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

Photolysis of trans-[(cyclam)Mn-III(N-3)(2)](ClO4) (1) in methanol at -35 degrees C with similar to 350 nm light produces blue [{trans-[(cyclam)Mn-V(N)]}(2)(mu-N-3)](ClO4)(3). 3H(2)O (2) and dinitrogen (cyclam = 1,4,8,11-tetraazacyclotetradecane). 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 [LMnIII(N-3)(3)], where L represents the macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane, in CH3CN at 20 degrees C with 253.7 nm light produces colorless crystals of [{LMnII(N-3)}(2)(mu-N-3)(2)] (8) (photoreduction), whereas photolysis with 350 nm light at -35 degrees C gives the blue photooxidation product [LMnV(N)(N-3)(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 Angstrom). All nitridomanganese(V) complexes display significant temperature-independent paramagnetism indicative of a low-spin d(2) 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). N-15 NMR spectroscopy revealed an enormous deshielding of the nitrido group in 4, 6, and 7 (delta = 693-699 ppm referenced to CH3NO2 at 0 ppm). Electrochemically, complex 4 undergoes a reversible one-electron oxidation generating a stable nitridomanganese(VI) species (d(1)) which has been characterized by UV-Vis and EPR spectroscopy.