The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform
Wanda Ziemkowska - One of the best experts on this subject based on the ideXlab platform.
-
Reactions of trialkylAluminium with sterically hindered diols
Journal of Organometallic Chemistry, 1998Co-Authors: Wanda Ziemkowska, Stanisław Pasynkiewicz, Tadeusz GłowiakAbstract:Abstract The reactions of trialkylAluminium R3Al (R=Me, Et) with 2,4-pentanediols [(CH3)2(OH)CCH2C(CH3)2OH (A)], [(CH3)2(OH)CCH2CH(OH)CH3 (Ḇ)] and 2,5-dimethyl-2,5-hexanediol (C) were studied. Sterically hindered 2,4-pentanediols (A, Ḇ) react with alkylAluminium compounds to form mainly cyclic compounds 1–3 of a formula R5Al3[diol(−2H)]2 possessing one central five-coordinated Aluminium Atom and two terminal four-coordinated Aluminium Atoms. All the compounds were characterised by means of NMR spectra, elemental analysis and molecular weight determination. The molecular structure of the solid Me5Al3[O(CH3)2CCH2C(CH3)2O]2 1 was determined by X-ray diffraction analysis. Substituted at terminal carbon Atoms 2,5-dimethyl-2,5-hexanediol (C) forms organoAluminium oligomers exclusively. The influence of the diol carbonchain lengths and its substituents on the yield of the cyclic complexes and organoAluminium oligomers are discussed.
-
Reactions of trimethylAluminium with aliphatic diols
Journal of Organometallic Chemistry, 1996Co-Authors: Wanda Ziemkowska, Stanisław PasynkiewiczAbstract:The reactions of trimethylAluminium with aliphatic diols, derivatives of 1,4-butandiol and 1,3-propadiol were studied. A mixtures of linear and cyclic organoAluminium compounds were the products of these reactions carried out for AIME3: diol molar ratios of 3:2 or greater. One of the products isolated in all the studied reactions was a complex of a formula Me5Al3[diol(-2H)]2 possessing one central five-coordinated Aluminium Atom and two terminal four-coordinated Aluminium Atoms. All the complexes were characterized by means of 1H, 13C and 27Al NMR spectra, elemental analysis and molecular weight determination.
-
Reactions of trimethylAluminium with 2-[methyl-bis(trimethylsiloxy)silyl]but-2-ene-1,4-diol: Synthesis and structure of [Al(CH3)]-[OCH2(SiMe(OSiMe3)2)C(H)CH2O]2[Al(CH3)2]2
Journal of Organometallic Chemistry, 1992Co-Authors: Stanisław Pasynkiewicz, Wanda ZiemkowskaAbstract:Abstract The reaction of trimethylAluminium with 2-[methyl-bis(trimethylsiloxy)silyl]but-2-ene-1,4-diol was studied. A viscous liquid identified as complex 1 , [Al(CH 3 )][OCH 2 (SiMe(OSiMe 3 ) 2 )CCH)CH 2 O] 2 -[Al(CH 3 ) 2 ] 2 , was formed for molar ratios Me 3 Al/diol > 3:2.The structure of complex 1 was determined by means of 1 H, 13 C NMR, elemental analysis and molecular weight determination. The central, five-coordinated Aluminium Atom is bonded to four oxygen Atoms and for the methyl group, terminal Aluminium Atoms are four-coordinated. At molar ratios Me 3 Al/diol = 1:1 and 2:3, dimers or/and higher associates insoluble or sparingly soluble in organic solvents are formed.
Helen A. Joly - One of the best experts on this subject based on the ideXlab platform.
-
EPR spectroscopic study of the reaction of ground-state Aluminium Atoms with cyclic alcohols in a rotating cryostat
Physical Chemistry Chemical Physics, 2020Co-Authors: Helen A. Joly, James A. Howard, Gustavo A. ArtecaAbstract:Ground-state Aluminium Atoms have been reacted with methanol, ethanol and 2-methylpropan-2-ol, in an adamantane matrix, in a rotating cryostat at 77 K. We found no electron paramagnetic resonance (EPR) evidence under these experimental conditions for Aluminium Atom insertion into the C–C, C–H or O–H bonds of these alcohols. There are, however, several mononuclear Aluminium species formed with large Aluminium hyperfine interactions (hfi) (1206–1537 MHz). A comparison of the magnetic parameters with those determined for similar systems suggests that in the Aluminium–methanol reaction, Al(OCH3)2 is the major product. In addition, our results suggest that HOAlOCH3 and Al(OH)2 are present in the reaction mixture. We have calculated the Aluminium hfi for these species using density functional theory (DFT) methods and the results are in close agreement with the experimental values. The Aluminium–ethanol reaction gives Al(OCH2CH3)2 and HOAlOCH2CH3 while only HOAlOC(CH3)3 is observed from reaction of Aluminium Atoms with 2-methylpropan-2-ol.
-
Electron paramagnetic resonance study of the reaction of ground-state Aluminium Atoms with a series of ethers in a rotating cryostat
Journal of the Chemical Society Faraday Transactions, 1990Co-Authors: J. H. Bernard Chenier, James A. Howard, Helen A. Joly, Marc Leduc, Brynmor MileAbstract:Ground-state Al Atoms react with symmetric cyclic and acyclic ethers at 77 K in a rotating cryostat to give a host of mononuclear organoAluminium compounds. Magnetic parameters determined from EPR spectra given by Al Atoms and acyclic ethers are consistent with the formation of novel C—C and C—H Aluminium Atom insertion products. A third species has been tentatively assigned to the product given by Al Atom insertion into the C—O bond. In addition a carbon-centred radical is formed by loss of a hydrogen Atom from carbon adjacent to the alkoxyl group. In contrast the cyclic ethers are resistant to alumino hydride formation and in most cases a carbon radical resulting from ring opening at the C—O bond is formed. Mono- and di-ligand complexes, Al[ether] and Al[ether]2, are tentatively identified and may be the primary intermediates for all the reactions that occur.
R Hippler - One of the best experts on this subject based on the ideXlab platform.
-
Aluminium Atom density and temperature in a dc magnetron discharge determined by means of blue diode laser absorption spectroscopy
Journal of Physics D, 2005Co-Authors: Matthias Wolter, Hoang Tung Do, H Steffen, R HipplerAbstract:Diode laser absorption studies of Aluminium Atoms produced in a direct current (dc) magnetron discharge with argon as well as argon/nitrogen and argon/oxygen mixtures as working gas are reported. The measured Al Atom density increases with increasing discharge power. The observed temperature being in the range of 340–420 K rises with increasing power but shows little pressure dependence. A small admixture of oxygen gas leads to a complete disappearance of the absorption signal, a result which is not yet fully understood.
James A. Howard - One of the best experts on this subject based on the ideXlab platform.
-
EPR spectroscopic study of the reaction of ground-state Aluminium Atoms with cyclic alcohols in a rotating cryostat
Physical Chemistry Chemical Physics, 2020Co-Authors: Helen A. Joly, James A. Howard, Gustavo A. ArtecaAbstract:Ground-state Aluminium Atoms have been reacted with methanol, ethanol and 2-methylpropan-2-ol, in an adamantane matrix, in a rotating cryostat at 77 K. We found no electron paramagnetic resonance (EPR) evidence under these experimental conditions for Aluminium Atom insertion into the C–C, C–H or O–H bonds of these alcohols. There are, however, several mononuclear Aluminium species formed with large Aluminium hyperfine interactions (hfi) (1206–1537 MHz). A comparison of the magnetic parameters with those determined for similar systems suggests that in the Aluminium–methanol reaction, Al(OCH3)2 is the major product. In addition, our results suggest that HOAlOCH3 and Al(OH)2 are present in the reaction mixture. We have calculated the Aluminium hfi for these species using density functional theory (DFT) methods and the results are in close agreement with the experimental values. The Aluminium–ethanol reaction gives Al(OCH2CH3)2 and HOAlOCH2CH3 while only HOAlOC(CH3)3 is observed from reaction of Aluminium Atoms with 2-methylpropan-2-ol.
-
Electron paramagnetic resonance study of the reaction of ground-state Aluminium Atoms with a series of ethers in a rotating cryostat
Journal of the Chemical Society Faraday Transactions, 1990Co-Authors: J. H. Bernard Chenier, James A. Howard, Helen A. Joly, Marc Leduc, Brynmor MileAbstract:Ground-state Al Atoms react with symmetric cyclic and acyclic ethers at 77 K in a rotating cryostat to give a host of mononuclear organoAluminium compounds. Magnetic parameters determined from EPR spectra given by Al Atoms and acyclic ethers are consistent with the formation of novel C—C and C—H Aluminium Atom insertion products. A third species has been tentatively assigned to the product given by Al Atom insertion into the C—O bond. In addition a carbon-centred radical is formed by loss of a hydrogen Atom from carbon adjacent to the alkoxyl group. In contrast the cyclic ethers are resistant to alumino hydride formation and in most cases a carbon radical resulting from ring opening at the C—O bond is formed. Mono- and di-ligand complexes, Al[ether] and Al[ether]2, are tentatively identified and may be the primary intermediates for all the reactions that occur.
Gustavo A. Arteca - One of the best experts on this subject based on the ideXlab platform.
-
EPR spectroscopic study of the reaction of ground-state Aluminium Atoms with cyclic alcohols in a rotating cryostat
Physical Chemistry Chemical Physics, 2020Co-Authors: Helen A. Joly, James A. Howard, Gustavo A. ArtecaAbstract:Ground-state Aluminium Atoms have been reacted with methanol, ethanol and 2-methylpropan-2-ol, in an adamantane matrix, in a rotating cryostat at 77 K. We found no electron paramagnetic resonance (EPR) evidence under these experimental conditions for Aluminium Atom insertion into the C–C, C–H or O–H bonds of these alcohols. There are, however, several mononuclear Aluminium species formed with large Aluminium hyperfine interactions (hfi) (1206–1537 MHz). A comparison of the magnetic parameters with those determined for similar systems suggests that in the Aluminium–methanol reaction, Al(OCH3)2 is the major product. In addition, our results suggest that HOAlOCH3 and Al(OH)2 are present in the reaction mixture. We have calculated the Aluminium hfi for these species using density functional theory (DFT) methods and the results are in close agreement with the experimental values. The Aluminium–ethanol reaction gives Al(OCH2CH3)2 and HOAlOCH2CH3 while only HOAlOC(CH3)3 is observed from reaction of Aluminium Atoms with 2-methylpropan-2-ol.
