The Planar Cyclooctatetraene Bridge in Bis-Metallic Macrocycles: Isolating or Conjugating?
A minor modification of the reported procedure for the synthesis of a corrole dimer that is fused by the cyclooctatetraene (COT) unit, (H3tpfc)2COT, allowed for its isolation in 18% yield. Of the two redox isomers that this interesting macrocycle does form, the current focus is on the reduced form, in which each subunit resembles that of monomeric corroles with a trianionic N4coordination core. The corresponding bis-gallium(III) complex was prepared as an entry into the potentially rich coordination chemistry of (H3tpfc)2COT. Both X-ray crystallography and DFT calculations disclosed that the COT moiety is essentially planar with very unusual nonalternating C-C bonds. The same holds true for the bis-gallium(III) complexes [(Ga-tpfc)2]COT(py)2and [(Ga-tpfc)2]COT(py)4, obtained with one and two pyridine molecules coordinated to each metal ion, respectively. The electronic spectra of both the free base and the gallium(III) complexes display an extremely low energy band (λmaxat 720-724 nm), which points toward extensive π delocalization through the COT bridge. This aspect was fully addressed by examining the interactions between the two corrole subunits in terms of electrochemistry and DFT calculations of the oxidized and reduced macrocycle. The new near-IR bands that appear upon both oxidation (λmax1250 nm) and reduction (λmax1780 nm) serve as additional supporting evidence for this conclusion.
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.
Susovan
S
Bhowmik
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.
Monica
M
Kosa
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.|Chemistry Department, Nuclear Research Centre Negev , Beer-Sheva, Israel.
Amir
A
Mizrahi
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.
Natalia
N
Fridman
Chemistry Department, Nuclear Research Centre Negev , Beer-Sheva, Israel.
Magal
M
Saphier
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.
Amnon
A
Stanger
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology , Haifa 32000, Israel.
Zeev
http://orcid.org/0000-0003-1170-2115
Z
Gross