Synthesis and Reactivity of Indenyl Ruthenium(II) Complexes Containing the Labile Ligand 1,5-Cyclooctadiene (COD): Catalytic Activity of [Ru(η5-C9H7)Cl(COD)

Abstract

The treatment of [RuCl2(COD)]n with KC9H7 in THF leads to the formation of [Ru(η5-C9H7)Cl(COD)] (1) (80% yield) in a one-pot synthesis. Complex 1 is also formed by the reaction of [RuCl2(COD)]n with NaC9H7 in THF followed by treatment of the intermediate complex [Ru(η5-C9H7)(η2-η3-C8H11)] (2) with HCl. Substitution of the labile COD ligand by bulky phosphines PR3 (R = Cy, iPr3) can be achieved at room temperature in THF to give 16-electron species [Ru(η5-C9H7)Cl(PR3)], which react with CO (1 atm) to afford complexes [Ru(η5-C9H7)Cl(CO)(PR3)] (R = Cy (3a), iPr (3b)). Chelate complexes [Ru(η5-C9H7)Cl{(κ2-P,N)-o-Ph2PC6H4C(H)NtBu}] (4) and [Ru(η4-C9H7){κ1-(P)-Ph2PCH2C(O)tBu}{κ2-(P,O)Ph2PCHC(O)tBu}] (5) have been similarly prepared by reaction with the bidentate ligands. [Ru(η5-C9H7)Cl(NBD)] (NBD = norbornadiene) (6) has been prepared through an exchange reaction of 1 with NBD and characterized by X-ray diffraction. Neutral complexes [Ru(η5-C9H7)X(COD)] (X = FBF3 (7), N3 (8)) were prepared from complex 1 by metathesis reactions of the chloride ligand by AgBF4 and NaN3 respectively. The treatment of 7 in CH2Cl2 with an excess of pyridine and acetonitrile gives cationic complexes [Ru(η5-C9H7)(COD)L][BF4] in good yield (L = py (9), CH3CN (10)). The structure of complex 9 has been determined by X-ray diffraction. Complex 1 catalyzes [2+2] and [4+2] cycloaddition reactions of norbornene and 1,5-cyclooctadiene with alkynes to give exotricyclic [4.2.1.0] coupling products and exotricyclo [4.2.2.0]dec-7-enes, respectively. These processes take place with high efficiency and selectivity. Complex 1 is also active in the catalytic hydration of terminal alkynes to afford ketones in high yield and selectivity.