Premium
Copper(II) Complexes of a Hexadentate Mixed‐Donor N 3 S 3 Macrobicyclic Cage: Facile Rearrangements and Interconversions
Author(s) -
Bell Craig A.,
Bernhardt Paul V.,
Gahan Lawrence R.,
Martínez Manuel,
Monteiro Michael J.,
Rodríguez Carlos,
Sharrad Clint A.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902611
Subject(s) - chemistry , bromide , copper , ligand (biochemistry) , crystallography , electron paramagnetic resonance , ion , electrochemistry , cage , stereochemistry , inorganic chemistry , organic chemistry , electrode , receptor , biochemistry , physics , mathematics , nuclear magnetic resonance , combinatorics
Abstract 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.