Contacted Ion-Pair Lithium Alkylamidoaluminates: Intramolecular Alumination (Al-H Exchange) Traps for TMEDA and PMDETA

Exploring the reactivity of mixed-metal synergic bases, it is found that the lithium TMP aluminate (Bu3Al)-Bu-i(TMP)Li functions as a dual TMP/alkyl base, exhibiting 2-fold AMM Al (alkali-metal-mediated alumination) toward TMEDA to yield the heterobimetallic bis-(deprotonated TMEDA) derivative [Li{Me2NCH2CH2N(Me)CH2}(2)Al(Bu-i)(2)] (2). In contrast, the amide enriched aluminate (Bu2Al)-Bu-i(TMP)(2)Li acts as only a single-fold amido base toward TMEDA or PMDETA to afford the amine-deprotonated derivatives [Li{Me2NCH2CH2N(Me)CH2}(TMP)Al(Bu-i)(2)] (4) and [Li{Me2NCH2CH2N(Me)CH2CH2N(Me)CH2}(TMP)Al(Bu-i)(2)] (5), respectively. On their own, the aluminum compounds (Bu3Al)-Bu-i or (Bu2Al)-Bu-i(TMP) are not sufficiently strong bases to metalate TMEDA or PMDETA, so in 2, 4, and 5, the alpha-deprotonations of TMEDA and PMDETA are synergic in origin, as the intramolecular communication between Li and Al appears to activate the TMP and Bu-i bases. This special behavior can be attributed to intramolecular proximity effects between the active base component (TMP or Bu-i) and the ligating TMEDA or PMDETA molecule. X-ray crystallography studies reveal 2 is a contacted ion-pair ate containing two alpha-aluminated TMEDA ligands, which chelate the lithium cation Which is linked to the distorted tetrahedral Al center by two N bridges from the metalated junction of the TMEDA molecules. In contrast, 4 and 5 have a mixed NCH2-TMP bridging ligand set, completed by two terminal Bu-i ligands on Al and a chelating metalated TMEDA or PMDETA ligand attached to Li, respectively. In addition, the H-1, Li-7, and C-13{H-1} spectra of 2 (recorded in C6D6 solutions), 4, and 5 (recorded in cyclohexane solutions-d(12)) are disclosed.