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

The reaction of [P2N2]Li-2(dioxane)(2) with HfCl4(THF)(2) (where [P2N2] = PhP(CH2SiMe2NSiMe2CH2)(2)PPh) 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)(mu-eta(2):eta(2)-N-2) (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 H-2, gives the hafnium tetrahydride {[P2N2]Hf}(2)(m-H)(4) (7).