Unprecedented pairs of uranium (/) hydroxido and (//) oxido complexes supported by a seven-coordinate cyclen-anchored tris-aryloxide ligand

We present the synthesis and reactivity of a newly developed, cyclen-based tris-aryloxide ligand precursor, namely cyclen(Me)( t -Bu, t -Bu ArOH) 3 , and its coordination chemistry to uranium. The corresponding uranium( iii ) complex [U III ((OAr t -Bu, t -Bu ) 3 (Me)cyclen)] ( 1 ) was characterized by 1 H NMR analysis, CHN elemental analysis and UV/vis/NIR electronic absorption spectroscopy. Since no single-crystals suitable for X-ray diffraction analysis could be obtained from this precursor, 1 was oxidized with methylene chloride or silver fluoride to yield [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U IV (X)] (X = Cl ( 2 ), F ( 3 )), which were unambiguously characterized and successfully crystallized to gain insight into the molecular structure by single-crystal X-ray diffraction analysis (SC-XRD). Further, the activation of H 2 O and N 2 O by 1 is presented, resulting in the U( iv ) complex [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U IV (OH)] ( 4 ) and the U( v ) complex [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U V (O)] ( 6 ). Complexes 2 , 3 , 4 , and 6 were characterized by 1 H NMR analysis, CHN elemental analysis, UV/vis/NIR electronic absorption spectroscopy, IR vibrational spectroscopy, and SQUID magnetization measurements as well as cyclic voltammetry. Furthermore, chemical oxidation of 3 , 4 , and 6 with AgF or AgSbF 6 was achieved leading to complexes [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U V (F) 2 ] ( 5 ), [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U V (OH)][SbF 6 ] ( 7 ), and [(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U VI (O)][SbF 6 ] ( 8 ). Finally, reduction of 7 with KC 8 yielded a U( iv ) complex, spectroscopically and magnetochemically identified as K[(cyclen(Me)( t -Bu, t -Bu ArO) 3 )U IV (O)]. Employing the newly developed, hepta-dentate tris(aryloxide) ligand cyclen(Me)( t -Bu, t -Bu ArOH) 3 provides controlled access to the first U( iv / v ) hydroxido and U( iv / v / vi ) oxido complex pairs in a retained ligand environment.