Ruthenium Bidentate Phosphine Complexes for the Coordination and Catalytic Dehydrogenation of Amine– and Phosphine–Boranes

Addition of the amine–boranes H 3 B ⋅ NH 2 t Bu, H 3 B ⋅ NHMe 2 and H 3 B ⋅ NH 3 to the cationic ruthenium fragment [Ru(xantphos)(PPh 3 )(OH 2 )H][BAr F 4 ] ( 2 ; xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; BAr F 4 =[B{3,5‐(CF 3 ) 2 C 6 H 3 } 4 ] − ) affords the η 1 ‐BH bound amine–borane complexes [Ru(xantphos)(PPh 3 )(H 3 B ⋅ NH 2 t Bu)H][BAr F 4 ] ( 5 ), [Ru(xantphos)(PPh 3 )(H 3 B ⋅ NHMe 2 )H][BAr F 4 ] ( 6 ) and [Ru(xantphos)(PPh 3 )(H 3 B ⋅ NH 3 )H][BAr F 4 ] ( 7 ). The X‐ray crystal structures of 5 and 7 have been determined with [BAr F 4 ] and [BPh 4 ] anions, respectively. Treatment of 2 with H 3 B ⋅ PHPh 2 resulted in quite different behaviour, with cleavage of the BP interaction taking place to generate the structurally characterised bis‐secondary phosphine complex [Ru(xantphos)(PHPh 2 ) 2 H][BPh 4 ] ( 9 ). The xantphos complexes 2 , 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H 3 B ⋅ NHMe 2 . While the dppf species (dppf=1,1′‐bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh 3 )HCl] ( 3 ) and [Ru(dppf)(η 6 ‐C 6 H 5 PPh 2 )H][BAr F 4 ] ( 4 ) showed better, but still moderate activity, the agostic‐stabilised N‐heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] ( 12 ; ICy=1,3‐dicyclohexylimidazol‐2‐ylidene) proved to be the most efficient catalyst with a turnover number of 76 h −1 at room temperature.