The Dihydride−Osmium(IV) Complex [OsH2(κ 2-O2CCH3)(H2O)(PiPr3)2]BF4 as a Precursor for Carbon−Carbon Coupling Reactions

• Published in: Organometallics Vol. 19; no. 24; pp. 5098 - 5106
• Main Authors: Esteruelas, Miguel A, García-Yebra, Cristina, Oliván, Montserrat, Oñate, Enrique, Tajada, María A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27-11-2000
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om000475z

The dihydride−osmium(IV) complex [OsH2(κ 2-O2CCH3)(H2O)(PiPr3)2]BF4 (1) reacts with acetylene (1 atm) at 0 °C to give polyacetylene and the vinyl−carbyne derivative [Os(CHCH2)(κ 2-O2CCH3)(⋮CCH3)(PiPr3)2]BF4 (2). Both polyacetylene and 2 can also be obtained by reaction of [OsH(κ 2-O2CCH3)(⋮CCH3)(PiPr3)2]BF4 (3) with acetylene. Under an acetylene atmosphere, complex 2 yields polyacetylene in a slow but constant manner. Complex 2 reacts with carbon monoxide to give initially the carbene derivative [Os(κ 2-O2CCH3){C(CHCH2)CH3}(CO)(PiPr3)2]BF4 (4), by migratory insertion of the carbyne ligand of 2 into the Os−vinyl bond. Under a carbon monoxide atmosphere, complex 2 is unstable and evolves into [Os(κ 2-O2CCH3)(CO)2(PiPr3)2]BF4 (5). Treatment of 2 with KOH in methanol produces the deprotonation of the carbyne ligand and the formation of the vinyl−vinylidene derivative Os(CHCH2)(κ 2-O2CCH3)(CCH2)(PiPr3)2 (6), which reacts with carbon monoxide to give the butadienyl compound Os{C(CHCH2)CH2}{κ 1-OC(O)CH3}(CO)2(PiPr3)2 (7) by migratory insertion of the vinylidene ligand into the Os−vinyl bond. The structure of 7 has been determined by X-ray diffraction analysis. The geometry around the osmium atom can be rationalized as a distorted octahedron with the phosphine ligands occupying opposite positions. The remaining perpendicular plane is formed by the butadienyl ligand, the acetate, and the carbonyl groups mutually cis disposed. The Os−butadienyl distance is 2.195(5) Å, whereas the torsion angle in the diene is 50.7(8)°. The butadienyl ligand of 7 acts as a diene in Diels−Alder reactions. Thus, the addition of dimethyl acetylenedicarboxylate and maleic anhydride to benzene solutions of 7 affords the corresponding cycloaddition products (8) and (9). Treatment of 8 with HBF4·OEt2 gives 5 and dimethyl 1,4-cyclohexadiene-1,2-dicarboxylate.