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

Abstract

Reaction of [Mo₂Cp₂(μ-Cl)(μ-P^tBu₂)(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^tBu₂)(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^tBu₂)(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-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^tBu₂)(NO)₂] with Na(Hg) in either tetrahydrofuran or acetonitrile gave the unsaturated anion [W₂Cp₂(μ-P^tBu₂)(NO)₂]⁻ (calcd W–W = 2.601 Å), which upon reaction with (NH₄)PF₆ rendered the hydride-bridged derivative [W₂Cp₂(μ-H)(μ-P^tBu₂)(NO)₂], an air-sensitive 32-electron complex reacting with CO to give the electron-precise carbonyl derivative [W₂Cp₂(H)(μ-P^tBu₂)(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.

Reaction of [Mo₂Cp₂(μ-Cl)(μ-P^tBu₂)(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^tBu₂)(NO)]. Reaction of the latter with (NH₄)PF₆ yielded the diamagnetic cation [Mo₂Cp₂(μ-N)(O)(μ-P^tBu₂)(NO)]⁺ as a mixture of cis and trans isomers.