Homoleptic tetramethylaluminate complexes [Ln(AlMe4)3] (Ln=La, Nd, Y) reacted with HCpNMe2 (CpNMe2=1‐[2‐(N,N‐dimethylamino)‐ethyl]‐2,3,4,5‐tetramethyl‐cyclopentadienyl) in pentane at ?35 °C to yield half‐sandwich rare‐earth‐metal complexes, [{C5Me4CH2CH2NMe2(AlMe3)}Ln(AlMe4)2]. Removal of the N‐donor‐coordinated trimethylaluminum group through donor displacement by using an equimolar amount of Et2O at ambient temperature only generated the methylene‐bridged complexes [{C5Me4CH2CH2NMe(μ‐CH2)AlMe3}Ln(AlMe4)] with the larger rare‐earth‐metal ions lanthanum and neodymium. X‐ray diffraction analysis revealed the formation of isostructural complexes and the C? H bond activation of one aminomethyl group. The formation of Ln(μ‐CH2)Al moieties was further corroborated by 13C and 1H‐13C HSQC NMR spectroscopy. In the case of the largest metal center, lanthanum, this C? H bond activation could be suppressed at ?35 °C, thereby leading to the isolation of [(CpNMe2)La(AlMe4)2], which contains an intramolecularly coordinated amino group. The protonolysis reaction of [Ln(AlMe4)3] (Ln=La, Nd) with the anilinyl‐substituted cyclopentadiene HCpAMe2 (CpAMe2=1‐[1‐(N,N‐dimethylanilinyl)]‐2,3,4,5‐tetramethylcyclopentadienyl) at ?35 °C generated the half‐sandwich complexes [(CpAMe2)Ln(AlMe4)2]. Heating these complexes at 75 °C resulted in the C? H bond activation of one of the anilinium methyl groups and the formation of [{C5Me4C6H4NMe(μ‐CH2)AlMe3}Ln(AlMe4)] through the elimination of methane. In contrast, the smaller yttrium metal center already gave the aminomethyl‐activated complex at ?35 °C, which is isostructural to those of lanthanum and neodymium. The performance of complexes [{C5Me4CH2CH2NMe(μ‐CH2)AlMe3}‐ Ln(AlMe4)], [(CpAMe2)Ln(AlMe4)2], and [{C5Me4C6H4NMe(μ‐CH2)AlMe3}Ln(AlMe4)] in the polymerization of isoprene was investigated upon activation with [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4], and B(C6F5)3. The highest stereoselectivities were observed with the lanthanum‐based pre‐catalysts, thereby producing polyisoprene with trans‐1,4 contents of up to 95.6 %. Narrow molecular‐weight distributions (Mw/Mn<1.1) and complete consumption of the monomer suggested a living‐polymerization mechanism. 相似文献
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. 相似文献
The reactivity towards AlMe3 of discrete cationic ansa‐zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6‐tBu2‐Flu)(3‐tBu‐5‐Et‐Cp)}ZrMe2)] {Cp‐Flu} and rac‐[{Me2Si‐(2‐Me‐4‐Ph‐Ind)2}ZrMe2] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe3 adduct ( 3 b ) is reported. In the presence of excess AlMe3, the {SBI}‐based AlMe3 adduct 3 b undergoes a slow decomposition via C? H activation in a bridging methyl unit to yield a new species ( 4 b ) with a trimetallic {Zr(μ‐CH2)(μ‐Me)AlMe(μ‐Me)AlMe2} core. EXSY NMR data for the process 2 b ? 3 b → 4 b suggest very rapid and reversible binding of an additional AlMe3 molecule onto AlMe3 adduct 3 b . The resulting heterotrimetallic species intermediates exchange of methyl groups between different metal centers and slowly undergoes the C? H activation reaction towards 4 b . 相似文献
The reaction of monomeric [(TptBu,Me)LuMe2] (TptBu,Me=tris(3‐Me‐5‐tBu‐pyrazolyl)borate) with primary aliphatic amines H2NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(TptBu,Me)LuMe(NHR)], the solid‐state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(TptBu,Me)LnMe({μ2‐Me}AlMe3)] (Ln=Y, Ho) reacted selectively and in high yield with H2NR, according to methane elimination, to afford heterobimetallic complexes: [(TptBu,Me)Ln({μ2‐Me}AlMe2)(μ2‐NR)] (Ln=Y, Ho). X‐ray structure analyses revealed that the monomeric alkylaluminum‐supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by 1H and 13C NMR spectroscopic studies at variable temperatures and 1H–89Y HSQC NMR spectroscopy. Treatment of [(TptBu,Me)LnMe(AlMe4)] with H2NtBu gave dimethyl compounds [(TptBu,Me)LnMe2] as minor side products for the mid‐sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative‐scale amounts of complexes [(TptBu,Me)LnMe2] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(TptBu,Me)LnMe(AlMe4)] with N,N,N′,N′‐tetramethylethylenediamine (tmeda). The solid‐state structures of [(TptBu,Me)HoMe(AlMe4)] and [(TptBu,Me)HoMe2] were analyzed by XRD. 相似文献
A series of Al(III) chloride [LAl‐Cl]; Al(III) alkoxide [LAl‐OR]2; and Zn(II) [LZn]2 complexes with Schiff base ligands were obtained. 1H NMR and X‐ray diffraction studies indicate that [LAl‐Cl] complexes have Cs symmetry and the Al center is penta‐coordinated. The Al(III) alkoxide complex [L5Al‐OiPr]2 is a dimer bridged by OiPr? with the Al center in a distorted octahedral environment. Zn complexes [LZn]2 are double helix dimers with tetra‐coordinated Zn centers. The catalytic activity for the ring‐opening polymerization of rac‐lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three‐carbon bridge; more flexible four‐carbon bridges lower the activity. 相似文献
A series of Zn (II), Pd (II) and Cd (II) complexes, [(L) n MX 2 ] m (L = L‐a–L‐c; M = Zn, Pd; X = Cl; M = Cd; X = Br; n, m = 1 or 2), containing 4‐methoxy‐N‐(pyridin‐2‐ylmethylene) aniline ( L‐a ), 4‐methoxy‐N‐(pyridin‐2‐ylmethyl) aniline ( L‐b ) and 4‐methoxy‐N‐methyl‐N‐(pyridin‐2‐ylmethyl) aniline ( L‐c ) have been synthesized and characterized. The X‐ray crystal structures of Pd (II) complexes [L 1 PdCl 2 ] (L = L‐b and L‐c) revealed distorted square planar geometries obtained via coordinative interaction of the nitrogen atoms of pyridine and amine moieties and two chloro ligands. The geometry around Zn (II) center in [(L‐a)ZnCl 2 ] and [(L‐c)ZnCl 2 ] can be best described as distorted tetrahedral, whereas [(L‐b) 2 ZnCl 2 ] and [(L‐b) 2 CdBr 2 ] achieved 6‐coordinated octahedral geometries around Zn and Cd centers through 2‐equivalent ligands, respectively. In addition, a dimeric [(L‐c)Cd(μ ‐ Br)Br] 2 complex exhibited typical 5‐coordinated trigonal bipyramidal geometry around Cd center. The polymerization of methyl methacrylate in the presence of modified methylaluminoxane was evaluated by all the synthesized complexes at 60°C. Among these complexes, [(L‐b)PdCl 2 ] showed the highest catalytic activity [3.80 × 104 g poly (methyl methacrylate) (PMMA)/mol Pd hr?1], yielding high molecular weight (9.12 × 105 g mol?1) PMMA. Syndio‐enriched PMMA (characterized using 1H‐NMR spectroscopy) of about 0.68 was obtained with Tg in the range 120–128°C. Unlike imine and amine moieties, the introduction of N‐methyl moiety has an adverse effect on the catalytic activity, but the syndiotacticity remained unaffected. 相似文献
Syntheses and structures of five imido‐bridged dinuclear titanium complexes and two (bis)ligand‐coordinated mononuclear titanium complexes are reported. Addition of 1 or 2 equiv. of Schiff base ligand (((1H‐pyrrol‐2‐yl)methylene)amino)‐2,3‐dihydro‐1H‐inden‐2‐ol (H2L) to Ti(NMe2)4 resulted in transamination with 4 equiv. of dimethylamides generating a (bis)ligand‐coordinated complex Ti(L)2 ( 1 ). Treatment of Ti(NMe2)4 with 1 equiv. of tBuNH2 followed by addition of 1 equiv. of H2L afforded an imido‐bridged complex [Ti(L)(NtBu)]2 ( 2 ). 1:1:1:1 reaction of Ti(NMe2)4/RNH2/H2L/py(or phen) produced imido‐bridgedcomplexes [Ti(L)(NPh)(py)]2 ( 3 ), [Ti(L)(4‐F‐PhN)(py)]2·Tol ( 4 ·Tol), [Ti(L)(4‐Cl‐PhN)(py)]2·Tol·THF ( 5 ·Tol·THF), [Ti(L)(4‐Br‐PhN)(py)]2·Tol ( 6 ·Tol) and a (bis)ligand‐coordinated complex Ti(L)2·phen ( 7 ) (py = pyridine, phen = 1,10‐phenanthroline). Attempts to prepare the monomeric titianium imido complexes were unsuccessful. DFT studies show that the assumed compound which contains Ti = N species is less stable than imido‐bridged Ti‐N(R)‐Ti complexes, providing the better understanding of the experimental results. 相似文献
The solution structure of AlMe2F and its reactivity with a prototypical ansa‐metallocene have been investigated by advanced NMR techniques, in an attempt to indirectly shed some light on the structure and working principles of methylalumoxane (MAO) mixtures in olefin polymerization. In solution, AlMe2F gives rise to a complex equilibrium of oligomeric species, including a heterocubane [(Me2Al)4F4] tetramer, resembling the behavior of MAO. This complex mixture reacts with (ETH)ZrMe2 (ETH=rac ‐[ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)]) to afford [(ETH)ZrMeδ+(μ‐F)(AlMe2F)nAlMe3δ−] inner‐sphere ion pairs through successive insertions/deinsertions of AlMe2F units into the Zr⋅⋅⋅(μ‐F) bond. 相似文献
Syntheses and Structures of Bis(4,4′‐t‐butyl‐2,2′‐bipyridine) Ruthenium(II) Complexes with functional Derivatives of Tetramethyl‐bibenzimidazole [(tbbpy)2RuCl2] reacts with dinitro‐tetramethylbibenzimidazole ( A ) in DMF to form the complex [(tbbpy)2Ru( A )](PF6)2 ( 1a ) (tbbpy: bis(4,4′‐t‐butyl)‐2,2′bipyridine). Exchange of the two PF6? anions by a mixture of tetrafluor‐terephthalat/tetrafluor‐terephthalic acid results in the formation of 1b in which an extended hydrogen‐bonded network is formed. According to the 1H NMR spectra and X‐ray analyses of both 1a and 1b , the two nitro groups of the bibenzimidazole ligand are situated at the periphery of the complex in cis position to each other. Reduction of the nitro groups in 1a with SnCl2/HCl results in the corresponding diamino complex 2 which is a useful starting product for further functionalization reactions. Substitution of the two amino groups in 2 by bromide or iodide viaSandmeyer reaction results in the crystalline complexes [(tbbpy)2Ru( C )](PF6)2 and [(tbbpy)2Ru( D )](PF6)2 ( C : dibromo‐tetrabibenzimidazole, D : diiodo‐tetrabibenzimidazole). Furthermore, 2 readily reacts with 4‐t‐butyl‐salicylaldehyde or pyridine‐2‐carbaldehyde under formation of the corresponding Schiff base RuII complexes 5 and 6 . 1H NMR spectra show that the substituents (NH2, Br, I, azomethines) in 2 ‐ 6 are also situated in peripheral positions, cis to each other. The solid state structure of both 2 , and 3 , determined by X‐ray analyses confirm this structure. In addition, the X‐ray diffraction analyses of single crystals of the complexes [(tri‐t‐butyl‐terpy)(Cl)Ru( A )] ( 7 ) and [( A )PtCl2] ( 8 ) display also that the nitro groups in these complexes are in a cis‐arrangement. 相似文献
Summary: A DFT method has been applied for quantum‐chemical calculations of the molecular structure of charge‐neutral complex LFeMe(μMe)2AlMe2 which is formed in system LFeMe2 + AlMe3 (L = 2,6‐bis(imino)pyridyl). Calculations suggested the formation of highly polarized complex LFeMe(μMe)2AlMe2 ( II ) in system LFeMe2 + AlMe3, characterized by r(Fe μMe) = 3.70 Å and r(Al μMe) = 2.08 Å and deficient electron density on fragment [LFeMe]Q (Q = +0.80 e). Polarization of the complex progresses with the bounding of two AlMe3 molecules (complex LFeMe(μMe)2AlMe2 · 2AlMe3 ( III )) and with replacement of AlMe3 by MeAlCl2 (complex LFeMe(μMe)2AlCl2 ( IV )). The activation energy of ethylene insertion into the Fe Me bond of these complexes has been calculated. It was found that the heat of π‐complex formation increases with increasing of polarization extent in the order II < III < IV . Activation energy of the insertion of coordinated ethylene into Fe Me bond decreases in the same order: II > III > IV .
Calculated model complex (NH3)3FeMe2; tridentate bis(imino)pyridyl ligand was substituted by three coplanar NH3 groups. 相似文献
New [(N?,N,N?)ZrR2] dialkyl complexes (N?,N,N?=pyrrolyl‐pyridyl‐amido or indolyl‐pyridyl‐amido; R=Me or CH2Ph) have been synthesised and tested as pre‐catalysts for ethene and propene polymerisation in combination with different activators, such as B(C6F5)3, [Ph3C][B(C6F5)4], [HNMe2Ph][B(C6F5)4] or solid AlMe3‐depleted methylaluminoxane (DMAO). Polyethylene (Mw>2 MDa and Mw/Mn = 1.3–1.6) has been produced if pre‐catalysts were activated with 1000 equivalents of DMAO (based on Al) [activity >1000 kgPE (mol[Zr] h mol atm)?1] or by using a higher pre‐catalyst concentration and a mixture of [HNPhMe2][B(C6F5)4] (1 equiv) and AliBu2H (60 equiv). In the case of propene polymerisation, activity has been observed only if pre‐catalysts were treated with an excess of AliBu2H prior to addition of DMAO, which led to highly isotactic polypropylene ([mmmm]>95 %). Neutral pre‐catalysts and ion pairs derived from their activation have been characterised in solution by using advanced 1D and 2D NMR spectroscopy experiments. The detection and rationalisation of intercationic NOEs clearly showed the formation of dimeric species in which some pyrrolyl or indolyl π‐electron density of one unit is engaged in stabilising the metal centre of the other unit, which relegates the counterions in the second coordination sphere. The solid‐state structure of the dimeric indolyl‐pyridyl‐amidomethylzirconium derivative, determined by X‐ray diffraction studies, points toward a weak Zr???η3‐indolyl interaction. It can be hypothesised that the formation of dimeric cationic species hampers monomer coordination (especially of less reactive α‐olefins) and that addition of AliBu2H is crucial to split the homodimers. 相似文献
The reaction of 2‐methoxybenzyl alcohol with one molar equiv of R2AIX in diethyl ether at 0°C gives [(2‐MeOC6H4CH2‐μ‐O)AlRX]2 ( 1 : R = Et, X = Cl, 2 : R = X = Et). In addition, 2,4‐di‐tert‐butylphenol reacts with iBu3Al affording a four‐coordinated aluminum compound [(μ‐2,4‐tBu2‐C6H4O)Al(iBu)2]2 ( 4 ). Single crystal X‐ray structure analysis of 4 shows a C2h‐symmetry with a planar Al2O2 core. Ring‐opening polymerization (ROP) of caprolactones initiated by 1, 4 and [(μ‐OCH2C6H4OMe)Al(iBu)2]2 ( 3 ) is performed and polyesters with narrow molecular weight distributions were obtained from the “living” ROP of caprolactones. 1H NMR spectroscopic studies of PCL reveal that the initiator of 1 and 3 is through the Al‐OAr function, but the initiator of 4 is through the Al‐ iBu group. 相似文献