Synthesis, Structures, and DFT Bonding Analysis of New Titanium Hydrazido(2−) Complexes

The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2−)
species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically
demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric μ-η2,η1-bridged compounds
Ti2(μ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2{μ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3
showed the formation of N−H···Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an
excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(NtBu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(μ-η2,η1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2{μ-η2,η1-NN(CH2)5}2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2−) chemistry
of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2{HC(Me2pz)3} (9, structurally characterized), and Ti(NNPh2)Cl2{HC(nBupz)3} (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC(nBupz)3 = tris(4-nbutylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2{HC(pz)3}
(I) and the corresponding imido compounds Ti(NMe)Cl2{HC(pz)3} (II) and Ti(NPh)Cl2{HC(pz)3} (III). The NNPh2
ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metal⋮ligand triple
bond), but with one of the TiNα π components significantly destabilized by a π* interaction with the lone pair of
the Nβ atom. The NR ligand σ donor ability was found to be NMe > NPh > NNPh2, whereas the overall (σ + π)
donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti−N atom−atom overlap populations,
and fragment-charge analysis. DFT calculations on the hydrazido ligand in a μ-η2,η1-bridging mode showed
involvement of the NN π electrons in donation to one of the Ti centers. This TiN2 interaction is best represented
as a metallocycle.