Organic chemistry of dinuclear metal centres. Part 13. Synthesis, structure, and reactivity of [Ru2(CO)4(η5: η5′-C5H4CH2C5H4)

Abstract

Reaction of [Ru3(CO)12] with bis(cyclopentadienyl)methane in boiling toluene gives [Ru2(CO)4(η5:η5′-C5H4CH2C5H4)](1) in good yield. The molecular structure has been determined by X-ray diffraction. The structure was solved by heavy-atom methods and refined by least squares to give a final R 0.045 for 3 009 unique, observed diffractometer data. Crystals of (1) are orthorhombic, space group Pbca, with Z= 16 in a unit cell of dimensions a= 18.066(9), b= 14.321(6), and c= 22.156(10)A. The molecule consists of a staggered (OC)2Ru–Ru(CO)2 unit bridged by a bis(cyclopentadienylene)methane ligand which is η5-bound to each ruthenium atom. I.r. spectroscopy reveals that this structure dominates in solution, but that a low concentration of a carbonyl-bridged isomer is also present. Sequential treatment of complex (1) with LiMe, tetrafluoroboric acid, and NaBH4 affords the bis-µ-ethylidene complex [Ru2(CO)2(µ-CHMe)2(η5:η5′-C5H4CH2C5H4)](7) the structure of which has also been determined by X-ray diffraction, and solved and refined as above to a final R 0.025 for 1 813 data. Crystals of (7) are monoclinic, space group P21/n(non-standard setting of P21/c, no.14), with Z= 4 in a unit cell of dimensions a= 8.702(3), b= 12.653(4), c= 14.508(6)A, and β= 98.01(3)°. The molecule contains an (OC)Ru–Ru(CO) unit bridged by two ethylidene groups so as to give a highly folded Ru2(µ-C)2 core. The methyl groups of the ethylidenes are oriented anti with respect to a bridging bis(cyclopentadienylene)methane ligand bound in an η5 : η5′ fashion as for complex (1). Although the µ-C ⋯µ-C distance in complex (7) is relatively short (3.11 A), thermolysis induces alkylidene linking less efficiently than for related η-C5H5 complexes with a non-folded geometry, a difference attributed to the reduced flexibility in (7) arising from the coupling of the η-C5 rings. Reaction of complex (1) with Li[BHEt3]–water affords the µ-methylene complex [Ru2(CO)2(µ-CO)(µ-CH2)(η5:η5′-C5H4CH2C5H4)]. Photolysis of (1) in the presence of diphenylacetylene gives [Ru2(CO)2(µ-CO)(µ-σ: σ-C2Ph2)(η5: η5′-C5 H4CH2C5H4)], containing a ‘parallel’ two-electron alkyne ligand. The Ru–Ru bond of (1) is cleaved by iodine to yield [Ru2I2(CO)4(η5:η5′-C5H4CH2C5H4)], which is readily converted into[Ru2Me2(CO)4(η5: η5′- C5H4CH2C5H4)] on treatment with Li[CuMe2].