Coordinatively Unsaturated Ruthenium Phosphine\nHalf-Sandwich Complexes:  Correlations to Structure\nand Reactivity

Abstract

A number of 16e two-legged piano-stool complexes [Cp*Ru(PP)][BAr‘₄] have been prepared\nby reaction of NaBAr‘₄ with either [Cp*RuCl(PP)] (PP = (PEt₃)₂, ⁱPr₂PCH₂CH₂PⁱPr₂ (dippe),\n(PPh₃)₂) or [Cp*RuCl(PR₃)] plus PR₃ (PR₃ = PMeⁱPr₂, PPhⁱPr₂) in fluorobenzene under argon.\nThe complexes [Cp*Ru(PEt₃)₂][BAr‘₄], [Cp*Ru(dippe)][BAr‘₄], and [Cp*Ru(PMeⁱPr₂)₂][BAr‘₄]\nhave been structurally characterized by X-ray crystallography. Attempts to isolate analogous\nspecies containing other phosphine ligands such as PⁱPr₃, PCy₃, and PMe₃ led to the sandwich\nderivative [Cp*Ru(η⁶-FPh)][BAr‘₄], which was also structurally characterized. Both [Cp*Ru(PPh₃)₂][BAr‘₄] and [Cp*Ru(PPhⁱPr₂)₂][BAr‘₄] are unstable and rearrange to the 18e sandwich\nspecies [Cp*Ru(η⁶-C₆H₅PR₂)][BAr‘₄] and to [Cp*Ru(η⁶-C₆H₅POR₂)][BAr‘₄] (R = Ph, ⁱPr) under\ntrace amounts of oxygen. The geometry of the 16e complexes as well as their affinity for an\nadditional ligand depend on the substituents on the phosphorus. The reactivity with respect\nto the addition of N₂, PR₃, O₂, H₂, and HCl to form 18e derivatives has been studied. Some\nmodel systems have been analyzed using density functional theory (DFT) calculations. Also\nincluded are comparative studies on the NN counterparts. The moieties [CpRu(PP)]⁺ (PP =\n(PH₃)₂, H₂PCH₂CH₂PH₂) adopt typically pyramidal structures (i.e. in the absence of bulky\nand rigid substituents on P) versus planar structures of [CpRu(NN)]⁺ (NN = (NH₃)₂, H₂NCH₂CH₂NH₂). [CpRu(PP)]⁺ is more stable but has nevertheless a higher affinity of adding\na σ ligand than [Cp*Ru(NN)]⁺.