2-Thia-1,3,5-triaza-7-phosphaadamantane 2,2-Dioxide (PASO2). Comparative Structural and Reactivity Investigation with the Water-Soluble Phosphine Ligand 1,3,5-triaza-7-phosphaadamantane (PTA)

Abstract

The derivative 2-thia-1,3,5-triaza-phosphaadamantane 2,2-dioxide (PASO2) has been characterized by spectroscopy and by X-ray crystallography. Unlike its PTA (1,3,5-triaza-7-phosphaadamantane) analogue, replacement of a −CH2− unit in PTA with −SO2− renders PASO2 largely insoluble in water at ambient temperature (<0.70 g/L vs 236 g/L for PTA). This latter property makes it of no use as a water-solubilizing ligand for organometallic complexes. Interestingly, alkylation of PASO2 with methyl iodide occurs quantitatively at the phosphorus center to afford the iodide salt. This derivative has also been characterized by X-ray crystallography and 1H/31P NMR spectroscopy, where the 31P resonance was observed to be shifted downfield relative to PASO2 (−39.2 vs −115.9 ppm). Although PTA has long been thought to react with methyl iodide to provide exclusively a monoalkylated product at one of the nitrogen centers, a close examination of this process via 31P NMR spectroscopy has shown monomethylation to take place at b...