Syntheses And Properties Of Chromium Radicals And Tetraazacyclophane Diradicals

Radicals are molecules or ions containing unpaired electrons.Radicals are quite reactive with high energies,and thus,they play crucial roles in structural chemistry,life science,stoichiometric chemistry and electronic functional materials.Organotransition metal-centered radicals are of fundamental importance in catalysis and small molecule activation for breaking 18-electron rule.The key to generate and detect organotransition metal radicals is the electrochemical method with the spectroscopic characterization of these metal-centered radicals.On the other hand,to synthesis of stable organotransition radicals is still a challenge.Our group has successfully isolated lots of radical cations by using weakly coordinated polyfluoroaluminate as counter anions.We herein report the isolation and crystal structures and spectroscopic characterization of various persistent organotransition metal radical cations containing chromium element,which are stabilized with polyfluoroaluminate anions.We isolated two half-sandwich seventeen-electron chromium radical cations[(C6Me6)Cr(CO)3]·+(1·+)and[(C6Me6)Cr(CO)2(PPh3)]·+(2·+).These radicals are characterized with single-crystal X-ray diffraction,EPR and FT-IR spectroscopy.EPR spectra and DFT calculations show that the spin density mainly residues on chromium atoms.Moreover,1'+can undergo substitution with PPh3 to produce 2·+.Complex Cr(CO)3(?6,?5-C6H5C5H4)CO(CO)2(3)was transformed to a hetero-metalloradical[Cr(CO)3(?6,?5-C6H5C5H4)Co(CO)2]·+(3·+)with one-electron oxidation.DFT calculations of 3·+ indicate a Cr-Co hemi-bond with wiberg bond order of 0.278.The longest absorption around 1031 nm is significantly red-shifted,which indicates the promising applications in optical communications.Two-electron oxidation of Cr(CO)3(?6,?6-C6H5C6H5)Cr(CO)3(4)afforded a decomposed product 5,which became crystals of 6 through a crystal-to-crystal transformation by dipping of crystals of 5 in pentane.The magnetic dates indicate the complex 6 possess single-molecule magnetic behavior.We successfully isolated a diphosphene chromium radical cation[Cr(CO)2(Mes*P=PMes*)Cr(CO)3]·+(Mes*=2,4,6-But3C6H2)(10·+)upon one-electron oxidation of(Mes*P=P Mes*)[Cr(CO)3]2(7)and studied the properties of 10·+ with single crystal X-ray diffraction,EPR spectroscopy,IR spectroscopy and DFT calculations.The P-P bond is end-on coordinated to the Cr metal.The spin density of 10·+ is mainly residues on one Cr atom and two P atoms.The combined experimental and theoretical study indicates there is a 3c-3e ?-bond through Cr-P-P linkage.We also synthesized three tetraaza[1.1.1.1]m,p,m,p-cyclophane diradical cations with different remote substituents,i.e.112+-132+(112+,R=tBu;122+,R=OMe;132+,R=Me).These radicals are studied with X-ray diffraction,EPR spectroscopy,super conducting quantum interference device(SQUID)measurements and DFT calculations.112+-132+have triplet ground states with ferromagnetic interaction.Different substituents can tune the solid-state structures and intermolecular electronic interaction,with 112+as a moner,122+as a dimer and 132+as a one-dimensional antiferromagnetic chain.