Half‐Sandwich Benzylidene Ruthenium Complexes Bearing Phosphanyl‐Pyridine Ligands: Reactivity towards Nucleophiles and Electrophiles

Abstract

AbstractThe chelating hemilabile phosphanyl‐pyridines PiPr2XC5H4N (X = NH, the previously described diisopropylphosphanyl‐pyrid‐2‐ylamine, 1a; X = S, the novel diisopropylphosphanylmercaptopyridine, 1b) have been prepared to be used as ligands in the synthesis of the new half‐sandwich chloro complexes [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2XC5H4N)Cl] (X = NH, 2a; S, 2b). These versatile starting compounds react with phenyldiazomethane to yield the novel carbene ruthenium complexes [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2XC5H4N)(=CHC6H5)][BAr′4] (Ar′ = 3,5‐C6H3(CF3)2; X = NH, 3a; S 3b); 3a has been characterized by X‐ray crystallography. Compound 3a reacts as a Brønsted base with an excess amount of triflic acid to give [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2NHC5H4N)(η2‐CH2C6H5)][CF3SO3]2 (4a), the first example of a structurally characterized η2‐benzylruthenium complex. The benzylidene complex 3a can also be deprotonated by bases, KOtBu or KN(SiMe3)2, thereby yielding neutral complex [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2NC5H4N)(=CHC6H5)] (5a). The cationic complex [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2NHC5H4N)(PMe3)][BAr′4] (6a) has been prepared from 3a by straightforward and quick reaction with trimethylphosphane. Compound 3a also shows characteristic carbene reactivity against nucleophiles like NaBH4/CH3OH to afford alkyl compound [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2NHC5H4N)(η1‐CH2C6H5)] (7a). The reaction of carbene complex 3b with LiCH3 yields the neutral alkyl complex [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2SC5H4N)(η1‐CH2CH2C6H5)] (8b), which contains a β hydrogen atom.