H(OEt 2 ) 2 [P(1,2‐O 2 C 6 Cl 4 ) 3 ]: Synthesis, Characterization, and Application as a Single‐Component Initiator for the Carbocationic Polymerization of Olefins

The development of novel Brønsted acids featuring the hexacoordinate phosphorus(V) anion [TRISPHAT] − {[ 1 ] − =[P(1,2‐O 2 C 6 Cl 4 ) 3 ] − } are reported. The title compound, H(OEt 2 ) 2 [ 1 ], was synthesized from 1,2‐(HO) 2 C 6 Cl 4 (3 equiv) and PCl 5 in the presence of diethyl ether. This compound was fully characterized by 1 H, 31 P and 13 C NMR spectroscopy, X‐ray crystallography and elemental microanalysis. Dissolution of H(OEt 2 ) 2 [ 1 ] in acetonitrile results in the slow precipitation of crystalline H(OEt 2 )(NCMe)[ 1 ], which was characterized by X‐ray diffraction; however, in CD 2 Cl 2 solution the [TRISPHAT] − anion protonated and ring‐opened. The weighable, solid H(OEt 2 ) 2 [ 1 ] was found to be a competent initiator for the polymerization of n ‐butyl vinyl ether, α‐methylstyrene, styrene and isoprene at a variety of temperatures and monomer‐to‐initiator ratios. At low temperatures, polymers with M n >10 5 were obtained for n ‐butyl vinyl ether and α‐methylstyrene whereas slightly lower molecular weights were obtained with styrene and isoprene (10 4 < M n <10 5 ). The poly(α‐methylstyrene) synthesized at −78 °C is syndiotactic‐rich (ca. 87 % rr ) whereas the polystyrene obtained at −50 °C is atactic. The polyisoprene obtained possessed all possible modes of enchainment as well as branched and/or cyclic structures that are often observed in polyisoprene.