CO2 uptake potential of cerium(III) triazolates and tetrazolates

Abstract

Cerous triazolates and tetrazolates were synthesised utilising Ce[N(SiMe3)2]3 as precursor. The transaminiation with HtzMe,Me (tzMe,Me = 3,5-dimethyl-1,2,4-triazolyl), HtrzBz (trzBz = 1,2,3-benzotriazolyl) and HtetPh (tetPh = 5-phenyltetrazolyl) gave insoluble, white solids while HtzPh,Ph (tzPh,Ph = 3,5-diphenyl-1,2,4-triazolyl) led to the isolation of the monomeric complex Ce(tzPh,Ph)3(thf)3. Triazolate [Ce(tzMe,Me)3]n favoured exhaustive CO2 insertion, while less basic triazolate [Ce(trzBz)3]n and tetrazolate [Ce(tetPh)3]n displayed only partial and no insertion, respectively. Ce(tzPh,Ph)3(thf)3 reacts 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) (az = tzMe,Me, trzBz, tetPh), which however do no insert CO2 at ambient temperature. Treatment of (Me3TACN)Ce(trzBz)3(thf) with CO2 resulted in the separation of Me3TACN and precipitation of a white powder. The respective pyrazolate (Me3TACN)Ce(pzMe,Me)3 (pzMe,Me = 3,5-dimethylpyrazolyl) featuring more basic azolato ligands engaged in CO2 insertion forming the previously reported complex [Ce4(pzMe,Me∙CO2)12]