Copper(II) complexes of a hexadentate mixed-donor N3S3 macrobicyclic cage: facile rearrangements and interconversions.
The potentially hexadentate mixed-donor cage ligand 1-methyl-8-amino-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]eicosane (AMME-N(3)S(3)sar; sar=sarcophagine) displays variable coordination modes in a complex with copper(II). In the absence of coordinating anions, the ligand adopts a conventional hexadentate N(3)S(3) binding mode in the complex [Cu(AMME-N(3)S(3)sar)](ClO(4))(2) that is typical of cage ligands. This structure was determined by X-ray crystallography and solution spectroscopy (EPR and NIR UV/Vis). However, in the presence of bromide ions in DMSO, clean conversion to a five-coordinate bromido complex [Cu(AMME-N(3)S(3)sar)Br](+) is observed that features a novel tetradentate (N(2)S(2))-coordinated form of the cage ligand. This copper(II) complex has also been characterized by X-ray crystallography and solution spectroscopy. The mechanism of the reversible interconversion between the six- and five-coordinated copper(II) complexes has been studied and the reaction has been resolved into two steps; the rate of the first is linearly dependent on bromide ion concentration and the second is bromide independent. Electrochemistry of both [Cu(AMME-N(3)S(3)sar)](2+) and [Cu(AMME-N(3)S(3)sar)Br](+) in DMSO shows that upon reduction to the monovalent state, they share a common five-coordinated form in which the ligand is bound to copper in a tetradentate form exclusively, regardless of whether a six- or five-coordinated copper(II) complex is the precursor.
Bell
Craig A
CA
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.
Bernhardt
Paul V
PV
Gahan
Lawrence R
LR
Martínez
Manuel
M
Monteiro
Michael J
MJ
Rodríguez
Carlos
C
Sharrad
Clint A
CA
D053961:Azabicyclo Compounds / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*
C548742:1-methyl-8-amino-3,13,16-trithia-6,10,19-triazabicyclo(6.6.6)eicosane; D053961:Azabicyclo Compounds; D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D003300:Copper