Preparation and reactivity of half-sandwich dioxygen complexes of ruthenium

Abstract

Dioxygen complexes [Ru(η⁵-C₅Me₅)(η²-O₂){P(OEt)₃}₂]BPh₄ (1) and [Ru(η⁵-C₅Me₅)(η²-O₂)(PPh₃){P(OR)₃}]BPh₄ (2, 3) [R = Me (2), Et (3)] were prepared by allowing chloro-complexes RuCl(η⁵-C₅Me₅)[P(OEt)₃]₂ and RuCl(η⁵-C₅Me₅)(PPh₃)[P(OR)₃] to react with air (1 atm) in the presence of NaBPh₄. Substitution of the η²-O₂ in 1–3 by alkenes [CH₂CH₂, CHCHCO(O)CO] and terminal alkynes (PhCCH) afforded [Ru(η⁵-C₅Me₅)(η²-CH₂CH₂){P(OEt)₃}L]BPh₄ (4) [L = P(OEt)₃ (a), PPh₃ (b)], [Ru(η⁵-C₅Me₅){η²-CHCHCO(O)CO}{P(OEt)₃}₂]BPh₄ (5) and [Ru(η⁵-C₅Me₅){CC(H)Ph}{P(OEt)₃}₂]BPh₄ (6) derivatives. Protonation of dioxygen complexes 1–3 with triflic acid yielded phosphate complexes [Ru(κ¹-OTf)(η⁵-C₅Me₅){P(O)(OEt)₃}₂] (7) and [Ru(κ¹-OTf)(η⁵-C₅Me₅){P(O)Ph₃}{P(O)(OMe)₃}] (8). A reaction path for the formation of complexes 7 and 8 is proposed by DFT studies. Besides phosphate complex 7, protonation of 1 under a CH₂CH₂ atmosphere (1 atm) afforded acetic acid. Treatment of complexes 7 and 8 with ^tBuNC afforded the tris(isocyanide) derivative [Ru(η⁵-C₅Me₅)(^tBuNC)₃]BPh₄ (9). The complexes were characterised spectroscopically (IR and NMR) and by X-ray crystal structure determination of 1, 2 and 3.