2-Aminopyrrolines: New chiral amidinate ligands with a rigid well-defined molecular structure and their coordination to Ti-IV

The use of an amino-oxazolinate (NNox = κ2-2,6-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(NNox)2(NMe2)2] (2) which was thermally converted to the ring-opened decomposition products [Ti(NNox){κ3-N(2,6-C6H3Me2)C(NMe2)NC(iPr)CH2O}(NMe2)] (3) and [Ti{κ3-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‘) (HNRNR‘). Their reaction with [Ti(NMe2)4] gave the thermally stable complexes [Ti(NRNR‘)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 1H NMR spectroscopy

New sandwich and half-sandwich titanium hydrazido compounds

[EN] New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2-) compounds were prepared by tert-butyl imide/N,N'-disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(N(t)Bu)Cl(PY) (1) with Ph(2)NNH(2) gave the terminal hydrazide Cp*Ti(NNPh(2))Cl(py) (4), whereas the corresponding reaction of CpTi(N(t)Bu)Cl(py) gave the dimer Cp(2)Ti(2)(mu-eta(1):eta(1)-NNPh(2))-(mu-eta(2):eta(1)-NNPh(2))Cl(2). Reaction of 1 with Me(2)NNH(2) (1 equiv) also gave a dimer, Cp*(2)Ti(2)(mu-eta(1):eta(1)-NNMe(2)) (mu-eta(2):eta(1)-NNMe(2))Cl(2), (8), while the reaction with 2 equiv of Me(2)NNH(2) gave Cp*Ti(eta(2)-NHNMe(2))(2)Cl (7) containing two eta(2)-bound hydrazide(1-) ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NH(t)Bu)(eta(2)-NHNMe(2))Cl, observed by NMR spectroscopy. Reaction of 4 with LiNHNPh(2) gave the mixed hydrazide(2-)/hydrazide(1-) derivative Cp*Ti(NNPh(2))-(NHNPh(2))(py) (10). The corresponding reaction of 1 formed Cp*Ti(N(t)Bu)(NHNPh(2))(py), which rearranged to Cp*Ti-(NH(t)Bu)(NNPh(2))(py). The titanocene derivative Cp(2)Ti(NNPh(2))(py) (14) was prepared by reaction of Cp(2)Ti(N(t)Bu)(py) (13) with Ph(2)NNH(2), whereas the corresponding reaction with Me(2)NNH(2) gave mixtures including CpTi(NH(t)Bu)(mu-eta(1):eta(1)-NNMe(2)) (mu-eta(2):eta(1)-NNMe(2))TiCp(eta(1)-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the Cp rings and on the imido N, in 14 this is the HOMO-1 and one of the Ti=-N(alpha)pi-bonding MOs is the HOMO, destabilized by an N(alpha)-N(beta) antibonding interaction.We thank the EPSRC, British Council, MESR, and the Spanish Ministerio de Educacion y Ciencia for support. We thank Andrew Cowley for help with some of the X-ray structures.Selby, JD.; Feliz Rodriguez, M.; Schwarz, AD.; Clot, E.; Mountford, P. (2011). New sandwich and half-sandwich titanium hydrazido compounds. Organometallics. 30:2295-2307. doi:10.1021/om200068kS229523073