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.

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 1 H 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 1 H 2D DOSY, 29 Si 2D DOSY and 1 H { 29 Si} 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.

Thermal treatment of [Os3(CO)12] with diphenyl(2‐thienyl)phosphane, Ph2P(C4H3S), results in the formation of [Os3(CO)12–x{Ph2P(C4H3S)}x] (x = 1–3, 1–3), but no C–H bond activation was observed. Reaction of [H2Os3(CO)10] with diphenyl(2‐thienyl)phosphane at ambient temperature affords [HOs3(μ‐H)(CO)10{Ph2P(C4H3S)}] (4), but when the samereaction is repeated at elevated temperatures, the cyclometallated species [(μ‐H)Os3(CO)9{μ3‐Ph2P(C4H2S)}] (5) and[(μ‐H)Os3(CO)8{μ3‐Ph2P(C4H2S)}{Ph2P(C4H3S)}] (6) are formed. In addition, two more products, tentatively assigned as [(μ‐H)Os3(CO)6{μ3‐Ph2P(C4H2S)}{μ‐Ph2P(C4H3S)}{Ph2P(C4H3S)}] (7) and [(μ‐H)Os3(CO)7{μ‐Ph2P(C4H2S)}{μ‐Ph2P(C4H3S)}{Ph2P(C4H3S)}] (8) are obtained. The dynamic behaviours of 2, 5 and 6 have been studied by variable‐temperature (VT) 1H and 31P{1H} NMR spectroscopy. The VT 31P{1H} NMR spectra of [Os3(CO)10{Ph2P(C4H3S)}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 1H NMR spectra of 5 indicate the presence of two isomers which are proposed to arise from an oscillation of the σ,η2‐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 1H‐187Os 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)

The cluster [Ru3(CO)12] normally reacts readily with tertiary phosphines and diphosphines in the presence of Me3NO to give simple phosphine-substituted derivatives by a reaction involving nucleophilic attack of the amine oxide at CO leading to CO2 formation. However, the corresponding reaction of [Ru3(CO)12] with (R)-BINAP [2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl] in the presence of Me3NO does not give [Ru3(CO)10(BINAP)], as expected, but instead an 80% yield of the dihydroxy complex [Ru3(μ-OH)2(CO)8{μ-(R)-BINAP}] (1) as the first example of a μ-BINAP complex. NMR coalescence effects are observed in the 1H NMR spectra, but by using a 13CO-enriched sample, we were able to show that the fluxionality is not cluster-centered since the 13C{1H} NMR spectrum for the CO ligands is invariant over a wide temperature range. COSY spectra were used to show that there is restricted rotation about two of the four P−Ph bonds while the other two are rotating freely. From a single-crystal XRD study it can be seen that two Ph groups are unimpeded while the other two are closely aligned to the naphthyl rings in a graphitic manner and it is this that leads to the restricted rotation. This bridging ligand adopts quite a different conformation about the C−PPh2 bonds to that in free BINAP, the structure of which was also determined for comparison, and somewhat different from that in known chelating BINAP complexes. In contrast, the direct thermal reaction of (R)-BINAP with [Ru3(CO)12] in octane gives, in addition to traces of two uncharacterized species, a 38% yield of the cluster [Ru3(μ-H){μ-(R)-BINAP-H}(CO)9] (2), in which we believe that ortho metalation has occurred at one of the four Ph rings to form the first example of a cyclometalated BINAP ligand. We have been unable to obtain simple derivatives such as [Ru3(CO)11(BINAP)] or [Ru3(CO)10(BINAP)], although we have shown that the osmium analogues may be synthesized.

The first use of silicon-29 diffusion-ordered NMR spectroscopy (DOSY) is reported, in a study of the speciation of aqueous silicates.