Synthesis and Characterization of Dimeric, Trimeric, and Tetrameric Gallophosphonates and Gallophosphates.
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.
Mason
Mark R.
MR
Department of Chemistry and Center for Chemical Catalysis, University of Louisville, Louisville, Kentucky 40292, and Department of Chemistry, University of Idaho, Moscow, Idaho 83844.
Perkins
Alisa M.
AM
Matthews
R. Mark
RM
Fisher
James D.
JD
Mashuta
Mark S.
MS
Vij
Ashwani
A