Palladium Coordination Compounds of σ³λ⁵-Phosphoranes:  First Examples of Phosphonio−Methylene(imino)metallophosphorane [(R₃P)(Me₃Si)CP(ML_n)NSiMe₃] and Phosphonio−Methylene(oxo)phosphorane [(R₃P)(Me₃Si)CP(O)NSiMe₃] Ligands

Abstract

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(SiMe3)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)(PPh3)PN(SiMe3)2)](PF6) (IV) or [(Ph3P)(MeCN)Pd(η2-C(Cl)(PPh3)PN(SiMe3)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(SiMe3)(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(SiMe3)(PEt3)PN(SiMe3)]Pd(PEt3)I (VIIIa-b) and reacts with traces of water to generate Cl(Et3P)Pd[η2-C(SiMe3)(PEt3)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.

Influence of the Leaving Group on C–H Activation Pathways in Palladium Pincer Complexes

“…As mentioned before, three-membered palladacycles are rare, and only one crystallographically confirmed example of C–H bond activation in a i Pr 3 P group exists to date . However, a few three-membered metallacycles containing Pd, P, and C have been reported, with P–Pd–C angles in the range of 41.19–47.99°. − Furthermore, the metrical parameters of [{PC­(sp 3 )­H 2 P} act Pd­(OAc)] are similar to those reported by Protasiewicz and co-workers for [( i Pr 3 P)­( i Pr 2 CMe 2 )­Pd­(py)] …”