Kinetic and Thermodynamic Acidity of Hydrido Transition-Metal Complexes. 3. Thermodynamic Acidity of Common Mononuclear Carbonyl Hydrides

Article abstract of DOI:10.1021/ja00269a022

The pK_a values of the common mononuclear carbonyl hydrides have been determined in acetonitrile by IR measurement of the position of deprotonation equilibria with various nitrogen bases and potassium phenolate.The resulting values cover a range of about 20 pK_a units, from 8.3 for HCo(CO)4 to 26.6 for CpW(CO)2(PMe3)H.Hydrides with η⁵-C5Me5 ligands are appreciably weaker acids than the corresponding hydrides with η⁵-C5H5 ligands (e.g., the pK_a of (η⁵-C5Me5)Fe(CO)2H is 26.3, while that of (η⁵-C5H5)Fe(CO)2H is 19.4).The acidities of the group 8 carbonyl hydrides H2M(CO)4 decrease in the order Fe > Ru > Os.