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

By Paul S. Pregosin, Roland W. Kunz

For virtually 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 endless number of 1H NHR experiences 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 through C, N, P and F used to be essentially famous. regardless of the attract, the technical problems taken 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, usually protons, led to a signal-to-noise challenge whose severity successfully excluded the examine of steel complexes with unfa­ vorable solubility features. the 1st very important step forward got here with the arrival of wide 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 problems ob­ served singlet whilst wide-band decoupling is hired (see Fig. 1). regardless of this development research of extra attention-grabbing molecules, corresponding to catalytically lively complexes used to be pressured to watch for the devel­ opment of Fourier rework tools on account that in simple terms with rather quick sign averaging equipment might adequate signal-to-noise ratios be achieved.

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III One-Bond Metal-Phosphorus Coupling Constants A Survey The previous paragraphs have concerned themselves with the qualitative aspects of the theory of one-and two-bond phosphorus couplings involving metals. In a number of instances we have cited specific if somewhat selective literature to support these ideas. The section which follows provides a more comprehensive survey of the types of molecules for which one-bond metal-phosphorus couplings have been reported. 0 !. 0 280 260 240 220 ~ 200 i>.

Moving to a different coordination number, there is an exceptionally large difference (> 50 ppm) between the chemical shift of axial and equatorial ligands in the five coordinate ruthenium complexes RUX 2 (PPh 3 )3 with the axial phosphorus at lower field [201]. 4 ppm for X = Br. g. 3 ppm [201]. The effect on 31p for the ruthenium complexes is probably the same as that mentioned for RuH(OH) (PPh 3 ) 2 (solvent) above, except that now the Chemical Shifts 54 complex is suggested to have a square pyramidal structure and the low field resonance is assigned to the apical and not the equatorial phosphine.

14 and 15 are reasonable for some simple octahedral compl~xes one can proceed further. We will assume that an excitation from One orbital to another of the same symmetry contributes a negative sign to 2 J (p,p) while a transition involving orbitals One-Bond Metal-Phosphorus Coupling Constants 31 ,,. , .. '. , .... ,\/ ~\ \ x ® I"~ '\\ \,\ ~\ ~ \'\, \ \ \ \ \ \ \ ' \ \ \ ) A'g(2) • A2u . A,g(l ) Trans complex D4h y 4 5 ,\ '\ \ a) ~ \ \ \\ \ \\ , , ',\ ,, " ' ,\,' " \ --'--<, \ \ Metal orbitals Fig_ 14.

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