Alkyne/Methylene Coupling Reactions at Adjacent Rh/Os Centers:  Stepwise Transformations from C₁- through C₄-Bridged Species

Reaction of the methylene-bridged complex [RhOs(CO) 3 (μ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (dppm = μ-Ph 2 PCH 2 PPh 2 ) with dimethyl acetylenedicarboxylate or hexafluorobutyne results in alkyne insertion into the Rh−CH 2 bond, yielding [RhOs(CO) 3 (μ-η 1:η 1 -RC C(R)CH 2 )(dppm) 2 ][CF 3 SO 3 ] (R = CO 2 Me ( 5 ), CF 3 ( 6 )). Carbonyl removal from each of these species results in a Rh-bound carbonyl being replaced by a triflate ion. Reaction of 5 with diazomethane results in CH 2 insertion into the Rh−C(R) bond with accompanying C−H activation of the original osmium-bound CH 2 group, yielding [RhOs(CO) 3 (μ-η 1:η 1 -CH 2 C(R) C(R)CH)(μ-H)(dppm) 2 ][CF 3 SO 3 ] (R = CO 2 Me). Reaction of the alkyne-bridged species [RhOs(CO) 3 (μ-η 1:η 1 -RC CR)(dppm) 2 ][CF 3 SO 3 ] (R = CO 2 Me) with diazomethane at −78 °C yields [RhOs(CO) 3 (μ-η 1:η 1 -CH 2 C(R) CR)(dppm) 2 ][CF 3 SO 3 ] ( 12 ), which upon warming to ambient temperature, in the absence of diazomethane, undergoes alkyne deinsertion to yield [RhOs(CO) 3 (η 2 -RC⋮CR)(μ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] ( 13 ). This species and the inserted product ( 12 ) appear to be in equilibrium, so reaction of 13 with diazomethane proceeds via 12 to give [RhOs(CO) 3 (η 1:η 1 -CH 2 CH 2 C(R) CR)(dppm) 2 ][CF 3 SO 2 ] ( 14 ), in which the hydrocarbyl fragment is chelating to Os and interacting with Rh via an agostic interaction with one of the Os-bound CH 2 hydrogens. Upon standing for weeks, or more rapidly upon refluxing, compound 14 transforms into an isomer ( 15 ) in which the C 4 unit has migrated from sites on Os adjacent to Rh to sites on Os remote from Rh. An X-ray structure determination of compound 15 as the BF 4 - salt confirms the geometry of this final species. Reaction of the hexafluorobutyne-bridged species [RhOs(CO) 3 (μ-η 1:η 1 -RC CR)(dppm) 2 ][CF 3 SO 3 ] (R = CF 3 ) with diazomethane does not give a product analogous to that described for dimethyl acetylenedicarboxylate, but yields the isomer 6 . These carbon−carbon bond forming processes are discussed.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.