Palladium coordination compounds of σ³λ⁵-phosphoranes: First examples of phosphonio-methylene(imino)metallophosphorane [(R₃P)(Me₃Si)C=P(ML_n)=NSiMe₃] and phosphonio-methylene(oxo)phosphorane [(R₃P)(Me₃Si)C=P(=O)NSiMe₃] ligands

The oxidative addition reaction of Pd(PPh₃)₄ with Cl₂C=PN(SiMe₃)₂ forms the phosphavinyl phosphonium complex Cl(Ph₃P)Pd[η²-C(Cl)(PPh₃)=PN(SiMe ₃)₂] (IIIa), which results from PPh₃ migration from Pd to carbon in the η¹-phosphavinyl intermediate trans-Cl(Ph₃P)₂Pd-[C(Cl)=PN(SiMe₃)₂] (IIa). The reaction of Pd(dba)(dppe) with Cl₂C=PN(SiMe₃)₂ forms the η¹-phosphavinyl complex cis-Cl(dppe)Pd[C(Cl)=PN(SiMe₃)₂] (VI), which does not undergo phosphine migration. Compound IIIa undergoes substitution of the chloride ligand by PPh₃ or MeCN in the presence of KPF₆ to generate [(Ph₃P)₂Pd(η₂-C(Cl)(PPh ₃)=PN(SiMe₃)₂)](PF₆) (IV) or [(Ph₃P)(MeCN)Pd(η²-C(Cl)(PPh₃)=PN(SiMe ₃)₂)](PF₆) (V), respectively; the structure of V was determined by X-ray diffraction studies. The reaction of Pd(PEt₃)₄ with Cl₂C= PN(SiMe₃)₂ forms the η¹-phosphavinyl complex trans-Cl(Et₃P)₂Pd[C(Cl)=PN(SiMe₃)₂] (IIb), which does not undergo PEt₃ migration. When 2 equiv of Pd(PEt₃)₄ are reacted with Cl₂C= PN(SiMe₃)₂ the phosphonio-methylene(imino)metallophosphorane complex Pd(PEt₃)(Cl)[μ-η¹:η²-C(SiMe ₃)(PEt₃)=P=N(SiMe₃)]Pd(PEt₃)Cl (VIIa-b) forms as a 1:1 isomeric mixture. Compound VIIa-b reacts with MeI or NaI to generate Pd(PEt₃)(I)[μ-η¹:η²-C(SiMe ₃)(PEt₃)= P=N(SiMe₃)]Pd(PEt₃)I (VIIIa-b) and reacts with traces of water to generate Cl(Et₃P)Pd-[η²-C(SiMe₃)(PEt ₃)=P(=O)NH(SiMe₃)] (IX). The structure of VIIIb was partially determined, and the structure of IX was determined by X-ray diffraction studies. Compounds VIIa-b, VIIIa-b, and IX exhibit the first examples of coordinated methylene(imino, oxo)phosphorane ligands.