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 cluster cores of the type [Re 6 (μ 3 -Q) 8 ] 2+ (Q = S, Se) has recently been realized in this laboratory by the protocol of dimensional reduction of solid frameworks containing bridged cores. A new series of triethylphosphine-ligated hexanuclear rhenium clusters has been prepared from the starting cluster [Re 6 S 8 Br 6 ] 4 - by ligand substitution of terminal bromide ligands using excess Et 3 P in DMF at elevated temperatures. These clusters are of the general formula [Re 6 S 8 (PEt 3 ) n Br 6 - n ] ( n - 4)+ ( n = 2−6). The following compounds were synthesized: (Bu 4 N) 2 [ cis -Re 6 S 8 (PEt 3 ) 2 Br 4 ] (in limited quantity), (Bu 4 N) 2 [ trans -Re 6 S 8 (PEt 3 ) 2 Br 4 ], (Bu 4 N)[ mer -Re 6 S 8 (PEt 3 ) 3 Br 3 ], (Bu 4 N)[ fac -Re 6 S 8 (PEt 3 ) 3 Br 3 ], cis -[Re 6 S 8 (PEt 3 ) 4 Br 2 ], trans -[Re 6 S 8 (PEt 3 ) 4 Br 2 ], [Re 6 S 8 (PEt 3 ) 5 Br]Br, and [Re 6 S 8 (PEt 3 ) 6 ]Br 2 . All clusters exhibit characteristic 31 P NMR spectra, and all except (Bu 4 N)[ fac -Re 6 S 8 (PEt 3 ) 3 Br 3 ] have been characterized by X-ray crystallography. The [Re 6 S 8 ] 2+ core is analogous to the [Re 6 Se 8 ] 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 -[Re 6 S 8 (PEt 3 ) 2 Br 4 ] 2 -, are accessible with the [Re 6 S 8 ] 2+ core but not with [Re 6 Se 8 ] 2+ . This set of clusters, together with [Re 6 Se 8 (PEt 3 ) n I 6 - n ] (n - 4)+ ( n = 3−6) prepared earlier, constitute an array of building blocks for the potential synthesis of multicluster assemblies by halide ligand substitution with bridging ligands or with ligands subject to removal by thermolysis.