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

Abstract

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 ∆G rot q 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.

Synthesis and characterization of organo-scandium and yttrium complexes stabilized by phosphinoamide ligands

“…17- 22 We have had success using a motif involving two amido donors flanking a central phosphine, generically named 'NPN', for early transition metal chemistry. [23][24][25][26][27] Recent ligand designs in our laboratory have been focused on modifying the nitrogen-phosphorus linkers of the NPN ligand backbone (see Fig. 1).…”

Phosphine- and thiophosphorane-amine ligands: Lithiation and coordination to Rh(I)

“…In particular, Fryzuk and co-workers, developed [PN Si P] and [N 2 P 2 ] ligands based on the ÀSiMe 2 CH 2 -backbone, which gave group 4 and 5 metal complexes able to activate N 2 [1]. Zirconium complexes featuring a more rigid [NPN] ligand were also reported [2]. The [PNP] ligand developed by Liang et al [3] and Ozerov and co-workers [4] may appear similar since it also features aromatic rings linked by heteroatoms but the nitrogen atom is central and the phosphorus donors are located at the periphery [5].…”

Dinitrogen activation by group 4 and group 5 metal complexes supported by phosphine-amido containing ligand manifolds

“…Synthesis of Mes NPN*.Using N-mesityl-4-toluamine, the bromination occurs at the 2-position of the p-tolyl group in high yield. Subsequent lithium halogen exchange and amine deprotonation by n-butyllithium followed by dichlorophenylphosphine quench resulted in the desired lithiated ligand Li[ Mes NPN*] in 2 steps from commercially available starting materials (Scheme 20)[82]. We also modified the synthesis of Mes NPN* by replacement of the mesityl groups on the amido donors with less sterically encumbering aryl groups such as N-p-Me-phenyl and N-p-isopropylphenyl to generate tol NPN* and iPr NPN*[83].…”