Syntheses and Structures of Bis-Amidinate-Alane Complexes

Insertion reactions of alpha,omega-bis-carbodiimides (RNCN)(2)X (1-5: R = Et, t-Bu, Ph; X = C3H6, C4H8) with 2 equiv of AlMe3 yielded the dinuclear tethered bis-amidinate-alane complexes [RNC(Me)NAlMe2](2)X (R = Et, X = C4H8 (6); R = t-Bu, X = C3H6 (7), C4H8 (8)). Analogous reactions with 4 equiv of AlMe3 resulted in the coordination of two additional AlMe3 molecules, yielding the tetranuclear bis-amidinate complexes [EtN(AlMe3)C(Me)NAlMe2](2)X (X = C3H6 (9), C4H8 (10)) and [t-BuNC(Me)N(AlMe3)AlMe2](2)X (X = C3H6 (11), C4H8 (12)). In addition, equimolar reactions between (RNCN)(2)X (R = Et, X = C3H6, C4H8; R = Ph, X = C4H8) and 2 equiv of AlMe3 at elevated temperatures occurred with intramolecular cyclization and formation of [EtNC(Me)NC3H6N(AlMe3)CNEt]AlMe2 (13) and [RNC(Me)NC4H8N(AlMe3)CNR]AlMe2 (R = Et (14), Ph (15)). Hydrolysis of 11 gave the protonated free ligand PhNC(Me)NC4H8N(H)CNPh (16) in high yield. 6-6 were characterized by elemental analyses, multinuclear NMR (H-1, C-13) and IR spectroscopy, and single-crystal X-ray diffraction (7, 10-14, 16).