Preparation and Reactions of Organoruthenium(IV) Complexes

Abstract

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. © 1991, The Chemical Society of Japan. All rights reserved.