M.J. Stchedroff

University of Turin

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2D and 3D DOSY methods for studying mixtures of oligomeric dimethylsiloxanes

Physical Chemistry Chemical Physics (2004)

M.J. Stchedroff Alan M. Kenwright Gareth A. Morris Mathias Nilsson Robin K. Harris

Diffusion-ordered spectroscopy (DOSY) is a powerful method for the NMR analysis of many types of mixture without the need for physical separation, and requires only relatively standard spectrometer hardware. The principal requirements for high resolution analysis using DOSY, that the basic NMR spectrum be well-resolved and that it have good signal-to-noise ratio, pose a dilemma where multiple chemically similar species with NMR-active heteronuclei are involved. Generally the 1H spectrum of such a mixture has good sensitivity but relatively poor chemical shift resolution, while for heteronuclei the situation is reversed. The dilemma is illustrated for the case of a mixture of cyclic dimethylsiloxanes, and the results of a range of 1H 2D DOSY, 29Si 2D DOSY and 1H {29Si} 3D DOSY–HMQC experiments are compared. In selecting the most appropriate technique to use for a given sample it is necessary to balance conflicting requirements for speed, resolution and accuracy, and to consider the balance between systematic and random errors. Results are presented for three different concentrations of a mixture of cyclic siloxanes containing between 4 and 20 monomer units. The diffusion coefficients measured show an inverse half power law relationship with molecular mass.

10.1039/b403960b

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Citations (58)

CCDC 203205: Experimental Crystal Structure Determination

The Cambridge Structural Database (2006)

Nitsa Kiriakidou Kazemifar M.J. Stchedroff M.A. Mottalib S. Selva Magda Monari

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

10.5517/cc6tg0g

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Synthesis, Characterization, and Dynamic Behaviour of Triosmium Clusters Containing the Tridentate Ligand {Ph₂PCH₂CH₂}₂S (PSP)

European Journal of Inorganic Chemistry (2013)

Roger Persson M.J. Stchedroff Roberto Gobetto Carl J. Carrano Michael G. Richmond

Abstract Reaction of [Os 3 (CO) 11 (NCMe)] with bis‐diphenylphosphanylethylene sulfide, {Ph 2 PCH 2 CH 2 } 2 S (PSP), leads to the formation of [Os 3 (CO) 11 (PSP)] and [{Os 3 (CO) 11 } 2 (μ‐PSP)] in good yield. Similarly, treatment of [Os 3 (CO) 10 (NCMe) 2 ] with PSP affords the cluster [Os 3 (CO) 10 (μ‐PSP)], in which the two phosphanes of the PSP ligand coordinate to different osmium atoms of the same triosmium unit. Reaction of [Os 3 (CO) 11 (PSP)] with [Os 3 (CO) 10 (NCMe) 2 ] yields the compound 1,2‐[{Os 3 (CO) 11 }(μ 3 ‐PSP){Os 3 (CO) 10 }] in which the thioether moiety and one of the phosphane groups of the PSP ligand are coordinated equatorially to the {Os 3 (CO) 10 } subunit. The cluster 1,2‐[{Os 3 (CO) 11 }(μ 3 ‐PSP){Os 3 (CO) 10 }] is also formed when [Os 3 (CO) 11 (PSP)] is oxidatively decarbonylated by reaction with trimethylamine N ‐oxide. The metastable cluster 1,2‐[{Os 3 (CO) 11 }(μ 3 ‐PSP){Os 3 (CO) 10 }] undergoes slow isomerisation at room temperature to form 1,1‐[{Os 3 (CO) 11 }(μ 3 ‐PSP){Os 3 (CO) 10 }] in which the thioether and phosphane moieties coordinate in a chelating mode to one of the {Os 3 (CO) 10 } subunits with the thioether moiety in an axial position. The dynamic behaviour of these clusters has been investigated by variable‐temperature 13 C{ 1 H} and 13 P{ 1 H} NMR spectroscopy. The solid‐state structures of [{Os 3 (CO) 11 } 2 (μ‐PSP)] and [Os 3 (CO) 10 (μ‐PSP)] are reported.

Osmium

Thioether

Moiety

Cluster chemistry

10.1002/ejic.201201403

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Citations (10)

Syntheses and Fluxional Processes of Diphenyl(2‐thienyl)phosphane Derivatives of Triosmium Clusters

European Journal of Inorganic Chemistry (2006)

Nitsa Kiriakidou Kazemifar M.J. Stchedroff M. Abdul Mottalib S. Selva Magda Monari

Abstract Thermal treatment of [Os 3 (CO) 12 ] with diphenyl(2‐thienyl)phosphane, Ph 2 P(C 4 H 3 S), results in the formation of [Os 3 (CO) 12– x {Ph 2 P(C 4 H 3 S)} x ] ( x = 1–3, 1 – 3 ), but no C–H bond activation was observed. Reaction of [H 2 Os 3 (CO) 10 ] with diphenyl(2‐thienyl)phosphane at ambient temperature affords [HOs 3 (μ‐H)(CO) 10 {Ph 2 P(C 4 H 3 S)}] ( 4 ), but when the samereaction is repeated at elevated temperatures, the cyclometallated species [(μ‐H)Os 3 (CO) 9 {μ 3 ‐Ph 2 P(C 4 H 2 S)}] ( 5 ) and[(μ‐H)Os 3 (CO) 8 {μ 3 ‐Ph 2 P(C 4 H 2 S)}{Ph 2 P(C 4 H 3 S)}] ( 6 ) are formed. In addition, two more products, tentatively assigned as [(μ‐H)Os 3 (CO) 6 {μ 3 ‐Ph 2 P(C 4 H 2 S)}{μ‐Ph 2 P(C 4 H 3 S)}{Ph 2 P(C 4 H 3 S)}] ( 7 ) and [(μ‐H)Os 3 (CO) 7 {μ‐Ph 2 P(C 4 H 2 S)}{μ‐Ph 2 P(C 4 H 3 S)}{Ph 2 P(C 4 H 3 S)}] ( 8 ) are obtained. The dynamic behaviours of 2 , 5 and 6 have been studied by variable‐temperature (VT) 1 H and 31 P{ 1 H} NMR spectroscopy. The VT 31 P{ 1 H} NMR spectra of [Os 3 (CO) 10 {Ph 2 P(C 4 H 3 S)} 2 ] ( 2 ) demonstrate that a mixture of two isomers, which are in rapid exchange at room temperature, is present and that the less common cis ‐ trans isomer, whose structure has been determined by X‐ray crystallography, is favoured for this cluster. The VT 1 H NMR spectra of 5 indicate the presence of two isomers which are proposed to arise from an oscillation of the σ,η 2 ‐vinyl group of the thienyl moiety between two metal atoms. A similar fluxional process is proposed to occur in 6 and the assignment of the room‐temperature structure(s) of this cluster was confirmed by 1 H‐ 187 Os 2D HMQC spectroscopy. In addition to 2 , the solid‐state structures of 3 , 5 and 6 have been determined by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

10.1002/ejic.200501141

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Citations (23)

Synthesis, Characterization, and Novel Fluxional Mechanisms of Triosmium Clusters Containing the Highly Flexible Ligand Ph₂PC₂H₄SC₂H₄SC₂H₄PPh₂(PSSP)

Organometallics (2010)

Roger Persson M.J. Stchedroff B. Uebersezig Roberto Gobetto Jonathan W. Steed

Treatment of Ph2PC2H4SC2H4SC2H4PPh2 (PSSP) with [Os3(CO)11(NCMe)] under mild conditions yields [{Os3(CO)11}2(μ-PSSP)], 1, and [Os3(CO)11(PSSP)], 2. In cluster 1 the ligand links two trinuclear cluster subunits, coordinating via its phosphine moieties. In cluster 2, the ligand is coordinated through one of the phosphine groups, while the remaining part of the PSSP ligand is oriented in a dangling mode. Treatment of [Os3(CO)10(NCMe)2] with PSSP yields 1,2-[Os3(CO)10(PSSP)], 3. NMR data presented in this paper indicate that a concerted cis/trans isomerism with respect to the phosphines operates in the cluster. This type of process has not been observed previously for a bridging ligand, but has been detected in the case of corresponding triosmium clusters with bis-monodentate phosphine ligands. Oxidative decarbonylation of [{Os3(CO)11}2(μ-PSSP)], 1, with Me3NO yields cluster [{Os3(CO)10}2(μ-PSSP)], 4. This cluster consists of two P,S-bridged cluster units. In solution at room temperature, 4 undergoes a slow rearrangement from a 1,2-bridging to a 1,1-chelating coordination mode. The crystal structures of clusters 1, 3, and 4 are reported.

Decarbonylation

10.1021/om900966c

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Citations (11)

CCDC 267505: Experimental Crystal Structure Determination

The Cambridge Structural Database (2006)

M.J. Stchedroff V. Moberg Ernesto Rodríguez A.E. Aliev Jark Böttcher

10.5517/cc8zc6s

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Citations (0)

Enhanced mobility of the cluster Ru3(CO)12 in the solid state formed in situ by the reaction of CO and Ru3(CO)6(μ-CO)(μ3∶η2∶η3∶η5-C12H8) on silica

Chemical Communications (2000)

Silvio Aime Roberto Gobetto Daniela Giusti M.J. Stchedroff Alejandro J. Arce

The reaction of Ru3(CO)6(μ-CO)(μ3∶η2 ∶η3∶η5-C12H 8) (physisorbed on SiO2) with CO in the solid state leads to Ru3(CO)12 and acenaphthylene in quantitative yields; the Ru3(CO)12 generated in situ is highly mobile leading to a reduced chemical shielding anisotropy.

Acenaphthylene

10.1039/b002641g

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Citations (4)

A one-shot sequence for high-resolution diffusion-ordered spectroscopy

Magnetic Resonance in Chemistry (2002)

Michelle D. Pelta Gareth A. Morris M.J. Stchedroff Stephen J. Hammond

Abstract Diffusion‐ordered spectroscopy (DOSY) is a powerful method for the NMR analysis of mixtures such as crude synthetic products, biofluids or biological extracts. Mixtures can be analysed without the need for any physical separation, and the method requires only standard NMR pulsed field gradient hardware. Existing pulse sequences for DOSY require extensive and time‐consuming phase cycling for clean results. A new sequence is reported here which allows clean spectra with good lineshapes to be obtained using as little as one transient per gradient value. Asymmetric bipolar field gradient pulse pairs are used in conjunction with extra balancing gradient pulses, selecting a unique coherence transfer pathway but minimizing eddy current effects and field‐frequency lock disturbance. Using the new sequence, high‐resolution proton DOSY spectra can be obtained in less than 1 min. Copyright © 2002 John Wiley & Sons, Ltd.

Pulse sequence

Pulsed field gradient

Sequence (biology)

10.1002/mrc.1107

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Citations (252)

CCDC 717582: Experimental Crystal Structure Determination

The Cambridge Structural Database (2011)

Roger Persson M.J. Stchedroff B. Uebersezig Roberto Gobetto J.W. Steed

10.5517/ccs2ptb

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Citations (0)