Chromium(II) Pincer Complexes with Dearomatized PNP and PNC Ligands: A Comparative Study of Their Catalytic Ethylene Oligomerization Activity

Monodeprotonation of the 2,6-bis­(di-tert-butylphosphinomethyl) pyridine (tBuPNtBuP) at the α-lutidinyl-CH2 position with 1 equiv of KCH2C6H5 and concomitant dearomatization of the heterocycle afforded K­(tBuP*NatBuP) (tBuP*= di-tert-butyl vinylic P donor, tBuP = PtBu2, Na = anionic amido N donor); its transmetalation with [CrCl2(THF)2] afforded the CrII complex [Cr­(tBuP*NatBuP)­Cl] (A). The X-ray diffraction analysis of A established a slightly distorted square-planar coordination geometry at the metal center and confirmed retention of the dearomatized coordinated ligand. The catalytic activity of A in ethylene oligomerization was studied and compared with that of the related CrII complexes [Cr­(tBuP*NaCNHC)­Cl] (B) and [Cr­{Cr­(tBuP*NatBuP*)­Cl}2] (C) previously reported [Chem. Commun., 2015, 51, 10699 and Dalton Trans., 2016, 45, 2800, respectively].