Mono‐Oxido‐Bridged Heterobimetallic and Heterotrimetallic Compounds Containing Titanium(IV) and Chromium(III)

Abstract

AbstractA series of oxido‐bridged heterobi‐ and heterotrimetallic complexes, [(tmtaa)Ti=O→Cr(Por)Cl] and [(tmtaa)Ti=O→Cr(Por)←O=Ti(tmtaa)]+ (tmtaa = 7,16‐dihydro‐6,8,15,17‐tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine; Por = 5,10,15,20‐tetraarylporphyrin), have been synthesized. To the best of our knowledge, these complexes are the first structurally characterized examples to contain a Ti=O→Cr or Ti=O→Cr←O=Ti structural motif. Crystal structures of representative heterobimetallic compounds, including the Ti=O→Cr binuclear complex 2 and two separate trimers, [Ti=O→Cr←O=Ti]SbF6 (10) and [Ti=O→Cr←O=Ti]Cl (12), are reported. The bi‐ and trimetallic molecules have similar structural parameters, including Ti–O, Cr–O, and Ti–O–Cr bond lengths and angles with a linear Ti=O→Cr geometry. Magnetic studies showed that a high‐spin CrIII (S = 3/2) center is present in both the bi‐ and trinuclear molecules. The redox potentials for CrIV/III (ΔE = 320 mV) and Por/Por·– (ΔE = 260 mV) can be tuned by modifying the porphyrin ligand. By determining the thermodynamics and kinetics of the formation of these complexes by titration experiments and electrochemistry, it was found that the bi‐ and trimetallic species undergo isomerization in solution, allowing easy substitution of the apical chlorido ligand.