Synthesis and Reactivity of 10- and 12-Vertex Cobalt−Monocarborane Anions Containing Multiple Metal Centers

Distorted commo-Cobaltacarboranes Based on the 5,6-Dicarba-nido-decaborane(12): The First Bimetal Cobalt-Copper Zwitterion-Containing Cluster with Four (B-H)4···Cu Bonds Not Showing Fluxional Behavior in Solution

Treatment of a recently reported complex [Ph₄P][closo,nido-CoH(2,4-C₂B₈H₁₀)(7,8-C₂B₈H₁₁)] (1) either by H₂O₂ in acetone or NaH in THF leads to the loss of both the bridging and terminal hydrides yielding the diamagnetic salt of an anionic commo-cobaltacarborane [Ph₄P][Co(2,4-isonido-C₂B₈H₁₀)₂] (2) with the {CoC₂B₈}-cluster units adopting a distorted skeletal geometry of the isonido-type. The anionic commo complex 2 reacts with in situ generated cationic [CuPPh₃]⁺ species to give stable copper-cobalt zwitterion [Ph₃PCu][Co(2,4-isonido-C₂B₈H₁₀)₂] (3) with four two-electron, three-center (B-H)₄···Cu bonds, and exhibits no fluxional behavior in solution. Complex 3, at the same time, in CH₂Cl₂ in the presence of 2-fold excess of PPh₃ readily converts to a new anionic species [(Ph₃P)₃Cu][Co(2,4-isonido-C₂B₈H₁₀)₂] (4) which retains initial isonido geometry. All newly obtained diamagnetic commo complexes were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of complexes 2 and 3.

Highly active and stereospecific polymerization of 1,3-butadiene catalyzed by dinuclear cobalt(II) complexes bearing 3-aryliminomethyl-2-hydroxybenzaldehydes

A series of cobalt(II) complexes bearing 3-aryliminomethyl-2-hydroxybenzaldehydes (tridentate [NOO] ligands) was prepared and characterized by FT-IR and elemental analysis along with single-crystal X-ray diffraction. The X-ray diffraction analysis revealed that a dinuclear centrosymmetrical structure formed, in which each cobalt atom is surrounded by two bridged ligands and two acetate groups as a distorted octahedron. These dinuclear cobalt complexes displayed high catalytic activities for the polymerization of 1,3-butdiene on activation with organoaluminum cocatalysts to yield cis-1,4-polybutadiene with high selectivity. Ethylaluminum sesquichloride (EASC) was found to be the most efficient cocatalyst resulting in high conversion of butadiene and cis-1,4 content in the polymers with moderate molecular weight. The high catalytic activity and stereoselectivity could be achieved in a wide range of reaction conditions. All the dinuclear cobalt complexes (C1-C6) yielded predominantly cis-1,4-polybutadienes (> 96%) with negligible amounts of trans-1,4 (< 2.4%) and 1,2-vinyl (< 1.5%) products under the Al/Co molar ratio of 80 at 25 °C. The ligand modification by varying the substituents at the 4-position of phenol and on the imino-N aryl ring showed slight influence on the catalytic activity and microstructure of the resulting polymers.

Synthesis and reactivity of fluorinated ferracarborane anions

The ferracarborane [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10,1-Fe2CB7H8] reacts in CH2Cl2 with 3 molar equivalents of Ag[PF6] to yield the trifluoro-substituted species [N(PPh3)2][7,8,9-F3-6,6,6,10,10,10-(CO)6-closo-6,10,1-Fe2CB7H5]. Compound undergoes structural rearrangement in toluene at reflux temperatures, forming [N(PPh3)2][8,9,10-F3-6,6,6,7,7,7-(CO)6-closo-6,7,1-Fe2CB7H5]. Alternatively, reaction of either or with a 10-fold excess of Ag[PF6] in CH2Cl2 forms two species: namely, [N(PPh3)2][2,7,9,10-F4-6,6,6,8,8,8-(CO)6-closo-6,8,1-Fe2CB7H4], in which one further B-F substitution has occurred and the {Fe2CB7} cluster core has rearranged, plus a mono-iron co-product, [N(PPh3)2][3,8,9-F3-7,7,7-(CO)3-closo-7,1-FeCB7H5] that is formed by polyhedral contraction. Treatment of with [NO][BF4] in CH2Cl2 results in CO substitution at the 4-connected iron vertex [Fe10], producing the zwitterionic complex [7,8,9-F3-6,6,6,10,10-(CO)5-10-NO-closo-6,10,1-Fe2CB7H5]. Addition of Me3NO to a mixture of and PEt3 in CH2Cl2 also results in CO substitution, forming the isomeric species [N(PPh3)2][7,8,9-F3-6,6,m,10,10-(CO)5-n-PEt3-closo-6,10,1-Fe2CB7H5] [m=6, n=10; m=10, n=6] in a 5:1 ratio. Treatment of with [NO][BF4] and then CNBut in CH2Cl2 allows further, successive CO substitution at Fe10 to yield first a neutral, zwitterionic complex [7,8,9-F3-6,6,6,10-(CO)4-10-NO-10-PEt3-closo-6,10,1-Fe2CB7H5] and then [7,8,9-F3-6,6,6-(CO)3-10-CNBut-10-NO-10-PEt3-closo-6,10,1-Fe2CB7H5]. The molecular structures of compounds and have been established by X-ray diffraction.