title: 2-Aminopyrrolines: new chiral amidinate ligands with a rigid well-defined molecular structure and their coordination to Ti(IV).
abstract: The use of an amino-oxazolinate (NN(ox) = kappa2-2,6-dimethylphenylamido-4(S)-isopropyloxazoline) as a chiral analogue to amidinate ligands in the chemistry of titanium was found to lead to undesired side reactions. The reaction of 2,6-dimethylphenylamido-4(S)-isopropyloxazoline with [Ti(NMe2)4] afforded the bis(amidinato) complex [Ti(NN(ox))2(NMe2)2] (2) which was thermally converted to the ring-opened decomposition products [Ti(NN(ox)){kappa3-N(2,6-C6H3Me2)C(NMe2)NC(iPr)CH2O}(NMe2)] (3) and [Ti{kappa3-N(2,6-C6H3Me2)C(NMe2)-NC(iPr)CH2O}2] (4). The NMR spectra of 4 recorded at low temperature displayed two sets of resonances corresponding to two symmetric isomers in a 2:5 ratio, the probable geometries of which were established by ONIOM (QM/MM) simulations. To suppress ring opening of the oxazolines, their oxygen atom was formally replaced by a CH2 group in the synthesis of a series of amino-pyrroline protioligands 2-RN(H)(5-C4H5NR') (HN(R)N(R')). Their reaction with [Ti(NMe2)4] gave the thermally stable complexes [Ti(N(R)N(R'))2(NMe2)2], of which three derivatives were characterized by X-ray diffraction. They are stereochemically dynamic and undergo reversible ligand rearrangements in solution, for which the activation parameters were determined by variable-temperature (1)H NMR spectroscopy.
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Ward
authors.forename: Hélène
authors.initials: H
authors.lastname: Risler
authors.forename: Katharina
authors.initials: K
authors.lastname: Weitershaus
authors.forename: Stéphane
authors.initials: S
authors.lastname: Bellemin-Laponnaz
authors.forename: Hubert
authors.initials: H
authors.lastname: Wadepohl
authors.forename: Lutz H
authors.initials: LH
authors.lastname: Gade