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

• Published in: Inorganic chemistry Vol. 44; no. 23; pp. 8442 - 8458
• Main Authors: Parsons, Thomas B, Hazari, Nilay, Cowley, Andrew R, Green, Jennifer C, Mountford, Philip
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.11.2005
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic051271j

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( n Bupz)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( n Bupz)3 = tris(4- n butylpyrazolyl)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.