Synthesis, structural studies, kinetic stability, and oxidation catalysis of the late first row transition metal complexes of 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane

Abstract

Synthetic details for 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.5.2]pentadecane, the dimethyl ethylene cross-bridged homocyclen ligand are presented for the first time. Its novel Mn(2+), Fe(2+), Mn(3+), and Fe(3+) complexes have been synthesized and characterized. X-ray crystal structures were obtained for both manganese complexes, along with five additional Co(3+), Cu(2+), and Zn(2+) structures, the first structural characterization of complexes of this ligand. Each complex has the cis-V configuration of the cross-bridged macrocycle ring, leaving cis labile binding sites for interaction of the complex with oxidants and/or substrates. The copper(II) complex kinetic stability in 5 M HCl and at elevated temperatures was determined and compared to related complexes in the literature. The electronic properties of the manganese and iron complexes were evaluated using solid state magnetic moment determination and acetonitrile solution electronic spectroscopy, revealing high spin metal complexes in all cases. Cyclic voltammetry in acetonitrile of the divalent iron and manganese complexes revealed reversible redox processes, suggesting catalytic reactivity involving electron transfer processes are possible for both complexes. Screening of the Mn(2+) and Fe(2+) complexes for oxidation catalysis using hydrogen peroxide as the terminal oxidant showed both complexes are worthy of continued development.

Aspartate‐Based CXCR4 Chemokine Receptor Binding of Cross‐Bridged Tetraazamacrocyclic Copper(II) and Zinc(II) Complexes

“…Cross‐bridged tetraazamacrocycles offer an advantage for this purpose in that they very slowly decomplex from the Cu 2+ ion in aqueous solution due to the rigidity and topological complexity provided by the short cross‐bridge . The likely major mechanism of inactivation of Cu 2+ complexes in vivo is through loss of ligand resulting in free, inactive Cu 2+ ,. However, an additional proposed indicator of in vivo stability is resistance toward reduction to Cu + followed by loss of the more labile Cu + ion .…”

“…As noted above, reversibility of the Cu 2+ /Cu + reduction wave has been used as an indicator of potential in vivo stability, along with kinetic inertness towards aqueous hydrolysis. In combination with the kinetic stability of the cyclam‐based ligand 1 , the reversibility of the reduction of these cyclam‐based ligands bodes well for their in vivo stability.…”

“…Macrocycle–metal interactions : For the purposes of this discussion, two closely related crystal structures from recently published work will be included for relevant comparisons: [Zn 9 (OAc)(H 2 O)] + (for the structure of 9 , please see Figure below) and [Cu 3 (OAc)] + . Crystallographic details for the seven new crystal structures in this work, along with selected bond lengths and angles, are presented in Tables S2 and S3 in the Supporting Information.…”

Synthesis and structural studies of two pyridine-armed reinforced cyclen chelators and their transition metal complexes

“…Synthesis of decahydro-2a,4a,6a,8a-tetraazacyclopenta[fg]acenaphthylene was carried out via literature methods. [11]…”

“…[8] [9] Recently we have been interested in the use of this complex type as oxidation catalysts. [10] [11] [12] A recent papers by Que, et al, has shown that addition of a pyridyl pendant arm to a tetraazamacrocycle can result in new and improved oxidation catalysis. [13] The literature contains numerous other pyridyl pendant armed tetraazamacrocycles, indicating a general interest in the community and known synthetic techniques for adding pendant pyridyl donors.…”