title: Metal fragment isomerisation upon grafting a d(2) ML4 perhydrocarbyl Os complex on a silica surface: origin and consequence.
abstract: Grafting of Os bisalkylidene complexes, [Os(=CHtBu)(2)(CH(2)tBu)(2)], on a silica partially dehydroxylated at 700 degrees C selectively yields an alkylidyne complex [([triple bond]SiO)Os([triple bond]CtBu)(CH(2)tBu)(2)] according to mass balance analysis, IR and solid state NMR spectroscopies, but 70% of the silanols remains unreacted. Grafting corresponds to a replacement of one alkyl by a siloxy ligand and induces the isomerisation of the metal fragment from a bis-alkylidene to an alkyl alkylidyne. Molecular (B3PW91) and periodic DFT-calculations show that the bis-alkylidene is the energetically favoured isomer for the perhydrocarbyl complex, while the alkyl alkylidyne isomer is more stable when one of the alkyl ligands is replaced by a siloxy ligand. The change of the nature of the ligand is accompanied with a change of geometry: from a distorted tetrahedral structure for [Os(=CHtBu)(2)(CH(2)tBu)(2)] to a butterfly-geometry with apical siloxy and alkylidyne ligands for [([triple bond]SiO)Os([triple bond]CtBu)(CH(2)tBu)(2)]. Finally, DFT calculations show that grafting occurs via a sigma-bond metathesis between the silanol and a metal-alkyl bond and not through the typical addition of the silanol onto the alkylidene ligand.
authors.affiliation: Institut de Chimie de Lyon, C2P2, CNRS-Université Lyon 1-ESCPE Lyon, F-308-43 Boulevard du 11 Novembre 1918, F-69616, Villeurbanne Cedex, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Berthoud
authors.forename: Nuria
authors.initials: N
authors.lastname: Rendón
authors.forename: Frédéric
authors.initials: F
authors.lastname: Blanc
authors.forename: Xavier
authors.initials: X
authors.lastname: Solans-Monfort
authors.forename: Christophe
authors.initials: C
authors.lastname: Copéret
authors.forename: Odile
authors.initials: O
authors.lastname: Eisenstein