Synthesis, Structure, and Reactivity of [{Ir(cod)(μ-OSiMe 3 )} 2 ] with Styrene and Vinylsilanes: Catalytic Activation of the Vinylic dC-H Bond Bogdan Marciniec,* Ireneusz Kownacki, and Maciej Kubicki Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland Received January 28, 2002 This paper reports the first successful synthesis of iridium-siloxide complex [{Ir(cod)(µ- OSiMe 3 )} 2 ](I), whose structure has been determined by X-ray diffraction. Complex I has an A-frame bis-square planar geometry and is a selective catalyst of silylative heterocoupling of styrene with vinyltrisubstituted silanes CH 2 dCHSiR 3 (A) (where R 3 ) Me 3 , Me 2 Ph, (OEt) 3 ), Me 2 (OSiMe 3 ), Me(OSiMe 3 ) 2 ) and/or of hydrovinylation (co-dimerization) of styrene with vinylsilanes CH 2 dCHSi(OR′) 3 (B) (where R′ ) SiMe 3 , tert-Bu). Results of a stoichiometric study of I with substrates and labeling experiments (GC-MS and 1 H NMR analysis) with the deuterated styrene indicate the exchange of the vinylic proton and a non-metallacarbene mechanism of the two reactions proceeding via generation of active Ir-H intermediates by oxidative addition of dC-H to monomeric iridium-siloxide complexes. All the data allowed us to propose a reasonable mechanism of the silylative coupling, which does not involve migratory insertion of olefin into the Ir-Si bond as well as a mechanism of the hydroviny- lation (co-dimerization) of styrene with vinyltris(trimethylsiloxy)silane. Introduction Molecular complexes incorporating M-O-Si bonds (where M ) transition metal) seem to be good models for metal complexes immobilized on silica and/or silicate surfaces. 1 While siloxide complexes of early transition elements are well-characterized, the data on the late transition metal-siloxides in molecular form have been scarce. 2 Siloxy derivatives of ruthenium, 3 nickel, 4 plati- num, 5 iron, 6 cobalt, 7 and rhodium 8-11 and to a minor extent also osmium 13 and iridium 5c have been synthe- sized and characterized spectroscopically, and the struc- tures of most of them have been resolved by X-ray studies. The complexes containing a Rh-O-Si bond have recently become a subject of great interest. These complexes included [{Rh(cod)(µ-OSiPh 3 )} 2 ], 7,8 [{Rh(di- ene)(µ-OSiMe 3 )} 2 ], where diene ) cyclooctadiene (cod) 9a,c and norbornadiene (nbd), 9c and [{Rh(CO) 2 (µ-OSiR 3 )} 2 ], where R ) Me, 10 Ph. 8a Unfortunately, the reactivity and catalytic activity of the molecular well-defined catalysts have been illustrated in only a few exemplary reac- tions. 11,12 The complex [{Rh(cod)(µ-OSiMe 3 )} 2 ] appeared to be a very effective catalyst in hydrosilylation of al- kenes 12a and silylative coupling of vinylsilanes with alkenes. 12b,c The stoichiometric reactions of the catalyst with the substrates as well as with deuterated sub- strates enabled us to establish the mechanistic path- ways of these catalytic processes. The Vaska analogue of iridium siloxide, i.e., [Ir(CO)- (PPh 3 ) 2 (OSiMe 3 )], first synthesized and characterized spectroscopically by Schmidbaur and Adlkofer, 5c is to our knowledge the only iridium complex containing a * Corresponding author. 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