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 ((PNP)-P-tBu-P-tBu) at the alpha-lutidinyl-CH2 position with 1 equiv of KCH2C6H5 and concomitant dearomatization of the heterocycle afforded K(P-tBu*(NaP)-P-tBu) (P-tBu* = di-tert-butyl vinylic P donor, P-tBu = PtBu2, N-a = anionic amido N donor); its transmetalation with [CrCl2(THF)(2)] afforded the Cr-II complex [Cr(P-tBu*(NaP)-P-tBu)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 Cr-II complexes [Cr(P-tBu*(NaP)-P-tBu] (B) and [Cr{Cr(P-tBu*(NaP)-P-tBu)Cl}(2)] (C) previously reported [Chem. Commun., 2015, 51, 10699 and Dalton Trans., 2016, 45, 2800, respectively].