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 pK_a 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 solution, but was crystallized as the trans isomer, as shown by X-ray crystallography. Water solubility of (C₅H₅)(PTA)(CO)₂WH was negligible. The water-soluble metal−metal-bonded bimetallic complexes [(C₅H₄CO₂H)(CO)₃W]₂, [(C₅H₄CO₂H)(PMe₃)(CO)₂W]₂, and {(C₅H₄CO₂H)[P(OMe)₃](CO)₂W}₂ were prepared by reaction of the metal hydrides with trityl radical (Ph₃C^•).