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

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 possible limitless number of 1H NHR reports involved essentially with carbon chemistry. sometimes a "novel" nucleus used to be studied and, even in these early days, the poten- thirteen 14 31 19 tial provided by way of C, N, P and F used to be in actual fact famous. regardless of the attract, the technical problems fascinated with measuring a few of these nuclei have been faraway from trivial. Small magnetic moments and occasional ordinary 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 vital leap forward got here with the appearance of huge band 1H-decoupling. for instance, the featureless extensive 31p resonance linked to the widely used ligand triphenyl phosphine is switched over to a pointy, extra conveniently ob­ served singlet whilst wide-band decoupling is hired (see Fig. 1). regardless of this development research of extra attention-grabbing molecules, equivalent to catalytically energetic complexes used to be compelled to watch for the devel­ opment of Fourier rework equipment because in basic terms with quite quick sign averaging equipment may possibly enough signal-to-noise ratios be accomplished.

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Additional info for 31P and 13C NMR of Transition Metal Phosphine Complexes (NMR Basic Principles and Progress)

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A clear sign that 31p chemical shifts are a composite from several sources, comes from a consideration of the effects of geometric isomerism on the phosphorus resonance position. Consider the square planar complexes cis and trans -HC1 2 (PRnPh (3-n) ) 2 abbreviated as shown CI CI P-M-CI P-M-P P cis (XXXI) trans (XXXII) I I I I CI in XXXI and XXXII. It is well known [200] that 6 31 p lower field by 9-11 ppm than 6 31 P . C7-S appears at for M = Pd(II) whereas the re31 t rans 31 Ptrans > 6 ~is [61].

6 ppm, l J (Rh,P) = 108 Hz the proposition that these have different structures 41 One-Bond Metal-Phosphorus Coupling Constants seems dubious although the complex RhCl(NO) (tpp) , which is known to have a square pyramidal structure, shows 1J (Rh,P) 2 = 106 Hz for the trans-P atoms [124]. 5 Hz and is thought not to have apical phosphine atoms [119]. Its 1H spectrum suggests that the two phosphines are not trans. Data for Rh(NO) (PPh 3 )3 and Rh(NO) C1 2 (PPh 3 )2 have been reported [125]. COMe I ~\\\CI ~/IIRh" Ph3P1111.

3% respectively). These two isotopic one-bond couplings are readily distinguishable and have been observed in the complexes CdI 2 P 2 , = PMe 2 Ph, PMePh 2 , PEt 3 , PEt 2 Ph, PEtPh 2 [101] and the dimeric species t Cd 2 X4 (PBU 3 )2' X = Cl, Br, I, SCN [102]. For comparable molecules the dimeric species show a much larger one-bond coupling in analogy with P mercury complexes. Typical values for 1J (113 Cd ,p) in the monomeric and dimeric species are ~ 1200 Hz and ~ 2000 Hz, respectively. One-Bond Metal-Phosphorus Coupling Constants 37 Group Va There are two reports [23,24] of vanadium phosphorus one-bond couplings.

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