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 N-3- and N-4-donor ligands, along with new hydrazido synthons. Reaction of Ti((NBu)-Bu-t)Cl-2(py)(3) or Ti((NBu)-Bu-t)Cl-2(py')(3) (py' = 4-(NC5H4Bu)-Bu-t) with Ph2NNH2 gave excellent yields of the corresponding monomeric hydrazides Ti(NNPh2)Cl-2(L)(3) (L = py (7) or py'), which have been structurally characterized. Application of a dynamic vacuum to 7 formed [Ti(NNPh2)Cl-2(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 N-4- or O2N2-donor ligands were also synthesized from 4 by an analogous method. The identity of the N2N ligand affects the Ti=N-alpha and N-alpha-N-beta 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(3d(pi))-N(2p(pi)) interactions has an indirect and significant effect on the N-alpha-N-beta bond.