A New Arene-Bridged Diamidophosphine Ligand and Its Coordination Chemistry with Zirconium(IV)

The arene-bridged dilithium diamidophosphine ligand, [(2,4,6-Me 3 C 6 H 2 )NLi-2-(5-MeC 6 H 3 )] 2 PPh, [NPN]*Li 2, was prepared from (2,4,6-Me 3 C 6 H 2 )(2-Br-4-MeC 6 H 3 )NH, n BuLi, and PhPCl 2 in Et 2 O and isolated as a dioxane adduct in ∼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(NMe 2 ) 4 in toluene produced [NPN]*Zr(NMe 2 ) 2 in 90% isolated yield. Addition of excess Me 3 SiCl to [NPN]*Zr(NMe 2 ) 2 converts it to [NPN]*ZrCl 2 in high yield. The solid-state structure of [NPN]*ZrCl 2 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 Δ G rot ⧧ of MesC ipso −N is approximately 15.5 ± 0.3 kcal mol - 1 . The thermally labile and light-sensitive zirconium dimethyl complex [NPN]*ZrMe 2 was prepared from [NPN]*ZrCl 2 and MeMgCl in Et 2 O in 80% yield.