Synthesis and Characterization of Dimeric, Trimeric, and Tetrameric Gallophosphonates and Gallophosphates<sup>⊥</sup>

THF/toluene solutions of phosphonic or phosphoric acids were reacted with <sup>t</sup>Bu<sub>3</sub>Ga at low temperature to yield the cyclic dimers [<sup>t</sup>Bu<sub>2</sub>GaO<sub>2</sub>P(OH)R]<sub>2</sub> (R = Ph, Me, <sup>t</sup>Bu, H, OH; <b>1</b>−<b>5</b>). Poor crystallinity and variable thermal stabilities of <b>1</b>−<b>5</b> necessitated derivatization with Me<sub>3</sub>SiNMe<sub>2</sub> to yield [<sup>t</sup>Bu<sub>2</sub>GaO<sub>2</sub>P(OSiMe<sub>3</sub>)R]<sub>2</sub> (R = Ph, Me, <sup>t</sup>Bu, H, OSiMe<sub>3</sub>; <b>6</b>−<b>10</b>), which were more amenable to purification and characterization. In solution, trans isomers were predominant for <b>6</b> and <b>7</b> at ambient temperature, whereas the cis isomer of <b>8</b> was predominant. NMR spectroscopy demonstrated cis−trans interconversion for <b>6</b>−<b>8</b> and crossover experiments showed interconversion to occur by, or be accompanied with, an intermolecular exchange process. Thermolysis of <b>3</b> in refluxing toluene yielded the cluster [(<sup>t</sup>BuGa)<sub>2</sub>(<sup>t</sup>Bu<sub>2</sub>Ga)(O<sub>3</sub>P<sup>t</sup>Bu)<sub>2</sub>{O<sub>2</sub>P(OH)<sup>t</sup>Bu}] (<b>11</b>), which was converted to [(<sup>t</sup>BuGa)<sub>2</sub>(<sup>t</sup>Bu<sub>2</sub>Ga)(O<sub>3</sub>P<sup>t</sup>Bu)<sub>2</sub>{O<sub>2</sub>P(OSiMe<sub>3</sub>)<sup>t</sup>Bu}] (<b>12</b>) with Me<sub>3</sub>SiNMe<sub>2</sub>. Thermolysis of <b>1</b>−<b>3</b> in refluxing diglyme, or solid-state pyrolysis at 250 °C in vacuo, yielded [<sup>t</sup>BuGaO<sub>3</sub>PR]<sub>4</sub> (R = Ph, <sup>t</sup>Bu, Me; <b>13</b>−<b>15</b>). The gallophosphate [<sup>t</sup>BuGaO<sub>3</sub>P(OSiMe<sub>3</sub>)]<sub>4</sub> (<b>16</b>) was similarly obtained by reaction of <sup>t</sup>Bu<sub>3</sub>Ga with H<sub>3</sub>PO<sub>4</sub> in refluxing diglyme, followed by trimethylsilylation with Me<sub>3</sub>SiNMe<sub>2</sub>. Compounds <b>13</b>−<b>16</b> possess cuboidal Ga<sub>4</sub>P<sub>4</sub>O<sub>12</sub> cores analogous to double-four-ring secondary building units in the gallophosphates cloverite, gallophosphate-A, and ULM-5. The thermal, hydrolytic, and oxidative stabilities of <b>13</b>−<b>16</b> are discussed, as are observed intermolecular exchange processes. In addition to characterization of <b>1</b>−<b>16</b> by multinuclear (<sup>1</sup>H, <sup>13</sup>C, <sup>31</sup>P) NMR spectroscopy, infrared spectroscopy, mass spectrometry, and elemental analysis, molecular structures for compounds <b>6</b>, <b>8</b>, <b>10</b>, <b>12</b>, <b>14</b>, <b>15</b>, and <b>16</b> were determined by X-ray crystallography.