Dedicated to Professor Dr. Wolfgang Luttke on the occasion of his 75th birthday (13. IX. 95)The solution structure and the aggregation behavior of (E)-2-lithio-l-(2-lithiophenyl)-l-phenylpent-l-ene (1) and (Z)-2-lithio-l-(24ithiophenyl)ethene (2) were investigated by one-and two-dimensional 'H-, I3C-, and 6Li-NMR spectroscopy. In Et@, both systems form diniers which show homonuclear scalar 6Li,6Li spin-spin coupling. In the case of 2, extensive 6Li,'H coupling is observed. In tetrahydrofuran and in the presence of 2 mol of N,N,N',N'-tetramethylethylenediamine (tmeda), the dimeric structure of 1 coexists with a monomer. The activation parameters for intra-aggregate exchange in the diniers of 1 and 2 (1 (Et,O): A H # = 62.6 h 13.9 kJ/mol, AS # = 5.8 * 14.0 J/mol K, A G '(263) = 61.1 kJ/mol; 2 (dimethoxyethane): A H # = 36.9 h 6.5 kJ/mol, AS # = -61 h 25 J/mol K, AG # (263) = 54.0 kJ/mol) and the thermodynamic parameters for the dimer-monomer equilibrium for 1 (AHa = 26.7 f 5.5 kJ/mol, AS" = 63 * 27 J/mol K), where the monomer is favored at low temperature, were determined by dynamic NMR studies.Introduction. -Modern NMR spectroscopy provides a number of 1D-and 2D-pulse sequences which have paved the way for extended and more detailed NMR investigations of organolithium compounds, in particular of systems which contain several nonequivalent Li-sites [2-61. Apart from simple spin-echo spectroscopy [7] [8], 2D 6Li or 'Li-exchange spectroscopy (EXSY) [2], heteronuclear ID 'H, or 2D [lo] Overhauser measurements, and homo-as well as heteronuclear shift correlations of the hLi,6Li [ 1 11 and 'Li,I3C [I21 type are of great importance. In favorable cases with regard to line width and relaxation behavior, even 7Li,7Li-COSY [ 131 and iH,7Li-Overhauser measurements [14] could be performed. In addition, information about the aggregation states of organolithium compounds can be obtained from deuterium-induced isotope shifts of the 6Li-resonance [ 151.In the following we report results from the application of a number of these NMR techniques to two 6Li-labelled dilithiostyrene compounds, (E)-2-lithio-1 -(2-lithiophenyl)-1 -phenylpent-1-ene (I) [16] and (Z)-2-lithio-l-(2-lithiophenyl)ethene (2; arbitrary numbering) [ 171. These systems are related to (E)-l-lithio-2-(2-lithiophenyl)-l-phenylhex-l-

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A density matrix treatment is presented which describes the main features of INADEQUATE experiments for spin-1 AX spin systems. It is shown that apart from two-spin double quantum peaks, which carry correlation information, one-spin double quantum peaks are to be expected. In the latter, homoculear spin-spin coupling is amplified in the F, domain where the signal splitting amounts to 45. The theoretical predictions are verified for the 'H,'H AX system of 3,3'-[D,]norcamphor. In addition, experimental results for a 6Li,6Li A,X, or A A X X spin system are presented and the influence of spin-lattice relaxation on the relative intensity of the one-spin double quantum peaks for 6Li,6Li experiments is demonstrated. KEY WORDS NMR; 'H NMR; 6Li NMR; spin-1 nuclei; double quantum spectroscopy; INADEQUATE; coupling constants Double quantum spectroscopy (DQS) has been a popular NMR experiment in connection with molecular structure elucidation. In particular, proton and carbon DQS,'.' the latter termed INADEQUATE for the natural abundance situation, have found much application. We have shown recently,"' with specific reference to 'H and 6Li, that multiple quantum spectroscopy in the isotropic phase is invaluable in visualizing spin connectivity even when nuclei with spin > 1/2 are involved, in particular because indirect spin-spk couplings for these nuclei are often not resolved. This is especially true for the spin-1 group nuclei (2H, 6Li, 14N).In this work, we explored in detail some properties of the double quantum INADEQUATE spectra of spin-1 nuclei. In connection with spin-1 isotopes, two different varieties of double quantum coherences (DQC) are to be distinguished, uiz. one-spin and two-spin DQC4*' (Scheme 1, dotted and dashed lines, respectively). Considering a two-spin-1 AX system, the standard double quantum preparation sequencegives rise to the following density matrix for cp = x, starting from thermal equilibrium :* Authors to whom correspondence should be addressed. It is worth noting that the sequence leads to one-spin DQC that is in phase quadrature with two-spin DQC, e.g. one-spin DQC of phase T x and two-spin DQC of phase +_ y, respectively, in Eqns (2) and (3). From the above, it is clear that the Preparation of two-spin DQC is optimum for z = 1/(45), whereas the preparation of the one-spin DQC is optimal at z = 1/ (25). In reality, of course, the process of coherent transfer in these systems is a severely damped oscillation.

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Heteronuclear TOCSY (HEHAHA) experiments for (1) H,(6) Li spin pairs in organolithium compounds with adjacent strongly coupled (1) H,(1) H spin systems showed unexpected cross peak behaviour: for n-butyllithium (1) H,(6) Li cross peaks were completely missing, whereas for the dimer of (Z)-2-lithio-1-(o-lithiophenyl)ethane, a cross peak for remote protons was observed even at very short mixing times. It was assumed that strong magnetization transfer within the proton spin systems was responsible for these results, which prevented unambiguous chemical shift assignments. Selective experiments with the (6) Li,(1) H-HET-PLUSH-TACSY sequence then showed the expected (6) Li,(1) H cross peaks for the transfer via the directly coupled (1) H and (6) Li nuclei. For n-butyllithium transfer to H(Cα) via an unresolved heteronuclear coupling constant below 0.1 Hz is unambiguously observed. Cross peaks in the 2D (6) Li,(1) H-HET-PLUSH-TACSY spectra for the dimer of (Z)-2-lithio-1-(o-lithiophenyl)ethane are readily explained by the measured coupling network and the corresponding active mixing conditions.