Syntheses and Structures of Bis-Amidinate–Alane Complexes

Insertion reactions of α,ω-bis-carbodiimides (RNCN)₂X (<b>1</b>–<b>5</b>: R = Et, <i>t</i>-Bu, Ph; X = C₃H₆, C₄H₈) with 2 equiv of AlMe₃ yielded the dinuclear tethered bis-amidinate–alane complexes [RNC­(Me)­NAlMe₂]₂X (R = Et, X = C₄H₈ (<b>6</b>); R = <i>t</i>-Bu, X = C₃H₆ (<b>7</b>), C₄H₈ (<b>8</b>)). 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]₂X (X = C₃H₆ (<b>9</b>), C₄H₈ (<b>10</b>)) and [<i>t</i>-BuNC­(Me)­N­(AlMe₃)­AlMe₂]₂X (X = C₃H₆ (<b>11</b>), C₄H₈ (<b>12</b>)). In addition, equimolar reactions between (RNCN)₂X (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 (<b>13</b>) and [RNC­(Me)­NC₄H₈N­(AlMe₃)­CNR]­AlMe₂ (R = Et (<b>14</b>), Ph (<b>15</b>)). Hydrolysis of <b>11</b> gave the protonated free ligand PhNC­(Me)­NC₄H₈N­(H)­CNPh (<b>16</b>) in high yield. <b>6</b>–<b>16</b> were characterized by elemental analyses, multinuclear NMR (¹H, ¹³C) and IR spectroscopy, and single-crystal X-ray diffraction (<b>7</b>, <b>10</b>–<b>14</b>, <b>16</b>)