Download 31P and 13C NMR of Transition Metal Phosphine Complexes by Paul S. Pregosin, Roland W. Kunz PDF

By Paul S. Pregosin, Roland W. Kunz

For nearly 1 / 4 of a century the phrases "nuclear magnetic reso­ nance" have been synonymous with proton I,leasurements. in this interval the literature abounded with a doubtless endless number of 1H NHR reviews involved basically with carbon chemistry. sometimes a "novel" nucleus was once studied and, even in these early days, the poten- thirteen 14 31 19 tial provided through C, N, P and F was once essentially well-known. regardless of the attract, the technical problems enthusiastic about measuring a few of these nuclei have been faraway from trivial. Small magnetic moments and occasional typical abundance together with spin-spin coupling from different nuclei, commonly protons, ended in a signal-to-noise challenge whose severity successfully excluded the learn of steel complexes with unfa­ vorable solubility features. the 1st very important step forward got here with the arrival of huge band 1H-decoupling. for instance, the featureless vast 31p resonance linked to the widely used ligand triphenyl phosphine is switched over to a pointy, extra without difficulty ob­ served singlet while wide-band decoupling is hired (see Fig. 1). regardless of this development research of extra fascinating molecules, reminiscent of catalytically lively complexes was once compelled to anticipate the devel­ opment of Fourier rework tools for the reason that purely with fairly fast sign averaging equipment may possibly adequate signal-to-noise ratios be achieved.

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Extra resources for 31P and 13C NMR of Transition Metal Phosphine Complexes

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A typical 31p{1H} spectrum shows a main-band to satellite ratio of ~ 10:1. The molecules HgX 2 (PBU 3 n )2' X = a variety of anionic ligands, have been investigated by four different groups [49-51,99]. When phosphite replaces phosphine the one-bond coupling increases markedly [49]. 1J (Hg,P) values for the dimeric species Hg 2 C1 4P 2 have been measured and are generally significantly larger 1 than those for the corresponding mononuclear complexes ( J(Hg,P) n 1 n HgC1 2 (PBU 2 Ph)2 = 5035 Hz; J(Hg,P) Hg 2 C1 4 (PBU 2 Ph)2 7514 Hz [50]).

The effect on o31p of changing a single ligand is nicely demonstrated by the complexes trans -PdCI 2 (phosphine)X [196] and this is shown in Table 25. For such dB-square planar complexes one normally thinks of the trans- influence (see Chapter 2) of the ligands. As can be seen from the Table an increase in the trans influence of the X group shifts the 31p resonance to higher field. It may well be the case that this observation is valid for several other second row transition elements. 5 ppm. [116].

The effect of M is nearly the same for both ends of the bidentate. An interesting new empiricism, noted by several authors but accented by Garrou [203], concerns the "ring contribution" 8 R to the chemical shift in chelating phosphines. This phenomenon is defined as the difference between the coordination chemical shift, 8, of a ais substituted bis phosphine complex and the observed 8 value for an equivalent phosphorus in a chelate complex. Put briefly, this effect results in a deshielding of the phosphorus resonance by ~ 21 - 33 ppm for chelating phosphorus atoms in 5-membered rings whereas this resonances is shifted to higher field by amounts varying from 2 to 25 ppm for four and six membered chelate rings.

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