Another substantial improvement in catalytic performance was found when P i Pr3 was substituted for P n Bu3, with the silanes showing the same trend for the two phosphines ( give 2 in excellent yield (93%) in only 20 minutes at 20 o C (Table ). This is amongst the best catalytic aromatic HDF performance so far reported by a main-group-element catalyst. Pleasingly, this combination of phosphine and silane were also the cheapest and most readily available that were tested. In addition, P n Bu3 and Ph2SiH2 gave HDF that was selective for 2 under these conditions, no other HDF products were observed, e.g. other regioisomers and/or multiple HDFs.