CO₂ uptake potential of cerium(III) triazolates and tetrazolates

Cerous triazolates and tetrazolates were synthesised utilising Ce[N(SiMe₃)₂]₃ as a precursor. The transamination with Htz^Me,Me (tz^Me,Me = 3,5-dimethyl-1,2,4-triazolyl), Htrz^Bz (trz^Bz = 1,2,3-benzotriazolyl) and Htet^Ph (tet^Ph = 5-phenyltetrazolyl) gave insoluble, white solids, while Htz^Ph,Ph (tz^Ph,Ph = 3,5-diphenyl-1,2,4-triazolyl) led to the isolation of the monomeric complex Ce(tz^Ph,Ph)₃(thf)₃. Triazolate [Ce(tz^Me,Me)₃]_n favoured exhaustive CO₂ insertion, while the less basic triazolate [Ce(trz^Bz)₃]_n and tetrazolate [Ce(tet^Ph)₃]_n displayed only partial and no insertion, respectively. Ce(tz^Ph,Ph)₃(thf)₃ reacted with CO₂ in aromatic solvents but the product could not be identified. Addition of the azoles to Ce[N(SiMe₃)₂]₃/Me₃TACN mixtures afforded discrete complexes (Me₃TACN)Ce(az)₃(thf) (Me₃TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane; az = tz^Me,Me, trz^Bz, tet^Ph), which, however, do not insert CO₂ at ambient temperature. Treatment of (Me₃TACN)Ce(trz^Bz)₃(thf) with CO₂ resulted in the separation of Me₃TACN and precipitation of a white powder. The respective pyrazolate (Me₃TACN)Ce(pz^Me,Me)₃ (pz^Me,Me = 3,5-dimethylpyrazolyl) featuring more basic azolato ligands engaged in CO₂ insertion, forming the previously reported complex [Ce₄(pz^Me,Me·CO₂)₁₂].