LIGAND SUBSTITUTION-REACTIONS OF [RE6S8BR6](4-) - A BASIS-SET OF RE6S8 CLUSTERS FOR BUILDING MULTICLUSTER ASSEMBLIES

Access to the molecular solution chemistry of face-capped octahedral c luster cores of the type [Re-6(mu(3)-Q)(8)](2+) (Q = S, Se) has recent ly been realized in this laboratory by the protocol of dimensional red uction of solid frameworks containing bridged cores. Anew series of tr iethylphosphine-ligated hexanuclear rhenium clusters has been prepared from the starting cluster [Re6S8Br6](4-) by ligand substitution of te rminal bromide Ligands using excess Et3P in DMF at elevated temperatur es. These clusters are of the general formula [Re6S8(PEt3)(n)Br6-n]((n -4)+) (n = 2-6). The following compounds were synthesized: (Bu4N)(2)[c is-Re6S8(PEt3)(2)Br-4] (in limited quantity), (Bu4N)(2)[trans-Re6S8(PE t3)(2)Br-4], (BU4N)[mer-Re6S8(PEt3)(5)Br-3], (BU4N)[fac-Re6S8(PEt3)(3) Br-3], cis-[Re6S8(PEt3)(4)Br-2], trans-[Re6S8(PEt3)(4)Br-2], [Re6S8(PE t3)(5)Br]Br, and [Re6S8(PEt3)(6)]Br-2. All clusters exhibit characteri stic P-31 NMR spectra, and all except (Bu4N)[fac-Re6S8(PEt3)(3)Br-3] h ave been characterized by X-ray crystallography. The [Re6S8](2+) core is analogous to the [Re6S8](2+) core also under investigation in this laboratory, but it has the advantage of increased thermal control over the substitution process. Both disubstituted isomers. cis- and trans- [Re6S8(PEt3)(2)-Br-4](2-), are accessible with the [Re6S8](2+) core bu t not with [Re6Se8](2+). This set of clusters, together with [Re6Se8(P Et3)(n)I6-n]((n-4)+) (n = 3-6) prepared earlier, constitute an array o f building blocks for the potential synthesis of multicluster assembli es by halide Ligand substitution with bridging ligands or with ligands subject to removal by thermolysis.