Water-Soluble Tungsten Hydrides: Synthesis, Structures, and Reactions of (C5H4CO2H)(CO)3WH and Related Complexes

The water-soluble metal hydride (C5H4CO2H)(CO)3WH (1) was prepared and characterized. The crystal structure of this complex determined by X-ray diffraction shows it to be dimeric in the solid state, due to OH···O hydrogen bonds between the CO2H groups. The pKa of the W−H proton was determined to be 5.8 (±0.2) in water. While the CO2H site of (C5H4CO2H)(CO)3WH is more acidic than the W−H proton in water, the order of thermodynamic acidity is inverted in organic solvents. Deprotonation of (C5H4CO2H)(CO)3WH with KH in THF, followed by counterion exchange, gives [(C5H4CO2H)(CO)3W]-NBu4+ (2). This anion is also dimeric through intermolecular hydrogen bonding of the CO2H groups, as shown by X-ray crystallography. The reaction of PMe3 or P(OMe)3 with (C5H4CO2H)(CO)3WH gives substitution of a CO ligand and formation of (C5H4CO2H)(PR3)(CO)2WH (R = Me, OMe). Reaction of PTA (PTA = phosphatriazaadamantane) with (C5H5)(CO)3WH gives (C5H5)(PTA)(CO)2WH. This complex exists as an equilibrating cis/trans mixture in solut...