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

• Published in: European Journal of Inorganic Chemistry 2010-04, Vol.2010 (12), p.1767-1776
• Main Authors: Macías-Arce, Ignacio, Puerta, M. Carmen, Valerga, Pedro
• Format: Article
• Language: English
• Subjects: Carbenes; Half-sandwich complexes; N ligands; P,N ligands; Ruthenium; β-Elimi­nation
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200901162

The 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. The synthesis and characterization ofcarbenes [Ru(η5‐C5Me5)(κ2‐P,N‐PiPr2XC5H4N)(=CHC6H5)][BAr′4] (X = NH 3a, S 3b) that contain chelating hemilabilephosphanyl‐pyridine ligands are reported. Compound 3a shows ambiphilic character when reacting with Brønsted acids and hydride. Reaction of 3b with LiCH3 yields a 2‐phenylethyl ruthenium complex stable towards β elimination.