An acidity scale of phosphonium tetraphenylborate salts and ruthenium dihydrogen complexes in dichloromethane

Equilibrium constants (K-DM) for reactions between acids and bases of the title compounds in CD2Cl2 (DM) have been determined by P-31 and H-1 NMR spectroscopy at room temperature. [HPCy3]BPh4 and [HPCy3]BF4, with pK(DM) assigned by literature convention to 9.7, have been used as the anchor compounds for the pK(DM) determinations. A continuous scale of pK(DM) values covering the range 9.7 to 5.7 is created with the acidic compounds [HPR3]BPh4. Those acids with pK(DM) greater than 6 are stable, while those with more acidic cations HPR3+ protonate BPh4- to produce R3PBPh3 and benzene. The literature pK(THF) values reported for [HPBu2Ph]BPh4, [HPMePh2]BPh4, and [HPEtPh2]BPh4 are questionable because of this protonation reaction. NOE and PGSE H-1 NMR techniques are used to show that [HPCy2Ph]BPh4 in DM exists as ion pairs and higher aggregates up to quadrupoles at the concentrations used in the acid-base studies. The new dihydrogen complexes [Ru(H-2)Cl(PPh3)(2)(dach)]BF4 (dach = (1R,2R)-(-)-diaminocyclohexane) and [Ru(H-2)Cl{tmeP(2)(NH)(2)}]BF4 (tmeP(2)(NH)(2) = PPh2C6H4CH2NHCMe2CMe2NHCH2C6H4PPh2) were prepared by reaction of RuHCl(PPh3)(2)(dach) and RuHCl{tmeP(2)(NH)(2)} with HBF4. Their crystal structures are reported, and the pK(DM) values of their BPh4- salts were determined to be 8.6 and 6.9, respectively.