Tantalum hydrides dihydrides

The cationic tantalum dihydride Cp2(CO)Ta(H)2]+ reacts at room temperature with acetone to generate the alcohol complex [Cp2(C0)Ta(H01Pr)]+, which was isolated and characterized [45]. The mechanism appears to involve protonation of the ketone by the dihydride, followed by hydride transfer from the neutral hydride. The OH of the coordinated alcohol in the cationic tantalum alcohol complex can be deprotonated to produce the tantalum alkoxide complex [Cp2(C0)Ta(01Pr)]. Attempts to make the reaction catalytic by carrying out the reaction under H2 at 60 °C were unsuccessful. The strong bond between oxygen and an early transition metal such as Ta appears to preclude catalytic reactivity in this example. 

Moise and coworkers had shown that a cationic dihydride of tantalum, Cp2(CO)Ta(H)2, reacts with acetone to give the alcohol complex Cp2(CO)Ta(HO Pr) [45]. This reaction was proposed to occur by proton transfer from the dihydride, followed by hydride transfer to the protonated ketone. Unfortunately, attempts to make this reaction catalytic under H2 were not successful. Early transition metals like Ta form strong bonds to oxygen, with no alcohol being observed at 60 °C in attempted catalytic reactions. 

---