Solvent-Assisted N–O Bond Cleavage and Metal–Metal Bond Formation in the Reduction of Binuclear Nitrosyl Complexes [M₂Cp₂(μ-X)(μ-P<i>^t</i>Bu₂)(NO)₂] (MX = MoCl, WI): An Experimental and Theoretic

Reaction of [Mo₂Cp₂(μ-Cl)(μ-P<i>^t</i>Bu₂)(NO)₂] with Na(Hg) in tetrahydrofuran gave a very air-sensitive species formulated as the oxido-nitrido radical [Mo₂Cp₂(N)(μ-O)(μ-P<i>^t</i>Bu₂)(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-P<i>^t</i>Bu₂)(NO)]⁺ as a mixture of <i>cis</i> and <i>trans</i> 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-κ_N:η² coordination mode, then by rearrangements into the μ-κ_N:κ_O and bent μ-κ_O:η² modes, according to calculations. In contrast, reduction of the related ditungsten complex [W₂Cp₂(μ-I)(μ-P<i>^t</i>Bu₂)(NO)₂] with Na(Hg) in either tetrahydrofuran or acetonitrile gave the unsaturated anion [W₂Cp₂(μ-P<i>^t</i>Bu₂)(NO)₂]^- (calcd W-W = 2.601 Å), which upon reaction with (NH₄)PF₆ rendered the hydride-bridged derivative [W₂Cp₂(μ-H)(μ-P<i>^t</i>Bu₂)(NO)₂], an air-sensitive 32-electron complex reacting with CO to give the electron-precise carbonyl derivative [W₂Cp₂(H)(μ-P<i>^t</i>Bu₂)(CO)(NO)₂], selectively formed with terminal CO and H ligands <i>cis</i> and <i>trans</i> to the bridging P atom, respectively, and Cp ligands arranged in <i>syn</i> conformation.