Entrapment of tert-butyllithium and lithium tert-butylamide monomers by partially lithiated derivatives of aluminum and gallium primary amide complexes

The lithiation of the dimeric trisamido group 13 derivatives {M[N(H)t-Bu](3 )}(2) (la, Mit Al; Ib, M = Ga) by alkyllithium reagents RLi (R = t-Bu or Me ), at different stoichiometries, was investigated. On the basis;of NMR data , the initial lithiation of la occurs at the bridging N(H)t-Bu groups to gi ve the mono- and dilithiated derivatives Li-x[Al-2(Nt-Bu)(x)(NHt-Bu)(6-x)] (x = 1, 2). The reaction of 1a with t-BuLi in a 1:3 molar ratio in n-pentan e at 23 degreesC produces {Li[Al(Nt-Bu)(NHt-BU)(2)]}(2). (t-BuLi) (2) in 67 % yield, whereas the treatment of 1a with MeLi in diethyl ether at 23 degre esC yields {Li[Al(Nt-Bu)(NHt-Bu)(2)]}(2). [LiN(H)t-Bu] (7) and {Li[Al(Nt-Bu )(NHt-Bu)(2)]}(2) (8). The gallium analogue of 7, i.e.; {Li[Ga(Nt-Bu)(NBt-B u)(2)]}(2). [LiN(H)t- Bu] (5), was obtained in 47% yield by the reaction of Ib with t-BuLi in a:1:3 molar ratio in n-pentane at 23 degreesC. The struc tures of 2, 5, and 7- have been determined by X-ray crystallography and wer e shown to involve the entrapment of a monometric t-BuLi or LiN(H)t-Bu frag ment by a dilithiated derivative of la or Ib. The six fused four-membered r ings give-rise to a concave, lounge-chair arrangement for the 12-atom [Li3A l2N6E(E = C or N)] clusters of 2, 5, and 7. Variable-temperature H-1 NMR sp ectra of 2, 5, and 7 in C7D8 over the range -90 to 23 degreesC reveal a flu xional process involving Li-N bond breaking and formation.