A Dinitrogen Complex without Donor Ligands: Isolation and Characterization of a [Mn(CO)

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 N2 ligands carrying a clear negative partial charge. Here, we present the synthesis, isolation, and characterization of the complex salt [Mn(CO)5(η1-N2)]+[F(Al(ORF)3)2]- (RF = C(CF3)3) that resulted from the oxidation of Mn2(CO)10 under a dinitrogen atmosphere in pentafluorobenzene solvent. The IR/Raman spectra reveal a high N2 frequency of 2301/2303 cm-1 close to free N2 gas (2330 cm-1) 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.