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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Additional info for 31P and 13C NMR of Transition Metal Phosphine Complexes
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 . 4 ppm for X = Br. g. 3 ppm . 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.