Studies of Phosphorus -31 Nuclear Magnetic Resonance -in the Solid State
Duchamp, James C.
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For a number of years the study of both experimental and theoretical aspects of nuclear magnetic resonance spectroscopy of a variety of nuclei in the solid state have been the primary interests in the laboratory of Professor K. W. Zilm of the Yale University Chemistry Department1,2. Problemsinvolving l3C,29Si, 119Sn,31p,129Xeand183Whaveallbeen addressed recently using solid state techniques, some of which have been developed in this laboratory. Instrumentation used in these studies include 100 MHz. and 300 MHz. NMR spectrometers and various low temperature and magic angle spinning probes. Computer facilities and programs have been developed for use in theoretical aspects of the work. Immediately prior to my arrival at Yale Professor Zilm discovered that the solid state 31p NMR spectra of 1,2-bis[2,4,6-tri-tert-butylphenyl] diphosphine 1 showed a two lines each having some 1 structure. In the proton decoupled spectrum in solution there is only one line with no J-coupling. The multiplets found in the solid state do not have the proper intensities based on the solution theory. Two-dimensional spectroscopy showed a scalar coupling (J-coupling) interaction between two slightly inequivalent phosphorus atoms. Phosphorus 31 NMR has been actively studied in the liquid state since the early sixties. The 2 100% natural abundance of 31P made it more suitable for study before the advent of modem pulse NMR and excitation techniques developed for more dilute nuclei such as l3e. J-couplings for the liquid state for the P-P bond have been reported previously3. Other more recent work in the solid state concerning the P-P indirect (dipolar) coupling has been done by Waugh and co\Vorkers4. Based on single crystal studies of tetraethyl diphosphosphine disulfide and tetrabutyl diphosphine disulfide they suggest that P-P bonds show a sizable indirect nuclear coupling anisotropy. With all these considerations in mind we decided to make further studies of phosphorus bonding in general, and more specifically phosphorus-phosphorus bonding. These studies took place in three parts: development of a simulation to generate free induction decays for an isolated two spin system; examination of tetrarnethyl diphosphine disulfide 2, tetraethyl diphosphine disulfide 3., . R1 = Me, Et, n-Bu, Ph 2 ~~ ~ tetrabutyl diphosphine disulfide~, tetraphenyl diphosphine disuifide.2. and tetraphenyl diphosphine .6 for P-P J-coupling and structural information; and studying the relationship between chemical shifts of 31P and l3e in homologous systems.