31P and 13C NMR of Transition Metal Phosphine Complexes 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 doubtless endless number of 1H NHR reports 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 by means of C, N, P and F used to be sincerely well-known. regardless of the attract, the technical problems excited by measuring a few of these nuclei have been faraway from trivial. Small magnetic moments and coffee traditional abundance together with spin-spin coupling from different nuclei, in general protons, ended in 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 appearance of large band 1H-decoupling. for instance, the featureless large 31p resonance linked to the generally used ligand triphenyl phosphine is switched over to a pointy, extra comfortably 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 was once compelled to look forward to the devel­ opment of Fourier rework equipment given that in simple terms with really quick sign averaging tools might enough signal-to-noise ratios be achieved.

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On the other hand the effect on o31p of introducing substituents at the para-positions in the complexes cis and transPdCI 2 (P(p-R-C 6 H4 )3)2' R rather small « = CI, H, CH 3 , OCH 3 , is 3 ppm), suggesting that resonance effects through aromatic systems do not markedly affect the phosphorus chemical shift [198 ]. A similar trend is observed for some d 10 complexes of Ag(I) and (see Table 26). For the complexes HgX 2 P 2 P = PPh 3 , P(cyclohexyl)3' PBU~, X = N0 3 , CI, Br, I, the phosphorus chemical shift Hg(II) moves to higher field in the order I > Br > CI > N0 3 , which is the order expected based on the coordinating ability (and ionization potential) for the ligand atom [82].

A listing of typical 'J(Pt,P) values for a variety of molecular types is shown in Tables 3 - 9 (Chap. G). Coupling to Main Group Metals The literature concerned with the values 'J(M,P) for the case where M is not a transition metal is relatively sparse; however, the onebond metal-phosphorus coupling where the metal comes from group IV a has received some attention. The reduced one-bond phosphorus-carbon [159], phosphorus-tin [36,38] and phosphorus-lead [36] couplings in the molecules PR 3 , R = phenyl or alkyl, PhnP(S~1e3)3_n and Ph 2 PPbMe 3 are negative.

2) 1/2 p, z s ~ ~~ ~ 0'4 - 0"2 0"2+ 0"4 -0", - 0'3 0', + 0"2+ 0'3+ 0"4 Metal orb itals Trans planar Phosphorus orbitals Fig . 16. The MO scheme for a trans planar complex with symmetry D2h [92 ] D2h A~ ~ ~. y @ x 3 0',- 0'2+ 0"3- 0"4 0",- 0'2- 0'3+0"4 0', + 0'2- 0'3- 0'4 0",+ 0"2+0'3+ 0'4 Metal Tetrahedral orbi tals compl ex Td Phosph0C4s orbita ls Fig . 17. The MO scheme for a tetrahedral complex with symmetry, Td [92 ] contains metal d-orbital character, an increase in the separation of the nd- and (n+ 1 )p-levels should result in a decrease in the magnitude of 2 J (p,p).

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