Imines in the Titanium Coordination Sphere: Highly Reactive Titanaaziridines and Larger Titanacycles Formed by Subsequent C–C Coupling Reactions

Abstract

The reductive complexation of aldimines is one of the promising synthetic tools to obtain titanaaziridines by reaction of the corresponding titanium halides and magnesium as a reducing agent. The effects of the substitution pattern of the imine ligand and the nature of the titanium fragment on the degree of activation of the η 2 -coordinated N-C double bond were investigated. With Cp # TiCl 3 (Cp # = cyclopentadienyl or pentamethylcyclopentadienyl) as the precursor for the reductive complexation of the imines N-(4-methylbenzylidene)aniline (2e) and 2-methyl-1-pyrroline (7), the formation of diazatitanacyclopentanes by McMurry-like C-C coupling is found. A six-membered titanacycle 8 is obtained by a Michael-like coupling reaction of 7. By these insights, it is

Reactions of 2‐Substituted Pyridines with Titanocenes and Zirconocenes: Coupling versus Dearomatisation

“…In both reactions, the 2‐substituted pyridine was not quantitatively converted, giving an explanation for the yields of 5 and 9 (<50 %). But, the NMR and MS spectra of the reaction solutions show no hints for other quantitatively formed side products as they can be imagined by Michael‐ or McMurry‐like reductive coupling reactions or a comproportionation reaction towards 5 or 9 . An analogous mechanism was recently discussed in the formation of a pyridonate‐supported titanium(III) complex by Schafer et al .…”

“…In both reactions, the 2-substituted pyridine was not quantitatively converted, giving an explanation for the yields of 5 and 9 (< 50 %). But, the NMR and MS spectra of the reactions olutions show no hints for other quantitatively formed side productsa st hey can be imagined by Michael-or McMurry-like reductive coupling reactions [20] or ac omproportionation reactiont owards 5 or 9.A na nalogous mechanism was recently discussed in the formation of ap yridonate-supported titanium(III) complex by Schafer et al [21] Furthermore, the in situ EPR experiments gave no hints for as econd single electron containing species,w hich might be hidden in the NMR experiments. Unfortunately,these results yield no satisfactorily explanation for the formation of compounds 5 and 9 and their unusualspectroscopic data.…”

From Five to Seven: Ring Expansion of Monoazadiene Titanium Complexes by Insertion of Aldehydes, Ketones and Nitriles

“…The four‐membered rings exist as azatitanacyclobutanes IVa or ‐butenes IVb, which can be generated via [2+2] cycloaddition reactions of olefins or alkynes– and titanium imido species, or by employing titanium carbenes and carbodiimides . The family of the five‐membered rings is represented by insertion products of olefins and acetylenes into titanaaziridines, leading to azatitanacylopentanes Va and −3‐pentenes Vb ,. The isomeric azatitanacyclo‐2‐pentenes Vc are formed by complexation of 1‐azabutadiene ligands .…”

Crystal structure of 1,1-bis(η 5-adamantylcyclopentadienyl)-3-phenyl-2-trimethylsilyl-2,3-dihydroisotitanazole, C42H55NSiTi

“…To the best of our knowledge, reactions of titanaaziridines and alkynes in the catalytic hydroaminoalkylation have not been reported until now. However, in stochiometric reactions there are a few examples of 5-membered ring insertion products [4,11,12]. Usually, such products are generated from mono and doubly aryl, alkyl-and trimethylsilyl-substituted alkynes.…”

“…This is the first structurally characterized dihydroisotitanazole employing the smallest possible substituted alkyne acetylene. The Ti1-N1 (2.0049(7) Å) and the Ti1-C42 (2.1248(9) Å) bonds are in the expected range of dihydroisotitanazoles [4,12]. The former acetylene C-C triple bond is now elongated to a typical C-C double bond with 1.3363(12) Å between C41-C42 in the insertion product [13].…”