Reactions of Os(<i>η</i>⁵-C₅H₅)Cl(PⁱPr₃)₂ with NHCPh₂ and PPh₃:  The Unit Os(<i>η</i>⁵-C₅H₅)(PⁱPr₃) as Support for the Study of the Competitive Alkane−Arene Intramolecular C−H Activation

Abstract

The cyclopentadienyl complex Os( η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 ( 1 ) reacts with benzophenone imine to give the cationic orthometalated derivative ( 2a ), containing the hydride ligand and the metalated phenyl group mutually cisoid disposed. Treatment of 2a with NaOCH 3 affords the neutral species ( 3 ), which by protonation with HBF 4 ·OEt 2 gives ( 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( η 5 -C 5 H 5 )Cl(PPh 3 )(P i Pr 3 ) ( 5 ). Treatment of 5 with TlPF 6 affords the orthometalated triphenylphosphine derivative ( 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 NaOCH 3 produces the extraction of the hydride ligand and the formation of the neutral species ( 7 ), which in methanol under reflux gives OsH( η 5 -C 5 H 5 )(PPh 3 )(P i Pr 3 ) ( 8 ). Protonation of 8 with HBF 4 ·OEt 2 affords the cationic dihydride [OsH 2 ( η 5 -C 5 H 5 )(PPh 3 )(P i Pr 3 )]BF 4 ( 9 ).