Reduction of hafnium(IV) complexes in the presence of molecular nitrogen: Attempts to form dinitrogen complexes of the heaviest group 4 element

Abstract

The reaction of [P2N2]Li2(dioxane)2 with HfCl4(THF)2 (where [P2N2] = PhP(CH2SiMe2NSiMe2CH2)2PPh) results in the formation of the hafnium dichloride complex [P2N2]HfCl2 (1). The behaviour of 1 as a potential precursor in the generation of a dinitrogen coordination complex is described. Reduction of 1 with potassium-graphite (C8K), under dinitrogen, under a variety of conditions led to a number of products, one of which is the dinuclear derivative with bridging P-phenyl groups that has the general formula {[P2N2]Hf}2 (2). Reduction of the hafnium diiodide [P2N2]HfI2 (3) — prepared via the reaction of 1 with excess Me3SiI — with C8K results in the formation of ([P2N2]Hf)2(µ-η2:η2-N2) (4) as the major product of the reaction, while {[P2N2]Hf}2 (2) and [P2N2]Hf(C7H8) (5) appear to be minor products. Reaction of 1 with 2 equiv of MeMgCl gives [P2N2]HfMe2 (6), which, upon exposure to an atmosphere of H2, gives the hafnium tetrahydride {[P2N2]Hf}2(m-H)4 (7).Key words: hafnium, dinitrogen, reduction, coordination chemistry, hydride, mixed donor ligands.