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

Abstract

The reactions of early-transition-metal complexes with HO 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 HO, i.e., the addition of HO to the W≡C bond and ligand hydrolysis. Four tungsten alkylidyne complexes, W(≡CSiMe)(CHSiMe) (A-1), W(≡CSiMe)(CHBu) (B-1), W(≡CBu)(CHBu) (C-1), and W(≡CBu)(OBu) (D-1), have been compared. The DFT studies provide an energy profile of the two competing pathways. An additional HO molecule can serve as a proton shuttle, accelerating the HO 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 HO addition and ligand-hydrolysis reactions. These new mechanistic findings may lead to the further development of metal complex precursors.

“Canopy Catalysts” for Alkyne Metathesis: Molybdenum Alkylidyne Complexes with a Tripodal Ligand Framework

“…Importantly, the spectra do not provide any indication for protonation of the alkylidyne: ligand exchange rather than destruction of the operative Mo≡CR unit is (mainly) accountable for the loss of activity. This observation is in line with recent experimental as well as computational data from the literature. , Although water remains ultimately detrimental, a half-life on the order of 1 h is a chemical virtue without precedent in metal alkylidyne chemistry in general; it is fully appreciated if one considers the extreme sensitivity of earlier generations of alkyne metathesis catalysts, not least the otherwise very powerful complex 3 and its precursors. − ,, In this context, we reiterate that it has become common practice to supplement the reaction mixtures with molecular sieves. , Although this additive primarily serves as a sequestering agent for the released 2-butyne in reactions conducted at RT, it ensures a level of dryness and hence a lifespan of a canopy catalyst that allow certain applications to be carried out in technical-grade solvents that need not be rigorously dried and purified prior to use. Indeed, under these standard conditions, the test reaction used to benchmark the catalyst performance proceeded quantitatively in technical-grade toluene (87 ppm water) as well as in toluene containing residual EtOH (5300 ppm) in the presence of MS 5 Å.…”

“…This observation is in line with recent experimental as well as computational data from the literature. 21,63 Although water remains ultimately detrimental, a half-life on the order of 1 h is a chemical virtue without precedent in metal alkylidyne chemistry in general; it is fully appreciated if one considers the extreme sensitivity of earlier generations of alkyne metathesis catalysts, not least the otherwise very powerful complex 3 and its precursors. [7][8][9][10]34,64 In this context, we reiterate that it has become common practice to supplement the reaction mixtures with molecular sieves.…”

183W NMR Spectroscopy Guides the Search for Tungsten Alkylidyne Catalysts for Alkyne Metathesis

“…knowledge, 19 is only the second example for the formation of a alkyl ligand by controlled double-protonation of an alkylidyne and the first reported case in which a monomeric oxo-complex is obtained in this way. [54][55][56][57] Next, the phenyl groups on the silicon bridges of the tripodal framework were replaced by more electron-donating alkyl substituents (note that complex 3 as the currently best canopy catalyst of the molybdenum series carries methyl rather than phenyl groups). [11] As expected, the spectral response is a shift of the 183 W signal to higher frequencies, even though complexes 16 b (R = Et) and 16 c (R = CH 2 CHMe 2 ) are still much more deshielded than the parent complex 4 b (Figure 6).…”

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

“…84,85 Studies of the hydrolysis of organo-transition metal complexes are uncommon; however, isolated examples of reactions of complexes containing metal−carbon multiple bonds have been reported, for example, the reactions of W(≡E t Bu)(CH2 t Bu)3 (E = C, Si) and Mo(=CH t Bu)(CH2 t Bu)2(≡N t Bu), with excess water. [86][87][88][89] In such examples, partial hydrolysis occurs with enhanced reactivity at the M−C/N multiple bonds. The products retain some single M−C bonds highlighting the relative stability of M−C bonds in heavier transition metal complexes, where significant covalency is present.…”