Weng Sang Ng

A triple-decker complex with a central metallabenzene

It was established in the 1980s that benzene can act as a bridging ligand to form triple-decker complexes.[1, 2] Recent studies on the chemistry of metallabenzenes revealed that transition metal containing metallabenzenes can display chemical properties similar to those of benzene.[3] For example, they can undergo electrophilic substitution reactions[4] and can form 6-metallabenzene complexes.[5] These results imply that metallabenzenes may also function as bridging ligands in tripleor 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(H2O)(nbd)]BF4 (1; Cp* -C5Me5, nbd norbornadiene)[6] with HCO2Na in dry THF produced the bimetallic complex 2 along with nortricyclene and a small amount of the known complex [Cp*RuH(nbd)] (Scheme 1).[7] Analytically pure samples of 2 were obtained by column chromatography. The structure of 2 was deduced on the basis of its mass spectrum and 1H as well as 13C{1H} NMR spectroscopic data. The ion peak at m/z 566 corresponding to the composition {Cp* 2 Ru2(C7H8)} suggests that 2 is a bimetallic complex. The 1H and 13C{1H} NMR data indicate that 2 is a fluxional hydride complex. The room-temperature 1H NMR spectrum in C6D6 displayed a hydride signal at 16.57 and a broad Cp* signal at 1.88. However, the 1H NMR spectrum at 250 K in CD2Cl2 showed a sharp hydride signal at 16.85 and two Cp* signals at 1.77 and 1.85, that is, the two Ru atoms in 2 are inequivalent at this temperature. The presence of the bridging C7H7 ligand is supported by its 13C and 1H NMR spectroscopic data. In particular, the 13C{1H} NMR spectrum at 250 K in CD2Cl2 showed the signals of the and -CH groups of the , vinylic group at 156.31 and 60.84, respectively; that of the bridgehead CH group at 47.02; and those of the olefinic CH groups of the cyclopentadiene at 26.24, 49.86, 58.86, and 66.37. In the 1H NMR spectrum, the signals of the and -CH groups of the , -vinylic group were observed at 5.94 and 3.91, that of the bridgehead proton at 3.47, and Scheme 1. Preparation of the triple-decker complex 4.