Chromium(III) scorpionate complexes supported by tris(2-pyridyl)phosphine-derived ligands: synthesis, structure, and electrochemical and catalytic properties.

The first examples of chromium(III) scorpionate-type complexes supported by tris(2-pyridyl)phosphine-derived ligands are reported. Reactions of [Cr(THF)3Cl3] with tris(2-pyridyl)phosphine (Py3P) and its chalcogen derivatives, Py3PS and Py3PSe, afforded the scorpionates [Cr(Py3PX)Cl3] (X = none, S, Se), featuring facial N,N',N″-coordination of the ligand. In contrast, reaction with tris(2-pyridyl)phosphine oxide (Py3PO) results in an unexpected ligand transformation, yielding the phosphinite complex [Cr(Py2PO2)(H2O)Cl2] containing the in situ generated [Py2P(O)O]- ligand. X-Ray diffraction analysis established the molecular structures of the complexes, while EPR spectroscopy confirmed the high-spin state of the Cr(III) centres and revealed pronounced rhombic distortion of octahedral Cr3+ ions for the phosphinite derivative. Cyclic voltammetry demonstrates that the PX functionality significantly influences the redox behaviour of the complexes. Preliminary catalytic studies show that only the phosphine complex [Cr(Py3P)Cl3] is active in ethylene oligomerization and polymerization. Notably, replacing the co-catalyst from MAO to Et3Al dramatically switches the reaction outcome from selective oligomerization to exclusive polymerization. These results establish tris(2-pyridyl)phosphine-derived ligands as a new platform for Cr(III) scorpionate chemistry and provide insight into their structural and functional properties.