Bridging and Terminal Half-Sandwich Ruthenium Dinitrogen Complexes and Related Derivatives: A Structural Study

The reaction of [CpRuCl(P)2] [(P)2 = dippe (1,2-bis(diisopropylphosphino)ethane; (PEt3)2; (PMeiPr2)2] with Na[BAr‘4] (Ar‘4 = 3,5-bis(trifluoromethyl)phenyl) in fluorobenzene under argon generates the corresponding cationic 16-electron species [CpRu(P)2]+, which reacts with trace amounts of dinitrogen present even in high-purity argon furnishing the dinitrogen-bridged complexes [{CpRu(P)2}2(μ-N2)][BAr‘4]2 [(P)2 = dippe 1a; (PEt3)2 1b; (PMeiPr2)2 1c]. If the reaction is performed under dinitrogen, the terminal dinitrogen complexes [CpRu(N2)(P)2][BAr‘4] [(P)2 = dippe 2a; (PMeiPr2)2 2c] are obtained. Compound 1b was obtained irrespectively of the atmosphere used, and no terminal dinitrogen complex has been detected. The crystal structures of 1a, 1b, and 2a have been determined. During one attempt to isolate the 16-electron complex [CpRu(PMeiPr2)2][BAr‘4], the 18-electron tris(phosphine) derivative [CpRu(PMeiPr2)3][BAr‘4], 3, was obtained instead, and it was structurally characterized. Halide abstraction from [CpRuCl(PMeiPr2)(PPh3)] under dinitrogen using Na[BAr‘4] yielded [CpRu(N2)(PMeiPr2)(PPh3)][BAr‘4], 2d, but under argon the complex [CpRu(PMeiPr2)(PPh3)][BAr‘4], 4, which contains a rare η3-coordinated PPh3 ligand as shown by X-ray crystallography, was isolated.