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Osmium-acyl decarbonylation promoted by Tp-mediated allenylidene abstraction: A new role of the Tp ligand

AuthorsBajo, Sonia ; Esteruelas, Miguel A. ; López, Ana M. ; Oñate, Enrique
Issue Date2014
PublisherAmerican Chemical Society
CitationOrganometallics 33(15): 4057-4066 (2014)
AbstractPhenylacetylene and 1,1-diphenyl-2-propyn-1-ol displace the pyridyl and ethylene ligands of OsTp{κ1-C[NC5H 3Me]}(η2-CH2=CH2)(P iPr3) (1) to afford the alkynyl-vinylidene derivatives OsTp(C≡CR)(=C=CHR)(PiPr3) (Tp = hydridotris(pyrazolyl)borate; R = Ph, (2), C(OH)Ph2 (3)). Stirring of toluene solutions of 3 in the presence of neutral aluminum oxide initially produces the dehydration of the vinylidene ligand to give the alkynyl-allenylidene OsTp{C≡CC(OH)Ph2}(=C=C=CPh 2)(PiPr3) (4), which subsequently undergoes a Meyer-Schuster rearrangement to yield the acyl-allenylidene OsTp{C(O)CH=CPh 2}(=C=C=CPh2)(PiPr3) (5). In toluene, at 60 °C, the B-H bond of the Tp ligand of 5 abstracts the allene from the osmium coordination sphere by means of a 1,1-hydroboration of the Os-Cα double bond. As a result, the acyl decarbonylation takes place to form Os(Ph2C=C=CHTp)(CH=CPh2)(CO)(P iPr3) (6). In acetonitrile at 60 °C, the allene tautomerizes into the alkyne to afford Os(Ph2HCC≡CTp)(CH= CPh2)(CO)(PiPr3) (7). The abstraction modifies the reactivity of the system toward HBF4. Thus, while the protonation of 5 leads to the alkylidyne [OsTp{C(O)CH=CPh2}(≡CCH=CPh 2)(PiPr3)]BF4 (8), the protonation of 6 and 7 gives the alkylidenes [Os(Ph2C=C=CHTp)(=CHCHPh 2)(CO)(PiPr3)]BF4 (9) and [Os( Ph2HCC≡CTp)(=CHCHPh2)(CO)(PiPr 3)]BF4 (10). Both 9 and 10 are unstable in solution. In dichloromethane, at room temperature, they evolve into the corresponding olefin derivatives [Os(Ph2C=C=CHTp)(η2-CH2= CPh2)(CO)(PiPr3)]BF4 (11) and [Os(Ph2HCC≡CTp)(η2-CH2=CPh 2)(CO)(PiPr3)]BF4 (12) by means of a Cβ,Cα-hydrogen shift on the alkylidene ligand. © 2014 American Chemical Society.
Identifiersdoi: 10.1021/om500569m
issn: 0276-7333
e-issn: 1520-6041
Appears in Collections:(ISQCH) Artículos
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