Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

Abstract

This report describes the synthesis and characterization of a new series of group 4 complexes supported by a trianionic ONO3– pincer-type ligand. Treating TiCl4 with the proligand [CF3–ONO]­H3 (1) and NEt3 in benzene afforded {[CF3–ONO]­TiCl3}­{HNEt3}2 (2). By means of a lithium transmetalation route, the neutral monochloride complex [CF3–ONO]­TiCl­(THF) (3) was synthesized in 91% yield. The analogous Hf­(IV) derivative could not be obtained using this method. Instead, transmetalation with thallium­(I) resulted in the formation of the seven-coordinate complex [CF3–ONHO]­HfCl2(THF)2 (4-(THF) 2 ), which was characterized by combustion analysis and X-ray crystallography. Applying vacuum to 4-(THF) 2 liberated the THF ligands to provide the five-coordinate THF-free complex [CF3–ONHO]­HfCl2 (4). Alkylation of complex 4 with alkyllithium or Grignard reagents resulted in a mixture of unidentifiable products. However, access to the neutral complex 3 enabled the subsequent preparation of organotitanium complexes [CF3–ONO]­TiR­(THF) (5-R; R = Me, Bn, Mes). Single-crystal X-ray analysis of 5-Me indicated that the organotitanium complexes are mononuclear. Single-crystal X-ray diffraction and NMR studies in solution confirmed that complex 5-Mes exhibits rare through-space 19F–19F coupling (5 Hz).

Trianionic Pincer Complexes of Niobium and Tantalum as Precatalysts for ROMP of Norbornene

“…Even addition of PMe 3 (and heating to 100 °C) does not induce α-hydrogen abstraction. Displaying similar stability, Ti­(IV)-alkyl complexes supported by the [CF 3 –ONO] 3– ligand fail to react with substrates (H 2 , CH 2 CH 2 , and CO 2 ) …”

“…Displaying similar stability, Ti(IV)-alkyl complexes supported by the [CF 3 −ONO] 3− ligand fail to react with substrates (H 2 , CH 2 CH 2 , and CO 2 ). 66 Despite the apparent stability of 7, in situ alkylidene formation was probed through addition of norbornene (NBE) (Scheme 4). Addition of 1.5 equiv of norbornene to a C 6 D 6 solution of 7 in a sealable NMR tube at ambient temperature shows immediate growth of resonances between 5 to 5.5 ppm in the 1 H NMR spectrum.…”

“…Among the numerous trianionic pincer and pincer-type ligands known, the [CF 3 –ONO] 3– ligand, in particular, engenders unique reactivity to metal complexes. The combination of weakly basic fluoro alkoxides and a π-donating amido donor within the [CF 3 –ONO] 3– motif generates metal complexes with interesting structure/bonding relationships − and reactivity. ,, Specific to metal–carbon multiple bonds, the lone pair of electrons on the central amido donor within the [CF 3 –ONO] 3– ligand can align with adjacent M = C or MC π-bonds, thereby enhancing their nucleophilicity via the inorganic enamine effect. ,, …”

A Tautomeric λ3/λ5-Phosphane Pair and Its Ambiphilic Reactivity

“…Considering that numerous λ 5 -dioxyspirophosphanes with fascinating stereochemical properties are known,it is not surprising that this research field is rapidly emerging at presentin particular with respect to the development of novel organic transformations . In view of the unusual structure of C 5 and its novelty in main group chemistry, it needs to be noted that formally related [ONO]-coordinated metal complexes have been explored in detail by Veige and co-workers . However, there is a fundamental difference between these [OPO]- and [ONO]-systems, which becomes obvious upon inspection of the respective protonated forms.…”

Synthesis and characterization of a family of M2+ complexes supported by a trianionic ONO3− pincer-type ligand: towards the stabilization of high-spin square-planar complexes

“…22 Holland illus-trated a set of conditions to promote high-spin square-planar molecular compounds: (1) charge from anionic ligands to reduce the metal acidity and prevent coordination from additional ligands, (2) alkali metal counterions to stabilize the negative charge, (3) strong π-donor ligands to destabilize the sterically preferred tetrahedral geometry, and most importantly, (4) weak σ-donating ligands to minimize the antibonding character of the d x 2 −y 2 orbital. 23 Our group recently reported the trianionic pincer-type ligand 2,2′-(azanediylbis(2,1-phenylene))bis(1,1,1,3,3,3-hexafluoropropan-2-ol) ([CF 3 -ONO]H 3 ; 1) and its coordination to W(VI), [24][25][26][27] Ta(V), 28 Hf(IV), 29 Ti(IV), 29 Fe(III), 30 and Fe(II) 31 metal centers. Ligand 1 contains all the prerequisites described by Holland.…”