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ABSTRACT: Addition of excess CF3CO2H (HTFA) to [Rh2Pt2(CO)7(PPh3)3], I, under nitrogen results in the formation of a salt (X2+ Y2�), which contains only the second example of a di-cationic carbonyl hydride tetra-nuclear
cluster, [H2Rh2Pt2(CO)7(PPh3)3]2+, X2+, and a presently partially characterized polymetallic anion Y2�. The
di-cation X2+ has been characterized by mass spectrometry and a variety of multinuclear NMR methods.
Since there is no difference in the electron count for I and X2+, it is probable that both I and X2+ adopt
similar butterfly metallic frameworks with a Rh–Rh hinge; in X2+, there are two bridging hydrides to
the same wing-tip Pt but the phosphine site occupancies on the Rh2Pt2-framework in I and X2+ are
different.
Inorganica Chimica Acta. 01/2010;
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ABSTRACT: A new version of one-dimensional (1)H experiment has been developed to probe ligand binding to macromolecular targets. The experiment, called transient NOE-exchange relay, is similar to the 'reverse NOE pumping' technique [A. Chen, M.J. Shapiro, J. Am. Chem. Soc. 122 (2000) 414-415]. The T(2) filter is used to erase protein magnetization, and the saturation then spreads from protein to bound ligand (via NOE) and further to a free ligand (via on-off exchange). The ligand signals, monitored as a function of mixing time, present a familiar 'dip' pattern characteristic of transient NOE or transient exchange experiments. In addition to the T(2) filter, we have also implemented a T(1) filter which makes use of the fact that the selective T(1)(-1) rates in macromolecules are much higher than those in small ligands. To model the experiment, complete relaxation and exchange matrix analysis has been invoked. This formalism was further used as a starting point to develop a simplified treatment where the relaxation and exchange components are represented by 2x2 matrix and, in addition, there is a special term responsible for coupling of ligand magnetization to the protein spin bath. The proposed experimental scheme has been tested on a system of peanut agglutinin complexed with Me-beta-D-galactopyranoside, which is known to be in a slow exchange regime. The results suggest that the NOE-exchange-relay experiment can be used at the advanced stages of the drug development process to confirm high-affinity ligand binding.
Journal of Magnetic Resonance 08/2007; 187(1):44-51. · 2.14 Impact Factor
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ABSTRACT: The optically active ligand R,R-PHAZAN (1,3-bis[(1R)-1-Phenylethyl]-2-(2-thienyl)-1,3,2-diazaphospholane) has been prepared and the products resulting from the reactions with Rh6(CO)15NCMe, H3RhOs3(CO)12, and H4Ru4(CO)12 have been investigated by X-ray crystallography and a variety of multinuclear NMR methods. X-ray studies show that PHAZAN can behave as a bidentate ligand in
Rh6(CO)14(l2,j2-R,R-PHAZAN) (with coordination through P and S) or a monodentate ligand (through P coordination) in H4Ru4(CO)11(j1-R,R-PHAZAN) and NMR studies show that these structures are retained in solution. In Rh6(CO)14(l2,j2-R,R-PHAZAN), edge-bridging coordination of PHAZAN results in the formation of an additional two novel chiral centres and these are observed in solution. Reaction of PHAZAN with H3RhOs3(CO)12 results in cleavage of the thienyl group and formation of the phosphido cluster,
H2RhOs3(CO)11(l2-PNN), (PNN = 1,3-bis-(1-phenylethyl)-[1,3,2]diazaphospholidine-2-yl). A variety of NMR measurements show that the hydride site-occupancies in the solid state are retained in solution and there is evidence for interaction of an ortho-phenyl hydrogen and a hydride through ‘‘dihydrogen’’ bonding.
Journal of Organometallic Chemistry 01/2007; · 2.38 Impact Factor
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ABSTRACT: Both Rh4(CO)12 and Rh6(CO)16 exhibit CO-fluxionality and modern, variable temperature, NMR methods allow the unambiguous assignment of the three terminal CO resonances and, for Rh4(CO)12, show that the mechanism of CO-fluxionality, which has been controversial for a long time, unambiguously involves the merry-go-round process; Rh6(CO)16, which was previously thought to be static, is also shown to be fluxional, although the rate of CO-exchange is much less than found for substituted derivatives, and possible pathways for this CO-exchange are discussed.
Inorganica Chimica Acta 01/2006; · 1.85 Impact Factor
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ABSTRACT: Multiple-metal spin transitions which distort the HMQC spectra of rhodium carbonyl clusters are discussed. These effects are seen whenever the detector nucleus, e.g. 13C or 31P, couples to more than one metal spin and are not restricted to detector ligands occupying edge- or face-bridging sites. These effects are illustrated in, but not limited to, the 13C-{103Rh} and 31P-{103Rh} HMQC spectra of [Rh6(CO)15L], (where L = P(4-F-C6H4)3), [Rh4(CO)11{P(OPh)3}], [Rh6C(CO)15]2- and [Rh2(carboxylate)2PPh3]. The effect is to modulate the intensity and position of the correlations in the metal dimension; cross peaks are displaced from the true chemical shift, additional cross peaks are seen and the intensity of the coherences varies as a function of the preparation delay, d2, and coupling constant, and may go to zero at the conventional value of 1/(2J). Analyses of the relevant spin systems are given together with experimental strategies to overcome these effects.
Magnetic Resonance in Chemistry 10/2004; 42(9):769-75. · 1.44 Impact Factor
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ABSTRACT: A new version of one-dimensional 1H experiment has been developed to probe ligand binding to macromolecular targets. The experiment, called transient NOE-exchange relay, is similar to the ‘reverse NOE pumping’ technique [A. Chen, M.J. Shapiro, J. Am. Chem. Soc. 122 (2000) 414–415]. The T2 filter is used to erase protein magnetization, and the saturation then spreads from protein to bound ligand (via NOE) and further to a free ligand (via on–off exchange). The ligand signals, monitored as a function of mixing time, present a familiar ‘dip’ pattern characteristic of transient NOE or transient exchange experiments. In addition to the T2 filter, we have also implemented a T1 filter which makes use of the fact that the selective rates in macromolecules are much higher than those in small ligands. To model the experiment, complete relaxation and exchange matrix analysis has been invoked. This formalism was further used as a starting point to develop a simplified treatment where the relaxation and exchange components are represented by 2 × 2 matrix and, in addition, there is a special term responsible for coupling of ligand magnetization to the protein spin bath. The proposed experimental scheme has been tested on a system of peanut agglutinin complexed with Me-β-d-galactopyranoside, which is known to be in a slow exchange regime. The results suggest that the NOE-exchange-relay experiment can be used at the advanced stages of the drug development process to confirm high-affinity ligand binding.
Journal of Magnetic Resonance.
