Synthesis and Structures of Solvated Monoclusters and Bridged Di- and Triclusters Based on the Cubic Building Block [Re(6)(&mgr;(3)-Se)(8)](2+).

The cluster formulated as [Re(6)Se(7)(SeH)I(6)](3)(-) has been previously shown to undergo ligand substitution reactions to generate the family [Re(6)Se(8)(PEt(3))(n)()I(6)(-)(n)()](()(n)()(-)(4)+) (n = 3-6), several members of which form solvate clusters upon treatment with Ag(I) in acetonitrile. Here it is demonstrated that additional de-iodination reactions afford solvate clusters useful in building up bridged cluster arrays. In dichloromethane/solv (5:1 v/v) in the presence of 2 equiv of AgSbF(6) at room temperature, trans-[Re(6)Se(8)(PEt(3))(4)I(2)] forms trans-[Re(6)Se(8)(PEt(3))(4)(solv)(2)](2+) (solv = MeCN (5), DMF (6), Me(2)SO (7)). The hexaiodo cluster with 6 equiv of AgSbF(6) gives the fully solvated clusters [Re(6)Se(8)(solv)(6)](2+) (solv = DMF (9), Me(2)SO (10), py (11)). In refluxing chlorobenzene for 3 days, [Re(6)Se(8)(PEt(3))(5)(MeCN)](2+) (1) and 4,4'-bipyridine (4,4'-bpy) yield [Re(6)Se(8)(PEt(3))(5)(4,4'-bpy)](2+) (12); similarly, cis- and trans-[Re(6)Se(8)(PEt(3))(4)(MeCN)(2)](2+) afford the cis- and trans-14 isomers, respectively, of [Re(6)Se(8)(PEt(3))(4)(4,4'-bpy)(2)](2+). Clusters 1 and 12 (or 1 and 1/2 equiv of 4,4-bpy) under the same conditions afford the bridged dicluster {[Re(6)Se(8)(PEt(3))(5)](2)(4,4'-bpy)}(4+) (15). The related diclusters {[Re(6)Se(8)(PEt(3))(5)](2)(L-L)}(4+) (L-L = 4,4'-py(2)C(2)H(2) (16), 4,4'-py(2)C(2)H(4) (17) (4,4'-py(2)C(2)H(2) = trans-1,2-bis(4-pyridyl)ethylene, 4,4'-py(2)C(2)H(4) = trans-1,2-bis(4-pyridyl)ethane)) are obtained by analogous methods. Reaction of 14 and 2 equiv of 1 in refluxing dichloromethane produces the linear tricluster {[Re(18)Se(24)(PEt(3))(14)(4,4'-bpy)(2)}(6+). All clusters were isolated as SbF(6)(-) salts in yields of ca. 60-90% and were characterized by their (1)H and (31)P NMR spectra and by mass spectrometry. In addition, the structures of 10 clusters (5-7, 9-12, 14-16) were confirmed by X-ray structure determinations. All clusters are based on the cubic [Re(6)(&mgr;(3)-Se)(8)](2+) core whose dimensions are insensitive to the nature and substitution pattern of the ligands. All substitution reactions, as indicated, proceed with retention of stereochemistry. Appropriate choice of solvate cluster leads to the unambiguous formation of 14-17, and should allow the construction of these and other cluster array shapes with variable bridging ligands. On the basis of voltammetric and EPR properties, clusters originally described as the monoprotonated species [Re(6)Se(7)(SeH)I(6)](3)(-) and [Re(6)S(7)(SH)Br(6)](3)(-) are reformulated as the oxidized 23-electron clusters [Re(6)Se(8)I(6)](3)(-) and [Re(6)S(8)Br(6)](3)(-).