Reactivity of OsH₂Cl₂(PiPr₃)₂toward Diolefins:  New Reactions Involving C−H and C−C Activation and C−C and C−P Bond Formation Processes

The dihydrido-dichloro complex OsH 2 Cl 2 (P i Pr 3 ) 2 ( 1 ) reacts with 1,5-cyclooctadiene in toluene under reflux to give the isopropenylphosphine derivative OsCl 2 (η 4 -COD){[η 2 -CH 2 C(CH 3 )]P i Pr 2 } ( 2 ), which has been characterized by X-ray diffraction analysis. The coordination geometry around the osmium atom of 2 can be rationalized as a highly distorted octahedron. The distortion is due to the ring constraint imposed by the bidentate isopropenylphosphine ligand, which acts with a bite angle of 56.0(1)°. In toluene at 85 °C, the reaction of 1 with 1,5-cyclooctadiene leads to the hydrido compound OsHCl 2 (η 4 -C 8 H 11 P i Pr 3 )(P i Pr 3 ) ( 3 ). The molecular structure of this complex has also been determined by an X-ray investigation. The X-ray diffraction analysis of 3 demonstrates the η 4 -binding mode of the carbocyclic ligand [C 8 H 11 P i Pr 3 ] + . The coordination geometry around the osmium center can be rationalized as a distorted octahedron with the triisopropylphosphine, a chlorine atom, and the carbocyclic ligand forming the equatorial plane. Complex 3 reacts with 1,5-cyclooctadiene and 2,5-norbornadiene (NBD) to give 2 and OsCl 2 (η 4 -NBD){[η 2 -CH 2 C(CH 3 )]P i Pr 2 } ( 8 ), respectively. Complex 8 can also be obtained, under refluxing toluene, from 1 and 2,5-norbornadiene. Similarly, the reaction of 1 with tetrafluorobenzobarrelene (TFB) affords a mixture of the propenylphosphine isomers OsCl 2 (η 4 -TFB){(η 2 -CH 2 CHCH 2 )P i Pr 2 } ( 9 ) and OsCl 2 (η 4 -TFB){[η 2 -CH 2 C(CH 3 )]P i Pr 2 } ( 10 ), which can also be prepared from 3 and tetrafluorobenzobarrelene. The molecular structure of 9 has been determined by X-ray diffraction analysis. The coordination geometry around the osmium can be described as a distorted octahedron, and as for 2, the distortion is mainly due to the ring constraint imposed by the bidentate olefin−phosphine ligand, which in this case acts with a bite angle of 74.8(1)°.