Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis.

The reactions of early-transition-metal complexes with H2O have been investigated. An understanding of these elementary steps promotes the design of precursors for the preparation of metal oxide materials or supported heterogeneous catalysts. Density functional theory (DFT) calculations have been conducted to investigate two elementary steps of the reactions between tungsten alkylidyne complexes and H2O, i.e., the addition of H2O to the W≡C bond and ligand hydrolysis. Four tungsten alkylidyne complexes, W(≡CSiMe3)(CH2SiMe3)3 (A-1), W(≡CSiMe3)(CH2tBu)3 (B-1), W(≡CtBu)(CH2tBu)3 (C-1), and W(≡CtBu)(OtBu)3 (D-1), have been compared. The DFT studies provide an energy profile of the two competing pathways. An additional H2O molecule can serve as a proton shuttle, accelerating the H2O addition reaction. The effect of atoms at the α and β positions has also been examined. Because the lone-pair electrons of an O atom at the α position can interact with the orbital of the proton, the barrier of the ligand-hydrolysis reaction for D-1 is dramatically reduced. Both the electronic and steric effects of the silyl group at the β position lower the barriers of both the H2O addition and ligand-hydrolysis reactions. These new mechanistic findings may lead to the further development of metal complex precursors.