The interaction of hydrogen with tri-µ-chloro-hexakis(trimethylsilylmethyl)-triangulo-trirhenium(III), its adducts with carbon monoxide, triphenylphosphine, and pyridine and with tri-µ-chloro-chloropentakis-(trimethylsilylmethyl)-triangulo-trirhenium(III). The X-ray crystal structures of hydridononakis(trimethylsilylmethyl)bis[tri-µ-chloro-triangulo-trirhenium(III)], tri-µ-chloro-chlorohydridotetrakis(trimethyl-silylmethyl)(triphenylphosphine)-triangulo-trirhenium(III), and syn,syn,-anti-trichloro-tris(µ-trimethylsilylmethyl)-tris(trimethylsilylmethyl)-triangulo-trirhenium(III)

Abstract

The interaction of tri-µ-chloro-hexakis(trimethylsilylmethyl)-triangulo-trirhenium(III), Re₃(µ-Cl)₃(CH₂SiMe₃)₆, with dihydrogen in tetrahydrofuran leads to a hexanuclear hydrido-alkyl (Me₃SiCH₂)₅(µ-Cl)₃Re₃–Re₃(µ-Cl)₃H-(CH₂SiMe₃)₄,(1), whose structure has been determined by X-ray diffraction. Crystals are triclinic, space group p, with a= 15.950(5), b= 16.351(6), c= 16.386(6)Å, α= 62.31(2), β= 94.25(3), γ= 99.77(3)°, and Z= 2. The structure was solved and refined to an R of 0.055 using 6 796 unique observed data (out of 10 203 measured). The two Re₃ triangles are linked by a single Re–Re bond of length 2.993(1)Å which constitutes, in each case, one of the terminal, out-of-plane bonds on six-co-ordinated Re. The Re–Re distances in the Re₃ triangle [2.390–2.420(1)Å] are slightly disturbed by the asymmetry of the co-ordinated ligands.

Hydrogenation of Re₃Cl₃(CH₂SiMe₃)₆ in benzene, by contrast, produces a hexanuclear hydrido-alkyl, Re₆(µ-Cl)₆H₆(CH₂SiMe₃)₆, (2), for which a structure with two triangulo-Re₃Cl₃ units linked by alkyl bridges and with terminal hydrogen atoms is proposed.

The interaction of the alkyl Re₃(µ- Cl)₃Cl(CH₂SiMe₃)₅, which has a terminal Re–Cl group, with hydrogen in the presence of triphenylphosphine gives a green complex, Re₃(µ-Cl)₃ClH(CH₂SiMe₃)₄(PPh₃), (3), whose structure has been determined by X-ray diffraction. These crystals are also triclinic, space group p with a= 17.732(3), b= 13.212(3), c= 11.723(4)Å, α= 90.95(3), β= 95.04(3), γ= 83.74(2)°, and Z= 2. The final R value is 0.063 for 3 704 (8 536) observed data. The Re–Re distances in the Re₃ triangle [2.382(1)–2.411(2)Å] show the expected variation with rhenium co-ordination number. The phosphine is quite weakly bound [Re–P = 2.617(7)Å].

The interaction of hydrogen with the adducts Re₃(µ-Cl)₃(CH₂SiMe₃)₆L₃, L = CO, PPh₃, pyridine (py), and H₂O, has been studied. For L = CO and PPh₃, reductive cleavage of the cluster occurs to give the rhenium (II) metal–metal bonded dimers Re₂Cl₂(CH₂SiMe₃)₂(CO)₂, (4), and Re₂Cl₂(CH₂SiMe₃)₂(PPh₃)₂, (5). For L = py the triangulo-trirhenium cluster is retained in the paramagnetic rhenium(II) alkyl Re₃(µ-Cl)₃(CH₂SiMe₃)₃(py)₃, (6), whose e.s.r. spectrum is discussed. For L = H₂O, a polynuclear cluster, probably [Re₃(µ-Cl)₃(CH₂SiMe₃)₃(OH₂)₃]₆, (7), is obtained.

The hydride (2) isomerises alk-1-enes under nitrogen and hydrogenates them under hydrogen, but the catalytic reaction decays due to the formation of a non-hydride hexanuclear species, Re₆(µ-Cl)₆(CH₂SiMe₃)₆, (8). Thermal decomposition of (2) leads to a dodecameric species, Re₁₂(µ-Cl)₁₂(CH₂SiMe₃)₆, (9).

The hydrogenation of the red supernatant from the synthesis of Re₃(µ-Cl)₃(CH₂SiMe₃)₆ leads to a red isomer of this blue species, which X-ray structural determination shows to have bridging alkyl groups and to be Re₃Cl₃(µ-CH₂SiMe₃)₃(CH₂SiMe₃)₃, (10), and syn,syn,anti-terminal chlorine atoms. The compound is monoclinic, space group P2₁/n, with a= 17.939(2), b= 11.280(1), c= 22.933(4)Å, β= 109.98(1)°, and Z= 4. The final R value is 0.048 for 5 293 (8 487) observed data. The Re–Re distances here are 2.337–2.359(1)Å and are shorter than in the isomeric chloride-bridged species. Small distortions in the Re₃C₃ cluster are attributed to intramolecular crowding.

New aryl triangulo-clusters Re₃(µ-Cl)₃R₆, R = C₆H₅, (11), and C₆H₄Me-p, (12), and the bridged methyl Re₃(µ-CH₃)₃(CH₂SiMe₃)₆(13), are described.