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

Abstract

The dihydrido-dichloro complex OsH2Cl2(PiPr3)2 (1) reacts with 1,5-cyclooctadiene in toluene under reflux to give the isopropenylphosphine derivative OsCl2(η4-COD){[η2-CH2C(CH3)]PiPr2} (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 OsHCl2(η4-C8H11PiPr3)(PiPr3) (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 η4-binding mode of the carbocyclic ligand [C8H11PiPr3]+. 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 OsCl2(η4-NBD){[η2-CH2C(CH3)]PiPr2} (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 OsCl2(η4-TFB){(η2-CH2CHCH2)PiPr2} (9) and OsCl2(η4-TFB){[η2-CH2C(CH3)]PiPr2} (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)°.