SYNTHESES OF MIXED-METAL SULFIDE CUBANE-TYPE CLUSTERS WITH THE NOVEL PDMO3S4 CORE AND REACTIVITIES OF THE UNIQUE TETRAHEDRAL PD SITE SURROUNDED BY SULFIDE LIGANDS TOWARD ALKENES, CO, (T)BUNC, AND ALKYNES

An incomplete cubane-type cluster [Mo3S4(H2O)(9)]Cl-4 (1) reacted with Pd black in aqueous HCl to give a mixed-metal cubane-type cluster [PdMo3S4(H2O)(9)Cl]Cl-3 (2). Treatment of 2 with 3.3 equiv of 1,4,7-triazacyclononane (tacn) afforded a well-defined single cubane-type cluster [PdMo3S4(tacn)(3)Cl]Cl-3 (3), while an anion metathesis of 2 by 4-toluenesulfonate (TsO) resulted in the formation of a double cubane-type cluster [Pd2Mo6S8(H2O)(18)] (OTs)(8) (4). Detailed structures of both 3 and 4 have been determined by X-ray crystallography. Crystal data for 3.4H(2)O: orthorhombic, space group P2(1)2(1)2(1), a = 17.549(3) Angstrom, b = 20.032(4) Angstrom, c = 10.256(2) Angstrom, V = 3605 Angstrom(3), Z = 4, and R (R(w)) = 0.051 (0.062) for 4014 reflections. For 4.24H(2)O: triclinic, space group P1, a = 15.799(4) Angstrom, b = 18.079(6) Angstrom, c = 11.873(1) Angstrom, alpha = 108.75(2)degrees, beta = 108.73(1)degrees, gamma = 70.87(3)degrees, V = 2944 Angstrom(3), Z = 1, R (R(w)) = 0.028 (0.036) for 10 089 reflections. Cluster 3 was converted into a series of single cubane-type clusters [PdMo3S4(tacn)(3)(L)](4+) containing alkenes, CO, and (t)BuNC coordinated to the tetrahedral Pd site, by the initial anion exchange forming [PdMo3S4(tacn)(3)Cl]X(3) (8a, X = ClO4; 8b, X = BF4; 8c, X = PF6) followed by treatment with these molecules. The alkene cluster [PdMo3S4(tacn)(3)(cis-HOCH2CH=CHCH2OH)](ClO4)(4) (5a') and the carbonyl cluster [PdMo3S4(tacn)(3)(CO)]Cl(ClO4)(3) (6a) have been fully characterized by X-ray analyses. Crystal data for 5a'.2H(2)O: monoclinic, space group P2(1)/m, a = 12.314(1) Angstrom, b = 12.732(2) Angstrom, c = 15.736(2) Angstrom, beta = 94.01(1)degrees, V = 2461 Angstrom(3), Z = 2, R (R(w)) = 0.068 (0.081) for 2743 reflections. For 6a.3H(2)O: orthorhombic, space group Pbca, a = 15.485(13) Angstrom, b = 23.900(6) Angstrom, c = 23.326(7) Angstrom, V = 8633 Angstrom(3), Z = 8, and R (R(w)) = 0.061 (0.069) for 7761 reflections. Interestingly, cluster 8c catalyzes the reaction of a series of alkynic acid esters R(2)C-CCOOR(1) with alcohols R(3)OH to give the trans addition products (Z)-(R(3)O)R(2)C=CHCOOR(1) (R(1) = Me, Et, (t)Bu, Ph, R(2) = H, R(3) = Me; R(1) = R(3) = Me, R(2) = COOMe, Me; R(1) = Ph, R(2) = Et, R(3) = Me; R(1) = Me, R(2) = H, R(3) = Et, PhCH(2)) with quite high selectivity under mild conditions with retention of the cluster core.