Reaction of Pentafulvene Titanium and Zirconium Complexes with Phosphorus Ylides: Stoichiometric Reactions and Catalytic Intramolecular Proton Shuttles
Oswald T., Fischer M., Struckmann N., Schmidtmann M., Beckhaus R.
The reaction of penta- A nd benzofulvene complexes of group 4 (M = Ti, Zr) with different phosphorus ylides is reported. Employing the bis(Î• 5 :Î• 1 -pentafulvene)titanium complexes Ti1a and Ti1b, the reactions with the corresponding phosphorus ylides Y1-5 result in a spontaneous single C-H bond activation and metallocene ylide complexes Ti2a-e can be isolated in good yields. On the basis of these results, this reactivity pattern has been extended to the mono(Î• 5 :Î• 1 -pentafulvene) and-benzofulvene complexes Ti3, Zr1a,b, and Zr1a,b-benzo. Transferring this to the titanium complex Ti3, an additional equilibrium between the reaction product (Î• 5 -C 5 Me 5 )(Î• 5 -Cp Ad )Ti(Cl)CHPPh 3 (Ti4a) and the corresponding "tuck-in" complex (Î• 5 :Î• 1 -C 5 Me 4 CH 2 )(Î• 5 -Cp Ad )TiCl (Ti4b) can be observed. In Ti4b, a methyl group of the Cp∗-ligand is activated by the coordinated phosphorus ylide. Using this intramolecular C-H activation, Ti4b can be synthesized by catalytic amounts (3 mol %) of the phosphorus ylide Y1 in quantitative yield. Subsequently, the reaction of Ti4b with different carbonyl and nitrile compounds has been investigated. In both cases, an insertion of the functional group into the newly formed Ti-CH 2 bond is observed, and the insertion products Ti5-9 are isolated in good yields. Using a sterically demanding nitrile, the titanium-imine complex Ti7 is isolated. Upon heating of Ti7, a thermally induced subsequent nonreversible 1,3-H-shift can be observed, forming the titanium-enamine complex Ti7a. With reduced steric demand of the appropriate nitrile, this shift directly takes place even under mild reaction conditions with no observation of the titanium-imine species. By utilization of acetonitrile as substrate, a dimeric titanium-imine-enamine complex Ti10 is formed, due to an occurring subsequent C-C bond formation reaction.