Trifluoroborate-appended cyclen complexes of paramagnetic transition metals (Ni2+, Co2+) as fast-relaxing 19F MRI probes

For the first time, trifluoroborate groups (BF3) have been investigated as sensitive probes for 19F Magnetic Resonance Imaging (MRI) in paramagnetic complexes. Using a macrocyclic BF3-appended cyclen ligand, complexes of Ni2+ and Co2+ cations were synthesized and exhibited very fast T1 and T2 relaxation times that improve 19F MRI detection. Notably, the cobalt complex presents the fastest 19F MRI relaxation reported to date for a Co2+-based probe.