Tribenzyl Complexes Research Articles

Molecular Thorium Trihydrido Clusters Stabilized by Cyclopentadienyl Ligands.

Hydrogenolysis of alkyl-substituted cyclopentadienyl (CpR ) ligated thorium tribenzyl complexes [(CpR )Th(p-CH2 -C6 H4 -Me)3 ] (1-6) afforded the first examples of molecular thorium trihydrido complexes [(CpR )Th(μ-H)3 ]n (CpR =C5 H2 (t Bu)3 or C5 H2 (SiMe3 )3 , n=5; C5 Me4 SiMe3 , n=6; C5 Me5 , n=7; C5 Me4 H, n=8; 7-10 and 12) and [(Cp# )12 Th13 H40 ] (Cp# =C5 H4 SiMe3 ; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra-nuclear octahydrido thorium dibenzylidene complex [(Cpttt )Th(μ-H)2 ]4 (μ-p-CH-C6 H4 -Me)2 (Cpttt =C5 H2 (t Bu)3 ) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single-crystal X-ray analysis. Hydride positions in [(CpMe4 )Th(μ-H)3 ]8 (CpMe4 =C5 Me4 H) were further precisely confirmed by single-crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12.

Molecular Thorium Trihydrido Clusters Stabilized by Cyclopentadienyl Ligands

AbstractHydrogenolysis of alkyl‐substituted cyclopentadienyl (CpR) ligated thorium tribenzyl complexes [(CpR)Th(p‐CH2‐C6H4‐Me)3] (1–6) afforded the first examples of molecular thorium trihydrido complexes [(CpR)Th(μ‐H)3]n (CpR=C5H2(tBu)3 or C5H2(SiMe3)3, n=5; C5Me4SiMe3, n=6; C5Me5, n=7; C5Me4H, n=8; 7–10 and 12) and [(Cp#)12Th13H40] (Cp#=C5H4SiMe3; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra‐nuclear octahydrido thorium dibenzylidene complex [(Cpttt)Th(μ‐H)2]4(μ‐p‐CH‐C6H4‐Me)2 (Cpttt=C5H2(tBu)3) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. Hydride positions in [(CpMe4)Th(μ‐H)3]8 (CpMe4=C5Me4H) were further precisely confirmed by single‐crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12.

Aminotroponiminato Hafnium and Zirconium Complexes: Synthesis and Ethylene/1-Octene Copolymerization Study

Four new aminotroponiminato hafnium and zirconium tribenzyl complexes were prepared by reacting neutral ligands with the corresponding tetrabenzyl complexes. Aminotroponimine ligands were prepared in four steps starting from tropolone. An air-stable ethoxy-amino-tropylium cation intermediate isolated during ligand synthesis was found to react directly with amines significantly faster than the neutral intermediate proposed previously. This tropylium cation represents a convenient way to prepare a large array of aminotroponimines. An ethylene/1-octene copolymerization study conducted at 120 °C demonstrated that the aminotroponiminato hafnium and zirconium complexes are catalytically active, but their activity is lower than that observed for the corresponding imino–enamido complexes. Polymer analysis data (GPC and DSC) indicated that aminotroponiminato complexes generate at least two catalytically active species under polymerization conditions.

Alkene Polymerization Catalysts Bearing Tridentate Phenoxyamine Ligands with sp3 C Donors

AbstractThe reaction of vinyl‐appended phenoxyamine 2 with tetrabenzyltitanium provided the phenoxyaminetitanium(II) alkene complex [rac‐Lig2TiBn], arising from intramolecular vinyl‐group insertion followed by toluene elimination. Whereas [rac‐Lig2TiBn] was inactive for olefin polymerization upon benzyl abstraction, treatment with ethylene led to the formation of stable titanacyclopentane complex [rac‐Lig2(CH2)2TiBn]. Alternatively, six‐membered metallacyclic complexes [rac‐Lig1ZrBn2‐a/b] and [rac‐Lig1HfBn2‐a/b] were obtained from reaction of vinyl‐appended phenoxyamine 1 with tetrabenzylzirconium or tetrabenzylhafnium in a further rare example of intramolecular vinyl‐group insertion into neutral tribenzyl group IV precursors. Living and isoselective polymerization of 1‐hexene was promoted by [rac‐Lig1HfBn2‐a/b]/B(C6F5)3 at 0 °C, whereas [rac‐Lig1ZrBn2‐a/b]/B(C6F5)3 catalyzed the living and isoselective polymerization of propylene ([m4]=0.76) at 0 °C. This catalyst system was employed for the synthesis of a diblock copolymer featuring an isotactic polypropylene semicrystalline block and poly(ethylene‐co‐propylene) amorphous block.

Synthesis and reactivity of the yttrium-alkyl-carbene complex [Y(BIPM)(CH2C6H5)(THF)] (BIPM = {C(PPh2NSiMe3)2})

Reaction of [YI(3)(THF)(3.5)] with three equivalents of [KBz] (Bz = CH(2)C(6)H(5)) affords the tri-benzyl complex [Y(Bz)(3)(THF)(3)] () in excellent yield. Complex reacts with H(2)C(PPh(2)NSiMe(3))(2) (H(2)BIPM) to afford the yttrium-alkyl-carbene complex [Y(BIPM)(Bz)(THF)] (, BIPM = {C(PPh(2)NSiMe(3))(2)}). Compound reacts with one equivalent of benzophenone to give the alkoxy 1,2-migratory insertion product [Y(BIPM)(OCPh(2)Bz)(THF)] () rather than the alkene Wittig-product Ph(2)C[double bond, length as m-dash]C(PPh(2)NSiMe(3))(2). Reaction of with one or more equivalents of benzophenone does not afford any detectable alkene products, rather it apparently catalyses rearrangement of monomeric to afford dimeric [{Y(micro-BIPM)(OCPh(2)Bz)}(2)] (). Investigations reveal that formation of is proportional to the amount of benzophenone added, but the benzophenone is recovered at the end of the reaction. Reaction of with diphenyldiazene affords the 1,2-migratory insertion product [Y(BIPM){N(Ph)N(Ph)(Bz)}(THF)] () Compounds , , , , and have been variously characterised by X-ray crystallography, multi-nuclear NMR spectroscopy, FTIR spectroscopy, and CHN micro-analyses. Density functional theory calculations on reveal the HOMO to be localised at the Y-C(alkyl) bond which is commensurate with the observed reactivity.

Neutral and Cationic Rare Earth Metal Alkyl and Benzyl Compounds with the 1,4,6-Trimethyl-6-pyrrolidin-1-yl-1,4-diazepane Ligand and Their Performance in the Catalytic Hydroamination/Cyclization of Aminoalkenes

A new neutral tridentate 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane (L) was prepared. Reacting L with trialkyls M(CH(2)SiMC(3))(3)(THF)(2) (M = Sc, Y) and tribenzyls M(CH(2)Ph)(3)(THF)(3) (M = Sc, La) yielded trialkyl complexes (L)M(CH(2)SiMe(3))(3) (M = Sc, 1; M = Y, 2) and tribenzyl complexes (L)M(CH(2)Ph)(3) (M = Sc, 3; M = La, 4). Complexes I and 2 can be converted to their corresponding ionic compounds [(L)M(CH(2)SiMe(3))(2)(THF)][B(C(6)H(5))(4)] (M = Sc, 5; M = Y, 6) by reaction with [PhNMe(2)H] [B(C(6)H(5))(4)] in THE Complexes 3 and 4 can be converted to cationic species [(L)M(CH(2)Ph)(2)](+) by reaction with [PhNMe(2)H][B(C(6)F(5))(4)] in C(6)D(5)Br in the absence of THE The neutral complexes 1-4 and their cationic derivatives were studied as catalysts for the hydroamination/cyclization of 2,2-diphenylpent-4-en-1-amine and N-methylpent-4-en-1-amine reference substrates and compared with ligand-free Sc, Y, and La neutral and cationic catalysts. The most effective catalysts in the series were the cationic L-yttrium catalyst (for 2,2-diphenylpent-4-en-1-amine) and the cationic lanthanum systems (for N-methylpent-4-en-1-amine). For the La catalysts, evidence was obtained for release of L from the metal during catalysis.

Synthesis of Hafnium and Zirconium Imino−Amido Complexes from Bis-imine Ligands. A New Family of Olefin Polymerization Catalysts

The reaction of 2,6-diisopropylaniline-based bis-imine ligands (4, 9) with M(CH2Ph)4 (M = Hf, Zr) led to formation of novel imino−amido tribenzyl complexes via migratory insertion of a benzyl group...

Synthesis and Structure of Trialkyltantalum Complexes Stabilized by Aminopyridinato Ligands

Abstract(4‐Methylpyridin‐2‐yl)(trimethylsilyl)amine (1), (6‐methylpyridin‐2‐yl)(trimethylsilyl)amine (2), and (2,6‐diisopropylphenyl)(pyridin‐2‐yl)amine (3) were deprotonated and used as ligands to synthesize trialkyltantalum complexes. The reaction of 2 equiv. of 1 or 2 with pentabenzyltantalum afforded tribenzyltantalum(V) complexes by toluene elimination. Analogous reaction using 3 failed. Lithiation of 3 followed by the reaction with tribenzyltantalum dichloride gave rise to the corresponding tribenzyl complex. Other alkyltantalum complexes stabilized by this ligand environment can be prepared by treating tantalum pentachloride with 2 equiv. oflithiated 3 to form a bis(aminopyridinato)tantalum trichloride. The reaction of this trichloride with 3 equiv. of alkyllithium compounds like methyllithium affords the corresponding trialkyltantalum complexes. X‐ray diffraction studies of four of the synthesized complexes were carried out. They adopt two different coordination environments, either slightly distorted capped octahedrons (sterically less demanding aminopyridinato ligands) or pentagonal bipyramids (bulkier aminopyridinato ligands). The alkyl species were surprisingly stable at elevated temperatures and no formation of mixed alkyl/alkylidene complexes was observed. Alkyl cation formation and the behaviour of a selection of these compounds in olefin polymerization were explored. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Lanthanum Tribenzyl Complexes as Convenient Starting Materials for Organolanthanum Chemistry

Simple tribenzyl complexes of lanthanum, [La(CH2C6H4-4-R)3(THF)3] (R = H (1a), Me (1b)), were prepared in a remarkably straightforward fashion from LaBr3(THF)4 and potassium benzyl reagents. Single-crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and η2 binding of the benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction of 1a with the amidine ArNCPhNHAr (Ar = 2,6-Pri2C6H3) affords the corresponding mono(amidinate) dibenzyl derivative 2. Complex 1b reacts with LiCH2C6H4-4-Me to give the THF-free anion [La(CH2C6H4-4-Me)4]- (3). Reactions of 1 with 1 or 2 equiv of [PhNMe2H][B(C6X5)4] (X = H, F) generate the corresponding mono- and dicationic benzyl species [La(CH2C6H4-4-R)2(THF)4]+ (4) and [La(CH2C6H4-4-R)(THF)6]2+ (5), which were structurally characterized. Scouting ethylene polymerization experiments indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl species is more efficient...

Preparation and characterization of iminopyrrolyl hafnium complexes as catalyst precursors for α-olefin polymerization

Amido, chloro, and benzyl hafnium complexes bearing 2-( N-aryliminomethyl)pyrrole [(R-pyr)H, 1a: R = DIP = 2-{ N-(2,6-diisopropylphenyl)iminomethyl}, 1b: R = XYL = 2-{ N-(2,6-dimethylphenyl)iminomethyl}, 1c: R = ANI = 2-{ N-(4-methoxyphenyl)iminomethyl}, 1d: R = TOL = 2-{ N-(4-methylphenyl)iminomethyl}] were prepared and characterized. The coordination modes of (R-pyr) 2Hf(NMe 2) 2 ( 2a– d) depend on the bulkiness of the aromatic substituent at the imine nitrogen of the ligands. In contrast, all (R-pyr) 2HfCl 2 ( 3a– d) have a C 2-symmetric octahedral structure. These diamido- and dichloro-bis(iminopyrrolyl)hafnium complexes, when combined with MMAO, become active catalysts for ethylene polymerization. Two types of hafnium benzyl complexes, (DIP-pyr)Hf(CH 2Ph) 3 ( 4a) and (DIP-pyr) 2Hf(CH 2Ph) 2 ( 5a), were prepared by the alkane elimination reaction from reactions of Hf(CH 2Ph) 4 with controlled amounts of iminopyrrole ( 1a). The mono(iminopyrrolyl)hafnium tribenzyl complex ( 4a) exhibited a high catalytic activity for 1-hexene polymerization.

Tribenzyl Tantalum(V) Complexes of Amine Bis(phenolate) Ligands: Investigation of α-Abstraction vs Ligand Backbone β-Abstraction Paths

The synthesis, structure, and reactivity of tribenzyl Ta(V) complexes of amine bis(phenolate) ligands were investigated as a function of the ligands' structure: i.e., the steric bulk of the phenolate substituents and the presence of a “side arm” donor. The tribenzyl complexes were prepared by toluene-elimination reactions of Ta(CH2Ph)5 with the ligand precursors. They were found to be of octahedral mer geometry, with the side-arm donor (if present) unbound. These complexes underwent two well-defined toluene elimination reactions determined by the structural features of the ligands. An α-abstraction reaction, leading to alkyl−alkylidene complexes, occurred only if the phenolate ortho substituents were small (H, Cl) and a side-arm donor was present. Bulkier phenolate substituents (Me) or the lack of a side-arm donor led to a β-abstraction process from the ligand backbone, forming a dibenzyl complex with a metallaazacyclopropane ring. The side-arm donor, if present, was found to bind to the metal in both pat...

C−H Bond Activation Processes in Cationic and Neutral Titanium Benzyl Compounds with Cyclopentadienyl−Arene Ligands

Titanium tribenzyl complexes with cyclopentadienyl−arene ligands, (η5-C5H4CMe2Ar)Ti(CH2Ph)3 (Ar = 3,5-Me2C6H3 (1), Ph (2)), were synthesized. Reaction of 1 with either B(C6F5)3 or [Ph3C][B(C6F5)4] affords the cation [(η,5η-C5H4CMe2-3,5-Me2C6H3)Ti(η-CH2Ph)2]+ (3), in which the pendant arene group and the benzyl ligands show fluxional behavior. Reaction of 2 with B(C6F5)3, leads to rapid ortho cyclometalation of the pendant arene to give the contact ion pair [(η5:η1-C5H4CMe2C6H4)Ti(η1-CH2Ph)][η6-PhCH2B(C6F5)3] (4) and toluene. Reaction of 2 with [Ph3C][B(C6F5)4] also leads to ligand ortho metalation, giving [(η5:η1-C5H4CMe2C6H4)Ti(η2-CH2Ph)][B(C6F5)4] (5) with a η2-benzyl group. Thermolysis of compounds 1 and 2 (50 °C, 50 h) results in the ortho-cyclometalated dibenzyl species (η5:η1-C5H4CMe2Ar‘)Ti(CH2Ph)2 (Ar‘ = 3,5-Me2C6H2 (6), C6H4 (7)) and toluene. The thermolysis of 1 follows first-order kinetics (k ≈ 10-5 s-1 at 333 K) with ΔH⧧ = 24 ± 2 kcal mol-1 and ΔS⧧ = −5 ± 5 cal mol-1 K-1. For the thermolysis of the related titanium trialkyl (η5-C5H4CMe2Ph)Ti(CH2SiMe3)3 (9), activation parameters of ΔH⧧ = 21 ± 2 kcal mol-1 and ΔS⧧ = −18 ± 4 cal mol-1 K-1 were found. Deuterium labeling studies with (η5-C5H4CMe2C6D5)Ti(CH2Ph)3 (2-d5) show that thermolysis of the neutral compound involves initial formation of an alkylidene intermediate, followed by o-CH addition to the TiC bond. In the corresponding cationic species, ortho cyclometalation proceeds via direct σ-bond metathesis.

Zirconium complexes of a tacn-derived amido ligand and ring-opening to form a new diamido-amino pincer

The tribenzyl complex (Pri2tacn)Zr(CH2Ph)3 eliminates toluene upon heating with concomitant ring-opening of the anionic ancillary macrocycle to yield [CH2CHNCH2- CH2N(Pri)CH2CH2NPri ]Zr(CH2Ph)2; the latter features a new class of dianionic pincer ligand.

Low-Coordinate (Arylimido)vanadium(V) Alkyls: Synthesis and Reactivity of V(NAr)(CH2Ph)3 (Ar = C6H3-2,6-Pri2)

The syntheses of a series of stable vanadium(V) alkyls have been achieved by the support of arylimido ligation. The (arylimido)vanadium(V) tribenzyl complex V(NAr)(CH2Ph)3 (Ar = C6H3-2,6-Pri2) has been prepared in high yield by the treatment of V(NAr)Cl3·THF with PhCH2MgCl. This compound, which represents the first structurally characterized vanadium(V) trialkyl complex, is a valuable synthetic precursor to a series of other vanadium(V) dialkyl derivatives with supporting alkoxide, aryloxide, and amido functionalities.

Synthesis of bis ( tert-butyl)cyclopentadienyl derivatives of titanium and zirconium. NMR spectra and dynamic behaviour of the base-free [Zr(1,3- tBu 2- η5-C 5H 3)(CH 2Ph) 2] + cation

Reaction of Si(1,3- tBu 2-C 5H 3)Me 3 with MCl 4 (M = Ti, Zr) in toluene or hexane at room temperature affords the new trichloromonociclopentadienyl-type derivatives [ M(1,3- tBu 2-η 5- C 5 H 3) Cl 3] ( M = Ti ( 2), Zr ( 3)] . Treatment of complexes 2 and 3 with appropriate alkylating reagents in hexane gives the 1,3-di( tert-butyl)cyclopentadienyl trialkyl titanium and zirconium complexes [ M(1,3- tBu 2-η 5- C 5 H 3) R 3] [ M = Ti, R = CH 3 ( 4), CH 2 Ph (5) ; M = Zr, R = CH 3 ( 6), CH 2 Ph ( 7), CH 2 CMe 2 Ph( 8) ]. Interestingly, when 2 reacts with 3.1 equivalents of LiCH 2CMe 2Ph in hexane at room temperature the ring- tert-butyl-metallated complex [Ti(1- tBu-3-CMe 2CH 2- η 5-C 5H 3) (CH 2CMe 2Ph) 2] (bd9) was isolated in 90% yield. The cationic mono(1,3-di-( tert-butyl)cyclopentadienyl) dibenzyl zirconium species [Zr(1,3- tBu 2- η 5-C 5H 3)(CH 2Ph 2] +, generated in situ by reaction of the tribenzyl complex 7 with B(C 6F 5) 3 or [CPh 3] +[B(C 6F 5) 4] − reagents, is reported and their dynamic NMR behaviour in CD 2Cl 2 solutions at low temperatures is studied.

Synthesis of NaAlRn(CH2Ph)4-n type alkylbenzyl aluminum complexes

1. In reactions of benzylsodium with R3Al in toluene, compounds NaAlR3(CH2Ph), where R=Me, Et, and i-Bu, have been obtained as individual entities. 2. Benzylsodium with AlCl3 in toluene gives sodium tetrabenzylaluminate. 3. It has been established by27Al NMR that in reaction of benzylsodium with R2AlCl in toluene a mixture of NaAlR2(CH2Ph)2, NaAl(CH2Ph)4 and NaAlR3(CH2Ph)(R=Me, Et, and i-Bu) is formed. A reaction of benzylsodium with EtAlCl2 gives a mixture of NaAl(CH2Ph)4 and NaAlEt2-(CH2Ph)2 (the tribenzyl complex NaAlR(CH2Ph)3 is not formed in this case).