Synthetic, spectral, structural, and catalytic aspects of some piano-stool complexes containing 2-(2-diphenylphosphanylethyl)pyridine

Abstract

Reactions of the complexes [(η⁵-C₅H₅)Ru(PPh₃)₂Cl], [{(η⁶-arene)Ru(μ-Cl)Cl}₂] (η⁶-arene = C₆H₆, C₁₀H₁₄, and C₆Me₆) and [{(η⁵-C₅Me₅)M(μ-Cl)Cl}₂] (M = Rh, Ir) with 2-(2-diphenylphosphanylethyl)pyridine (PPh₂Etpy) were investigated. Neutral κ¹-P-bonded complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂EtPy)(PPh₃)Cl] (1) and [(η⁶-arene)Ru(κ¹-P-PPh₂EtPy)Cl₂] [arene = C₆H₆, (2). C₁₀H₁₄, (3), and C₆Me₆, (4) were isolated from the reactions of [(η⁵-C₅H₅)Ru(PPh₃)₂Cl] and [{(η⁶-arene)Ru(μ-Cl)Cl}₂] with PPh₂EtPy. Treatment of 1–4 with NH₄BF₄/NH₄PF₆ in methanol allows the synthesis of cationic κ²-P,N-chelated complexes [(η⁵-C₅H₅)Ru(κ²-P,N-PPh₂EtPy)(PPh₃)]⁺ (5) and [(η⁶-arene)Ru(κ²-P-N-PPh₂EtPy)Cl]⁺ [arene = C₆H₆, (6), C₆H₁₄, (7), and C₆Me₆ (8)]. On the other hand, the dimers [{(η⁵-C₅Me₅)M(μ-Cl)Cl}₂] (M = Rh or Ir) reacted with PPh₂EtPy in methanol to afford cationic κ²-P,N-chelated complexes [(η⁵-C₅Me₅)M(κ²-P-N-PPh₂EtPy)Cl]⁺ [M = Rh, (9); Ir, (10)]. Complex 10 reacted with an excess amount of sodium azide or sodium chloride to afford the complexes [(η⁵-C₅Me₅)Ir(κ¹-P-PPh₂EtPy)X₂] (X = N₃^–11; Cl^–, 12), establishing the hemilabile nature of the coordinated PPh₂EtPy. The complexes were characterized by elemental analyses and various physicochemical techniques. The molecular structures of 1, 5, 6, 9, and 10 were determined crystallographically, and the catalytic potentials of 1–10 were evaluated towards transfer-hydrogenation reactions under aqueous conditions.