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)-TEMP)TaMe(3)(indolyl) (5), were isolated in space group P2(1)/c with a = 8.957(2) Angstrom, b = 28.540(6) Angstrom, c = 14.695(3) Angstrom, beta = 99.40(3)degrees, V = 3706.1(14) Angstrom(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 H-1 and C-13 NMR and gas chromatographic/mass spectroscopic data. The characteristics and scope of the room temperature arene hydrogenation process are discussed.