Bimetallic complexes containing lithium and boron. Studies on the reactions of (ArBMe 3)Li · OEt 2 complexes with the electron donors OEt 2 and THF by means of 1H, 7Li, 11B, and 13C NMR spectroscopy

Abstract

The stabilities of the toluene and THF solutions of complexes (Ar 1BMe 3)Li·OEt 2 (I), Ar 1 = C 6H 4CH 2NMe 2−2 and (Ar 2BMe 3)Li·OEt 2 (II) and Ar 2 = C 6H 4-( S)-CHMeNMe 2−2 were investigated at various temperatures by means of 1H, 7Li, 11B, and 13C NMR spectroscopy. I is stable in toluene and only inversion of configuration on nitrogen and on C(1) aromatic carbon was observed. II is less stable in toluene than I, and beside the intramolecular dynamic processes dissociation with release of ether was detected. Complex I reacts with THF with donation of ether to THF and product IV, Ar 1BMe 3)Li·THF, was isolated and characterized in toluene solution. IV reacts further with THF forming V, [LiMe] n ·[THF], with cleavage of the LiC 2B bond. II dissolved in THF leads to the (Ar 2BMe 3)(Li· nTHF) complex, VI. The mechanism of the bond cleavage of the LiC 2B core in I and in II in the reaction with THF is discussed.