Teja S. Ertel

XAFS Spectroscopy of Liquid and Amorphous Systems: Presentation and Verification of a Newly Developed Program Package

A program package for XAFS data analysis, especially of liquid and amorphous samples, has been developed. For the first time a consequent error propagation is presented for all functions to be calculated in the course of the data analysis. The structural investigation of the Grignard compound CH3MgBr in diethyl ether is taken as an example for the various steps of the data analysis.

Supported organometallic complexes. Part XX. Hydroformylation of olefins with rhodium(I) hybrid catalysts

Abstract The rhodium(I) complexes HRh(CO)[Ph2P(CH2)xSi(OMe)3]3 [1a,b(T0)3; a: x=3, b: x=6; T: T-type silicon atom, three oxygen neighbors] were sol–gel processed with the bifunctional cocondensation agent (MeO)3Si(CH2)6Si(OMe)3 (T–C6–T) and in a separate reaction also with three additional equivalents of the phosphine ligand Ph2P(CH2)xSi(OMe)3 [2a,b(T0)]. The resulting stationary phases 1a(Tn)3(Tn–C6–Tn)y, 1a(Tn)3[2a(Tn)]3(Tn–C6–Tn)y, and 1b(Tn)3[2b(Tn)]3(Tn–C6–Tn)y (n=0–3, number of Si–O–Si bonds; y: content of cocondensation agent) show a relatively narrow particle size distribution. The structural integrity of the rhodium complex 1 after the polycondensation was established by an EXAFS structure elucidation of the polysiloxane 1a(Tn)3. The obtained stationary phases proved to be efficient catalysts for the hydroformylation of 1-hexene in the presence of a wide variety of solvents in the interphase. Application of the materials containing non-coordinated ligands raised the selectivity toward hydroformylation up to 92% and the n/iso ratio to 14:1 with an average turnover number of 164 molsub molcat−1 h−1. Higher olefins than 1-hexene were also hydroformylated with catalyst D and similar turnover frequencies and selectivities were obtained. 31P CP/MAS NMR relaxation time studies (TPH, T1ρH) were carried out in the presence (interphase) or absence (stationary phase) of a swelling solvent to investigate the dynamic behavior of the catalytically active polymer 1a(Tn)3[2a(Tn)]3(Tn–C6–Tn)y. The highest mobility of the nonpolar reactive centers was achieved in nonpolar solvents like toluene, while more polar solvents like ethanol afforded the highest mobility of the overall polymer. (1H,31P) 2D WISE NMR experiments performed on the same material revealed a substantial decrease of the line width for the swollen polymer. 29Si CP/MAS NMR experiments revealed a high degree of cross-linking and a larger content of cocondensation agent than introduced before condensation.

EXAFS study of zirconium alkoxides as precursor in the sol-gel process: I. Structure investigation of the pure alkoxides

The properties of materials obtained by sol-gel processing show a certain dependence on the type of metal alkoxide and the solvent. Some authors assumed that these effects are caused by the degree of oligomerization of the metal alkoxides and their solvation. In order to obtain information on the structure and molecular complexity of the metal alkoxide we performed an EXAFS study on primary zirconium alkoxides Zr(OR)4, with OR = n-propoxide and n-butoxide in solution of their parent alcohol. The EXAFS data for zirconium iso-propoxide have been used as a reference, because its solid state structure is known from X-ray analysis. The Zr-Zr correlations which were observed for all investigated systems provide evidence for an oligomeric structure. Because the analysis of the co-ordination spheres around the central Zr-atom revealed different Zr-O bond lengths, some of the formerly postulated structure models can be ruled out. We propose solvated dimers or trimers or mixtures of both species as possible structures of zirconium propoxide and zirconium butoxide in solution of their parent alcohol.

EXAFS study of zirconium alkoxides as precursors in the sol-gel process: II. The influence of the chemical modification

EXAFS studies of primary zirconium alkoxides Zr(OR)4 with OR = n-propoxide and n-butoxide, dissolved in their corresponding alcohols and chemically modified with acetylacetone (Hacac) and acetic acid (HOAc) in different molal ratios, are presented. The EXAFS-spectroscopic results, supported by FT-IR-studies, indicate a different chemical behavior of the complexing agents. In contrast to acetylacetone, the addition of acetic acid does not change the oligomeric structure of the zirconium alkoxides. Amazingly, the modification with acetic acid leads, in comparison to the pure compounds, to a shortened metal centre distance, whereas in the reaction with acetylacetone the Zr-Zr distance is not changed. With the determined distances and a rough quantitative inclusion of the coordination numbers it was possible to deduce detailed structure models.

Structural Investigations of Tetra- and Octasubstituted (Phthalocyanine)ruthenium Complexes by EXAFS Spectroscopy

To obtain more structural information of (phthalocyaninato)ruthenium compounds, an EXAFS investigation was carried out on amorphous tBu4PcRu (1), tBu4PcRu(3-Clpy)2 (2), PcRu(3-Fpy)2 (3) and (C5H11O)8PcRu(3-Clpy)2 (4). Structural models for the four compounds are deduced from the atomic distances determined around the metal centre. A dimeric structure was found for 1, while bisaxial arrangement of the ligands was shown for 2, 3 and 4, and the structural parameters were also determined.

Magnesium and bromine exafs studies of grignard compounds in solution

Abstract The Grignard compounds MeMgBr and EtMgBr in n-Bu2O were studied at room temperature and — 85°C by extended X-ray absorption fine structure (EXAFS) spectroscopy above the magnesium and bromine K edges. The magnesium EXAFS studies were performed in the fluorescence mode with an UHV compatible cell for liquid samples. At both temperatures, dimers of the Grignard compounds are observed. By a combined analysis of the magnesium and bromine EXAFS spectra, the structure of the dimers of the Grignard compounds is deduced. Copyright

Control of the basicity of the Ir(tdppcymome)(CO)Cl complex with methoxymethyl functional groups at the ligand backbone [tdppcymome=cis,cis-1,3,5-(PPh2)3-1,3,5-(CH2OCH3)3-C6H6]

Abstract Treatment of the tripodal ligand cis,cis-1,3,5-tris(diphenylphosphino)-1,3,5-tris(methoxymethyl)cyclohexane (tdppcymome) (L) with Ir(PPh3)2(CO)Cl leads to the trigonal bipyramidal complex 4. Ir(tdppcymome)(CO)Cl (4) is protonated by the strong and weak acid HBF4 and NH4PF6, respectively. The oxidative addition of H2 forces the chlorine to dissociate irreversibly from the metal center of 4. In a CO atmosphere complex 4 forms the dicarbonyl complex [Ir(tdppcymome)(CO)2]Cl (6). The reaction of 4 with ethylene in the presence of NaBPh4 gives the ethylene complex [Ir(tdppcymome)(CO)(C2H4)]BPh4 (8). At elevated temperatures 8 looses ethylene under the formation of the orthometalated complex 9. This complex can also be generated directly from 4 and NaBPh4. EXAFS investigations on the carbonyl chlorocomplexes 1–4 display a remarkable change in the Ir–C bond length dependent on the functional group in the ligand backbone, while their ν(CO) absorptions correlate with the group electronegativity of the functional groups.

EXAFS studies of a chiral rhenium lactone complex and its precursors including multiple scattering calculations

Abstract EXAFS studies of a chiral rhenium complex with an ‘axially prostereogenic’ biaryl lactone as ligand and its precursors in CH 2 Cl 2 and acetone solutions, respectively, are presented. The results of the data analysis for the precursors CpRe(CO) 3 , [CpRe(CO) 2 (NO)]BF 4 and [CpRe(CO)(NO)(PPh 3 )]BF 4 in acetone, obtained with the commonly used single-electron single-scattering theory with different theoretical amplitude and phase functions, are compared with those obtained by including multiple scattering effects. It is shown that the EXAFS spectroscopical investigation of a series of compounds with known structures and with an increasing degree of complexity is a great help for interpreting the EXAFS function of a related compound for which the structure in solution is unknown.

EXAFS investigations of metal organic molecules with the goal of studying homogeneously catalytic systems in situ

Abstract The investigations of Grignard compounds are very instructive for understanding the principles of getting structural information on highly complex and simultaneously metal activated systems by means of EXAFS spectroscopy. The structural investigations of a model system for Friedel-Crafts alkylation and some metal complexes (metal = Zr, Mo, W, Re), which activate carbonyl groups selectively with respect to the subsequent ring cleavage of axially prosterogenic biaryl lactones, are reported. As an actual field of metal organic research temperature dependent in situ EXAFS studies of the CH-activation of substituted olefins are presented. It was possible to observe the course of the rearrangement reaction of an iridium olefin complex to the corresponding hydrido (vinyl) iridium complex.

Structural investigations on PZT precursors for thin film preparation

Abstract The coordination of Pb and Zr atoms in the liquid precursors (LPs), Pb(OAc) 2 and Ti/Zr(OPr n ) 4 solvated in a mixture of compounds of lead zirconate titanate (PZT) for thin film preparation was studied by EXAFS spectroscopy. The Pb coordination in the LPS is affected by the sol preparation. No significant differences of the Pb and Zr coordination of the dried powders (DPs) were detected.