Nitridomanganese(V) and -(VI) complexes containing macrocyclic amine ligands

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  • Karsten Meyer
  • Bendix, Jesper
  • Nils Metzler-Nolte
  • Thomas Weyhermüller
  • Karl Wieghardt

Photolysis of trans-[(cyclam)Mn(III)(N3)2](ClO4) (1) in methanol at - 35 °C with ~350 nm light produces blue [{trans-[(cyclam)Mn(V)(N)]}2(μ- N3)](ClO4)3·3H2O (2) and dinitrogen (cyclam = 1,4,8,11- tetraacyclotetradecane). A series of six-coordinate complexes trans- [(cyclam)Mn(V)(N)Y](n+), where Y represents Cl, n = 1 (3); CH3CN, n = 2 (4); ClO4-, n = 1 (5); CF3CO2-, n = 1 (6), was also synthesized. From a methanol solution of 2 and addition of NaCN the species cis- [(cyclam)Mn(V)(N)(CN)](ClO4) (7) was obtained. Photolysis of [LMn(III)(N3)3], where L represents the macrocycle 1,4,7-trimethyl-1,4,7- triazacyclononane, in CH3CN at 20 °C with 253.7 nm light produces colorless crystals of [{LMn(II)(N3)}2(μ-N3)2] (8) (photoreduction), whereas photolysis with 350 nm light at -35 °C gives the blue photooxidation product [LMn(V)(N)(N3)2] (9). Complexes 1-7 were characterized by X-ray crystallography. Compounds 2-7 contain the nitridomanganese(V) unit (Mn≡ N 1.51-1.54 Å). All nitridomanganese(V) complexes display significant temperature-independent paramagnetism indicative of a low-spin d2 electron configuration. In the electronic spectra four d-d transitions have been identified for the first time which were unambiguously assigned by single crystal polarized UV/vis/NIR and magnetic circular dichroism (MCD) spectroscopy. The spectra were satisfactorily analyzed in the frame of ligand-field theory (angular overlap method). 15N NMR spectroscopy revealed an enormous deshielding of the nitrido group in 4, 6, and 7 (δ = 693-699 ppm referenced to CH3NO2 at 0 ppm). Electrochemically, complex 4 undergoes a reversible one-electron oxidation generating a stable nitridomanganese(VI) species (d1) which has been characterized by UV-Vis and EPR spectroscopy.

Original languageEnglish
JournalJournal of the American Chemical Society
Volume120
Issue number29
Pages (from-to)7260-7270
Number of pages11
ISSN0002-7863
DOIs
Publication statusPublished - 29 Jul 1998

ID: 240004312