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

Abstract

The ring enlargement reactions at ambient temperatures of non C-terminus substituted monoazabutadiene (η -RN=CHCH=CH ) titanium complexes 2 are investigated. The insertion of aldehydes/ketones (five examples) and nitriles (four examples) into the Ti-C bonds result in expansion of the five-membered rings to uncommon seven-membered titanacycles 3 and 4 in good yields. These new compounds are fully characterized by NMR spectroscopy and single-crystal X-ray diffraction. In subsequent reactions, the seven-membered ring systems are protolyzed and the released organic fragments are isolated. Whereas the aldehyde/ketone insertion products 3 form substituted δ-amino alcohols 5 after reduction with NaBH CN, the nitrile insertion products 4 form substituted pyrroles 6 via cyclization.

Selective propargylic C(sp3)–H activation of methyl-substituted alkynes versus [2 + 2] cycloaddition at a titanium imido template

“…All these chemical shifts are in good agreement to other structurally characterized titanium azadienes, 11,13 e.g. the recently reported complex VI 13 ( Table 1 ).…”

“…Highly characteristic is the 13 C{ 1 H} NMR signal at δ 13 C{ 1 H} = 64.9 ppm with a negative phase in the 13 C{ 1 H} DEPT 135 NMR spectrum, being in the typical region for methylene groups in position α to titanium. 13 The signals of the respective chemically non-equivalent Ti–CH 2 hydrogen atoms are localized at δ 1 H = 0.82 and 2.37 ppm. Both signals couple in the 1 H/ 1 H COSY spectrum to a multiplet signal at δ 1 H = 5.10 ppm with the corresponding 13 C{ 1 H} NMR signal at δ 13 C{ 1 H} = 111.6 ppm.…”

“… 11,12 The hitherto only other reported procedure of preparing TiCH 2 substituted titanium azadiene complexes employs allylamines and (Fv Ad ) 2 Ti. 13 Complex 2a is obtained in a good isolated yield of 75% and shows good solubilities in aliphatic and aromatic hydrocarbons such as n -hexane, toluene, and tetrahydrofuran. Multinuclear NMR spectroscopy is already indicative for the formation of the five-membered heterocycle 2a (Fig.…”

Direct Access to Titanocene Imides via Bis(η5:η1-penta-fulvene)titanium Complexes and Primary Amines

“…The Ti−N bond lengths (2.0448 and 2.0105 Å) lie in the range for titanium nitrogen containing titanacycles. 18a, 28 The N−C bond lengths of 1.3739 and 1.3808 Å are typical of N− C sp 2 single bonds. 24 The C35−O1 bond length (1.2473 Å) is a O−C sp 2 double bond.…”

Crystal structure of the η4-ketimine titanium complex (diphenylamido-κN){3-methyl-6-[(4-methylphenyl)(phenylazanidyl)methylidene]cyclohexa-2,4-dien-1-yl-κ2N,C1}(η5-pentamethylcyclopentadienyl)titanium(IV)

“…However, the follow-up chemistry with various multiple bond substrates of the complexes with formulae [( 5 -Cp # )Ti( 4 -C 21 H 19 N)(Cl)] (# = H 5 , Me 5 ) shows a hidden 2 -imine reactivity to five-membered titanacycles (Fischer et al, 2017), being of high interest due to the importance of 2 -bound imine titanium complexes in industrially relevant hydroaminoalkylation reaction of alkenes (for a recent review on hydroaminoalkylation reactions, see: Chong et al, 2014). In contrast, classical monoazabutadiene complexes (Manssen et al, 2017b;Scholz et al 1998Scholz et al , 2004 show ring-enlargement reactions to seven-membered titanacycles, using similar substrates (Manssen et al, 2017a;Scholz et al, 1998). Moreover, the ligand framework of the non-classical monoazabutadiene complexes mentioned above is important for their unexpected reactivities.…”