Metal hydride NMR

Figure 2.86 The 1H NMR spectrum in the hydride region of the isomers of [IrH3(PEt2Ph)j] top, /ac-isomer bottom, mer-isomer. (Reproduced with permission from E.L. Muetterties (ed.), Transition Metal Hydrides, published by Marcel Dekker, 1971, p. 80.)...

A related study with a similar ruthenium catalyst led to the structural and NMR characterization of an intermediate that has the crucial Ru—C bond in place and also shares other features with the BEMAP-ruthenium diacetate mechanism.33 This mechanism, as summarized in Figure 5.4, shows the formation of a metal hydride prior to the complexation of the reactant. In contrast to the mechanism for acrylic acids shown on p. 378, the creation of the new stereocenter occurs at the stage of the addition of the second hydrogen. 

The metal-hydride region H NMR spectrum of a sample that had been irradiated up to the point of the red coloration is shown in Figure la. This spectrum shows the formation of... 

One must always keep in mind that in aqueous solutions the transition metal hydride catalysts may participate in further (or side) reactions in addition to being involved in the main catalytic cycle. H and P NMR studies established that in acidic solutions [RhCl(TPPMS)3] gave cis-fac-and ci5-7 er-[RhClH2(TPPMS)3] [86,88], while in neutral and basic solutions these were transformed to [RhHX(TPPMS)3] (X = H2O or Cl ) [86]. Simultaneous pH-potentiometiic titrations revealed, that deprotonation of the dihydride becomes significant only above pH 7, so this reaction of the catalyst plays no important role in the pH effects depicted on Figs. 3.2.a and 3.2.b. 

Table 10.1 lists kinetic data for the protonation of transition metal hydrides obtained through various spectroscopic (NMR, UV, IR) and electrochemical methods using stopped-flow mixing techniques. Most kinetic experiments have... 

The subject of polyhydride complexes was included as part of a larger, comprehensive review of metal hydride complexes by Kaesz and Saillant (19), and their interesting NMR behavior has been summarized by Jesson (20). The... 

This chapter presents results of NMR studies of several heavy metal hydrides, including both a summary of completed work by Lau et al. (i) on a binary hydride, Th4His, and preliminary results on several carbonyl hydrides, H2Os3(CO)io, H4Os4(CO)i2, and H4Ru4(CO)i2. The binary hydride, Th4Hi5, has attracted interest recently with the discovery of its super-conducting properties (2) and the carbonyl hydrides are metal cluster hydrides (3) which are of interest as models in the study of catalysis (4). 

Efforts to understand the state of hydrogen in metals and metal hydrides have involved the use of NMR for many years. This study combines the conventional solid state NMR techniques with more recently developed high-resolution, solid state NMR techniques (5,6). Conventional NMR techniques furnish information on dipolar interactions and thus can furnish static geometrical information on hydrogen positions and information on proton motion within such solids. The newer multiple pulse techniques suppress proton-proton dipolar interaction and allow information on other, smaller interactions to be obtained. This chapter reports what the authors believe is the first observation of the powder pattern of the chemical shift tensor of a proton that is directly bonded to a heavy metal. 

NICOL AND VAUGHAN NMR Study of Heavy Metal Hydrides... 

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