Incorporation of a tripodal ligand with a (N,O,O)-donor set into a new family of nickel and cobalt spin clusters

The reaction of Ni(OAc)₂, NiX₂ (X = Cl, Br) or CoCl₂ with the proligand 2-amino-2-methyl-1,3-propanediol (ampdH₂) affords a new family of tetranuclear complexes. The syntheses of [Ni₄(OAc)₄(ampdH)₄] (1) and [M₄X₄(ampdH)₄] (M = Ni, X = Cl, 2; M = Ni, X = Br, 3; M = Co, X = Cl, 4) are reported, together with the single crystal X-ray structures of 1, 2 and 4 and the magnetochemical characterization of 1, 3 and 4. Each member of this family of complexes displays a low symmetry structure that incorporates a {M₄O₄} core unit based on a distorted cubane. Magnetic measurements reveal ferromagnetic exchange interactions for 1, 3 and 4. These give rise to S = 4 ground state spins for the tetranuclear Ni complexes and an anisotropic effective S′ = 2 ground state for the Co complex.     

Synthesis and Characterization of the Face-Centered Cubic Clusters [(Me<Subscript>3</Subscript>tacn)<Subscript>8</Subscript>M<Subscript>8</Subscript>Pt<Subscript>6</Subscript>(CN)<Subscript>24</Subscript>]<Superscript>12+</Superscript> (M = Cr,Mo)

Incorporation of a 5d transition metal into the face-centered cubic metal-cyanide cluster geometry is accomplished for the first time with the isolation of a series of compounds featuring [(Me₃tacn)₈M₈Pt₆(CN)₂₄]¹²⁺ (M = Cr, Mo) clusters. Reaction of [(Me₃tacn)Cr(CN)₃] and K₂[PtCl₄] in a boiling aqueous solution generates [(Me₃tacn)₈Cr₈Pt₆(CN)₂₄]Cl₁₂ · 27H₂O (1), wherein Pt^II centers reside at the face-centering sites and the cyanide ligands have reoriented to give Pt^II–C≡N–Cr^III linkages. The cyclic voltammogram obtained for a solution of 1 in DMSO exhibits a quasireversible reduction event centered at E _1/2 = ?1.59 V versus Cp₂Fe^0/1+. Reaction of 1 with K₂[Pt(CN)₄] in aqueous solution affords [(Me₃tacn)₈Cr₈Pt₆(CN)₂₄][Pt(CN)₄]₆ · 6H₂O (2), in which each face of the cubic cluster is capped by a staggered tetracyanoplatinate anion with a Pt–Pt separation of 3.1552(7) Å. Attempts to perform analogous cluster-forming reactions with [(Me₃tacn)Mo(CN)₃] revealed a tendency toward cluster decomposition to give mixtures of insoluble products, including [(Me₃tacn)₈Mo₈Pt₆(CN)₂₄][Pt(CN)₄]₆ · 46H₂O (3) and [(Me₃tacn)₈Mo₈Pt₆(CN)₂₄][Pt(CN)₄]_2.5[Pt(CN)₃Br]₂Br₃ · 6H₂O (4). Crystallographic analyses revealed these compounds to contain the anticipated [(Me₃tacn)₈Mo₈Pt₆(CN)₂₄]¹²⁺ cluster in fully- and partially-capped forms, respectively. Unfortunately, the insolubility of these molybdenum-containing products precluded characterization of the cluster by cyclic voltammetry.     

Asymmetric total synthesis of (-)-indicol by a carbene cyclization-cycloaddition cascade strategy

The first total synthesis of a secodolastane, (-)-indicol, has been accomplished. The key reaction is a rhodium(II)-mediated carbene cyclization-cycloaddition cascade, by which the core bicyclo[5.4.0]undecane skeleton was assembled. In this one-pot reaction, a domino series of transformations resulting in the construction of three sigma bonds and three stereocenters was realized in good yield.     

Rhodium-catalyzed [2+2+1+1] cyclocarbonylative coupling of alkynes with carbon monoxide affording tetrasubstituted p-benzoquinones

In this strategy, the tetrasubstituted benzoquinones have been prepared directly by a [2+2+1+1] cyclocarbonylative coupling reaction of internal alkynes with CO in the presence of [RhCl(CO)2]2. The low concentration of CO in the reaction is the crucial point for the chemoselective formation of tetrasubstituted benzoquinones in good to high yields. Functional groups such as chloro, methoxy, cyano, vinyl, fluoro, and carboxylate are tolerated under the reaction conditions.     

Enantioselective hydrogenation with self-assembling rhodium phosphane catalysts: influence of ligand structure and solvent

Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0-99 % ee Complexation studies and DFT calculations were performed to explain these differences.     

Copper halide-bridged ruthenium telluride carbonyl complexes: discovery of the semiconducting cluster chain polymer {[PPh4]2[Te2Ru4(CO)10Cu4Br2Cl2].THF}infinity

A new series of Te-Ru-Cu carbonyl complexes was prepared by the reaction of K(2)TeO(3) with [Ru(3)(CO)(12)] in MeOH followed by treatment with PPh(4)X (X=Br, Cl) and [Cu(MeCN)(4)]BF(4) or CuX (X=Br, Cl) in MeCN. When the reaction mixture of K(2)TeO(3) and [Ru(3)(CO)(12)] was first treated with PPh(4)X followed by the addition of [Cu(MeCN)(4)]BF(4), doubly CuX-bridged Te(2)Ru(4)-based octahedral clusters [PPh(4)](2)[Te(2)Ru(4)(CO)(10)Cu(2)X(2)] (X=Br, [PPh(4)](2)[1]; X=Cl, [PPh(4)](2)[2]) were obtained. When the reaction mixture of K(2)TeO(3) and [Ru(3)(CO)(12)] was treated with PPh(4)X (X=Br, Cl) followed by the addition of CuX (X=Br, Cl), three different types of CuX-bridged Te-Ru carbonyl clusters were obtained. While the addition of PPh(4)Br or PPh(4)Cl followed by CuBr produced the doubly CuBr-bridged cluster 1, the addition of PPh(4)Cl followed by CuCl led to the formation of the Cu(4)Cl(2)-bridged bis-TeRu(5)-based octahedral cluster compound [PPh(4)](2)[{TeRu(5)(CO)(14)}(2)Cu(4)Cl(2)] ([PPh(4)](2)[3]). On the other hand, when the reaction mixture of K(2)TeO(3) and [Ru(3)(CO)(12)] was treated with PPh(4)Br followed by the addition of CuCl, the Cu(Br)CuCl-bridged Te(2)Ru(4)-based octahedral cluster chain polymer {[PPh(4)](2)(Te(2)Ru(4)(CO)(10)Cu(4)Br(2)Cl(2)).THF}(infinity) ({[PPh(4)](2)[4].THF}(infinity)) was produced. The chain polymer {[PPh(4)](2)[4].THF}(infinity) is the first ternary Te-Ru-Cu cluster and shows semiconducting behavior with a small energy gap of about 0.37 eV. It can be rationalized as resulting from aggregation of doubly CuX-bridged clusters 1 and 2 with two equivalents of CuCl or CuBr, respectively. The nature of clusters 1-4 and the formation and semiconducting properties of the polymer of 4 were further examined by molecular orbital calculations at the B3LYP level of density functional theory.     

Hydroaminomethylation with novel rhodium-carbene complexes: an efficient catalytic approach to pharmaceuticals

Starting from [{Rh(cod)Cl}(2)] and 1,3-dimesitylimidazole-2-ylidenes the novel [RhCl(cod)(carbene)] complexes 1-5 have been synthesized, characterized, and tested in the hydroaminomethylation of aromatic olefins. The influence of different ligands and reaction parameters on the catalytic activity was investigated in detail applying 1,1-diphenylethylene and piperidine as a model system. The scope and limitations of the novel catalysts is shown in the preparation of 16 biologically active 1-amino-3,3-diarylpropenes. In general, high chemo- and regioselectivity as well as good yields of the desired products were achieved.