Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

This paper reports a general method for the synthesis of new terminal titanium diphenyl hydrazido(2−) complexes containing dianionic N3- and N4-donor ligands, along with new hydrazido synthons. Reaction of Ti(NtBu)Cl2(py)3 or Ti(NtBu)Cl2(py′)3 (py′ = 4-NC5H4tBu) with Ph2NNH2 gave excellent yields of the corresponding monomeric hydrazides Ti(NNPh2)Cl2(L)3 (L = py (7) or py′), which have been structurally characterized. Application of a dynamic vacuum to 7 formed [Ti(NNPh2)Cl2(py)2]2 (4). Both 4 and 7 are entry points to new titanium hydradizo complexes on reaction with metalated reagents. In this way, four new five-coordinate diamide-amine complexes Ti(NNPh2)(“N2N”)(py) were made (“N2N” = MeN(CH2CH2NSiMe3)2, Me3SiN(CH2CH2NSiMe3)2, MeN(CH2CH2CH2NSiMe3)2, (2-NC5H4)C(Me)(CH2NSiMe3)2) and structurally characterized. Five- and six-coordinate terminal titanium hydrazides containing dianionic N4- or O2N2-donor ligands were also synthesized from 4 by an analogous method. The identity of the “N2N” ligand affects the TiNα and Nα−Nβ distances of the TiN−NPh2 functional group. A detailed DFT analysis of the bonding in these and a range of model complexes is presented using molecular orbital and natural bond orbital methods. The competition between N(amide) and N(hydrazide) Ti(3dπ)−N(2pπ) interactions has an indirect and significant effect on the Nα−Nβ bond.