Synthesis and Reactivity of Low-Coordinate Titanium Synthons Supported by a Reduced Redox-Active Ligand

Abstract

To further explore the reactivity and redox capability of the bis-arylimino acenaphthylene ligand (BIAN) in early transition metal complexes, the coordinatively unsaturated titanium synthons, [(dpp-BAAN)Ti(R)2] ([dpp-BAAN](2-) = N,N'-bis(2,6-diisopropylphenylamido)acenaphthylene and R = O(t)Bu (2) or CH2C(CH3)3 (3)), in which the BAAN ligand is reduced by two electrons, were isolated in good yields via sterically induced radical elimination reactions. Addition of p-tolyl azide to complex 3 initiated reductive elimination of the neopentyl ligands to generate a putative imido species. The imido species was trapped by a second oxidative addition of chloride ligands to yield the titanium imido complex, [(dpp-BIAN)Ti[═N(4-C6H4Me)]Cl2 (4). These reactions demonstrate that the BAAN ligand can provide redox equivalents for enhanced reactivity that includes oxidative addition and reductive elimination at d(0) metal centers.

Unusually Strong Long-range Electronic Coupling Across Redox-Active Bridges in M3+/M4+ Mixed-Valence Complexes of Group 4 Congeners

“…The molecular structure of 3, on the contrary, reveals a deviation from planarity, whereby the hafnium metal centers are puckered ~0.57 Å out of the ligand plane, bending towards the ligand in a prone fashion. 82,[102][103] This trend was also confirmed computationally. This may be indicative of interactions between hafnium and the π-electrons of the C=N bonds.…”

“…Electronically, it can act as a reservoir, whereby electrons can be transferred with ease between the ligand and the central atom. [74][75][76][77][78][79] For example, in complexes with early transition metals, this ligand system has displayed electronic properties such as delocalization, [80][81] intramolecular electron transfer, 82 and valence tautomerism. 80 The bifunctional BIAN derivative, tetrakis(imino)pyracene (TIP), has been developed by Cowley and coworkers; 83 and similar to its parent, electron transfer between the ligand and a central atom has been observed.…”

An Isolable Azide Adduct of Titanium(II) Follows Bifurcated Deazotation Pathways to an Imide

“…This sterically accessible and highly reducing d 2 complex forms adducts with π-acids such as AdNC and N 2 , [(Tp t Bu,Me )­TiCl­(CNAd)] ( 1 CNAd ) and [{(Tp t Bu,Me )­TiCl} 2 (μ-N 2 )] ( 2 ), respectively, whereas it quantitatively extrudes N 2 upon reaction with Me 3 SiN 3 to afford the prototypical Ti IV silylimide complex, [(Tp t Bu,Me )­TiCl­(NSiMe 3 )] . Although this entry to titanium imide complexes is universal, − the unique geometry of 1 prompted us to further explore its reactivity toward other azides: Under an Ar atmosphere, treatment of a benzene solution of 1 with the organic azide, AdN 3 , led to a dark yellow two-component reaction mixture (Scheme ). 1 H NMR spectroscopy revealed two diamagnetic species; the first, [(Tp t Bu,Me )­TiCl­(γ-N 3 Ad)] ( 3 ), displayed a single set of pyrazole resonances, in line with rapid interconversion on the 1 H NMR time scale.…”

Unusually Strong Long-range Electronic Coupling Across Redox-Active Bridges in M3+/M4+ Mixed-Valence Complexes of Group 4 Congeners

“…Electronically, it can act as a reservoir, whereby electrons can be transferred with ease between the ligand and the central atom. [74][75][76][77][78][79] For example, in complexes with early transition metals, this ligand system has displayed electronic properties such as delocalization, [80][81] intramolecular electron transfer, 82 and valence tautomerism. 80 The bifunctional BIAN derivative, tetrakis(imino)pyracene (TIP), has been developed by Cowley and coworkers; 83 and similar to its parent, electron transfer between the ligand and a central atom has been observed.…”