A new arene-bridged diamidophosphine ligand and its coordination chemistry with zirconium(IV)

The arene-bridged dilithium diamidophosphine ligand, [(2,4,6-Me3C6H2)NLi-2-(5-MeC6H3)](2)PPh, [NPN]*Li-2, was prepared from (2,4,6-Me3C6H2)(2-Br-4-MeC6H3)NH, (BuLi)-Bu-n, and PhPCl2 in Et2O and isolated as a dioxane adduct in similar to 85% yield. The solid-state structure of [NPN]*Li-2(THF)2 as determined by X-ray diffraction shows both lithiums bridged by the amido nitrogens with one Li ion coordinated to the phosphine donor. The reaction of [NPN]*H-2 and Zr(NMe2)(4) in toluene produced [NPN]*Zr(NMe2)(2) in 90% isolated yield. Addition of excess Me3SiCl to [NPN]*Zr(NMe2)(2) converts it to [NPN]*ZrCl2 in high yield. The solid-state structure of [NPN] *ZrCl2 as determined by X-ray diffraction shows the Zr center is a distorted trigonal bipyramid with the phosphine and the chloride apical. The ortho-Me’s on the N-mesityl moiety are inequivalent in both the Li and Zr complexes of [NPN]* by NMR spectroscopy, while in [NPN]*H-2 MesN ortho-Me’s appear as broad singlets. VT-NMR of [NPN]*H-2 indicated that Delta G(rot)(double dagger) of MesC(ipso)-N is approximately 15.5 +/- 0.3 kcal mol(-1). The thermally labile and light-sensitive zirconium dimethyl complex [NPN]*ZrMe2 was prepared from [NPN]*ZrCl2 and MeMgCl in Et2O in 80% yield.