FLP behaviour of cationic titanium complexes with tridentate Cp,O,N-ligands: highly efficient syntheses and activation reactions of C–X bonds (X = Cl, F)

Abstract

Titanium FLPs! Solvent- and catalyst-free Aza-Michael reaction provides β-amino ketones which were employed as ligand precursors for the convenient synthesis of novel cationic titanium complexes with tridentate Cp,O,N-ligand frameworks, which activate C–X bonds in a FLP-like manner.

Unexpected Selective Methyl Group Abstractions from SiMe3 Moieties of CH2SiMe3 Ligands To Give New Cationic Titanium Complexes

“…The data of the 11 B{ 1 H}, 19 F{H}, and 13 C{ 1 H} NMR spectra unambiguously support that the methyl borate anion MeB(C 6 F 5 ) 3 − was indeed formed during the reaction of complex 2 with B(C 6 F 5 ) 3 ( δ 11 B{ 1 H}=−14.9 ppm; δ 19 F{ 1 H}=−167.7 ( m ‐F Ar B), −165.0 (t, 3 J F,F =20.3 Hz, p ‐F Ar B), −133.4 ( o ‐F Ar B), Δ δ 19 F{ 1 H}( m , p ‐F Ar )=2.7 ppm; δ 1 H=0.38 ppm (s(br), 3 H); δ 13 C{ 1 H}=9.8 ppm). The data are in good agreement with other reported cationic Group 4 complexes that bear this specific borate anion –. The Δ δ 19 F{ 1 H}( m , p ‐F Ar ) parameter introduced by Horton et al.…”

“…The Horton parameter of Δ δ 19 F{ 1 H}( m , p ‐F Ar )=2.5 ppm for complex 6 a confirms that the methylborate anion is noncoordinating, which supports the results obtained from the ESI‐HRMS data . The NMR spectroscopic data are identical to those of other Group 4 complexes with the MeB(C 6 F 5 ) 3 − anion –…”

“…Such insertion reactions into the Ti−C q, exo bond have previously been shown to give stabilized complexes as a result of the transition from pentafulvene ligands to bidentate σ,π‐chelating ligand frameworks. This strategy already enabled the synthesis of cationic complexes with tridentate ligand frameworks,– and a hypothesis was made that stated the free electron pair localized at the nitrogen atom of the insertion products might subsequently stabilize the generated silylium ion after the reaction with B(C 6 F 5 ) 3 (Scheme ).…”

To Coordinate or not to Coordinate: The Special Role of Chalcogen Ether Functionalities in the Design of Twofold Functionalized Cyclopentadienyl Ligands [Cp,O,Ch (Ch = S, Se)]

“…Inspired by pioneering work concerning the solvent‐ and catalyst free synthesis of various β‐substituted diphenylphosphino ketones, and β‐amino ketones, which are accessible without any further purification steps starting from methyl vinyl ketone and appropriate secondary amines and phosphines, the analogous synthesis of β‐thio ketones was targeted. The reactions of methyl vinyl ketone with propane‐2‐thiol and benzylthiol resulted in clean conversions (shown by 1 H NMR analysis) to the corresponding 1,4‐addition products L1a and L1b within 16 h of vigorous stirring at room temperature (Scheme ).…”

“…Further studies dealt with the corresponding Cp,N,P and Cp,O,N ligand systems and their respective titanium complexes. They proved to be rare examples of titanium based frustrated Lewis pairs, hence they were able to activate acetone, phenylacetylene, dihydrogen, or, in the case of the Cp,O,N congeners they were even capable of activating carbon–halogen bonds (Scheme , middle) , . These recent examples have already shown the high versatility of this approach, which might offer tuning potentials comparable to those of the ubiquitous and comprehensively analyzed class of pincer ligands (Scheme , middle).…”