Solvent-Assisted N–O Bond Cleavage and Metal–Metal Bond Formation in the Reduction of Binuclear Nitrosyl Complexes [M2Cp2(μ-X)(μ‑PtBu2)(NO)2] (MX = MoCl, WI): An Experimental and Theoretical Study

Reaction of [Mo2Cp2(μ-Cl)(μ-PtBu2)(NO)2] with Na(Hg) in tetrahydrofuran gave a very air-sensitive species formulated as the oxido–nitrido radical [Mo2Cp2(N)(μ-O)(μ-PtBu2)(NO)] according to density functional theory (DFT) calculations, which follows from a fast N–O bond cleavage of a nitrosyl ligand. Reaction of the latter with (NH4)PF6 yielded the diamagnetic cation [Mo2Cp2(μ-N)(O)(μ-PtBu2)(NO)]+ as a mixture of cis and trans isomers, which display bent-bridging nitrido and terminal oxido ligands, isolated as the corresponding BAr’4– salts (Ar’ = 3,5-C6H3(CF3)2; Mo–Mo = 2.8365(5) and 2.836(1) Å, respectively). The N–O bond cleavage leading to this radical presumably involves stepwise nitrosyl rearrangements at the dimetal center, first as a solvent-assisted one from terminal to the linear μ-κN:η2 coordination mode, then by rearrangements into the μ-κN:κO and bent μ-κO:η2 modes, according to calculations. In contrast, reduction of the related ditungsten complex [W2Cp2(μ-I)(μ-PtBu2)(NO)2] with Na(Hg) in either tetrahydrofuran or acetonitrile gave the unsaturated anion [W2Cp2(μ-PtBu2)(NO)2]− (calcd W–W = 2.601 Å), which upon reaction with (NH4)PF6 rendered the hydride-bridged derivative [W2Cp2(μ-H)(μ-PtBu2)(NO)2], an air-sensitive 32-electron complex reacting with CO to give the electron-precise carbonyl derivative [W2Cp2(H)(μ-PtBu2)(CO)(NO)2], selectively formed with terminal CO and H ligands cis and trans to the bridging P atom, respectively, and Cp ligands arranged in syn conformation.