Phospha Derivatives of Tris(2-aminoethyl)amine (tren) and Tris(3-aminopropyl)amine (trpn): Synthesis and Complexation Studies with Group 4 Metals

The N,N′,N″-triphenyl-substituted derivative of tris­(2-aminoethyl)­phosphine (Ph₃-phospha-tren, P­(CH₂CH₂NHR)₃, R = Ph) and four derivatives of the related tris­(3-aminopropyl)­phosphine (phospha-trpn, P­(CH₂CH₂CH₂NHR)₃, R = ⁱPr, ^tBu, Si^tBuMe₂, Ph) have been synthesized in addition to the parent phospha-trpn. Out of these ligand systems, only the N,N′,N″-triphenyl-substituted phospha-trpn derivative P­(CH₂CH₂CH₂NHPh)₃ was found to be suitable for coordination to group 4 metals. For titanium, zirconium, and hafnium, the C₃-symmetric endo-P-configured dimethylamido complexes ^Ph[PN₃]­M­(NMe₂) of the former ligand have been prepared and converted into the corresponding triflates ^Ph[PN₃]­M­(OTf). Starting from these triflates, the benzyl complexes ^Ph[PN₃]­M­(Bn) (M = Ti, Zr, Hf) have been obtained via reaction with Bn₂Mg­(THF)₂. In case of titanium, the benzyl species ^Ph[PN₃]­Ti­(Bn) is prone to thermal elimination of toluene, which results in the formation of a cyclometalated species. These findings are discussed in context with the very few group 4 trisamidophosphine complexes that have been reported earlier.