Syntheses of Tantalum(V) Complexes Containing Tetramethylpyrrolyl, Pyrrolyl, and Indolyl Ligands.

The reaction of TaMe(3)Cl(2) with the lithium salt of tetramethylpyrrole (Li-TMP) led to the formation of (eta(5)-TMP)TaMe(3)Cl (1). Reactions of 1 with a series of anionic ligands have been carried out to form products of the formula (eta(5)-TMP)TaMe(3)X, where X = SR, Me, pyrrolyl, or indolyl. Crystals of (eta(5)-TMP)TaMe(3)(indolyl) (5), were isolated in space group P2(1)/c with a = 8.957(2) Å, b = 28.540(6) Å, c = 14.695(3) Å, beta = 99.40(3) degrees, V = 3706.1(14) Å(3), and Z = 8. The structure confirmed the eta(5)-bonding mode of the tetramethylpyrrolyl ligand and the eta(1)-N-coordination mode of the indolyl ligand.The derivatives (eta(5)-TMP)TaMe(3)X showed limited stability, and decomposition products which formed in toluene solutions at room temperature have been identified in some cases. The reaction of (eta(5)-TMP)TaMe(3)(pyrrolyl) with hydrogen (2-3 atm) in benzene-d(6) solution at room temperature was studied. The stoichiometric formation of cyclohexane-d(6) by hydrogenation of an equivalent of solvent was confirmed by (1)H and (13)C NMR and gas chromatographic/mass spectroscopic data. The characteristics and scope of the room temperature arene hydrogenation process are discussed.

Valence tautomerism and metal-mediated catechol oxidation for complexes of copper prepared with 9,10-phenanthrenequinone.

Bis(pyridine)(9,10-phenanthrenequinone)(9,10-phenanthrenediolato)copper(II), Cu(py)(2)(PhenCat)(PhenBQ), has been prepared by treating copper metal with 9,10-phenanthrenequinone in pyridine solution. In dilute solution, both Cu(py)(2)(PhenCat)(PhenBQ) and the related complex Cu(tmeda)(PhenCat)(PhenBQ) lose PhenBQ to form Cu(II)L(2)(PhenCat), where L(2)= tmeda, 2 py. EPR spectra recorded at temperatures between 300 and 77 K reveal the presence of species with radical and metal localized spins together at equilibrium. Equilibria between Cu(II)L(2)(PhenCat) and Cu(I)L(2)(PhenSQ) redox isomers are solvent dependent, with a shift to higher temperature for polar solvents. Both complexes are oxygen sensitive, reacting with dioxygen to give complexes of diphenic acid. Structural characterization on products obtained with tmeda show that dioxygen insertion across the C-C bond within the chelate ring leads to dimeric products with adjacent Cu(II) ions bridged by diphenate ligands. The addition of O(2) to Cu(tmeda)(PhenCat) in acetonitrile solution at 0 degrees C appears to form a peroxo complex, tentatively identified as Cu(tmeda)(O(2))(PhenQ) on the basis of iodometric titration, as the precursor to the diphenate complex.