Synthesis and Characterization of Zr and Hf Triazenido Complexes with Rare κ¹N-Coordination Built Directly in the Coordination Sphere of the Metal

Abstract

The synthesis and characterization of triazenido complexes of the group IV metals zirconium and hafnium is reported. The reaction of the group IV pentafulvene complexes Cp*(π–η5:σ–η1-pentafulvene)-zirconium(IV) and -hafnium(IV)chlorides with the sterically demanding 2,6-dimesitylphenyl azide results in the insertion of the γ-nitrogen atom of the ligand precursor into the polarized M–Cexo (Cexo: exocyclic carbon atom) bond of the pentafulvene ligand, forming a formal Cp,N,N tridentate ligand system. The molecular structures of the furnished complexes reveal the rare κ1 N coordination of the γ-nitrogen atom to the zirconium or hafnium center along with a localized Nα–Nβ double bond. Unusually, in one case, the ligand system shows additional coordination of the α-nitrogen atom to the central metal atom and well-balanced N–N distances, thus, forming the chelating κ2 N,N coordination mode of the triazenido ligand. The potential use of the formed complexes as precursors for cationic group IV cationic complexes was investigated by reaction with methyl lithium.

Syntheses and Characterization of Ti(III)/Ti(IV) Triazenido Complexes

“…As the chemistry of bis (π‐η 5 : σ‐η 1 ‐pentafulvene) titanium complexes is characterized by a broad range of E−H activation and Ti−C functionalization reactions, [15] the insertion of Me 3 SiN 3 into the Ti−C exo bond of the pentafulvene moiety of the bis (π‐η 5 : σ‐η 1 ‐pentafulvene) titanium complex produced a κ 1 N ‐triazenido Ti(IV) complex [14] . While the reaction of 2,6‐dimesitylphenyl azide with mono (π‐η 5 : σ‐η 1 ‐pentafulvene) titanium complexes did not yield the desired triazenido complexes, the same reaction with the Zr and Hf analogs led to κ 1 N ‐triazenido Zr(IV) and Hf(IV) complexes, as reported recently by us [6] . In this work, we demonstrate the reactivity of the recently developed ethylene complexes Cp*Ti(η 2 ‐C 2 H 4 )(η 5 ‐C 5 H 4 CR 2 H) with 1,3‐diphenyltriazene [16] and report diamagnetic κ 2 N,N ‐triazenido Ti(IV) complexes (Figure 1).…”

“…[14] While the reaction of 2,6-dimesitylphenyl azide with mono (πη 5 : σ-η 1 -pentafulvene) titanium complexes did not yield the desired triazenido complexes, the same reaction with the Zr and Hf analogs led to k 1 N-triazenido Zr(IV) and Hf(IV) complexes, as reported recently by us. [6] In this work, we demonstrate the reactivity of the recently developed ethylene complexes Cp*Ti(η 2 -C 2 H 4 )(η 5 -C 5 H 4 CR 2 H) with 1,3diphenyltriazene [16] and report diamagnetic k 2 N,N-triazenido Ti(IV) complexes (Figure 1).…”

“…Recent studies also include Ti(IV) and Nb(V) triazenido complexes with asymmetrical triazenido ligands [13] . Although these approaches produced a chelating coordination mode of the triazenido anion, we reported group IV metal complexes with the rare κ 1 N ‐coordination mode [6,14] . As the chemistry of bis (π‐η 5 : σ‐η 1 ‐pentafulvene) titanium complexes is characterized by a broad range of E−H activation and Ti−C functionalization reactions, [15] the insertion of Me 3 SiN 3 into the Ti−C exo bond of the pentafulvene moiety of the bis (π‐η 5 : σ‐η 1 ‐pentafulvene) titanium complex produced a κ 1 N ‐triazenido Ti(IV) complex [14] .…”

“…The anionic triazenido ligand is a potent and many-sided chelate in inorganic chemistry. [1] Apart from its usual chelating coordination mode, [2][3][4] it can also act as a monodentate [5,6] or bridging ligand. [7] A triazenido metal complex can be synthesized in different ways, either by deprotonation of a triazene, [3,4] by salt-metathesis reaction with a triazenido anion [4] or via insertion of an organic azide into a metal-alkyl [8] or metalhydride [9] bond.…”

“…[13] Although these approaches produced a chelating coordination mode of the triazenido anion, we reported group IV metal complexes with the rare k 1 N-coordination mode. [6,14] As the chemistry of bis (π-η 5 : σ-η 1pentafulvene) titanium complexes is characterized by a broad range of EÀ H activation and TiÀ C functionalization reactions, [15] the insertion of Me 3 SiN 3 into the TiÀ C exo bond of the pentafulvene moiety of the bis (π-η 5 : σ-η 1 -pentafulvene) titanium complex produced a k 1 N-triazenido Ti(IV) complex. [14] While the reaction of 2,6-dimesitylphenyl azide with mono (πη 5 : σ-η 1 -pentafulvene) titanium complexes did not yield the desired triazenido complexes, the same reaction with the Zr and Hf analogs led to k 1 N-triazenido Zr(IV) and Hf(IV) complexes, as reported recently by us.…”