An Experimental and Computational Investigation Rules Out Direct Nucleophilic Addition on the N₂ Ligand in Manganese Dinitrogen Complex [Cp(CO)₂ Mn(N₂ )]

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO)₂ Mn(N₂ )] (1, Cp=η⁵ -cyclopentadienyl, C₅ H₅ ) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N₂ )MnCOPh]Li (3) that is stable only below -40 °C. Full characterization of 3 (including single crystal X-ray diffraction) was performed. This complex decomposes quickly above -20 °C with N₂ loss to give a phenylate complex [Cp(CO)₂ MnPh]Li (2). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO)₂ MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so-far unique behavior of the N₂ ligand in 1. DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal-coordinated N₂ remains to be demonstrated.