Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Methylaluminoxane‐free ethylene polymerization with in situ activated zirconocene triisobutylaluminum catalysts and silica‐supported stabilized borate cocatalysts

Heterogenization of tris(pentafluorophenyl)borane [B(C₆F₅)₃] on a silica support stabilized with chlorotriphenylmethane (CICPh₃) and N,N‐dimethylaniline (HNMe₂Ph) creates the following supported borane cocatalysts: [HNMe₂Ph]⁺[B(C₆F₅)₃‐SiO₂]^? and [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^?. These supported catalysts were reacted with Cp₂ZrCl₂ TIBA in situ to generate active metallocene species in the reactor. Triisobutylaluminum (TIBA) was a good coactivator for dichloro‐zirconocene, acting as the prealkylating agent to generate cationic zirconocene (Cp₂ZrC₄H₉⁺). The catalytic performances were determined from the kinetics of ethylene‐consumption profiles that were independent of the time dedicated to the activation of the catalysts. The scanning electron microscopy‐energy dispersive X‐ray measurements showed that B(C₆F₅)₃ dispersed uniformly on the silica support. Under our reaction conditions, the [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? system had higher productivity and weight‐average molecular weight than the [HNMe₂Ph]⁺[B(C₆F₅)₃‐SiO₂]^? system. For the [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? system, the productivity increased with the amount catalyst; however, the polydispersity index of polyethylene synthesized did not change. The final shape of polymer particles was a larger‐diameter version of the original support particle. The polymer particles synthesized with supported [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? catalysts had larger diameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3240–3248, 2002     

Polymerization of methyl methacrylate and other polar monomers with alkylaluminum initiators bearing bidentate and tridentate N‐ and O‐donor ligands

Dimethylaluminum complexes bearing bidentate amidate, oxypyridine, and salicylaldimine N,O‐ligands and tridentate N,N′,N″‐pyridyliminoamide ligands were synthesized and spectroscopically characterized. The complexes were investigated in both neutral and borane‐activated cationic forms, along with bidentate N,N′‐ligated aluminum amidinates, as catalysts for the polymerization of methyl methacrylate, ?‐caprolactone, and propylene oxide. The neutral complexes generally did not carry out polymerization, but the polymerization/oligomerization of all three monomers was achieved when the various catalysts were activated with B(C₆F₅)₃ or [Ph₃C]⁺[B(C₆F₅)₄]^?. The N,O‐ligated cations were much less active for polymerization than the analogous, more stable N,N′‐ligated amidinate cations; both types of cationic complexes catalyzed the ring‐opening cationic polymerization of tetrahydrofuran. B(C₆F₅)₃ and [Ph₃C]⁺[B(C₆F₅)₄]^? also independently carried out the oligomerization of propylene oxide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1633–1651, 2002     

Unusual Hafnium–Pyridylamido/ERn Heterobimetallic Adducts (ERn=ZnR2 or AlR3)

NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)–pyridylamido catalytic system for olefin polymerization, [{N^?,N,C_Nph^?}HfMe][B(C₆F₅)₄] ( 1 , Nph=naphthyl), interacts with ER_n (E=Al or Zn, R=alkyl group) to afford unusual heterobimetallic adducts [{N^?,N}HfMe(μ‐C_Nph)(μ‐R)ER_n?1][B(C₆F₅)₄] in which the cyclometalated Nph acts as a bridge between Hf and E. ¹H VT (variable‐temperature) EXSY NMR spectroscopy provides direct evidence of reversible alkyl exchanges in heterobimetallic adducts, with ZnR₂ showing a higher tendency to participate in this exchange than AlR₃. 1‐Hexene/ER_n competitive reactions with 1 at 240 K reveal that the formation of adducts is strongly favored over 1‐hexene polymerization. Nevertheless, a slight increase in the temperature (to >265 K) initiates 1‐hexene polymerization.     

Divalent Lanthanide Tetraisobutylaluminates: Reactivity and Living Isoprene Polymerization

Lanthanide (Ln) tetraisobutylaluminates constitute key components in commercial 1,3-diene polymerization catalysts, and likewise are the homogeneous rare-earth-metal catalysts of prime industrial importance. Discrete divalent rare-earth-metal complexes [Ln(AliBu₄)₂] (Ln=Sm, Eu, Yb) reported here display the first structurally characterized homoleptic metal tetraisobutylaluminates. Treatment of [Ln(AliBu₄)₂] with C₂Cl₆ gives access to Sm^II/Sm^III mixed-valence cluster [Sm₆Cl₈(AliBu₄)₆] and the Yb^II cluster [Yb₄Cl₄(AliBu₄)₄], respectively. Reaction with B(C₆F₅)₃ leads to hydride abstraction and formation of arene-coordinated hydroborates such as [Sm{HB(C₆F₅)₃}₂(toluene)₂]. Complexes [Ln(AliBu₄)₂] engage in single-component isoprene polymerization, affording high cis-1,4 polyisoprenes with narrow molecular weight distributions. Binary [Yb(AliBu₄)₂]/[HNPhMe₂][B(C₆F₅)₄] fabricates polyisoprene in a perfectly living manner. The catalytically active species are scrutinized by NMR spectroscopy.     

Rare‐Earth‐Metal–Hydrocarbyl Complexes Bearing Linked Cyclopentadienyl or Fluorenyl Ligands: Synthesis,Catalyzed Styrene Polymerization,and Structure–Reactivity Relationship

A series of rare‐earth‐metal–hydrocarbyl complexes bearing N‐type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH₂SiMe₃)₃(thf)₂] with equimolar amount of the electron‐donating aminophenyl‐Cp ligand C₅Me₄H‐C₆H₄‐o‐NMe₂ afforded the corresponding binuclear monoalkyl complex [({C₅Me₄‐C₆H₄‐o‐NMe(μ‐CH₂)}Y{CH₂SiMe₃})₂] ( 1 a ) via alkyl abstraction and C? H activation of the NMe₂ group. The lutetium bis(allyl) complex [(C₅Me₄‐C₆H₄‐o‐NMe₂)Lu(η³‐C₃H₅)₂] ( 2 b ), which contained an electron‐donating aminophenyl‐Cp ligand, was isolated from the sequential metathesis reactions of LuCl₃ with (C₅Me₄‐C₆H₄‐o‐NMe₂)Li (1 equiv) and C₃H₅MgCl (2 equiv). Following a similar procedure, the yttrium‐ and scandium–bis(allyl) complexes, [(C₅Me₄‐C₅H₄N)Ln(η³‐C₃H₅)₂] (Ln=Y ( 3 a ), Sc ( 3 b )), which also contained electron‐withdrawing pyridyl‐Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl‐Flu ligand (C₁₃H₉‐C₅H₄N) by [Ln(CH₂SiMe₃)₃(thf)₂] generated the rare‐earth‐metal–dialkyl complexes, [(η³‐C₁₃H₈‐C₅H₄N)Ln(CH₂SiMe₃)₂(thf)] (Ln=Y ( 4 a ), Sc ( 4 b ), Lu ( 4 c )), in which an unusual asymmetric η³‐allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH₂C₆H₄‐o‐NMe₂)₃], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η³‐C₁₃H₈‐C₅H₄N)Y(CH₂C₆H₄‐o‐NMe₂)₂] ( 5 ). Complexes 1 – 5 were fully characterized by ¹H and ¹³C NMR and X‐ray spectroscopy, and by elemental analysis. In the presence of both [Ph₃C][B(C₆F₅)₄] and AliBu₃, the electron‐donating aminophenyl‐Cp‐based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph₃C][B(C₆F₅)₄] only, the electron‐withdrawing pyridyl‐Cp‐based complexes 3 , in particular scandium complex 3 b , exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99 %) polystyrene, whereas their bulky pyridyl‐Flu analogues ( 4 and 5 ) in combination with [Ph₃C][B(C₆F₅)₄] and AliBu₃ displayed much‐lower activity to afford syndiotactic‐enriched polystyrene.     

Two new dimeric cadmium(II) and zinc(II) sulfate complexes with 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine and 2,2:6′,2′′‐ter­pyridine

The structures of two new sulfate complexes are reported, namely di‐μ‐sulfato‐κ³O,O′:O′′‐bis{aqua­[2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine‐κ³N¹,N²,N⁶]­cadmium(II)} tetra­hydrate, [Cd₂(SO₄)₂(C₁₆H₁₂N₆)₂(H₂O)₂]·4H₂O, and di‐μ‐sulfato‐κ²O:O′‐bis­[(2,2′:6′,2′′‐ter­pyridine‐κ³N¹,N^1′,N^1′′)­zinc(II)] dihydrate, [Cd₂(SO₄)₂(C₁₅H₁₁N₃)₂]·2H₂O, the former being the first report of a Cd(tpt) complex [tpt is 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine]. Both compounds crystallize in the space group P and form centrosymmetric dimeric structures. In the cadmium complex, the metal center is heptacoordinated in the form of a pentagonal bipyramid, while in the zinc complex, the metal ion is in a fivefold environment, the coordination geometry being intermediate between square pyramidal and trigonal bipyramidal. Packing of the dimers leads to the formation of planar structures strongly linked by hydrogen bonding.     

Dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate and bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ2N,N′)copper(I) tetrafluoroborate

The single‐crystal X‐ray structures of dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate, C₁₄H₁₂N₂O₄, and the copper(I) coordination complex bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ²N,N′)copper(I) tetrafluoroborate, [Cu(C₁₄H₁₂N₂O₄)₂]BF₄, are reported. The uncoordinated ligand crystallizes across an inversion centre and adopts the anticipated anti pyridyl arrangement with coplanar pyridyl rings. In contrast, upon coordination of copper(I), the ligand adopts an arrangement of pyridyl donors facilitating chelating metal coordination and an increased inter‐pyridyl twisting within each ligand. The distortion of each ligand contrasts with comparable copper(I) complexes of unfunctionalized 2,2′‐bipyridine.     

Ansa‐Complexes of [Mn(η5‐C5H5)(η6‐C6H6)]: Preparation,Characterization, and Reactivity of [n]Manganoarenophanes (n=1, 2, 3)

We report the synthesis of [n]manganoarenophanes (n=1, 2) featuring boron, silicon, germanium, and tin as ansa‐bridging elements. Their preparation was achieved by salt‐elimination reactions of the dilithiated precursor [Mn(η⁵‐C₅H₄Li)(η⁶‐C₆H₅Li)]?pmdta (pmdta=N,N,N′,N′,N′′‐pentamethyldiethylenetriamine) with corresponding element dichlorides. Besides characterization by multinuclear NMR spectroscopy and elemental analysis, the identity of two single‐atom‐bridged derivatives, [Mn(η⁵‐C₅H₄)(η⁶‐C₆H₅)SntBu₂] and [Mn(η⁵‐C₅H₄)(η⁶‐C₆H₅)SiPh₂], could also be determined by X‐ray structural analysis. We investigated for the first time the reactivity of these ansa‐cyclopentadienyl–benzene manganese compounds. The reaction of the distannyl‐bridged complex [Mn(η⁵‐C₅H₄)(η⁶‐C₆H₅)Sn₂tBu₄] with elemental sulfur was shown to proceed through the expected oxidative addition of the Sn?Sn bond to give a triatomic ansa‐bridge. The investigation of the ring‐opening polymerization (ROP) capability of [Mn(η⁵‐C₅H₄)(η⁶‐C₆H₅)SntBu₂] with [Pt(PEt₃)₃] showed that an unexpected, unselective insertion into the C_ipso?Sn bonds of [Mn(η⁵‐C₅H₄)(η⁶‐C₆H₅)SntBu₂] had occurred.     

Efficient terpolymerization of ethylene and styrene with α‐olefins by aryloxo‐modified half‐titanocene‐based catalysts and cocatalyst systems

Aryloxo‐modified half‐titanocenes, Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* ( 1 ), ^tBuC₅H₄ ( 2 )], catalyze terpolymerization of ethylene and styrene with α‐olefin (1‐hexene and 1‐decene) efficiently in the presence of cocatalyst, affording high‐molecular‐weight polymers with unimodal distributions (compositions). Efficient comonomer incorporations have been achieved by these catalysts. The content of each comonomer (α‐olefin, styrene, etc.) could be controlled by varying the comonomer concentration charged, and resonances ascribed to styrene and α‐olefin repeated insertion were negligible. The terpolymerization with p‐methylstyrene (p‐MS) in place of styrene also proceeded in the presence of [PhN(H)Me₂][B(C₆F₅)₄] and AlⁱBu₃ cocatalyst, and p‐MS was incorporated in an efficient matter, affording high‐molecular‐weight polymers with uniform molecular weight distributions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2565–2574     

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis,Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y^III dialkyl complexes supported by tridentate N^?,N,N monoanionic methylthiazole– or benzothiazole–amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole‐containing system through an unprecedented metal‐to‐ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N^?,N,N^?,S^? ligand as the result of metal‐to‐ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring‐opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph₃C⁺[B(C₆F₅)₄]^?, were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.     

Formation and Reactivity of an Aluminabenzene Ligand at Pentadienyl‐Supported Rare‐Earth Metals

The half‐open rare‐earth‐metal aluminabenzene complexes [(1‐Me‐3,5‐tBu₂‐C₅H₃Al)(μ‐Me)Ln(2,4‐dtbp)] (Ln=Y, Lu) are accessible via a salt metathesis reaction employing Ln(AlMe₄)₃ and K(2,4‐dtbp). Treatment of the yttrium complex with B(C₆F₅)₃ and tBuCCH gives access to the pentafluorophenylalane complex [{1‐(C₆F₅)‐3,5‐tBu₂‐C₅H₃Al}{μ‐C₆F₅}Y{2,4‐dtbp}] and the mixed vinyl acetylide complex [(2,4‐dtbp)Y(μ‐η¹:η³‐2,4‐tBu₂‐C₅H₄)(μ‐CCtBu)AlMe₂], respectively.     

Formation of an Imino‐Stabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene

The novel amino(imino)stannylene 1 was prepared by conversion of HNIPr (NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) with one equivalent of Lappert’s tin reagent (Sn[N(SiMe₃)₂]₂). Treatment of 1 with DMAP (4‐dimethylaminopyridine) yields its Lewis acid–base adduct 2 . The reaction of 1 with one equivalent of trimethylsilyl azide results in replacement of the amino group at the tin center by an N₃ substituent with concomitant elimination of N(SiMe₃)₃ to afford dimeric [N₃SnNIPr]₂ ( 3 ). Remarkably, the reaction of 1 with B(C₆F₅)₃ produces the novel tin(II) monocation 4 ⁺[MeB(C₆F₅)₃]^? comprising a four‐membered stannacycle through methyl‐abstraction from the trimethylsilyl group.     

Structural Variations and Molecular Dynamics of Rare‐Earth Metal Complexes with the N,N‐Bis(2‐{pyrid‐2‐yl}ethyl)hydroxylaminato Ligand

The reaction of the donor‐functionalised N,N‐bis(2‐{pyrid‐2‐yl}ethyl)hydroxylamine and [LnCp₃] (Cp=cyclopentadiene) resulted in the formation of bis(cyclopentadienyl) hydroxylaminato rare‐earth metal complexes of the general constitution [Ln(C₅H₅)₂{ON(C₂H₄‐o‐Py)₂}] (Py= pyridyl) with Ln=Lu ( 1 ), Y ( 2 ), Ho ( 3 ), Sm ( 4 ), Nd ( 5 ), Pr ( 6 ), La ( 7 ). These compounds were characterised by elemental analysis, mass spectrometry, NMR spectroscopy (for compounds 1 , 2 , 4 and 7 ) and single‐crystal X‐ray diffraction experiments. The complexes exhibit three different aggregation modes and binding motifs in the solid state. The late rare‐earth metal atoms (Lu, Y, Ho and Sm) form monomeric complexes of the formula [Ln(C₅H₅)₂{η²‐ON(C₂H₄‐η¹‐o‐Py)(C₂H₄‐o‐Py)}] ( 1 – 4 , respectively), in which one of the pyridyl nitrogen donor atoms is bonded to the metal atom in addition to the side‐on coordinating hydroxylaminato unit. The larger Nd³⁺ and Pr³⁺ ions in 5 and 6 make the hydroxylaminato unit capable of dimerising through the oxygen atoms. This leads to the dimeric complexes [(Ln(C₅H₅)₂{μ‐η¹:η²‐ON(C₂H₄‐o‐Py)₂})₂] without metal–pyridine bonds. Compound 7 exhibits a dimeric coordination mode similar to the complexes 5 and 6 , but, in addition, two pyridyl functions coordinate to the lanthanum atoms leading to the [(La(C₅H₅)₂{ON(C₂H₄‐o‐Py)}{μ‐η¹:η²‐ON(C₂H₄‐η¹‐o‐Py)})₂] complex. The aggregation trend is directly related to the size of the metal ions. The complexes with coordinative pyridine–metal bonds show highly dynamic behaviour in solution. The two pyridine nitrogen atoms rapidly change their coordination to the metal atom at ambient temperature. Variable‐temperature (VT) NMR experiments showed that this dynamic exchange can be frozen on the NMR timescale.     

A non‐PFT (polymerization filling technique) approach to poly(ethylene‐co‐norbornene)/MWNTs nanocomposites by in situ copolymerization with scandium half‐sandwich catalyst

The in situ synthesis of ethylene‐co‐norbornene copolymers/multi‐walled carbon nanotubes (MWNTs) nanocomposites was achieved by rare‐earth half‐sandwich scandium precursor [Sc(η⁵‐C₅Me₄SiMe₃)(η¹‐CH₂SiMe₃)₂(THF)] (1) activated by [Ph₃C][B(C₆F₅)₄], through a non‐PFT (Polymerization Filling Technique) approach. MWNTs nanocomposites with low aluminum residue were obtained with excellent yields even though small amounts of triisobutylaluminium were needed as scavenger to prevent catalyst poisoning by MWNT impurities. MWNT bundles were disaggregated and highly coated with Poly(ethylene‐co‐norbornene) [P(E‐co‐N)] as revealed by transmission electron microscopy. Interestingly, P(E‐co‐N) copolymers showed T_g over 130 °C as well as norbornene content over 50 mol %; both values were higher than those obtained by the cationic active species in 1 /[Ph₃C][B(C₆F₅)₄]. A series of copolymerization reactions by 1 /[Ph₃C][B(C₆F₅)₄]/AlⁱBu₃ without MWNTs produced copolymers with the same unexpected features. The NMR analysis revealed the presence of rac‐ENNE and rac‐ENNNE sequences. Thus, AlⁱBu₃ changed the stereoirregular alternating copolymer microstructure produced by 1 /[Ph₃C][B(C₆F₅)₄]. We conclude that AlⁱBu₃ is not only a scavenger for CNT impurities, but it reacts with the THF ligand to give coordinatively unsaturated active species. Finally, P(E‐co‐N)/MWNT masterbatches were mixed with commercial TOPAS to produce cyclic olefin copolymer nanocomposites with excellent dispersion of filler. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5709–5719, 2009     

On the Triple Role of Fluoride Ions in Palladium‐Catalyzed Stille Reactions

The mechanism of Stille reactions (cross‐coupling of ArX with Ar′SnnBu₃) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans‐[ArPdBr(PPh₃)₂] (Ar=Ph, p‐(CN)C₆H₄) with Ar′SnBu₃ (Ar′=2‐thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate‐determining transmetallation by formation of trans‐[ArPdF(PPh₃)₂], which reacts with Ar′SnBu₃ (Ar′=Ph, 2‐thiophenyl) at room temperature, in contrast to trans‐[ArPdBr(PPh₃)₂], which is unreactive. However, the concentration ratio [F^?]/[Ar′SnBu₃] must not be too high, because of the formation of unreactive anionic stannate [Ar′Sn(F)Bu₃]^?. This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans‐[ArPdAr′(PPh₃)₂] generated in the transmetallation step.     

Univalent Gallium Complexes of Simple and ansa‐Arene Ligands: Effects on the Polymerization of Isobutylene

Using [Ga(C₆H₅F)₂]⁺[Al(OR^F)₄]^?( 1 ) (R^F=C(CF₃)₃) as starting material, we isolated bis‐ and tris‐η⁶‐coordinated gallium(I) arene complex salts of p‐xylene (1,4‐Me₂C₆H₄), hexamethylbenzene (C₆Me₆), diphenylethane (PhC₂H₄Ph), and m‐terphenyl (1,3‐Ph₂C₆H₄): [Ga(1,4‐Me₂C₆H₄)_2.5]⁺ ( 2⁺ ), [Ga(C₆Me₆)₂]⁺ ( 3⁺ ), [Ga(PhC₂H₄Ph)]⁺ ( 4⁺ ) and [(C₆H₅F)Ga(μ‐1,3‐Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺ ( 5²⁺ ). 4⁺ is the first structurally characterized ansa‐like bent sandwich chelate of univalent gallium and 5²⁺ the first binuclear gallium(I) complex without a Ga?Ga bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI‐BP86/SV(P) level), [Ga(PhC₂H₄Ph)]⁺[Al(OR^F)₄]^?( 4 ) and [(C₆H₅F)Ga(μ‐1,3‐Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺{[Al(OR^F)₄] ^?}₂ ( 5 ), featuring ansa‐arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR‐PIB). In comparison to the recently published 1 and the [Ga(1,3,5‐Me₃C₆H₃)₂]⁺[Al(OR^F)₄]^? salt ( 6 ) (1,3,5‐Me₃C₆H₃=mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR‐PIB with high contents of terminal olefinic double bonds (α‐contents=84–93 %), low molecular weights (M_n=1000–3000 g mol^?1) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6 , the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism.     

Bis(tetra‐n‐butylammonium) bis(μ‐1,2‐dicyanoethene‐1,2‐dithiolato‐κ3S,S′:S′)bis[(1,2‐dicyanoethene‐1,2‐dithiolato‐κ2S,S′)cobalt(III)]

In the title compound, (C₁₆H₃₆N)₂[Co(C₄N₂S₂)₂]₂, pairs of [Co(C₄N₂S₂)₂]^? anions combine to form discrete crystallographically centrosymmetric dimers, which stack along the c axis, surrounded by the counter‐cations. The metal atom in the anion has a five‐coordinate distorted square‐pyramidal geometry.     

Exploring the Limits of Frustrated Lewis Pair Chemistry with Alkynes: Detection of a System that Favors 1,1‐Carboboration over Cooperative 1,2‐P/B‐Addition

The zirconocene complex [{(C₆F₅)₂B‐(CH₂)₃‐Cp}(Cp‐PtBu₂)ZrCl₂] ( 6 ; Cp=cyclo‐C₅H₄) was prepared by hydroboration of [(allyl‐Cp)(Cp‐PtBu₂)ZrCl₂] ( 5 ) with HB(C₆F₅)₂ (“Piers’ borane”). It represents a frustrated Lewis pair (FLP) in which both the Lewis acid and the Lewis base were attached at the metallocene framework. Its reaction with 1‐pentyne did not result in the 1,2‐addition of or deprotonation reaction by the FLP, but rather in the 1,1‐carboboration of the triple bond, thereby obtaining a Z/E mixture (1.2:1) of the respective organometallic substituted alkenes 7 . The analogous reaction of 1‐pentyne with the phosphorous‐free system [{(C₆F₅)₂B‐(CH₂)₃‐Cp)}CpZrCl₂] ( 9 ) gave the respective 1,1‐carboboration products ( Z‐10 / E‐10 ≈1.3:1).     

A new photoluminescent coordination polymer constructed with an N‐donor ligand having extended coordination capabilities derived from quinoline and pyridine

Employment of the organic 2‐(pyridin‐4‐yl)quinoline‐4‐carboxylic acid ligand with extended coordination capabilities leads to the formation of the one‐dimensional copper(II) coordination polymer catena‐poly[[diaquacopper(II)]‐bis[μ‐2‐(pyridin‐4‐yl)quinoline‐4‐carboxylato]‐κ²N²:O;κ²O:N], {[Cu(C₁₅H₉N₂O₂)₂(H₂O)₂]·2H₂O}_n, under hydrothermal conditions. The ligand, isolated as its hydrochloride salt, namely, 4‐(4‐carboxyquinolin‐2‐yl)pyridinium chloride monohydrate, C₁₅H₁₁N₂O₂⁺·Cl^?·H₂O, reveals a pseudosymmetry element (translation a/2) in its crystal structure. The additional pyridyl N atom, in comparison with the previously reported analogues with an arene ring instead of the pyridyl ring in the present ligand molecule, promotes the formation of a one‐dimensional coordination polymer, rather than discrete molecules. This polymer shows photoluminescent properties with bathochromic/hypsochromic shifts of the ligand absorption bands, leading to a single band at 479 nm. The Cu^II ions are involved in weak antiferromagnetic interactions within dimeric units, as evidenced by SQUID magnetometry.