Neutral Imino-Methyl Benzenesulfonate-Ligated Pd(II) Complexes and Implications in Ethylene Polymerization

A reaction between
sodium 2-formylbenzenesulfonate and aniline revealed the near-quantitative
(91%) formation of sodium-2-((phenylimino)­methyl)­benzenesulfonate L1. The identity of L1 was unambiguously ascertained
using spectroscopic and analytical methods. The scope of this methodology
was widened and various electron-donating amines were treated with
sodium 2-formylbenzenesulfonate, and a small library of 6 imine ligands L2–L6 was generated. When L2 was treated
with [(COD)­PdMeCl], instead of the anticipated [L2PdMe­(DMSO)]
complex, the formation of [(DMSO)2Pd2Cl2Me2] Pd-Dim was observed. Nevertheless,
the desired imino-methyl benzenesulfonate-ligated palladium complex
[L2PdMe­(Lu)] C1 was obtained by in situ
abstraction of chloride and addition of bulky 2,6-lutidine as the
donor group. The observation of characteristic Pd–Me protons
at 0.06 ppm and the corresponding carbon at −8.1 ppm indicated
the formation of C1. These 1D NMR observations were corroborated
by 2D C–H correlation spectra and mass analysis, and the existence
of C1 was unambiguously ascertained. Along the same lines, L4 and L5 were treated with a palladium precursor
to produce [L4/5PdMe­(Lu)]-type complexes C2–C3 in 55–84% yield, and their identity was established by using
a combination of spectroscopic tools, analytical methods, and single-crystal
X-ray diffraction. The synthetic utility of C1–C3 has been demonstrated by utilizing these complexes in the insertion
polymerization of ethylene to polyethylene.