Me(2)CuLi*LiCN in diethyl ether prefers a homodimeric core structure [Me(2)CuLi](2) and not a heterodimeric one [Me(2)CuLi*LiCN]: (1)H, (6)Li HOE and (1)H, (1)H NOE studies by NMR.
H-Li distances and (1)H-(1)H dipolar interactions in Me(2)CuLiLiCN and Me(2)CuLi in diethyl ether (Et(2)O), obtained by NMR spectroscopy, were used to gain structural information about the contact ion pair of the salt-containing organocuprate Me(2)CuLiLiCN in this solvent. The H-Li distances of Me(2)CuLiLiCN and Me(2)CuLi in Et(2)O, resulting from the initial buildup rates in conjunction with the motional correlation times, are almost identical, indicating a similar homodimeric core structure [Me(2)CuLi](2) for both samples. However, the H-Li distances obtained for Me(2)CuLiLiCN do not rigorously exclude a heterodimeric structure [Me(2)CuLiLiCN] as proposed by ab initio calculations. Therefore, (1)H-(1)H dipolar interactions were investigated by SYM-BREAK-NOE/ROE-HSQC experiments, which allow for the observation of NOEs between equivalent protons. Since these experiments showed similar (1)H-(1)H dipolar interactions of Me(2)CuLiLiCN and Me(2)CuLi, we propose that for Me(2)CuLiLiCN a homodimeric core structure [Me(2)CuLi](2) indeed is predominant in Et(2)O.
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Contribution from the Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany. ru@chemie.uni-marburg.de
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