Reactions of Water and Ammonia with Bis(pentamethylcyclopentadienyl) Complexes of Zirconium and Hafnium

Article abstract of DOI:10.1021/ja00331a015

The propensity for the group 4B metal center to form extremely strong bonds with oxygen and nitrogen donors is often invoked as an important driving force in the reductions of carbon monoxide and dinitrogen with organometallic derivatives of these metals, e.g., Cp*2MLx (Cp*=η⁵-C5Me5; M=Ti, Zr, Hf).In order to assess some of the fundamental bonding properties of hydroxide, oxo, and amide ligands with bis(pentamethylcyclopentadienyl) derivatives of zirconium and hafnium, the reactivities of water and ammonia with several Cp*2MLx (M=Zr, Hf) complexes have been examined.Water reacts in a clean, stepwise manner with Cp*2MH2 (M=Zr, Hf) to afford Cp*2M(H)(OH), (Cp*2MH)2O, Cp*2M(OH)2, and finally Cp*2M(OH)2*H2O.Cp*2M(H)(Cl) yields Cp*2M(OH)(Cl).Cp*2MH2 reacts with Cp*2M(OH)(X) (X=Cl, OH, H) to afford Cp*2(X)M-O-M(H)Cp*2.In all cases, conversion of a M-H bond to an M-O bond is accompanied by H2 evolution.Similarly, ammonia reacts rapidly with Cp*2MH2 to yield Cp*2M(H)(NH2) and H2.Excess ammonia or Cp*2MH2 do not react further, although exchange with free (15)NH3 is observed.Cp*2Hf(H)(NH2) reacts with H2O to afford Cp*2Hf(H)(OH) and NH3, but not Cp*2Hf(OH)(NH2).Free water undergoes rapid proton exchange and slower oxygen exchange with the hydroxo derivatives. (Cp*2ZrN2) N2 reacts rapidly and cleanly with an equivalent of water to produce N2 (3 equiv) and (Cp*2ZrH)2O.Evidence in support of a stepwise oxidative addition of both O-H bonds via the intermediacy of Cp*2Zr(H)(OH) is presented. 1H and 17O NMR spectra of these new compounds are also tabulated.