Heteronuclear second-order coupling effects in platinum-lead-bonded compounds

JOURNAL

OF MAGNETIC

47, 156-l

RESONANCE

58 (1982)

Heteronuclear Second-Order Coupling Effects in Platinum-Lead-Bonded Compounds STUART

CARR,

RAY

COLTON,

AND

DAINIS

Department of Inorganic Chemistry, University of Melbourne, Received

November

DAKTERNIEKS

Parkville 3052, Victoria, Australia

19, 198 1

As part of NMR investigations of chemical shifts and couplings of heavy nuclei bonded to each other we have been examining compounds with direct platinu ti nd platinum-lead bonds and now report second-order coupling effects betwee 19 and zo7Pb in platinum-lead compounds. This communication has bee prompted by the recent report (I) of isotopic heteronuclear second-order ~0~~1~~ between ‘17Sn and “‘Sn in (Ru(SnC1,),C1)4- and (Os(SnC1,),C1)4-. As an example we take the compound cis-Pt(PPh,),(Ph)(PbPh3) for which the 31P NMR spectrum (2) in dichloromethane consists of two main doublets (6 24.85 ppm, 6 20.80 ppm) arising from the nonequivalent phosphines (2J(31P-3’ Hz). The doublet at higher frequency has satellites (‘J(‘95Pt-31P) = 2 2J(207Pb-31P) = 3460 Hz), which are consistent with a phosphorus tram to and the doublet at lower frequency has couplings (1J(g5Pt-31P) = 1965 Hz, 31P) = 260 Hz), which are consistent with a phosphorus cis to the lead atom. The “*Pt NMR spectrum at 21.3 1 MHz (Fig. 1) of cis-Pt(PPh3),(Ph)(PbFhs) has a central doublet of doublets resulting from coupling to the different phospbor~s atoms and two sets of *“Pb satellites (with the same phosphorus couplings) each f intensity approximately 12% relative to the central multiplet. The two sets of llites are not symmetrically disposed about the central multiplet, their tion being 180 Hz above the frequency of the main multiplet. The *07P spectrum at 20.84 MHz (Fig. 1) is of similar appearance (with different ph uplings) with lg5Pt satellites ( 16% of the central multiplet) unsymmetrically dissed about the central multiplet by 180 Hz to the lower frequency side of the spectrum. Spectra recorded at higher field (lg5Pt at 42.70 MHz, 207Pb at 41.74 MHz) show the asymmetry is decreased to 85 Hz. That the asymmetry is attributable to second-order coupling effects in the satellite spectrum rather than a large isotope effect is endorsed by several experimental observations. The above variation of the asymmetry with frequency is quite the opposite of that expected for an isotope effect, The central multiplets of both spectra have sharp, well-defined lines. In the platinum-195 spectrum this central multiplet corresponds to lg5Pt bonded to lead nuclei with spin 0 (*O’Pb 24%, “‘Pb 52%). gnitude of the asymmetry of the satellites suggests that for a genuine isoto ct the peaks of the central multiplet should be significantly broadened, if split into two multiplets, corresponding to lg5Pt bonded to each of those two nuclei. 156 0022-2364/82/040156-03$02.00/O Copyright 0 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.

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FIG. 1. lg5Pt (at 21.31 MHz) and *O’Pb (at 20.84 MHz) NMR spectra showing the asymmetry satellites relative to the central multiplets. The lower diagram represents the relative spacings first-order and second-order (satellite) spectra (phosphorus couplings not shown).

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Similarly in the ‘07Pb spectrum the central multiplet would be broadened or separated because of the spin-0 platinum isotopes (194Pt 33%, “‘Pt 25%, lg8Pt 7%) (1). It also seems unlikely that both platinum and lead nuclei would show an effect of the same magnitude. The chemical shift difference for lg5Pt and “‘Pb (0.48 MHz) camp ‘J(207Pb-195Pt) (18,375 Hz) implies that the observed satellite spectra are second order. Calculations based on the assumption that the platinum-195 and lead-207 satellite spectra are part of an ABXZ spectrum (where X, Z are the tw phosphorus nuclei) predict the positions of the central multiplets of both 195Pt an “‘Pb spectra to within the experimental error (+lO Hz). This also shows that any isotope effect is very small; which agrees with observations for other nuclei (3). This is the first time second-order coupling effects have been observed between two different elements. Similar results have also been obtained for an extended series of platinum-lead compounds with various substituents on platinum and lead and also for compounds with two lead groups bonded to one platinum. In analogous platinum-tin-bond compounds no similar effect was observed, all spectra being strictly first order. more detailed report of the work described will appear at a later stage. The spectra were recorded on a JEOL FX 100 spectrometer at 2.3 T a JEOL FX 200 at 4.6 T. The 31P spectra were referenced to 85% H,PO,; the and 207Pb were both referenced to 70% tetramethyl lead in toluene to provide a common reference for both halves of the AB spectrum. ACKNOWLEDGMENT

We thank Dr. R. Brownlee of La Trobe University for access to the JEOL FX 200 spectrometer. REFERENCES

1. C. R. LASSIGNE, E. J. WELLS, L. J. FARRUGIA, AND 3. R. JAMES, J. Magn. Reson. 43,488 (1981). 2. T. A. K. AL-ALLAF, G. BUTLER, C. EABORN, AND A. PIDCOCK, .I Organometal. Chem. 188, 335 (1980). 3. R. K. HARRIS AND B. E. MANN, Eds., “NMR and the Periodic Table,” Academic Press, New York/London, 1978.