Low-Temperature N–O Bond Cleavage and Reversible N–P Bond Formation Processes in the Reactions of the Unsaturated Anions [M2(η5-C5H5)2(μ-PCy2)(μ-CO)2]− (M = Mo, W) with the Nitrosyl Complex [Re(η5-C5H4Me)(CO)2(NO)]+

Abstract

The unsaturated anion [Mo2Cp2(μ-PCy2)(μ-CO)2](-) (Na(+) salt) reacted rapidly with [ReCp'(CO)2(NO)]BF4 in a dichloromethane solution at 253 K to give the oxo nitride tetracarbonyl complex [Mo2ReCp2Cp'(μ-N)(μ-O)(μ-PCy2)(CO)4] as the major product (Cp = η(5)-C5H5; Cp' = η(5)-C5H4Me). This complex underwent spontaneous decarbonylation at room temperature to give the unsaturated tricarbonyl derivative [Mo2ReCp2Cp'(μ-N)(μ-O)(μ-PCy2)(CO)3], a very dioxygen-sensitive molecule rapidly evolving upon manipulation to give the dioxo nitride dicarbonyl complex [Mo2ReCp2Cp'(μ-N)(μ-O)(μ-PCy2)(O)(CO)2] in modest yield. The latter product was obtained as a mixture of isomers, with the major ones differing in the relative arrangement (cis and trans) of their MoCp moieties [Mo-Mo = 2.7707(8) Å in the cis isomer]. The ditungsten anion [W2Cp2(μ-PCy2)(μ-CO)2](-) (Na(+) salt) also reacted rapidly with [ReCp'(CO)2(NO)]BF4 in a dichloromethane solution at 253 K to give an analogous oxo nitride complex, [W2ReCp2Cp'(μ-N)(μ-O)(μ-PCy2)(CO)4], but instead of releasing CO, this complex undergoes at room temperature a reversible insertion of the nitride ligand into a W-PCy2 bond, to reach an equilibrium with its phosphinoimido-bridged isomer [W2ReCp2Cp'(μ3-N:N:P-NPCy2)(O)(CO)4], which displays a V-shaped metal core [W-W = 3.0564(7) Å; W-Re = 2.9021(6) Å]. Decarbonylation of this mixture in a refluxing toluene solution led to partial degradation and condensation of these heterometallic species, to give [ReCp'(CO)3] and the pentanuclear oxo nitride complex [W4ReCp4Cp'(μ2-N)(μ3-N)(μ-O)(O)(μ-PCy2)2(CO)3], a very air-sensitive molecule displaying both linear and trigonal nitride ligands bound to rather unsaturated ditungsten centers [W-W = 2.7246(6) and 2.7900(6) Å].