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, tBuNC, and alkynes

Article abstract of DOI:10.1021/ja00087a025

An incomplete cubane-type cluster [Mo₃S₄(H₂O)₉]Cl₄ (1) reacted with Pd black in aqueous HC1 to give a mixed-metal cubane-type cluster [PdMo₃S₄(H₂O)₉Cl]Cl₃ (2). Treatment of 2 with 3.3 equiv of 1,4,7-triazacyclononane (tacn) afforded a well-defined single cubane-type cluster [PdMo₃S₄(tacn)₃Cl]Cl₃ (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 3·4H₂O: orthorhombic, space group P2₁2₁2₁ a = 17.549(3) A?, V = 20.032(4) A?, c = 10.256(2) A?, V = 3605 A?³, Z = 4, and R (R_w) = 0.051 (0.062) for 4014 reflections. For 4·24H₂O: triclinic, space group P1, a = 15.799(4) A?, b = 18.079(6) A?, c = 11.873(1) A?, α = 108.75(2)^o, β = 108.73(1)^o, γ = 70.87(3)^o, V = 2944 A?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 ^tBuNC coordinated to the tetrahedral Pd site, by the initial anion exchange forming [PdMo₃S₄(tacn)₃C1]X₃ (8a, X = ClO₄; 8b, X = BF₄; 8c, X = PF₆) followed by treatment with these molecules. The alkene cluster [PdMo₃S₄(tacn)₃(cis-HOCH ₂CH=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′·2H₂O: monoclinic, space group P2₁/m, a = 12.314(1) A?, b = 12.732(2) A?, c = 15.736(2) A?, β= 94.01(1)^o, V = 2461 A?³, Z = 2, R (R_w) = 0.068 (0.081) for 2743 reflections. For 6a·3H₂O: orthorhombic, space group Pbca, a = 15.485(13) A?, b = 23.900(6) A?, c = 23.326(7) A?, V = 8633 A?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 R²C≡CCOOR¹ with alcohols R³OH to give the trans addition products (Z)-(R³O)R²C=CHCOOR¹ (R¹ = Me, Et, ^tBu, Ph, R² = H, R³ = Me; R¹ = R³ = Me, R² = COOMe, Me; R¹ = Ph, R² = Et, R³ = Me; R¹ = Me, R² = H, R³ = Et, PhCH₂) with quite high selectivity under mild conditions with retention of the cluster core.