Equiv Of AlMe3 Research Articles

Synthesis and structural characterization of monomeric aluminum keto‐imine complexes: Catalytic activity toward CO2/styrene oxide coupling and ε‐caprolactone ring opening polymerization

AbstractA series of benzoylacetone‐imine ligands, PhCOCHCMeNHR (L1H, R = CH2Ph; L2H, R = CH2Ph‐4‐Me; and L3H, R = CH2Ph‐4‐OMe), are first synthesized following the condensation of benzoylacetone and 4‐substituted benzylamine. Later, reacting L1H–L3H with one equivalent of AlMe3 in toluene, the monomeric Al derivatives are generated, (PhCOCHCMeNR)AlMe2 (1, R = CH2Ph; 2, R = CH2Ph‐4‐Me; 3, R = CH2Ph‐4‐OMe). All the ligands and metal derivatives are characterized by 1H and 13C NMR spectroscopy. Single crystal X‐ray diffraction analysis reveals the geometry of all ligands and complex 2. As supporting catalysts, the Al derivatives, 1–3, are effective to initiate the coupling of CO2 and styrene oxide to form cyclic carbonates. Although employing TBAI (tetra‐n‐butylammonium iodide), TBAC, tetrabutylammonium chloride, and TBAB (tetra butyl ammonium bromide) as cocatalyst, the optimized catalytic system exhibits the best conversion of epoxide in presence of TBAI under the reaction temperature and time, respectively, 90°C and 6 hr, respectively. The ring opening polymerization of ε‐caprolactone is also appraised subjecting the Al derivatives, 1–3, as catalysts in presence of benzyl alcohol and all the conversions of ε‐caprolactone reach over 95% at the reaction condition of 100°C and 1 hr.

Aluminum derivatives incorporating 4,4′-methylenebis(cyclohexyl) linked dehydroacetic acid-imine ligands: structural aspects, CO2/styrene oxide coupling reaction

A series of methylene-bis-cyclohexyl amine ligands, LMeH2, LPhH2 and LDAH2 are generated from the reaction of 4,4′-methylenebis(cyclohexylamine) with 2,4-pentanedione, benzoylacetone, and dehydroacetic acid, respectively in methanol. Later, the combination of LMeH2, LPhH2, and LDAH2 with two equivalents of AlMe3 in methylene chloride initiate the di-aluminum compounds, LMe[AlMe2]2, LPh[AlMe2]2 and LDA[AlMe2]2. As supporting catalysts, the Al-derivatives are effective in the coupling of CO2 with epoxide to form cyclic carbonates. Interestingly, the optimized catalyst system displays > 90% conversion of the epoxides in solvent free condition while employing TBAI (tetra-n-butylammonium iodide) and TBAB (tetra butyl ammonium bromide) as co-catalyst.

Aluminium complexes supported by a thioether-bridged salen ligand: synthesis, characterization and application in ε-caprolactone homopolymerization and copolymerization with L-lactide

Several aluminium alkyl and alkyloxide complexes supported by a thioether-bridged salen ligand were synthesized by the protonolysis reaction. Reactions of N,N’-bis(3,5-di-tert-butylsalicylidene)-2,2’-diaminophenylsulfide (H2L) with one or two equivalents of AlMe3 in toluene at 100 °C afforded the corresponding mono- and binuclear aluminium methyl complexes LAlMe (1) and L(AlMe2)2 (2). Treatment of the in situ generated complex 1 with one equivalent of ROH (R = PhCH2, iPr, CH3OCH2CH2) produced the desired aluminium alkyloxide complexes LAlOCH2Ph (3), LAl(OiPr) (4) and LAlO(CH2)2OCH3 (5). All the molecular structures were established by single crystal X-ray diffraction studies. It was found that aluminium alkyloxide complexes 3-5 showed higher catalytic activity for the homopolymerization of ε-caprolactone (ε-CL) than corresponding aluminium methyl complexes 1 and 2. Furthermore, these alkyloxide complexes were also efficient initiators for the copolymerization of L-lactide and ε-CL to give practically random copolymers.

A series of aluminium complexes based on a β-diketiminate ligand: Synthesis, structures and their application to ring-opening polymerization of ε-caprolactone

A series of aluminum complexes based on a β-diketiminate ligand HL (HL = N{-4-[(2,6-diisopropyl-phenylamino)pent-3-en-2-ylidene]-6-methyl}pyridin-2- amine) have been prepared and characterized spectroscopically and structurally. Reactions of the HL ligand with one equivalent of AlMe3, AlEt3 and AlEt2Cl, respectively, in toluene, gave complexes [LAlMe2] (1), [LAlEt2] (2) and [LAlEtCl] (3) in high yields. Complexes 1 and 2 contain four-coordinated mononuclear aluminum center. The aluminum center of 3 is five-coordinated. Complexes 1–3 were used to catalyze the ring-opening polymerization of ε-caprolactone. Complexes 1–3 are very rare cases of aluminum alkyl compounds supported by β-diketiminate ligands, which show moderate activity toward the ring-opening polymerization (ROP) of ε-caprolactone (CL) in the absence of benzyl alcohol. However, in the presence of benzyl alcohol, the polymerization rate is remarkably accelerated and the conversions are greatly improved. The monomer conversion and number average molecular weight of poly(ε-caprolactone) (PCL) catalyzed by 1–3 shows a linear relationship. This result indicates that the polymerizations mediated by 1–3 exhibited controllable manner.

Tetranuclear complexes of group 12 and 13 supported on a polynucleating ligand and activity studies in the ROP of rac-lactide

A polynucleating ligand (L-H4) containing four N,O bidentate sites was cleanly metallated by four equivalents of AlMe3, GaMe3 and ZnEt2 resulting in tetranuclear complexes L(MMe2)4 (M = Al (1), Ga (2)) and L(ZnEt(CH3CN)0.5)4 (3). The Al complex shows the best catalytic activity for the ring-opening polymerization (ROP) of rac-lactide (rac-LA) in the present family of tetranuclear compounds. Polymerization studies indicate the lack of cooperativity between metal centers in the ROP of rac-LA, despite having a ligand platform which binds to four metal centers.

Zwitterionic Trivalent (Alkyl)lanthanide Complexes in Ziegler-Type Butadiene Polymerization

The organolanthanide complexes Ln{C(SiHMe2)3}3 (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) react with 1 or 2 equiv of B(C6F5)3 to yield the well-defined zwitterionic species Ln{C(SiHMe2)3}2HB(C6F5)3 (Ln = La, 2a; Ce, 2b; Pr, 2c; Nd, 2d) or LnC(SiHMe2)3{HB(C6F5)3}2 (Ln = La, 3a; Ce, 3b; Pr, 3c; Nd, 3d), respectively. These complexes are shown to contain labile, bridging Si–H⇀Ln and o-F→Ln interactions based upon the observation of low one-bond silicon–hydrogen coupling constants (1JSiH) in 1H NMR spectra of 2a and 3a, the presence of one set of C6F5 signals in the 19F NMR spectra of 2a and 3a, the detection of only m-F and p-F resonances in the 19F NMR spectra of 2b–d and 3b–d, two νSiH bands in the IR spectra of 2a–d, and X-ray crystallography analyses of 2b and 3d. In addition, a hexahaptotoluene molecule is coordinated to neodymium in 3d. Reactions of 1a and (AlMe3)2 yield labile adducts. With greater than 3 equiv of AlMe3, exchange between free and bound AlMe3 groups was observed in EXSY NMR experiments. Com...

Structural aspects and ring opening polymerization of ε-caprolactone using mono- and di-aluminum compounds incorporating bidentate pyrrole-morpholine ligands

A series of Al-compounds incorporating the bidentate pyrrole-morpholine precursor C4H3NH [2-CH2N(CH2CH2)2O] (1) and aluminum-alkyl have been conveniently synthesized and characterized by 1H and 13C NMR spectroscopy. Reacting one or two equivalents of 1 with AlMe3 in toluene afforded AlMe2{C4H3N [2-CH2N(CH2CH2)2O]} (2) and AlMe{C4H3N [2-CH2N(CH2CH2)2O]}2 (3), respectively, in moderate yield. Furthermore, compound (4), AlMe2{C4H3N [2-CH2N(CH2CH2)2O]}·AlMe3, was acquired either by the combination of 2 and one equivalent of AlMe3 or directly from the reaction between 1 and two equivalents of AlMe3. The molecular structures of 1, 2, and 4, were determined by single crystal X-ray diffractometry in solid state, showing a distorted tetrahedral arrangement around the Al atom in 2 and 4. All the aluminum compounds could effectively initiate the ring-opening polymerization (ROP) of ε-caprolactone in a well-controlled manner with molecular weight distributions (PDI = 1.03–1.49).

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a–1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the 4-position of the N-aryl group with the most electron donating i-Pr derivative exhibiting the highest activity (1b > 1a > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp.

Synthesis of Titanium Complexes Containing an Amine Triphenolate Ligand of the Type [TiX{(O-2,4-R2C6H2)-6-CH2}3N] and the Ti–Al Heterobimetallic Complexes with AlMe3: Effect of a Terminal Donor Ligand in Ethylene Polymerization

The synthesis of various titanatranes containing tris(aryloxo)amine ligands, TiX[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me (1), tBu (2); X = OiPr (a), OtBu (b), OCH(CF3)2 (c), OC(CF3)3 (d), Cl (e)], and some reactions with Al alkyls have been explored. The Ti–Al heterobimetallic complexes [TiMe{(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-Me2-C6H2-6-CH2)}N]-[Me2Al(μ2-OR′)] [R′ = tBu (3b), CH(CF3)2 (3c), C(CF3)3 (3d)] were isolated by reaction of 1b–d with 1 equiv of AlMe3, whereas reaction of 2b with AlMe3 in toluene did not take place under the same conditions, and the reaction of 2c afforded the methyl complex TiMe[{(O-2,4-tBu2C6H2)-6-CH2}3N]. Structures of 3b,c were determined by X-ray crystallography. These complexes exhibited high catalytic activities for ethylene polymerization in n-octane in the presence of MAO, and the activity by 1 and 2 was affected by the terminal donor ligand (X) as well as the substituent on the atrane ligand (R). The activities by 1c,d increased upon addition of AlMe3, and the corresponding hete...

Synthesis, Crystal Structures and their Utilities in Tishchenko Reaction of N,O-Bidentate Aluminum Compounds

Deprotonolysis of the N,O-bidentate pyridyl functionalized alkoxy ligands, 1,1-dimethyl-2-(pyridin-2-yl)ethanol (L 1 H), 1-phenyl-2-(pyridin-2-yl)ethanol (L 2 H) and 1,1-diphenyl-2-(pyridin-2-yl)ethanol (L 3 H), with 1 equiv of AlMe3 gave the corresponding dimeric metal-monoalkyl compounds [L 1 AlMe2]2 (1), [L 2 AlMe2]2 (2), and [L 3 AlMe2]2 (3), respectively. Compounds 1–3 were characterized by 1H and 13C NMR spectroscopy analysis, and the molecular structures of 1 and 2 were further confirmed by X-ray diffraction analysis. In the presence of i PrOH, aluminum compounds 1–2 exhibited excellent catalytic activity for the solvent-free Tishchenko reaction under mild conditions. In addition, the catalyst 3 can be easily isolated and recycled three times without a significant decrease in activity.

Synthesis and characterization of tri-dentate pyrrole-morpholine ligands and their corresponding aluminum, magnesium, and zinc compounds

A series of metal compounds containing tri-dentate monoanionic pyrrole-morpholine ligands was synthesized and characterized. The reaction of O(CH2CH2)2NH·HCl, pyrrole and formaldehyde generated a new type of tri-dentate pyrrole-morpholine ligand, C4H2NH{2,5-[CH2N(CH2CH2)2O]2} (1), in high yield. The reaction of 1 with one equivalent of AlMe3 and ZnMe2 in toluene generated AlMe2{C4H2N{2,5-[CH2N(CH2CH2)2O]2}} (2) and {ZnMe{C4H2N{2,5-[CH2N(CH2CH2)2O]2}}}2 (4), respectively, in moderate yield. The reaction of two equivalents of 1 with MgnBu2 in THF generated a bis-pyrrolyl Mg compound, Mg{C4H2N{2,5-[CH2N(CH2CH2)2O]2}}2(THF) (3), in moderate yield. Compound 4 is sensitive to air and moisture and it decomposed into a hexa-Zn compound, {(ZnMe)2{C4H2N-{2,5-[CH2N(CH2CH2)2O]2}(μ4-O)2(μ2-ZnMe)2} (5), when a small amount of moisture leaked into the flask during the recrystallization process. Compounds 1–4 were characterized by 1H and 13C NMR spectra and the structures of 1, 3, and 5 were also determined by single crystal X-ray diffractometry. Compounds 2 and 3 were tested as initiators for the ring opening polymerization of ε-caprolactone and 3 showed excellent activity.

Mukaiyama Aldol Reactions Catalyzed by a Trimeric Organo Aluminum(III) Alkoxide

Mukaiyama aldol reactions of enol ethers with a variety of aldehydes and ketones are efficiently catalyzed at 0–25 °C by the sterically bulky trimeric organo aluminum(III) alkoxide 1 synthesized via the reaction of 3 equiv of AlMe3 with tripodal tris(2-hydroxy-3-tert-butyl-5-methylphenyl) methane and the elimination of 3 equiv of methane. Comparisons of its catalytic properties with the less sterically hindered analogue 2, the more sterically hindered analogue 3, a monomeric aluminum near-analogue 4, and a dimeric alumatrane 5 revealed that 1 possesses superior activity.

Synthesis, structure, and catalytic activity of organoaluminum complexes with chiral biaryl Schiff-base ligands

A new series of organoaluminum complexes have been prepared by alkane elimination in good yields from AlMe3 and chiral biaryl Schiff-base NO2 ligands, 1H2-7H2, which are derived from (S)-2-amino-2′-hydroxy-1,1′-binaphthyl or (S)-2-amino-2′-hydroxy-6,6′-dimethyl-1,1′-biphenyl, respectively. However, solvent plays an important role in the formation of the aluminum complexes. For example, treatment of ligand 1H2 with 1 equiv of AlMe3 in THF gives the mononuclear complex (1)AlMe(THF) (8) in 90% yield. While reaction of 2H2, 3H2, 4H2, 5H2, 6H2 or 7H2 with 1 equiv of AlMe3 in benzene gives the binuclear complexes {(2)AlMe}2 (9), {(3)AlMe}2 (10), {(4)AlMe}2 (11), {(5)AlMe}2 (12), {(6)AlMe}2 (13) and {(7)AlMe}2 (14), respectively, in good yields. Complexes 8–14 have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complexes 8–14 are active catalysts for the polymerization of rac-lactide in the presence of isopropanol, leading to the heterotactic-rich polylactides.

Aluminium Complexes of a Sterically Demanding Bis(iminophosphorane)methandiide

The reaction of the sterically demanding bis(iminophosphorane)methane, {DipN=P(Ph2)}2CH2, H2L 1 (where Dip = 2,6-iPr2C6H3), with one or two equivalents of AlMe3 in toluene under varying conditions led to the methanide complex [HLAlMe2] 4, and the methandiide complex [L(AlMe2)2] 5, respectively. Iterative iodination of complex 5 with I2 in toluene yielded the complexes [L(AlMeI)2] 6 and [L(AlI2)2] 7. The complexes 4–7 were structurally characterised. The methanide 4 forms a puckered six-membered ring without Al-C(methanide) contact and the complexes 5 and 6 show coordination of the methandiide ligand to two Al atoms forming two four-membered rings on the central spirocyclic carbon centre. Complex 7 shows an asymmetric coordination mode of the two Al centres to the methandiide ligand in the solid state with an almost planar, severely distorted three-coordinate methandiide carbon atom and only one short Al–C bond.

Synthesis of a Tin(II) 1,3-Benzobis(thiophosphinoyl)methanediide Complex and Its Reactions with Aluminum Compounds

The synthesis of a tin(II) 1,3-benzobis(thiophosphinoyl)methanediide complex and its reactions with aluminum compounds are reported. The reaction of the 1,3-benzodiphosphole disulfide [1,3-C6H4(PhP═S)2CH2] (4) with [Sn{N(SiMe3)2}2] in refluxing toluene afforded the tin(II) 1,3-benzobis(thiophosphinoyl)methanediide [{μ-1,3-C6H4(PhP═S)2C}Sn]2 (5). The X-ray crystal structure of 5 shows that it has a 1,3-dimetallacyclobutane structure. The reaction of 5 with 1 equiv of AlCl3 in CH2Cl2 afforded [1,3-C6H4(PhP═S)2C(Sn){Sn(S═PPh)2C(AlCl3)-1,3-C6H4}] (6). The reaction proceeds via an insertion of a AlCl3 molecule into one of the Sn–C bonds in 5. The reaction of 5 with 2 equiv of AlCl3 in CH2Cl2 afforded [1,3-C6H4(PhP═S)2C(Sn)(AlCl3)] (7). The reaction appears to proceed via the formation of compound 6, which then undergoes an insertion with another AlCl3 molecule to form compound 7. The transmetalation reaction of 5 with 2 equiv of AlMe3 in CH2Cl2 afforded [1,3-C6H4(PhP═S)2CAlMe]2 (8), which contains a terminal Cmethanediide–Al bond.

Syntheses, Structures, and Reactivities of Homometallic Rare‐Earth‐Metal Multimethyl Methylidene and Oxo Complexes

Unsolvated, trinuclear, homometallic, rare-earth-metal multimethyl methylidene complexes [{(NCN)Ln(μ(2)-CH(3))}(3)(μ(3)-CH(3))(μ(3)-CH(2))] (NCN = L = [PhC{NC(6)H(4)(iPr-2,6)(2)}(2)](-); Ln = Sc (2a), Lu (2b)) have been synthesized by treatment of [(L)Ln{CH(2)C(6)H(4)N(CH(3))(2)-o}(2)] (Ln = Sc (1a), Lu (1b)) with two equivalents of AlMe(3) in toluene at ambient temperature in good yields. Treatment of 1 with three equivalents of AlMe(3) gives the heterometallic trinuclear complexes [(L)Ln(AlMe(4))(2)] (Ln = Sc (3a), Lu (3b)) in good yields. Interestingly, 2 can also be generated by recrystallization of 3 in THF/toluene, thereby indicating that the THF molecule can also induce C-H bond activation of 2. Reaction of 2 with one equivalent of ketones affords the trinuclear homometallic oxo-trimethyl complexes [{(L)Ln(μ(2) -CH(3))}(3) (μ(3)-CH(3))(μ(3)-O)] (Ln = Sc(4a), Lu(4b)) in high yields. Complex 4b reacts with one equivalent of cyclohexanone to give the methyl abstraction product [{(L)Lu(μ(2) -CH(3) )}(3) (μ(3) -OC(6)H(9))(μ(3)-O)] (5b), whereas reaction of 4b with acetophenone forms the insertion product [{(L)Lu(μ(2)-CH(3))}(3){μ(3)-OCPh(CH(3))(2)}(μ(3)-O)] (6b). Complex 4a is inert to ketone under the same conditions. All these new complexes have been characterized by elemental analysis, NMR spectroscopy, and confirmed by X-ray diffraction determination.

Synthesis and Structural Characterization of a Novel Aluminum Amidato Derivative Exhibiting a Rare 16-Membered Wheel Containing Four Aluminum Centers

Reaction of 2 equiv of AlMe3 with 1,2-C6H4{NHC(t-Bu)O}2 gives the tetranuclear aluminum compound [{AlMe2(1,2-C6H4{NC(t-Bu)O}2)}AlMe2]2 (1), the molecular structure of which exhibits a novel central 16-membered ring formed by four AlMe2 units and four NCO fragments. Treatment of 1 with 1 equiv of B(C6F5)3 affords the ionic species [{(AlMe2)3(AlMe)(1,2-C6H4{NC(t-Bu)O}2)2][MeB(C6F5)3] (2).

Aluminum Complexes of Fluorinated β-Diketonate Ligands: Syntheses, Structures, Intramolecular Reduction, and Use in Ring-Opening Polymerization of Lactide

Routes toward heteroleptic Al complexes supported by fluorinated β-diketonate ligands have been studied. Reactions of pro-ligands (acacR1,R2)H (R1 = R2 = CF3, “(hfacac)H”; R1 = CF3, R2 = tBu) with 0.5 equiv of AlMe3 or AlMe2Cl systematically yielded the corresponding homoleptic complexes Al(hfacac)3 (1) and Al(acacCF3,tBu)3 (2). Compound 2 exists in CD2Cl2 solution as a mixture of fac- and mer-isomers. Heteroleptic complexes [Al(acacR1,R2)2(OiPr)]n (R1 = R2 = CF3, 3; R1 = CF3, R2 = tBu, 4) were cleanly prepared from the reaction of the corresponding (acacR1,R2)H pro-ligands and 0.5 equiv of AlMe2(OiPr). Reaction of (hfacac)H and 0.5 equiv of Al(OiPr)3 at room temperature afforded 3 contaminated by other products, of which [κ2:μ2-(hfacac)5(OiPr)4Al3] (5) was isolated. When the same reaction was carried out at 55 °C, (S,R)-[κ,μ:κ2-(4H-hfacac)(hfacac)Al(THF)]2 (6), which contains a μ-bridging dianionic ligand (4H-hfacac)2− that arises from the reduction of one carbonyl group in (hfacac)−, was isolated in moderate yield (22%). Single-crystal X-ray diffraction studies revealed that complexes 3, 6, and 7 ([Al(hfacac)2(OH)]2, the hydrolysis product of 3) are dinuclear in the solid state with μ-bridging isopropoxide or hydroxide groups, while 5 features a symmetric trinuclear structure with the two terminal Al atoms supported by two (hfacac)− ligands and bridged via μ-isopropoxide groups to a central Al atom supported by a single (hfacac)− ligand. The Al-OiPr complexes 3 and 4 are effective initiators for the ring-opening polymerization of racemic lactide in THF or toluene solutions, giving atactic PLAs, end-capped by OiPr and OH groups, with controlled molecular weights (Mn up to 30 300 g·mol−1) and relatively narrow polydispersities (Mw/Mn = 1.10−1.32).

Formation of a Titanium Complex with a Ti═CHAl2Structural Unit from LTiMe3and Trimethylaluminum

The reaction of LTiCl3 (1) (L = HC(CMeN(2,6-iPr2C6H3))2, nacnac) with MeLi·(Et2O)0.14 in toluene afforded the stable Ti(IV) alkyl complex LTiMe3 (1). Reaction of 1 with 2 equiv of AlMe3 in toluene ...

Catalytic and Stoichiometric Reactions by Half‐Metallocene Diene Complexes of Niobium and Tantalum

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