Synthesis and Characterization of the Titanium Bisamide Ti{N(H)Ar^iPr₆}₂(Ar^iPr₆= C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)₂and Its TiCl{N(H)Ar^iPr₆}₂Precursor: Ti(II) → Ti(IV) Cyclization

Abstract

The titanium bisamido complex Ti{N(H)Ar(iPr6)}2 (Ar(iPr6) = C6H3-2,6-(C6H2-2,4,6-(i)Pr3)2 (2), along with its three-coordinate titanium(III) precursor, TiCl{N(H)Ar(iPr6)}2 (1), have been synthesized and characterized. Compound 1 was obtained via the stoichiometric reaction of LiN(H)Ar(iPr6) with the Ti(III) complex TiCl3·2NMe3 in trimethylamine. Reduction of 1 with 1 equiv of KC8 afforded Ti{N(H)Ar(iPr6)}2 (2) in moderate yield. Both 1 and 2 were characterized by X-ray crystallography, NMR, and IR spectroscopy, magnetic studies, and by density functional theory (DFT) computations. The precursor 1 has quasi-four-coordinate coordination at the titanium atom, with bonding to two amido nitrogens and a chlorine as well as a secondary interaction to a flanking aryl ring of a terphenyl substituent. Compound 2 displays a very distorted four-coordinate metal environment in which the titanium atom is bound to two amido nitrogens and to two carbons from a terphenyl aryl ring. This structure is in sharp contrast to the expected two-coordinate linear structure that was observed in its first row metal (V-Ni) analogues. Magnetic studies confirm a d(1) electron configuration for 1 but indicate that Ti{N(H)Ar(iPr6)}2 (2) is diamagnetic at ambient temperature consistent with the oxidation of titanium to Ti(IV). The different structure of 2 is attributed to the high reducing tendency of the Ti(II) in comparison to the other metals.

Strong Preference of the Redox‐Neutral Mechanism over the Redox Mechanism for the TiIV Catalysis Involved in the Carboamination of Alkyne with Alkene and Diazene

“…Power and co-workersa ssigned the + 4o xidations tate to the similar titanium complex( Ti{N(-H)AriPr 6 } 2 )due to the observed diamagnetic nature of the complex. [30] In agreement with the experimental assignment,o ur LOBA and NRTc alculations indicate the complex to be aT i IV complex (see Figure S17 in the Supporting Information).…”

“…Nevertheless, LOBA and NRT calculations assigned the +4 oxidation state to both R12R and R12P , which indicates that the masked Ti II complex R12P could actually be considered as a Ti IV complex. Power and co‐workers assigned the +4 oxidation state to the similar titanium complex (Ti{N(H)Ar i Pr 6 } 2 ) due to the observed diamagnetic nature of the complex . In agreement with the experimental assignment, our LOBA and NRT calculations indicate the complex to be a Ti IV complex (see Figure S17 in the Supporting Information).…”

C(sp3)−H Oxidative Addition and Transfer Hydrogenation Chemistry of a Titanium(II) Synthon: Mimicry of Late‐Metal Type Reactivity

“…Inspection of the metrical parameters within the capping arene moiety reveals severe ring distortions indicative of aromaticity loss and presence of aprominent 1,4-cyclohexadiene dianion resonance form. [8] Consequently,these features are consistent with predominant Ti IV resonance character, [11] as opposed to aT i II canonical form. [10] Accordingly,t he meta and ortho proton resonances of the masking ring shift upfield from the aromatic region, appearing as at riplet and ad oublet at 4.62 and 2.99 ppm, respectively,i nt he 1 HNMR spectrum of 1 in C 6 D 6 .…”

C(sp3)−H Oxidative Addition and Transfer Hydrogenation Chemistry of a Titanium(II) Synthon: Mimicry of Late‐Metal Type Reactivity

“…Consequently, these features are consistent with predominant Ti IV resonance character, as opposed to a Ti II canonical form. Nonetheless, masked early‐metal complexes have been shown to be rich electron reservoirs of which 1 is no exception …”