Fluorenyl Ligand Research Articles

NHC-ligated indenyl- and fluorenyl-substituted Alanes and Gallanes: synthons towards indenyl- and fluorenyl-bridged (AlC)n-heterocycles (n = 2,3).

Indenyl-(Ind) and fluorenyl-(Fl) substituted NHC-stabilized alanes and gallanes (NHC)·EH2R 1-12 (NHC = IiPrMe, IiPr, IMeMe; E = Al, Ga; R = Ind, Fl) were prepared via reaction of the corresponding NHC-iodoalanes and -gallanes with LiInd and LiFl, respectively. Analogously, the alane adducts with two Ind/Fl substituents (NHC)·AlHR213-18 (NHC = IiPrMe, IiPr, IMeMe; R = Ind, Fl) were obtained by using two equivalents of LiInd/LiFl. Elimination of indene and fluorene was induced thermally affording unusual dimeric and trimeric NHC-alane adducts {(NHC)·AlH2}2-μ-Fl 19-20 and {(NHC)·AlH-μ-R}n21-23 (R = Ind, Fl; n = 2, 3) with bridging indenyl and fluorenyl ligands.

Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes.

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl3 with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH2PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH2SiMe3 in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH2Py)Ln(CH2SiMe3)2(THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y3+ in the η5/κ1 mode to form a constrained geometry configuration. In the presence of excess AliBu3, and on activation with 1 equiv of [Ph3C][B(C6F5)4] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/AliBu3/[Ph3C][B(C6F5)4] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the pMOS-to-St feed ratios.

Triisobutylaluminium-promoted formation of lanthanide hydrides.

Discrete lanthanide(III) isobutylaluminates Ln[N(SiMe3)2](HAliBu3)(AliBu4) (Ln = La, Pr, Nd) are obtained from Ln[N(SiMe3)2]3 and triisobutylaluminium (TIBA). Nd[N(SiMe3)2](HAliBu3)(AliBu4) reacts with crown ether to give the ion pair [Nd(18-c-6){N(SiMe3)2}(HAliBu3)][AliBu4], featuring a strong Nd-H interaction in the solid state. The equimolar reaction of La[N(SiMe3)2](HAliBu3)(AliBu4) with fluorene resulted in the concomitant formation of [(μ-fluorenyl)3La2(μ-H)(HAliBu3)2] and (fluorenyl)2La[N(SiMe3)2]. [(μ-Fluorenyl)3La2(μ-H)(HAliBu3)2] features fluorenyl ligands with a μ-η6:η6 coordination around the hydrido-bridged dilanthanum core motif. The reported complexes are the first crystallographically characterized, ancillary ligand-free lanthanide(III) tetraisobutylaluminates, and display potential model systems for Ziegler-type polymerization catalysis.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

Cyclopentadienyl Complexes of the Alkaline Earths in Light of the Periodic Trends.

The electron-rich cyclopentadienyl and the analogous indenyl and fluorenyl ligands (collectively denoted here as Cp') have been impactful in stabilizing electron-deficient metal centers including the highly electropositive alkaline earths. Being in the s-block, the group 2 metals follow a major periodic variation in their atomic and ionic properties which is reflected in those Cp' compounds. This article presents an overview of this class of compounds for all the five metals from beryllium to barium (radium is excluded for its radioactivity), highlighting their systematic variation.

Imidazoline-2-imine Functionalized Fluorenyl Rare-Earth Metal Complexes: Synthesis and Their Application in the Polymerization of ortho-Methoxystyrene

We report the preparation of novel imidazoline-2-imine functionalized fluorenyl ligands with an ethylene bridge and their corresponding rare-earth metal complexes. Upon the activation of borate and triisobutyl aluminum (TIBA), all the rare-earth metal complexes could promote the syndiotactic polymerization of ortho-methoxystyrene (up to >99% rrrr), accompanying with the polar group activation effect via σ–π chelation of the methoxy and vinyl groups. The polymerization of 2-vinylprydiene was also performed.

Sandwich and Half-Sandwich Ln(II) (Ln = Sm, Yb) Complexes with Bulky Fluorenyl Ligands. Competitive Abstraction of H or SiMe3 from 2,7-tBu2-9-SiMe3-Fluorene by an Amido Anion

Sandwich and Half-Sandwich Ln(II) (Ln = Sm, Yb) Complexes with Bulky Fluorenyl Ligands. Competitive Abstraction of H or SiMe₃ from 2,7-<i>t</i>Bu₂-9-SiMe₃-Fluorene by an Amido Anion

Insights into Rare-Earth Metal Complex-Mediated Hydroamination

Since the precise understanding of the underlying mechanism is important for the rational design of catalysts, much attention has been paid for hydroamination reactions catalyzed by organolanthanides during the past three decades. Distinct mechanisms were proposed on the basis of some key experimental features. It is a challenge to distinguish these mechanisms. The present study focuses on this controversial topic by synthesizing an almost entire range of rare-earth metal bisalkyl complexes (Py-CH2-Flu)Ln(CH2SiMe3)2(THF)x (Ln = Sc (1), Lu (2), Tm (3), Er (4), Ho (5), Y (6), Dy (7), Tb (8), Gd (9), and Pr (10)) stablized by a pyridine methylene fluorenyl ligand to catalyze intramolecular hydroamination (IAHA) of prototypical 1-amino-2,2-diphenyl-4-pentene and intermolecular hydroamination (IEHA) of styrene and pyrrolidine. Among them, thulium-, terbium-, and gadolinium-based catalysts were investigated for the first time. As observed for all the reported catalytic systems, the rate of IAHA increased almost linearly with increasing metal ion radius, whereas the reactivity pattern in IEHA with respect to the ionic radius size follows the opposite trend. Kinetic studies were carried out to obtain the empirical rate law v = k[Ln]1.0[S]0.0 for IAHA and v = k[Ln]1.0[St]1.0[pyrrolidine]0.0 for IEHA. The zero-order dependence on amine was attributed to the population ratio between the rare-earth metal amido adduct and its precursor being larger than 104. Density functional theory studies on scandium, yttrium, and praseodymium complex-mediated IAHA and IEHA were investigated using a stepwise σ-insertive mechanism and a concerted noninsertive mechanism, respectively. The results suggested the prevailing mechanism to be a stepwise σ-insertive pathway that involves the insertion of C═C into the Ln–N bond and protonolysis of the Ln–C bond. The protonolysis reaction is the turnover-limiting step. The reason behind the influence of the metal ion radius on the catalytic activity was elucidated.

Synthesis and photophysics of gold(i) alkynyls bearing a benzothiazole-2,7-fluorenyl moiety: a comparative study analyzing influence of ancillary ligand, bridging moiety, and number of metal centers on photophysical properties.

Three new gold(i) alkynyl complexes (Au-ABTF(0-2)) containing a benzothiazole fluorenyl moiety, with either an organic phosphine or N-heterocyclic carbene as ancillary ligand, have been synthesized and photophysically characterized. All three complexes display highly structured ground-state absorption and luminescence spectra. Dual-luminescence is observed in all three complexes at room temperature in toluene after three freeze-pump-thaw cycles. The phosphine complexes (Au-ABTF(0-1)) exhibit similar photophysics with fluorescent quantum yields ∼0.40, triplet-state quantum yields ∼0.50, and fluorescent lifetimes ∼300 ps. The carbene complex Au-ABTF2 displays different behavior; having a fluorescent quantum yield of 0.23, a triplet-state quantum yield of 0.61, and a fluorescent lifetime near 200 ps, demonstrating that the ancillary ligand alters excited-state dynamics. The compounds exhibit strong (on the order of 105 M-1 cm-1) and positive excited-state absorption in both their singlet and triplet excited states spanning the visible region. Delayed fluorescence resulting from triplet-triplet annihilation is also observed in freeze-pump-thaw deaerated samples of all the complexes in toluene. DFT calculations (both static and time-resolved) agree with the photophysical data where phosphine complexes have slightly larger S1-T2 energy gaps (0.28 eV and 0.26 eV) relative to the carbene complex (0.21 eV). Comparison of the photophysical properties of Au-ABTF(0-2) to previously published dinuclear gold(i) complexes and mononuclear gold(i) aryl complexes bearing the same benzothiazole-2,7-fluorenyl moiety are made. Structure-property relationships regarding ancillary ligand, bridging moiety, and number of metal centers are drawn.

Thermally Stable Half-Sandwich Benzhydryl Ln(II) (Ln = Sm, Yb) Complexes Supported by Sterically Demanding Carbazolyl and Fluorenyl Ligands

A series of new isolable and thermally stable half-sandwich Ln(II) benzhydryl complexes coordinated by the sterically demanding ligands tert-butylcarbazol-9-yl [tBu4Carb]Ln[(p-tBu-C6H4)2CH](L) (Ln = Sm, L = DME (4); Ln = Yb, L = DME (5); Ln = Yb, L = TMEDA (6)) and 2,7-di-tert-butyl-fluoren-9-trimethylsilylyl [2,7-tBu2-9-Me3Si-C13H6]Yb[(p-tBu-C6H4)2CH](DME) (7) were synthesized by the alkane elimination reaction of [(p-tBu-C6H4)2CH]2Ln(Ln) (Ln = Sm, Yb) with tBu4CarbH and 2,7-tBu2-9-Me3Si-C13H7. X-ray analysis revealed that in 4, 5, and 7 the benzhydryl ligand is coordinated to the metal ion in an η3 coordination mode, while in 6 it is η1-bound. The type of coordination of the benzhydryl ligands in diamagnetic 5–7 is retained in their C6D6 solutions. Complexes 4–7 demonstrated unprecedented thermal stability and do not undergo decomposition after heating their solutions in C6D6 or toluene at 100 °C for 72 h. The reactions of [tBu4Carb]Ln[(p-tBu-C6H4)2CH](DME) (Ln = Sm (4), Ln = Yb (5)) with an excess of DME led to the formation of the symmetrical bis(carbazolyl) complex products [tBu4Carb]2Ln(DME)4 (Ln = Sm (8), Yb (9)) isolated in the form of separated ion pairs.

Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C₁-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes.

A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η3 manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol−1·h−1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure.

Rapid Syndiospecific (Co)Polymerization of Fluorostyrene with High Monomer Conversion.

Fluoromonomers are difficult to polymerize through a coordination mechanism owing to the strong chelation between fluorine and catalysts and the electron-deficient double-bond. We report herein the unprecedented polymerization of para-fluorostyrene (pFS) with excellent activity (1.12×107 g molLn-1 h-1 ), distinguished syndioselectivity (rrrr >99 %) and high conversion (98.4 %) using rare-earth-metal catalysts bearing a pyridyl methylene fluorenyl ligand. DFT calculations reveal polar fluorine loses overwhelming coordination priority to the active central metal ion due to the sterically bulky and electron-donating CGC-ligand, thus its power of poisoning the active species is dramatically weakened. Based on this, copolymerization of pFS and styrene (St) has been successfully achieved with high activity and controllable pFS insertion. Conversely, the unlinked half-sandwich rare-earth-metal system shows relatively lower activity, because both the transition-states and intermediates incorporate a μ1 -F chelated pFS.

Substituent Effects of Adamantyl Group on Amido Ligand in Syndiospecific Polymerization of Propylene with Ansa-Dimethylsilylene(Fluorenyl)(Amido) Zirconium Complex.

A series of new fluorenylamido-ligated zirconium complexes bearing an electron-donating adamantyl group on the amido ligand were synthesized and characterized by elemental analysis, 1H NMR, and single crystal X-ray analysis. The coordination mode of the fluorenyl ligand to the zirconium metal was η3 manner, and all the complexes were Cs-symmetric in solution. The complexes showed moderate activity (1.0 × 105 g-polymer mol-Zr−1·h−1), even at a low Al/Zr ratio of 50. The increase of propylene pressure improved the activity by one order of magnitude (up to 1.0 × 106 g-polymer mol-Ti−1·h−1). All catalyst systems gave syndiotactic polypropylene, where the complex containing the 3,6-di-t-butyl fluorenyl ligand was more effective for the enhancement of the syndiospecificity. The increase of propylene pressure also improved the syndiospecificity with the syndiotactic pentad of 0.96 and the melting point of 159 °C.

Fluorenyl Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-Earth Metals: Synthesis, Structure, and Isoprene Polymerization

Aiming at half-sandwich complexes of the type (FluR)Ln(AlMe4)2, homoleptic tetramethylaluminates Ln(AlMe4)3 (Ln = Y, La, Nd, and Lu) were treated with equimolar amounts of R-substituted potassium fluorenyls. The salt metathesis reaction of La(AlMe4)3 with K(Flu) (Flu = fluorenyl = C13H9) and K(FlutBu) (FlutBu = di(tert-butyl) fluorenyl) selectively gave the desired half-sandwich complexes (FluR)La(AlMe4)2. The corresponding reactions of Y(AlMe4)3 with K(Flu)/K(FlutBu) and Lu(AlMe4)3 with K(FlutBu) gave mixtures of half-sandwich and sandwich complexes, while treatment of Lu(AlMe4)3 with K(Flu) produced only the lutetocene complex (Flu)2Lu(AlMe4). Sterically more demanding 1-trimethylsilyl fluorenyl (FluSi) allowed for the isolation of half-sandwich complexes for the entire Ln(III) size range (Ln = La, Nd, Y, and Lu), in crystalline yields up to 94%. Upon activation with routinely employed borate or borane activators [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4], and B(C6F5)3, highly active initiators for isoprene polymerization were obtained. The catalyst activity as well as molecular weight (distribution) and stereoregularity of the obtained polyisoprenes are governed by the rare-earth metal size, fluorenyl ligand, and cocatalyst: highest activity for La/FluSi/[Ph3C][B(C6F5)4], lowest Mw/Mn = 1.11 for La/Flu/[PhNMe2H][B(C6F5)4], maximum trans-1,4 selectivity = 85% for La/FlutBu/[PhNMe2H][B(C6F5)4], maximum cis-1,4 selectivity = 78% for Lu/FluSi/[Ph3C][B(C6F5)4]. The formations of the active species were investigated by NMR spectroscopy revealing not only established cationization pathways but also fluorenyl abstraction in lanthanum complexes (Flu)La(AlMe4)2 and (FlutBu)La(AlMe4)2 by trityl borate [Ph3C][B(C6F5)4]. The reaction of half-sandwich complexes (FluR)Ln(AlMe4)2 with equimolar amounts of Me2AlCl did not give access to catalytically active species. Crystallization of binary mixtures (FluSi)Y(AlMe4)2/Me2AlCl in distinct molar ratios of 1:1 and 1:1.7 yielded complexes [(FluSi)Y(AlMe4)(μ-Cl)]2 and (FluSi)6Y6Cl12, respectively.

Living Polymerization of Propylene with ansa-Dimethylsilylene(fluorenyl)(cumylamido) Titanium Complexes.

A series of ansa-silylene(fluorenyl)(amido) titanium complexes (1a–1c, 2a, and 2b) bearing various substituents on the amido and fluorenyl ligands are synthesized and characterized by elemental analysis, 1H NMR, and single crystal X-ray analysis. The coordination mode of the fluorenyl ligand to the titanium metal is η3 manner in each complex. The propylene polymerization is conducted with these complexes at 0 and 25 °C in a semi batch-type method, respectively. The catalytic activity of 1a–1c bearing cumyl-amido ligand is much higher than that of 2a and 2b bearing naphthyl group in amido ligand. High molecular weight polypropylenes are obtained with narrow molecular weight distribution, suggesting a living nature of these catalytic systems at 0 °C. The polymers produced are statistically atactic, regardless of the structure of the complex and the polymerization temperature.

Rare-earth metal hydrides supported by silicon-bridged boratabenzene fluorenyl ligands: synthesis, structure and reactivity.

The reactions of rare-earth metal benzyl complexes supported by silicon-bridged boratabenzene fluorenyl ligands with PhSiH3 in toluene gave the corresponding dinuclear hydrides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-H)(THF)]2 (3-Ln; Ln = La, Nd, Gd), wherein the rare-earth metal ions are linked by both silicon-bridged boratabenzene fluorenyl ligands and hydrido ligands. The reactivity of these hydrides toward unsaturated substrates was studied. Among these, alkynides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-CCPh)]2 (4-Ln; Ln = La, Nd) were obtained via the σ-bond metathesis reaction, when 3-Ln (Ln = La, Nd) was treated with phenylacetylene. While reacting with 3-hexyne, the mono-addition product [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln]2(μ-H)[μ-C(Et)[double bond, length as m-dash]C(H)Et] (5-Ln; Ln = La, Nd) was formed. Further investigations on the reactivity of 3-La displayed that benzonitrile and tert-butyl isonitrile readily inserted into the La-H bonds, affording an azomethine complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ-N[double bond, length as m-dash]C(H)Ph}]2 (6-La) and an N-tert-butylformimidoyl complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ,η2-C(H)[double bond, length as m-dash]NtBu}]2 (7-La), respectively. The reaction with N,N'-diisopropylcarbodiimide at room temperature or at 75 °C gave a dimeric complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La]2(μ-H)[μ-N(iPr)CHN(iPr)] (8-La) or a monomeric complex [Me2Si(C13H8)(C5H4BNEt2)]La[N(iPr)CHN(iPr)] (9-La), respectively.

Theoretical investigation of the mechanism of syndiospecific propylene polymerization using ansa-dimethylsilylene(fluorenyl)(amido)titanium complexes

Theoretical study on the propylene polymerization using ansa-dimethylsilylene(fluorenyl)(amido)dimethyltitanium complexes were performed and related to the experimental results. The calculated activation energies for coordination-insertion of propylene via four different conformations after the first monomer insertion showed that propylene coordinates to the titanium center avoiding the steric repulsion of polymer chain, which was placed toward the amido group. The bulkiness of the amido groups was closely related to the frequency of the chain-migration without monomer insertion, probably because the bulky amido group would force the fluorenyl ligand to coordinate to the titanium center in η1-manner. These theoretical results well explained the experimental ones.

Synthesis and Structure of Silicon-Bridged Boratabenzene Fluorenyl Rare-Earth Metal Complexes

A silicon-bridged boratabenzene fluorenyl ligand [Me2Si(C13H8)(C5H4BNEt2)]2– (L2–) was designed and synthesized. By employment of this ligand, two divalent rare-earth metal complexes [Me2Si(C13H8)(C5H4BNEt2)]Ln(THF)2 (Ln = Sm (1), Yb (2)) were obtained from salt metathesis of K2[Me2Si(C13H8)(C5H4BNEt2)] (K2L) with LnI2(THF)2 in THF. Complex 2 undergoes redox reaction with cyclooctatetraene to give a trivalent Yb complex [(C8H8)Yb]2[μ-{Me2Si(C13H8)(C5H4BNEt2)}2] (3), accompanied with oxidative coupling of two fluorenyl groups. A series of chloro-bridged trimeric trivalent rare-earth metal complexes [Li(THF)4]2[{[Me2Si(C13H8)(C5H4BNEt2)]Ln(μ-Cl)Li(THF)3}3(μ-Cl)3(μ3-Cl)2] (Ln = Nd (4), Sm (5), and Gd (6)) were synthesized by reactions of Li2[Me2Si(C13H8)(C5H4BNEt2)] (Li2L) with LnCl3 in THF. Treatment of K2[Me2Si(C13H8)(C5H4BNEt2)] (K2L) with LnI3(THF)n gave the monomeric complexes [Me2Si(C13H8)(C5H4BNEt2)]LnI(THF) (Ln = La (7), Nd (8), Sm (9), and Gd (10)). These iodides were subsequently reacted with K[CH2...

Iridium complexes containing N-donor-functionalized η1-fluorenyl ligands

Iridium complexes of two different nitrogen-donor-functionalized fluorenyl ligands have been synthesized and characterized, L1Ir(COD) and L2Ir(COD), where L1−=[9-(2-dimethylamino)ethyl]fluorenyl anion, L2−=[9-(2-ortho-pyridyl)ethyl]fluorenyl anion, and COD=1,5-cyclooctadiene. The structures of both ligands (in their protonated form) and of both complexes were determined by single-crystal X-ray crystallography. Structural consequences of the nature of the nitrogen ligand (dimethylamino substituent versus ortho-pyridyl substituent) are significantly different Ir–N distances (shorter for L2Ir(COD)) and indirect cis-influence on the COD ligand resulting in a shorter Ir–olefin bond cis to the nitrogen donor in L2Ir(COD). Both complexes act as precatalysts for arene hydrogenation.

Copolymerization of isoprene with ethylene catalyzed by cationic half‐sandwich fluorenyl scandium catalysts

ABSTRACTIsoprene polymerization and copolymerization with ethylene can be carried out by using cationic half‐sandwich fluorenyl scandium catalysts in situ generated from half‐sandwich fluorenyl scandium dialkyl complexes Flu'Sc(CH2SiMe3)2(THF)n, activator, and AliBu3 under mild conditions. In the isoprene polymerization, all of these cationic half‐sandwich fluorenyl scandium catalysts exhibit high activities (up to 1.89 × 107 g/molSc h) and mainly cis−1,4 selectivities (up to 93%) under similar conditions. In contrast, these catalysts showed different activities and regio‐/stereoselectivities being significantly dependent on the substituents of the fluorenyl ligands in the copolymerization of isoprene with ethylene under an atmosphere of ethylene (1 atm) at room temperature, affording the random copolymers with a wide range of cis−1,4‐isoprene contents (IP content: 64 − 97%, cis−1,4‐IP units: 65 − 79%) or almost alternating copolymers containing mainly 3,4‐IP‐alt‐E or/and cis−1,4‐IP‐alt‐E sequences. Moreover, novel high performance polymers have been prepared via selective epoxidation of the vinyl groups of the 1,4‐isoprene units in the IP‐E copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2898–2907