Cationic Metallocene Research Articles

Formation and structural properties of salicylaldiminato complexes of zirconium and titanium

The metallocene cation [Cp2ZrCH3(THF)+] (2, with BPh4− anion) reacts with N-isopropylsalicylaldimine (1a) by liberation of methane and formation of the pseudotetrahedral [(κO,κN-salicylaldiminato)ZrCp2+] complex 3 that was characterized by X-ray diffraction. Deprotonation of 1a by treatment with n-butyllithium yields the corresponding lithiated reagent 4a, that exhibits a tetrameric structure in the crystal, featuring a cubic Li4O4 core structure. Treatment of 4a with Zr(NMe2)2Cl2(dme) (5) yields the octahedral bis(N-isopropylsalicylaldiminato)Zr(NMe2)2 complex 7a. The X-ray crystal structure analysis of 7a has revealed that the aldiminato oxygen atoms of the κO,κN-chelate ligand are oriented trans to each other at the central metal atom. Treatment of the N-isopropyl, the N-cyclohexyl- and the N-(2,6-diisopropylphenyl)salicylimines (1a,b,d) with the reagent Zr(NMe2)4 (6) directly results in the formation of the respective octahedral (lig)2Zr(NMe2)2 complexes 7a, 7b (also characterized by X-ray diffraction), and 7d in good yields. Treatment of 7b and 7d with Me3Si-Cl replaced the -NMe2 substituents by chloride to yield the corresponding lig2ZrCl2 complexes 8b and 8d, respectively. The X-ray crystal structure analysis of 8d showed an octahedral coordination with the aldiminato nitrogen atoms of the κO,κN-chelate ligands now being trans-oriented at zirconium. Complex 8b undergoes an enantiomerization process that is followed by dynamic NMR spectroscopy (ΔG≠enant. (268 K)≈12 kcal mol−1). Titanium tetrachloride forms a neutral 1:2 adduct with 1d. The NMR analysis and X-ray crystal structure analysis of the resulting bisbetaine-type adduct 9d reveals the formation of an octahedral titanium complex that contains two trans-Ti-O(aryl) bonds. The phenolic hydrogen atoms were transferred to the aldimine nitrogens to form an intramolecular iminium salt. Two equivalents of HCl are removed from 9d by treatment with NEt3 to yield the bis[N-(2,6-diisopropylphenyl)salicylaldiminato]TiCl2 complex 10d (characterized by X-ray diffraction). In a one-pot procedure TiCl4 reacts with N-phenylsalicylaldimine (1c) and triethylamine in a 1:2:2 ratio to directly yield the corresponding (κO,κN-lig)2TiCl2 complex 10c. The X-ray crystal structure analysis of 10c reveals a trans-orientation of ligand oxygen atoms, just like in the adduct intermediate 9. Upon activation with methylalumoxane the complexes 8d, 10c, and 10d form catalysts for the polymerization of ethene.

Functionalized polystyrene as a versatile support for olefin polymerization catalysts

Heterogeneous polyolefin catalysts based on metallocenium salts of weakly coordinating anions can be prepared via a series of simple reactions from lightly crosslinked chloromethylated polystyrene beads. Catalytic sites are distributed homogeneously throughout the polystyrene particles. The nonporous nature of these catalysts affords a high degree of control over the olefin uptake rate, avoiding problems of premature catalyst fragmentation that often plague high-surface-area heterogeneous catalysts based on highly reactive species. The choice of amine as the means of binding or templating allows catalysts based on a wide variety of metallocenes to be readily prepared by the same synthetic approach. The dative interactions between the metallocene cation and the amine functionality of the support material are sufficient to prevent extraction under polymerization conditions to yield excellent particle morphology of the polyolefin product, but they are not so strong as to affect the nature of the polyolefin produced. The polymer-supported catalysts have been used effectively for the polymerization of ethylene and polypropylene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2979–2992, 2000

Formation of the [(s-trans-η4-Butadiene)TaCp*Cp]+ Cation and Its Reaction with Organic Carbonyl Derivatives

(Butadiene)TaCp*Cl2 (6) was treated with CpNa to yield (η2-butadiene)TaCp*CpCl (7). Subsequent reaction with [Cp2ZrCH3+][CH3B(C6F5)3−] resulted in transfer of the chloride ligand from tantalum to zirconium with formation of the [(s-trans-η4-butadiene)TaCp*Cp]+ cation [8, with CH3B(C6F5)3− anion]. Complex 8 was characterized spectroscopically and by an X-ray crystal structure analysis. The group-5 [(s-trans-η4-C4H6)TaCp*Cp]+ bent metallocene cation complex 8 reacts with ketones (acetone, adamantanone) to yield the corresponding seven-membered 2-tantalatetrahydrooxepine cation complexes (9, 10). 1-Cyanoadamantane reacts with 8 to yield the 2-tantala-3,6-dihydro-2H-azepine cation system 11. Activation of 8 with methylalumoxane gives an active ethene polymerization catalyst.

Group-4 Metallocene Cation Complexes of Oligopeptides: Reaction of [Cp2ZrCH3(THF)+BPh4] with Boc-Protected Di- and Tripeptide Esters

Group-4 Metallocene Cation Complexes of Oligopeptides: Reaction of [Cp2ZrCH3(THF)+BPh4] with Boc-Protected Di- and Tripeptide Esters

Group-4 Metallocene Cation Complexes of Oligopeptides: Reaction of [Cp2ZrCH3(THF)+BPh4−] with Boc-Protected Di- and Tripeptide Esters

Group-4 Metallocene Cation Complexes of Oligopeptides: Reaction of [Cp2ZrCH3(THF)+BPh4−] with Boc-Protected Di- and Tripeptide Esters

Oxidation of [M(η-C5H5)2], M = Cr, Fe or Co, by the new Brønsted acid H2O·B(C6F5)3 yielding the salts [M(η-C5H5)2]+A−, where A− = [(C6F5)3B(μ-OH)B(C6F5)3]− or [(C6F5)3BOH · · · H2OB(C6F5)3]− †

The Bronsted acids H2O·B(C6F5)3 and D2O·B(C6F5)3 have been synthesized. Reaction of neutral divalent metallocenes [M(η-C5H5)2], M = Cr, Fe or Co, with two equivalents of H2O·B(C6F5)3 2a resulted in metallocene oxidation and formation of salts containing [M(η-C5H5)2]+ cations together with the hydroxoborate anion [HOB(C6F5)3]– which is hydrogen bonded to the second acid equivalent, namely [M(η-C5H5)2][(F5C6)3BOH· · ·H2OB(C6F5)3], M = Cr 3a, Fe 4a or Co 5a. Treatment of one equivalent of 2a and one equivalent of B(C6F5)3 1 with [M(η-C5H5)2] yielded salts containing the same metallocene cations but now with µ-OH bridged anions, as in [M(η-C5H5)2][(F5C6)3B(µ-OH)B(C6F5)3], where M = Cr 3b or Co 5b. All products have been characterised by NMR spectroscopy, elemental analysis, and the single-crystal structures of 2a, 3a, 4a, and 5a have been determined.

Developing a fulvene route to C 1 -bridged “constrained geometry” Ziegler catalyst systems

6-dimethylamino-6-methylfulvene (7) was converted to the [(C5H4)–CMe2–NMe2]− ligand system (8) by treatment with methyllithium. Its reaction with MCl4 (M = Zr, Ti) followed by treatment with CH3Li gave the respective [(C5H4)–CMe2–NMe2]2M(CH3)2 complexes (12). Their reaction with B(C6F5)3 led to reactive metallocene cation complexes that instantaneously underwent CH activation at a N–CH3 group to yield the metallacyclic cation complexes 15. (tert-butylaminomethyl)fluorene was prepared by the addition of tert-butylisocyanate to fluorenyllithium followed by hydride reduction. Deprotonation by a variety of bases gave rise to a series of competing and consecutive reactions to yield several unusually structured products, among them a fluorenyl-anellated η5-1-azapentadienyl anion equivalent (25) and [(flu)-CH2–NCMe3]Li2 (23). An improved way of generating synthetically useful C1-linked [Cp–C1(R) n –NR1]2- dianion equivalents was developed starting from 6-amino-6-methylfulvene (26). N-silylation followed by double deprotonation with, e.g., lithium diisopropylamide cleanly furnished the respective [(C5H4)–C(=CH2)–NSiMe3]2- dianion 33 (isolated as the dilithio derivative). Its reaction with Cl2Zr(NEt2)2 in THF gave [η5:κ-N-(C5H4)–C(=CH2)–NSiMe3]Zr(NEt2)2 36. Activation of 36 with methylalumoxane in toluene led to the formation of a C1-linked “constrained geometry” Ziegler catalyst that polymerized ethylene similarly as the [(C5Me4)SiMe2NCMe3]ZrCl2 derived literature system.

Unexpected alkyl-substituent exchange during the formation of a cationic bis(zirconocene) complex that contains a planar four-co-ordinate carbon atom

Treatment of the alkyl Group 4 metallocene cation reagent [ZrCp2{CH2Si(CH3)3}(THF)]+[BPh4]– 2b with bis(propynyl)zirconocene 1a yielded the cationic dimetallic complex [(ZrCp2)2(µ-η1∶η2-CH3CCCH3){µ-κ2-CCCH2Si(CH3)3}]+ 3d with BPh4– anion. Complex 3d was characterized spectroscopically and by a crystal structure analysis. It contains a planar four-co-ordinate carbon atom, which is stabilized by the interaction with both Group 4 metal centres. Finding the CH2Si(CH3)3 substituent, that originates from the alkylzirconocene reagent, attached at the µ-acetylide ligand in the final product is unusual. A reversible alkynyl carbometallation sequence is proposed to account for the observed selective formation of 3d. Complex 3d reacted with alkyl isocyanides RNC (R = CMe2CH2CMe3, CMe3, or cyclohexyl) by replacement of the µ-η1∶η2-CH3CCCH3 ligand to form the µ-isocyanide complexes [(ZrCp2)2(µ-η1-C∶η2-C,N-RNC){µ-κ2-CCCH2Si(CH3)2}]+ (with BPh4– anion) of which one was characterized by a crystal structure analysis.

Supported Organometallics. Highly Electrophilic Cationic Metallocene Hydrogenation and Polymerization Catalysts Formed via Protonolytic Chemisorption on Sulfated Zirconia

Supported Organometallics. Highly Electrophilic Cationic Metallocene Hydrogenation and Polymerization Catalysts Formed via Protonolytic Chemisorption on Sulfated Zirconia

Reaction of ( σ-alkynyl) Group 4 metallocene cation complexes with alkyl- and arylisocyanides

The cations [(RCp) 2M(–CC–CH 3)(THF) +] ( 2a– d) [(RCp) 2M=Cp 2Ti, Cp 2Zr, (MeCp) 2Zr, and Cp 2Hf] were generated in situ by treatment of the respective bis(propynyl) Group 4 metallocenes (RCp) 2M(–CC–CH 3) 2 ( 1a– d) with N, N-dimethylanilinium tetraphenylborate. Addition of excess tert-butylisocyanide gave the isonitrile insertion/addition products [(RCp) 2M( η 2-Me 3C–NC–CC–CH 3)( κ-CN–CMe 3) +] ( 8a– d). Complex 8b was characterized by X-ray diffraction. It contains a η 2-iminoacyl ligand with N-inside orientation and there is a κ- tert-butylisocyanide coordinated to the cationic metallocene framework. Complex 8b exhibits the typical structural characteristics of a d o-configurated isonitrile complex (bond lengths 2.350(4) and 1.148(4) Å for the Zr– C N–R unit). Insertion of 2,6-dimethylphenylisocyanide into the Zr–C(sp) σ-bond of in situ generated [Cp 2Hf–CC–CH 3 +] cation 2d leads to the formation of the analogous cationic hafnocene complex 8e.

Formation of Metallocene-Stabilized Planar-Tetracoordinate Carbon Compounds by a Protonation Route

Bis(alkynyl)zirconocene and -hafnocene complexes 4 react with (butadiene)zirconocene or -hafnocene, respectively, to yield the binuclear σ,π-acetylide bridged complexes [(Cp2M)2(μ-C≡C−R)2] 7 (M = Zr, Hf; R = CH3, C2H5, or CH2Ph). The complexes 7 are selectively protonated upon treatment with N,N-dimethylanilinium tetraphenylborate or tetrakis(pentafluorophenyl)borate to yield the dinuclear metallocene cation complexes [(Cp2M1)(μ-RCC1−H)(μ-C≡C−R)M2Cp2+] 13 (M1 = M2 = Zr, a−c; M1 = Zr, M2 = Hf, h; M1 = M2 = Hf, i) that contain a planar-tetracoordinate carbon atom (C1-H) bearing a hydrogen substituent. Complex 13a was characterized by X-ray diffraction. It reveals an agostic interaction of the C1-H moiety with the M2Cp2 unit. The planar-tetracoordinate carbon unit C1-H of 13a exhibits 13C/1H NMRchemical shifts of δ = 161.0 and −0.11 and a coupling constant of 1JCH = 103 Hz. Selective protonation of (μ-alkynyl)bis(group 4 metallocene) complexes containing other additional bridging ligands provides a rather general synthetic entry to planar-tetracoordinate carbon containing complexes of this type: [Cp2M1(μ-C≡C−CH3)(μ-Cl)M2Cp2] (10a−c, M1, M2 = Zr, Hf) and[Cp2M1(μ-C≡C−CH3)(μ-CH3)M2Cp2] (11a,b) selectively add a proton from [(HNMe2Ph)+(BAr4)−] at carbon atom C1 of the acetylide ligand to yield the corresponding “anti-van′t Hoff/LeBel complexes” [Cp2M1(μ-CH3CC1-H)(μ-X)M2Cp2+] (13d−g and k, X = Cl, CH3), respectively.

Zirconocenes as Initiators for Carbocationic Isobutene Homo- and Copolymerizations

The zirconocene complexes Cp2ZrMe2 and Cp*2ZrMe2 activated with B(C6F5)3 initiate the carbocationic polymerization of isobutene and isobutene−isoprene copolymerizations to IIR rubbers at temperatures as high as −30 °C. Unlike conventional metal halide initiators, these metallocene-based initiator systems produce both homo- and copolymers of broadly similar molecular weights. Copolymers prepared in the presence of ca. 2 mol % isoprene show a diene incorporation rate of 1.4−1.7%, with the typical 1,4-trans structure. Comparison of the effectiveness of zirconocene dialkyls with that of the metallocene hydrolysis products Cp*2Zr(OH)2 and (Cp2ZrMe)2(μ-O) in the presence of B(C6F5)3 suggests that initiation by traces of protons is less efficient than initiation by cationic metallocene alkyl species, while oxo-bridged complexes (Cp‘2ZrMe)2(μ-O)/B(C6F5)3 (Cp‘ = C5H5 or C5H4SiMe3) are inactive.

Reaction of „Jordan′s Cation”︁ [Cp2ZrCH3(thf)]+ with Amino Acid‐Derived Isocyanates—A First Synthetic Route to Oligopeptide‐Modified Group 4 Bent Metallocene Cation Systems

AbstractThe organometallic cation [Cp2ZrCH3(thf)]+, employed as the tetraphenylborate salt (1), reacts cleanly in 1:1 stoichiometry with the isocyanates 2 derived from valine methyl ester or valylvaline methyl ester, respectively. In each case addition of the Zr–CH3 group to the isocyanate sp‐carbon center is observed with formation of a functionalized zirconocene cation derivative containing a chelating N‐metallated N‐acetylvaline methyl ester (3a) or N‐acetylvalylvaline methyl ester (3b) moiety, respectively, coordinated in the bent metallocene s̀‐ligand plane. The spectroscopic data of 3, supported by an X‐ray crystal structure analysis of the zirconated dipeptide derivative 3b, have revealed the presence of chelating (η1‐O:η1‐N)‐coordination of the terminal N‐acetyl groups in addition to a Zr–O=C interaction with the adjacent valyl amido group.

Evidence for Internal Ion Pair Formation upon Insertion of Reactive Alkene in the Zirconium–Carbon Bond of the cp2Zr(μ‐C4h6)b(c6f5)3 Metallocene‐Boron‐Betaine Ziegler Catalyst System

AbstractTreatment of the (butadiene)ML2 complexes 1 [ML2 = Cp2Zr (a), Cp2Hf (b), and (.‐C5H4CH3)2Zr (c)] with B(C6F5)3 gives the 1:1 addition products (CH2CHCHCH2–B(C6F5_3)ML2 (3a–c). At –40°C the betaine complex 3a inserts one equivalent of methylenecyclopropane to give the regioisomeric insertion products 5a and 6a in a 60:40 ratio. These products exhibit the cyclopropylidene moiety in the α‐ and β‐positions, respectively, relative to zirconium. The corresponding hafnocene complexes 5b and 6b are obtained in a 70:30 ratio starting from 3b. The reaction of 3(a–c) with allene gives a single insertion product (7a–c) in each case where the exo‐methylene group is in the α‐position to the metal center ([2,1]‐insertion). The complexes 5–7 are chiral. They all exhibit a pronounced ·‐interaction of the internal –C4H=C5H− double bond of the s̀‐ligand chain with the metal center in addition to a metallocene/–C6H2–[B] ion pair interaction. The relative contributions of the cationic metallocene end of the dipolar complexes 5–7 are quite dependent on the steric and electronic properties of the respective metallocene units involved. This is revealed by a comparison to typical 13C‐NMR parameters of the complexes 5–7 with a pair of suitable model complexes, namely the ethylene insertion product 4 into the betaine system 3a and its THF adduct 4.THF.

Uncovering Alternative Reaction Pathways Taken by Group 4 Metallocene Cations: Facile Intramolecular CH Activation of Cp−(Dimethylamino)alkyl Substituents by a Methylzirconocene Cation

Alkyl- and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,N-dimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium systems Li[C5H4−CR1...

Acetone and Acetophenone Adducts of the Zwitterionic Zirconocene Cp*[η5-C5Me4CH2B(C6F5)3]ZrC6H5

The recently reported zwitterionic complex Cp*[η5-C5Me4CH2B(C6F5)3]ZrC6H5, 1, reacts rapidly with 1 equiv of acetone or acetophenone to form the adducts Cp*[η5-C5Me4CH2B(C6F5)3]Zr(C6H5)[OC(CH3)R] (R = CH3, 2a; C6H5, 2b) in ∼85% yield. Spectroscopic evidence in favor of this assignment is presented; the adduct nature of the complexes was also confirmed in each case via an X-ray structural analysis. The ketone ligands are bound in an η1 end-on fashion (the Zr−OC angles are near linear at 174.2° and 166.1° for 2a and 2b, respectively), allowing for a π-component to the Zr−O bonding. Unlike other fleetingly observed ketone adducts of nonzwitterionic cationic metallocenes, the ketone ligands in compounds 2 do not undergo insertion into the Zr−C bond neither upon thermolysis nor in the presence of excess ketone.

The influence of methylalumoxane (MAO) on the isoselective propene polymerization with the homogeneous metallocene Me 2Si(Benz[e]Ind) 2ZrCl 2

The isoselective propene polymerization using the homogeneous Me 2Si(Benz[e]Ind) 2ZrCl 2/MAO catalyst system was investigated. The influence of the concentrations of metallocene and MAO activator on polymerization kinetics and microstructure of the resulting polymer was studied. Catalyst activity was found to be independent of zirconocene concentration and only a function of total MAO concentration. Polypropene microstructure was not affected by either MAO or zirconocene concentration. The polymerization behavior is compared to that of Me 2Si(2-Me-Benz[e]Ind) 2ZrCl 2/MAO. A model is presented to account for the equilibria present in the polymerization medium. This model takes into account the interactions between metallocene cation and excess MAO, thus explaining the influence of MAO concentration on catalyst activity in propene polymerization.

Very Large Counteranion Modulation of Cationic Metallocene Polymerization Activity and Stereoregulation by a Sterically Congested (Perfluoroaryl)fluoroaluminate

We communicate here the unusual structural and cocatalytic features of a new, stable (perfluoroaryl)aluminate anion, tris(2,2`,2``-nonafluorobiphenyl)flouroaluminate (PBA{sup -}). Noteworthy features include very large ion pairing/metallocenium ancillary ligand structural effects on olefin polymerization activity and stereoselectivity. These results considerably expand what is known about the consequences of strong cation-anion interactions for group 4-mediated olefin polymerization. For anions that coordinatively `intrude` into the cation coordination sphere, the effects can be dramatic. 15 refs., 1 tab.

Cationic Metallocene Polymerization Catalysts Based on Tetrakis(pentafluorophenyl)borate and Its Derivatives. Probing the Limits of Anion “Noncoordination” via a Synthetic, Solution Dynamic, Structural, and Catalytic Olefin Polymerization Study

The synthesis and properties of two soluble, weakly coordinating derivatives of the tetrakis(perfluoroaryl)borate anion B(4-C6F4TBS)4- and B(4-C6F4TIPS)4- (TBS = tert-butyldimethylsilyl and TIPS = triisopropylsilyl) are reported. Reaction of the trityl salts of the above anions with a variety of zirconium and thorium L2MMe2 complexes in benzene or toluene affords the cationic ion-paired methyl complexes L2MMe+X- or the corresponding hydrido complexes L2MH+X- (L2 = bis(cyclopentadienyl)- or cyclopentadienylamido-type ligand) when the reaction is carried out under dihydrogen. The solid state structure of the complex (Me5Cp)2ThMe+B(C6F5)4- has been characterized by X-ray diffraction. The B(C6F5)4--based zirconocenium methyl complexes L2MMe+ are unstable at room temperature with respect to, among other factors, intramolecular C−H activation of the ligand framework. In general, the thermal stabilities of the B(C6F4TBS)4-- and B(C6F4TIPS)4--derived complexes are greater than those of the corresponding B(C6F5)4-...

Alternating copolymerization of alkenes and carbon monoxide catalyzed by cationic palladium complexes

AbstractIn the late 1940s, Reppe discovered a nickel catalyst for the co‐oligomerization of ethene and carbon monoxide. Since then, various groups have made attempts to develop more efficient catalysts for this reaction. The recent discovery of a new class of very active palladium catalysts now allows, for the first time, ready access to a large variety of high‐molecular‐weight alkene/carbon‐monoxide co‐ and terpolymers. The catalysts comprise a cis‐coordinated palladium(II) species associated with weakly or non‐coordinating anions. Their discovery has made it possible to develop a viable process for the commercial production of the first members of the new family of CARILON‐olefin/carbon monoxide copolymers.In this brief review, we highlight some key phenomena in polyketone catalysis. The elementary reaction steps in the palladium‐catalyzed polyketone formation during chain propagation, initiation and termination are outlined. The role of bidentate ligands and the reasons for perfect alternation in polymer chain growth are dicussed. The attractive feature of the catalysts, that they also catalyze the co‐ and terpolymerization of olefins higher than ethene with carbon monoxide, is briefly noted. A parallel between polyketone catalysis by cationic palladium complexes and modern polyolefin catalysis by cationic metallocene complexes is suggested.