How to Stabilize η3-Silapropargyl/Alkynylsilyl Complex of [CpL2M]+(L = CO, PMe3, or PF3 and M = W or Mo): Theoretical Prediction

We theoretically investigated here how to stabilize a new transition metal η3-silapropargyl/alkynylsilyl complex CpL2M(η3-R22SiCCR1) (M = W or Mo; L = CO, PMe3, or PF3; Cp = C5H5; R1 = H, Me, tBu, or CF3; R2 = H, Me, or F) which is an interesting silicon analogue of a transition metal η3-propargyl complex. Though this complex was experimentally proposed as an intermediate in the synthesis of a tungsten acetylide−silylene complex Cp(CO)2W(CCtBu)(SiPh2), it has not been synthesized yet. From theoretical computations with DFT method, we wish to propose that the combination of electron-withdrawing CF3 on C, σ-electron-withdrawing/π-electron-donating F on Si, Mo center, and CO is the best to stabilize the η3-silapropargyl/alkynylsilyl form. However, the combination of bulky tBu on C, either H or Me on Si, W center, and PMe3 is the best to stabilize the acetylide−silylene form, which is also an interesting species. The reasons are discussed herein.