A Dinitrogen Complex without Donor Ligands: Isolation and Characterization of a [Mn(CO)(η-N)] Salt.

Dinitrogen complexes are intermediates in nitrogen fixation. Until now, all isolated molecular dinitrogen complexes have relied on ancillary ligands that are net electron donors, yielding N ligands carrying a clear negative partial charge. Here, we present the synthesis, isolation, and characterization of the complex salt [Mn(CO)(η-N)][F(Al(OR))] (R = C(CF)) that resulted from the oxidation of Mn(CO) under a dinitrogen atmosphere in pentafluorobenzene solvent. The IR/Raman spectra reveal a high N frequency of 2301/2303 cm close to free N gas (2330 cm) that indicates little π-back-donation. QTAIM and CD-NOCV analyses show that the carbonyl ligands act as net acceptor ligands that induce the formation of an inversely polarized dinitrogen ligand with a +0.2 charge on the terminal atom that holds the potential to be susceptible to nucleophilic attack.