Colorimetric Detection of Small Molecules by a Frustrated Lewis Pair Containing a Phosphorus-Functionalized CycloheptatrienylCyclopentadienyl Titanium Sandwich Complex

The phosphorus-functionalized cycloheptatrienylcyclopentadienyl (ChtCp) titanium sandwich complex [(η7-C7H7)Ti(η5-C5H4PtBu2)] (7) forms a frustrated Lewis pair (FLP) in combination with the borane B(C6F5)3, and this FLP undergoes heterolytic cleavage of dihydrogen and fixation of carbon dioxide and nitrous oxide with a noticeable colorimetric response, which is visible to the naked eye. In their UV/Vis spectra, the H2, CO2 and N2O fixation products exhibit a bathochromic shift of the absorption band that can be assigned to a HOMOLUMO excitation of the ChtCp titanium (troticene) moiety.