It was established in the 1980s that benzene can act as a bridging ligand to form triple-decker complexes. [1, Recent studies on the chemistry of metallabenzenes revealed that transition metal containing metallabenzenes can display chemical properties similar to those of benzene. For example, they can undergo electrophilic substitution reactions and can form h 6 -metallabenzene complexes. These results imply that metallabenzenes may also function as bridging ligands in triple-or poly-decker complexes. However, such complexes have not yet been reported, although the possibility of obtaining triple-decker complexes with a central metallabenzene was suggested in 1994. [5e] Here we describe the synthesis and characterization of the first tripledecker complex with a central metallabenzene.
Treatment of [Cp*Ru(H 2 O)(nbd)]BF 4 (1; Cp* h 5 -C 5 Me 5 , nbd norbornadiene) with HCO 2 Na in dry THF produced the bimetallic complex 2 along with nortricyclene and a small amount of the known complex [Cp*RuH(nbd)] (Scheme 1). Analytically pure samples of 2 were obtained by column chromatography. The structure of 2 was deduced on the basis of its mass spectrum and 1 H as well as 13 C{ 1 H} NMR spectroscopic data. The ion peak at m/z 566 corresponding to the composition {Cp* 2 Ru 2 (C 7 H 8 )} suggests that 2 is a bimetallic complex. The 1 H and 13 C{ 1 H} NMR data indicate that 2 is a fluxional hydride complex. The room-temperature 1 H NMR spectrum in C 6 D 6 displayed a hydride signal at d Γ 16.57 and a broad Cp* signal at d 1.88. However, the 1 H NMR spectrum at 250 K in CD 2 Cl 2 showed a sharp hydride signal at d Γ 16.85 and two Cp* signals at d 1.77 and 1.85, that is, the two Ru atoms in 2 are inequivalent at this temperature. The presence of the bridging C 7 H 7 ligand is supported by its 13 C and 1 H NMR spectroscopic data. In particular, the 13 C{ 1 H} NMR spectrum at 250 K in CD 2 Cl 2 showed the signals of the aand b-CH groups of the m-s,pvinylic group at d 156.31 and 60.84, respectively; that of the bridgehead CH group at d 47.02; and those of the olefinic CH groups of the cyclopentadiene at d 26. 24, 49.86, 58.86, and 66.37. In the 1 H NMR spectrum, the signals of the aand b-CH groups of the m-s,p-vinylic group were observed at d 5.94 and 3.91, that of the bridgehead proton at d 3.47, and Scheme 1. Preparation of the triple-decker complex 4.