Reactivity of OsH2Cl2((PPr3)-Pr-i)(2) toward diolefins: New reactions involving C-H and C-C activation and C-C and C-P bond formation processes

The dihydrido-dichloro complex OsH2Cl2((PPr3)-Pr-i)(2) (1) reacts with 1,5-cyclooctadiene in toluene under reflux to give the isopropenylphosphine derivative OsCl2(eta(4)-COD){[eta(2)-CH2=C(CH3)](PPr2)-Pr-i} (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)degrees. In toluene at 85 degrees C, the reaction of 1 with 1,5-cyclooctadiene leads to the hydride compound OsHCl2(eta(4)-(C8H11PPr3)-Pr-i)((PPr3)-Pr-i) (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 eta(4)-binding mode of the carbocyclic ligand [(C8H11PPr3)-Pr-i](+) 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(eta(4)-NBD){[eta(2)-CH2=C(CH3)](PPr2)-Pr-i} (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(eta(4)-TFB){(eta(2)-CH2=CHCH2)(PPr2)-Pr-i} (9) and OsCl2(eta(4)-TFB){[eta(2)-CH2=C(CH3)](PPr2)-Pr-i} (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)degrees.