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

The reaction of TaMe3Cl2
with the lithium salt of tetramethylpyrrole (Li−TMP) led to the
formation of (η5-TMP)TaMe3Cl (1). Reactions of
1 with a series of anionic ligands have been carried out to
form products of the
formula (η5-TMP)TaMe3X, where X = SR,
Me, pyrrolyl, or indolyl. Crystals of
(η5-TMP)TaMe3(indolyl)
(5),
were isolated in space group P21/c
with a = 8.957(2) Å, b = 28.540(6)
Å, c = 14.695(3) Å, β = 99.40(3)°,
V
= 3706.1(14) Å3, and Z = 8. The
structure confirmed the η5-bonding mode of the
tetramethylpyrrolyl ligand
and the η1-N-coordination mode of the indolyl ligand.The
derivatives (η5-TMP)TaMe3X showed
limited stability,
and decomposition products which formed in toluene solutions at room
temperature have been identified in some
cases. The reaction of
(η5-TMP)TaMe3(pyrrolyl) with
hydrogen (2−3 atm) in benzene-d6 solution at
room
temperature was studied. The stoichiometric formation of
cyclohexane-d6 by hydrogenation of an equivalent
of
solvent was confirmed by 1H and 13C NMR and gas
chromatographic/mass spectroscopic data. The
characteristics
and scope of the room temperature arene hydrogenation process are
discussed.