E–H (E = N and P) Bond Activation of PhEH₂ by a Trinuclear Yttrium Methylidene Complex: Theoretical Insights into Mechanism and Multimetal Cooperation Behavior

E–H (E = N and P) bond activation of PhEH₂ by a trinuclear yttrium methylidene complex to give a μ₃-EPh species has been investigated through DFT calculations. It has been revealed that the reaction involves three major steps, i.e., activation of one of the two E–H bonds, intramolecular isomerization, and the subsequent activation of the second E–H bond. The first E–H bond activation is a mono-metal-assisted σ-bond metathesis (σ-BM) process, while the second E–H bond activation is achieved by the cooperation of three metal sites. The effect of the phenyl group in PhEH₂ has also been examined. It has been found that the phenyl group in PhNH₂ showed a significant steric effect for the N–H activation, but in the case of PhPH₂, such steric effect was not observed. The relatively low energy barriers and significant exergonic feature lead us to predict that the trinuclear yttrium methylidene complex should be also effective for activation of NH₃ and PH₃. In addition, a general behavior of the activation of CX (X = O and S) and E–H (E = C, N, and P) bonds by multialkyl-bridged trinuclear rare-earth complexes has been described, which could be beneficial for further studies on the chemical transformations at multimetallic frameworks.