Preparation and Reactions of Organoruthenium(IV) Complexes

Oxidative addition of Ru(η⁵-C₅R₅)L₂X (R = H or CH₃; L=CO or Ph₃P; X=C1 or Br) or [Ru(η⁵-C₅Me₅)Cl₂]2 with allylic halides gives new series of allylruthenium(F) complexes, Ru-(η⁵-C₅R₅)(η³-CH₂CHR'CH₂)X₂. The structure of the representative one (R=CH₃; X=Br) was determined unequivocally by single crystal X-ray analysis and ¹H-and ^l3C-NMR spectroscopy. These allylruthenium (IV) complexes and the known Ru (1-3: 6-7: 10-12-η-C₁₂H₁₈) Cl₂ were successfully methylated by means of CH₈MgX or equimolar quantity of CH₃Li to yield thermally stable allylhalomethylruthenium(IV) complexes. These alkyl complexes induces selective reductive elimination accompanying the carbon-carbon bond formation between methyl and allyl ligands in the presence of CO, t-BuNC, etc., at elevated temperatures. Alkylation with an excess CH₃Li or Me₃Al furnished purely organometallic dimethyl complexes, Ru(η⁵-C₅R₅)(η³-C₃H₅)(CH₃)₂, which were converted to Ru(C₅R₅)(η³-CH₂CHCH-CH₃)L (L=CO or t-BuNC) upon heating with evolution of methane. Alternatively, extremely facile β-hydride elimination followed by the OH bond-forming reductive elimination took place even below — 20°C, when Et₃Al or BrMg (CH₂)₄MgBr were employed as alkylating reagents. The reactivity of the Ru(IV)-C bonds are, therefore, in the following order, β-elimination>reductive elimination to form C-H bonds> reductive elimination to form C-C bonds. It is noteworthy that the insertion of CO, t-BuNC, or alkenes into the Ru(IV)-C bonds was never observed at all. On the other hand, cationic ruthenium active species, [Ru(C₅R₅) (η⁴-butadiene)]⁺ induces oxidative cyclization with the second molecule of butadiene to give stoichiometric and catalytic linear di- and trimerization (R = H) or cyclodimerization (R=CH₃) of butadiene.