The first thermally stable half-sandwich titanium zwitterionic complex

Thermally stable zwitterionic complex [(η5-C5Me5)Ti(Ot-Bu)2](δ+)[(μ-Me)B(C6F5)3](δ−) (5) was formed by mixing equimolar quantities of [(η5-C5Me5)TiMe(Ot-Bu)2] and [B(C6F5)3]. The compound was recrystallized from hot toluene and has been stable so far for 1 year at ambient temperature in the solid state and in toluene solution. The 1H, 19F and 1D NOESY NMR spectra in C6D6 solution proved the inner sphere ion pair structure of 5. The X-ray crystal structure of 5 revealed that the bridging methyl group is σ-bonded to boron, and all its C–H bonds fulfil criteria for agostic bonding interaction with the titanium atom. In contrast to the stable solution in C6D6 compound 5 decomposed in CD2Cl2 solvent within hours at room temperature.

Graphical abstractThermally stable zwitterionic complex [(η5-C5Me5)Ti(Ot-Bu)2](δ+)[(μ-Me)B(C6F5)3](δ−) (5) forms from equimolar quantities of [(η5-C5Me5)TiMe(Ot-Bu)2] and [B(C6F5)3]. The 1H, 19F and 1D NOESY NMR spectra in C6D6 solution proved the inner sphere ion pair structure of 5. The X-ray crystal structure of 5 revealed that the C–H bonds of bridging methyl group fulfil criteria for agostic bonding interaction with the titanium atom.Figure optionsDownload full-size imageDownload as PowerPoint slide