Synthesis, Structural Diversity, and Ethylene Polymerization Reactivity of Nickel(0)/(II) and Palladium(II) Complexes Supported by {PN(H)P}- and {PN(H)P(O)}-Type (Pro)Ligands

A series of (pro)ligands based on {PN(H)P} and {PN(H)P(O)}
frameworks,
as well as their MeO-aryl-functionalized analogues {PN(H)POMe} and di(thio)oxidized {P(O)N(H)P(O)OMe} and {P(S)N(H)P(S)OMe}, were synthesized in good yields, and their solution and
solid-state structures were confirmed by multinuclear NMR spectroscopy
(1H, 31P{1H}, 13C{1H}) and X-ray diffraction. The coordination chemistry of these
(pro)ligands with Ni(II), Ni(0), and Pd(II) precursors was explored.
A range of different products was obtained in moderate to high yields
and characterized in solution and in the solid state by using NMR
spectroscopy and single-crystal X-ray diffraction. Regardless of the
nature of the aryl substitution, the alkyl–Ni complexes exhibited
remarkable instability in solution, undergoing rapid decomposition.
Preliminary ethylene polymerization studies were conducted under homogeneous
conditions using the prepared Ni and Pd complexes with selected activators,
including MAO, Et2AlCl, [Ph3C]+[B(C6F5)4]−, Na+[B(C6F5)4]−, and
[H(OEt2)2]+[NH2{B(C6F5)3}2]−. DFT studies were undertaken to help decipher the oligo- and polymerization
results obtained with the Ni-based systems.