Site Selectivity in the Reactions of the Hexanuclear Platinum Cluster [Pt6(µ-PtBu2)4(CO)6][CF3SO3]2

The previously reported hexanuclear cluster [Pt-6(mu-PtBu2)(4)(CO)(6)](2+) [Y](2) (1-Y-2: Y=CF3SO3-) contains a central Pt-4 tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y-2 with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt-6(mu-PtBu2)(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt-6(mu-PtBu2)(4)(CO)(4)X-2] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt-6[mu-PtBu2)(4)(CO)(4)ICI] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt-6(mu-PtBu2)(4)(CO)(4)L-2](2+)[Y](2) (7-Y-2: L=(CO)-C-13; 8-Y-2: L=CNtBu; 9-Y-2: L= PMe3) were obtained by reaction of an excess of the ligand L with 1-Y-2. Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TIPF6 to afford [Pt-6(mu-PtBu2)(4) (CO)(4)L-2](2+) [Z](2) (Z=PF6-, 10-Z(2): L= MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y-2 are also prone to nucleophilic addition (Nu(-): H-, MeO-) affording the acyl derivatives [Pt-6(mu-PtBu2)(4)(CO)(4)(CONU)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt-6(mu-PtBu2)(4)(CO)(4)H-2] (14), which was more cleanly prepared by reacting 3 with NaBH4. In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt-6(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y-2: R=tBu; 16-Y-2(2-) : R=-C6H4-4-C CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y-2 are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.