Organosulphur–transition-metal chemistry. Part 5. Face bonding of cycloheptatrienyl and cyclo-octatetraene ligands in sulphur–ruthenium clusters: crystal and molecular structure of [Ru3(CO)6(µ3-SBut){µ3-(η7-C7H7)}]

Abstract

The sulphur–ruthenium cluster complex [Ru₃H(CO)₉(µ₃-SBu^t)] reacts with cycloheptatriene in boiling heptane to give [Ru₃(CO)₆(µ₃-SBu^t){µ₃-(η⁷-C₇H₇)}] and [Ru₂(CO)₄(µ-SBu^t){µ-(η⁷-C₇H₇)}]. The former contains a face-bridging cycloheptatrienyl ligand, established through an X-ray diffraction study. Crystals are monoclinic, space group C2/c, with eight molecules in a unit cell of dimensions a= 14.875(6), b= 8.902(6), c= 30.977(2)Å, and β= 94.785(4)°. The structure has been solved by conventional techniques, revealing the ruthenium atoms to be present in isosceles triangular units disordered in ca. 2 : 1 ratio via a 60° rotation in the ruthenium plane. Refinement was by least squares for 3 860 data to R 0.041. The ruthenium triangle is bridged on one side by a µ₃-SBu^t ligand and on the other by a face-bonded C₇H₇ ring which is planar and lies parallel to the face at a distance of 2.07 Å. The hydrogens of the C₇H₇ ligand are inclined away from the metal triangle as a result of π-orbital reorientation. The ruthenium–carbon (ring) distances are compatible with bonding of the C₇H₇ ligand in η², η²,η³ fashion to the metal triangle, each atom of which bears two terminal carbonyl groups, but n.m.r. spectra show that the ring rotates freely relative to the face in solution. The high-field ¹³C n.m.r. shift (38.7 p.p.m.) for the µ₃-(η⁷-C₇H₇) ligand is characteristic, comparing with 61.0 p.p.m. for similarly fluxional µ-(η⁷-C₇H₇) in [Ru₂(CO)₄(µ-SBu^t){µ-(η⁷-C₇H₇)}]. Treating [Ru₃(CO)₆(µ₃-SBu^t){µ₃-(η⁷-C₇H₇)}] with CO results in cluster fragmentation to yield [Ru₂(CO)₄(µ-SBu^t){µ-(η⁷-C₇H₇)}], a reaction attributed to the ability of both SBu^t and C₇H₇ ligands to vary their mode of co-ordination. Reactions of [Ru₃H(CO)₉(µ-SBu^t)] with cyclo-octatetraene, cyclo-octatriene, and cyclo-pentadiene also effect cluster breakdown, forming [Ru₂(CO)₄(µ-SBu^t){µ-(η⁷-C₈H₉)}] or [Ru₂(µ-H)(CO)₂(µ-SBu^t)(η-C₅H₅)₂].

The sulphur–ruthenium cluster in [Ru₃H₂(CO)₉(µ₃-S)] is less easily destroyed. The reaction with cyclo-octatetraene provides [Ru₃(CO)₆(µ₃-S){µ₃-(η⁸-C₈H₈)}], containing rare face-bonded fluxional C₈H₈, while with cycloheptatriene the complexes [Ru₃(CO)₄(µ₃-S)(η⁵-C₇H₉){µ₃-(η⁷-C₇H₇)}], [Ru₄(CO)₆(µ₃-S)(η⁵-C₇H₉){µ₃-(η⁷-C₇H₇)}], and [Ru₄(CO)₈(µ₄-S){µ-(η⁷-C₇H₇)}₂] are obtained, partly characterised using the ¹³C n.m.r. criterion of the C₇H₇ bonding mode.