Synthesis and Characterization of Dimeric, Trimeric, and Tetrameric Gallophosphonates and Gallophosphates

Abstract

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

NMR analysis of GaPO4 crystal growth in mixtures of phosphoric and sulfuric acids

“…This correlation for which 31 P chemical shift in MAS spectra moves in the direction of high field, when an increasing number of gallium surrounds the phosphate, is in agreement with our attribution of liquid state gallophosphate NMR spectra. The unique known gallophosphate structure in solution is a dimeric organogallophosphate [ t Bu 2 GaO 2 P(OH) 2 ] 2 .THF [44]. The 31 P NMR of this compound in benzene showed a signal at À6.3 ppm [44], which is very close to the chemical shift range of P 2 (À7 to À8 ppm) observed in the present aqueous solutions.…”

“…The unique known gallophosphate structure in solution is a dimeric organogallophosphate [ t Bu 2 GaO 2 P(OH) 2 ] 2 .THF [44]. The 31 P NMR of this compound in benzene showed a signal at À6.3 ppm [44], which is very close to the chemical shift range of P 2 (À7 to À8 ppm) observed in the present aqueous solutions.…”

Fluoride‐Ion Encapsulation within a Silsesquioxane Cage

“…This suggests that the fluoride ion must be acting as a template for formation of the cage and that once inside, it can only escape when the cage is broken down. Such a templating role for the fluoride ion has been proposed in molecular sieve synthesis, and Roesky et al [16] and Mason et al [17] have attempted to encapsulate a fluoride ion in alumino-and gallophosphonate models of the double four-ring (D4R) cage without success. However, Morris et al have successfully used a hydrothermal synthesis involving HF to prepare the germanium oxide D4R cage containing a fluoride ion.…”

Fluoride‐Ion Encapsulation within a Silsesquioxane Cage

“…This suggests that the fluoride ion must be acting as a template for formation of the cage and that once inside, it can only escape when the cage is broken down. Such a templating role for the fluoride ion has been proposed in molecular sieve synthesis, and Roesky et al16 and Mason et al17 have attempted to encapsulate a fluoride ion in alumino‐ and gallophosphonate models of the double four‐ring (D4R) cage without success. However, Morris et al have successfully used a hydrothermal synthesis involving HF to prepare the germanium oxide D4R cage containing a fluoride ion 15.…”