Fluorenyl Ligand Research Articles

Synthesis, Structure and Reactivity of Lanthanocene Complexes

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Synthesis, Structure and Reactivity of Lanthanocene Complexes

AbstractA variety of lanthanocene complexes, e. g. chlorides, hydrocarbyls, amides, hydrides and divalent derivatives, were synthesized by using a series of designed cyclopentadienyl, indenyl and fluorenyl ligands with ring bridges or donor‐functionalized sidearms. X‐Ray crystallographic analyses reveal the formation of intramolecular coordination bonds between central metals and heteroatoms (O, N) in sidearms or bridging chains. Some applications of these complexes are also discussed in this account.

“Alkaline-Earth Metals in a Box”: Structures of Solvent-Separated Ion Pairs

During our research on homoleptic organocalcium compounds, we found that fluorenylcalcium complexes show unusual solution behavior and precipitate from nonpolar solvents after addition of THF. Their solid-state structures reveal the unexpected rupture of both metal-carbanion bonds by the polar solvent THF. The crystal structures of five new Mg and Ca solvent-separated ion pairs are described. The compound [Ca(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is the first organometallic complex of a Group 2 element that crystallizes as a completely solvent-separated ion pair. The driving forces for its formation are: 1) the strong Ca-THF bond; 2) the stability of the free [Me(3)Si(fluorenyl)](-) ion; 3) encapsulation of [Ca(2+)(thf)(6)] in a "box", the walls of which consist of anionic fluorenyl ligands and benzene molecules; and 4) the presence of numerous (THF)C- H...pi interactions. The magnesium analogue [Mg(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is isostructural. Bis(7,9-diphenylcyclopenta[a]acenaphthadienyl)calcium also crystallizes as a completely solvent-separated ion pair and can likewise be described as a [Ca(2+)(thf)(6)] species in a box of delocalized anions and benzene molecules. In addition, the structures of two Ph(4)B(-) complexes of Mg and Ca are described. [Mg(2+)(thf)(6)][Ph(4)B(-)](2) crystallizes as a completely solvent-separated ion pair and also shows a solvated metal cation bonded via C-H.pi interactions in a cavity formed by Ph(4)B(-) ions. [(thf)(4)CaBr(+)][Ph(4)B(-)] has a structure in which one of the anionic ligands is still bonded to the Ca atom. Bridging bromide ligands result in the formation of the dimer [(thf)(4)CaBr(+)](2).

Catalytic regioselective introduction of allyl alcohol into the nonpolar polyolefins: development of one-pot synthesis of hydroxyl-capped polyolefins mediated by a new metallocene IF catalyst.

A new catalytic regioselective one-pot synthesis of hydroxyl-capped polyolefins is reported. This synthesis employs a new stereorigid bridged metallocene having an indenyl and a fluorenyl ligand named IF catalyst 1, exhibiting high catalytic performances. Here, we report on (1) the first example of allyl alcohol incorporation into the nonpolar polymer backbone using IF catalyst 1 and methylaluminoxane with high activity, high molecular weight, and high polar monomer uptake at high temperature, and (2) the first example of predominant end-site-selective introduction of an alcohol group into the polyolefins. Moreover, we observed the mixed regioselectivity by the type of alkylaluminum.

A dioxotetraamine fluorenyl ligand and its nickel(II) complex — crystal structure and fluorescent sensing properties in aqueous solution

A new ligand consisting of fluorenyl and dioxotetraaza units, namely, 2,10-diamino-6-(9 H-fluoren-9-yl)-4,8-diazaundecane-5,7-dione ( L), and its nickel(II) complex were synthesized. The crystal structure of [Ni(H −2L)] showed that Ni(II) is in a square planar coordination environment. Studies of solution chemistry of the ligand and its nickel(II) complex indicate that the ligand can form a stable complex with Ni 2+ ions and fluorescence quenching of the ligand is accompanied by the coordination of the metal ion to the dioxotetraaza unit and electron transfer from the Ni(II) center to fluorenyl in aqueous solution.

Fluorenyl derivatives of early transition elements: a synthetic and structural study

The tetracarbonyls of niobium(I) and tantalum(I), M(η 5-9-phenylfluorenyl)(CO) 4, have been prepared from the dinuclear tetracarbonyl anions [M 2(μ-Cl) 3(CO) 8] − and Li(9-phenylfluorenyl). A slightly distorted four-legged piano stool geometry, due to the presence of the sterically demanding phenyl substituent, has been found in the case of the niobium derivative. The crystal and molecular structures of Zr(fluorenyl) 2Me 2 and of the 9-phenyl-substituted derivative have been solved. The structure of Zr(fluorenyl) 2Me 2 is similar to that of the known dichloride, Zr(fluorenyl) 2Cl 2, where fluorenyl ligands of different hapticity are present. On the other hand, the use of the more sterically demanding phenyl-substituted fluorenyl ligand in Zr(η 5-9-phenylfluorenyl) 2Me 2, induces the fluorenyl ligands to be symmetrically and pentahapto-coordinated to zirconium.

Aminofluorenyl−Pentamethylcyclopentadienyl and Bis(aminofluorenyl) Derivatives of Group 4 Metals

New group 4 compounds containing a 9-(dialkylamino)fluorenyl ligand have been prepared, and their properties and reactivities have been briefly investigated. Single-crystal X-ray analysis of {9-(N,N-dimethylamino)fluorenyl}2ZrCl2 (4) reveals strong zirconium−nitrogen dative bonds. The asymmetric unit contains two molecules with an unusual coordination of aminofluorenyl ligands, best described as comprised of a strong Zr−N dative interaction and essentially an η1-fluorenyl coordination, supplemented by a weak additional CC dative interaction of one double bond of one of the benzo units. The barrier to rotation around the C−N bond of {9-(N,N-diisopropylamino)fluorenyl}(pentamethylcyclopentadienyl)ZrCl2 (9) has been determined: ΔG⧧(−25 °C) = 11.1 kcal·mol-1. Unlike related aminoborollide complexes, aminofluorenyl complexes resist quaternization by alkyl halides. Several aminofluorenyl complexes have been tested for propylene polymerization behavior in the presence of methylaluminoxane (MAO); atactic polypropylene is obtained with very low activities. The syntheses of 9-(dialkylamino)fluorene compounds are described, as are the syntheses of group 4 compounds via the corresponding 9-(dialkylamino)fluorenide lithium salts.

Novel 18-crown-6 organometallic rubidium and cesium complexes containing cyclopentadienyl, indenyl, pentamethylcyclopentadienyl, and fluorenyl as carbanions

The synthesis of base-free cyclopentadienyl-, indenyl-, pentamethylcyclopentadienyl-, and fluorenylrubidium and -cesium is described. Reactions of these compounds with the hexadentate Lewis base 18-crown-6 yielded new complexes of the type [MR(18-crown-6)] and [{RbFl(18-crown-6)} 2(L)] (M=Rb, Cs; R=Cp, Ind, Cp*, Fl; L=dimethoxyethane, dioxane). All complexes were characterized by NMR spectroscopy and X-ray structure analysis. The dominating structure element in the investigated complexes is an [MR(18-crown-6)] unit in which the alkali metal ion is in close contact with the six oxygen atoms of the crown ether. In addition, a multihapto π-interaction between the cation and carbanion was found. For all isolated complexes containing the fluorenyl ligand, [MFl(18-crown-6)] and [{RbFl(18-crown-6)} 2(L)], only a η 2 coordination of the aromatic C–C bond between the C 5- and C 6-ring to the metal ions was observed.

High-temperature ethylene/?-olefin copolymerization with a zirconocene catalyst: Effects of the zirconocene ligand and polymerization conditions on copolymerization behavior

Copolymerizations of ethylene and α-olefin with various zirconocene compounds at a high temperature were carried out to study the relationship between the ligand structure of zirconocene compounds and the copolymerization behavior. All of the indenyl-based zirconocene compounds in combination with dimethylanilinium tetrakis (pentafluorophenyl) borate/triisobutylaluminum produced only low molecular weight copolymers at a high temperature, regardless of the substituents and bridged structures of the zirconocene compounds. However, zirconocene compounds with a fluorenyl ligand gave rise to a significant increase in the activity and molecular weight of the copolymers by the selection of a diphenylmethylene bridge structure even at a high temperature. Ethylene/1-hexene copolymers obtained with the fluorenyl-based catalysts contained inner double bonds accompanied by the generation of hydrogen, presumably because of a C-H bond activation mechanism. The contents of the inner double bonds were significantly influenced by the polymerization conditions, including the 1-hexene feed content, polymerization temperature, and ethylene pressure.

Enantiospecific synthesis of a planar chiral fluorenylzirconium ansa-metallocene: synthesis and structures of [1-(9-fluorenyl)- and [1-(1-methyl-9-fluorenyl)-2-(2-indenyl)naphthalene]zirconium dichloride

Di-lithiation of +ac(R)-1-methyl-9-[2-(2-indenyl)-1-naphthyl]fluorene, +ac(R)-6, generates an axially chiral fluorenyl ligand, (a-S)-10, which on reaction with ZrCl4 enantiospecifically provides the planar chiral ansa-zirconocene (p-S)-[1-(1-methyl-9-fluorenyl)-2-(2-indenyl)naphthalene]zirconium dichloride, (p-S)-8; single crystal X-ray structures have been determined for the racemic ansa-zirconocene rac-8 and the related Cs-symmetric ansa-zirconocene 7.

Exocyclic Coordination of the η3-Fluorenyl Anion: Experimental and Theoretical Study

The novel (η5-Ind)Mo(η3-Flu)(CO)2 (Ind = indenyl, C9H7; Flu = fluorenyl, C13H9) can be readily prepared from (η5-Ind)MoCl3(CO)2 and LiFlu in toluene (90% yield). X-ray crystallographic studies show an exocyclic η3 coordination for the fluorenyl ligand, which is also predicted from dft calculations.

Ethylene/1-hexene copolymerization with Ph2C(Cp)(Flu)ZrCl2 derivatives: correlation between ligand structure and copolymerization behavior at high temperature

Ethylene homo- and copolymerization with 1-hexene were performed in the presence of diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) derivatives activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH.(C 6 F 5 )4)/triisobutylaluminium (i-Bu 3 Al) or methylaluminoxane (MAO) to study the role of the substituent on activity, comonomer incorporation and molecular weight. C 1 symmetric metallocenes which have several substituents in β-position of the cyclopentadienyl ligand produce lower molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst at 200 °C, whereas the copolymerization reactivity is significantly influenced by the volume of the substituent: the trimethylsilyl substituted derivative produces ethylene/1-hexene copolymers with a broad chemical composition distribution. Polyethylene obtained with the diphenylmethylidene(cyclopentadienyl)(indenyl)zirconium dichloride (Ph 2 C(Cp)(Ind)ZrCl 2 ) based catalyst is branched, and the molecular weight distribution and the chemical composition distribution are significantly affected by the cocatalyst. C s symmetric metallocenes which have alkyl substituents in 2,7 position of the fluorenyl ligand produce higher molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst with equal copolymerization reactivity.

Unbridged bivalent lanthanidocenes for isotactic and stereomultiblock polymerization of methyl methacrylate

Bivalent organolanthanides with unbridged substituted indenyl or fluorenyl ligands (1-SiMe 3 Ind) 2 Yb-THF (I), (9-SiMe 3 Flu) 2 Yb-THF (II), were found to efficiently catalyze the stereoregular polymerization of methyl methacrylate. The microstructure of resultant polymers was shown to be dependent of a conformation that the ligands adopt at the polymerization temperature. The formation of isotactic rich PMMAs from complex II was proposed to be associated with the fluctuation of the 9-trimethylsilylfluorenyls around a C 2 symmetric twisted-conformation. The formation of the multi(syndioPMMA-block-iso-PMMA) polymers from the mixture of rac- and meso-isomers of I was rationalized on the basis of competing conjugate addition and inversion of the metallocene conformation. Surprisingly, both rac- and meso-isomers of I were found to operate with similar activity and stereospecifity, although the stereospecific operation of the meso-form was not completely understandable.

Unbridged bivalent lanthanidocenes for isotactic and stereomultiblock polymerization of methyl methacrylate

Bivalent organolanthanides with unbridged substituted indenyl or fluorenyl ligands (1-SiMe3Ind)2YTHF (I), (9-SiMe3Flu)2YTHF (II), were found to efficiently catalyze the stereoregular polymerization of methyl methacrylate. The microstructure of resultant polymers was shown to be dependent of a conformation that the ligands adopt at the polymerization temperature. The formation of isotactic rich PMMAs from complex II was proposed to be associated with the fluctuation of the 9-trimethylsilylfluorenyls around a C2 symmetric twisted-conformation. The formation of the multi(syndioPMMA-block-iso-PMMA) polymers from the mixture of rac- and meso-isomers of I was rationalized on the basis of competing conjugate addition and inversion of the metallocene conformation. Surprisingly, both rac- and meso-isomers of I were found to operate with similar activity and stereospecifity, although the stereospecific operation of the meso-form was not completely understandable. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1599–1606, 1998

Ethene-Norbornene Copolymerization with Homogeneous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 4. Development of Molecular Weights.

The molecular weights of ethene-norbornene copolymers, produced with various metallocene- and amidocyclopentadienyl-methylaluminoxane (MAO) catalysts, have been determined by high-temperature gel-permeation chromatography: with one exception, increasing molecular weights were found with an increasing norbornene content in the copolymer. This observation is due to the fact that the beta-hydride elimination process is not possible in the case of norbornene, because of special steric conditions of the cis-2,3-exo inserted norbornene; other possible termination reactions are discussed, considering the specialties of the norbornene. The effect of the catalyst structure on the molecular weights is discussed in terms of steric and electronic factors of the different ligands: sterically less hindered ligands produce ethene-norbornene copolymers with relatively low molecular weights; ligands with a larger extension and electron-pushing effect such as the fluorenyl ligand, induced the formation of high molecular weights. Additional alkyl groups at the indenyl or fluorenyl ligand increased the molecular weights additionally.

Fluorenyl complexes of zirconium and hafnium as catalysts for olefin polymerization

In the continuously expanding panorama of Group 4 metallocene complexes and the extensive research devoted to their use as olefin polymerization catalysts, fluorenyl complexes of zirconium and hafnium play a very special role. This singularity can be explained in terms of a particularly versatile bonding potential of the fluorenyl ligand causing a facile change from η5 → η3 → η1 (ring slippage) and thus providing new coordination sites in catalytic cycles. The substitution of fluorenyl ligands in unbridged or bridged (ansa) metallocene complexes allows the variation of steric requirements and symmetry of these complexes. Both parameters have a strong influence on the catalytic activity and stereospecifity as soon as these catalyst precursors are activated with cocatalysts like methylalumoxane (MAO). Synthetic methods, X-ray structures and catalyst activities are discussed for several compounds together with updated literature.

The First Monofluorenyl Zirconium Trichloride

AbstractThe monofluorenyl zirconium complex [(.(5):.1‐C13H8CH2CH2OMe)ZrCl2(μ‐Cl)]2, (2), has been obtained bby reaction of the respective fluorenyl lithium derivative with ZrCl4 in diethyl ether. A single‐crystal X‐ray structural analysis shows that 2 is a chloride‐bridged dimer, in which the fluorenyl ligand is bonded in a transitional tri‐ to pentahapto fashion. The relatively weak fluorenyl–zirconium bond is stabilized by intramolecular coordination of the ether sidechain attached to the fluorenyl backbone. Despite this, the bidentate ligand is easily detached upon dissolution of 2 in THF. Simultaneous ether cleavage produces spiro[cyclopropane‐1,9′‐fluorene].

Sterisch überladene Zirconocenkomplexe—erstes Beispiel für einen σ-gebundenen Fluorenylliganden

The reaction of Cp 2ZrCl 2 (C p = η 5-C 5H 5) with one or two equivalents of fluorenyl lithium (C 13H 9Li) results in the formation of the mono and disubstitution products Cp 2Zr( η 1-C 13H 9)Cl and Cp 2Zr( η 1-C 13H 9) 2. The corresponding Cp′ derivative (Cp′ = η 5-C 5H 4Me) gives analogous products. Instead of fluorenyl lithium, 2,7-di(methyl) fluorenyl lithium can also be applied in the reaction. The η 1 bonding mode of the fluorenyl ligand in Cp 2Zr( η 1-C 13H 9)Cl could be demonstrated by an X-ray structure. The dynamic behaviour of the cyclopentadienyl ligands in the products is described by temperature-dependent 1H NMR spectroscopy.

Syntheses and characterization of zirconium and hafnium complexes of amido-fluorenyl ligands [(NBut)SiMe2CH2(C13H8)]2− and [(NPri)SiMe2CH2(C13H8)]2−

Abstract The reaction of PriN(H)SiMe2CH2Cl with two equivalents of fluorenyllithium in THF led to [PriN(H)SiMe2CH2(C13H8)]Li(THF) (1) in high yield. X-ray diffraction studies of 1 revealed a monomeric structure with an η2-coordinated fluorenyl ligand. Lithiation followed by the treatment with zirconium or hafnium tetrachloride afforded the corresponding dichloro complexes [(η1-NPri)SiMe2CH2(η5-C13H8)]ZrCl2 (2) and [(η1-NPri)SiMe2CH2(η5-C13H8)]HfCl2 (3). These metal adducts were characterized by NMR spectroscopy, and in the case of 3 also by X-ray diffraction. Compound 3 shows a weak interaction between the formally 14-electron Hf center and the C-H of the isopropyl group. The dialkyl compound [(η1-NBut)SiMe2CH2(η5-C13H8)]Zr(CH2SiMe3)2 (4) was prepared from Me3SiCH2MgCl and [(η1-NBut)SiMe2CH2(η5-C13H8)]ZrCl2. The NMR spectroscopic and X-ray data point to a fairly congested environment around the zirconium atom. In contrast to the —SiMe2— bridged analogs, the —SiMe2CH2— linked amido-fluorenyl complex 4 features a relatively unstrained ligand backbone with a close to ideal trigonal planar geometry at the amido nitrogen atom.

Structural Studies of {9-[2-(Dimethylamino)ethyl]fluorenyl}lithium Compounds

Two lithium compounds of the substituted fluorenyl ligand 9-[2-(dimethylamino)ethyl]fluorenyl (FlN) have been prepared and isolated. The X-ray crystal structures of FlNLi·Et2O (2) and FlNLi·2THF (3) have been obtained. In 2 the lithium atom is coordinated η5 to the fluorenyl anion while 3 exhibits an η2 arrangement. Structural details have been analyzed to provide additional insights regarding the nature of the lithium-π interactions in organolithium compounds with delocalized π-systems.