Tetranuclear Ruthenium Cyclopentadienyl and Pentamethylcyclopentadienyl Complexes Containing Bridging Nitrido Ligands

Tetranuclear Ru μ-nitrido complexes have been synthesized by reactions of Ru(II) cyclopentadienyl and pentamethylcyclopentadienyl complexes with Ru(VI) terminal nitrides. Treatment of [RuCp₂] (Cp = η⁵-C₅H₅) with [L_OEtRu^VI(N)Cl₂] (L_OEt^- = [CpCo{P(O)(OEt)₂}₃]^-) (1) afforded a tetranuclear Ru^IV₂-Ru^III₂ μ-nitrido complex, [CpRu{(μ-N)RuCl₂L_OEt}{(μ-Cl)RuClL_OEt}{(μ-NC₅H₄NH)RuCl₂L_OEt}] (2), that contains a bridging monodeprotonated cyclopent-4-ene-1,3-diimine ligand. The formation of 2 possibly involves the migratory insertion of the Ru nitride with a Ru-η¹-C₅H₅ intermediate derived from the η⁵-η¹ ring slippage of [RuCp₂] and subsequent C-H activation of the cyclopentadienylimido ligand by another molecule of 1. Treatment of [Cp∗Ru(MeCN)₃](PF₆) (Cp∗ = η⁵-C₅Me₅) with [L_OEtM(N)Cl₂] afforded [{Cp∗Ru(μ-N)M(L_OEt)}₂(μ-Cl)₄](PF₆)₂ (M = Ru (3), Os (4)). Treatment of [Cp∗Ru(MeCN)₃](PF₆) with mer-[Ru(N)Cl₃(AsPh₃)₂] yielded [{Cp∗Ru(μ-N)RuCl(AsPh₃)}₂(μ-Cl)₄(μ-O₂PF₂)](PF₆) (5), which contains a bridging difluorophosphate ligand. The crystal structures of 2, 3, and 5 have been determined. The short Cp∗Ru-N distances in 3 (1.777(7) Å) and 5 (1.772(7) and 1.775(7) Å) are indicative of the Ru^IV=N=Ru^IV bonding description.