Thesis (doctoral)--Technische Hochschule, Aachen, 2000.

Zugl.: Karlsruhe, Univ., Diss., 2009 / Hergestellt on demand. - Zusätzliches Online-Angebot unter http://uvka.ubka.uni-karlsruhe.de/shop/isbn/978-3-86644-392-1

The transition metal complexes cyclopentadienylrhenium tricarbonyl [CpRe(CO)3, Cp = cyclopentadienyl] and (isopropylcyclopentadienyl)rhenium tricarbonyl [(i-PrCp)Re(CO)3, i-Pr = isopropyl] were photolysed in alkanes at low temperature and the resulting alkane complexes, of the general formula Cp'Re(CO)2(alkane) (Cp' = Cp or (i-PrCp)), were studied using NMR spectroscopy. Characteristic proton chemical shifts (δ) and couplings (3JHH) were observed for alkane complexes of several linear, branched and cyclic alkanes of up to eight carbons. Alkanes with chemically distinct methyl (CH3) and/or methylene (CH2) units were observed alternatively binding through each unit to rhenium. No bound methine unit was observed. Large C-H coupling constants (1JCH) were observed for protons of several bound CH3 and CH2 units, indicating the bound C-H is intact. These species are, thus, alkane sigma (σ) complexes, wherein the alkane has an agostic (M-H-C, 3 centre 2 electron) interaction with the rhenium centre. The CH3 binding mode of (i-PrCp)Re(CO)2(1-pentane) was elucidated; sequential deuteration in the bound CH3 revealed an equilibrium isotope effect (EIE) in the remaining proton/s, confirming that only one C-H has an agostic interaction with rhenium at any instant . NMR parameters δ(1H) (-8.22), δ(13C) ( 42.4) and 1JCH (85 Hz) for the complexed C-H reveal it is unequivocally intact and yet strongly interacting with the rhenium centre, hallmarks for the agostic interaction. Intramolecular exchange was identified between pentane complex isomers Cp'Re(CO)2(1-pentane), Cp'Re(CO)2(2-pentane) and Cp'Re(CO)2(3-pentane). Equilibrium constants were determined, revealing a preference for CH2 binding over CH3. The inequivalent hydrogens found in methylene groups of cyclohexane at low temperature permitted simultaneous observation of axial and equatorial C-H protons of a bound CH2 in CpRe(CO)2(cyclohexane); an EIE, upon deuteration, indicated rapid exchange between complexed C-H bonds in the bound CH2 unit. The rhenium centre was found to prefer complexation of the axial C-H bond, over the equatorial, with K ~2.9. Intermolecular exchange of alkane ligands with free solvent was directly observed, in the competitive complexation of the [CpRe(CO)2] fragment to different alkanes in binary mixtures. The preference cyclohexane > cyclopentane > pentane > isobutane was established and equilibrium constants determined. The kinetics were followed by NMR and modelled, revealing rate constants; decay rates were also determined.

Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.

Linear dichroism in Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy has been used to determine molecular orientation at surfaces and in microscopic domains. However, the molecular orientation of n-alkanes cannot be derived unambiguously from their NEXAFS spectra due to the inadequate understanding of the character of the relevant spectroscopic features in the NEXAFS spectra of n-alkanes (i.e. C 1s to sigma*C-H, C 1s to sigma*C-C transitions).<p>We have studied the linear dichroism in the NEXAFS spectra of n-alkane thin films by using angular dependent NEXAFS spectroscopy to explore the molecular orientation of hexacontane (HC, n-C60H122). The HC thin films were epitaxially grown onto the cleaved NaCl (001) surfaces by physical vapor deposition. NEXAFS spectra of the HC thin film were acquired at different angles using STXM microscopy. A detailed analysis of the angular dependence of the NEXAFS spectra of the HC thin film helps to understand the relationship between the linear dichroism and the molecular orientation in n-alkane molecules. This linear dichroism in the NEXAFS spectroscopy of n-alkanes is relevant for quantitative measurements of molecular orientation, such as for the microanalysis of crystalline organic materials. <p>The linear dichroism of the NEXAFS resonances for n-alkanes has also been studied by ab initio calculations. These calculations were carried out on an isolated n-alkane molecule and a cluster of n-alkane molecules. The calculations on an isolated n-alkane molecule are used to study the linear dichroism for the NEXAFS resonances above the C 1s IP. The cluster calculations account for matrix effects in the NEXAFS features of condensed n-alkanes. A comparison of calculations on an isolated molecule and on a cluster of molecules provides information on how the NEXAFS spectra change from gas phase to condensed phase and determines the linear dichroism of each NEXAFS feature below the C 1s IP.<p>In the process of preparing n-alkane thin films for the study of linear dichroism, the morphology and molecular orientation of n-alkane thin films with different chain length (n-C36H74 and n-C60H122) have also been investigated by the NEXAFS spectroscopy and microscopy. These thin films were epitaxially grown onto cleaved NaCl (001) surfaces by physical vapor deposition. The results revealed that the morphology and molecular orientation of n-alkane thin films depend on the chain length and deposition parameters, such as substrate temperature. These observations have been rationalized by the thermodynamics of nucleation and the kinetics of growth.

Linear dichroism in Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy has been used to determine molecular orientation at surfaces and in microscopic domains. However, the molecular orientation of n-alkanes cannot be derived unambiguously from their NEXAFS spectra due to the inadequate understanding of the character of the relevant spectroscopic features in the NEXAFS spectra of n-alkanes (i.e. C 1s to sigma*C-H, C 1s to sigma*C-C transitions).<p>We have studied the linear dichroism in the NEXAFS spectra of n-alkane thin films by using angular dependent NEXAFS spectroscopy to explore the molecular orientation of hexacontane (HC, n-C60H122). The HC thin films were epitaxially grown onto the cleaved NaCl (001) surfaces by physical vapor deposition. NEXAFS spectra of the HC thin film were acquired at different angles using STXM microscopy. A detailed analysis of the angular dependence of the NEXAFS spectra of the HC thin film helps to understand the relationship between the linear dichroism and the molecular orientation in n-alkane molecules. This linear dichroism in the NEXAFS spectroscopy of n-alkanes is relevant for quantitative measurements of molecular orientation, such as for the microanalysis of crystalline organic materials. <p>The linear dichroism of the NEXAFS resonances for n-alkanes has also been studied by ab initio calculations. These calculations were carried out on an isolated n-alkane molecule and a cluster of n-alkane molecules. The calculations on an isolated n-alkane molecule are used to study the linear dichroism for the NEXAFS resonances above the C 1s IP. The cluster calculations account for matrix effects in the NEXAFS features of condensed n-alkanes. A comparison of calculations on an isolated molecule and on a cluster of molecules provides information on how the NEXAFS spectra change from gas phase to condensed phase and determines the linear dichroism of each NEXAFS feature below the C 1s IP.<p>In the process of preparing n-alkane thin films for the study of linear dichroism, the morphology and molecular orientation of n-alkane thin films with different chain length (n-C36H74 and n-C60H122) have also been investigated by the NEXAFS spectroscopy and microscopy. These thin films were epitaxially grown onto cleaved NaCl (001) surfaces by physical vapor deposition. The results revealed that the morphology and molecular orientation of n-alkane thin films depend on the chain length and deposition parameters, such as substrate temperature. These observations have been rationalized by the thermodynamics of nucleation and the kinetics of growth.

The transition metal complexes cyclopentadienylrhenium tricarbonyl [CpRe(CO)3, Cp = cyclopentadienyl] and (isopropylcyclopentadienyl)rhenium tricarbonyl [(i-PrCp)Re(CO)3, i-Pr = isopropyl] were photolysed in alkanes at low temperature and the resulting alkane complexes, of the general formula Cp'Re(CO)2(alkane) (Cp' = Cp or (i-PrCp)), were studied using NMR spectroscopy. Characteristic proton chemical shifts (δ) and couplings (3JHH) were observed for alkane complexes of several linear, branched and cyclic alkanes of up to eight carbons. Alkanes with chemically distinct methyl (CH3) and/or methylene (CH2) units were observed alternatively binding through each unit to rhenium. No bound methine unit was observed. Large C-H coupling constants (1JCH) were observed for protons of several bound CH3 and CH2 units, indicating the bound C-H is intact. These species are, thus, alkane sigma (σ) complexes, wherein the alkane has an agostic (M-H-C, 3 centre 2 electron) interaction with the rhenium centre. The CH3 binding mode of (i-PrCp)Re(CO)2(1-pentane) was elucidated; sequential deuteration in the bound CH3 revealed an equilibrium isotope effect (EIE) in the remaining proton/s, confirming that only one C-H has an agostic interaction with rhenium at any instant . NMR parameters δ(1H) (-8.22), δ(13C) ( 42.4) and 1JCH (85 Hz) for the complexed C-H reveal it is unequivocally intact and yet strongly interacting with the rhenium centre, hallmarks for the agostic interaction. Intramolecular exchange was identified between pentane complex isomers Cp'Re(CO)2(1-pentane), Cp'Re(CO)2(2-pentane) and Cp'Re(CO)2(3-pentane). Equilibrium constants were determined, revealing a preference for CH2 binding over CH3. The inequivalent hydrogens found in methylene groups of cyclohexane at low temperature permitted simultaneous observation of axial and equatorial C-H protons of a bound CH2 in CpRe(CO)2(cyclohexane); an EIE, upon deuteration, indicated rapid exchange between complexed C-H bonds in the bound CH2 unit. The rhenium centre was found to prefer complexation of the axial C-H bond, over the equatorial, with K ~2.9. Intermolecular exchange of alkane ligands with free solvent was directly observed, in the competitive complexation of the [CpRe(CO)2] fragment to different alkanes in binary mixtures. The preference cyclohexane > cyclopentane > pentane > isobutane was established and equilibrium constants determined. The kinetics were followed by NMR and modelled, revealing rate constants; decay rates were also determined.

Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.

Stuttgart, Univ., Diss., 1999.

Techn. University, Diss., 2005--München.