A Terphenyl Supported Dioxophosphorane Dimer: the Light Congener of Lawesson's and Woollins' Reagents.

Thermolysis of a 1,3-dioxa-2-phospholane supported by the terphenyl ligand Ar iPr4 (Ar iPr4 =[C 6 H 3 -2,6-(C 6 H 3 -2,6-iPr 2 )]) at 150 °C gives [Ar iPr4 PO 2 ] 2 via loss of ethene. [Ar iPr4 PO 2 ] 2 was characterised by X-ray crystallography and NMR spectroscopy; it contains a 4-membered P-O-P-O ring and is the isostructural oxygen analogue of Lawesson's and Woollins' reagents. The dimeric structure of [Ar iPr4 PO 2 ] 2 was found to persist in solution through VT NMR spectroscopy and DOSY, supported by DFT calculations. The addition of DMAP to the 1,3-dioxa-2-phospholane facilitates the loss of ethene to give Ar iPr4 (DMAP)PO 2 after days at room temperature, with this product also characterised by X-ray crystallography and NMR spectroscopy. Replacement of the DMAP with pyridine induces ethene loss from the 1,3-dioxa-2-phospholane to provide gram-scale samples of [Ar iPr4 PO 2 ] 2 in 75 % yield in 2 days at only 100 °C.