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 [P 2 N 2 ]Li 2 (dioxane) 2 with HfCl 4 (THF) 2 (where [P 2 N 2 ] = PhP(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh) results in the formation of the hafnium dichloride complex [P 2 N 2 ]HfCl 2 (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 (C 8 K), 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 {[P 2 N 2 ]Hf} 2 (2). Reduction of the hafnium diiodide [P 2 N 2 ]HfI 2 (3) -prepared via the reaction of 1 with excess Me 3 SiI -with C 8 K results in the formation of ([P 2 N 2 ]Hf) 2 (µ-η 2 :η 2 -N 2 ) (4) as the major product of the reaction, while {[P 2 N 2 ]Hf} 2 (2) and [P 2 N 2 ]Hf(C 7 H 8 ) (5) appear to be minor products. Reaction of 1 with 2 equiv of MeMgCl gives [P 2 N 2 ]HfMe 2 (6), which, upon exposure to an atmosphere of H 2 , gives the hafnium tetrahydride {[P 2 N 2 ]Hf} 2 (m-H) 4 (7).Résumé : La réaction du [P 2 N 2 ]Li 2 (dioxane) 2 avec le HfCl 4 (THF) 2 {dans lequel [P 2 N 2 ] = PhP(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh} conduit à la formation du complexe de dichlorure d'hafnium, [P 2 N 2 ]HfCl 2 (1). On décrit le comportement du complexe 1 comme précurseur potentiel pour générer un complexe de coordination du diazote. La déduction de 1 à l'aide de potassium sur graphite (C 8 K), sous atmosphère de diazote, dans diverses conditions expérimentales conduit à la formation d'un certain nombre de produits, dont l'un est un dérivé dinucléaire de formule générale {[P 2 N 2 ]Hf} 2 (2) portant des groupes P-phényles agissant comme ponts. La réduction par le C 8 K du complexe de diiodure d'hafnium, [P 2 N 2 ]HfI 2 (3), préparé par le biais d'une réaction de 1 avec un excès de Me 3 SiI, conduit à la formation du complexe {([P 2 -N 2 ]Hf) 2 (µ-η 2 :η 2 -N 2 ) (4) comme produit majeur de la réaction alors qu'il semble y avoir formation {[P 2 N 2 ]Hf} 2 (2) et de [P 2 N 2 ]Hf(C 7 H 8 ) (5) comme sous-produits. La réaction de 1 avec deux équivalents de MeMgCl conduit à la formation de [P 2 N 2 ]HfMe 2 (6) qui, mis dans une atmosphère de H 2 , fournit le tétrahydrure d'hafnium, {[P 2 N 2 ]Hf} 2 (µ-H) 4 (7).

Hafnium alkyl complexes of the anionic PNP pincer ligand and possible alkylidene formation

“…The longest HfeP distances were found in 5 which probably reflects the increased steric pressure from the larger alkyl groups, as well. This trend and the approximate values are reminiscent of Fryzuk's (P 2 N 2 )HfX 2 [26] and and ( Si PNP Me )HfX 3 [17,27] complexes where for X ¼ Cl, the HfeP distances (ca. 2.7 Å) were ca.…”

“…The HfeMe bond distances in Fryzuk's ( Si PNP Me )HfMe 3 [17] and (P 2 N 2 )HfMe 2 [26] are in the 2.24e2.27 Å range, and the ZreMe bond distances in our (PNP)ZrMe 3 are in the 2.25e2.29 Å range [11]. Scott and Lippard reported a series of Zr and Hf bis(trimethylsilylmethyl) complexes supported by N 4 dianionic tropocoronand ligands with MeC bonds ranging from 2.24 to 2.35 Å [21].…”

Synthesis, characterization and coordination chemistry of a macrocyclic ligand containing arsenic donors

“…Work with [P 2 N 2 ]Hf complexes has shown that the iodide complex can be a more productive starting material than the chloride. 33 The synthesis of [As 2 N 2 ]ZrI 2 (3) is outlined in eqn. (2).…”

“…13,52 Reductive pathways to dinitrogen complexes of hafnium have shown that the use of a diiodide precursor can give coordinated dinitrogen complexes where reduction of a dichloride species fails to do so. 33,53 If these reductions are performed in the absence of dinitrogen, phosphorus-phenyl activation occurs, giving rise to a highly activated arene bridged dimer. 54 Reduction pathways have also been used in the preparation of dinitrogen complexes of titanium.…”

Chiral Macrocyclic N2P2 Ligands and Iron(II): A Marriage of Interest

“…The synthesis of such macrocyclic N 2 P 2 ligands is challenging, though, because it requires the control of the configuration at phosphorus. In fact, only a few P-containing macrocycles have been prepared, and N 2 P 2 macrocycles are even rarer and mostly achiral (Chart ). − …”