Electronic Effects in Phosphino‐Iminophosphorane PdII Complexes upon Varying the N Substituent

Abstract

AbstractThree series of palladium(II) complexes supported by a phosphine‐iminophosphorane ligand built upon an ortho‐phenylene core were investigated to study the influence of the iminophosphorane N substituent. Cis‐dichloride palladium(II) complexes 1 in which the N atom bears an isopropyl (iPr, 1 a), a phenyl (Ph, 1 b), a trimethylsilyl (TMS, 1 c) group or an H atom (1 d) were synthesized in high yield. They were characterized by NMR, IR spectroscopy, HR‐mass spectrometry, elemental analysis, and X‐ray diffraction. A substantial bond length difference between the Pd−Cl bonds was observed in 1. Complexes 1 a–d were converted into [Pd(LR)Cl(CNtBu)](OTf)] 2 a–d whose isocyanide is located trans to the iminophosphorane. The corresponding dicationic complexes [Pd(LR)(CNtBu)2](OTf)2 3 a–d were also synthesized, however they exhibited lower stability in solution than 2, the isopropyl derivative 3 a being the most stable of the series. Molecular modeling was performed to rationalize the regioselectivity of the substitution of the single chloride by isocyanide (from 1 to 2) and to study the electronic distribution in the complexes. In particular differences between the TMS and H containing complexes vs. the iPr and Ph ones were found. This suggests that the nature of the N substituent is far from innocent and can help tune the reactivity of iminophosphorane complexes.