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

The chelating hemilabile phosphanyl‐pyridines P i Pr 2 XC 5 H 4 N (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(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 XC 5 H 4 N)Cl] (X = NH, 2a ; S, 2b ). These versatile starting compounds react with phenyldiazomethane to yield the novel carbene ruthenium complexes [Ru(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 XC 5 H 4 N)(=CHC 6 H 5 )][BAr′ 4 ] (Ar′ = 3,5‐C 6 H 3 (CF 3 ) 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(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 NHC 5 H 4 N)(η 2 ‐CH 2 C 6 H 5 )][CF 3 SO 3 ] 2 ( 4a ), the first example of a structurally characterized η 2 ‐benzylruthenium complex. The benzylidene complex 3a can also be deprotonated by bases, KO t Bu or KN(SiMe 3 ) 2 , thereby yielding neutral complex [Ru(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 NC 5 H 4 N)(=CHC 6 H 5 )] ( 5a ). The cationic complex [Ru(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 NHC 5 H 4 N)(PMe 3 )][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 NaBH 4 /CH 3 OH to afford alkyl compound [Ru(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 NHC 5 H 4 N)(η 1 ‐CH 2 C 6 H 5 )] ( 7a ). The reaction of carbene complex 3b with LiCH 3 yields the neutral alkyl complex [Ru(η 5 ‐C 5 Me 5 )(κ 2 ‐ P , N ‐P i Pr 2 SC 5 H 4 N)(η 1 ‐CH 2 CH 2 C 6 H 5 )] ( 8b ), which contains a β hydrogen atom.