Arrested disproportionation in trivalent, mononuclear, and non-metallocene complexes of Zr(III) and Hf(III)

Reduction of the group 4 transition metal precursors [(PN)₂MCl₂] (M = Zr (1), and Hf (2)); PN⁻ = (N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide), both readily prepared by transmetallation of 2 LiPN with [MCl₄(THF)₂], with a slight excess of KC₈, resulted in the isolation of the trivalent complexes [(PN)₂MCl] (M = Zr (3), and Hf (4)). Complexes 1–4 were all identified by solid-state X-ray diffraction analysis, whereas in the case of 3 and 4 low temperature X-band EPR spectroscopy allowed for the identification of these metal-centered d¹ radicals. A comparison with the isostructural and isoelectronic but more stable [(PN)₂TiCl] is also presented.