Cationic Aluminum Complexes Research Articles

Chiral Tetra-coordinate Aluminum Cation in Catalysis

Although the application of cationic aluminum complexes in catalysis has been extensively investigated, the incorporation of an aluminum cation into a chiral environment is less explored. In this s...

Cationic aluminum complexes supported on tridentate O,N,O platform and activity studies in the ring opening polymerization of ε-caprolactone

A tridentate ligand (LONO-H2) containing O,N,O donors was cleanly metallated by one equivalent of Me2AlCl, followed by chloride abstraction by GaCl3, AlCl3, or Na[BArF24], resulting in cationic Al complexes with the corresponding counter ion [LONOAl(THF)3]+[A]− (A = [GaCl4]− (1), [AlCl4]− (2), [BArF24]− (3)). Complexes 1 and 3 are efficient catalysts for the polymerization of neat ε-caprolactone at room temperature.

Cationic aluminum, gallium, and indium complexes in catalysis

The introduction of cationic charge allows cationic group 13 complexes to be excellent Lewis acid catalysts. Cationic aluminum, gallium, and indium complexes in catalysis are comprehensively reviewed based on the reaction type.

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone.

The first structures exhibiting bidentate (N, O) chelation of a morpholine group to a p-block element (aluminum) have been prepared and characterized by X-ray diffraction methods: Al[L]+ [WCA]-, where [L] = 4-(2-aminoethyl)morpholinylamino- N, N-bis(2-methylene-4,6- tert-butylphenolate) and [WCA]- is a weakly coordinating anion. These compounds are easily synthesized by reacting Al[L]Cl with an equimolar amount of anhydrous Lewis acid and were characterized by elemental analyses, ESI-MS, MALDI-TOF MS, 1H, 13C{1H}, and multinuclear NMR spectroscopy. DFT calculations showed that Al[L]+ cations containing bidentate NO coordination of the morpholine group are at least 21.1 kJ/mol more stable when compared to hypothetical monodentate (N bound) structures. When combined with protic co-initiators (EtOH, glycerol carbonate), the cationic complexes, where [WCA]- = [GaCl4]- or [InCl4]-, are living catalyst systems for the polymerization of ε-caprolactone, producing polycaprolactone with narrow dispersity ( D̵ = 1.00-1.05). Employing glycidol as a co-initiator furnished polymers with narrow dispersity ( D̵ = 1.01-1.07) but experimental molecular weights diverged considerably from the calculated values. Similar reactivity toward ROP was observed for all complexes containing a stable [WCA]- but where [WCA]- = [AlCl4]-, upon combination with alcohols, alcoholysis was observed. Kinetic studies (Eyring analyses) allowed the determination of activation parameters, which were consistent with a coordination-insertion mechanism for the catalysts containing [WCA]- = [GaCl4]- or [InCl4]-. End group analyses using MALDI-TOF mass spectrometry and 1H NMR spectroscopy showed hydroxyl and ester end groups within the polymer, corroborating the proposed mechanism. Stoichiometric reactions of EtOH, glycidol or tert-butyl alcohol with the complex, where [WCA]- = [GaCl4]-, showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.

Synthesis and characterization of neutral and cationic aluminum complexes supported by a furfuryl-containing aminophenolate ligand for ring-opening polymerization of ε-caprolactone

Mononuclear aluminum complexes supported by novel furfuryl-containing aminophenolate ligand are reported along with CL polymerization.

An Investigation of the Symmetric and Asymmetric Cleavage Products in the System Aluminum Trihalide/1-Butylimidazole.

Mixtures of AlX3 (X=Cl, Br) with 1-butylimidazole (BuIm) in various ratios were investigated. The mixtures were characterized by multinuclear (1 H, 27 Al, 13 C, and 15 N) NMR, IR, and Raman spectroscopy and in part by single-crystal X-ray diffraction. Depending on the molar fraction x(AlBr3 ) of the AlBr3 -based mixtures, the cationic aluminum complexes [Al(BuIm)6 ]3+ and [AlBr2 (BuIm)4 ]+ , the neutral adduct [AlBr3 (BuIm)], as well as the anions Br- , [AlBr4 ]- , and [Al2 Br7 ]- could be identified as the products of the symmetric and asymmetric cleavage of dimeric Al2 Br6 . Furthermore, there are hints at the formation of [AlBr2 (BuIm)2 ]+ or related cations. Comparison of the AlBr3 /BuIm system with AlCl3 -based mixtures revealed the influence of the halide: In contrast to AlBr3 , the trication [Al(BuIm)6 ]3+ could not be detected as main product in a 1:6 mixture of AlCl3 and BuIm. Additionally, [AlCl3 (BuIm)] crystallizes from a mixture with x(AlCl3 )=0.60 at room temperature, whereas the corresponding AlBr3 -based mixture remains liquid even at +6 °C. Three AlBr3 -based mixtures are liquid at room temperature, whereas all other mixtures are solids with melting points between 46 and 184 °C. The three liquid mixtures exhibit medium to high viscosities (117 to >1440 mPa s), low conductivities (0.03-0.20 mS cm-1 ), but high densities (1.80-2.21 g cm-3 ). Aluminum could be successfully deposited from one of the neat Lewis acidic mixtures of the AlBr3 -based system.

One-Component Aluminum(heteroscorpionate) Catalysts for the Formation of Cyclic Carbonates from Epoxides and Carbon Dioxide.

New neutral and zwitterionic chiral NNO-donor scorpionate ligands 1 and 2 were designed to obtain new mononuclear and dinuclear NNO-heteroscorpionate aluminum complexes. Reaction of 1 with [AlR3 ] (R=Me, Et) in a 1:1 or 1:2 molar ratio afforded the neutral mononuclear alkyl complexes [AlR2 (κ2 -bpzappe)] {R=Me (3), Et (4); bpzappeH=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]-1-phenylethanol} and bimetallic complexes [{AlR2 (κ2 -bpzappe)}(μ-O){AlR3 }] [R=Me (5), Et (6)]. By reaction of complexes 3-6 with PhCH2 Br, mononuclear and dinuclear cationic aluminum complexes [AlR2 (κ2 -bbpzappe)]Br {R=Me (7), Et (8); bbpzappeH=N-benzyl-4-[2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-hydroxy-1-phenylethyl]-N,N-dimethylbenzenaminium bromide} and [{AlR2 (κ2 -bbpzappe)}(μ-O){AlR3 }]Br [R=Me (9), Et (10)] were synthesized. Both neutral aluminum complexes in the presence of Bu4 NBr and cationic aluminum complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide. Amongst them, complex 10 was found to be an efficient one-component catalyst for the synthesis of cyclic carbonates from both monosubstituted and internal epoxides and was shown to have broad substrate scope.

Hydrosilylation of Olefins Catalyzed by Well-Defined Cationic Aluminum Complexes: Lewis Acid versus Insertion Mechanisms

The cationic aluminum complex [NacNacAlH]+ (2; NacNac = CH{C(Me)N(2,6-Pri2C6H3)}2) can be easily generated from NacNacAlH2 by hydride abstraction and functions as a catalyst for the hydrosilylation of olefins and alkynes. Mechanistic studies suggest that, although olefin insertion into the Al–H bond is very facile, the catalysis does not proceed by an insertion/metathesis mechanism but likely by Lewis acid activation. Stoichiometric reactions of 2 with alkynes furnished unexpected products of C≡C addition across the NacNacAl moiety to give tripodal aluminum cations, which are also potent catalysts for the hydrosilylation of alkynes.

Haloaluminate-Free Cationic Aluminum Complexes: Structural Characterization and Physicochemical Properties

The large electrochemical activities of haloaluminate anions [AlnX3n+1]−, anionic complexes derived from AlX3 and Lewis basic fertilizers, have significantly contributed to the development of industrial coatings and more recently also to electrochemical energy storage. In contrast, cationic metal complexes have just emerged as a class of species interesting as multivalent main charge carriers for Mg, Ca, and especially here Al batteries. Despite the potential of such complexes to efficiently deliver Al3+ cations at the electrode|electrolyte interfaces, very few cationic aluminum complexes that do not contain moisture sensitive [AlnX3n+1]− counteranions have been reported due to the few, and difficult to synthesize, commercially available parent aluminum salts. Here a range of cationic aluminum complexes with different ligands and anionic structures were successfully synthesized by complexation of AlCl3 with certain ligands to create fully solvated [Al(L)6]Cl3 complexes and subsequent application of anion ...

Synthesis and structure of the first discrete dinuclear cationic aluminum complexes.

The reactions of the charge neutral dinuclear aluminum tetraalkyl complexes of di-Schiff base ligands, i.e. [AlMe2{ON}-R-{ON}AlMe2] (1a, R = 1,3-propylene; 1b, R = 1,3-cyclohexylene) with B(C6F5)3 and [H(Et2O)2](+)[H2N{B(C6F5)3}2](-) were investigated. When B(C6F5)3 was used as the cationizing agent (1 or 2 equiv. vs. Al), only monocationic dinuclear complexes [2a,b]+[MeB(C6F5)3]- were obtained. In contrast, with [H(Et2O)2](+)[H2N{B(C6F5)3}2](-), both mixed-dicationic [3a,b·(OEt2)2]2+[MeB(C6F5)3]-[H2N{B(C6F5)3}2]- and homo-dicationic [3a,b·(OEt2)2]2+[H2N{B(C6F5)3}2]-2 ion-pairs were prepared. All cationic complexes were characterized by (1)H, (13)C, (19)F and (11)B NMR spectroscopy, and an X-ray diffraction study was performed for [3b·(OEt2)2]2+[H2N{B(C6F5)3}2]-2.

Neutral Methyl and Cationic Aluminum Complexes Supported by a trans-1,2-Cyclooctanediyl-Bridged [OSSO]-Type Bis(phenolato) Ligand: Synthesis, Structures, and Use in Catalysis for Propylene Oxide Polymerization

Treatment of trans-1,2-cyclooctanediyl-bridged [OSSO]-type bis(phenolate) 1 with Me3Al in hexane led to the formation of methylaluminum 4 as colorless crystals. X-ray diffraction analysis of 4 revealed that the aluminum center adopts a distorted-trigonal-bipyramidal geometry which occupies the axial positions with one phenoxide oxygen and one sulfur atoms. The dealkylation reaction of 4 with 1 equiv of B(C6F5)3 in C6D6 afforded the novel cationic aluminum species 52+ as a dimeric structure, which was isolated in the form of a [MeB(C6F5)3]− salt. In the crystal structure of 52+, one aluminum atom has a distorted-trigonal-bipyramidal environment, in which phenoxide and μ-bridging oxygen atoms are located at two axial positions, whereas the other aluminum atom has a distorted-square-pyramidal geometry, which occupies the axial position with a nonbridged oxygen atom. The cationic species 52+ promoted the ring-opening polymerization (ROP) of propylene oxide to give an atactic polymer in 44% yield with a low molecular weight (Mn = 2500) and a very narrow molecular weight distribution (PDI = 1.04).

Neutral and Cationic Aluminum Complexes Supported by Acetamidate and Thioacetamidate Heteroscorpionate Ligands as Initiators for Ring-Opening Polymerization of Cyclic Esters

The synthesis, structures, and ring-opening polymerization (ROP) activity of heteroscorpionate aluminum alkyl and aryloxide complexes are reported. The reactions of the acetamide and thioacetamide heteroscorpionate protio ligands pbptamH (pbptamH = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide), pbpamH (pbpamH = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide), sbpamH (sbpamH = N-sec-butyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide), and (S)-mbpamH ((S)-mbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide) with 1 equiv of AlR3 (R = Me, Et, iBu) proceed in very high yields to give the neutral heteroscorpionate dialkyl aluminum complexes [AlR2{κ2-pbptam}] (R = Me (1), Et (2)), [AlR2{κ2-pbptam}] (R = Me (3), Et (4), iBu (5)), [AlR2{κ2-pbptam}] (R = Me (6), Et (7), iBu (8)), and [AlR2{κ2-(S)-mbpam}] (R = Me (9), Et (10)). In the solid state, complexes 1−10 adopt a tetrahedral structure with the heteroscorpionate ligands arranged in a κ2 coordination mode; in the case of the thioacetamidate derivatives 1 and 2 a κ2NN coordination mode is observed, whereas the acetamidate derivatives 3−10 present a κ2NO coordination mode. The structures in solution of 1−10 were investigated by VT NMR spectroscopy, and fluxional exchange between coordinated and noncoordinated pyrazole rings was observed, producing interconversion between the different isomers. Compounds 7 and 10 were used as convenient starting materials for the synthesis of the aryloxide aluminum compounds [Al(OR)2{κ2-sbpam}] (11) and [Al(OR)2{κ2-(S)-mbpam}] (12) (R = 2,6-Me2C6H3O) by reaction with the corresponding 2,6-dimethylphenol. The complexes [AlMe{κ3-pbptam}][MeB(C6F5)3] (13), [AlMe{κ3-pbptam}][B(C6F5)4] (14), [AlEt{κ3-pbptam}][B(C6F5)4] (15), [AlEt{κ3-sbpam}][B(C6F5)4] (16), and [AlEt{κ3-(S)-mbpam}][B(C6F5)4] (17) are derived from the ionization of the neutral dialkyl aluminum complexes 1, 2, 7, and 10 with the alkyl abstracting reagent B(C6F5)3 or [Ph3C][B(C6F5)4]. The NMR data were consistent with an overall Cs-symmetric structure for 13−15 and C1-symmetric structure for 16 and 17, which indicates an effective κ3 coordination of the corresponding heteroscorpionate ligand to the cationic aluminum center. The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 1, 2, and 7 were also established. Finally, exhaustive comparative catalytic studies of the aluminum complexes 1−10, 13, and 14 in the ring-opening polymerization of rac-lactide, l-lactide, and ε-caprolactone are also described.

Synthesis and Structure of Neutral and Cationic Aluminum Complexes Supported by Bidentate O,P-Phosphinophenolate Ligands and Their Reactivity with Propylene Oxide and ε-Caprolactone

The O,P-type phosphinophenol ligands 1a−c were found to readily react with 1 equiv of AlMe3 to afford in high yields the corresponding Al chelate complexes {η2-O,P-(2-PPh2-4-R′-6-R-C6H2O)}AlMe2, 2a−c (R = Me, R′ = H, 2a; R = Ph, R′ = H, 2b; R = tBu, R′ = Me, 2c). The bis-adduct Al methyl complexes {η2-O,P-(2-PPh2-4-R′-6-R-C6H2O)}2AlMe (R = Ph, R′ = H, 3b; R = tBu, R′ = Me, 3c) also formed quantitatively upon reaction of phosphinophenols 1b,c with 0.5 equiv of AlMe3. Both the mono- and bis-adduct Al methyl species 2a−c and 3b,c are stable monomeric species whether in solution or in the solid state and remain stable in coordinating solvents such as thf. In contrast, the bis-adduct Al methyl complex 3c undergoes a ligand exchange reaction in the presence of an alcohol source (iPrOH, BnOH) to generate the homoleptic tris-adduct Al complex {η2-O,P-(2-PPh2-4-Me-6-tBu-C6H3O)}3Al (5c), as determined from X-ray crystallographic studies. Both the mono- and bis-adduct Al methyl species 2b,c and 3b,c react fast with B(C6F5)3 via a methide abstraction reaction to afford the stable and well-defined Al cationic species {η2-O,P-(2-PPh2-6-Ph-C6H3O)}Al(Me)(THF)+ (6b,c+) and {η2-O,P-(2-PPh2-4-R′-6-R-C6H3O)}2Al+ (7b,c+), respectively, which were found to be highly active in propylene oxide polymerization to afford atactic poly(propylene oxide). These cations also readily initiate the ring-opening polymerization of ε-caprolactone via successive ring-opening insertions of the monomer into the Al−O phenoxide bond of the phosphinophenolate chelating ligand to exclusively afford linear poly(ε-caprolactone) capped, at the ester end, with a (phosphino oxide)phenolate group, as deduced from NMR and MALDI-TOF data. In these cationic systems, the PO− chelating moiety may thus act as both a supporting ligand and an initiating group for the ROP of ε-CL.

Neutral and Cationic Heteroscorpionate Aluminum Complexes: Synthesis, Structure, and Ring-Opening Polymerization of ε-Caprolactone

Treatment of 2,4-di-tert-butyl-6-(bis(3,5-dimethylpyrazol-1-yl)methyl)phenol (bpzmp-H) as tridentate ligand with aluminum trialkyls affords the corresponding heteroscorpionate aluminum complexes (bpzmp)AlR2 (R = Me (1); R = Et (2); R = iBu (3)) in high yield. In the solid state, complexes 1−3 were isolated as racemic mixtures in which each stereoisomer adopts a tetrahedral structure with the bpzmp ligand κ2-coordinated to the metal via the phenoxy group and the imino nitrogen of one of pyrazolyl rings. The investigation of the solution structure of 1−3 by means of VT 1H NMR spectroscopy revealed fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers. The activation enthalpy (ΔH#) for racemization processes (10.1 ± 0.2 kcal·mol-1 (1); 11.6 ±0.3 kcal·mol-1 (2); 14.1 ± 0.2 kcal·mol-1 (3)) was dependent on steric hindrance at the aluminum center. Reaction of 1 or 2 with B(C6F5)3 proceeds through net alkyl abstraction, forming the expected cationic aluminum complexes [(bpzmp)AlR]+[RB(C6F5)3]- (R = Me (4); R = Et (5)), in which the bpzmp fragment acts as a tridentate ligand. The ionization reaction of 3 with Lewis acidic compounds (B(C6F5)3 or [Ph3C][B(C6F5)4]) proceeds by net β-H abstraction from the isobutyl group, forming [(bpzmp)AliBu]+[HB(C6F5)3]- (6) along with isobutene; in contrast, reaction with the Brönsted acid [HNMe2Ph][B(C6F5)4] proceeds by protonolysis of the isobutyl group. Complex 4 is active in ring-opening polymerization of ε-caprolactone (ε-CL), producing high-molecular-weight polymers. The 1H NMR monitoring of the reaction between 4 and ε-CL in 1:1 molar ratio showed that the initiation involves monomer insertion into the Al−O bond of the bpzmp fragment, forming the intermediate [(bpzphe)AlMe]+[MeB(C6F5)4]- (bpzphe = 2,4-di-tert-butyl-6-(bis(3,5-dimethylpyrazol-1-yl)methyl)phenyl 6-hydroxyhexanoate (8). The growth of the polymer chain occurs through continuous insertions of the monomer in the Al−alkoxide bond.

Neutral and Cationic Aluminum and Titanium Complexes Incorporating Sterically Demanding Organosilicon Ligands

New complexes of aluminum and titanium containing sterically demanding ligands and their reaction with B(C6F5)3 are reported. Treatment of [(Ph2MeSiCH2CH2)3Si]NCN[Si(CH2CH2SiMePh2)3] (1) or Si(CH2CH2SiMePh2)3OH (2) with 1 equiv of AlMe3 results in the formation of the neutral dimethylaluminum complexes {MeC[NSi(CH2CH2SiMePh2)3]2}AlMe2 (3) and [(Ph2MeSiCH2CH2)3SiOAlMe2]2 (4). Reaction of 3 with 1 equiv of B(C6F5)3 forms the neutral complex {MeC[NSi(CH2CH2SiMePh2)3]2}AlMe(C6F5) (5) and BMe(C6F5)2. In the case of 4, the analogous reaction produced the dimer [(Ph2MeSiCH2CH2)3SiOAl]2Me3(C6F5) (6). Treatment of 1 with Ti(C5Me5)Me3 fails to afford the corresponding amidinate complex. However, reaction of 2 with the same titanium half-sandwich complex cleanly gives Ti(C5Me5)[OSi(CH2CH2SiMePh2)3]Me2 (7). Reaction of 7 with 1 equiv of B(C6F5)3 leads to the formation of the ion pair {Ti(C5Me5)[OSi(CH2CH2SiMePh2)3]Me}[BMe(C6F5)3] (8), which is relatively stable at room temperature, slowly decomposing (t1/2 ≈ 48 h) to...

Synthesis and Structure of Neutral and Cationic Aluminum Complexes Incorporating Bis(oxazolinato) Ligands

Treatment of the bis(oxazolines) 1,1-bis[4,4-dimethyl-1,3-oxazolin-2-yl]ethane (1a, {BOX-Me2}H) and 1,1-bis[(4S)-4-isopropyl-1,3-oxazolin-2-yl]ethane (1b, {BOX-(S)-iPr}H) with nBuLi, followed by the addition of 1 equiv of ClAlMe2, affords the corresponding dimethyl Al complexes {BOX-Me2}AlMe2 (2a) and {BOX-(S)-iPr}AlMe2 (2b) in reasonable yields. The dichloro Al complex {BOX-Me2}AlCl2 (3a) was synthesized in a similar way using 1 equiv of AlCl3. Compounds 2a,b and 3a are monomeric four-coordinate mono[bis(oxazolinato)aluminum] complexes, on the basis of X-ray analyses for 2b and 3a and NMR data for 2a,b and 3a. The dimethylaluminum complexes {BOX-Me2}AlMe2 (2a) and {BOX-(S)-iPr}AlMe2 (2b) react in C6D5Br with B(C6F5)3 to yield the quantitative formation of cations {BOX-Me2}AlMe+ (4a+) and {BOX-(S)-iPr}AlMe+ (4b+), respectively, as fully dissociated MeB(C6F5)3- salts. Cations 4a,b+, which are most likely either base-free three-coordinate cationic species or four-coordinate cationic Al−C6D5Br adducts, are unstable at room temperature in C6D5Br and decompose to unidentified species. When these ionization reactions are performed in the presence of a Lewis base L (L = THF, NMe2Ph), corresponding four-coordinate Al−L Lewis base adducts are cleanly generated, {BOX-Me2}Al(Me)(L)+ (5a+, L = THF; 6a+, L = NMe2Ph) and {BOX-(S)-iPr}Al(Me)(L)+ (5b+, L = THF; 6b+, L = NMe2Ph), as determined by solution studies and, in the case of 6a+, by X-ray analysis. In contrast, the reaction of {BOX-Me2}AlMe2 (2a) with [Ph3C][B(C6F5)4] yields the bis(imine) Al cation 7a+, as determined by NMR and X-ray analysis. The formation of 7a+ most likely proceeds via a hydride abstraction by Ph3C+ at the Me group located at the back of the bis(oxazolinato) ligand in 2a.

Neutral and Cationic Aluminum Complexes Supported by Sterically Bulky Amidinate Ligands

Aluminum complexes supported by sterically bulky amidinate ligands containing terphenyl substituents on the backbone carbon atoms are described. Three amidinate ligands featuring differing substitu...

Fiber charge characteristics of pulp suspension containing aluminum sulfate

Fiber charge characteristics of pulp suspensions containing aluminum sulfate were investigated with relation to adsorption behavior of aluminum components on the pulp fibers by streaming potential measurement using a particle charge detector, X-ray photoelectron spectroscopy, and X-ray fluorescence analysis. When aluminum sulfate was added to a pulp suspension prepared using deionized water, a streaming potential of the suspension went from negative to slightly negative according to the adsorption of aluminum components on the pulp fibers. Subsequent addition of a dilute NaOH solution to the suspension drastically cationized the fibers in the pH range of around 5 by predominant and homogeneous adsorption of cationic aluminum complexes on the fiber surfaces. However, the aluminum flocs that formed heterogeneously on the fiber surfaces at higher pH by further alkali addition made nearly no contribution to cationization of the fibers, although the abundant aluminum components were retained in the pulp sheets. Therefore, only aluminum cations adsorbed uniformly on the fiber surfaces perform well to control the charge properties of the pulp fibers at the wet end; and the preferential aluminum adsorption behavior on the fiber surfaces, by utilizing the required amounts of hydroxyl ions, probably accounts for the effective cationization of the fibers under acidic to neutral papermaking conditions.

Cationic aluminum alkyl complexes incorporating aminotroponiminate ligands.

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N'-diisopropylaminotroponiminate ligand ((i)Pr(2)-ATI(-)) are described. The reaction of ((i)Pr(2)-ATI)AlR(2) (1a-e,g,h; R = H (a), Me (b), Et (c), Pr (d), (i)Bu (e), Cy (g), CH(2)Ph (h)) with [Ph(3)C][B(C(6)F(5))(4)] yields ((i)()Pr(2)-ATI)AlR(+) species whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph(3)C][B(C(6)F(5))(4)] to produce dinuclear monocationic complexes [([(i)Pr(2)-ATI] AlR)(2)(mu-R)][(C(6)F(5))(4)] (2a,b). The cation of 2b contains two ((i)()Pr(2)-ATI)AlMe(+) units linked by an almost linear Al-Me-Al bridge; 2a is presumed to have an analogous structure. 2b does not react further with [Ph(3)C][B(C(6)F(5))(4)]. However, 1a reacts with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to afford ((i Pr(2)-ATI)Al(C(6)F(5))(mu-H)(2)B(C(6)F(5))(2) (3) and other products, presumably via C(6)F(5)(-) transfer and ligand redistribution of a [((i)()Pr(2)-ATI)AlH][(C(6)F(5))(4)] intermediate. 1c-e react with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to yield stable base-free [((i)Pr(2)-ATI)AlR][B(C(6)F(5))(4)] complexes (4c-e). 4c crystallizes from chlorobenzene as 4c(ClPh).0.5PhCl, which has been characterized by X-ray crystallography. In the solid state the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph pi-stacking interaction. 1g,h react with [Ph(3)C][B(C(6)F(5))(4)] to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5g,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][(BC(6)F(5))(4)] intermediates. 1c,h react with B(C(6)F(5))(3) to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5c,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][RB(C(6)F(5))(3)] intermediates. The reaction of 4c-e with MeCN or acetone yields [((i)Pr(2)-ATI)Al(R)(L)][B(C(6)F(5))(4)] adducts (L = MeCN (8c-e), acetone (9c-e)), which undergo associative intermolecular L exchange. 9c-e undergo slow beta-H transfer to afford the dinuclear dicationic alkoxide complex [(((i)Pr(2)-ATI)Al(mu-O(i)()Pr))(2)][B(C(6)F(5))(4)](2) (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization of tert-butyl acetylene by an insertion/sigma-bond metathesis mechanism involving [((i)Pr(2)-ATI)Al(C=C(t)Bu)][B(C(6)F(5))(4)] (13) and [((i)Pr(2)-ATI)Al(CH=C((t)()Bu)C=C(t)Bu)][B(C(6)F(5))(4)] (14) intermediates. 13 crystallizes as the dinuclear dicationic complex [([(i Pr(2)-ATI]Al(mu-C=C(t)Bu))(2)][B(C(6)F(5))(4)](2).5PhCl from chlorobenzene. 4e catalyzes the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react with ethylene-d(4) by beta-H transfer to yield [((i)Pr(2)-ATI)AlCD(2)CD(2)H][B(C(6)F(5))(4)] initially. Polyethylene is also produced in these reactions by an unidentified active species.

Syntheses of cationic four-coordinated aluminum complexes: counter-ion induced aggregation through the NH⋯I hydrogen bonds

Synthesis of cationic aluminum complexes from the reactions of Lewis bases with Me 2AlI is reported. The reactions of two molar equivalents of ( S)-(−)-1-phenylethylamine, ( R)-(−)-pantolactone (PLH), or ( S)-(−)-ethyl lactate (ELH) with Me 2AlI ( 1), generated in situ from the reaction of Me 3Al with one molar equivalent of I 2 in toluene at room temperature, afford white crystalline solids [Me 2Al(( S)-NH 2(Ph)C(H)CH 3) 2] +I − ( 2), [(PL) 2Al] +I − ( 3) or [(EL) 2Al] +I − ( 4), respectively. However, Me 3Al reacts with one molar equivalent of PLH producing [(Me 2Al(μ-PL)) 2 ( 5). The reaction of Me 2AlI with 2,2′-ethylidene-bis-(4,6-di- tert-butylphenol) (EDBPH 2) yields [Al(EDBP)I(Et 2O)] ( 6) which further reacts with one molar equivalent or two molar equivalents of OPPh 3 giving a neutral complex [Al(EDBP)(OPPh 3)I] ( 7) or a cationic complex [Al(EDBP)(OPPh 3) 2] +I − ( 8). However, the cationic aluminum derivative [Al(EDBP)(HMPA) 2] +I − ( 9) is prepared from the reaction of 6 with excess of HMPA. Crystal structures of 2, 5, and 8 determined by X-ray diffraction method are also presented.