Dimeric Aluminum Chloride Complexes of <i>N</i>-Alkoxyalkyl-β-ketoimines: Activation with Propylene Oxide To Form Efficient Lactide Polymerization Catalysts

The ter- and tetradentate N-alkoxyalkyl-β-ketoimines CH3C(O)CH2C(NCH2CHROH)CH3 {L1-3} react with diethylaluminum chloride to afford the dimeric chloride bridged complexes [{L1-3}AlCl]2 (1a−c), which are activated by addition of propylene oxide or cyclohexene oxide to afford efficient initiators for the ring-opening polymerization of (d,l)-lactide. The active species is believed to be a chloroalkoxide formed by nucleophilic ring opening of a coordinated PO by migration of the chloride coordinated to the adjacent aluminum center. The resulting polymers have a high molecular weight, close to that calculated for the monomer:initiator ratio of 100, and a narrow molecular weight distribution. While the corresponding aluminum methyl dimer [{L1}AlMe]2 (2a), formed by reaction of L1 (R = H) with AlMe3, is a poor inititaor for the polymeriation of (d,l)-lactide, addition of 2-chloroethanol affords a catalyst with an activity comparable to that of 1a/PO. The molecular weight and molecular weight distribution of the resulting polylactide is similar to that obtained with 1a/PO and consistent with formation of a similar chloroalkoxide initiator

Dimeric Aluminum Chloride Complexes of <i>N</i>-Alkoxyalkyl-β-ketoimines: Activation with Propylene Oxide To Form Efficient Lactide Polymerization Catalysts

The ter- and tetradentate N-alkoxyalkyl-β-ketoimines CH3C(O)CH2C(NCH2CHROH)CH3 {L1-3} react with diethylaluminum chloride to afford the dimeric chloride bridged complexes [{L1-3}AlCl]2 (1a−c), which are activated by addition of propylene oxide or cyclohexene oxide to afford efficient initiators for the ring-opening polymerization of (d,l)-lactide. The active species is believed to be a chloroalkoxide formed by nucleophilic ring opening of a coordinated PO by migration of the chloride coordinated to the adjacent aluminum center. The resulting polymers have a high molecular weight, close to that calculated for the monomer:initiator ratio of 100, and a narrow molecular weight distribution. While the corresponding aluminum methyl dimer [{L1}AlMe]2 (2a), formed by reaction of L1 (R = H) with AlMe3, is a poor inititaor for the polymeriation of (d,l)-lactide, addition of 2-chloroethanol affords a catalyst with an activity comparable to that of 1a/PO. The molecular weight and molecular weight distribution of the resulting polylactide is similar to that obtained with 1a/PO and consistent with formation of a similar chloroalkoxide initiator

<i>N</i>-Alkoxy-β-ketoiminate Complexes of Groups 4 and 5: Synthesis and Characterization of the Complexes [(η⁵-C₅H₄R)M{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cl<i>_n</i>] (M = Ti, <i>n</i> = 1; M = Nb, <i>n</i> = 2; R = H, Me; R‘ = H, Me), [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cl₂(thf)], and [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}₂]

The synthesis and characterization of a range of N-alkoxo β-ketoiminate complexes of groups 4 and 5 are reported. Reactions between the acylic N-hydroxyalkyl β-ketoimines CH3C(O)CH2C(NCH2CHR‘OH)CH3 (R‘ = H, Me) and [(η5-C5H4R)TiCl3] (R = H, Me) in the presence of triethylamine afford the monocyclopentadienyl derivatives [(η5-C5H4R)Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl] (R = H, R‘ = H, 2a; R = Me, R‘ = H, 2b; R = H, R‘ = Me, 2c; R = Me, R‘ = Me, 2d). Complex 2a adopts a square pyramidal coordination geometry with the Cp occupying the apical site and the terdentate ketoiminate and chloride occupying basal positions. Upon standing in thf, solutions of 2a−d containing NEt3HCl deposit deep orange crystals of [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2(thf)] (R‘ = H, 3a; R‘ = Me, 3b) via protonolysis of the Ti−Cp bond. Alternatively, compounds 3a and 3b can be prepared in near quantitative yield either from the reaction between [TiCl4(thf)2] and the corresponding acylic N-hydroxyalkyl β-ketoimine, in the presence of NEt3, or via a ligand exchange reaction between [Ti(OPri)2Cl2] and the N-hydroxyalkyl β-ketoimine. Variable-temperature 1H NMR studies of 3a and 3b have shown that stereoisomers of these complexes interchange via a dissociative dynamic process, involving the trigonal bypyramidal intermediate [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2]. The free energy of activation associated with this exchange has been determined (ΔG⧧ = 45.5 kJ mol-1, 3a; ΔG⧧ = 47.0 kJ mol-1, 3b). Surprisingly, treatment of [Ti(OPri)4] with N-hydroxyalkyl β-ketoimine (1:1) results in complete alcoholysis to afford [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}2] (R‘ = H, 4a; R‘ = Me, 4b), which contain two meridianally coordinated terdentate ketoiminate ligands. The reactions between N-hydroxyalkyl β-ketoimine derivatives and [(η5-C5H4R)NbCl4] afford [(η5-C5H4R)Nb{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2] (R = H, R‘ = H, 5a; R = Me, R‘ = H, 5b; R = H, R‘ = Me, 5c; R = Me, R‘ = Me, 5d). A single-crystal X-ray study of 5a revealed a structure based on an octahedral geometry, such that the nitrogen of the mer-terdentate ligand is trans to the Cp and the two chloro ligands mutually trans. The single-crystal X-ray structures of 2a, 3a, 3b, 4a·CH2Cl2, and 5a are reported

AFM images for POM interdigitated electrodes

A Digital Instruments Multimode-8 with a NanoScope V controller and E scanners (Bruker) was used for acquiring AFM images. The AFM data were analysed with NanoScope Analysis 1.50 software (Bruker). The AFM was operated in tapping mode. An isolation table (Veeco Inc., Metrology Group) was used to minimise vibrational noise. Aluminium-coated silicon tips on silicon cantilevers (Tap300Al-G, BudgetSensors) were used for imaging. The nominal tip curvature radius was approximately <10 nm, resonant frequency ~300 kHz and spring constant k ~ 40 Nm-1. The film thickness was measured by using the AFM tip at a strong force in contact mode to scratch away a 1 µm2 area of the of the film (aspect ratio 20:1), exposing the glass underneath. A new tip was then used to image the area in tapping mode over the scratch to measure the height in the z-direction of the film.</p

AFM images of interdigitated ITO electrodes with thin film of POM deposited

A Digital Instruments Multimode-8 with a NanoScope V controller and E scanners (Bruker) was used for acquiring AFM images. The AFM data were analysed with NanoScope Analysis 1.50 software (Bruker). The AFM was operated in tapping mode. An isolation table (Veeco Inc., Metrology Group) was used to minimise vibrational noise. Aluminium-coated silicon tips on silicon cantilevers (Tap300Al-G, BudgetSensors) were used for imaging. The nominal tip curvature radius was approximately <10 nm, resonant frequency ~300 kHz and spring constant k ~ 40 Nm-1. The film thickness was measured by using the AFM tip at a strong force in contact mode to scratch away a 1 µm2 area of the of the film (aspect ratio 20:1), exposing the glass underneath. A new tip was then used to image the area in tapping mode over the scratch to measure the height in the z-direction of the film.</p

<i>N</i>-Alkoxy-β-ketoiminate Complexes of Groups 4 and 5: Synthesis and Characterization of the Complexes [(η⁵-C₅H₄R)M{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cl<i>_n</i>] (M = Ti, <i>n</i> = 1; M = Nb, <i>n</i> = 2; R = H, Me; R‘ = H, Me), [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cl₂(thf)], and [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}₂]

The synthesis and characterization of a range of N-alkoxo β-ketoiminate complexes of groups 4 and 5 are reported. Reactions between the acylic N-hydroxyalkyl β-ketoimines CH3C(O)CH2C(NCH2CHR‘OH)CH3 (R‘ = H, Me) and [(η5-C5H4R)TiCl3] (R = H, Me) in the presence of triethylamine afford the monocyclopentadienyl derivatives [(η5-C5H4R)Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl] (R = H, R‘ = H, 2a; R = Me, R‘ = H, 2b; R = H, R‘ = Me, 2c; R = Me, R‘ = Me, 2d). Complex 2a adopts a square pyramidal coordination geometry with the Cp occupying the apical site and the terdentate ketoiminate and chloride occupying basal positions. Upon standing in thf, solutions of 2a−d containing NEt3HCl deposit deep orange crystals of [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2(thf)] (R‘ = H, 3a; R‘ = Me, 3b) via protonolysis of the Ti−Cp bond. Alternatively, compounds 3a and 3b can be prepared in near quantitative yield either from the reaction between [TiCl4(thf)2] and the corresponding acylic N-hydroxyalkyl β-ketoimine, in the presence of NEt3, or via a ligand exchange reaction between [Ti(OPri)2Cl2] and the N-hydroxyalkyl β-ketoimine. Variable-temperature 1H NMR studies of 3a and 3b have shown that stereoisomers of these complexes interchange via a dissociative dynamic process, involving the trigonal bypyramidal intermediate [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2]. The free energy of activation associated with this exchange has been determined (ΔG⧧ = 45.5 kJ mol-1, 3a; ΔG⧧ = 47.0 kJ mol-1, 3b). Surprisingly, treatment of [Ti(OPri)4] with N-hydroxyalkyl β-ketoimine (1:1) results in complete alcoholysis to afford [Ti{CH3C(O)CHC(NCH2CHR‘O)CH3}2] (R‘ = H, 4a; R‘ = Me, 4b), which contain two meridianally coordinated terdentate ketoiminate ligands. The reactions between N-hydroxyalkyl β-ketoimine derivatives and [(η5-C5H4R)NbCl4] afford [(η5-C5H4R)Nb{CH3C(O)CHC(NCH2CHR‘O)CH3}Cl2] (R = H, R‘ = H, 5a; R = Me, R‘ = H, 5b; R = H, R‘ = Me, 5c; R = Me, R‘ = Me, 5d). A single-crystal X-ray study of 5a revealed a structure based on an octahedral geometry, such that the nitrogen of the mer-terdentate ligand is trans to the Cp and the two chloro ligands mutually trans. The single-crystal X-ray structures of 2a, 3a, 3b, 4a·CH2Cl2, and 5a are reported

Polymerization of Ethylene by the Electrophilic Mixed Cyclopentadienylpyridylalkoxide Complexes [CpM{NC₅H₄(CR₂O)-2}Cl₂] (M = Ti, Zr, R = Ph, Prⁱ)

The group 4 mixed-ligand compounds [CpM{NC5H4(CR2O)-2}Cl2] (M = Ti; R = Pri (1a), Ph (1b); M = Zr, R = Pri (2a), Ph (2b)) have been prepared and characterized. Single-crystal X-ray analyses reveal that 1a and 2b adopt four-legged piano-stool structures in which the cyclopentadienyl ligand is asymmetrically bonded and the pyridylalkoxide is bidentate. Toluene solutions of [CpM{NC5H4(CR2O)-2}Cl2] and methylaluminoxane catalyze the polymerization of ethylene, generating high molecular weight polymers with narrow molecular weight distributions. The activity of the titanium- and zirconium-based catalysts are comparable

Synthesis and Reactivity of the Methoxozirconium Pentatungstate (<i>ⁿ</i>Bu₄N)₆[{(μ-MeO)ZrW₅O₁₈}₂]: Insights into Proton-Transfer Reactions, Solution Dynamics, and Assembly of {ZrW₅O₁₈}^2- Building Blocks

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(μ-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(μ-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4−8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(μ-MeO)(μ-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6−8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(μ3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces

Tetrahydrofuran Adducts of Bismuth Trichloride and Bismuth Tribromide

Tetrahydrofuran Adducts of Bismuth Trichloride and Bismuth Tribromid

Tetrahydrofuran Adducts of Bismuth Trichloride and Bismuth Tribromide

Tetrahydrofuran Adducts of Bismuth Trichloride and Bismuth Tribromid