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Synthesis and Reactivity of Osmium Complexes Containing a Cyclopentadienyl Ligand with a Pendant Phosphine Donor Group

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journal contribution
posted on 07.06.2004, 00:00 by Miguel A. Esteruelas, Ana M. López, Enrique Oñate, Eva Royo
The unsaturated six-coordinate complex OsH2Cl2(PiPr3)2 (1) reacts with Li[C5H4(CH2)2PPh2] to give (2). This dihydride is fairly acidic and can be deprotonated with KOH in methanol. The reaction of the resulting monohydride (3) with chloroform affords (4). The extraction of the chloride ligand with TlPF6 causes the selective C−H activation of one of the methyl groups of the triisopropylphosphine ligands to give (5), which is isolated as a mixture of stereoisomers. Complex 4 also reacts with phenylacetylene in the presence of TlPF6. The reaction leads to the hydride-alkynyl-osmium(IV) derivative (6), which is not stable and evolves into the vinylidene (7). Deprotonation of 7 with methanol solutions of KOH yields the neutral alkynyl compound (8). The addition of HPF6·H2O to 8 regenerates 7. Similarly to phenylacetylene, 1,1-diphenyl-2-propyn-1-ol reacts with 4 and TlPF6 to give the hydride-hydroxyalkynyl derivative (9), which dehydrates to produce the allenylidene (10). Addition of HPF6·H2O to 10 affords the dicationic alkenyl carbyne (11). Complexes 2 and 4 have been characterized by X-ray diffraction analysis.