complexes: [(η 5-C 5H 4)CH 2(2-C 4H 3N)]Ti(NMe 2) 2 and [1,3-{CH 2(2-C 4H 3N)} 2(η 5-C 5H 3)]Ti(NMe 2)

Reaction of ansa-cyclopentadienyl pyrrolyl ligand (C 5H 5)CH 2(2-C 4H 3NH) ( 2) with Ti(NMe 2) 4 affords bis(dimethylamido)titanium complex [(η 5-C 5H 4)CH 2(2-C 4H 3N)]Ti(NMe 2) 2 ( 3) via amine elimination. A cyclopentadiene ligand with two pendant pyrrolyl arms, a mixture of 1,3- and 1,4-{CH 2(2-C 4H 3NH)} 2C 5H 4 ( 4), undergoes an analogous reaction with Ti(NMe 2) 4 to give [1,3-{CH 2(2-C 4H 3N)} 2(η 5-C 5H 3)]Ti(NMe 2) ( 5). Molecular structures of 3 and 5 have been determined by single crystal X-ray diffraction studies.

Titanium eta1-pyrrolyl complexes: electronic and structural characteristics imposed by the N,N-di(pyrrolyl-alpha-methyl)-N-methylamine (dpma) ligand.

A new tridentate pyrrolyl-based ligand (dpma) has been utilized in the syntheses of two unusual titanium complexes. The trigonal bipyramidal species allow direct structural comparison between dialkylamido, pyrrolyl, and amine ligands within the same coordination sphere. Pyrrolyl ligands have greatly reduced π-donating ability relative to dialkylamides, which leads to Ti−N(pyrrolyl) distances that are ∼0.14 A longer than the dimethylamido substituents. Reduced π-donation relative to dialkylamido by the pyrrolyl substituents seems to result in enhanced Lewis acidity for dpma derivatives.