Ulrich Reinöhl

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.

Investigation of the Crystallisation Behaviour of Lead Titanate (PT), Lead Zirconate (PZ) and Lead Zirconate Titanate (PZT) by EXAFS-Spectroscopy and X-Ray Diffraction

Two solid solutions of lead zirconium titanates PbZrxTi1 − xO3 (x = 0.1 and 0.35) as well as the reference compounds lead titanate and lead zirconate were prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol-gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by EXAFS spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD).It follows from the analysis of the EXAFS data that the local order of the amorphous phases seems to be completely different from that of the crystalline phase. There is no indication of a preformation of the local order of the perovskite structure. The analysis of our EXAFS spectra can be interpreted very consistently with the assumption that in the amorphous samples a segregation exists on molecular level and the low crystallisation temperatures are a consequence of very short diffusion paths.

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.

EXAFS and X-ray diffraction studies on sol-gel prepared zirconium titanium oxides

A series of solid solutions of zirconium titanium oxides (ZTs) ZrxTi1� xO2 ðx ¼ 0:1; 0:18; 0:45Þ was prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol–gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD). The sample with an intermediate zirconium content ðZr0:45Ti0:55O2Þ exhibits significant structural changes in course of the calcination, whereas the differences between the amorphous and the crystalline state are quite small in titanium-rich samples. 2002 Elsevier Science B.V. All rights reserved.