Group 4 Imido Complexes Stabilized by a Tridentate Diamido-Donor Ligand

Reaction of the lithium amides [(2-C5H4N)C(CH3){CH2N(Li)SiMe3}2]2 (2a) and [(2-C5H4N)C(CH3){CH2N(Li)SiMe2tBu}2]2 (2b) with the imidotransition metal complexes [Ti(NtBu)Cl2(py)3], [Ti(N-2,6-C6H3iPr2)Cl2(py)3],
and [Zr(N-2,6-C6H3iPr2)Cl2(thf)2] yielded the five-coordinate imido-titanium and -zirconium complexes [{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe2R)2}Ti(NR‘)(py)] (R = Me, R‘ = tBu:  3a, R= tBu, R‘ = tBu:  3b, R = Me,
R‘ = 2,6-C6H3iPr2:  4a, R = Me, R‘ = 2,6-C6H3Me2:  4b) and [{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe3)2}Zr(N-2,6-C6H3iPr2)(py)] (5). The tridentate diamido-pyridine ligand adopts a facial coordination mode in the distorted
trigonal bipyramidal complexes with the imido ligand occupying an equatorial position, as was established by
X-ray diffraction for 3a and 5. Sublimation of 3a and 4a yielded the pure four-coordinate imidotitanium complexes
[{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe3)2}Ti(NR‘)] (R‘ = tBu:  6, 2,6-C6H3iPr2:  7) which were structurally
characterized by X-ray crystallography. Reaction of 3a with the Lewis acid B(C6F5)3 also led to abstraction of
the axially bound pyridine ligand and the formation of the adduct [py−B(C6F5)3] and 6. Reaction of 6 with thf,
PMe3, and pyridine led to the formation of pentacoordinate complexes [{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe3)2}Ti(NtBu)(thf)] (8), [{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe3)2}Ti(NtBu)(PMe3)] (9), and [{κ3N-(2-C5H4N)C(CH3)(CH2NSiMe3)2}Ti(NtBu)(py)] (3a) in which the donor ligands occupy axial positions.