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Hydroosmiation of allenes and reductive elimination of olefin in unsaturated osmium(IV) polyhydrides: Hydride versus chloride

AutorEsteruelas, Miguel A. ; Larramona, Carmen ; Oñate, Enrique
Fecha de publicación2013
EditorAmerican Chemical Society
CitaciónOrganometallics 32(9): 2567-2575 (2013)
ResumenThe replacement of a chloride in OsH2Cl2(P iPr3)2 (1) by a hydride, to afford OsH 3Cl(PiPr3)2 (2), produces dramatic changes in the behavior of the system. Complex 1 hydrogenates the sterically most hindered C-C double bond of gem-disubstituted allenes. In contrast, the trihydride 2 reacts with 1,1-dimethylallene and 1-methyl-1-(trimethylsilyl) allene to give the alkenyl derivates OsH2Cl{C(CH3)- C(CH3)R}(PiPr3)2 (R = CH3 (3), SiMe3 (4)), which do not undergo reductive elimination of olefin in spite of the coplanar cis disposition of the metalated carbon atom and one of the hydride ligands. The X-ray structure of 3 proves that the α-methyl substituent of the alkenyl group cancels the unsaturated character of the metal center. Complex 2 also reacts with ethyl allenecarboxylate. The reaction leads to the metallafuran OsH 2Cl{κ2C,O-[C(CH3)-CHC(O)OEt]}(P iPr3)2 (5), which has been also characterized by X-ray diffraction analysis. DFT calculations suggest that the formation of 3 and 4 is a consequence of the coplanar cisoid disposition of the hydride ligand and the CH2 group of the allene in a hydride-dihydrogen-π-allene intermediate. The DFT calculations also show that 3 and 4 are thermodynamic sinks and that the reductive elimination of the olefin is kinetically disfavored. © 2013 American Chemical Society.
Identificadoresdoi: 10.1021/om400041m
issn: 0276-7333
e-issn: 1520-6041
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