Metallomacrocycles as ligands: synthesis and characterisation of aluminium-bridged bisglyoximato complexes of palladium and iron

Abstract

Dialuminiummacrocycles based on bisglyoximato moieties were prepared and their coordination chemistry with Fe II and Pd II was investigated. The bridging aluminium centers were supported by several types of tetradentate diphenoxide diamine ligands. The nature of the ancillary ligands bound to aluminium was found to affect the overall geometry and symmetry of the metallomacrocycles. Enantiopure, chiral diphenoxide ligands based on the (R,R)-trans-1,2-diaminocyclohexane backbone afforded cleanly one metallomacrocycle isomer. The size and electronic properties of remote substituents on aluminium-bound ligands affected the binding mode and electronic properties of the central iron.A structurally characterized iron complex shows trigonal prismatic coordination mode, with phenoxide bridges between iron and aluminium. Increasing the size of the phenoxide substituents led to square bipyramidal coordination at iron. Employing p-NO 2 -instead of p-tBu-substituted phenoxide as supporting ligands for aluminium caused a 0.27 V positive shift of the Fe III /Fe II reduction potential. These results indicate that the present synthetic approach can be applied to a variety of metallomacrocycles based on bisglyoximato motifs to affect the chemistry at the central metal.

Selective Nitrite Reduction at Heterobimetallic CoMg Complexes

“…The synthesis of well-defined heterobimetallic complexes remains a frontier area of inorganic synthesis due to the inherent challenges associated with site-selective metalation. One effective approach involves the use of ambidentate ligands, including oximato groups, − with differentiated metal-binding sites.…”

“…Herein, we elaborate on this concept in the context of a heterobimetallic CoMg system that coordinates and reduces the nitrite anion. Our approach exploits diimine–dioximes as binucleating ligands, allowing a Mg 2+ cation to be placed in proximity to a redox-active transition metal. − We hypothesized that the Lewis acidic site would enhance the binding affinity of NO 2 – to a low-valent Co center in analogy to the proposed role of the active-site histidine residues in nitrite reductases.…”

A doubly deprotonated diimine dioximate metalloligand as a synthon for multimetallic complex assembly

“…The rates presented here compare favorably with other cobalt catalysts. Complex 4 affords an i cat /i p of ∼5 at 100 mV s −1 , 23 which can be compared to other complexes that catalyze proton reduction in CH 3 CN, 16,28,36 though these complexes have lower rates than some diglyoxime counterparts (i.e. -[Co(dmgBF 2 )(MeCN) 2 ] i cat /i p ∼40 at 100 mV s −1 ).…”

“…The synthesis of bimetallic diimine monoxime monoximate complexes has been previously explored through in situ deprotonation of the oxime. [16][17][18][19] This strategy has provided access to a variety of bimetallic complexes however it is not broadly generalizable.…”

Boron, aluminium, gallium, indium and thallium

“…291 Mixed metal thorium-aluminium clusters were synthesised including oxobridged Th 2 Al 6 and Th 2 Al 8 clusters 292 A number of metalla-macrocycles incorporating aluminium and gallium were synthesised and used to make heterometallic structures. 293,294 Gd 3 Al heterometallic metallostars were reported utilising 8-hydroxyquinoline derived ligands. The compounds have potential as in vitro bimodal contrast agents, and exhibited bright green luminescence upon excitation.…”