Reactions of Os(η5-C5H5)Cl(PiPr3)2 with NH=CPh2 and PPh3: The unit Os(η5-C5H5)(PiPr3) as support for the study of the competitive alkane−arene intramolecular C−H activation

Abstract

The cyclopentadienyl complex Os(η5-C5H5)Cl(P1Pr 3)2 (1) reacts with benzophenone imine to give the cationic orthometalated derivative [OsH(η55-C5H5){NH=C(Ph)C6H 4}(PiPr3)]Cl (2a), containing the hydride ligand and the metalated phenyl group mutually cisoid disposed. Treatment of 2a with NaOCH3 affords the neutral species Os(η5-C5H5){NH=C(Ph)C6H 4}(PPr3) (3), which by protonation with HBF4-OEt2 gives [OsH(η5-C5H5){NH=C(Ph)C6H 4}-(PPr3)]BF4 (4). The structure of 4 was determined by an X-ray investigation. The geometry around the osmium center can be described as a four-legged piano-stool geometry, with the hydride ligand transoid disposed to the metalated phenyl group and cisoid to the NH of the imine. The separation between the hydride and the NH hydrogen atom is about 2.5 Å. Complex 1 also reacts with triphenylphosphine. In this case the reaction product is the mixed-ligand compound Os(η5-C4H5)Cl(PPh3)(P iPr3) (5). Treatment of 5 with TlPF6 affords the orthometalated triphenylphosphine derivative [OsH(η5-C5H5)(PPh2C 6H4}(PiPr3)]PF6 (6). The structure of 6 was also determined by an X-ray investigation. As for 4, the geometry around the osmium center can be described as a four-legged piano-stool geometry with the hydride ligand and the metalated phenyl group in transoid positions. Treatment of 6 with NaOCH3 produces the extraction of the hydride ligand and the formation of the neutral species Os(η5-C5H5)(PPh2C 6H4)(PiPr3) (7), which in methanol under reflux gives OsH(η5-C5H5)(PPh3)-(PPr 3) (8). Protonation of 8 with HBF4-OEt2 affords the cationic dihydride [OsH2(η5-C5H5)(PPh 3)(PiPr3)]BF4 (9).