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

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