Structure and Bonding\nAnalysis of the Cationic Electrophilic Phosphinidene Complexes of\nIron, Ruthenium, and Osmium [(η⁵‑C₅Me₅)(CO)₂M{PNⁱPr₂}]⁺, [(η⁵‑C₅H₅)(CO)₂M{PNR₂}]⁺ (R = Me, ⁱPr), and [(η⁵‑C₅H₅)(PMe₃)₂M{PNMe₂}]⁺ (M = Fe, Ru, Os)

Abstract

Quantum-chemical DFT calculations for the electronic,\nmolecular structure and M–PNR₂ bonding analyses\nof the experimentally known cationic electrophilic phosphinidene complexes\n[(η⁵-C₅Me₅)­(CO)₂M­{PNⁱPr₂}]⁺ and of the model complexes\n[(η⁵-C₅H₅)­(CO)₂M­{PNR₂}]⁺ (R = ⁱPr, Me) and [(η⁵-C₅H₅)­(PMe₃)₂M­{PNMe₂}]⁺ were carried out using BP86/TZ2P/ZORA level\nof theory. The calculated geometrical parameters of the studied complexes\nare in good agreement with the reported experimental values. The short\nM–P bond distances and calculated Pauling bond orders (range\nof 1.23–1.68), suggest the presence of M–P multiple\nbond characters. The Hirshfeld charge analysis shows that the overall\ncharge flows from phosphinidene ligand to metal fragment. The M–P\nσ-bonding orbitals are well-occupied (>1.80<i>e</i>). The energy decomposition analysis revealed that the contribution\nof the electrostatic interaction Δ<i>E</i>_elstat is, in all studied complexes, significantly larger (55.2–62.6%)\nthan the orbital interactions Δ<i>E</i>_orb. The orbital interactions between metal and PNR₂ in [(η⁵-C₅H₅)­(L)₂M­{PNR₂}]⁺ arise mainly from M ← PNR₂ σ-donation.\nThe π-bonding contribution (19–36%) is much smaller than\nthe σ-bonding. The interaction energies, as well as bond dissociation\nenergies, depend on the auxiliary ligand framework around the metal\nand decrease in the order (η⁵-C₅H₅) > (η⁵-C₅Me₅) and\nCO > PMe₃. Upon substitution of R = ⁱPr with\nsmaller group R = Me, the M–PNR₂ bond strength slightly\ndecreases.