Preparation and reactivity of half-sandwich dioxygen complexes of ruthenium.

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 [CH2[double bond, length as m-dash]CH2, [upper bond 1 start]CH[double bond, length as m-dash]CHCO(O)C[upper bond 1 end]O] and terminal alkynes (PhC[triple bond, length as m-dash]CH) afforded [Ru(η5-C5Me5)(η2-CH2[double bond, length as m-dash]CH2){P(OEt)3}L]BPh4 (4) [L = P(OEt)3 (a), PPh3 (b)], [Ru(η5-C5Me5){η2-[upper bond 1 start]CH[double bond, length as m-dash]CHCO(O)C[upper bond 1 end]O}{P(OEt)3}2]BPh4 (5) and [Ru(η5-C5Me5){[double bond, length as m-dash]C[double bond, length as m-dash]C(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 CH2[double bond, length as m-dash]CH2 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.